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Title: The Variation of Animals and Plants under Domestication — Volume 2
Author: Darwin, Charles
Language: English
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http://www.esp.org/rjr



THE VARIATION OF

ANIMALS AND PLANTS

UNDER DOMESTICATION

BY

CHARLES DARWIN, M.A., F.R.S., ETC.

IN TWO VOLUMES

VOLUME II.



CONTENTS.


CHAPTER 2.XIII.--INHERITANCE continued--REVERSION OR ATAVISM.

DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS,
FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS--REVERSION IN FERAL
ANIMALS AND PLANTS--REVERSION IN CROSSED VARIETIES AND SPECIES--REVERSION
THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT--IN
DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL--THE ACT OF CROSSING A DIRECT
CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS--OTHER PROXIMATE CAUSES
OF REVERSION--LATENT CHARACTERS--SECONDARY SEXUAL CHARACTERS--UNEQUAL
DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCE WITH ADVANCING AGE OF
CHARACTERS DERIVED FROM A CROSS--THE GERM, WITH ALL ITS LATENT CHARACTERS, A
WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERS DUE IN SOME CASES TO
REVERSION.


CHAPTER 2.XIV.--INHERITANCE continued.--FIXEDNESS OF CHARACTER--PREPOTENCY--
SEXUAL LIMITATION--CORRESPONDENCE OF AGE.

FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF INHERITANCE--
PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN CROSSED
BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER; SOMETIMES DUE TO
THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREED AND LATENT IN THE
OTHER--INHERITANCE AS LIMITED BY SEX--NEWLY-ACQUIRED CHARACTERS IN OUR
DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE, SOMETIMES LOST BY ONE
SEX ALONE--INHERITANCE AT CORRESPONDING PERIODS OF LIFE--THE IMPORTANCE OF THE
PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS EXHIBITED IN DOMESTICATED ANIMALS: AS
EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF INHERITED DISEASES; SOMETIMES
SUPERVENING EARLIER IN THE CHILD THAN IN THE PARENT--SUMMARY OF THE THREE
PRECEDING CHAPTERS.


CHAPTER 2.XV.--ON CROSSING.

FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS--WHEN THE
NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE OTHER--THE RATE
OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY THE CONDITIONS OF
LIFE, AND BY NATURAL SELECTION--ALL ORGANIC BEINGS OCCASIONALLY INTERCROSS;
APPARENT EXCEPTIONS--ON CERTAIN CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR
EXCLUSIVELY THOSE WHICH HAVE SUDDENLY APPEARED IN THE INDIVIDUAL--ON THE
MODIFICATION OF OLD RACES, AND THE FORMATION OF NEW RACES BY CROSSING--SOME
CROSSED RACES HAVE BRED TRUE FROM THEIR FIRST PRODUCTION--ON THE CROSSING OF
DISTINCT SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES.


CHAPTER 2.XVI.--CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--
INFLUENCE OF DOMESTICATION ON FERTILITY.

DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED--VARIOUS
CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL
PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED--VARIETIES OF
MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, RENDERED IN SOME
DEGREE MUTUALLY STERILE--DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY
NATURAL TO SPECIES WHEN CROSSED--ON THE INCREASED FERTILITY OF UNCROSSED
ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION.


CHAPTER 2.XVII.--ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF
CLOSE INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID TENDENCIES--GENERAL
EVIDENCE OF THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON THE EVIL EFFECTS OF
CLOSE INTERBREEDING--CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN
THE SAME PARKS--SHEEP--FALLOW-DEER--DOGS, RABBITS, PIGS--MAN, ORIGIN OF HIS
ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS, GENERAL
CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS, FRUIT-TREES,
PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED SIZE OF HYBRID
PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON CERTAIN PLANTS WHICH EITHER
NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE, BOTH ON THE MALE
AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDIVIDUALS EITHER OF THE SAME OR
ANOTHER SPECIES--CONCLUSION.


CHAPTER 2.XVIII.--ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF
LIFE: STERILITY FROM VARIOUS CAUSES.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE--STERILITY
FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY AND IN
MENAGERIES--MAMMALS, BIRDS, AND INSECTs--LOSS OF SECONDARY SEXUAL CHARACTERS
AND OF INSTINCTS--CAUSES OF STERILITY--STERILITY OF DOMESTICATED ANIMALS FROM
CHANGED CONDITIONS--SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS--STERILITY OF
PLANTS FROM CHANGED CONDITIONS OF LIFE--CONTABESCENCE OF THE ANTHERS--
MONSTROSITIES AS A CAUSE OF STERILITY--DOUBLE FLOWERS--SEEDLESS FRUIT--
STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION--FROM
LONG-CONTINUED PROPAGATION BY BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF
DOUBLE FLOWERS AND SEEDLESS FRUIT.


CHAPTER 2.XIX.--SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.

ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON FERTILITY--CLOSE
INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS OF LIFE--
VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THE DIFFERENCE IN FERTILITY
BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM--
LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF HETEROSTYLED PLANTS--
STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE
SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS WHY DOMESTIC
VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS BEEN LAID ON THE
DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES--
CONCLUSION.


CHAPTER 2.XX.--SELECTION BY MAN.

SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION--
RESULTS OF METHODICAL SELECTION--CARE TAKEN IN SELECTION--SELECTION WITH
PLANTS--SELECTION CARRIED ON BY THE ANCIENTS AND BY SEMI-CIVILISED PEOPLE--
UNIMPORTANT CHARACTERS OFTEN ATTENDED TO--UNCONSCIOUS SELECTION--AS
CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED
THROUGH THE ACTION OF UNCONSCIOUS SELECTION--INFLUENCE OF DIFFERENT BREEDERS
ON THE SAME SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS
OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST
VALUED BY MAN.


CHAPTER 2.XXI.--SELECTION, continued.

NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH APPEAR
OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLE TO
SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE
CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTION OF
A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTION IS
APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO
DEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN
EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE--
CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE
ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE
VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT TO THE POWER OF
SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH DOMESTIC RACES HAVE
ORIGINATED--SUMMARY.


CHAPTER 2.XXII.--CAUSES OF VARIABILITY.

VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES ASSIGNED BY
VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF EVERY KIND DUE TO
CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH CHANGES--CLIMATE, FOOD,
EXCESS OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS OF GRAFTING ON THE
VARIABILITY OF SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO
CHANGED CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE
INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE VARIABILITY
--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW CHARACTERS--VARIABILITY FROM
THE COMMINGLING OF CHARACTERS AND FROM REVERSION--ON THE MANNER AND PERIOD OF
ACTION OF THE CAUSES WHICH EITHER DIRECTLY, OR INDIRECTLY THROUGH THE
REPRODUCTIVE SYSTEM, INDUCE VARIABILITY.



CHAPTER 2.XXIII.--DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF
LIFE.

SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS,
IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES--LOCAL
DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC.--
PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF
POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE
THROUGH THE DEFINITE ACTION OF EXTERNAL CONDITIONS--COMPARISON OF AMERICAN AND
EUROPEAN TREES--GALLS--EFFECTS OF PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO
THE BELIEF IN THE POTENT INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL
SERIES OF VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE
OF CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY
UNNATURAL TREATMENT--SUMMARY.


CHAPTER 2.XXIV.--LAWS OF VARIATION--USE AND DISUSE, ETC.

NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON THE
EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS OF LIFE--
ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY WHICH THIS CAN BE
EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS.


CHAPTER 2.XXV.--LAWS OF VARIATION, continued.--CORRELATED VARIABILITY.

EXPLANATION OF TERM CORRELATION--CONNECTED WITH DEVELOPMENT--MODIFICATIONS
CORRELATED WITH THE INCREASED OR DECREASED SIZE OF PARTS--CORRELATED VARIATION
OF HOMOLOGOUS PARTS--FEATHERED FEET IN BIRDS ASSUMING THE STRUCTURE OF THE
WINGS--CORRELATION BETWEEN THE HEAD AND THE EXTREMITIES--BETWEEN THE SKIN AND
DERMAL APPENDAGES--BETWEEN THE ORGANS OF SIGHT AND HEARING--CORRELATED
MODIFICATIONS IN THE ORGANS OF PLANTS--CORRELATED MONSTROSITIES--CORRELATION
BETWEEN THE SKULL AND EARS--SKULL AND CREST OF FEATHERS--SKULL AND HORNS--
CORRELATION OF GROWTH COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL
SELECTION--COLOUR AS CORRELATED WITH CONSTITUTIONAL PECULIARITIES.


CHAPTER 2.XXVI.--LAWS OF VARIATION, continued.--SUMMARY.

THE FUSION OF HOMOLOGOUS PARTS--THE VARIABILITY OF MULTIPLE AND HOMOLOGOUS
PARTS--COMPENSATION OF GROWTH--MECHANICAL PRESSURE--RELATIVE POSITION OF
FLOWERS WITH RESPECT TO THE AXIS, AND OF SEEDS IN THE OVARY, AS INDUCING
VARIATION--ANALOGOUS OR PARALLEL VARIETIES--SUMMARY OF THE THREE LAST
CHAPTERS.


CHAPTER 2.XXVII.--PROVISIONAL HYPOTHESIS OF PANGENESIS.

PRELIMINARY REMARKS.
FIRST PART:--THE FACTS TO BE CONNECTED UNDER A SINGLE POINT OF VIEW, NAMELY,
THE VARIOUS KINDS OF REPRODUCTION--REGROWTH OF AMPUTATED PARTS--GRAFT-HYBRIDS
--THE DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE
FUNCTIONAL INDEPENDENCE OF THE UNITS OF THE BODY--VARIABILITY--INHERITANCE--
REVERSION.
SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY ASSUMPTIONS
ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE SEVERAL CLASSES OF
FACTS SPECIFIED IN THE FIRST PART--CONCLUSION.


CHAPTER 2.XXVIII.--CONCLUDING REMARKS.

DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE AND
DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES FAVOURABLE TO
SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE QUESTION WHETHER EACH
PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED.


INDEX.



THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION.


VOLUME II.

CHAPTER 2.XIII.

INHERITANCE continued--REVERSION OR ATAVISM.

DIFFERENT FORMS OF REVERSION.
IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP,
IN CULTIVATED PLANTS.
REVERSION IN FERAL ANIMALS AND PLANTS.
REVERSION IN CROSSED VARIETIES AND SPECIES.
REVERSION THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR
FRUIT.
IN DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL.
THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH
INSTINCTS.
OTHER PROXIMATE CAUSES OF REVERSION.
LATENT CHARACTERS.
SECONDARY SEXUAL CHARACTERS.
UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY.
APPEARANCE WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS.
THE GERM, WITH ALL ITS LATENT CHARACTERS, A WONDERFUL OBJECT.
MONSTROSITIES.
PELORIC FLOWERS DUE IN SOME CASES TO REVERSION.

The great principle of inheritance to be discussed in this chapter has been
recognised by agriculturists and authors of various nations, as shown by the
scientific term ATAVISM, derived from atavus, an ancestor; by the English
terms of REVERSION, or THROWING-BACK; by the French PAS-EN-ARRIERE; and by the
German RUCKSCHLAG, or RUCKSCHRITT. When the child resembles either grandparent
more closely than its immediate parents, our attention is not much arrested,
though in truth the fact is highly remarkable; but when the child resembles
some remote ancestor or some distant member in a collateral line,--and in the
last case we must attribute this to the descent of all the members from a
common progenitor,--we feel a just degree of astonishment. When one parent
alone displays some newly-acquired and generally inheritable character, and
the offspring do not inherit it, the cause may lie in the other parent having
the power of prepotent transmission. But when both parents are similarly
characterised, and the child does not, whatever the cause may be, inherit the
character in question, but resembles its grandparents, we have one of the
simplest cases of reversion. We continually see another and even more simple
case of atavism, though not generally included under this head, namely, when
the son more closely resembles his maternal than his paternal grand-sire in
some male attribute, as in any peculiarity in the beard of man, the horns of
the bull, the hackles or comb of the cock, or, as in certain diseases
necessarily confined to the male sex; for as the mother cannot possess or
exhibit such male attributes, the child must inherit them, through her blood,
from his maternal grandsire.

The cases of reversion may be divided into two main classes which, however, in
some instances, blend into one another; namely, first, those occurring in a
variety or race which has not been crossed, but has lost by variation some
character that it formerly possessed, and which afterwards reappears. The
second class includes all cases in which an individual with some
distinguishable character, a race, or species, has at some former period been
crossed, and a character derived from this cross, after having disappeared
during one or several generations, suddenly reappears. A third class,
differing only in the manner of reproduction, might be formed to include all
cases of reversion effected by means of buds, and therefore independent of
true or seminal generation. Perhaps even a fourth class might be instituted,
to include reversions by segments in the same individual flower or fruit, and
in different parts of the body in the same individual animal as it grows old.
But the two first main classes will be sufficient for our purpose.

REVERSION TO LOST CHARACTERS BY PURE OR UNCROSSED FORMS.

Striking instances of this first class of cases were given in the sixth
chapter, namely, of the occasional reappearance, in variously-coloured breeds
of the pigeon, of blue birds with all the marks characteristic of the wild
Columba livia. Similar cases were given in the case of the fowl. With the
common ass, as the legs of the wild progenitor are almost always striped, we
may feel assured that the occasional appearance of such stripes in the
domestic animal is a case of simple reversion. But I shall be compelled to
refer again to these cases, and therefore here pass them over.

The aboriginal species from which our domesticated cattle and sheep are
descended, no doubt possessed horns; but several hornless breeds are now well
established. Yet in these--for instance, in Southdown sheep--"it is not
unusual to find among the male lambs some with small horns." The horns, which
thus occasionally reappear in other polled breeds, either "grow to the full
size," or are curiously attached to the skin alone and hang "loosely down, or
drop off." (13/1. 'Youatt on Sheep' pages 20, 234. The same fact of loose
horns occasionally appearing in hornless breeds has been observed in Germany;
Bechstein 'Naturgesch. Deutschlands.' b. 1 s. 362.) The Galloways and Suffolk
cattle have been hornless for the last 100 or 150 years, but a horned calf,
with the horn often loosely attached, is occasionally produced. (13/2. 'Youatt
on Cattle' pages 155, 174.)

There is reason to believe that sheep in their early domesticated condition
were "brown or dingy black;" but even in the time of David certain flocks were
spoken of as white as snow. During the classical period the sheep of Spain are
described by several ancient authors as being black, red, or tawny. (13/3.
'Youatt on Sheep' 1838 pages 17, 145.) At the present day, notwithstanding the
great care which is taken to prevent it, particoloured lambs and some entirely
black are occasionally, or even frequently, dropped by our most highly
improved and valued breeds, such as the Southdowns. Since the time of the
famous Bakewell, during the last century, the Leicester sheep have been bred
with the most scrupulous care; yet occasionally grey-faced, or black-spotted,
or wholly black lambs appear. (13/4. I have been informed of this fact through
the Rev. W.D. Fox on the excellent authority of Mr. Wilmot: see also remarks
on this subject in an article in the 'Quarterly Review' 1849 page 395.) This
occurs still more frequently with the less improved breeds, such as the
Norfolks. (13/5. Youatt pages 19, 234.) As bearing on this tendency in sheep
to revert to dark colours, I may state (though in doing so I trench on the
reversion of crossed breeds, and likewise on the subject of prepotency) that
the Rev. W.D. Fox was informed that seven white Southdown ewes were put to a
so-called Spanish ram, which had two small black spots on his sides, and they
produced thirteen lambs, all perfectly black. Mr. Fox believes that this ram
belonged to a breed which he has himself kept, and which is always spotted
with black and white; and he finds that Leicester sheep crossed by rams of
this breed always produce black lambs: he has gone on recrossing these crossed
sheep with pure white Leicesters during three successive generations, but
always with the same result. Mr. Fox was also told by the friend from whom the
spotted breed was procured, that he likewise had gone on for six or seven
generations crossing with white sheep, but still black lambs were invariably
produced.

Similar facts could be given with respect to tailless breeds of various
animals. For instance, Mr. Hewitt (13/6. 'The Poultry Book' by Mr. Tegetmeier
1866 page 231.) states that chickens bred from some rumpless fowls, which were
reckoned so good that they won a prize at an exhibition, "in a considerable
number of instances were furnished with fully developed tail-feathers." On
inquiry, the original breeder of these fowls stated that, from the time when
he had first kept them, they had often produced fowls furnished with tails;
but that these latter would again reproduce rumpless chickens.

Analogous cases of reversion occur in the vegetable kingdom; thus "from seeds
gathered from the finest cultivated varieties of Heartsease (Viola tricolor),
plants perfectly wild both in their foliage and their flowers are frequently
produced;" (13/7. Loudon's 'Gardener's Mag.' volume 10 1834 page 396: a
nurseryman, with much experience on this subject, has likewise assured me that
this sometimes occurs.) but the reversion in this instance is not to a very
ancient period, for the best existing varieties of the heartsease are of
comparatively modern origin. With most of our cultivated vegetables there is
some tendency to reversion to what is known to be, or may be presumed to be,
their aboriginal state; and this would be more evident if gardeners did not
generally look over their beds of seedlings, and pull up the false plants or
"rogues" as they are called. It has already been remarked, that some few
seedling apples and pears generally resemble, but apparently are not identical
with, the wild trees from which they are descended. In our turnip (13/8.
'Gardener's Chronicle' 1855 page 777.) and carrot-beds a few plants often
"break "--that is, flower too soon; and their roots are generally hard and
stringy, as in the parent-species. By the aid of a little selection, carried
on during a few generations, most of our cultivated plants could probably be
brought back, without any great change in their conditions of life, to a wild
or nearly wild condition: Mr. Buckman has effected this with the parsnip
(13/9. Ibid 1862 page 721.); and Mr. Hewett C. Watson, as he informs me,
selected, during three generations, "the most diverging plants of Scotch kail,
perhaps one of the least modified varieties of the cabbage; and in the third
generation some of the plants came very close to the forms now established in
England about old castle-walls, and called indigenous."

REVERSION IN ANIMALS AND PLANTS WHICH HAVE RUN WILD.

In the cases hitherto considered, the reverting animals and plants have not
been exposed to any great or abrupt change in their conditions of life which
could have induced this tendency; but it is very different with animals and
plants which have become feral or run wild. It has been repeatedly asserted in
the most positive manner by various authors, that feral animals and plants
invariably return to their primitive specific type. It is curious on what
little evidence this belief rests. Many of our domesticated animals could not
subsist in a wild state; thus, the more highly improved breeds of the pigeon
will not "field" or search for their own food. Sheep have never become feral,
and would be destroyed by almost every beast of prey. (13/10. Mr. Boner speaks
('Chamois-hunting' 2nd edition 1860 page 92) of sheep often running wild in
the Bavarian Alps; but, on making further inquiries at my request, he found
that they are not able to establish themselves; they generally perish from the
frozen snow clinging to their wool, and they have lost the skill necessary to
pass over steep icy slopes. On one occasion two ewes survived the winter, but
their lambs perished.) In several cases we do not know the aboriginal parent-
species, and cannot possibly tell whether or not there has been any close
degree of reversion. It is not known in any instance what variety was first
turned out; several varieties have probably in some cases run wild, and their
crossing alone would tend to obliterate their proper character. Our
domesticated animals and plants, when they run wild, must always be exposed to
new conditions of life, for, as Mr. Wallace (13/11. See some excellent remarks
on this subject by Mr. Wallace 'Journal Proc. Linn. Soc.' 1858 volume 3 page
60.) has well remarked, they have to obtain their own food, and are exposed to
competition with the native productions. Under these circumstances, if our
domesticated animals did not undergo change of some kind, the result would be
quite opposed to the conclusions arrived at in this work. Nevertheless, I do
not doubt that the simple fact of animals and plants becoming feral, does
cause some tendency to reversion to the primitive state; though this tendency
has been much exaggerated by some authors.

[I will briefly run through the recorded cases. With neither horses nor cattle
is the primitive stock known; and it has been shown in former chapters that
they have assumed different colours in different countries. Thus the horses
which have run wild in South America are generally brownish-bay, and in the
East dun-coloured; their heads have become larger and coarser, and this may be
due to reversion. No careful description has been given of the feral goat.
Dogs which have run wild in various countries have hardly anywhere assumed a
uniform character; but they are probably descended from several domestic
races, and aboriginally from several distinct species. Feral cats, both in
Europe and La Plata, are regularly striped; in some cases they have grown to
an unusually large size, but do not differ from the domestic animal in any
other character. When variously-coloured tame rabbits are turned out in
Europe, they generally reacquire the colouring of the wild animal; there can
be no doubt that this does really occur, but we should remember that oddly-
coloured and conspicuous animals would suffer much from beasts of prey and
from being easily shot; this at least was the opinion of a gentleman who tried
to stock his woods with a nearly white variety; if thus destroyed, they would
be supplanted by, instead of being transformed into, the common rabbit. We
have seen that the feral rabbits of Jamaica, and especially of Porto Santo,
have assumed new colours and other new characters. The best known case of
reversion, and that on which the widely spread belief in its universality
apparently rests, is that of pigs. These animals have run wild in the West
Indies, South America, and the Falkland Islands, and have everywhere acquired
the dark colour, the thick bristles, and great tusks of the wild boar; and the
young have reacquired longitudinal stripes. But even in the case of the pig,
Roulin describes the half-wild animals in different parts of South America as
differing in several respects. In Louisiana the pig (13/12. Dureau de la Malle
'Comptes Rendus' tome 41 1855 page 807. From the statements above given, the
author concludes that the wild pigs of Louisiana are not descended from the
European Sus scrofa.) has run wild, and is said to differ a little in form,
and much in colour, from the domestic animal, yet does not closely resemble
the wild boar of Europe. With pigeons and fowls (13/13. Capt. W. Allen, in his
'Expedition to the Niger' states that fowls have run wild on the island of
Annobon, and have become modified in form and voice. The account is so meagre
and vague that it did not appear to me worth copying; but I now find that
Dureau de la Malle ('Comptes Rendus' tome 41 1855 page 690) advances this as a
good instance of reversion to the primitive stock, and as confirmatory of a
still more vague statement in classical times by Varro.), it is not known what
variety was first turned out, nor what character the feral birds have assumed.
The guinea-fowl in the West Indies, when feral, seems to vary more than in the
domesticated state.

With respect to plants run wild, Dr. Hooker (13/14. 'Flora of Australia' 1859
Introduction page 9.) has strongly insisted on what slight evidence the common
belief in their reversion to a primitive state rests. Godron (13/15. 'De
l'Espece' tome 2 pages 54, 58, 60.) describes wild turnips, carrots, and
celery; but these plants in their cultivated state hardly differ from their
wild prototypes, except in the succulency and enlargement of certain parts,--
characters which would certainly be lost by plants growing in poor soil and
struggling with other plants. No cultivated plant has run wild on so enormous
a scale as the cardoon (Cynara cardunculus) in La Plata. Every botanist who
has seen it growing there, in vast beds, as high as a horse's back, has been
struck with its peculiar appearance; but whether it differs in any important
point from the cultivated Spanish form, which is said not to be prickly like
its American descendant, or whether it differs from the wild Mediterranean
species, which is said not to be social (though this may be due merely to the
nature of the conditions), I do not know.]

REVERSION TO CHARACTERS DERIVED FROM A CROSS, IN THE CASE OF SUB-VARIETIES,
RACES, AND SPECIES.

When an individual having some recognisable peculiarity unites with another of
the same sub-variety, not having the peculiarity in question, it often
reappears in the descendants after an interval of several generations. Every
one must have noticed, or heard from old people of children closely resembling
in appearance or mental disposition, or in so small and complex a character as
expression, one of their grandparents, or some more distant collateral
relation. Very many anomalies of structure and diseases (13/16. Mr. Sedgwick
gives many instances in the 'British and Foreign Med.-Chirurg. Review' April
and July 1863 pages 448, 188.) of which instances have been given in the last
chapter, have come into a family from one parent, and have reappeared in the
progeny after passing over two or three generations. The following case has
been communicated to me on good authority, and may, I believe, be fully
trusted: a pointer-bitch produced seven puppies; four were marked with blue
and white, which is so unusual a colour with pointers that she was thought to
have played false with one of the greyhounds, and the whole litter was
condemned; but the gamekeeper was permitted to save one as a curiosity. Two
years afterwards a friend of the owner saw the young dog, and declared that he
was the image of his old pointer-bitch Sappho, the only blue and white pointer
of pure descent which he had ever seen. This led to close inquiry, and it was
proved that he was the great-great-grandson of Sappho; so that, according to
the common expression, he had only 1/16th of her blood in his veins. I may
give one other instance, on the authority of Mr. R. Walker, a large cattle-
breeder in Kincardineshire. He bought a black bull, the son of a black cow
with white legs, white belly and part of the tail white; and in 1870 a calf
the gr.-gr.-gr.-gr.-grandchild of this cow was born coloured in the same very
peculiar manner; all the intermediate offspring having been black. In these
cases there can hardly be a doubt that a character derived from a cross with
an individual of the same variety reappeared after passing over three
generations in the one case, and five in the other.

When two distinct races are crossed, it is notorious that the tendency in the
offspring to revert to one or both parent-forms is strong, and endures for
many generations. I have myself seen the clearest evidence of this in crossed
pigeons and with various plants. Mr. Sidney (13/17. In his edition of 'Youatt
on the Pig' 1860 page 27.) states that, in a litter of Essex pigs, two young
ones appeared which were the image of the Berkshire boar that had been used
twenty-eight years before in giving size and constitution to the breed. I
observed in the farmyard at Betley Hall some fowls showing a strong likeness
to the Malay breed, and was told by Mr. Tollet that he had forty years before
crossed his birds with Malays; and that, though he had at first attempted to
get rid of this strain, he had subsequently given up the attempt in despair,
as the Malay character would reappear.

This strong tendency in crossed breeds to revert has given rise to endless
discussions in how many generations after a single cross, either with a
distinct breed or merely with an inferior animal, the breed may be considered
as pure, and free from all danger of reversion. No one supposes that less than
three generations suffices, and most breeders think that six, seven, or eight
are necessary, and some go to still greater lengths. (13/18. Dr. P. Lucas,
'Hered. Nat.' tome 2 pages 314, 892: see a good practical article on the
subject in 'Gardener's Chronicle' 1856 page 620. I could add a vast number of
references, but they would be superfluous.) But neither in the case of a breed
which has been contaminated by a single cross, nor when, in the attempt to
form an intermediate breed, half-bred animals have been matched together
during many generations, can any rule be laid down how soon the tendency to
reversion will be obliterated. It depends on the difference in the strength or
prepotency of transmission in the two parent-forms, on their actual amount of
difference, and on the nature of the conditions of life to which the crossed
offspring are exposed. But we must be careful not to confound these cases of
reversion to characters which were gained by a cross, with those under the
first class, in which characters originally common to BOTH parents, but lost
at some former period, reappear; for such characters may recur after an almost
indefinite number of generations.

The law of reversion is as powerful with hybrids, when they are sufficiently
fertile to breed together, or when they are repeatedly crossed with either
pure parent-form, as in the case of mongrels. It is not necessary to give
instances. With plants almost every one who has worked on this subject, from
the time of Kolreuter to the present day, has insisted on this tendency.
Gartner has recorded some good instances; but no one has given more striking
ones than Naudin. (13/19. Kolreuter gives curious cases in his 'Dritte
Fortsetzung' 1766 ss. 53, 59; and in his well-known 'Memoirs on Lavatera and
Jalapa.' Gartner 'Bastarderzeugung' ss. 437, 441, etc. Naudin in his
"Recherches sur l'Hybridite" 'Nouvelles Archives du Museum' tome 1 page 25.)
The tendency differs in degree or strength in different groups, and partly
depends, as we shall presently see, on whether the parent-plants have been
long cultivated. Although the tendency to reversion is extremely general with
nearly all mongrels and hybrids, it cannot be considered as invariably
characteristic of them; it may also be mastered by long-continued selection;
but these subjects will more properly be discussed in a future chapter on
Crossing. From what we see of the power and scope of reversion, both in pure
races, and when varieties or species are crossed, we may infer that characters
of almost every kind are capable of reappearing after having been lost for a
great length of time. But it does not follow from this that in each particular
case certain characters will reappear; for instance, this will not occur when
a race is crossed with another endowed with prepotency of transmission.
Sometimes the power of reversion wholly fails, without our being able to
assign any cause for the failure: thus it has been stated that in a French
family in which 85 out of above 600 members, during six generations, had been
subject to night-blindness, "there has not been a single example of this
affection in the children of parents who were themselves free from it."
(13/20. Quoted by Mr. Sedgwick in 'Med.-Chirurg. Review' April 1861 page 485.
Dr. H. Dobell in 'Med.-Chirurg. Transactions' volume 46 gives an analogous
case in which, in a large family, fingers with thickened joints were
transmitted to several members during five generations; but when the blemish
once disappeared it never reappeared.)

REVERSION THROUGH BUD-PROPAGATION--PARTIAL REVERSION, BY SEGMENTS IN THE SAME
FLOWER OR FRUIT, OR IN DIFFERENT PARTS OF THE BODY IN THE SAME INDIVIDUAL
ANIMAL.

In the eleventh chapter many cases of reversion by buds, independently of
seminal generation, were given--as when a leaf-bud on a variegated, a curled,
or laciniated variety suddenly reassumes its proper character; or as when a
Provence-rose appears on a moss-rose, or a peach on a nectarine-tree. In some
of these cases only half the flower or fruit, or a smaller segment, or mere
stripes, reassume their former character; and here we have reversion by
segments. Vilmorin (13/21. Verlot 'Des Varietes' 1865 page 63.) has also
recorded several cases with plants derived from seed, of flowers reverting by
stripes or blotches to their primitive colours: he states that in all such
cases a white or pale-coloured variety must first be formed, and, when this is
propagated for a length of time by seed, striped seedlings occasionally make
their appearance; and these can afterwards by care be multiplied by seed.

The stripes and segments just referred to are not due, as far as is known, to
reversion to characters derived from a cross, but to characters lost by
variation. These cases, however, as Naudin (13/22. 'Nouvelles Archives du
Museum' tome 1 page 25. Alex. Braun (in his 'Rejuvenescence' Ray Soc. 1853
page 315) apparently holds a similar opinion.) insists in his discussion on
disjunction of character, are closely analogous with those given in the
eleventh chapter, in which crossed plants have been known to produce half-and-
half or striped flowers and fruit, or distinct kinds of flowers on the same
root resembling the two parent-forms. Many piebald animals probably come under
this same head. Such cases, as we shall see in the chapter on Crossing,
apparently result from certain characters not readily blending together, and,
as a consequence of this incapacity for fusion, the offspring either perfectly
resemble one of their two parents, or resemble one parent in one part, and the
other parent in another part; or whilst young are intermediate in character,
but with advancing age revert wholly or by segments to either parent-form, or
to both. Thus, young trees of the Cytisus adami are intermediate in foliage
and flowers between the two parent-forms; but when older the buds continually
revert either partially or wholly to both forms. The cases given in the
eleventh chapter on the changes which occurred during growth in crossed plants
of Tropaeolum, Cereus, Datura, and Lathyrus are all analogous. As, however,
these plants are hybrids of the first generation, and as their buds after a
time come to resemble their parents and not their grandparents, these cases do
not at first appear to come under the law of reversion in the ordinary sense
of the word; nevertheless, as the change is effected through a succession of
bud-generations on the same plant, they may be thus included.

Analogous facts have been observed in the animal kingdom, and are more
remarkable, as they occur in the same individual in the strictest sense, and
not as with plants through a succession of bud-generations. With animals the
act of reversion, if it can be so designated, does not pass over a true
generation, but merely over the early stages of growth in the same individual.
For instance, I crossed several white hens with a black cock, and many of the
chickens were, during the first year, perfectly white, but acquired during the
second year black feathers; on the other hand, some of the chickens which were
at first black, became during the second year piebald with white. A great
breeder (13/23. Mr. Teebay in 'The Poultry Book' by Mr. Tegetmeier 1866 page
72.) says, that a Pencilled Brahma hen which has any of the blood of the Light
Brahma in her, will "occasionally produce a pullet well pencilled during the
first year, but she will most likely moult brown on the shoulders and become
quite unlike her original colours in the second year." The same thing occurs
with light Brahmas if of impure blood. I have observed exactly similar cases
with the crossed offspring from differently coloured pigeons. But here is a
more remarkable fact: I crossed a turbit, which has a frill formed by the
feathers being reversed on its breast, with a trumpeter; and one of the young
pigeons thus raised at first showed not a trace of the frill, but, after
moulting thrice, a small yet unmistakably distinct frill appeared on its
breast. According to Girou (13/24. Quoted by Hofacker 'Ueber die
Eigenschaften' etc. s. 98.) calves produced from a red cow by a black bull, or
from a black cow by a red bull, are not rarely born red, and subsequently
become black. I possess a dog, the daughter of a white terrier by a fox-
coloured bulldog; as a puppy she was quite white, but when about six months
old a black spot appeared on her nose, and brown spots on her ears. When a
little older she was badly wounded on the back, and the hair which grew on the
cicatrix was of a brown colour, apparently derived from her father. This is
the more remarkable, as with most animals having coloured hair, that which
grows on a wounded surface is white.

In the foregoing cases, the characters which with advancing age reappeared,
were present in the immediately preceding generations; but characters
sometimes reappear in the same manner after a much longer interval of time.
Thus the calves of a hornless race of cattle which originated in Corrientes,
though at first quite hornless, as they become adult sometimes acquire small,
crooked, and loose horns; and these in succeeding years occasionally become
attached to the skull. (13/25. Azara 'Essais Hist. Nat. de Paraguay' tome 2
1801 page 372.) White and black Bantams, both of which generally breed true,
sometimes assume as they grow old a saffron or red plumage. For instance, a
first-rate black bantam has been described, which during three seasons was
perfectly black, but then annually became more and more red; and it deserves
notice that this tendency to change, whenever it occurs in a bantam, "is
almost certain to prove hereditary." (13/26. These facts are given on the high
authority of Mr. Hewitt in 'The Poultry Book' by Mr. Tegetmeier 1866 page
248.) The cuckoo or blue-mottled Dorking cock, when old, is liable to acquire
yellow or orange hackles in place of his proper bluish-grey hackles. (13/27.
'The Poultry Book' by Tegetmeier 1866 page 97.) Now as Gallus bankiva is
coloured red and orange, and as Dorking fowls and bantams are descended from
this species, we can hardly doubt that the change which occasionally occurs in
the plumage of these birds as their age advances, results from a tendency in
the individual to revert to the primitive type.

CROSSING AS A DIRECT CAUSE OF REVERSION.

It has long been notorious that hybrids and mongrels often revert to both or
to one of their parent-forms, after an interval of from two to seven or eight,
or, according to some authorities, even a greater number of generations. But
that the act of crossing in itself gives an impulse towards reversion, as
shown by the reappearance of long-lost characters, has never, I believe, been
hitherto proved. The proof lies in certain peculiarities, which do not
characterise the immediate parents, and therefore cannot have been derived
from them, frequently appearing in the offspring of two breeds when crossed,
which peculiarities never appear, or appear with extreme rarity, in these same
breeds, as long as they are precluded from crossing. As this conclusion seems
to me highly curious and novel, I will give the evidence in detail.

[My attention was first called to this subject, and I was led to make numerous
experiments, by MM. Boitard and Corbie having stated that, when they crossed
certain breeds of pigeons, birds coloured like the wild C. livia, or the
common dovecote--namely, slaty-blue, with double black wing-bars, sometimes
chequered with black, white loins, the tail barred with black, with the outer
feathers edged with white,--were almost invariably produced. The breeds which
I crossed, and the remarkable results attained, have been fully described in
the sixth chapter. I selected pigeons belonging to true and ancient breeds,
which had not a trace of blue or any of the above specified marks; but when
crossed, and their mongrels recrossed, young birds were often produced, more
or less plainly coloured slaty-blue, with some or all of the proper
characteristic marks. I may recall to the reader's memory one case, namely,
that of a pigeon, hardly distinguishable from the wild Shetland species, the
grandchild of a red-spot, white fantail, and two black barbs, from any of
which, when purely-bred, the production of a pigeon coloured like the wild C.
livia would have been almost a prodigy.

I was thus led to make the experiments, recorded in the seventh chapter, on
fowls. I selected long-established pure breeds, in which there was not a trace
of red, yet in several of the mongrels feathers of this colour appeared; and
one magnificent bird, the offspring of a black Spanish cock and white Silk
hen, was coloured almost exactly like the wild Gallus bankiva. All who know
anything of the breeding of poultry will admit that tens of thousands of pure
Spanish and of pure white Silk fowls might have been reared without the
appearance of a red feather. The fact, given on the authority of Mr.
Tegetmeier, of the frequent appearance, in mongrel fowls, of pencilled or
transversely-barred feathers, like those common to many gallinaceous birds, is
likewise apparently a case of reversion to a character formerly possessed by
some ancient progenitor of the family. I owe to the kindness of this excellent
observer the opportunity of inspecting some neck-hackles and tail-feathers
from a hybrid between the common fowl and a very distinct species, the Gallus
varius; and these feathers are transversely striped in a conspicuous manner
with dark metallic blue and grey, a character which could not have been
derived from either immediate parent.

I have been informed by Mr. B.P. Brent, that he crossed a white Aylesbury
drake and a black so-called Labrador duck, both of which are true breeds, and
he obtained a young drake closely like the mallard (A. boschas). Of the musk-
duck (Cairina moschata, Linn.) there are two sub-breeds, namely, white and
slate-coloured; and these I am informed breed true, or nearly true. But the
Rev. W.D. Fox tells me that, by putting a white drake to a slate-coloured
duck, black birds, pied with white, like the wild musk-duck, were always
produced. I hear from Mr. Blyth that hybrids from the canary and gold-finch
almost always have streaked feathers on their backs; and this streaking must
be derived from the original wild canary.

We have seen in the fourth chapter, that the so-called Himalayan rabbit, with
its snow-white body, black ears, nose, tail, and feet, breeds perfectly true.
This race is known to have been formed by the union of two varieties of
silver-grey rabbits. Now, when a Himalayan doe was crossed by a sandy-coloured
buck, a silver-grey rabbit was produced; and this is evidently a case of
reversion to one of the parent varieties. The young of the Himalayan rabbit
are born snow-white, and the dark marks do not appear until some time
subsequently; but occasionally young Himalayan rabbits are born of a light
silver-grey, which colour soon disappears; so that here we have a trace of
reversion, during an early period of life, to the parent varieties,
independently of any recent cross.

In the third chapter it was shown that at an ancient period some breeds of
cattle in the wilder parts of Britain were white with dark ears, and that the
cattle now kept half wild in certain parks, and those which have run quite
wild in two distant parts of the world, are likewise thus coloured. Now, an
experienced breeder, Mr. J. Beasley, of Northamptonshire (13/28. 'Gardener's
Chronicle and Agricultural Gazette' 1866 page 528.), crossed some carefully
selected West Highland cows with purely-bred shorthorn bulls. The bulls were
red, red and white, or dark roan; and the Highland cows were all of a red
colour, inclining to a light or yellow shade. But a considerable number of the
offspring--and Mr. Beasley calls attention to this as a remarkable fact--were
white, or white with red ears. Bearing in mind that none of the parents were
white, and that they were purely-bred animals, it is highly probable that here
the offspring reverted, in consequence of the cross, to the colour of some
ancient and half-wild parent-breed. The following case, perhaps, comes under
the same head: cows in their natural state have their udders but little
developed, and do not yield nearly so much milk as our domesticated animals.
Now there is some reason to believe (13/29. Ibid 1860 page 343. I am glad to
find that so experienced a breeder of cattle as Mr. Willoughby Wood,
'Gardener's Chronicle' 1869 page 1216, admits my principle of a cross giving a
tendency to reversion.) that cross-bred animals between two kinds, both of
which are good milkers, such as Alderneys and Shorthorns, often turn out
worthless in this respect.

In the chapter on the Horse reasons were assigned for believing that the
primitive stock was striped and dun-coloured; and details were given, showing
that in all parts of the world stripes of a dark colour frequently appear
along the spine, across the legs, and on the shoulders, where they are
occasionally double or treble, and even sometimes on the face and body of
horses of all breeds and of all colours. But the stripes appear most
frequently on the various kinds of duns. In foals they are sometimes plainly
seen, and subsequently disappear. The dun-colour and the stripes are strongly
transmitted when a horse thus characterised is crossed with any other; but I
was not able to prove that striped duns are generally produced from the
crossing of two distinct breeds, neither of which are duns, though this does
sometimes occur.

The legs of the ass are often striped, and this may be considered as a
reversion to the wild parent form, the Equus taeniopus of Abyssinia (13/30.
Sclater in 'Proc. Zoolog. Soc.' 1862 page 163.), which is generally thus
striped. In the domestic animal the stripes on the shoulder are occasionally
double, or forked at the extremity, as in certain zebrine species. There is
reason to believe that the foal is more frequently striped on the legs than
the adult animal. As with the horse, I have not acquired any distinct evidence
that the crossing of differently-coloured varieties of the ass brings out the
stripes.

But now let us turn to the result of crossing the horse and ass. Although
mules are not nearly so numerous in England as asses, I have seen a much
greater number with striped legs, and with the stripes far more conspicuous
than in either parent-form. Such mules are generally light-coloured, and might
be called fallow-duns. The shoulder-stripe in one instance was deeply forked
at the extremity, and in another instance was double, though united in the
middle. Mr. Martin gives a figure of a Spanish mule with strong zebra-like
marks on its legs (13/31. 'History of the Horse' page 212.), and remarks that
mules are particularly liable to be thus striped on their legs. In South
America, according to Roulin (13/32. 'Mem. presentes par divers Savans a
l'Acad. Royale' tome 6 1835 page 338.), such stripes are more frequent and
conspicuous in the mule than in the ass. In the United States, Mr. Gosse
(13/33. 'Letters from Alabama' 1859 page 280.), speaking of these animals,
says, "that in a great number, perhaps in nine out of every ten, the legs are
banded with transverse dark stripes."

Many years ago I saw in the Zoological Gardens a curious triple hybrid, from a
bay mare, by a hybrid from a male ass and female zebra. This animal when old
had hardly any stripes; but I was assured by the superintendent, that when
young it had shoulder-stripes, and faint stripes on its flanks and legs. I
mention this case more especially as an instance of the stripes being much
plainer during youth than in old age.

As the zebra has such a conspicuously striped body and legs, it might have
been expected that the hybrids from this animal and the common ass would have
had their legs in some degree striped; but it appears from the figures given
in Dr. Gray's 'Knowsley Gleanings' and still more plainly from that given by
Geoffroy and F. Cuvier (13/34. 'Hist. Nat. des Mammiferes' 1820 tome 1), that
the legs are much more conspicuously striped than the rest of the body; and
this fact is intelligible only on the belief that the ass aids in giving,
through the power of reversion, this character to its hybrid offspring.

The quagga is banded over the whole front part of its body like a zebra, but
has no stripes on its legs, or mere traces of them. But in the famous hybrid
bred by Lord Morton (13/35. 'Philosoph. Transact.' 1821 page 20.) from a
chestnut, nearly purely-bred, Arabian mare, by a male quagga, the stripes were
"more strongly defined and darker than those on the legs of "the quagga." The
mare was subsequently put to a black Arabian horse, and bore two colts, both
of which, as formerly stated, were plainly striped on the legs, and one of
them likewise had stripes on the neck and body.

The Equus indicus (13/36. Sclater in 'Proc. Zoolog. Soc.' 1862 page 163: this
species is the Ghor-Khur of N.W. India, and has often been called the Hemionus
of Pallas. See also Mr. Blyth's excellent paper in 'Journal of Asiatic Soc. of
Bengal' volume 28 1860 page 229.) is characterised by a spinal stripe, without
shoulder or leg stripes; but traces of these latter stripes may occasionally
be seen even in the adult (13/37. Another species of wild ass, the true E.
hemionus or Kiang, which ordinarily has no shoulder-stripes, is said
occasionally to have them; and these, as with the horse and ass, are sometimes
double: see Mr. Blyth in the paper just quoted and in 'Indian Sporting Review'
1856 page 320: and Col. Hamilton Smith in 'Nat. Library, Horses' page 318; and
'Dict. Class. d'Hist. Nat.' tome 3 page 563.) and Colonel S. Poole, who has
had ample opportunities for observation, informs me that in the foal, when
first born, the head and legs are often striped, but the shoulder-stripe is
not so distinct as in the domestic ass; all these stripes, excepting that
along the spine, soon disappear. Now a hybrid, raised at Knowsley (13/38.
Figured in the 'Gleanings from the Knowsley Menageries' by Dr. J.E. Gray.)
from a female of this species by a male domestic ass, had all four legs
transversely and conspicuously striped, had three short stripes on each
shoulder and had even some zebra-like stripes on its face! Dr. Gray informs me
that he has seen a second hybrid of the same parentage, similarly striped.

From these facts we see that the crossing of the several equine species tends
in a marked manner to cause stripes to appear on various parts of the body,
especially on the legs. As we do not know whether the parent-form of the genus
was striped, the appearance of the stripes can only hypothetically be
attributed to reversion. But most persons, after considering the many
undoubted cases of variously coloured marks reappearing by reversion in my
experiments on crossed pigeons and fowls, will come to the same conclusion
with respect to the horse-genus; and if so, we must admit that the progenitor
of the group was striped on the legs, shoulders, face, and probably over the
whole body, like a zebra.

Lastly, Professor Jaeger has given (13/39. 'Darwin'sche Theorie und ihre
Stellung zu Moral und Religion' page 85.) a good case with pigs. He crossed
the Japanese or masked breed with the common German breed, and the offspring
were intermediate in character. He then re-crossed one of these mongrels with
the pure Japanese, and in the litter thus produced one of the young resembled
in all its characters a wild pig; it had a long snout and upright ears, and
was striped on the back. It should be borne in mind that the young of the
Japanese breed are not striped, and that they have a short muzzle and ears
remarkably dependent.]

A similar tendency to the recovery of long lost characters holds good even
with the instincts of crossed animals. There are some breeds of fowls which
are called "everlasting layers," because they have lost the instinct of
incubation; and so rare is it for them to incubate that I have seen notices
published in works on poultry, when hens of such breeds have taken to sit.
(13/40. Cases of both Spanish and Polish hens sitting are given in the
'Poultry Chronicle' 1855 volume 3 page 477.) Yet the aboriginal species was of
course a good incubator; and with birds in a state of nature hardly any
instinct is so strong as this. Now, so many cases have been recorded of the
crossed offspring from two races, neither of which are incubators, becoming
first-rate sitters, that the reappearance of this instinct must be attributed
to reversion from crossing. One author goes so far as to say, "that a cross
between two non-sitting varieties almost invariably produces a mongrel that
becomes broody, and sits with remarkable steadiness." (13/41. 'The Poultry
Book' by Mr. Tegetmeier 1866 pages 119, 163. The author, who remarks on the
two negatives ('Journ. of Hort.' 1862 page 325), states that two broods were
raised from a Spanish cock and Silver-pencilled Hamburgh hen, neither of which
are incubators, and no less than seven out of eight hens in these two broods
"showed a perfect obstinacy in sitting." The Rev. E.S. Dixon ('Ornamental
Poultry' 1848 page 200) says that chickens reared from a cross between Golden
and Black Polish fowls, are "good and steady birds to sit." Mr. B.P. Brent
informs me that he raised some good sitting hens by crossing Pencilled
Hamburgh and Polish breeds. A cross-bred bird from a Spanish non-incubating
cock and Cochin incubating hen is mentioned in the 'Poultry Chronicle' volume
3 page 13, as an "exemplary mother." On the other hand, an exceptional case is
given in the 'Cottage Gardener' 1860 page 388 of a hen raised from a Spanish
cock and black Polish hen which did not incubate.) Another author, after
giving a striking example, remarks that the fact can be explained only on the
principle that "two negatives make a positive." It cannot, however, be
maintained that hens produced from a cross between two non-sitting breeds
invariably recover their lost instinct, any more than that crossed fowls or
pigeons invariably recover the red or blue plumage of their prototypes. Thus I
raised several chickens from a Polish hen by a Spanish cock,--breeds which do
not incubate,--and none of the young hens at first showed any tendency to sit;
but one of them--the only one which was preserved--in the third year sat well
on her eggs and reared a brood of chickens. So that here we have the
reappearance with advancing age of a primitive instinct, in the same manner as
we have seen that the red plumage of the Gallus bankiva is sometimes
reacquired both by crossed and purely-bred fowls of various kinds as they grow
old.

The parents of all our domesticated animals were of course aboriginally wild
in disposition; and when a domesticated species is crossed with a distinct
species, whether this is a domesticated or only a tamed animal, the hybrids
are often wild to such a degree, that the fact is intelligible only on the
principle that the cross has caused a partial return to a primitive
disposition. Thus, the Earl of Powis formerly imported some thoroughly
domesticated humped cattle from India, and crossed them with English breeds,
which belong to a distinct species; and his agent remarked to me, without any
question having been asked, how oddly wild the cross-bred animals were. The
European wild boar and the Chinese domesticated pig are almost certainly
specifically distinct: Sir F. Darwin crossed a sow of the latter breed with a
wild Alpine boar which had become extremely tame, but the young, though having
half-domesticated blood in their veins, were "extremely wild in confinement,
and would not eat swill like common English pigs." Captain Hutton, in India,
crossed a tame goat with a wild one from the Himalaya, and he remarked to me
how surprisingly wild the offspring were. Mr. Hewitt, who has had great
experience in crossing tame cock-pheasants with fowls belonging to five
breeds, gives as the character of all "extraordinary wildness" (13/42. 'The
Poultry Book' by Tegetmeier 1866 pages 165, 167.); but I have myself seen one
exception to this rule. Mr. S. J. Salter (13/43. 'Natural History Review' 1863
April page 277.) who raised a large number of hybrids from a bantam-hen by
Gallus sonneratii, states that "all were exceedingly wild." Mr. Waterton
(13/44. 'Essays on Natural History' page 917.) bred some wild ducks from eggs
hatched under a common duck, and the young were allowed to cross freely both
amongst themselves and with the tame ducks; they were "half wild and half
tame; they came to the windows to be fed, but still they had a wariness about
them quite remarkable."

On the other hand, mules from the horse and ass are certainly not in the least
wild, though notorious for obstinacy and vice. Mr. Brent, who has crossed
canary-birds with many kinds of finches, has not observed, as he informs me,
that the hybrids were in any way remarkably wild: but Mr. Jenner Weir who has
had still greater experience, is of a directly opposite opinion. He remarks
that the siskin is the tamest of finches, but its mules are as wild, when
young, as newly caught birds, and are often lost through their continued
efforts to escape. Hybrids are often raised between the common and musk duck,
and I have been assured by three persons, who have kept these crossed birds,
that they were not wild; but Mr. Garnett (13/45. As stated by Mr. Orton in his
'Physiology of Breeding' page 12.) observed that his hybrids were wild, and
exhibited "migratory propensities" of which there is not a vestige in the
common or musk duck. No case is known of this latter bird having escaped and
become wild in Europe or Asia, except, according to Pallas, on the Caspian
Sea; and the common domestic duck only occasionally becomes wild in districts
where large lakes and fens abound. Nevertheless, a large number of cases have
been recorded (13/46. M. E. de Selys-Longchamps refers ('Bulletin Acad. Roy.
de Bruxelles' tome 12 No. 10) to more than seven of these hybrids shot in
Switzerland and France. M. Deby asserts ('Zoologist' volume 5 1845-46 page
1254) that several have been shot in various parts of Belgium and Northern
France. Audubon ('Ornitholog. Biography' volume 3 page 168), speaking of these
hybrids, says that, in North America, they "now and then wander off and become
quite wild.") of hybrids from these two ducks having been shot in a completely
wild state, although so few are reared in comparison with purely-bred birds of
either species. It is improbable that any of these hybrids could have acquired
their wildness from the musk-duck having paired with a truly wild duck; and
this is known not to be the case in North America; hence we must infer that
they have reacquired, through reversion, their wildness, as well as renewed
powers of flight.

These latter facts remind us of the statements, so frequently made by
travellers in all parts of the world, on the degraded state and savage
disposition of crossed races of man. That many excellent and kind-hearted
mulattos have existed no one will dispute; and a more mild and gentle set of
men could hardly be found than the inhabitants of the island of Chiloe, who
consist of Indians commingled with Spaniards in various proportions. On the
other hand, many years ago, long before I had thought of the present subject,
I was struck with the fact that, in South America, men of complicated descent
between Negroes, Indians, and Spaniards, seldom had, whatever the cause might
be, a good expression. (13/47. 'Journal of Researches' 1845 page 71.)
Livingstone--and a more unimpeachable authority cannot be quoted,--after
speaking of a half-caste man on the Zambesi, described by the Portuguese as a
rare monster of inhumanity, remarks, "It is unaccountable why half-castes,
such as he, are so much more cruel than the Portuguese, but such is
undoubtedly the case." An inhabitant remarked to Livingstone, "God made white
men, and God made black men, but the Devil made halfcastes." (13/48.
'Expedition to the Zambesi' 1865 pages 25, 150.) When two races, both low in
the scale, are crossed the progeny seems to be eminently bad. Thus the noble-
hearted Humboldt, who felt no prejudice against the inferior races, speaks in
strong terms of the bad and savage disposition of Zambos, or half-castes
between Indians and Negroes; and this conclusion has been arrived at by
various observers. (13/49. Dr. P. Broca on 'Hybridity in the Genus Homo'
English translation 1864 page 39.) From these facts we may perhaps infer that
the degraded state of so many half-castes is in part due to reversion to a
primitive and savage condition, induced by the act of crossing, even if mainly
due to the unfavourable moral conditions under which they are generally
reared.

SUMMARY ON THE PROXIMATE CAUSES LEADING TO REVERSION.

When purely-bred animals or plants reassume long-lost characters,--when the
common ass, for instance, is born with striped legs, when a pure race of black
or white pigeons throws a slaty-blue bird, or when a cultivated heartsease
with large and rounded flowers produces a seedling with small and elongated
flowers,--we are quite unable to assign any proximate cause. When animals run
wild, the tendency to reversion, which, though it has been greatly
exaggerated, no doubt exists, is sometimes to a certain extent intelligible.
Thus, with feral pigs, exposure to the weather will probably favour the growth
of the bristles, as is known to be the case with the hair of other
domesticated animals, and through correlation the tusks will tend to be
redeveloped. But the reappearance of coloured longitudinal stripes on young
feral pigs cannot be attributed to the direct action of external conditions.
In this case, and in many others, we can only say that any change in the
habits of life apparently favour a tendency, inherent or latent in the
species, to return to the primitive state.

It will be shown in a future chapter that the position of flowers on the
summit of the axis, and the position of seeds within the capsule, sometimes
determine a tendency towards reversion; and this apparently depends on the
amount of sap or nutriment which the flower-buds and seeds receive. The
position, also, of buds, either on branches or on roots, sometimes determines,
as was formerly shown, the transmission of the character proper to the
variety, or its reversion to a former state.

We have seen in the last section that when two races or species are crossed
there is the strongest tendency to the reappearance in the offspring of long-
lost characters, possessed by neither parent nor immediate progenitor. When
two white, or red, or black pigeons, of well-established breeds, are united,
the offspring are almost sure to inherit the same colours; but when
differently-coloured birds are crossed, the opposed forces of inheritance
apparently counteract each other, and the tendency which is inherent in both
parents to produce slaty-blue offspring becomes predominant. So it is in
several other cases. But when, for instance, the ass is crossed with E.
indicus or with the horse--animals which have not striped legs--and the
hybrids have conspicuous stripes on their legs and even on their faces, all
that can be said is, that an inherent tendency to reversion is evolved through
some disturbance in the organisation caused by the act of crossing.

Another form of reversion is far commoner, indeed is almost universal with the
offspring from a cross, namely, to the characters proper to either pure
parent-form. As a general rule, crossed offspring in the first generation are
nearly intermediate between their parents, but the grandchildren and
succeeding generations continually revert, in a greater or lesser degree, to
one or both of their progenitors. Several authors have maintained that hybrids
and mongrels include all the characters of both parents, not fused together,
but merely mingled in different proportions in different parts of the body;
or, as Naudin (13/50. 'Nouvelles Archives du Museum' tome 1 page 151.) has
expressed it, a hybrid is a living mosaic-work, in which the eye cannot
distinguish the discordant elements, so completely are they intermingled. We
can hardly doubt that, in a certain sense, this is true, as when we behold in
a hybrid the elements of both species segregating themselves into segments in
the same flower or fruit, by a process of self-attraction or self-affinity;
this segregation taking place either by seminal or bud-propagation. Naudin
further believes that the segregation of the two specific elements or essences
is eminently liable to occur in the male and female reproductive matter; and
he thus explains the almost universal tendency to reversion in successive
hybrid generations. For this would be the natural result of the union of
pollen and ovules, in both of which the elements of the same species had been
segregated by self-affinity. If, on the other hand, pollen which included the
elements of one species happened to unite with ovules including the elements
of the other species, the intermediate or hybrid state would still be
retained, and there would be no reversion. But it would, as I suspect, be more
correct to say that the elements of both parent-species exist in every hybrid
in a double state, namely, blended together and completely separate. How this
is possible, and what the term specific essence or element may be supposed to
express, I shall attempt to show in the chapter on the hypothesis of
pangenesis.

But Naudin's view, as propounded by him, is not applicable to the reappearance
of characters lost long ago by variation; and it is hardly applicable to races
or species which, after having been crossed at some former period with a
distinct form, and having since lost all traces of the cross, nevertheless
occasionally yield an individual which reverts (as in the case of the great-
great-grandchild of the pointer Sappho) to the crossing form. The most simple
case of reversion, namely, of a hybrid or mongrel to its grandparents, is
connected by an almost perfect series with the extreme case of a purely-bred
race recovering characters which had been lost during many ages; and we are
thus led to infer that all the cases must be related by some common bond.

Gartner believed that only highly sterile hybrid plants exhibit any tendency
to reversion to their parent-forms. This erroneous belief may perhaps be
accounted for by the nature of the genera crossed by him, for he admits that
the tendency differs in different genera. The statement is also directly
contradicted by Naudin's observations, and by the notorious fact that
perfectly fertile mongrels exhibit the tendency in a high degree,--even in a
higher degree, according to Gartner himself, than hybrids. (13/51.
'Bastarderzeugung' s. 582, 438, etc.)

Gartner further states that reversions rarely occur with hybrid plants raised
from species which have not been cultivated, whilst, with those which have
been long cultivated, they are of frequent occurrence. This conclusion
explains a curious discrepancy: Max Wichura (13/52. 'Die Bastardbefruchtung...
der Weiden' 1865 s. 23. For Gartner's remarks on this head, see
'Bastarderzeugung' s. 474, 582.) who worked exclusively on willows which had
not been subjected to culture, never saw an instance of reversion; and he goes
so far as to suspect that the careful Gartner had not sufficiently protected
his hybrids from the pollen of the parent-species: Naudin, on the other hand,
who chiefly experimented on cucurbitaceous and other cultivated plants,
insists more strenuously than any other author on the tendency to reversion in
all hybrids. The conclusion that the condition of the parent-species, as
affected by culture, is one of the proximate causes leading to reversion,
agrees well with the converse case of domesticated animals and cultivated
plants being liable to reversion when they become feral; for in both cases the
organisation or constitution must be disturbed, though in a very different
way. (13/53. Prof. Weismann in his very curious essay on the different forms
produced by the same species of butterfly at different seasons ('Saison-
Dimorphismus der Schmetterlinge' pages 27, 28), has come to a similar
conclusion, namely, that any cause which disturbs the organisation, such as
the exposure of the cocoons to heat or even to much shaking, gives a tendency
to reversion.)

Finally, we have seen that characters often reappear in purely-bred races
without our being able to assign any proximate cause; but when they become
feral this is either indirectly or directly induced by the change in their
conditions of life. With crossed breeds, the act of crossing in itself
certainly leads to the recovery of long-lost characters, as well as of those
derived from either parent-form. Changed conditions, consequent on
cultivation, and the relative position of buds, flowers, and seeds on the
plant, all apparently aid in giving this same tendency. Reversion may occur
either through seminal or bud generation, generally at birth, but sometimes
only with an advance of age. Segments or portions of the individual may alone
be thus affected. That a being should be born resembling in certain characters
an ancestor removed by two or three, and in some cases by hundreds or even
thousands of generations, is assuredly a wonderful fact. In these cases the
child is commonly said to inherit such characters directly from its
grandparent, or more remote ancestors. But this view is hardly conceivable.
If, however, we suppose that every character is derived exclusively from the
father or mother, but that many characters lie latent or dormant in both
parents during a long succession of generations, the foregoing facts are
intelligible. In what manner characters may be conceived to lie latent, will
be considered in a future chapter to which I have lately alluded.

LATENT CHARACTERS.

But I must explain what is meant by characters lying latent. The most obvious
illustration is afforded by secondary sexual characters. In every female all
the secondary male characters, and in every male all the secondary female
characters, apparently exist in a latent state, ready to be evolved under
certain conditions. It is well known that a large number of female birds, such
as fowls, various pheasants, partridges, peahens, ducks, etc., when old or
diseased, or when operated on, assume many or all of the secondary male
characters of their species. In the case of the hen-pheasant this has been
observed to occur far more frequently during certain years than during others.
(13/54. Yarrell 'Phil. Transact.' 1827 page 268; Dr. Hamilton in 'Proc.
Zoolog. Soc.' 1862 page 23.) A duck ten years old has been known to assume
both the perfect winter and summer plumage of the drake. (13/55. 'Archiv.
Skand. Beitrage zur Naturgesch.' 8 s. 397-413.) Waterton (13/56. In his
'Essays on Nat. Hist.' 1838 Mr. Hewitt gives analogous cases with hen-
pheasants in 'Journal of Horticulture' July 12, 1864 page 37. Isidore Geoffroy
Saint-Hilaire in his 'Essais de Zoolog. Gen.' ('Suites a Buffon' 1842 pages
496-513), has collected such cases in ten different kinds of birds. It appears
that Aristotle was well aware of the change in mental disposition in old hens.
The case of the female deer acquiring horns is given at page 513.) gives a
curious case of a hen which had ceased laying, and had assumed the plumage,
voice, spurs, and warlike disposition of the cock; when opposed to an enemy
she would erect her hackles and show fight. Thus every character, even to the
instinct and manner of fighting, must have lain dormant in this hen as long as
her ovaria continued to act. The females of two kinds of deer, when old, have
been known to acquire horns; and, as Hunter has remarked, we see something of
an analogous nature in the human species.

On the other hand, with male animals, it is notorious that the secondary
sexual characters are more or less completely lost when they are subjected to
castration. Thus, if the operation be performed on a young cock, he never, as
Yarrell states, crows again; the comb, wattles, and spurs do not grow to their
full size, and the hackles assume an intermediate appearance between true
hackles and the feathers of the hen. Cases are recorded of confinement, which
often affects the reproductive system, causing analogous results. But
characters properly confined to the female are likewise acquired by the male;
the capon takes to sitting on eggs, and will bring up chickens; and what is
more curious, the utterly sterile male hybrids from the pheasant and the fowl
act in the same manner, "their delight being to watch when the hens leave
their nests, and to take on themselves the office of a sitter." (13/57.
'Cottage Gardener' 1860 page 379.) That admirable observer Reaumur (13/58.
'Art de faire Eclore' etc. 1749 tome 2 page 8.) asserts that a cock, by being
long confined in solitude and darkness, can be taught to take charge of young
chickens; he then utters a peculiar cry, and retains during his whole life
this newly acquired maternal instinct. The many well-ascertained cases of
various male mammals giving milk shows that their rudimentary mammary glands
retain this capacity in a latent condition.

We thus see that in many, probably in all cases, the secondary characters of
each sex lie dormant or latent in the opposite sex, ready to be evolved under
peculiar circumstances. We can thus understand how, for instance, it is
possible for a good milking cow to transmit her good qualities through her
male offspring to future generations; for we may confidently believe that
these qualities are present, though latent, in the males of each generation.
So it is with the game-cock, who can transmit his superiority in courage and
vigour through his female to his male offspring; and with man it is known
(13/59. Sir H. Holland 'Medical Notes and Reflections' 3rd edition 1855 page
31.) that diseases, such as hydrocele, necessarily confined to the male sex,
can be transmitted through the female to the grandson. Such cases as these
offer, as was remarked at the commencement of this chapter, the simplest
possible examples of reversion; and they are intelligible on the belief that
characters common to the grandparent and grandchild of the same sex are
present, though latent, in the intermediate parent of the opposite sex.

The subject of latent characters is so important, as we shall see in a future
chapter, that I will give another illustration. Many animals have the right
and left sides of their body unequally developed: this is well known to be the
case with flat-fish, in which the one side differs in thickness and colour and
in the shape of the fins, from the other, and during the growth of the young
fish one eye is gradually twisted from the lower to the upper surface. (13/60.
See Steenstrup on the 'Obliquity of Flounders' in Annals and Mag. of Nat.
Hist.' May 1865 page 361. I have given an abstract of Malm's explanation of
this wonderful phenomenon in the 'Origin of Species' 6th Edition page 186.) In
most flat-fishes the left is the blind side, but in some it is the right;
though in both cases reversed or "wrong fishes," are occasionally developed;
and in Platessa flesus the right or left side is indifferently the upper one.
With gasteropods or shell-fish, the right and left sides are extremely unlike;
the far greater number of species are dextral, with rare and occasional
reversals of development; and some few are normally sinistral; but certain
species of Bulimus, and many Achatinellae (13/61. Dr. E. von Martens in
'Annals and Mag. of Nat. Hist.' March 1866 page 209.) are as often sinistral
as dextral. I will give an analogous case in the great articulate kingdom: the
two sides of Verruca (13/62. Darwin 'Balanidae' Ray Soc. 1854 page 499: see
also the appended remarks on the apparently capricious development of the
thoracic limbs on the right and left sides in the higher crustaceans.) are so
wonderfully unlike, that without careful dissection it is extremely difficult
to recognise the corresponding parts on the opposite sides of the body; yet it
is apparently a mere matter of chance whether it be the right or the left side
that undergoes so singular amount of change. One plant is known to me (13/63.
Mormodes ignea: Darwin 'Fertilisation of Orchids' 1862 page 251.) in which the
flower, according as it stands on the one or other side of the spike, is
unequally developed. In all the foregoing cases the two sides are perfectly
symmetrical at an early period of growth. Now, whenever a species is as liable
to be unequally developed on the one as on the other side, we may infer that
the capacity for such development is present, though latent, in the
undeveloped side. And as a reversal of development occasionally occurs in
animals of many kinds, this latent capacity is probably very common.

The best yet simplest cases of characters lying dormant are, perhaps, those
previously given, in which chickens and young pigeons, raised from a cross
between differently coloured birds, are at first of one colour, but in a year
or two acquire feathers of the colour of the other parent; for in this case
the tendency to a change of plumage is clearly latent in the young bird. So it
is with hornless breeds of cattle, some of which acquire small horns as they
grow old. Purely bred black and white bantams, and some other fowls,
occasionally assume, with advancing years, the red feathers of the parent-
species. I will here add a somewhat different case, as it connects in a
striking manner latent characters of two classes. Mr. Hewitt (13/64. 'Journal
of Horticulture' July 1864 page 38. I have had the opportunity of examining
these remarkable feathers through the kindness of Mr. Tegetmeier.) possessed
an excellent Sebright gold-laced bantam hen, which, as she became old, grew
diseased in her ovaria, and assumed male characters. In this breed the males
resemble the females in all respects except in their combs, wattles, spurs,
and instincts; hence it might have been expected that the diseased hen would
have assumed only those masculine characters which are proper to the breed,
but she acquired, in addition, well-arched tail sickle-feathers quite a foot
in length, saddle-feathers on the loins, and hackles on the neck,--ornaments
which, as Mr. Hewitt remarks, "would be held as abominable in this breed." The
Sebright bantam is known (13/65. 'The Poultry Book' by Mr. Tegetmeier 1866
page 241.) to have originated about the year 1800 from a cross between a
common bantam and a Polish fowl, recrossed by a hen-tailed bantam, and
carefully selected; hence there can hardly be a doubt that the sickle-feathers
and hackles which appeared in the old hen were derived from the Polish fowl or
common bantam; and we thus see that not only certain masculine characters
proper to the Sebright bantam, but other masculine characters derived from the
first progenitors of the breed, removed by a period of above sixty years, were
lying latent in this henbird, ready to be evolved as soon as her ovaria became
diseased.

From these several facts it must be admitted that certain characters,
capacities, and instincts, may lie latent in an individual, and even in a
succession of individuals, without our being able to detect the least sign of
their presence. When fowls, pigeons, or cattle of different colours are
crossed, and their offspring change colour as they grow old, or when the
crossed turbit acquired the characteristic frill after its third moult, or
when rarely-bred bantams partially assume the red plumage of their prototype,
we cannot doubt that these qualities were from the first present, though
latent, in the individual animal, like the characters of a moth in the
caterpillar. Now, if these animals had produced offspring before they had
acquired with advancing age their new characters, nothing is more probable
than that they would have transmitted them to some of their offspring, who in
this case would in appearance have received such characters from their grand-
parents or more distant progenitors. We should then have had a case of
reversion, that is, of the reappearance in the child of an ancestral
character, actually present, though during youth completely latent, in the
parent; and this we may safely conclude is what occurs in all reversions to
progenitors, however remote.

This view of the latency in each generation of all the characters which appear
through reversion, is also supported by their actual presence in some cases
during early youth alone, or by their more frequent appearance and greater
distinctness at this age than during maturity. We have seen that this is often
the case with the stripes on the legs and faces of the several species of the
horse genus. The Himalayan rabbit, when crossed, sometimes produces offspring
which revert to the parent silver-grey breed, and we have seen that in purely
bred animals pale-grey fur occasionally reappears during early youth. Black
cats, we may feel assured, would occasionally produce by reversion tabbies;
and on young black kittens, with a pedigree (13/66. Carl Vogt 'Lectures on
Man' English translation 1864 page 411.) known to have been long pure, faint
traces of stripes may almost always be seen which afterwards disappear.
Hornless Suffolk cattle occasionally produce by reversion horned animals; and
Youatt (13/67. 'On Cattle' page 174.) asserts that even in hornless
individuals "the rudiment of a horn may be often felt at an early age."

No doubt it appears at first sight in the highest degree improbable that in
every horse of every generation there should be a latent capacity and tendency
to produce stripes, though these may not appear once in a thousand
generations; that in every white, black, or other coloured pigeon, which may
have transmitted its proper colour during centuries, there should be a latent
capacity in the plumage to become blue and to be marked with certain
characteristic bars; that in every child in a six-fingered family there should
be the capacity for the production of an additional digit; and so in other
cases. Nevertheless, there is no more inherent improbability in this being the
case than in a useless and rudimentary organ, or even in only a tendency to
the production of a rudimentary organ, being inherited during millions of
generations, as is well known to occur with a multitude of organic beings.
There is no more inherent improbability in each domestic pig, during a
thousand generations, retaining the capacity and tendency to develop great
tusks under fitting conditions, than in the young calf having retained, for an
indefinite number of generations rudimentary incisor teeth, which never
protrude through the gums.

I shall give at the end of the next chapter a summary of the three preceding
chapters; but as isolated and striking cases of reversion have here been
chiefly insisted on, I wish to guard the reader against supposing that
reversion is due to some rare or accidental combination of circumstances. When
a character, lost during hundreds of generations, suddenly reappears, no doubt
some such combination must occur; but reversions, to the immediately preceding
generations may be constantly observed, at least, in the offspring of most
unions. This has been universally recognised in the case of hybrids and
mongrels, but it has been recognised simply from the difference between the
united forms rendering the resemblance of the offspring to their grandparents
or more remote progenitors of easy detection. Reversion is likewise almost
invariably the rule, as Mr. Sedgwick has shown, with certain diseases. Hence
we must conclude that a tendency to this peculiar form of transmission is an
integral part of the general law of inheritance.

MONSTROSITIES.

A large number of monstrous growths and of lesser anomalies are admitted by
every one to be due to an arrest of development, that is, to the persistence
of an embryonic condition. But many monstrosities cannot be thus explained;
for parts of which no trace can be detected in the embryo, but which occur in
other members of the same class of animals occasionally appear, and these may
probably with truth be attributed to reversion. As, however, I have treated
this subject as fully as I could in my 'Descent of Man' (ch. 1 2nd edition), I
will not here recur to it.

[When flowers which have normally an irregular structure become regular or
peloric, the change is generally looked at by botanists as a return to the
primitive state. But Dr. Maxwell Masters (13/68. 'Natural Hist. Review' April
1863 page 258. See also his Lecture, Royal Institution, March 16, 1860. On
same subject see Moquin-Tandon 'Elements de Teratologie' 1841 pages 184, 352.
Dr. Peyritsch has collected a large number of very interesting cases 'Sitzb.
d. k. Akad. d. Wissensch.' Wien b. 60 and especially b. 66 1872 page 125.),
who has ably discussed this subject, remarks that when, for instance, all the
sepals of a Tropaeolum become green and of the same shape, instead of being
coloured with one prolonged into a spur, or when all the petals of a Linaria
become simple and regular, such cases may be due merely to an arrest of
development; for in these flowers all the organs during their earliest
condition are symmetrical, and, if arrested at this stage of growth, they
would not become irregular. If, moreover, the arrest were to take place at a
still earlier period of development, the result would be a simple tuft of
green leaves; and no one probably would call this a case of reversion. Dr.
Masters designates the cases first alluded to as regular peloria; and others,
in which all the corresponding parts assume a similar form of irregularity, as
when all the petals in a Linaria become spurred, as irregular peloria. We have
no right to attribute these latter cases to reversion, until it can be shown
that the parent-form, for instance, of the genus Linaria had had all its
petals spurred; for a chance of this nature might result from the spreading of
an anomalous structure, in accordance with the law, to be discussed in a
future chapter, of homologous parts tending to vary in the same manner. But as
both forms of peloria frequently occur on the same individual plant of the
Linaria (13/69. Verlot 'Des Varietes' 1865 page 89; Naudin 'Nouvelles Archives
du Museum' tome 1 page 137.), they probably stand in some close relation to
one another. On the doctrine that peloria is simply the result of an arrest of
development, it is difficult to understand how an organ arrested at a very
early period of growth should acquire its full functional perfection;--how a
petal, supposed to be thus arrested, should acquire its brilliant colours, and
serve as an envelope to the flower, or a stamen produce efficient pollen; yet
this occurs with many peloric flowers. That pelorism is not due to mere chance
variability, but either to an arrest of development or to reversion, we may
infer from an observation made by Ch. Morren (13/70. In his discussion on some
curious peloric Calceolarias quoted in 'Journal of Horticulture' February 24,
1863 page 152.) namely, that families which have irregular flowers often
"return by these monstrous growths to their regular form; whilst we never see
a regular flower realise the structure of an irregular one."

Some flowers have almost certainly become more or less completely peloric
through reversion, as the following interesting case shows. Corydalis tuberosa
properly has one of its two nectaries colourless, destitute of nectar, only
half the size of the other, and therefore, to a certain extent, in a
rudimentary state; the pistil is curved towards the perfect nectary, and the
hood, formed of the inner petals, slips off the pistil and stamen in one
direction alone, so that, when a bee sucks the perfect nectary, the stigma and
stamens are exposed and rubbed against the insect's body. In several closely
allied genera, as in Dielytra, etc., there are two perfect nectaries, the
pistil is straight, and the hood slips off on either side, according as the
bee sucks either nectary. Now, I have examined several flowers of Corydalis
tuberosa, in which both nectaries were equally developed and contained nectar;
in this we see only the redevelopment of a partially aborted organ; but with
this redevelopment the pistil becomes straight, and the hood slips off in
either direction, so that these flowers have acquired the perfect structure,
so well adapted for insect agency, of Dielytra and its allies. We cannot
attribute these coadapted modifications to chance, or to correlated
variability; we must attribute them to reversion to a primordial condition of
the species.

The peloric flowers of Pelargonium have their five petals in all respects
alike, and there is no nectary so that they resemble the symmetrical flowers
of the closely allied genus Geranium; but the alternate stamens are also
sometimes destitute of anthers, the shortened filaments being left as
rudiments, and in this respect they resemble the symmetrical flowers of the
closely allied genus Erodium. Hence we may look at the peloric flowers of
Pelargonium as having reverted to the state of some primordial form, the
progenitor of the three closely related genera of Pelargonium, Geranium, and
Erodium.

In the peloric form of Antirrhinum majus, appropriately called the" Wonder,"
the tubular and elongated flowers differ wonderfully from those of the common
snapdragon; the calyx and the mouth of the corolla consist of six equal lobes,
and include six equal instead of four unequal stamens. One of the two
additional stamens is manifestly formed by the development of a
microscopically minute papilla, which may be found at the base of the upper
lip of the flower of the common snapdragons in the nineteen plants examined by
me. That this papilla is a rudiment of a stamen was well shown by its various
degrees of development in crossed plants between the common and the peloric
Antirrhinum. Again, a peloric Galeobdolon luteum, growing in my garden, had
five equal petals, all striped like the ordinary lower lip, and included five
equal instead of four unequal stamens; but Mr. R. Keeley, who sent me this
plant, informs me that the flowers vary greatly, having from four to six lobes
to the corolla, and from three to six stamens. (13/71. For other cases of six
divisions in peloric flowers of the Labiatae and Scrophulariaceae see Moquin-
Tandon 'Teratologie' page 192.) Now, as the members of the two great families
to which the Antirrhinum and Galeobdolon belong are properly pentamerous, with
some of the parts confluent and others suppressed, we ought not to look at the
sixth stamen and the sixth lobe to the corolla in either case as due to
reversion, any more than the additional petals in double flowers in these same
two families. But the case is different with the fifth stamen in the peloric
Antirrhinum, which is produced by the redevelopment of a rudiment always
present, and which probably reveals to us the state of the flower, as far as
the stamens are concerned, at some ancient epoch. It is also difficult to
believe that the other four stamens and the petals, after an arrest of
development at a very early embryonic age, would have come to full perfection
in colour, structure, and function, unless these organs had at some former
period normally passed through a similar course of growth. Hence it appears to
me probable that the progenitor of the genus Antirrhinum must at some remote
epoch have included five stamens and borne flowers in some degree resembling
those now produced by the peloric form. The conclusion that peloria is not a
mere monstrosity, irrespective of any former state of the species, is
supported by the fact that this structure is often strongly inherited, as in
the case of the peloric Antirrhinum and Gloxinia and sometimes in that of the
peloric Corydalis solida. (13/72. Godron reprinted from the 'Memoires de
l'Acad. de Stanislas' 1868.)

Lastly I may add that many instances have been recorded of flowers, not
generally considered as peloric, in which certain organs are abnormally
augmented in number. As an increase of parts cannot be looked at as an arrest
of development, nor as due to the redevelopment of rudiments, for no rudiments
are present, and as these additional parts bring the plant into closer
relationship with its natural allies, they ought probably to be viewed as
reversions to a primordial condition.]

These several facts show us in an interesting manner how intimately certain
abnormal states are connected together; namely, arrests of development causing
parts to become rudimentary or to be wholly suppressed,--the redevelopment of
parts now in a more or less rudimentary condition,--the reappearance of organs
of which not a vestige can be detected,--and to these may be added, in the
case of animals, the presence during youth, and subsequent disappearance, of
certain characters which occasionally are retained throughout life. Some
naturalists look at all such abnormal structures as a return to the ideal
state of the group to which the affected being belongs; but it is difficult to
conceive what is meant to be conveyed by this expression. Other naturalists
maintain, with greater probability and distinctness of view, that the common
bond of connection between the several foregoing cases is an actual, though
partial, return to the structure of the ancient progenitor of the group. If
this view be correct, we must believe that a vast number of characters,
capable of evolution, lie hidden in every organic being. But it would be a
mistake to suppose that the number is equally great in all beings. We know,
for instance, that plants of many orders occasionally become peloric; but many
more cases have been observed in the Labiatae and Scrophulariaceae than in any
other order; and in one genus of the Scrophulariaceae, namely Linaria, no less
than thirteen species have been described in this condition (13/73. Moquin-
Tandon 'Teratologie' page 186.) On this view of the nature of peloric flowers,
and bearing in mind certain monstrosities in the animal kingdom, we must
conclude that the progenitors of most plants and animals have left an
impression, capable of redevelopment, on the germs of their descendants,
although these have since been profoundly modified.

The fertilised germ of one of the higher animals, subjected as it is to so
vast a series of changes from the germinal cell to old age,--incessantly
agitated by what Quatrefages well calls the tourbillon vital,--is perhaps the
most wonderful object in nature. It is probable that hardly a change of any
kind affects either parent, without some mark being left on the germ. But on
the doctrine of reversion, as given in this chapter, the germ becomes a far
more marvellous object, for, besides the visible changes which it undergoes,
we must believe that it is crowded with invisible characters, proper to both
sexes, to both the right and left side of the body, and to a long line of male
and female ancestors separated by hundreds or even thousands of generations
from the present time: and these characters, like those written on paper with
invisible ink, lie ready to be evolved whenever the organisation is disturbed
by certain known or unknown conditions.


CHAPTER 2.XIV.

INHERITANCE continued.--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUAL LIMITATION
--CORRESPONDENCE OF AGE.

FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF INHERITANCE.
PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN CROSSED
BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER; SOMETIMES DUE TO
THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREED AND LATENT IN THE
OTHER.
INHERITANCE AS LIMITED BY SEX.
NEWLY-ACQUIRED CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE
SEX ALONE, SOMETIMES LOST BY ONE SEX ALONE.
INHERITANCE AT CORRESPONDING PERIODS OF LIFE.
THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS EXHIBITED IN
DOMESTICATED ANIMALS: AS EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF
INHERITED DISEASES; SOMETIMES SUPERVENING EARLIER IN THE CHILD THAN IN
THE PARENT.
SUMMARY OF THE THREE PRECEDING CHAPTERS.

In the last two chapters the nature and force of Inheritance, the
circumstances which interfere with its power, and the tendency to Reversion,
with its many remarkable contingencies, were discussed. In the present chapter
some other related phenomena will be treated of, as fully as my materials
permit.

FIXEDNESS OF CHARACTER.

It is a general belief amongst breeders that the longer any character has been
transmitted by a breed, the more fully it will continue to be transmitted. I
do not wish to dispute the truth of the proposition that inheritance gains
strength simply through long continuance, but I doubt whether it can be
proved. In one sense the proposition is little better than a truism; if any
character has remained constant during many generations, it will be likely to
continue so, if the conditions of life remain the same. So, again, in
improving a breed, if care be taken for a length of time to exclude all
inferior individuals, the breed will obviously tend to become truer, as it
will not have been crossed during many generations by an inferior animal. We
have previously seen, but without being able to assign any cause, that, when a
new character appears, it is occasionally from the first constant, or
fluctuates much, or wholly fails to be transmitted. So it is with the
aggregate of slight differences which characterise a new variety, for some
propagate their kind from the first much truer than others. Even with plants
multiplied by bulbs, layers, etc., which may in one sense be said to form
parts of the same individual, it is well known that certain varieties retain
and transmit through successive bud-generations their newly-acquired
characters more truly than others. In none of these, nor in the following
cases, does there appear to be any relation between the force with which a
character is transmitted and the length of time during which it has been
transmitted. Some varieties, such as white and yellow hyacinths and white
sweet-peas, transmit their colours more faithfully than do the varieties which
have retained their natural colour. In the Irish family, mentioned in the
twelfth chapter, the peculiar tortoiseshell-like colouring of the eyes was
transmitted far more faithfully than any ordinary colour. Ancon and Mauchamp
sheep and niata cattle, which are all comparatively modern breeds, exhibit
remarkably strong powers of inheritance. Many similar cases could be adduced.

As all domesticated animals and cultivated plants have varied, and yet are
descended from aboriginally wild forms, which no doubt had retained the same
character from an immensely remote epoch, we see that scarcely any degree of
antiquity ensures a character being transmitted perfectly true. In this case,
however, it may be said that changed conditions of life induce certain
modifications, and not that the power of inheritance fails; but in every case
of failure, some cause, either internal or external, must interfere. It will
generally be found that the organs or parts which in our domesticated
productions have varied, or which still continue to vary,--that is, which fail
to retain their former state,--are the same with the parts which differ in the
natural species of the same genus. As, on the theory of descent with
modification, the species of the same genus have been modified since they
branched off from a common progenitor, it follows that the characters by which
they differ from one another have varied, whilst other parts of the
organisation have remained unchanged; and it might be argued that these same
characters now vary under domestication, or fail to be inherited, from their
lesser antiquity. But variation in a state of nature seems to stand in some
close relation with changed conditions of life, and characters which have
already varied under such conditions would be apt to vary under the still
greater changes consequent on domestication, independently of their greater or
less antiquity.

Fixedness of character, or the strength of inheritance, has often been judged
of by the preponderance of certain characters in the crossed offspring between
distinct races; but prepotency of transmission here comes into play, and this,
as we shall immediately see, is a very different consideration from the
strength or weakness of inheritance. (14/1. See 'Youatt on Cattle' pages 92,
69, 78, 88, 163; and 'Youatt on Sheep' page 325. Also Dr. Lucas 'L'Hered.
Nat.' tome 2 page 310.) It has often been observed that breeds of animals
inhabiting wild and mountainous countries cannot be permanently modified by
our improved breeds; and as these latter are of modern origin, it has been
thought that the greater antiquity of the wilder breeds has been the cause of
their resistance to improvement by crossing; but it is more probably due to
their structure and constitution being better adapted to the surrounding
conditions. When plants are first subjected to culture, it has been found
that, during several generations, they transmit their characters truly, that
is, do not vary, and this has been attributed to ancient characters being
strongly inherited: but it may with equal or greater probability be consequent
on changed conditions of life requiring a long time for their cumulative
action. Notwithstanding these considerations, it would perhaps be rash to deny
that characters become more strongly fixed the longer they are transmitted;
but I believe that the proposition resolves itself into this,--that characters
of all kinds, whether new or old, tend to be inherited, and that those which
have already withstood all counteracting influences and been truly
transmitted, will, as a general rule, continue to withstand them, and
consequently be faithfully inherited.

PREPOTENCY IN THE TRANSMISSION OF CHARACTER.

When individuals, belonging to the same family, but distinct enough to be
recognised, or when two well-marked races, or two species, are crossed, the
usual result, as stated in the previous chapter, is, that the offspring in the
first generation are intermediate between their parents, or resemble one
parent in one part and the other parent in another part. But this is by no
means the invariable rule; for in many cases it is found that certain
individuals, races, and species, are prepotent in transmitting their likeness.
This subject has been ably discussed by Prosper Lucas (14/2. 'Hered. Nat.'
tome 2 pages 112-120.), but is rendered extremely complex by the prepotency
sometimes running equally in both sexes, and sometimes more strongly in one
sex than in the other; it is likewise complicated by the presence of secondary
sexual characters, which render the comparison of crossed breeds with their
parents difficult.

It would appear that in certain families some one ancestor, and after him
others in the same family, have had great power in transmitting their likeness
through the male line; for we cannot otherwise understand how the same
features should so often be transmitted after marriages with many females, as
in the case of the Austrian Emperors; and so it was, according to Niebuhr,
with the mental qualities of certain Roman families. (14/3. Sir H. Holland
'Chapters on Mental Physiology' 1852 page 234.) The famous bull Favourite is
believed (14/4. 'Gardener's Chronicle' 1860 page 270.) to have had a prepotent
influence on the shorthorn race. It has also been observed (14/5. Mr. N.H.
Smith 'Observations on Breeding' quoted in 'Encyclop. of Rural Sports' page
278.) with English racehorses that certain mares have generally transmitted
their own character, whilst other mares of equally pure blood have allowed the
character of the sire to prevail. A famous black greyhound, Bedlamite, as I
hear from Mr. C.M. Brown "invariably got all his puppies black, no matter what
was the colour of the bitch;" but then Bedlamite "had a preponderance of black
in his blood, both on the sire and dam side."

[The truth of the principle of prepotency comes out more clearly when distinct
races are crossed. The improved Shorthorns, notwithstanding that the breed is
comparatively modern, are generally acknowledged to possess great power in
impressing their likeness on all other breeds; and it is chiefly in
consequence of this power that they are so highly valued for exportation.
(14/6. Quoted by Bronn 'Geshichte der Natur' b. 2 s. 170. See Sturm 'Ueber
Racen' 1825 s. 104-107. For the niata cattle see my 'Journal of Researches'
1845 page 146.) Godine has given a curious case of a ram of a goat-like breed
of sheep from the Cape of Good Hope, which produced offspring hardly to be
distinguished from himself, when crossed with ewes of twelve other breeds. But
two of these half-bred ewes, when put to a merino ram, produced lambs closely
resembling the merino breed. Girou de Buzareingues (14/7. Lucas 'L'Heredite
Nat.' tome 2 page 112.) found that of two races of French sheep the ewes of
one, when crossed during successive generations with merino rams, yielded up
their character far sooner than the ewes of the other race. Sturm and Girou
have given analogous cases with other breeds of sheep and with cattle, the
prepotency running in these cases through the male side; but I was assured on
good authority in South America, that when niata cattle are crossed with
common cattle, though the niata breed is prepotent whether males or females
are used, yet that the prepotency is strongest through the female line. The
Manx cat is tailless and has long hind legs; Dr. Wilson crossed a male Manx
with common cats, and, out of twenty-three kittens, seventeen were destitute
of tails; but when the female Manx was crossed by common male cats all the
kittens had tails, though they were generally short and imperfect. (14/8. Mr.
Orton 'Physiology of Breeding' 1855 page 9.)

In making reciprocal crosses between pouter and fantail pigeons, the pouter-
race seemed to be prepotent through both sexes over the fantail. But this is
probably due to weak power in the fantail rather than to any unusually strong
power in the pouter, for I have observed that barbs also preponderate over
fantails. This weakness of transmission in the fantail, though the breed is an
ancient one, is said (14/9. Boitard and Corbie 'Les Pigeons' 1824 page 224.)
to be general; but I have observed one exception to the rule, namely, in a
cross between a fantail and laugher. The most curious instance known to me of
weak power in both sexes is in the trumpeter pigeon. This breed has been well
known for at least 130 years: it breeds perfectly true, as I have been assured
by those who have long kept many birds: it is characterised by a peculiar tuft
of feathers over the beak, by a crest on the head, by a singular coo quite
unlike that of any other breed, and by much-feathered feet. I have crossed
both sexes with turbits of two sub-breeds, with almond tumblers, spots, and
runts, and reared many mongrels and recrossed them; and though the crest on
the head and feathered feet were inherited (as is generally the case with most
breeds), I have never seen a vestige of the tuft over the beak or heard the
peculiar coo. Boitard and Corbie (14/10. 'Les Pigeons' pages 168, 198.) assert
that this is the invariable result of crossing trumpeters with other breeds:
Neumeister (14/11. 'Das Ganze' etc. 1837 s. 39.), however, states that in
Germany mongrels have been obtained, though very rarely, which were furnished
with the tuft and would trumpet: but a pair of these mongrels with a tuft,
which I imported, never trumpeted. Mr. Brent states (14/12. 'The Pigeon Book'
page 46.) that the crossed offspring of a trumpeter were crossed with
trumpeters for three generations, by which time the mongrels had 7/8ths of
this blood in their veins, yet the tuft over the beak did not appear. At the
fourth generation the tuft appeared, but the birds though now having 15-16ths
trumpeter's blood still did not trumpet. This case well shows the wide
difference between inheritance and prepotency; for here we have a well-
established old race which transmits its characters faithfully, but which,
when crossed with any other race, has the feeblest power of transmitting its
two chief characteristic qualities.

I will give one other instance with fowls and pigeons of weakness and strength
in the transmission of the same character to their crossed offspring. The Silk
fowl breeds true, and there is reason to believe is a very ancient race; but
when I reared a large number of mongrels from a Silk hen by a Spanish cock,
not one exhibited even a trace of the so-called silkiness. Mr. Hewitt also
asserts that in no instance are the silky feathers transmitted by this breed
when crossed with any other variety. But three birds out of many raised by Mr.
Orton from a cross between a silk cock and a bantam hen had silky feathers.
(14/13. 'Physiology of Breeding' page 22; Mr. Hewitt in 'The Poultry Book' by
Tegetmeier 1866 page 224.) So that it is certain that this breed very seldom
has the power of transmitting its peculiar plumage to its crossed progeny. On
the other hand, there is a silk sub-variety of the fantail pigeon, which has
its feathers in nearly the same state as in the Silk fowl: now we have already
seen that fantails, when crossed, possess singularly weak power in
transmitting their general qualities; but the silk sub-variety when crossed
with any other small-sized race invariably transmits its silky feathers!
(14/14. Boitard and Corbie 'Les Pigeons' 1824 page 226.)

The well-known horticulturist, Mr. Paul, informs me that he fertilised the
Black Prince hollyhock with pollen of the White Globe and the Lemonade and
Black Prince hollyhocks reciprocally; but not one seedling from these three
crosses inherited the black colour of the Black Prince. So, again, Mr. Laxton,
who has had such great experience in crossing peas, writes to me that
"whenever a cross has been effected between a white-blossomed and a purple-
blossomed pea, or between a white-seeded and a purple-spotted, brown or maple-
seeded pea, the offspring seems to lose nearly all the characteristics of the
white-flowered and white-seeded varieties; and this result follows whether
these varieties have been used as the pollen-bearing or seed-producing
parents."

The law of prepotency comes into action when species are crossed, as with
races and individuals. Gartner has unequivocally shown (14/15.
'Bastarderzeugung' s. 256, 290, etc. Naudin 'Nouvelles Archives du Museum'
tome 1 page 149 gives a striking instance of prepotency in Datura stramonium
when crossed with two other species.) that this is the case with plants. To
give one instance: when Nicotiana paniculata and vincaeflora are crossed, the
character of N. paniculata is almost completely lost in the hybrid; but if N.
quadrivalvis be crossed with N. vincaeflora, this latter species, which was
before so prepotent, now in its turn almost disappears under the power of N.
quadrivalvis. It is remarkable that the prepotency of one species over another
in transmission is quite independent, as shown by Gartner, of the greater or
less facility with which the one fertilises the other.

With animals, the jackal is prepotent over the dog, as is stated by Flourens,
who made many crosses between these animals; and this was likewise the case
with a hybrid which I once saw between a jackal and a terrier. I cannot doubt,
from the observations of Colin and others, that the ass is prepotent over the
horse; the prepotency in this instance running more strongly through the male
than through the female ass; so that the mule resembles the ass more closely
than does the hinny. (14/16. Flourens 'Longevite Humaine' page 144 on crossed
jackals. With respect to the difference between the mule and the hinny I am
aware that this has generally been attributed to the sire and dam transmitting
their characters differently; but Colin, who has given in his 'Traite Phys.
Comp.' tome 2 pages 537-539, the fullest description which I have met with of
these reciprocal hybrids, is strongly of opinion that the ass preponderates in
both crosses, but in an unequal degree. This is likewise the conclusion of
Flourens, and of Bechstein in his 'Naturgeschichte Deutschlands' b. 1 s. 294.
The tail of the hinny is much more like that of the horse than is the tail of
the mule, and this is generally accounted for by the males of both species
transmitting with greater power this part of their structure; but a compound
hybrid which I saw in the Zoological Gardens, from a mare by a hybrid ass-
zebra, closely resembled its mother in its tail.) The male pheasant, judging
from Mr. Hewitt's descriptions (14/17. Mr. Hewitt who has had such great
experience in raising these hybrids says ('Poultry Book' by Mr. Tegetmeier
1866 pages 165-167) that in all, the head was destitute of wattles, comb, and
ear-lappets; and all closely resembled the pheasant in the shape of the tail
and general contour of the body. These hybrids were raised from hens of
several breeds by a cock-pheasant; but another hybrid, described by Mr.
Hewitt, was raised from a hen-pheasant, by a silver-laced Bantam cock, and
this possessed a rudimental comb and wattles.), and from the hybrids which I
have seen, preponderates over the domestic fowl; but the latter, as far as
colour is concerned, has considerable power of transmission, for hybrids
raised from five differently coloured hens differed greatly in plumage. I
formerly examined some curious hybrids in the Zoological Gardens, between the
Penguin variety of the common duck and the Egyptian goose (Anser aegyptiacus);
and although I will not assert that the domesticated variety preponderated
over the natural species, yet it had strongly impressed its unnatural upright
figure on these hybrids.

I am aware that such cases as the foregoing have been ascribed by various
authors, not to one species, race, or individual being prepotent over the
other in impressing its character on its crossed offspring, but to such rules
as that the father influences the external characters and the mother the
internal or vital organs. But the great diversity of the rules given by
various authors almost proves their falseness. Dr. Prosper Lucas has fully
discussed this point, and has shown (14/18. 'L'Hered. Nat.' tome 2 book 2
chapter 1.) that none of the rules (and I could add others to those quoted by
him) apply to all animals. Similar rules have been announced for plants, and
have been proved by Gartner (14/19. 'Bastarderzeugung' s. 264-266. Naudin
'Nouvelles Archives du Museum' tome 1 page 148 has arrived at a similar
conclusion.) to be all erroneous. If we confine our view to the domesticated
races of a single species, or perhaps even to the species of the same genus,
some such rules may hold good; for instance, it seems that in reciprocally
crossing various breeds of fowls the male generally gives colour (14/20.
'Cottage Gardener' 1856 pages 101, 137.); but conspicuous exceptions have
passed under my own eyes. It seems that the ram usually gives its peculiar
horns and fleece to its crossed offspring, and the bull the presence or
absence of horns.

In the following chapter on Crossing I shall have occasion to show that
certain characters are rarely or never blended by crossing, but are
transmitted in an unmodified state from either parent-form; I refer to this
fact here because it is sometimes accompanied on the one side by prepotency,
which thus acquires the false appearance of unusual strength. In the same
chapter I shall show that the rate at which a species or breed absorbs and
obliterates another by repeated crosses, depends in chief part on prepotency
in transmission.]

In conclusion, some of the cases above given,--for instance, that of the
trumpeter pigeon,--prove that there is a wide difference between mere
inheritance and prepotency. This latter power seems to us, in our ignorance,
to act in most cases quite capriciously. The very same character, even though
it be an abnormal or monstrous one, such as silky feathers, may be transmitted
by different species, when crossed, either with prepotent force or singular
feebleness. It is obvious, that a purely-bred form of either sex, in all cases
in which prepotency does not run more strongly in one sex than the other, will
transmit its character with prepotent force over a mongrelised and already
variable form. (14/21. See some remarks on this head with respect to sheep by
Mr. Wilson in 'Gardener's Chronicle' 1863 page 15. Many striking instances of
this result are given by M. Malingie-Nouel 'Journ. R. Agricult. Soc.' volume
14 1853 page 220 with respect to crosses between English and French sheep. He
found that he obtained the desired influence of the English breeds by crossing
intentionally mongrelised French breeds with pure English breeds.) From
several of the above-given cases we may conclude that mere antiquity of
character does not by any means necessarily make it prepotent. In some cases
prepotency apparently depends on the same character being present and visible
in one of the two breeds which are crossed, and latent or invisible in the
other breed; and in this case it is natural that the character which is
potentially present in both breeds should be prepotent. Thus, we have reason
to believe that there is a latent tendency in all horses to be dun-coloured
and striped; and when a horse of this kind is crossed with one of any other
colour, it is said that the offspring are almost sure to be striped. Sheep
have a similar latent tendency to become dark-coloured, and we have seen with
what prepotent force a ram with a few black spots, when crossed with white
sheep of various breeds, coloured its offspring. All pigeons have a latent
tendency to become slaty-blue, with certain characteristic marks, and it is
known that, when a bird thus coloured is crossed with one of any other colour,
it is most difficult afterwards to eradicate the blue tint. A nearly parallel
case is offered by those black bantams which, as they grow old, develop a
latent tendency to acquire red feathers. But there are exceptions to the rule:
hornless breeds of cattle possess a latent capacity to reproduce horns, yet
when crossed with horned breeds they do not invariably produce offspring
bearing horns.

We meet with analogous cases with plants. Striped flowers, though they can be
propagated truly by seed, have a latent tendency to become uniformly coloured,
but when once crossed by a uniformly coloured variety, they ever afterwards
fail to produce striped seedlings. (14/22. Verlot 'Des Varietes' 1865 page
66.) Another case is in some respects more curious: plants bearing peloric
flowers have so strong a latent tendency to reproduce their normally irregular
flowers, that this often occurs by buds when a plant is transplanted into
poorer or richer soil. (14/23. Moquin-Tandon 'Teratologie' page 191.) Now I
crossed the peloric snapdragon (Antirrhinum majus), described in the last
chapter, with pollen of the common form; and the latter, reciprocally, with
peloric pollen. I thus raised two great beds of seedlings, and not one was
peloric. Naudin (14/24. 'Nouvelles Archives du Museum' tome 1 page 137.)
obtained the same result from crossing a peloric Linaria with the common form.
I carefully examined the flowers of ninety plants of the crossed Antirrhinum
in the two beds, and their structure had not been in the least affected by the
cross, except that in a few instances the minute rudiment of the fifth stamen,
which is always present, was more fully or even completely developed. It must
not be supposed that this entire obliteration of the peloric structure in the
crossed plants can be accounted for by any incapacity of transmission; for I
raised a large bed of plants from the peloric Antirrhinum, artificially
fertilised by its own pollen, and sixteen plants, which alone survived the
winter, were all as perfectly peloric as the parent-plant. Here we have a good
instance of the wide difference between the inheritance of a character and the
power of transmitting it to crossed offspring. The crossed plants, which
perfectly resembled the common snapdragon, were allowed to sow themselves, and
out of a hundred and twenty-seven seedlings, eighty-eight proved to be common
snapdragons, two were in an intermediate condition between the peloric and
normal state, and thirty-seven were perfectly peloric, having reverted to the
structure of their one grand-parent. This case seems at first sight to offer
an exception to the rule just given, namely, that a character which is present
in one form and latent in the other is generally transmitted with prepotent
force when the two forms are crossed. For in all the Scrophulariaceae, and
especially in the genera Antirrhinum and Linaria, there is, as was shown in
the last chapter, a strong latent tendency to become peloric; but there is
also, as we have seen, a still stronger tendency in all peloric plants to
reacquire their normal irregular structure. So that we have two opposed latent
tendencies in the same plants. Now, with the crossed Antirrhinums the tendency
to produce normal or irregular flowers, like those of the common Snapdragon,
prevailed in the first generation; whilst the tendency to pelorism, appearing
to gain strength by the intermission of a generation, prevailed to a large
extent in the second set of seedlings. How it is possible for a character to
gain strength by the intermission of a generation, will be considered in the
chapter on pangenesis.

On the whole, the subject of prepotency is extremely intricate,--from its
varying so much in strength, even in regard to the same character, in
different animals,--from its running either equally in both sexes, or, as
frequently is the case with animals, but not with plants, much stronger in one
sex than the other,--from the existence of secondary sexual characters,--from
the transmission of certain characters being limited, as we shall immediately
see, by sex,--from certain characters not blending together,--and, perhaps,
occasionally from the effects of a previous fertilisation on the mother. It is
therefore not surprising that no one has hitherto succeeded in drawing up
general rules on the subject of prepotency.

INHERITANCE AS LIMITED BY SEX.

New characters often appear in one sex, and are afterwards transmitted to the
same sex, either exclusively or in a much greater degree than to the other.
This subject is important, because with animals of many kinds in a state of
nature, both high and low in the scale, secondary sexual characters, not
directly connected with the organs of reproduction, are conspicuously present.
With our domesticated animals, characters of this kind often differ widely
from those distinguishing the two sexes of the parent species; and the
principle of inheritance, as limited by sex, explains how this is possible.

[Dr. P. Lucas has shown (14/25. 'L'Hered. Nat.' tome 2 pages 137-165. See also
Mr. Sedgwick's four memoirs, immediately to be referred to.) that when a
peculiarity, in no manner connected with the reproductive organs, appears in
either parent, it is often transmitted exclusively to the offspring of the
same sex, or to a much greater number of them than of the opposite sex. Thus,
in the family of Lambert, the horn-like projections on the skin were
transmitted from the father to his sons and grandsons alone; so it has been
with other cases of ichthyosis, with supernumerary digits, with a deficiency
of digits and phalanges, and in a lesser degree with various diseases,
especially with colour-blindness and the haemorrhagic diathesis, that is, an
extreme liability to profuse and uncontrollable bleeding from trifling wounds.
On the other hand, mothers have transmitted, during several generations, to
their daughters alone, supernumerary and deficient digits, colour-blindness
and other peculiarities. So that the very same peculiarity may become attached
to either sex, and be long inherited by that sex alone; but the attachment in
certain cases is much more frequent to one than the other sex. The same
peculiarities also may be promiscuously transmitted to either sex. Dr. Lucas
gives other cases, showing that the male occasionally transmits his
peculiarities to his daughters alone, and the mother to her sons alone; but
even in this case we see that inheritance is to a certain extent, though
inversely, regulated by sex. Dr. Lucas, after weighing the whole evidence,
comes to the conclusion that every peculiarity tends to be transmitted in a
greater or lesser degree to that sex in which it first appears. But a more
definite rule, as I have elsewhere shown (14/26. 'Descent of Man' 2nd edition
page 32.) generally holds good, namely, that variations which first appear in
either sex at a late period of life, when the reproductive functions are
active, tend to be developed in that sex alone; whilst variations which first
appear early in life in either sex are commonly transmitted to both sexes. I
am, however, far from supposing that this is the sole determining cause.

A few details from the many cases collected by Mr. Sedgwick (14/27. On Sexual
Limitation in Hereditary Diseases 'Brit. and For. Med.-Chirurg. Review' April
1861 page 477; July page 198; April 1863 page 445; and July page 159. Also in
1867 'On the influence of Age in Hereditary Disease.'), may be here given.
Colour-blindness, from some unknown cause, shows itself much oftener in males
than in females; in upwards of two hundred cases collected by Mr. Sedgwick,
nine-tenths related to men; but it is eminently liable to be transmitted
through women. In the case given by Dr. Earle, members of eight related
families were affected during five generations: these families consisted of
sixty-one individuals, namely, of thirty-two males, of whom nine-sixteenths
were incapable of distinguishing colour, and of twenty-nine females, of whom
only one-fifteenth were thus affected. Although colour-blindness thus
generally clings to the male sex, nevertheless, in one instance in which it
first appeared in a female, it was transmitted during five generations to
thirteen individuals, all of whom were females. The haemorrhagic diathesis,
often accompanied by rheumatism, has been known to affect the males alone
during five generations, being transmitted, however, through the females. It
is said that deficient phalanges in the fingers have been inherited by the
females alone during ten generations. In another case, a man thus deficient in
both hands and feet, transmitted the peculiarity to his two sons and one
daughter; but in the third generation,--out of nineteen grandchildren, twelve
sons had the family defect, whilst the seven daughters were free. In ordinary
cases of sexual limitation, the sons or daughters inherit the peculiarity,
whatever it may be, from their father or mother, and transmit it to their
children of the same sex; but generally with the haemorrhagic diathesis, and
often with colour-blindness, and in some other cases, the sons never inherit
the peculiarity directly from their fathers, but the daughters alone transmit
the latent tendency, so that the sons of the daughters alone exhibit it. Thus
the father, grandson, and great-great-grandson will exhibit a peculiarity,--
the grandmother, daughter, and great-grand-daughter having transmitted it in a
latent state. Hence we have, as Mr. Sedgwick remarks, a double kind of atavism
or reversion; each grandson apparently receiving and developing the
peculiarity from his grandfather, and each daughter apparently receiving the
latent tendency from her grandmother.

From the various facts recorded by Dr. Prosper Lucas, Mr. Sedgwick, and
others, there can be no doubt that peculiarities first appearing in either
sex, though not in any way necessarily or invariably connected with that sex,
strongly tend to be inherited by the offspring of the same sex, but are often
transmitted in a latent state through the opposite sex.

Turning now to domesticated animals, we find that certain characters not
proper to the parent species are often confined to, and inherited by, one sex
alone; but we do not know the history of the first appearance of such
characters. In the chapter on Sheep, we have seen that the males of certain
races differ greatly from the females in the shape of their horns, these being
absent in the ewes of some breeds; they differ also in the development of fat
in the tail and in the outline of the forehead. These differences, judging
from the character of the allied wild species, cannot be accounted for by
supposing that they have been derived from distinct parent forms. There is,
also, a great difference between the horns of the two sexes in one Indian
breed of goats. The bull zebu is said to have a larger hump than the cow. In
the Scotch deer-hound the two sexes differ in size more than in any other
variety of the dog (14/28. W. Scrope 'Art of Deer Stalking' page 354.) and,
judging from analogy, more than in the aboriginal parent-species. The peculiar
colour called tortoise-shell is very rarely seen in a male cat; the males of
this variety being of a rusty tint.

In various breeds of the fowl the males and females often differ greatly; and
these differences are far from being the same with those which distinguish the
two sexes of the parent-species, the Gallus bankiva; and consequently have
originated under domestication. In certain sub-varieties of the Game race we
have the unusual case of the hens differing from each other more than the
cocks. In an Indian breed of a white colour shaded with black, the hens
invariably have black skins, and their bones are covered by a black
periosteum, whilst the cocks are never or most rarely thus characterised.
Pigeons offer a more interesting case; for throughout the whole great family
the two sexes do not often differ much; and the males and females of the
parent-form, the C. livia, are undistinguishable: yet we have seen that with
pouters the male has the characteristic quality of pouting more strongly
developed than the female; and in certain sub-varieties the males alone are
spotted or striated with black, or otherwise differ in colour. When male and
female English carrier-pigeons are exhibited in separate pens, the difference
in the development of the wattle over the beak and round the eyes is
conspicuous. So that here we have instances of the appearance of secondary
sexual characters in the domesticated races of a species in which such
differences are naturally quite absent.]

On the other hand, secondary sexual characters which belong to the species in
a state of nature are sometimes quite lost, or greatly diminished, under
domestication. We see this in the small size of the tusks in our improved
breeds of the pig, in comparison with those of the wild boar. There are sub-
breeds of fowls, in which the males have lost the fine-flowing tail-feathers
and hackles; and others in which there is no difference in colour between the
two sexes. In some cases the barred plumage, which in gallinaceous birds is
commonly the attribute of the hen, has been transferred to the cock, as in the
cuckoo sub-breeds. In other cases masculine characters have been partly
transferred to the female, as with the splendid plumage of the golden-spangled
Hamburgh hen, the enlarged comb of the Spanish hen, the pugnacious disposition
of the Game hen, and as in the well-developed spurs which occasionally appear
in the hens of various breeds. In Polish fowls both sexes are ornamented with
a topknot, that of the male being formed of hackle-like feathers, and this is
a new male character in the genus Gallus. On the whole, as far as I can judge,
new characters are more apt to appear in the males of our domesticated animals
than in the females (14/29. I have given in my 'Descent of Man' 2nd edition
page 223 sufficient evidence that male animals are usually more variable than
the females.), and afterwards to be inherited exclusively or more strongly by
the males. Finally, in accordance with the principle of inheritance as limited
by sex, the preservation and augmentation of secondary sexual characters in
natural species offers no especial difficulty, as this would follow through
that form of selection which I have called sexual selection.

INHERITANCE AT CORRESPONDING PERIODS OF LIFE.

This is an important subject. Since the publication of my 'Origin of Species'
I have seen no reason to doubt the truth of the explanation there given of one
of the most remarkable facts in biology, namely, the difference between the
embryo and the adult animal. The explanation is, that variations do not
necessarily or generally occur at a very early period of embryonic growth, and
that such variations are inherited at a corresponding age. As a consequence of
this the embryo, even after the parent-form has undergone great modification,
is left only slightly modified; and the embryos of widely-different animals
which are descended from a common progenitor remain in many important respects
like one another and probably like their common progenitor. We can thus
understand why embryology throws a flood of light on the natural system of
classification, as this ought to be as far as possible genealogical. When the
embryo leads an independent life, that is, becomes a larva, it has to be
adapted to the surrounding conditions in its structure and instincts,
independently of those of its parents; and the principle of inheritance at
corresponding periods of life renders this possible.

This principle is, indeed, in one way so obvious that it escapes attention. We
possess a number of races of animals and plants, which, when compared with one
another and with their parent-forms, present conspicuous differences, both in
their immature and mature states. Look at the seeds of the several kinds of
peas, beans, maize, which can be propagated truly, and see how they differ in
size, colour, and shape, whilst the full-grown plants differ but little.
Cabbages, on the other hand, differ greatly in foliage and manner of growth,
but hardly at all in their seeds; and generally it will be found that the
differences between cultivated plants at different periods of growth are not
necessarily closely connected together, for plants may differ much in their
seeds and little when full-grown, and conversely may yield seeds hardly
distinguishable, yet differ much when full-grown. In the several breeds of
poultry, descended from a single species, differences in the eggs and chickens
whilst covered with down, in the plumage at the first and subsequent moults,
as well as in the comb and wattles, are all inherited. With man peculiarities
in the milk and second teeth (of which I have received the details) are
inheritable, and longevity is often transmitted. So again with our improved
breeds of cattle and sheep, early maturity, including the early development of
the teeth, and with certain breeds of fowl the early appearance of secondary
sexual characters, all come under the same head of inheritance at
corresponding periods.

Numerous analogous facts could be given. The silk-moth, perhaps, offers the
best instance; for in the breeds which transmit their characters truly, the
eggs differ in size, colour, and shape: the caterpillars differ, in moulting
three or four times, in colour, even in having a dark-coloured mark like an
eyebrow, and in the loss of certain instincts;--the cocoons differ in size,
shape, and in the colour and quality of the silk; these several differences
being followed by slight or barely distinguishable differences in the mature
moth.

But it may be said that, if in the above cases a new peculiarity is inherited,
it must be at the corresponding stage of development; for an egg or seed can
resemble only an egg or seed, and the horn in a full-grown ox can resemble
only a horn. The following cases show inheritance at corresponding periods
more plainly, because they refer to peculiarities which might have supervened,
as far as we can see, earlier or later in life, yet are inherited at the same
period at which they first appeared.

[In the Lambert family the porcupine-like excrescences appeared in the father
and sons at the same age, namely, about nine weeks after birth. (14/30.
Prichard 'Phys. Hist. of Mankind' 1851 volume 1 page 349.) In the
extraordinary hairy family described by Mr. Crawfurd (14/31. 'Embassy to the
Court of Ava' volume 1 page 320. The third generation is described by Capt.
Yule in his 'Narrative of the Mission to the Court of Ava' 1855 page 94.),
children were produced during three generations with hairy ears; in the father
the hair began to grow over his body at six years old; in his daughter
somewhat earlier, namely, at one year; and in both generations the milk teeth
appeared late in life, the permanent teeth being afterwards singularly
deficient. Greyness of hair at an unusually early age has been transmitted in
some families. These cases border on diseases inherited at corresponding
periods of life, to which I shall immediately refer.

It is a well-known peculiarity with almond-tumbler pigeons, that the full
beauty and peculiar character of the plumage does not appear until the bird
has moulted two or three times. Neumeister describes and figures a brace of
pigeons in which the whole body is white except the breast, neck, and head;
but in their first plumage all the white feathers have coloured edges. Another
breed is more remarkable: its first plumage is black, with rusty-red wing-bars
and a crescent-shaped mark on the breast; these marks then become white, and
remain so during three or four moults; but after this period the white spreads
over the body, and the bird loses its beauty. (14/32. 'Das Ganze der
Taubenzucht' 1837 s. 24 tab. 4 figure 2 s. 21 tab. 1 figure 4.) Prize canary-
birds have their wings and tail black: "this colour, however, is only retained
until the first moult, so that they must be exhibited ere the change takes
place. Once moulted, the peculiarity has ceased. Of course all the birds
emanating from this stock have black wings and tails the first year." (14/33.
Kidd 'Treatise on the Canary' page 18.) A curious and somewhat analogous
account has been given (14/34. Charlesworth 'Mag. of Nat. Hist.' volume 1 1837
page 167.) of a family of wild pied rooks which were first observed in 1798,
near Chalfont, and which every year from that date up to the period of the
published notice, viz., 1837 "have several of their brood particoloured, black
and white. This variegation of the plumage, however, disappears with the first
moult; but among the next young families there are always a few pied ones."
These changes of plumage, which are inherited at various corresponding periods
of life in the pigeon, canary-bird, and rook, are remarkable, because the
parent-species passes through no such change.

Inherited diseases afford evidence in some respects of less value than the
foregoing cases, because diseases are not necessarily connected with any
change in structure; but in other respects of more value, because the periods
have been more carefully observed. Certain diseases are communicated to the
child apparently by a process like inoculation, and the child is from the
first affected; such cases may be here passed over. Large classes of diseases
usually appear at certain ages, such as St. Vitus's dance in youth,
consumption in early mid-life, gout later, and apoplexy still later; and these
are naturally inherited at the same period. But even in diseases of this
class, instances have been recorded, as with St. Vitus's dance, showing that
an unusually early or late tendency to the disease is inheritable. (14/35. Dr.
Prosper Lucas 'Hered. Nat.' tome 2 page 713.) In most cases the appearance of
any inherited disease is largely determined by certain critical periods in
each person's life, as well as by unfavourable conditions. There are many
other diseases, which are not attached to any particular period, but which
certainly tend to appear in the child at about the same age at which the
parent was first attacked. An array of high authorities, ancient and modern,
could be given in support of this proposition. The illustrious Hunter believed
in it; and Piorry (14/36. 'L'Hered. dans les Maladies' 1840 page 135. For
Hunter see Harlan 'Med. Researches' page 530.) cautions the physician to look
closely to the child at the period when any grave inheritable disease attacked
the parent. Dr. Prosper Lucas (14/37. 'L'Hered. Nat.' tome 2 page 850.), after
collecting facts from every source, asserts that affections of all kinds,
though not related to any particular period of life, tend to reappear in the
offspring at whatever period of life they first appeared in the progenitor.

As the subject is important, it may be well to give a few instances, simply as
illustrations, not as proof; for proof, recourse must be had to the
authorities above quoted. Some of the following cases have been selected for
the sake of showing that, when a slight departure from the rule occurs, the
child is affected somewhat earlier in life than the parent. In the family of
Le Compte blindness was inherited through three generations, and no less than
twenty-seven children and grandchildren were all affected at about the same
age; their blindness in general began to advance about the fifteenth or
sixteenth year, and ended in total deprivation of sight at the age of about
twenty-two. (14/38. Sedgwick 'Brit. and For. Med.-Chirurg. Review' April 1861
page 485. In some accounts the number of children and grandchildren is given
as 37; but this seems to be an error judging from the paper first published in
the 'Baltimore Med. and Phys. Reg.' 1809 of which Mr. Sedgwick has been so
kind as to send me a copy.) In another case a father and his four children all
became blind at twenty-one years old; in another, a grandmother grew blind at
thirty-five, her daughter at nineteen, and three grandchildren at the ages of
thirteen and eleven. (14/39. Prosper Lucas 'Hered. Nat.' tome 1 page 400.) So
with deafness, two brothers, their father and paternal grandfather, all became
deaf at the age of forty. (14/40. Sedgwick ibid July 1861 page 202.)

Esquirol gives several striking instances of insanity coming on at the same
age, as that of a grandfather, father, and son, who all committed suicide near
their fiftieth year. Many other cases could be given, as of a whole family who
became insane at the age of forty. (14/41. Piorry page 109; Prosper Lucas tome
2 page 759.) Other cerebral affections sometimes follow the same rule,--for
instance, epilepsy and apoplexy. A woman died of the latter disease when
sixty-three years old; one of her daughters at forty-three, and the other at
sixty-seven: the latter had twelve children, who all died from tubercular
meningitis. (14/42. Prosper Lucas tome 2 page 748.) I mention this latter case
because it illustrates a frequent occurrence, namely, a change in the precise
nature of an inherited disease, though still affecting the same organ.

Asthma has attacked several members of the same family when forty years old,
and other families during infancy. The most different diseases, such as angina
pectoris, stone in the bladder, and various affections of the skin, have
appeared in successive generations at nearly the same age. The little finger
of a man began from some unknown cause to grow inwards, and the same finger in
his two sons began at the same age to bend inwards in a similar manner.
Strange and inexplicable neuralgic affections have caused parents and children
to suffer agonies at about the same period of life. (14/43. Prosper Lucas tome
3 pages 678, 700, 702; Sedgwick ibid April 1863 page 449 and July 1863 page
162. Dr. J. Steinan 'Essay on Hereditary Disease' 1843 pages 27, 34.)

I will give only two other cases, which are interesting as illustrating the
disappearance as well as the appearance of disease at the same age. Two
brothers, their father, their paternal uncles, seven cousins, and their
paternal grandfather, were all similarly affected by a skin-disease, called
pityriasis versicolor; "the disease, strictly limited to the males of the
family (though transmitted through the females), usually appeared at puberty,
and disappeared at about the age of forty or forty-five years." The second
case is that of four brothers, who when about twelve years old suffered almost
every week from severe headaches, which were relieved only by a recumbent
position in a dark room. Their father, paternal uncles, paternal grandfather,
and granduncles all suffered in the same way from headaches, which ceased at
the age of fifty-four or fifty-five in all those who lived so long. None of
the females of the family were affected. (14/44. These cases are given by Mr.
Sedgwick on the authority of Dr. H. Stewart in 'Med.-Chirurg. Review' April
1863 pages 449, 477.)]

It is impossible to read the foregoing accounts, and the many others which
have been recorded, of diseases coming on during three or even more
generations in several members of the same family at the same age, especially
in the case of rare affections in which the coincidence cannot be attributed
to chance, and to doubt that there is a strong tendency to inheritance in
disease at corresponding periods of life. When the rule fails, the disease is
apt to come on earlier in the child than in the parent; the exceptions in the
other direction being very much rarer. Dr. Lucas (14/45. 'Hered. Nat.' tome 2
page 852.) alludes to several cases of inherited diseases coming on at an
earlier period. I have already given one striking instance with blindness
during three generations; and Mr. Bowman remarks that this frequently occurs
with cataract. With cancer there seems to be a peculiar liability to earlier
inheritance: Sir J. Paget, who has particularly attended to this subject, and
tabulated a large number of cases, informs me that he believes that in nine
cases out of ten the later generation suffers from the disease at an earlier
period than the previous generation. He adds, "In the instances in which the
opposite relation holds, and the members of later generations have cancer at a
later age than their predecessors, I think it will be found that the non-
cancerous parents have lived to extreme old ages." So that the longevity of a
non-affected parent seems to have the power of influencing the fatal period in
the offspring; and we thus apparently get another element of complexity in
inheritance.

The facts, showing that with certain diseases the period of inheritance
occasionally or even frequently advances, are important with respect to the
general descent-theory, for they render it probable that the same thing would
occur with ordinary modifications of structure. The final result of a long
series of such advances would be the gradual obliteration of characters proper
to the embryo and larva, which would thus come to resemble more and more
closely the mature parent-form. But any structure which was of service to the
embryo or larva would be preserved by the destruction at this stage of growth
of each individual which manifested any tendency to lose its proper character
at too early an age.

Finally, from the numerous races of cultivated plants and domestic animals, in
which the seeds or eggs, the young or old, differ from one another and from
those of the parent-species;--from the cases in which new characters have
appeared at a particular period, and afterwards been inherited at the same
period;--and from what we know with respect to disease, we must believe in the
truth of the great principle of inheritance at corresponding periods of life.

SUMMARY OF THE THREE PRECEDING CHAPTERS.

Strong as is the force of inheritance, it allows the incessant appearance of
new characters. These, whether beneficial or injurious,--of the most trifling
importance, such as a shade of colour in a flower, a coloured lock of hair, or
a mere gesture,--or of the highest importance, as when affecting the brain, or
an organ so perfect and complex as the eye,--or of so grave a nature as to
deserve to be called a monstrosity,--or so peculiar as not to occur normally
in any member of the same natural class,--are often inherited by man, by the
lower animals, and plants. In numberless cases it suffices for the inheritance
of a peculiarity that one parent alone should be thus characterised.
Inequalities in the two sides of the body, though opposed to the law of
symmetry, may be transmitted. There is ample evidence that the effects of
mutilations and of accidents, especially or perhaps exclusively when followed
by disease, are occasionally inherited. There can be no doubt that the evil
effects of the long-continued exposure of the parent to injurious conditions
are sometimes transmitted to the offspring. So it is, as we shall see in a
future chapter, with the effects of the use and disuse of parts, and of mental
habits. Periodical habits are likewise transmitted, but generally, as it would
appear, with little force.

Hence we are led to look at inheritance as the rule, and non-inheritance as
the anomaly. But this power often appears to us in our ignorance to act
capriciously, transmitting a character with inexplicable strength or
feebleness. The very same peculiarity, as the weeping habit of trees, silky
feathers, etc., may be inherited either firmly or not at all by different
members of the same group, and even by different individuals of the same
species, though treated in the same manner. In this latter case we see that
the power of transmission is a quality which is merely individual in its
attachment. As with single characters, so it is with the several concurrent
slight differences which distinguish sub-varieties or races; for of these,
some can be propagated almost as truly as species, whilst others cannot be
relied on. The same rule holds good with plants, when propagated by bulbs,
offsets, etc., which in one sense still form parts of the same individual, for
some varieties retain or inherit through successive bud-generations their
character far more truly than others.

Some characters not proper to the parent-species have certainly been inherited
from an extremely remote epoch, and may therefore be considered as firmly
fixed. But it is doubtful whether length of inheritance in itself gives
fixedness of character; though the chances are obviously in favour of any
character which has long been transmitted true or unaltered still being
transmitted true as long as the conditions of life remain the same. We know
that many species, after having retained the same character for countless
ages, whilst living under their natural conditions, when domesticated have
varied in the most diversified manner, that is, have failed to transmit their
original form; so that no character appears to be absolutely fixed. We can
sometimes account for the failure of inheritance by the conditions of life
being opposed to the development of certain characters; and still oftener, as
with plants cultivated by grafts and buds, by the conditions causing new and
slight modifications incessantly to appear. In this latter case it is not that
inheritance wholly fails, but that new characters are continually superadded.
In some few cases, in which both parents are similarly characterised,
inheritance seems to gain so much force by the combined action of the two
parents, that it counteracts its own power, and a new modification is the
result.

In many cases the failure of the parents to transmit their likeness is due to
the breed having been at some former period crossed; and the child takes after
his grandparent or more remote ancestor of foreign blood. In other cases, in
which the breed has not been crossed, but some ancient character has been lost
through variation, it occasionally reappears through reversion, so that the
parents apparently fail to transmit their own likeness. In all cases, however,
we may safely conclude that the child inherits all its characters from its
parents, in whom certain characters are latent, like the secondary sexual
characters of one sex in the other. When, after a long succession of bud-
generations, a flower or fruit becomes separated into distinct segments,
having the colours or other attributes of both parent-forms, we cannot doubt
that these characters were latent in the earlier buds, though they could not
then be detected, or could be detected only in an intimately commingled state.
So it is with animals of crossed parentage, which with advancing years
occasionally exhibit characters derived from one of their two parents, of
which not a trace could at first be perceived. Certain monstrosities, which
resemble what naturalists call the typical form of the group in question,
apparently come under the same law of reversion. It is assuredly an
astonishing fact that the male and female sexual elements, that buds, and even
full-grown animals, should retain characters, during several generations in
the case of crossed breeds, and during thousands of generations in the case of
pure breeds, written as it were in invisible ink, yet ready at any time to be
evolved under certain conditions.

What these conditions precisely are, we do not know. But any cause which
disturbs the organisation or constitution seems to be sufficient. A cross
certainly gives a strong tendency to the reappearance of long-lost characters,
both corporeal and mental. In the case of plants, this tendency is much
stronger with those species which have been crossed after long cultivation and
which therefore have had their constitutions disturbed by this cause as well
as by crossing, than with species which have always lived under their natural
conditions and have then been crossed. A return, also, of domesticated animals
and cultivated plants to a wild state favours reversion; but the tendency
under these circumstances has been much exaggerated.

When individuals of the same family which differ somewhat, and when races or
species are crossed, the one is often prepotent over the other in transmitting
its character. A race may possess a strong power of inheritance, and yet when
crossed, as we have seen with trumpeter-pigeons, yield to the prepotency of
every other race. Prepotency of transmission may be equal in the two sexes of
the same species, but often runs more strongly in one sex. It plays an
important part in determining the rate at which one race can be modified or
wholly absorbed by repeated crosses with another. We can seldom tell what
makes one race or species prepotent over another; but it sometimes depends on
the same character being present and visible in one parent, and latent or
potentially present in the other.

Characters may first appear in either sex, but oftener in the male than in the
female, and afterwards be transmitted to the offspring of the same sex. In
this case we may feel confident that the peculiarity in question is really
present though latent in the opposite sex! hence the father may transmit
through his daughter any character to his grandson; and the mother conversely
to her granddaughter. We thus learn, and the fact is an important one, that
transmission and development are distinct powers. Occasionally these two
powers seem to be antagonistic, or incapable of combination in the same
individual; for several cases have been recorded in which the son has not
directly inherited a character from his father, or directly transmitted it to
his son, but has received it by transmission through his non-affected mother,
and transmitted it through his non-affected daughter. Owing to inheritance
being limited by sex, we see how secondary sexual characters may have arisen
under nature; their preservation and accumulation being dependent on their
service to either sex.

At whatever period of life a new character first appears, it generally remains
latent in the offspring until a corresponding age is attained, and then is
developed. When this rule fails, the child generally exhibits the character at
an earlier period than the parent. On this principle of inheritance at
corresponding periods, we can understand how it is that most animals display
from the germ to maturity such a marvellous succession of characters.

Finally, though much remains obscure with respect to Inheritance, we may look
at the following laws as fairly well established.

FIRSTLY, a tendency in every character, new and old, to be transmitted by
seminal and bud generation, though often counteracted by various known and
unknown causes.

SECONDLY, reversion or atavism, which depends on transmission and development
being distinct powers: it acts in various degrees and manners through both
seminal and bud generation.

THIRDLY, prepotency of transmission, which may be confined to one sex, or be
common to both sexes.

FOURTHLY, transmission, as limited by sex, generally to the same sex in which
the inherited character first appeared; and this in many, probably most cases,
depends on the new character having first appeared at a rather late period of
life.

FIFTHLY, inheritance at corresponding periods of life, with some tendency to
the earlier development of the inherited character.

In these laws of Inheritance, as displayed under domestication, we see an
ample provision for the production, through variability and natural selection,
of new specific forms.


CHAPTER 2.XV.

ON CROSSING.

FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS.
WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE OTHER.
THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY THE
CONDITIONS OF LIFE, AND BY NATURAL SELECTION.
ALL ORGANIC BEINGS OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS.
ON CERTAIN CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH
HAVE SUDDENLY APPEARED IN THE INDIVIDUAL.
ON THE MODIFICATION OF OLD RACES, AND THE FORMATION OF NEW RACES BY CROSSING.
SOME CROSSED RACES HAVE BRED TRUE FROM THEIR FIRST PRODUCTION.
ON THE CROSSING OF DISTINCT SPECIES IN RELATION TO THE FORMATION OF DOMESTIC
RACES.

In the two previous chapters, when discussing reversion and prepotency, I was
necessarily led to give many facts on crossing. In the present chapter I shall
consider the part which crossing plays in two opposed directions,--firstly, in
obliterating characters, and consequently in preventing the formation of new
races; and secondly, in the modification of old races, or in the formation of
new and intermediate races, by a combination of characters. I shall also show
that certain characters are incapable of fusion.

The effects of free or uncontrolled breeding between the members of the same
variety or of closely allied varieties are important; but are so obvious that
they need not be discussed at much length. It is free intercrossing which
chiefly gives uniformity, both under nature and under domestication, to the
individuals of the same species or variety, when they live mingled together
and are not exposed to any cause inducing excessive variability. The
prevention of free crossing, and the intentional matching of individual
animals, are the corner-stones of the breeder's art. No man in his senses
would expect to improve or modify a breed in any particular manner, or keep an
old breed true and distinct, unless he separated his animals. The killing of
inferior animals in each generation comes to the same thing as their
separation. In savage and semi-civilised countries, where the inhabitants have
not the means of separating their animals, more than a single breed of the
same species rarely or never exists. In former times, even in the United
States, there were no distinct races of sheep, for all had been mingled
together. (15/1. 'Communications to the Board of Agriculture' volume 1 page
367.) The celebrated agriculturist Marshall (15/2. 'Review of Reports, North
of England' 1808 page 200.) remarks that "sheep that are kept within fences,
as well as shepherded flocks in open countries, have generally a similarity,
if not a uniformity, of character in the individuals of each flock;" for they
breed freely together, and are prevented from crossing with other kinds;
whereas in the unenclosed parts of England the unshepherded sheep, even of the
same flock, are far from true or uniform, owing to various breeds having
mingled and crossed. We have seen that the half-wild cattle in each of the
several British parks are nearly uniform in character; but in the different
parks, from not having mingled and crossed during many generations, they
differ to a certain small extent.

We cannot doubt that the extraordinary number of varieties and sub-varieties
of the pigeon, amounting to at least one hundred and fifty, is partly due to
their remaining, differently from other domesticated birds, paired for life
once matched. On the other hand, breeds of cats imported into this country
soon disappear, for their nocturnal and rambling habits render it hardly
possible to prevent free crossing. Rengger (15/3. 'Saugethiere von Paraguay'
1830 s. 212.) gives an interesting case with respect to the cat in Paraguay:
in all the distant parts of the kingdom it has assumed, apparently from the
effects of the climate, a peculiar character, but near the capital this change
has been prevented, owing, as he asserts, to the native animal frequently
crossing with cats imported from Europe. In all cases like the foregoing, the
effects of an occasional cross will be augmented by the increased vigour and
fertility of the crossed offspring, of which fact evidence will hereafter be
given; for this will lead to the mongrels increasing more rapidly than the
pure parent-breeds.

When distinct breeds are allowed to cross freely, the result will be a
heterogeneous body; for instance, the dogs in Paraguay are far from uniform,
and can no longer be affiliated to their parent-races. (15/4. Rengger
'Saugethiere' etc. s. 154.) The character which a crossed body of animals will
ultimately assume must depend on several contingencies,--namely, on the
relative members of the individuals belonging to the two or more races which
are allowed to mingle; on the prepotency of one race over the other in the
transmission of character; and on the conditions of life to which they are
exposed. When two commingled breeds exist at first in nearly equal numbers,
the whole will sooner or later become intimately blended, but not so soon,
both breeds being equally favoured in all respects, as might have been
expected. The following calculation (15/5. White 'Regular Gradation in Man'
page 146.) shows that this is the case: if a colony with an equal number of
black and white men were founded, and we assume that they marry
indiscriminately, are equally prolific, and that one in thirty annually dies
and is born; then "in 65 years the number of blacks, whites, and mulattoes
would be equal. In 91 years the whites would be 1-10th, the blacks 1-10th, and
the mulattoes, or people of intermediate degrees of colour, 8-10ths of the
whole number. In three centuries not 1-100th part of the whites would exist."

When one of two mingled races exceed the other greatly in number, the latter
will soon be wholly, or almost wholly, absorbed and lost. (15/6. Dr. W.F.
Edwards in his 'Caracteres Physiolog. des Races Humaines' page 24 first called
attention to this subject, and ably discussed it.) Thus European pigs and dogs
have been largely introduced in the islands of the Pacific Ocean, and the
native races have been absorbed and lost in the course of about fifty or sixty
years (15/7. Rev. D. Tyerman and Bennett 'Journal of Voyages' 1821-1829 volume
1 page 300.); but the imported races no doubt were favoured. Rats may be
considered as semi-domesticated animals. Some snake-rats (Mus alexandrinus)
escaped in the Zoological Gardens of London "and for a long time afterwards
the keepers frequently caught cross-bred rats, at first half-breds, afterwards
with less of the character of the snake-rat, till at length all traces of it
disappeared." (15/8. Mr. S.J. Salter 'Journal Linn. Soc.' volume 6 1862 page
71.) On the other hand, in some parts of London, especially near the docks,
where fresh rats are frequently imported, an endless variety of intermediate
forms may be found between the brown, black, and snake rat, which are all
three usually ranked as distinct species.

How many generations are necessary for one species or race to absorb another
by repeated crosses has often been discussed (15/9. Sturm 'Ueber Racen, etc.'
1825 s. 107. Bronn 'Geschichte der Natur' b. 2 s. 170 gives a table of the
proportions of blood after successive crosses. Dr. P. Lucas 'L'Heredite Nat.'
tome 2 page 308.); and the requisite number has probably been much
exaggerated. Some writers have maintained that a dozen or score, or even more
generations, are necessary; but this in itself is improbable, for in the tenth
generation there would be only 1-1024th part of foreign blood in the
offspring. Gartner found (15/10. 'Bastarderzeugung' s. 463, 470.), that with
plants, one species could be made to absorb another in from three to five
generations, and he believes that this could always be effected in from six to
seven generations. In one instance, however, Kolreuter (15/11. 'Nova Acta
Petrop.' 1794 page 393: see also previous volume.) speaks of the offspring of
Mirabilis vulgaris, crossed during eight successive generations by M.
longiflora, as resembling this latter species so closely, that the most
scrupulous observer could detect "vix aliquam notabilem differentiam" or, as
he says, he succeeded, "ad plenariam fere transmutationem." But this
expression shows that the act of absorption was not even then absolutely
complete, though these crossed plants contained only the 1-256th part of M.
vulgaris. The conclusions of such accurate observers as Gartner and Kolreuter
are of far higher worth than those made without scientific aim by breeders.
The most precise account which I have met with is given by Stonehenge (15/12.
'The Dog' 1867 pages 179-184.) and is illustrated by photographs. Mr. Hanley
crossed a greyhound bitch with a bulldog; the offspring in each succeeding
generation being recrossed with first-rate greyhounds. As Stonehenge remarks,
it might naturally be supposed that it would take several crosses to get rid
of the heavy form of the bulldog; but Hysterics, the gr-gr-granddaughter of a
bulldog, showed no trace whatever of this breed in external form. She and all
of the same litter, however, were "remarkably deficient in stoutness, though
fast as well as clever." I believe clever refers to skill in turning.
Hysterics was put to a son of Bedlamite, "but the result of the fifth cross is
not as yet, I believe, more satisfactory than that of the fourth." On the
other hand, with sheep, Fleischmann (15/13. As quoted in the 'True Principles
of Breeding' by C.H. Macknight and Dr. H. Madden 1865 page 11.) shows how
persistent the effects of a single cross may be: he says "that the original
coarse sheep (of Germany) have 5500 fibres of wool on a square inch; grades of
the third or fourth Merino cross produced about 8000, the twentieth cross
27,000, the perfect pure Merino blood 40,000 to 48,000." So that common German
sheep crossed twenty times successively with Merino did not by any means
acquire wool as fine as that of the pure breed. But in all cases, the rate of
absorption will depend largely on the conditions of life being favourable to
any particular character; and we may suspect that there would be a constant
tendency to degeneration in the wool of Merinos under the climate of Germany,
unless prevented by careful selection; and thus perhaps the foregoing
remarkable case may be explained. The rate of absorption must also depend on
the amount of distinguishable difference between the two forms which are
crossed, and especially, as Gartner insists, on prepotency of transmission in
the one form over the other. We have seen in the last chapter that one of two
French breeds of sheep yielded up its character, when crossed with Merinos,
very much more slowly than the other; and the common German sheep referred to
by Fleischmann may be in this respect analogous. In all cases there will be
more or less liability to reversion during many subsequent generations, and it
is this fact which has probably led authors to maintain that a score or more
of generations are requisite for one race to absorb another. In considering
the final result of the commingling of two or more breeds, we must not forget
that the act of crossing in itself tends to bring back long-lost characters
not proper to the immediate parent-forms.

With respect to the influence of the conditions of life on any two breeds
which are allowed to cross freely, unless both are indigenous and have long
been accustomed to the country where they live, they will, in all probability,
be unequally affected by the conditions, and this will modify the result. Even
with indigenous breeds, it will rarely or never occur that both are equally
well adapted to the surrounding circumstances; more especially when permitted
to roam freely, and not carefully tended, as is generally the case with breeds
allowed to cross. As a consequence of this, natural selection will to a
certain extent come into action, and the best fitted will survive, and this
will aid in determining the ultimate character of the commingled body.

How long a time it would require before such a crossed body of animals would
assume a uniform character within a limited area, no one can say; that they
would ultimately become uniform from free intercrossing, and from the survival
of the fittest, we may feel assured; but the characters thus acquired would
rarely or never, as may be inferred from the previous considerations, be
exactly intermediate between those of the two parent-breeds. With respect to
the very slight differences by which the individuals of the same sub-variety,
or even of allied varieties, are characterised, it is obvious that free
crossing would soon obliterate such small distinctions. The formation of new
varieties, independently of selection, would also thus be prevented; except
when the same variation continually recurred from the action of some strongly
predisposing cause. We may therefore conclude that free crossing has in all
cases played an important part in giving uniformity of character to all the
members of the same domestic race and of the same natural species, though
largely governed by natural selection and by the direct action of the
surrounding conditions.

ON THE POSSIBILITY OF ALL ORGANIC BEINGS OCCASIONALLY INTERCROSSING.

But it may be asked, can free crossing occur with hermaphrodite animals and
plants? All the higher animals, and the few insects which have been
domesticated, have separate sexes, and must inevitably unite for each birth.
With respect to the crossing of hermaphrodites, the subject is too large for
the present volume, but in the 'Origin of Species' I have given a short
abstract of the reasons which induce me to believe that all organic beings
occasionally cross, though perhaps in some cases only at long intervals of
time. (15/14. With respect to plants, an admirable essay on this subject (Die
Geschlechter-Vertheilung bei den Pflanzen: 1867) has been published by Dr.
Hildebrand who arrives at the same general conclusions as I have done. Various
other treatises have since appeared on the same subject, more especially by
Hermann Muller and Delpino.) I will merely recall the fact that many plants,
though hermaphrodite in structure, are unisexual in function;--such as those
called by C.K. Sprengel DICHOGAMOUS, in which the pollen and stigma of the
same flower are matured at different periods; or those called by me
RECIPROCALLY DIMORPHIC, in which the flower's own pollen is not fitted to
fertilise its own stigma; or again, the many kinds in which curious mechanical
contrivances exist, effectually preventing self-fertilisation. There are,
however, many hermaphrodite plants which are not in any way specially
constructed to favour intercrossing, but which nevertheless commingle almost
as freely as animals with separated sexes. This is the case with cabbages,
radishes, and onions, as I know from having experimented on them: even the
peasants of Liguria say that cabbages must be prevented "from falling in love"
with each other. In the orange tribe, Gallesio (15/15. 'Teoria della
Riproduzione Vegetal' 1816 page 12.) remarks that the amelioration of the
various kinds is checked by their continual and almost regular crossing. So it
is with numerous other plants.

On the other hand, some cultivated plants rarely or never intercross, for
instance, the common pea and sweet-pea (Lathyrus odoratus); yet their flowers
are certainly adapted for cross fertilisation. The varieties of the tomato and
aubergine (Solanum) and the pimenta (Pimenta vulgaris?) are said (15/16.
Verlot 'Des Varietes' 1865 page 72.) never to cross, even when growing
alongside one another. But it should be observed that these are all exotic
plants, and we do not know how they would behave in their native country when
visited by the proper insects. With respect to the common pea, I have
ascertained that it is rarely crossed in this country owing to premature
fertilisation. There exist, however, some plants which under their natural
conditions appear to be always self-fertilised, such as the Bee Ophrys (Ophrys
apifera) and a few other Orchids; yet these plants exhibit the plainest
adaptations for cross-fertilisation. Again, some few plants are believed to
produce only closed flowers, called cleistogene, which cannot possibly be
crossed. This was long thought to be the case with the Leersia oryzoides
(15/17. Duval Jouve 'Bull. Soc. Bot. de France' tome 10 1863 page 194. With
respect to the perfect flowers setting seed see Dr. Ascherson in 'Bot.
Zeitung' 1864 page 350.), but this grass is now known occasionally to produce
perfect flowers, which set seed.

Although some plants, both indigenous and naturalised, rarely or never produce
flowers, or if they flower never produce seeds, yet no one doubts that
phanerogamic plants are adapted to produce flowers, and the flowers to produce
seed. When they fail, we believe that such plants under different conditions
would perform their proper function, or that they formerly did so, and will do
so again. On analogous grounds, I believe that the flowers in the above
specified anomalous cases which do not now intercross, either would do so
occasionally under different conditions, or that they formerly did so--the
means for affecting this being generally still retained--and will again
intercross at some future period, unless indeed they become extinct. On this
view alone, many points in the structure and action of the reproductive organs
in hermaphrodite plants and animals are intelligible,--for instance, the fact
of the male and female organs never being so completely enclosed as to render
access from without impossible. Hence we may conclude that the most important
of all the means for giving uniformity to the individuals of the same species,
namely, the capacity of occasionally intercrossing, is present, or has been
formerly present, with all organic beings, except, perhaps, some of the
lowest.

[ON CERTAIN CHARACTERS NOT BLENDING.

When two breeds are crossed their characters usually become intimately fused
together; but some characters refuse to blend, and are transmitted in an
unmodified state either from both parents or from one. When grey and white
mice are paired, the young are piebald, or pure white or grey, but not of an
intermediate tint; so it is when white and common collared turtle-doves are
paired. In breeding Game fowls, a great authority, Mr. J. Douglas, remarks, "I
may here state a strange fact: if you cross a black with a white game, you get
birds of both breeds of the clearest colour." Sir R. Heron crossed during many
years white, black, brown, and fawn-coloured Angora rabbits, and never once
got these colours mingled in the same animal, but often all four colours in
the same litter. (15/18. Extract of a letter from Sir R. Heron 1838 given me
by Mr. Yarrell. With respect to mice see 'Annal. des Sc. Nat.' tome 1 page
180; and I have heard of other similar cases. For turtle-doves Boitard and
Corbie 'Les Pigeons' etc. page 238. For the Game fowl 'The Poultry Book' 1866
page 128. For crosses of tailless fowls see Bechstein 'Naturges. Deutsch.' b.
3 s. 403. Bronn 'Geschichte der Natur' b. 2 s. 170 gives analogous facts with
horses. On the hairless condition of crossed South American dogs see Rengger
'Saugethiere von Paraguay' s. 152; but I saw in the Zoological Gardens
mongrels, from a similar cross, which were hairless, quite hairy, or hairy in
patches, that is, piebald with hair. For crosses of Dorking and other fowls
see 'Poultry Chronicle' volume 2 page 355. About the crossed pigs, extract of
letter from Sir R. Heron to Mr. Yarrell. For other cases see P. Lucas
'L'Hered. Nat.' tome 1 page 212.) From cases like these, in which the colours
of the two parents are transmitted quite separately to the offspring, we have
all sorts of gradations, leading to complete fusion. I will give an instance:
a gentleman with a fair complexion, light hair but dark eyes, married a lady
with dark hair and complexion: their three children have very light hair, but
on careful search about a dozen black hairs were found scattered in the midst
of the light hair on the heads of all three.

When turnspit dogs and ancon sheep, both of which have dwarfed limbs, are
crossed with common breeds, the offspring are not intermediate in structure,
but take after either parent. When tailless or hornless animals are crossed
with perfect animals, it frequently, but by no means invariably, happens that
the offspring are either furnished with these organs in a perfect state, or
are quite destitute of them. According to Rengger, the hairless condition of
the Paraguay dog is either perfectly or not at all transmitted to its mongrel
offspring; but I have seen one partial exception in a dog of this parentage
which had part of its skin hairy, and part naked, the parts being distinctly
separated as in a piebald animal. When Dorking fowls with five toes are
crossed with other breeds, the chickens often have five toes on one foot and
four on the other. Some crossed pigs raised by Sir R. Heron between the solid-
hoofed and common pig had not all four feet in an intermediate condition, but
two feet were furnished with properly divided, and two with united hoofs.

Analogous facts have been observed with plants: Major Trevor Clarke crossed
the little, glabrous-leaved, annual stock (Matthiola), with pollen of a large,
red-flowered, rough-leaved, biennial stock, called cocardeau by the French,
and the result was that half the seedlings had glabrous and the other half
rough leaves, but none had leaves in an intermediate state. That the glabrous
seedlings were the product of the rough-leaved variety, and not accidentally
of the mother-plant's own pollen, was shown by their tall and strong habit of
growth. (15/19. 'Internat. Hort. and Bot. Congress of London' 1866.) in the
succeeding generations raised from the rough-leaved crossed seedlings, some
glabrous plants appeared, showing that the glabrous character, though
incapable of blending with and modifying the rough leaves, was all the time
latent in this family of plants. The numerous plants formerly referred to,
which I raised from reciprocal crosses between the peloric and common
Antirrhinum, offer a nearly parallel case; for in the first generation all the
plants resembled the common form, and in the next generation, out of one
hundred and thirty-seven plants, two alone were in an intermediate condition,
the others perfectly resembling either the peloric or common form. Major
Trevor Clarke also fertilised the above-mentioned red-flowered stock with
pollen from the purple Queen stock, and about half the seedlings scarcely
differed in habit, and not at all in the red colour of the flower, from the
mother-plant, the other half bearing blossoms of a rich purple, closely like
those of the paternal plant. Gartner crossed many white and yellow-flowered
species and varieties of Verbascum; and these colours were never blended, but
the offspring bore either pure white or pure yellow blossoms; the former in
the larger proportion. (15/20. 'Bastarderzeugung' s. 307. Kolreuter 'Dritte
Fortsetszung' s. 34, 39 however, obtained intermediate tints from similar
crosses in the genus Verbascum. With respect to the turnips see Herbert
'Amaryllidaceae' 1837 page 370.) Dr. Herbert raised many seedlings, as he
informed me, from Swedish turnips crossed by two other varieties, and these
never produced flowers of an intermediate tint, but always like one of their
parents. I fertilised the purple sweet-pea (Lathyrus odoratus), which has a
dark reddish-purple standard-petal and violet-coloured wings and keel, with
pollen of the painted lady sweet-pea, which has a pale cherry-coloured
standard, and almost white wings and keel; and from the same pod I twice
raised plants perfectly resembling both sorts; the greater number resembling
the father. So perfect was the resemblance, that I should have thought there
had been some mistake, if the plants which were at first identical with the
paternal variety, namely, the painted-lady, had not later in the season
produced, as mentioned in a former chapter, flowers blotched and streaked with
dark purple. I raised grandchildren and great-grandchildren from these crossed
plants, and they continued to resemble the painted-lady, but during later
generations became rather more blotched with purple, yet none reverted
completely to the original mother-plant, the purple sweet-pea. The following
case is slightly different, but still shows the same principle: Naudin (15/21.
'Nouvelles Archives du Museum' tome 1 page 100.) raised numerous hybrids
between the yellow Linaria vulgaris and the purple L. purpurea, and during
three successive generations the colours kept distinct in different parts of
the same flower.

From cases such as the foregoing, in which the offspring of the first
generation perfectly resemble either parent, we come by a small step to those
cases in which differently coloured flowers borne on the same root resemble
both parents, and by another step to those in which the same flower or fruit
is striped or blotched with the two parental colours, or bears a single stripe
of the colour or other characteristic quality of one of the parent-forms. With
hybrids and mongrels it frequently or even generally happens that one part of
the body resembles more or less closely one parent and another part the other
parent; and here again some resistence to fusion, or, what comes to the same
thing, some mutual affinity between the organic atoms of the same nature,
apparently comes into play, for otherwise all parts of the body would be
equally intermediate in character. So again, when the offspring of hybrids or
mongrels, which are themselves nearly intermediate in character, revert either
wholly or by segments to their ancestors, the principle of the affinity of
similar, or the repulsion of dissimilar atoms, must come into action. To this
principle, which seems to be extremely general, we shall recur in the chapter
on pangenesis.

It is remarkable, as has been strongly insisted upon by Isidore Geoffroy St.
Hilaire in regard to animals, that the transmission of characters without
fusion occurs very rarely when species are crossed; I know of one exception
alone, namely, with the hybrids naturally produced between the common and
hooded crow (Corvus corone and cornix), which, however, are closely allied
species, differing in nothing except colour. Nor have I met with any well-
ascertained cases of transmission of this kind, even when one form is strongly
prepotent over another, when two races are crossed which have been slowly
formed by man's selection, and therefore resemble to a certain extent natural
species. Such cases as puppies in the same litter closely resembling two
distinct breeds, are probably due to superfoetation,--that is, to the
influence of two fathers. All the characters above enumerated, which are
transmitted in a perfect state to some of the offspring and not to others,--
such as distinct colours, nakedness of skin, smoothness of leaves, absence of
horns or tail, additional toes, pelorism, dwarfed structure, etc.,--have all
been known to appear suddenly in individual animals and plants. From this
fact, and from the several slight, aggregated differences which distinguish
domestic races and species from one another, not being liable to this peculiar
form of transmission, we may conclude that it is in some way connected with
the sudden appearance of the characters in question.]

ON THE MODIFICATION OF OLD RACES AND THE FORMATION OF NEW RACES BY CROSSING.

We have hitherto chiefly considered the effects of crossing in giving
uniformity of character; we must now look to an opposite result. There can be
no doubt that crossing, with the aid of rigorous selection during several
generations, has been a potent means in modifying old races, and in forming
new ones. Lord Orford crossed his famous stud of greyhounds once with the
bulldog, in order to give them courage and perseverance. Certain pointers have
been crossed, as I hear from the Rev. W.D. Fox, with the foxhound, to give
them dash and speed. Certain strains of Dorking fowls have had a slight
infusion of Game blood; and I have known a great fancier who on a single
occasion crossed his turbit-pigeons with barbs, for the sake of gaining
greater breadth of beak.

In the foregoing cases breeds have been crossed once, for the sake of
modifying some particular character; but with most of the improved races of
the pig, which now breed true, there have been repeated crosses,--for
instance, the improved Essex owes its excellence to repeated crosses with the
Neapolitan, together probably with some infusion of Chinese blood. (15/22.
Richardson 'Pigs' 1847 pages 37, 42; S. Sidney's edition of 'Youatt on the
Pig' 1860 page 3.) So with our British sheep: almost all the races, except the
Southdown, have been largely crossed; "this, in fact, has been the history of
our principal breeds." (15/23. See Mr. W.C. Spooner's excellent paper on
Cross-Breeding 'Journal Royal Agricult. Soc.' volume 20 part 2: see also an
equally good article by Mr. Ch. Howard in 'Gardener's Chronicle' 1860 page
320.) To give an example, the "Oxfordshire Downs" now rank as an established
breed. (15/24. 'Gardener's Chronicle' 1857 pages 649, 652.) They were produced
about the year 1830 by crossing "Hampshire and in some instances Southdown
ewes with Cotswold rams:" now the Hampshire ram was itself produced by
repeated crosses between the native Hampshire sheep and Southdowns; and the
long-woolled Cotswold were improved by crosses with the Leicester, which
latter again is believed to have been a cross between several long-woolled
sheep. Mr. Spooner, after considering the various cases which have been
carefully recorded, concludes, "that from a judicious pairing of cross-bred
animals it is practicable to establish a new breed." On the continent the
history of several crossed races of cattle and of other animals has been well
ascertained. To give one instance: the King of Wurtemburg, after twenty-five
years' careful breeding, that is, after six or seven generations, made a new
breed of cattle from a cross between a Dutch and a Swiss breed, combined with
other breeds. (15/25. 'Bulletin de La Soc. d'Acclimat.' 1862 tome 9 page 463.
See also for other cases MM. Moll and Gayot 'Du Boeuf' 1860 page 32.) The
Sebright bantam, which breeds as true as any other kind of fowl, was formed
about sixty years ago by a complicated cross. (15/26. 'Poultry Chronicle'
volume 2 1854 page 36.) Dark Brahmas, which are believed by some fanciers to
constitute a distinct species, were undoubtedly formed (15/27. 'The Poultry
Book' by W.B. Tegetmeier 1866 page 58.) in the United States, within a recent
period, by a cross between Chittagongs and Cochins. With plants there is
little doubt that the Swede-turnip originated from a cross; and the history of
a variety of wheat, raised from two very distinct varieties, and which after
six years' culture presented an even sample, has been recorded on good
authority. (15/28. 'Gardener's Chronicle' 1852 page 765.)

Until lately, cautious and experienced breeders, though not averse to a single
infusion of foreign blood, were almost universally convinced that the attempt
to establish a new race, intermediate between two widely distinct races, was
hopeless "they clung with superstitious tenacity to the doctrine of purity of
blood, believing it to be the ark in which alone true safety could be found."
(15/29. Spooner in 'Journal Royal Agricult. Soc.' volume 20 part 2) Nor was
this conviction unreasonable: when two distinct races are crossed, the
offspring of the first generation are generally nearly uniform in character;
but even this sometimes fails to be the case, especially with crossed dogs and
fowls, the young of which from the first are sometimes much diversified. As
cross-bred animals are generally of large size and vigorous, they have been
raised in great numbers for immediate consumption. But for breeding they are
found utterly useless; for though they may themselves be uniform in character,
they yield during many generations astonishingly diversified offspring. The
breeder is driven to despair, and concludes that he will never form an
intermediate race. But from the cases already given, and from others which
have been recorded, it appears that patience alone is necessary; as Mr.
Spooner remarks, "nature opposes no barrier to successful admixture; in the
course of time, by the aid of selection and careful weeding, it is practicable
to establish a new breed." After six or seven generations the hoped-for result
will in most cases be obtained; but even then an occasional reversion, or
failure to keep true, may be expected. The attempt, however, will assuredly
fail if the conditions of life be decidedly unfavourable to the characters of
either parent-breed. (15/30. See Colin 'Traite de Phys. Comp. des Animaux
Domestiques' tome 2 page 536, where this subject is well treated.)

Although the grandchildren and succeeding generations of cross-bred animals
are generally variable in an extreme degree, some curious exceptions to the
rule have been observed both with crossed races and species. Thus Boitard and
Corbie (15/31. 'Les Pigeons' page 37.) assert that from a Pouter and a Runt "a
Cavalier will appear, which we have classed amongst pigeons of pure race,
because it transmits all its qualities to its posterity." The editor of the
'Poultry Chronicle' (15/32. Volume 1 1854 page 101.) bred some bluish fowls
from a black Spanish cock and a Malay hen; and these remained true to colour
"generation after generation." The Himalayan breed of rabbits was certainly
formed by crossing two sub-varieties of the silver-grey rabbit; although it
suddenly assumed its present character, which differs much from that of either
parent-breed, yet it has ever since been easily and truly propagated. I
crossed some Labrador and Penguin ducks, and recrossed the mongrels with
Penguins; afterwards most of the ducks reared during three generations were
nearly uniform in character, being brown with a white crescentic mark on the
lower part of the breast, and with some white spots at the base of the beak;
so that by the aid of a little selection a new breed might easily have been
formed. With regard to crossed varieties of plants, Mr. Beaton (15/33.
'Cottage Gardener' 1856 page 110.) remarks that "Melville's extraordinary
cross between the Scotch kale and an early cabbage is as true and genuine as
any on record;" but in this case no doubt selection was practised. Gartner
(15/34. 'Bastarderzeugung' s. 553.) has given five cases of hybrids, in which
the progeny kept constant; and hybrids between Dianthus armeria and deltoides
remained true and uniform to the tenth generation. Dr. Herbert likewise showed
me a hybrid from two species of Loasa which from its first production had kept
constant during several generations.

We have seen in the first chapter, that the several kinds of dogs are almost
certainly descended from more than one species, and so it is with cattle, pigs
and some other domesticated animals. Hence the crossing of aboriginally
distinct species probably came into play at an early period in the formation
of our present races. From Rutimeyer's observations there can be little doubt
that this occurred with cattle; but in most cases one form will probably have
absorbed and obliterated the other, for it is not likely that semi-civilised
men would have taken the necessary pains to modify by selection their
commingled, crossed, and fluctuating stock. Nevertheless, those animals which
were best adapted to their conditions of life would have survived through
natural selection; and by this means crossing will often have indirectly aided
in the formation of primeval domesticated breeds. Within recent times, as far
as animals are concerned, the crossing of distinct species has done little or
nothing towards the formation or modification of our races. It is not yet
known whether the several species of silk-moth which have been recently
crossed in France will yield permanent races. With plants which can be
multiplied by buds and cuttings, hybridisation has done wonders, as with many
kinds of Roses, Rhododendrons, Pelargoniums, Calceolarias, and Petunias.
Nearly all these plants can be propagated by seed, most of them freely; but
extremely few or none come true by seed.

Some authors believe that crossing is the chief cause of variability,--that
is, of the appearance of absolutely new characters. Some have gone so far as
to look at it as the sole cause; but this conclusion is disproved by the facts
given in the chapter on Bud-variation. The belief that characters not present
in either parent or in their ancestors frequently originate from crossing is
doubtful; that they occasionally do so is probable; but this subject will be
more conveniently discussed in a future chapter on the causes of Variability.

A condensed summary of this and of the three following chapters, together with
some remarks on Hybridism, will be given in the nineteenth chapter.


CHAPTER 2.XVI.

CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--INFLUENCE OF
DOMESTICATION ON FERTILITY.

DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED.
VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND
SEXUAL PREFERENCE.
VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED.
VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO,
RENDERED IN SOME DEGREE MUTUALLY STERILE.
DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES WHEN
CROSSED.
ON THE INCREASED FERTILITY OF UNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION
AND CULTIVATION.

The domesticated races of both animals and plants, when crossed, are, with
extremely few exceptions, quite prolific,--in some cases even more so than the
purely-bred parent-races. The offspring, also, raised from such crosses are
likewise, as we shall see in the following chapter, generally more vigorous
and fertile than their parents. On the other hand, species when crossed, and
their hybrid offspring, are almost invariably in some degree sterile; and here
there seems to exist a broad and insuperable distinction between races and
species. The importance of this subject as bearing on the origin of species is
obvious; and we shall hereafter recur to it.

It is unfortunate how few precise observations have been made on the fertility
of mongrel animals and plants during several successive generations. Dr. Broca
(16/1. 'Journal de Physiolog.' tome 2 1859 page 385.) has remarked that no one
has observed whether, for instance, mongrel dogs, bred inter se, are
indefinitely fertile; yet, if a shade of infertility be detected by careful
observation in the offspring of natural forms when crossed, it is thought that
their specific distinction is proved. But so many breeds of sheep, cattle,
pigs, dogs, and poultry, have been crossed and recrossed in various ways, that
any sterility, if it had existed, would from being injurious almost certainly
have been observed. In investigating the fertility of crossed varieties many
sources of doubt occur. Whenever the least trace of sterility between two
plants, however closely allied, was observed by Kolreuter, and more especially
by Gartner, who counted the exact number of seed in each capsule, the two
forms were at once ranked as distinct species; and if this rule be followed,
assuredly it will never be proved that varieties when crossed are in any
degree sterile. We have formerly seen that certain breeds of dogs do not
readily pair together; but no observations have been made whether, when
paired, they produce the full number of young, and whether the latter are
perfectly fertile inter se; but, supposing that some degree of sterility were
found to exist, naturalists would simply infer that these breeds were
descended from aboriginally distinct species; and it would be scarcely
possible to ascertain whether or not this explanation was the true one.

The Sebright Bantam is much less prolific than any other breed of fowls, and
is descended from a cross between two very distinct breeds, recrossed by a
third sub-variety. But it would be extremely rash to infer that the loss of
fertility was in any manner connected with its crossed origin, for it may with
more probability be attributed either to long-continued close interbreeding,
or to an innate tendency to sterility correlated with the absence of hackles
and sickle tail-feathers.

Before giving the few recorded cases of forms, which must be ranked as
varieties, being in some degree sterile when crossed, I may remark that other
causes sometimes interfere with varieties freely intercrossing. Thus they may
differ too greatly in size, as with some kinds of dogs and fowls: for
instance, the editor of the 'Journal of Horticulture, etc.' (16/2. December
1863 page 484.) says that he can keep Bantams with the larger breeds without
much danger of their crossing, but not with the smaller breeds, such as Games,
Hamburghs, etc. With plants a difference in the period of flowering serves to
keep varieties distinct, as with the various kinds of maize and wheat: thus
Colonel Le Couteur (16/3. On 'The Varieties of Wheat' page 66.) remarks, "the
Talavera wheat, from flowering much earlier than any other kind, is sure to
continue pure." In different parts of the Falkland Islands the cattle are
breaking up into herds of different colours; and those on the higher ground,
which are generally white, usually breed, as I am informed by Sir J. Sulivan,
three months earlier than those on the lowland; and this would manifestly tend
to keep the herds from blending.

Certain domestic races seem to prefer breeding with their own kind; and this
is a fact of some importance, for it is a step towards that instinctive
feeling which helps to keep closely allied species in a state of nature
distinct. We have now abundant evidence that, if it were not for this feeling,
many more hybrids would be naturally produced than in this case. We have seen
in the first chapter that the alco dog of Mexico dislikes dogs of other
breeds; and the hairless dog of Paraguay mixes less readily with the European
races, than the latter do with each other. In Germany the female Spitz-dog is
said to receive the fox more readily than will other dogs; a female Australian
Dingo in England attracted the wild male foxes. But these differences in the
sexual instinct and attractive power of the various breeds may be wholly due
to their descent from distinct species. In Paraguay the horses have much
freedom, and an excellent observer (16/4. Rengger 'Saugethiere von Paraguay'
s. 336.) believes that the native horses of the same colour and size prefer
associating with each other, and that the horses which have been imported from
Entre Rios and Banda Oriental into Paraguay likewise prefer associating
together. In Circassia six sub-races of the horse have received distinct
names; and a native proprietor of rank (16/5. See a memoir by MM. Lherbette
and De Quatrefages in 'Bull. Soc. d'Acclimat.' tome 8 July 1861 page 312.)
asserts that horses of three of these races, whilst living a free life, almost
always refuse to mingle and cross, and will even attack one another.

It has been observed, in a district stocked with heavy Lincolnshire and light
Norfolk sheep, that both kinds; though bred together, when turned out, "in a
short time separate to a sheep;" the Lincolnshires drawing off to the rich
soil, and the Norfolks to their own dry light soil; and as long as there is
plenty of grass, "the two breeds keep themselves as distinct as rooks and
pigeons." In this case different habits of life tend to keep the races
distinct. On one of the Faroe islands, not more than half a mile in diameter,
the half-wild native black sheep are said not to have readily mixed with the
imported white sheep. It is a more curious fact that the semi-monstrous ancon
sheep of modern origin "have been observed to keep together, separating
themselves from the rest of the flock, when put into enclosures with other
sheep." (16/6. For the Norfolk sheep see Marshall 'Rural Economy of Norfolk'
volume 2 page 136. See Rev. L. Landt 'Description of Faroe' page 66. For the
ancon sheep see 'Phil. Transact.' 1813 page 90.) With respect to fallow-deer,
which live in a semi-domesticated condition, Mr. Bennett (16/7. White 'Nat.
Hist. of Selbourne' edited by Bennett page 39. With respect to the origin of
the dark-coloured deer see 'Some Account of English Deer Parks' by E.P.
Shirley, Esq.) states that the dark and pale coloured herds, which have long
been kept together in the Forest of Dean, in High Meadow Woods, and in the New
Forest, have never been known to mingle: the dark-coloured deer, it may be
added, are believed to have been first brought by James I. from Norway, on
account of their greater hardiness. I imported from the island of Porto Santo
two of the feral rabbits, which differ, as described in the fourth chapter,
from common rabbits; both proved to be males, and, though they lived during
some years in the Zoological Gardens, the superintendent, Mr. Bartlett, in
vain endeavoured to make them breed with various tame kinds; but whether this
refusal to breed was due to any change in the instinct, or simply to their
extreme wildness, or whether confinement had rendered them sterile, as often
occurs, cannot be determined.

Whilst matching for the sake of experiment many of the most distinct breeds of
pigeons, it frequently appeared to me that the birds, though faithful to their
marriage vow, retained some desire after their own kind. Accordingly I asked
Mr. Wicking, who has kept a larger stock of various breeds together than any
man in England, whether he thought that they would prefer pairing with their
own kind, supposing that there were males and females enough of each; and he
without hesitation answered that he was convinced that this was the case. It
has often been noticed that the dovecote pigeon seems to have an actual
aversion towards the several fancy breeds (16/8. 'The Dovecote' by the Rev.
E.S. Dixon page 155; Bechstein 'Naturgesch. Deutschlands' b. 4 1795 page 17.)
yet all have certainly sprung from a common progenitor. The Rev. W.D. Fox
informs me that his flocks of white and common Chinese geese kept distinct.

These facts and statements, though some of them are incapable of proof,
resting only on the opinion of experienced observers, show that some domestic
races are led by different habits of life to keep to a certain extent
separate, and that others prefer coupling with their own kind, in the same
manner as species in a state of nature, though in a much less degree.

[With respect to sterility from the crossing of domestic races, I know of no
well-ascertained case with animals. This fact, seeing the great difference in
structure between some breeds of pigeons, fowls, pigs, dogs, etc., is
extraordinary, in contrast with the sterility of many closely allied natural
species when crossed; but we shall hereafter attempt to show that it is not so
extraordinary as it at first appears. And it may be well here to recall to
mind that the amount of external difference between two species is not a safe
guide for predicting whether or not they will breed together,--some closely
allied species when crossed being utterly sterile, and others which are
extremely unlike being moderately fertile. I have said that no case of
sterility in crossed races rests on satisfactory evidence; but here is one
which at first seems trustworthy. Mr. Youatt (16/9. 'Cattle' page 202.) and a
better authority cannot be quoted, states, that formerly in Lancashire crosses
were frequently made between longhorn and shorthorn cattle; the first cross
was excellent, but the produce was uncertain; in the third or fourth
generation the cows were bad milkers; "in addition to which, there was much
uncertainty whether the cows would conceive; and full one-third of the cows
among some of these half-breds failed to be in calf." This at first seems a
good case: but Mr. Wilkinson states (16/10. Mr. J. Wilkinson in 'Remarks
addressed to Sir J. Sebright' 1820 page 38.), that a breed derived from this
same cross was actually established in another part of England; and if it had
failed in fertility, the fact would surely have been noticed. Moreover,
supposing that Mr. Youatt had proved his case, it might be argued that the
sterility was wholly due to the two parent-breeds being descended from
primordially distinct species.

In the case of plants Gartner states that he fertilised thirteen heads (and
subsequently nine others) on a dwarf maize bearing yellow seed (16/11.
'Bastarderzeugung' s. 87, 169. See also the Table at the end of volume.) with
pollen of a tall maize having red seed; and one head alone produced good seed,
but only five in number. Though these plants are monoecious, and therefore do
not require castration, yet I should have suspected some accident in the
manipulation, had not Gartner expressly stated that he had during many years
grown these two varieties together, and they did not spontaneously cross; and
this, considering that the plants are monoecious and abound with pollen, and
are well known generally to cross freely, seems explicable only on the belief
that these two varieties are in some degree mutually infertile. The hybrid
plants raised from the above five seeds were intermediate in structure,
extremely variable, and perfectly fertile. (16/12. 'Bastarderzeugung' s. 87,
577.) In like manner Prof. Hildebrand (16/13. 'Bot. Zeitung' 1868 page 327.)
could not succeed in fertilising the female flowers of a plant bearing brown
grains with pollen from a certain kind bearing yellow grains; although other
flowers on the same plant, which were fertilised with their own pollen,
yielded good seed. No one, I believe, even suspects that these varieties of
maize are distinct species; but had the hybrids been in the least sterile, no
doubt Gartner would at once have so classed them. I may here remark, that with
undoubted species there is not necessarily any close relation between the
sterility of a first cross and that of the hybrid offspring. Some species can
be crossed with facility, but produce utterly sterile hybrids; others can be
crossed with extreme difficulty, but the hybrids when produced are moderately
fertile. I am not aware, however, of any instance quite like this of the
maize, namely, of a first cross made with difficulty, but yielding perfectly
fertile hybrids. (16/14. Mr. Shirreff formerly thought ('Gardener's Chronicle'
1858 page 771) that the offspring from a cross between certain varieties of
wheat became sterile in the fourth generation; but he now admits ('Improvement
of the Cereals' 1873) that this was an error.)

The following case is much more remarkable, and evidently perplexed Gartner,
whose strong wish it was to draw a broad line of distinction between species
and varieties. In the genus Verbascum, he made, during eighteen years, a vast
number of experiments, and crossed no less than 1085 flowers and counted their
seeds. Many of these experiments consisted in crossing white and yellow
varieties of both V. lychnitis and V. blattaria with nine other species and
their hybrids. That the white and yellow flowered plants of these two species
are really varieties, no one has doubted; and Gartner actually raised in the
case of both species one variety from the seed of the other. Now in two of his
works (16/15. 'Kenntniss der Befruchtung' s. 137; 'Bastarderzeugung' s. 92,
181. On raising the two varieties from seed see s. 307.) he distinctly asserts
that crosses between similarly-coloured flowers yield more seed than between
dissimilarly-coloured; so that the yellow-flowered variety of either species
(and conversely with the white-flowered variety), when crossed with pollen of
its own kind, yields more seed than when crossed with that of the white
variety; and so it is when differently coloured species are crossed. The
general results may be seen in the Table at the end of his volume. In one
instance he gives (16/16. 'Bastarderzeugung' s. 216.) the following details;
but I must premise that Gartner, to avoid exaggerating the degree of sterility
in his crosses, always compares the MAXIMUM number obtained from a cross with
the AVERAGE number naturally given by the pure mother-plant. The white variety
of V. lychnitis, naturally fertilised by its own pollen, gave from an AVERAGE
of twelve capsules ninety-six good seeds in each; whilst twenty flowers
fertilised with pollen from the yellow variety of this same species, gave as
the MAXIMUM only eighty-nine good seeds; so that we have the proportion of
1000 to 908, according to Gartner's usual scale. I should have thought it
possible that so small a difference in fertility might have been accounted for
by the evil effects of the necessary castration; but Gartner shows that the
white variety of V. lychnitis, when fertilised first by the white variety of
V. blattaria, and then by the yellow variety of this species, yielded seed in
the proportion of 622 to 438; and in both these cases castration was
performed. Now the sterility which results from the crossing of the
differently coloured varieties of the same species, is fully as great as that
which occurs in many cases when distinct species are crossed. Unfortunately
Gartner compared the results of the first unions alone, and not the sterility
of the two sets of hybrids produced from the white variety of V. lychnitis
when fertilised by the white and yellow varieties of V. blattaria, for it is
probable that they would have differed in this respect.

Mr. J. Scott has given me the results of a series of experiments on Verbascum,
made by him in the Botanic Gardens of Edinburgh. (16/17. The results have
since been published in 'Journ. Asiatic Soc. of Bengal' 1867 page 145.) He
repeated some of Gartner's experiments on distinct species, but obtained only
fluctuating results, some confirmatory, the greater number contradictory;
nevertheless these seem hardly sufficient to overthrow the conclusion arrived
at by Gartner from experiments tried on a larger scale. Mr. Scott also
experimented on the relative fertility of unions between similarly and
dissimilarly-coloured varieties of the same species. Thus he fertilised six
flowers of the yellow variety of V. lychnitis by its own pollen, and obtained
six capsules; and calling, for the sake of comparison, the average number of
good seed in each of their capsules one hundred, he found that this same
yellow variety, when fertilised by the white variety, yielded from seven
capsules an average of ninety-four seed. On the same principle, the white
variety of V. lychnitis by its own pollen (from six capsules), and by the
pollen of the yellow variety (eight capsules), yielded seed in the proportion
of 100 to 82. The yellow variety of V. thapsus by its own pollen (eight
capsules), and by that of the white variety (only two capsules), yielded seed
in the proportion of 100 to 94. Lastly, the white variety of V. blattaria by
its own pollen (eight capsules), and by that of the yellow variety (five
capsules), yielded seed in the proportion of 100 to 79. So that in every case
the unions of similarly-coloured varieties of the same species were more
fertile than the unions of dissimilarly-coloured varieties; when all the cases
are grouped together, the difference of fertility is as 100 to 86. Some
additional trials were made, and altogether thirty-six similarly-coloured
unions yielded thirty-five good capsules; whilst thirty-five dissimilarly-
coloured unions yielded only twenty-six good capsules. Besides the foregoing
experiments, the purple V. phoeniceum was crossed by a rose-coloured and a
white variety of the same species; these two varieties were also crossed
together, and these several unions yielded less seed than V. phoeniceum by its
own pollen. Hence it follows from Mr. Scott's experiments, that in the genus
Verbascum the similarly and dissimilarly-coloured varieties of the same
species behave, when crossed, like closely allied but distinct species.
(16/18. The following facts, given by Kolreuter in his 'Dritte Fortsetzung'
ss. 34, 39, appear at first sight strongly to confirm Mr. Scott's and
Gartner's statements; and to a certain limited extent they do so. Kolreuter
asserts, from innumerable observations, that insects incessantly carry pollen
from one species and variety of Verbascum to another; and I can confirm this
assertion; yet he found that the white and yellow varieties of Verbascum
lychnitis often grew wild mingled together: moreover, he cultivated these two
varieties in considerable numbers during four years in his garden, and they
kept true by seed; but when he crossed them, they produced flowers of an
intermediate tint. Hence it might have been thought that both varieties must
have a stronger elective affinity for the pollen of their own variety than for
that of the other; this elective affinity, I may add of each species for its
own pollen (Kolreuter 'Dritte Forts.' s. 39 and Gartner 'Bastarderz.' passim)
being a perfectly well-ascertained power. But the force of the foregoing facts
is much lessened by Gartner's numerous experiments, for, differently from
Kolreuter, he never once got ('Bastarderz.' s. 307) an intermediate tint when
he crossed the yellow and white flowered varieties of Verbascum. So that the
fact of the white and yellow varieties keeping true to their colour by seed
does not prove that they were not mutually fertilised by the pollen carried by
insects from one to the other.)

This remarkable fact of the sexual affinity of similarly-coloured varieties,
as observed by Gartner and Mr. Scott, may not be of very rare occurrence; for
the subject has not been attended to by others. The following case is worth
giving, partly to show how difficult it is to avoid error. Dr. Herbert (16/19.
'Amaryllidaceae' 1837 page 366. Gartner has made a similar observation.) has
remarked that variously-coloured double varieties of the Hollyhock (Althea
rosea) may be raised with certainty by seed from plants growing close
together. I have been informed that nurserymen who raise seed for sale do not
separate their plants; accordingly I procured seed of eighteen named
varieties; of these, eleven varieties produced sixty-two plants all perfectly
true to their kind; and seven produced forty-nine plants, half of which were
true and half false. Mr. Masters of Canterbury has given me a more striking
case; he saved seed from a great bed of twenty-four named varieties planted in
closely adjoining rows, and each variety reproduced itself truly with only
sometimes a shade of difference in tint. Now in the hollyhock the pollen,
which is abundant, is matured and nearly all shed before the stigma of the
same flower is ready to receive it (16/20. Kolreuter first observed this fact,
'Mem. de l'Acad. de St. Petersburg' volume 3 page 127. See also C.K. Sprengel
'Das Entdeckte Geheimniss' s. 345.); and as bees covered with pollen
incessantly fly from plant to plant, it would appear that adjoining varieties
could not escape being crossed. As, however, this does not occur, it appeared
to me probable that the pollen of each variety was prepotent on its own stigma
over that of all other varieties, but I have no evidence on this point. Mr. C.
Turner of Slough, well known for his success in the cultivation of this plant,
informs me that it is the doubleness of the flowers which prevents the bees
gaining access to the pollen and stigma; and he finds that it is difficult
even to cross them artificially. Whether this explanation will fully account
for varieties in close proximity propagating themselves so truly by seed, I do
not know.

The following cases are worth giving, as they relate to monoecious forms,
which do not require, and consequently cannot have been injured by,
castration. Girou de Buzareingues crossed what he designates three varieties
of gourd (16/21. Namely Barbarines, Pastissons, Giraumous: 'Annal. des Sc.
Nat.' tome 30 1833 pages 398 and 405.), and asserts that their mutual
fertilisation is less easy in proportion to the difference which they present.
I am aware how imperfectly the forms in this group were until recently known;
but Sageret (16/22. 'Memoire sur les Cucurbitaceae' 1826 pages 46, 55.), who
ranked them according to their mutual fertility, considers the three forms
above alluded to as varieties, as does a far higher authority, namely, M.
Naudin. (16/23. 'Annales des Sc. Nat.' 4th series tome 6. M. Naudin considers
these forms as undoubtedly varieties of Cucurbita pepo.) Sageret (16/24. 'Mem.
Cucurb.' page 8.) has observed that certain melons have a greater tendency,
whatever the cause may be, to keep true than others; and M. Naudin, who has
had such immense experience in this group, informs me that he believes that
certain varieties intercross more readily than others of the same species; but
he has not proved the truth of this conclusion; the frequent abortion of the
pollen near Paris being one great difficulty. Nevertheless, he has grown close
together, during seven years, certain forms of Citrullus, which, as they could
be artificially crossed with perfect facility and produced fertile offspring,
are ranked as varieties; but these forms when not artificially crossed kept
true. Many other varieties, on the other hand, in the same group cross with
such facility, as M. Naudin repeatedly insists, that without being grown far
apart they cannot be kept in the least true.

Another case, though somewhat different, may be here given, as it is highly
remarkable, and is established on excellent evidence. Kolreuter minutely
describes five varieties of the common tobacco (16/25. 'Zweite Forts.' s. 53
namely Nicotiana major vulgaris; (2) perennis; (3) transylvanica; (4) a sub-
var. of the last; (5) major latifol. fl. alb.) which were reciprocally
crossed, and the offspring were intermediate in character and as fertile as
their parents: from this fact Kolreuter inferred that they are really
varieties; and no one, as far as I can discover, seems to have doubted that
such is the case. He also crossed reciprocally these five varieties with N.
glutinosa, and they yielded very sterile hybrids; but those raised from the
var. perennis, whether used as the father or mother plant, were not so sterile
as the hybrids from the four other varieties. (16/26. Kolreuter was so much
struck with this fact that he suspected that a little pollen of N. glutinosa
in one of his experiments might have accidentally got mingled with that of
var. perennis, and thus aided its fertilising power. But we now know
conclusively from Gartner ('Bastarderz.' s. 34, 43) that the pollen of two
species never acts CONJOINTLY on a third species; still less will the pollen
of a distinct species, mingled with a plant's own pollen, if the latter be
present in sufficient quantity, have any effect. The sole effect of mingling
two kinds of pollen is to produce in the same capsule seeds which yield
plants, some taking after the one and some after the other parent.) So that
the sexual capacity of this one variety has certainly been in some degree
modified, so as to approach in nature that of N. glutinosa. (16/27. Mr. Scott
has made some observations on the absolute sterility of a purple and white
primrose (Primula vulgaris) when fertilised by pollen from the common primrose
('Journal of Proc. of Linn. Soc.' volume 8 1864 page 98); but these
observations require confirmation. I raised a number of purple-flowered long-
styled seedlings from seed kindly sent me by Mr. Scott, and, though they were
all in some degree sterile, they were much more fertile with pollen taken from
the common primrose than with their own pollen. Mr. Scott has likewise
described a red equal-styled cowslip (P. veris ibid page 106), which was found
by him to be highly sterile when crossed with the common cowslip; but this was
not the case with several equal-styled red seedlings raised by me from his
plant. This variety of the cowslip presents the remarkable peculiarity of
combining male organs in every respect like those of the short-styled form,
with female organs resembling in function and partly in structure those of the
long-styled form; so that we have the singular anomaly of the two forms
combined in the same flower. Hence it is not surprising that these flowers
should be spontaneously self-fertile in a high degree.)

These facts with respect to plants show that in some few cases certain
varieties have had their sexual powers so far modified, that they cross
together less readily and yield less seed than other varieties of the same
species. We shall presently see that the sexual functions of most animals and
plants are eminently liable to be affected by the conditions of life to which
they are exposed; and hereafter we shall briefly discuss the conjoint bearing
of this fact, and others, on the difference in fertility between crossed
varieties and crossed species.

DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY WHICH IS GENERAL WITH
SPECIES WHEN CROSSED.

This hypothesis was first propounded by Pallas (16/28. 'Act. Acad. St.
Petersburg' 1780 part 2 pages 84, 100.), and has been adopted by several
authors. I can find hardly any direct facts in its support; but unfortunately
no one has compared, in the case of either animals or plants, the fertility of
anciently domesticated varieties, when crossed with a distinct species, with
that of the wild parent-species when similarly crossed. No one has compared,
for instance, the fertility of Gallus bankiva and of the domesticated fowl,
when crossed with a distinct species of Gallus or Phasianus; and the
experiment would in all cases be surrounded by many difficulties. Dureau de la
Malle, who has so closely studied classical literature, states (16/29.
'Annales des Sc. Nat.' tome 21 1st series page 61.) that in the time of the
Romans the common mule was produced with more difficulty than at the present
day; but whether this statement may be trusted I know not. A much more
important, though somewhat different, case is given by M. Groenland (16/30.
'Bull. Bot. Soc. de France' December 27, 1861 tome 8 page 612.), namely, that
plants, known from their intermediate character and sterility to be hybrids
between Aegilops and wheat, have perpetuated themselves under culture since
1857, WITH A RAPID BUT VARYING INCREASE OF FERTILITY IN EACH GENERATION. In
the fourth generation the plants, still retaining their intermediate
character, had become as fertile as common cultivated wheat.

The indirect evidence in favour of the Pallasian doctrine appears to me to be
extremely strong. In the earlier chapters I have shown that our various breeds
of the dog are descended from several wild species; and this probably is the
case with sheep. There can be no doubt that the Zebu or humped Indian ox
belongs to a distinct species from European cattle: the latter, moreover, are
descended from two forms, which may be called either species or races. We have
good evidence that our domesticated pigs belong to at least two specific
types, S. scrofa and indicus. Now a widely extended analogy leads to the
belief that if these several allied species, when first reclaimed, had been
crossed, they would have exhibited, both in their first unions and in their
hybrid offspring, some degree of sterility. Nevertheless, the several
domesticated races descended from them are now all, as far as can be
ascertained, perfectly fertile together. If this reasoning be trustworthy, and
it is apparently sound, we must admit the Pallasian doctrine that long-
continued domestication tends to eliminate that sterility which is natural to
species when crossed in their aboriginal state.

ON INCREASED FERTILITY FROM DOMESTICATION AND CULTIVATION.

Increased fertility from domestication, without any reference to crossing, may
be here briefly considered. This subject bears indirectly on two or three
points connected with the modification of organic beings. As Buffon long ago
remarked (16/31. Quoted by Isid. Geoffroy St. Hilaire 'Hist. Naturelle
Generale' tome 3 page 476. Since this MS. has been sent to press a full
discussion on the present subject has appeared in Mr. Herbert Spencer's
'Principles of Biology' volume 2 1867 page 457 et seq.), domestic animals
breed oftener in the year and produce more young at a birth than wild animals
of the same species; they, also, sometimes breed at an earlier age. The case
would hardly have deserved further notice, had not some authors lately
attempted to show that fertility increases and decreases in an inverse ratio
with the amount of food. This strange doctrine has apparently arisen from
individual animals when supplied with an inordinate quantity of food, and from
plants of many kinds when grown on excessively rich soil, as on a dunghill,
becoming sterile: but to this latter point I shall have occasion presently to
return. With hardly an exception, our domesticated animals, which have been
long habituated to a regular and copious supply of food, without the labour of
searching for it, are more fertile than the corresponding wild animals. It is
notorious how frequently cats and dogs breed, and how many young they produce
at a birth. The wild rabbit is said generally to breed four times yearly, and
to produce each time at most six young; the tame rabbit breeds six or seven
times yearly, producing each time from four to eleven young; and Mr. Harrison
Weir tells me of a case of eighteen young having been produced at a birth, all
of which survived. The ferret, though generally so closely confined, is more
prolific than its supposed wild prototype. The wild sow is remarkably
prolific; she often breeds twice in the year, and bears from four to eight and
sometimes even twelve young; but the domestic sow regularly breeds twice a
year, and would breed oftener if permitted; and a sow that produces less than
eight at a birth "is worth little, and the sooner she is fattened for the
butcher the better." The amount of food affects the fertility of the same
individual: thus sheep, which on mountains never produce more than one lamb at
a birth, when brought down to lowland pastures frequently bear twins. This
difference apparently is not due to the cold of the higher land, for sheep and
other domestic animals are said to be extremely prolific in Lapland. Hard
living, also, retards the period at which animals conceive; for it has been
found disadvantageous in the northern islands of Scotland to allow cows to
bear calves before they are four years old. (16/32. For cats and dogs etc. see
Bellingeri in 'Annal. des Sc. Nat.' 2nd series, Zoolog. tome 12 page 155. For
ferrets Bechstein 'Naturgeschichte Deutschlands' b. 1 1801 s. 786, 795. For
rabbits ditto s. 1123, 1131; and Bronn 'Geschichte der Natur.' b. 2 s. 99. For
mountain sheep ditto s. 102. For the fertility of the wild sow, see Bechstein
'Naturgesch. Deutschlands' b. 1 1801 s. 534; for the domestic pig Sidney's
edition of 'Youatt on the Pig' 1860 page 62. With respect to Lapland see
Acerbi 'Travels to the North Cape' English translation volume 2 page 222.
About the Highland cows see 'Hogg on Sheep' page 263.)

[Birds offer still better evidence of increased fertility from domestication:
the hen of the wild Gallus bankiva lays from six to ten eggs, a number which
would be thought nothing of with the domestic hen. The wild duck lays from
five to ten eggs; the tame one in the course of the year from eighty to one
hundred. The wild grey-lag goose lays from five to eight eggs; the tame from
thirteen to eighteen, and she lays a second time; as Mr. Dixon has remarked,
"high-feeding, care, and moderate warmth induce a habit of prolificacy which
becomes in some measure hereditary." Whether the semi-domesticated dovecote
pigeon is more fertile than the wild rock-pigeon, C. livia, I know not; but
the more thoroughly domesticated breeds are nearly twice as fertile as
dovecotes: the latter, however, when caged and highly fed, become equally
fertile with house pigeons. I hear from Judge Caton that the wild turkey in
the United States does not breed when a year old, as the domesticated turkeys
there invariably do. The peahen alone of domesticated birds is rather more
fertile, according to some accounts, when wild in its native Indian home, than
in Europe when exposed to our much colder climate. (16/33. For the eggs of
Gallus bankiva see Blyth in 'Annals and Mag. of Nat. Hist.' 2nd series volume
1 1848 page 456. For wild and tame ducks Macgillivray 'British Birds' volume 5
page 37; and 'Die Enten' s. 87. For wild geese L. Lloyd 'Scandinavian
Adventures' volume 2 1854 page 413; and for tame geese 'Ornamental Poultry' by
Rev. E.S. Dixon page 139. On the breeding of Pigeons Pistor 'Das Ganze der
Taubenzucht' 1831 s. 48; and Boitard and Corbie 'Les Pigeons' page 158. With
respect to peacocks, according to Temminck 'Hist. Nat. Gen. des Pigeons' etc.
1813 tome 2 page 41, the hen lays in India even as many as twenty eggs; but
according to Jerdon and another writer quoted in Tegetmeier 'Poultry Book'
1866 pages 280, 282, she there lays only from four to nine or ten eggs: in
England she is said, in the 'Poultry Book' to lay five or six, but another
writer says from eight to twelve eggs.)

With respect to plants, no one would expect wheat to tiller more, and each ear
to produce more grain, in poor than in rich soil; or to get in poor soil a
heavy crop of peas or beans. Seeds vary so much in number that it is difficult
to estimate them; but on comparing beds of carrots in a nursery garden with
wild plants, the former seemed to produce about twice as much seed. Cultivated
cabbages yielded thrice as many pods by measure as wild cabbages from the
rocks of South Wales. The excess of berries produced by the cultivated
asparagus in comparison with the wild plant is enormous. No doubt many highly
cultivated plants, such as pears, pineapples, bananas, sugar-cane, etc., are
nearly or quite sterile; and I am inclined to attribute this sterility to
excess of food and to other unnatural conditions; but to this subject I shall
recur.]

In some cases, as with the pig, rabbit, etc., and with those plants which are
valued for their seed, the direct selection of the more fertile individuals
has probably much increased their fertility; and in all cases this may have
occurred indirectly, from the better chance of some of the numerous offspring
from the more fertile individuals having been preserved. But with cats,
ferrets, and dogs, and with plants like carrots, cabbages, and asparagus,
which are not valued for their prolificacy, selection can have played only a
subordinate part; and their increased fertility must be attributed to the more
favourable conditions of life under which they have long existed.


CHAPTER 2.XVII.

ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSE
INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING.
AUGMENTATION OF MORBID TENDENCIES.
GENERAL EVIDENCE OF THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON THE EVIL
EFFECTS FROM CLOSE INTERBREEDING.
CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME PARKS.
SHEEP.
FALLOW-DEER.
DOGS, RABBITS, PIGS.
MAN, ORIGIN OF HIS ABHORRENCE OF INCESTUOUS MARRIAGES.
FOWLS.
PIGEONS.
HIVE-BEES.
PLANTS, GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING.
MELONS, FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES.
ON THE INCREASED SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR
STERILITY.
ON CERTAIN PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT
ARE FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT
INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES.
CONCLUSION.

The gain in constitutional vigour, derived from an occasional cross between
individuals of the same variety, but belonging to distinct families, or
between distinct varieties, has not been so largely or so frequently
discussed, as have the evil effects of too close interbreeding. But the former
point is the more important of the two, inasmuch as the evidence is more
decisive. The evil results from close interbreeding are difficult to detect,
for they accumulate slowly, and differ much in degree with different species;
whilst the good effects which almost invariably follow a cross are from the
first manifest. It should, however, be clearly understood that the advantage
of close interbreeding, as far as the retention of character is concerned, is
indisputable, and often outweighs the evil of a slight loss of constitutional
vigour. In relation to the subject of domestication, the whole question is of
some importance, as too close interbreeding interferes with the improvement of
old races. It is important as indirectly bearing on Hybridism; and possibly on
the extinction of species, when any form has become so rare that only a few
individuals remain within a confined area. It bears in an important manner on
the influence of free intercrossing, in obliterating individual differences,
and thus giving uniformity of character to the individuals of the same race or
species; for if additional vigour and fertility be thus gained, the crossed
offspring will multiply and prevail, and the ultimate result will be far
greater than otherwise would have occurred. Lastly, the question is of high
interest, as bearing on mankind. I shall therefore discuss this subject at
full length. As the facts which prove the evil effects of close interbreeding
are more copious, though less decisive, than those on the good effects of
crossing, I shall, under each group of beings, begin with the former.

There is no difficulty in defining what is meant by a cross; but this is by no
means easy in regard to "breeding in and in" or "too close interbreeding,"
because, as we shall see, different species of animals are differently
affected by the same degree of interbreeding. The pairing of a father and
daughter, or mother and son, or brothers and sisters, if carried on during
several generations, is the closest possible form of interbreeding. But some
good judges, for instance Sir J. Sebright, believe that the pairing of a
brother and sister is much closer than that of parents and children; for when
the father is matched with his daughter he crosses, as is said, with only half
his own blood. The consequences of close interbreeding carried on for too long
a time, are, as is generally believed, loss of size, constitutional vigour,
and fertility, sometimes accompanied by a tendency to malformation. Manifest
evil does not usually follow from pairing the nearest relations for two,
three, or even four generations; but several causes interfere with our
detecting the evil--such as the deterioration being very gradual, and the
difficulty of distinguishing between such direct evil and the inevitable
augmentation of any morbid tendencies which may be latent or apparent in the
related parents. On the other hand, the benefit from a cross, even when there
has not been any very close interbreeding, is almost invariably at once
conspicuous. There is good reason to believe, and this was the opinion of that
most experienced observer Sir J. Sebright (17/1. 'The Art of Improving the
Breed, etc.' 1809 page 16.), that the evil effects of close interbreeding may
be checked or quite prevented by the related individuals being separated for a
few generations and exposed to different conditions of life. This conclusion
is now held by many breeders; for instance Mr. Carr (17/2. 'The History of the
Rise and Progress of the Killerby, etc. Herds' page 41.) remarks, it is a
well-known "fact that a change of soil and climate effects perhaps almost as
great a change in the constitution as would result from an infusion of fresh
blood." I hope to show in a future work that consanguinity by itself counts
for nothing, but acts solely from related organisms generally having a similar
constitution, and having been exposed in most cases to similar conditions.

That any evil directly follows from the closest interbreeding has been denied
by many persons; but rarely by any practical breeder; and never, as far as I
know, by one who has largely bred animals which propagate their kind quickly.
Many physiologists attribute the evil exclusively to the combination and
consequent increase of morbid tendencies common to both parents; and that this
is an active source of mischief there can be no doubt. It is unfortunately too
notorious that men and various domestic animals endowed with a wretched
constitution, and with a strong hereditary disposition to disease, if not
actually ill, are fully capable of procreating their kind. Close
interbreeding, on the other hand, often induces sterility; and this indicates
something quite distinct from the augmentation of morbid tendencies common to
both parents. The evidence immediately to be given convinces me that it is a
great law of nature, that all organic beings profit from an occasional cross
with individuals not closely related to them in blood; and that, on the other
hand, long-continued close interbreeding is injurious.

Various general considerations have had much influence in leading me to this
conclusion; but the reader will probably rely more on special facts and
opinions. The authority of experienced observers, even when they do not
advance the grounds of their belief, is of some little value. Now almost all
men who have bred many kinds of animals and have written on the subject, such
as Sir J. Sebright, Andrew Knight, etc. (17/3. For Andrew Knight see A. Walker
on 'Intermarriage' 1838 page 227. Sir J. Sebright 'Treatise' has just been
quoted.), have expressed the strongest conviction on the impossibility of
long-continued close interbreeding. Those who have compiled works on
agriculture, and have associated much with breeders, such as the sagacious
Youatt, Low, etc., have strongly declared their opinion to the same effect.
Prosper Lucas, trusting largely to French authorities, has come to a similar
conclusion. The distinguished German agriculturist Hermann von Nathusius, who
has written the most able treatise on this subject which I have met with,
concurs; and as I shall have to quote from this treatise, I may state that
Nathusius is not only intimately acquainted with works on agriculture in all
languages, and knows the pedigrees of our British breeds better than most
Englishmen, but has imported many of our improved animals, and is himself an
experienced breeder.

Evidence of the evil effects of close interbreeding can most readily be
acquired in the case of animals, such as fowls, pigeons, etc., which propagate
quickly, and, from being kept in the same place, are exposed to the same
conditions. Now I have inquired of very many breeders of these birds, and I
have hitherto not met with a single man who was not thoroughly convinced that
an occasional cross with another strain of the same sub-variety was absolutely
necessary. Most breeders of highly improved or fancy birds value their own
strain, and are most unwilling, at the risk, in their opinion, of
deterioration, to make a cross. The purchase of a first-rate bird of another
strain is expensive, and exchanges are troublesome; yet all breeders, as far
as I can hear, excepting those who keep large stocks at different places for
the sake of crossing, are driven after a time to take this step.

Another general consideration which has had great influence on my mind is,
that with all hermaphrodite animals and plants, which it might have been
thought would have perpetually fertilised themselves and been thus subjected
for long ages to the closest interbreeding, there is not a single species, as
far as I can discover, in which the structure ensures self-fertilisation. On
the contrary, there are in a multitude of cases, as briefly stated in the
fifteenth chapter, manifest adaptations which favour or inevitably lead to an
occasional cross between one hermaphrodite and another of the same species;
and these adaptive structures are utterly purposeless, as far as we can see,
for any other end.

[With CATTLE there can be no doubt that extremely close interbreeding may be
long carried on advantageously with respect to external characters, and with
no manifest evil as far as constitution is concerned. The case of Bakewell's
Longhorns, which were closely interbred for a long period, has often been
quoted; yet Youatt says (17/4. 'Cattle' page 199.) the breed "had acquired a
delicacy of constitution inconsistent with common management," and "the
propagation of the species was not always certain." But the Shorthorns offer
the most striking case of close interbreeding; for instance, the famous bull
Favourite (who was himself the offspring of a half-brother and sister from
Foljambe) was matched with his own daughter, granddaughter, and great-
granddaughter; so that the produce of this last union, or the great-great-
granddaughter, had 15-16ths, or 93.75 per cent of the blood of Favourite in
her veins. This cow was matched with the bull Wellington, having 62.5 per cent
of Favourite blood in his veins, and produced Clarissa; Clarissa was matched
with the bull Lancaster, having 68.75 of the same blood, and she yielded
valuable offspring. (17/5. I give this on the authority of Nathusius 'Ueber
Shorthorn Rindvieh' 1857 s. 71, see also 'Gardeners Chronicle' 1860 page 270.
But Mr. J. Storer, a large breeder of cattle, informs me that the parentage of
Clarissa is not well authenticated. In the first volume of the 'Herd Book' she
was entered as having six descents from Favourite, "which was a palpable
mistake," and in all subsequent editions she was spoken of as having only four
descents. Mr. Storer doubts even about the four, as no names of the dams are
given. Moreover, Clarissa bore "only two bulls and one heifer, and in the next
generation her progeny became extinct." Analogous cases of close interbreeding
are given in a pamphlet published by Mr. C. Macknight and Dr. H. Madden 'On
the True Principles of Breeding' Melbourne Australia 1865.) Nevertheless
Collings, who reared these animals, and was a strong advocate for close
breeding, once crossed his stock with a Galloway, and the cows from this cross
realised the highest prices. Bates's herd was esteemed the most celebrated in
the world. For thirteen years he bred most closely in and in; but during the
next seventeen years, though he had the most exalted notion of the value of
his own stock, he thrice infused fresh blood into his herd: it is said that he
did this, not to improve the form of his animals, but on account of their
lessened fertility. Mr. Bates's own view, as given by a celebrated breeder
(17/6. Mr. Willoughby Wood in 'Gardener's Chronicle' 1855 page 411; and 1860
page 270. See the very clear tables and pedigrees given in Nathusius
'Rindvieh' s. 72-77.), was, that "to breed in-and-in from a bad stock was ruin
and devastation; yet that the practice may be safely followed within certain
limits when the parents so related are descended from first-rate animals." We
thus see that there has been much close interbreeding with Shorthorns; but
Nathusius, after the most careful study of their pedigrees, says that he can
find no instance of a breeder who has strictly followed this practice during
his whole life. From this study and his own experience, he concludes that
close interbreeding is necessary to ennoble the stock; but that in effecting
this the greatest care is necessary, on account of the tendency to infertility
and weakness. It may be added, that another high authority (17/7. Mr. Wright
'Journal of Royal Agricult. Soc.' volume 7 1846 page 204. Mr. J. Downing (a
successful breeder of Shorthorns in Ireland) informs me that the raisers of
the great families of Shorthorns carefully conceal their sterility and want of
constitution. He adds that Mr. Bates, after he had bred his herd in-and-in for
some years, "lost in one season twenty-eight calves solely from want of
constitution.") asserts that many more calves are born cripples from
Shorthorns than from other and less closely interbred races of cattle.

Although by carefully selecting the best animals (as Nature effectually does
by the law of battle) close interbreeding may be long carried on with cattle,
yet the good effects of a cross between almost any two breeds is at once shown
by the greater size and vigour of the offspring; as Mr. Spooner writes to me,
"crossing distinct breeds certainly improves cattle for the butcher." Such
crossed animals are of course of no value to the breeder; but they have been
raised during many years in several parts of England to be slaughtered (17/8.
'Youatt on Cattle' page 202.); and their merit is now so fully recognised,
that at fat-cattle shows a separate class has been formed for their reception.
The best fat ox at the great show at Islington in 1862 was a crossed animal.

The half-wild cattle, which have been kept in British parks probably for 400
or 500 years, or even for a longer period, have been advanced by Culley and
others as a case of long-continued interbreeding within the limits of the same
herd without any consequent injury. With respect to the cattle at Chillingham,
the late Lord Tankerville owned that they were bad breeders. (17/9. 'Report
British Assoc. Zoolog. Sect.' 1838.) The agent, Mr. Hardy, estimates (in a
letter to me, dated May, 1861) that in the herd of about fifty the average
number annually slaughtered, killed by fighting, and dying, is about ten, or
one in five. As the herd is kept up to nearly the same average number, the
annual rate of increase must be likewise about one in five. The bulls, I may
add, engage in furious battles, of which battles the present Lord Tankerville
has given me a graphic description, so that there will always be rigorous
selection of the most vigorous males. I procured in 1855 from Mr. D. Gardner,
agent to the Duke of Hamilton, the following account of the wild cattle kept
in the Duke's park in Lanarkshire, which is about 200 acres in extent. The
number of cattle varies from sixty-five to eighty; and the number annually
killed (I presume by all causes) is from eight to ten; so that the annual rate
of increase can hardly be more than one in six. Now in South America, where
the herds are half-wild, and therefore offer a nearly fair standard of
comparison, according to Azara the natural increase of the cattle on an
estancia is from one-third to one-fourth of the total number, or one in
between three and four and this, no doubt, applies exclusively to adult
animals fit for consumption. Hence the half-wild British cattle which have
long interbred within the limits of the same herd are relatively far less
fertile. Although in an unenclosed country like Paraguay there must be some
crossing between the different herds, yet even there the inhabitants believe
that the occasional introduction of animals from distant localities is
necessary to prevent "degeneration in size and diminution of fertility."
(17/10. Azara 'Quadrupedes du Paraguay' tome 2 pages 354, 368.) The decrease
in size from ancient times in the Chillingham and Hamilton cattle must have
been prodigious, for Professor Rutimeyer has shown that they are almost
certainly the descendants of the gigantic Bos primigenius. No doubt this
decrease in size may be largely attributed to less favourable conditions of
life; yet animals roaming over large parks, and fed during severe winters, can
hardly be considered as placed under very unfavourable conditions.

With SHEEP there has often been long-continued interbreeding within the limits
of the same flock; but whether the nearest relations have been matched so
frequently as in the case of Shorthorn cattle, I do not know. The Messrs.
Brown during fifty years have never infused fresh blood into their excellent
flock of Leicesters. Since 1810 Mr. Barford has acted on the same principle
with the Foscote flock. He asserts that half a century of experience has
convinced him that when two nearly related animals are quite sound in
constitution, in-and-in breeding does not induce degeneracy; but he adds that
he "does not pride himself on breeding from the nearest affinities." In France
the Naz flock has been bred for sixty years without the introduction of a
single strange ram. (17/11. For the case of the Messrs. Brown see 'Gardener's
Chronicle' 1855 page 26. For the Foscote flock 'Gardener's Chronicle' 1860
page 416. For the Naz flock 'Bull. de la Soc. d'Acclimat.' 1860 page 477.)
Nevertheless, most great breeders of sheep have protested against close
interbreeding prolonged for too great a length of time. (17/12. Nathusius
'Rindvieh' s. 65; 'Youatt on Sheep' page 495.) The most celebrated of recent
breeders, Jonas Webb, kept five separate families to work on, thus "retaining
the requisite distance of relationship between the sexes" (17/13. 'Gardener's
Chronicle' 1861 page 631.); and what is probably of greater importance, the
separate flocks will have been exposed to somewhat different conditions.

Although by the aid of careful selection the near interbreeding of sheep may
be long continued without any manifest evil, yet it has often been the
practice with farmers to cross distinct breeds to obtain animals for the
butcher, which plainly shows that good of some kind is derived from this
practice. We have excellent evidence on this head from Mr. S. Druce (17/14.
'Journal R. Agricult. Soc.' volume 14 1853 page 212.), who gives in detail the
comparative numbers of four pure breeds and of a cross-breed which can be
supported on the same ground, and he gives their produce in fleece and
carcase. A high authority, Mr. Pusey, sums up the result in money value during
an equal length of time, namely (neglecting shillings), for Cotswolds 248
pounds, for Leicesters 223 pounds, for Southdowns 204 pounds, for Hampshire
Downs 264 pounds, and for the crossbred 293 pounds. A former celebrated
breeder, Lord Somerville, states that his half-breeds from Ryelands and
Spanish sheep were larger animals than either the pure Ryelands or pure
Spanish sheep. Mr. Spooner concludes his excellent Essay on Crossing by
asserting that there is a pecuniary advantage in judicious cross-breeding,
especially when the male is larger than the female. (17/15. Lord Somerville
'Facts on Sheep and Husbandry' page 6. Mr. Spooner in 'Journal of Royal
Agricult. Soc. of England' volume 20 part 2. See also an excellent paper on
the same subject in 'Gardener's Chronicle' 1860 page 321 by Mr. Charles
Howard.)

As some of our British parks are ancient, it occurred to me that there must
have been long-continued close interbreeding with the fallow-deer (Cervus
dama) kept in them; but on inquiry I find that it is a common practice to
infuse new blood by procuring bucks from other parks. Mr. Shirley (17/16.
'Some Account of English Deer Parks' by Evelyn P. Shirley 1867.), who has
carefully studied the management of deer, admits that in some parks there has
been no admixture of foreign blood from a time beyond the memory of man. But
he concludes "that in the end the constant breeding in-and-in is sure to tell
to the disadvantage of the whole herd, though it may take a very long time to
prove it; moreover, when we find, as is very constantly the case, that the
introduction of fresh blood has been of the very greatest use to deer, both by
improving their size and appearance, and particularly by being of service in
removing the taint of 'rickback,' if not of other diseases, to which deer are
sometimes subject when the blood has not been changed, there can, I think, be
no doubt but that a judicious cross with a good stock is of the greatest
consequence, and is indeed essential, sooner or later, to the prosperity of
every well-ordered park."

Mr. Meynell's famous foxhounds have been adduced, as showing that no ill
effects follow from close interbreeding; and Sir J. Sebright ascertained from
him that he frequently bred from father and daughter, mother and son, and
sometimes even from brothers and sisters. With greyhounds also there has been
much close interbreeding, but the best breeders agree that it may be carried
too far. (17/17. Stonehenge 'The Dog' 1867 pages 175-188.) But Sir J. Sebright
declares (17/18. 'The Art of Improving the Breed' etc. page 13. With respect
to Scotch deerhounds see Scrope 'Art of Deer Stalking' pages 350-353.), that
by breeding in-and-in, by which he means matching brothers and sisters, he has
actually seen the offspring of strong spaniels degenerate into weak and
diminutive lapdogs. The Rev. W.D. Fox has communicated to me the case of a
small lot of bloodhounds, long kept in the same family, which had become very
bad breeders, and nearly all had a bony enlargement in the tail. A single
cross with a distinct strain of bloodhounds restored their fertility, and
drove away the tendency to malformation in the tail. I have heard the
particulars of another case with bloodhounds, in which the female had to be
held to the male. Considering how rapid is the natural increase of the dog, it
is difficult to understand the large price of all highly improved breeds,
which almost implies long-continued close interbreeding, except on the belief
that this process lessens fertility and increases liability to distemper and
other diseases. A high authority, Mr. Scrope, attributes the rarity and
deterioration in size of the Scotch deerhound (the few individuals formerly
existing throughout the country being all related) in large part to close
interbreeding.

With all highly-bred animals there is more or less difficulty in getting them
to procreate quickly, and all suffer much from delicacy of constitution. A
great judge of rabbits (17/19. 'Cottage Gardener' 1861 page 327.) says, "the
long-eared does are often too highly bred or forced in their youth to be of
much value as breeders, often turning out barren or bad mothers." They often
desert their young, so that it is necessary to have nurse-rabbits, but I do
not pretend to attribute all these evil results to close interbreeding.
(17/20. Mr. Huth gives ('The Marriage of Near Kin' 1875 page 302) from the
'Bulletin de l'Acad. R. de Med. de Belgique' (volume 9 1866 pages 287, 305),
several statements made by a M. Legrain with respect to crossing brother and
sister rabbits for five or six successive generations with no consequent evil
results. I was so much surprised at this account, and at M. Legrain's
invariable success in his experiments, that I wrote to a distinguished
naturalist in Belgium to inquire whether M. Legrain was a trustworthy
observer. In answer, I have heard that, as doubts were expressed about the
authenticity of these experiments, a commission of inquiry was appointed, and
that at a succeeding meeting of the Society ('Bull. de l'Acad. R. de Med. de
Belgique' 1867 3rd series tome 1 no. 1 to 5), Dr. Crocq reported "qu'il etait
materiellement impossible que M. Legrain ait fait les experiences qu'il
annonce." To this public accusation no satisfactory answer was made.)

With respect to PIGS there is more unanimity amongst breeders on the evil
effects of close interbreeding than, perhaps, with any other large animal. Mr.
Druce, a great and successful breeder of the Improved Oxfordshires (a crossed
race), writes, "without a change of boars of a different tribe, but of the
same breed, constitution cannot be preserved." Mr. Fisher Hobbs, the raiser of
the celebrated Improved Essex breed, divided his stock into three separate
families, by which means he maintained the breed for more than twenty years,
"by judicious selection from the THREE DISTINCT FAMILIES." (17/21. Sidney's
edition of 'Youatt on the Pig' 1860 page 30; page 33 quotation from Mr. Druce;
page 29 on Lord Western's case.) Lord Western was the first importer of a
Neapolitan boar and sow. "From this pair he bred in-and-in, until the breed
was in danger of becoming extinct, a sure result (as Mr. Sidney remarks) of
in-and-in breeding." Lord Western then crossed his Neapolitan pigs with the
old Essex, and made the first great step towards the Improved Essex breed.
Here is a more interesting case. Mr. J. Wright, well known as a breeder,
crossed (17/22. 'Journal of Royal Agricult. Soc. of England' 1846 volume 7
page 205.) the same boar with the daughter, granddaughter, and great-
granddaughter, and so on for seven generations. The result was, that in many
instances the offspring failed to breed; in others they produced few that
lived; and of the latter many were idiotic, without sense, even to suck, and
when attempting to move could not walk straight. Now it deserves especial
notice, that the two last sows produced by this long course of interbreeding
were sent to other boars, and they bore several litters of healthy pigs. The
best sow in external appearance produced during the whole seven generations
was one in the last stage of descent; but the litter consisted of this one
sow. She would not breed to her sire, yet bred at the first trial to a
stranger in blood. So that, in Mr. Wright's case, long-continued and extremely
close interbreeding did not affect the external form or merit of the young;
but with many of them the general constitution and mental powers, and
especially the reproductive functions, were seriously affected.

Nathusius gives (17/23. 'Ueber Rindvieh' etc. s. 78. Col. Le Couteur, who has
done so much for the agriculture of Jersey, writes to me that from possessing
a fine breed of pigs he bred them very closely, twice pairing brothers and
sisters, but nearly all the young had fits and died suddenly.) an analogous
and even more striking case: he imported from England a pregnant sow of the
large Yorkshire breed, and bred the product closely in-and-in for three
generations: the result was unfavourable, as the young were weak in
constitution, with impaired fertility. One of the latest sows, which he
esteemed a good animal, produced, when paired with her own uncle (who was
known to be productive with sows of other breeds), a litter of six, and a
second time a litter of only five weak young pigs. He then paired this sow
with a boar of a small black breed, which he had likewise imported from
England; this boar, when matched with sows of his own breed, produced from
seven to nine young. Now, the sow of the large breed, which was so
unproductive when paired with her own uncle, yielded to the small black boar,
in the first litter twenty-one, and in the second litter eighteen young pigs;
so that in one year she produced thirty-nine fine young animals!

As in the case of several other animals already mentioned, even when no injury
is perceptible from moderately close interbreeding, yet, to quote the words of
Mr. Coate (who five times won the annual gold medal of the Smithfield Club
Show for the best pen of pigs), "Crosses answer well for profit to the farmer,
as you get more constitution and quicker growth; but for me, who sell a great
number of pigs for breeding purposes, I find it will not do, as it requires
many years to get anything like purity of blood again." (17/24. Sidney on the
'Pig' page 36. See also note page 34. Also Richardson on the 'Pig' 1847 page
26.)]

Almost all the animals as yet mentioned are gregarious, and the males must
frequently pair with their own daughters, for they expel the young males as
well as all intruders, until forced by old age and loss of strength to yield
to some stronger male. It is therefore not improbable that gregarious animals
may have been rendered less susceptible than non-social species to the evil
consequences of close interbreeding, so that they may be enabled to live in
herds without injury to their offspring. Unfortunately we do not know whether
an animal like the cat, which is not gregarious, would suffer from close
interbreeding in a greater degree than our other domesticated animals. But the
pig is not, as far as I can discover, strictly gregarious, and we have seen
that it appears eminently liable to the evil effects of close interbreeding.
Mr. Huth, in the case of the pig, attributes (page 285) these effects to their
having been "cultivated most for their fat," or to the selected individuals
having had a weak constitution; but we must remember that it is great breeders
who have brought forward the above cases, and who are far more familiar than
ordinary men can be, with the causes which are likely to interfere with the
fertility of their animals.

The effects of close interbreeding in the case of man is a difficult subject,
on which I will say but little. It has been discussed by various authors under
many points of view. (17/25. Dr. Dally has published an excellent article
(translated in the 'Anthropolog. Review' May 1864 page 65), criticising all
writers who have maintained that evil follows from consanguineous marriages.
No doubt on this side of the question many advocates have injured their cause
by inaccuracies: thus it has been stated (Devay 'Du Danger des Mariages' etc.
1862 page 141) that the marriages of cousins have been prohibited by the
legislature of Ohio; but I have been assured, in answer to inquiries made in
the United States, that this statement is a mere fable.) Mr. Tylor (17/26. See
his interesting work on the 'Early History of Man' 1865 chapter 10.) has shown
that with widely different races in the most distant quarters of the world,
marriages between relations--even between distant relations--have been
strictly prohibited. There are, however, many exceptions to the rule, which
are fully given by Mr. Huth (17/27. 'The Marriage of Near Kin' 1875. The
evidence given by Mr. Huth would, I think, have been even more valuable than
it is on this and some other points, if he had referred solely to the works of
men who had long resided in each country referred to, and who showed that they
possessed judgment and caution. See also Mr. W. Adam 'On Consanguinity in
Marriage' in the 'Fortnightly Review' 1865 page 710. Also Hofacker 'Ueber die
Eigenschaften' etc. 1828.) It is a curious problem how these prohibitions
arose during early and barbarous times. Mr. Tylor is inclined to attribute
them to the evil effects of consanguineous marriages having been observed; and
he ingeniously attempts to explain some apparent anomalies in the prohibition
not extending equally to the relations on the male and female side. He admits,
however, that other causes, such as the extension of friendly alliances, may
have come into play. Mr. W. Adam, on the other hand, concludes that related
marriages are prohibited and viewed with repugnance, from the confusion which
would thus arise in the descent of property, and from other still more
recondite reasons. But I cannot accept these views, seeing that incest is held
in abhorrence by savages such as those of Australia and South America (17/28.
Sir G. Grey 'Journal of Expeditions into Australia' volume 2 page 243; and
Dobrizhoffer 'On the Abipones of South America.'), who have no property to
bequeath, or fine moral feelings to confuse, and who are not likely to reflect
on distant evils to their progeny. According to Mr. Huth the feeling is the
indirect result of exogamy, inasmuch as when this practice ceased in any tribe
and it became endogamous, so that marriages were strictly confined to the same
tribe, it is not unlikely that a vestige of the former practice would still be
retained, so that closely-related marriages would be prohibited. With respect
to exogamy itself Mr. MacLennan believes that it arose from a scarcity of
women, owing to female infanticide, aided perhaps by other causes.

It has been clearly shown by Mr. Huth that there is no instinctive feeling in
man against incest any more than in gregarious animals. We know also how
readily any prejudice or feeling may rise to abhorrence, as shown by Hindus in
regard to objects causing defilement. Although there seems to be no strong
inherited feeling in mankind against incest, it seems possible that men during
primeval times may have been more excited by strange females than by those
with whom they habitually lived; in the same manner as according to Mr.
Cupples (17/29. 'Descent of Man' 2nd. edit page 524.), male deerhounds are
inclined towards strange females, while the females prefer dogs with whom they
have associated. If any such feeling formerly existed in man, this would have
led to a preference for marriages beyond the nearest kin, and might have been
strengthened by the offspring of such marriages surviving in greater numbers,
as analogy would lead us to believe would have occurred.

Whether consanguineous marriages, such as are permitted in civilised nations,
and which would not be considered as close interbreeding in the case of our
domesticated animals, cause any injury will never be known with certainty
until a census is taken with this object in view. My son, George Darwin, has
done what is possible at present by a statistical investigation (17/30.
'Journal of Statistical Soc.' June 1875 page 153; and 'Fortnightly Review'
June 1875.), and he has come to the conclusion, from his own researches and
those of Dr. Mitchell, that the evidence as to any evil thus caused is
conflicting, but on the whole points to the evil being very small.

[BIRDS.

In the case of the FOWL a whole array of authorities could be given against
too close interbreeding. Sir J. Sebright positively asserts that he made many
trials, and that his fowls, when thus treated, became long in the legs, small
in the body, and bad breeders. (17/31. 'The Art of Improving the Breed' page
13.) He produced the famous Sebright Bantams by complicated crosses, and by
breeding in-and-in; and since his time there has been much close interbreeding
with these animals; and they are now notoriously bad breeders. I have seen
Silver Bantams, directly descended from his stock, which had become almost as
barren as hybrids; for not a single chicken had been that year hatched from
two full nests of eggs. Mr. Hewitt says that with these Bantams the sterility
of the male stands, with rare exceptions, in the closest relation with their
loss of certain secondary male characters: he adds, "I have noticed, as a
general rule, that even the slightest deviation from feminine character in the
tail of the male Sebright--say the elongation by only half an inch of the two
principal tail feathers--brings with it improved probability of increased
fertility." (17/32. 'The Poultry Book' by W.B. Tegetmeier 1866 page 245.)

Mr. Wright states (17/33. 'Journal Royal Agricult. Soc.' 1846 volume 7 page
205; see also Ferguson on the Fowl pages 83, 317; see also 'The Poultry Book'
by Tegetmeier 1866 page 135 with respect to the extent to which cock-fighters
found that they could venture to breed in-and-in, viz., occasionally a hen
with her own son; "but they were cautious not to repeat the in-and-in
breeding.") that Mr. Clark, "whose fighting-cocks were so notorious, continued
to breed from his own kind till they lost their disposition to fight, but
stood to be cut up without making any resistance, and were so reduced in size
as to be under those weights required for the best prizes; but on obtaining a
cross from Mr. Leighton, they again resumed their former courage and weight."
It should be borne in mind that game-cocks before they fought were always
weighed, so that nothing was left to the imagination about any reduction or
increase of weight. Mr. Clark does not seem to have bred from brothers and
sisters, which is the most injurious kind of union; and he found, after
repeated trials, that there was a greater reduction in weight in the young
from a father paired with his daughter, than from a mother with her son. I may
add that Mr. Eyton of Eyton, the well-known ornithologist, who is a large
breeder of Grey Dorkings, informs me that they certainly diminish in size, and
become less prolific, unless a cross with another strain is occasionally
obtained. So it is with Malays, according to Mr. Hewitt, as far as size is
concerned. (17/34. 'The Poultry Book' by W.B. Tegetmeier 1866 page 79.)

An experienced writer (17/35. 'The Poultry Chronicle' 1854 volume 1 page 43.)
remarks that the same amateur, as is well known, seldom long maintains the
superiority of his birds; and this, he adds, undoubtedly is due to all his
stock "being of the same blood;" hence it is indispensable that he should
occasionally procure a bird of another strain. But this is not necessary with
those who keep a stock of fowls at different stations. Thus, Mr. Ballance, who
has bred Malays for thirty years, and has won more prizes with these birds
than any other fancier in England, says that breeding in-and-in does not
necessarily cause deterioration; "but all depends upon how this is managed. My
plan has been to keep about five or six distinct runs, and to rear about two
hundred or three hundred chickens each year, and select the best birds from
each run for crossing. I thus secure sufficient crossing to prevent
deterioration." (17/36. 'The Poultry Book' by W.B. Tegetmeier 1866 page 79.)

We thus see that there is almost complete unanimity with poultry-breeders
that, when fowls are kept at the same place, evil quickly follows from
interbreeding carried on to an extent which would be disregarded in the case
of most quadrupeds. Moreover, it is a generally received opinion that cross-
bred chickens are the hardiest and most easily reared. (17/37. 'The Poultry
Chronicle' volume 1 page 89.) Mr. Tegetmeier, who has carefully attended to
poultry of all breeds, says (17/38. 'The Poultry Book' 1866 page 210.) that
Dorking hens, allowed to run with Houdan or Creve-coeur cocks, "produce in the
early spring chickens that for size, hardihood, early maturity, and fitness
for the market, surpass those of any pure breed that we have ever raised." Mr.
Hewitt gives it as a general rule with fowls, that crossing the breed
increases their size. He makes this remark after stating that hybrids from the
pheasant and fowl are considerably larger than either progenitor: so again,
hybrids from the male golden pheasant and female common pheasant "are of far
larger size than either parent-bird." (17/39. Ibid 1866 page 167; and 'Poultry
Chronicle' volume 3 1855 page 15.) To this subject of the increased size of
hybrids I shall presently return.

With PIGEONS, breeders are unanimous, as previously stated, that it is
absolutely indispensable, notwithstanding the trouble and expense thus caused,
occasionally to cross their much-prized birds with individuals of another
strain, but belonging, of course, to the same variety. It deserves notice
that, when size is one of the desired characters, as with pouters (17/40. 'A
Treatise on Fancy Pigeons' by J.M. Eaton page 56.) the evil effects of close
interbreeding are much sooner perceived than when small birds, such as short-
faced tumblers, are valued. The extreme delicacy of the high fancy breeds,
such as these tumblers and improved English carriers, is remarkable; they are
liable to many diseases, and often die in the egg or during the first moult;
and their eggs have generally to be hatched under foster-mothers. Although
these highly-prized birds have invariably been subjected to much close
interbreeding, yet their extreme delicacy of constitution cannot perhaps be
thus fully explained. Mr. Yarrell informed me that Sir J. Sebright continued
closely interbreeding some owl-pigeons, until from their extreme sterility he
as nearly as possible lost the whole family. Mr. Brent (17/41. 'The Pigeon
Book' page 46.) tried to raise a breed of trumpeters, by crossing a common
pigeon, and recrossing the daughter, granddaughter, great-granddaughter, and
great-great-granddaughter, with the same male trumpeter, until he obtained a
bird with 15/16 of trumpeter's blood; but then the experiment failed, for
"breeding so close stopped reproduction." The experienced Neumeister (17/42.
'Das Ganze der Taubenzucht' 1837 s. 18.) also asserts that the offspring from
dovecotes and various other breeds are "generally very fertile and hardy
birds:" so again MM. Boitard and Corbie (17/43. 'Les Pigeons' 1824 page 35.),
after forty-five years' experience, recommend persons to cross their breeds
for amusement; for, if they fail to make interesting birds, they will succeed
under an economical point of view, "as it is found that mongrels are more
fertile than pigeons of pure race."

I will refer only to one other animal, namely, the Hive-bee, because a
distinguished entomologist has advanced this as a case of inevitable close
interbreeding. As the hive is tenanted by a single female, it might have been
thought that her male and female offspring would always have bred together,
more especially as bees of different hives are hostile to each other; a
strange worker being almost always attacked when trying to enter another hive.
But Mr. Tegetmeier has shown (17/44. 'Proc. Entomolog. Soc.' August 6, 1860
page 126.) that this instinct does not apply to drones, which are permitted to
enter any hive; so that there is no a priori improbability of a queen
receiving a foreign drone. The fact of the union invariably and necessarily
taking place on the wing, during the queen's nuptial flight, seems to be a
special provision against continued interbreeding. However this may be,
experience has shown, since the introduction of the yellow-banded Ligurian
race into Germany and England, that bees freely cross: Mr. Woodbury, who
introduced Ligurian bees into Devonshire, found during a single season that
three stocks, at distances of from one to two miles from his hives, were
crossed by his drones. In one case the Ligurian drones must have flown over
the city of Exeter, and over several intermediate hives. On another occasion
several common black queens were crossed by Ligurian drones at a distance of
from one to three and a half miles. (17/45. 'Journal of Horticulture' 1861
pages 39, 77, 158; and 1864 page 206.)

PLANTS.

When a single plant of a new species is introduced into any country, if
propagated by seed, many individuals will soon be raised, so that if the
proper insects be present there will be crossing. With newly-introduced trees
or other plants not propagated by seed we are not here concerned. With old-
established plants it is an almost universal practice occasionally to make
exchanges of seed, by which means individuals which have been exposed to
different conditions of life,--and this, as we have seen with animals,
diminishes the evil from close interbreeding,--will occasionally be introduced
into each district.

With respect to individuals belonging to the same sub-variety, Gartner, whose
accuracy and experience exceeded that of all other observers, states (17/46.
'Beitrage zur Kenntniss der Befruchtung' 1844 s. 366.) that he has many times
observed good effects from this step, especially with exotic genera, of which
the fertility is somewhat impaired, such as Passiflora, Lobelia, Fuchsia.
Herbert also says (17/47. 'Amaryllidaceae' page 371.), "I am inclined to think
that I have derived advantage from impregnating the flower from which I wished
to obtain seed with pollen from another individual of the same variety, or at
least from another flower, rather than with its own." Again, Professor Lecoq
ascertained that crossed offspring are more vigorous and robust than their
parents. (17/48. 'De la Fecondation' 2nd edition 1862 page 79.)

General statements of this kind, however, can seldom be fully trusted: I
therefore began a long series of experiments, continued for about ten years,
which will I think conclusively show the good effects of crossing two distinct
plants of the same variety, and the evil effects of long-continued self-
fertilisation. A clear light will thus be thrown on such questions, as why
flowers are almost invariably constructed so as to permit, or favour, or
necessitate the union of two individuals. We shall clearly understand why
monoecious and dioecious,--why dichogamous, dimorphic and trimorphic plants
exist, and many other such cases. I intend soon to publish an account of these
experiments, and I can here give only a few cases in illustration. The plan
which I followed was to grow plants in the same pot, or in pots of the same
size, or close together in the open ground; carefully to exclude insects; and
then to fertilise some of the flowers with pollen from the same flower, and
others on the same plant with pollen from a distinct but adjoining plant. In
many of these experiments, the crossed plants yielded much more seed than the
self-fertilised plants; and I have never seen the reversed case. The self-
fertilised and crossed seeds thus obtained were allowed to germinate in the
same glass vessel on damp sand; and as the seeds germinated, they were planted
in pairs on opposite sides of the same pot, with a superficial partition
between them, and were placed so as to be equally exposed to the light. In
other cases the self-fertilised and crossed seeds were simply sown on opposite
sides of the same small pot. I have, in short, followed different plans, but
in every case have taken all the precautions which I could think of, so that
the two lots should be equally favoured. The growth of the plants raised from
the crossed and self-fertilised seed, were carefully observed from their
germination to maturity, in species belonging to fifty-two genera; and the
difference in their growth, and in withstanding unfavourable conditions, was
in most cases manifest and strongly marked. It is of importance that the two
lots of seed should be sown or planted on opposite sides of the same pot, so
that the seedlings may struggle against each other; for if sown separately in
ample and good soil, there is often but little difference in their growth.

I will briefly describe two of the first cases observed by me. Six crossed and
six self-fertilised seeds of Ipomoea purpurea, from plants treated in the
manner above described, were planted as soon as they had germinated, in pairs
on opposite sides of two pots, and rods of equal thickness were given them to
twine up. Five of the crossed plants grew from the first more quickly than the
opposed self-fertilised plants; the sixth, however, was weakly and was for a
time beaten, but at last its sounder constitution prevailed and it shot ahead
of its antagonist. As soon as each crossed plant reached the top of its seven-
foot rod its fellow was measured, and the result was that, when the crossed
plants were seven feet high the self-fertilised had attained the average
height of only five feet four and a half inches. The crossed plants flowered a
little before, and more profusely than the self-fertilised plants. On opposite
sides of another SMALL pot a large number of crossed and self-fertilised seeds
were sown, so that they had to struggle for bare existence; a single rod was
given to each lot: here again the crossed plants showed from the first their
advantage; they never quite reached the summit of the seven-foot rod, but
relatively to the self-fertilised plants their average height was as seven
feet to five feet two inches. The experiment was repeated during several
succeeding generations, treated in exactly the same manner, and with nearly
the same result. In the second generation, the crossed plants, which were
again crossed, produced 121 seed-capsules, whilst the self-fertilised, again
self-fertilised, produced only 84 capsules.

Some flowers of the Mimulus luteus were fertilised with their own pollen, and
others were crossed with pollen from distinct plants growing in the same pot.
The seeds were thickly sown on opposite sides of a pot. The seedlings were at
first equal in height; but when the young crossed plants were half an inch,
the self-fertilised plants were only a quarter of an inch high. But this
degree of inequality did not last, for, when the crossed plants were four and
a half inches high, the self-fertilised were three inches, and they retained
the same relative difference till their growth was complete. The crossed
plants looked far more vigorous than the uncrossed, and flowered before them;
they produced also a far greater number of capsules. As in the former case,
the experiment was repeated during several succeeding generations. Had I not
watched these plants of Mimulus and Ipomoea during their whole growth, I could
not have believed it possible, that a difference apparently so slight as that
of the pollen being taken from the same flower, or from a distinct plant
growing in the same pot, could have made so wonderful a difference in the
growth and vigour of the plants thus produced. This, under a physiological
point of view, is a most remarkable phenomenon.

With respect to the benefit derived from crossing distinct varieties, plenty
of evidence has been published. Sageret (17/49. 'Memoire sur les
Cucurbitacees' pages 36, 28, 30.) repeatedly speaks in strong terms of the
vigour of melons raised by crossing different varieties, and adds that they
are more easily fertilised than common melons, and produce numerous good seed.
Here follows the evidence of an English gardener (17/50. Loudon's 'Gardener's
Mag.' volume 8 1832 page 52.): "I have this summer met with better success in
my cultivation of melons, in an unprotected state, from the seeds of hybrids
(i.e. mongrels) obtained by cross impregnation, than with old varieties. The
offspring of three different hybridisations (one more especially, of which the
parents were the two most dissimilar varieties I could select) each yielded
more ample and finer produce than any one of between twenty and thirty
established varieties."

Andrew Knight (17/51. 'Transact. Hort. Soc.' volume 1 page 25.) believed that
his seedlings from crossed varieties of the apple exhibited increased vigour
and luxuriance; and M. Chevreul (17/52. 'Annal. des Sc. Nat.' 3rd series, Bot.
tome 6 page 189.) alludes to the extreme vigour of some of the crossed fruit-
trees raised by Sageret.

By crossing reciprocally the tallest and shortest peas, Knight (17/53.
'Philosophical Transactions' 1799 page 200.) says: "I had in this experiment a
striking instance of the stimulative effects of crossing the breeds; for the
smallest variety, whose height rarely exceeded two feet, was increased to six
feet: whilst the height of the large and luxuriant kind was very little
diminished." Mr. Laxton gave me seed-peas produced from crosses between four
distinct kinds; and the plants thus raised were extraordinarily vigorous,
being in each case from one to two or three feet taller than the parent-forms
growing close alongside them.

Wiegmann (17/54. 'Ueber die Bastarderzeugung' 1828 s. 32, 33. For Mr.
Chaundy's case see Loudon's 'Gardener's Mag.' volume 7 1831 page 696.) made
many crosses between several varieties of cabbage; and he speaks with
astonishment of the vigour and height of the mongrels, which excited the
amazement of all the gardeners who beheld them. Mr. Chaundy raised a great
number of mongrels by planting together six distinct varieties of cabbage.
These mongrels displayed an infinite diversity of character; "But the most
remarkable circumstance was, that, while all the other cabbages and borecoles
in the nursery were destroyed by a severe winter, these hybrids were little
injured, and supplied the kitchen when there was no other cabbage to be had."

Mr. Maund exhibited before the Royal Agricultural Society (17/55. 'Gardener's
Chronicle' 1846 page 601.) specimens of crossed wheat, together with their
parent varieties; and the editor states that they were intermediate in
character, "united with that greater vigour of growth, which it appears, in
the vegetable as in the animal world, is the result of a first cross." Knight
also crossed several varieties of wheat (17/56. 'Philosoph. Transact.' 1799
page 201.), and he says "that in the years 1795 and 1796, when almost the
whole crop of corn in the island was blighted, the varieties thus obtained,
and these only, escaped in this neighbourhood, though sown in several
different soils and situations."

Here is a remarkable case: M. Clotzsch (17/57. Quoted in 'Bull. Bot. Soc.
France' volume 2 1855 page 327.) crossed Pinus sylvestris and nigricans,
Quercus robur and pedunculata, Alnus glutinosa and incana, Ulmus campestris
and effusa; and the cross-fertilised seeds, as well as seeds of the pure
parent-trees, were all sown at the same time and in the same place. The result
was, that after an interval of eight years, the hybrids were one-third taller
than the pure trees!

The facts above given refer to undoubted varieties, excepting the trees
crossed by Clotzsch, which are ranked by various botanists as strongly-marked
races, sub-species, or species. That true hybrids raised from entirely
distinct species, though they lose in fertility, often gain in size and
constitutional vigour, is certain. It would be superfluous to quote any facts;
for all experimenters, Kolreuter, Gartner, Herbert, Sageret, Lecoq, and
Naudin, have been struck with the wonderful vigour, height, size, tenacity of
life, precocity, and hardiness of their hybrid productions. Gartner (17/58.
Gartner 'Bastarderzeugung' s. 259, 518, 526 et seq.) sums up his conviction on
this head in the strongest terms. Kolreuter (17/59. 'Fortsetzung' 1763 s. 29;
'Dritte Fortsetzung' s. 44, 96; 'Act. Acad. St. Petersburg' 1782 part 2 page
251; 'Nova Acta' 1793 pages 391, 394; 'Nova Acta' 1795 pages 316, 323.) gives
numerous precise measurements of the weight and height of his hybrids in his
comparison with measurements of both parent-forms; and speaks with
astonishment of their "statura portentosa," their "ambitus vastissimus ac
altitudo valde conspicua." Some exceptions to the rule in the case of very
sterile hybrids have, however, been noticed by Gartner and Herbert; but the
most striking exceptions are given by Max Wichura (17/60. 'Die
Bastardbefruchtung' etc. 1865 s. 31, 41, 42.) who found that hybrid willows
were generally tender in constitution, dwarf, and short-lived.

Kolreuter explains the vast increase in the size of the roots, stems, etc., of
his hybrids, as the result of a sort of compensation due to their sterility,
in the same way as many emasculated animals are larger than the perfect males.
This view seems at first sight extremely probable, and has been accepted by
various authors (17/61. Max Wichura fully accepts this view
('Bastardbefruchtung' s. 43), as does the Rev. M.J. Berkeley in 'Journal of
Hort. Soc.' January 1866 page 70.); but Gartner (17/62. 'Bastarderzeugung' s.
394, 526, 528.) has well remarked that there is much difficulty in fully
admitting it; for with many hybrids there is no parallelism between the degree
of their sterility and their increased size and vigour. The most striking
instances of luxuriant growth have been observed with hybrids which were not
sterile in any extreme degree. In the genus Mirabilis, certain hybrids are
unusually fertile, and their extraordinary luxuriance of growth, together with
their enormous roots (17/63. Kolreuter 'Nova Acta' 1795 page 316.) have been
transmitted to their progeny. The result in all cases is probably in part due
to the saving of nutriment and vital force through the sexual organs acting
imperfectly or not at all, but more especially to the general law of good
being derived from a cross. For it deserves especial attention that mongrel
animals and plants, which are so far from being sterile that their fertility
is often actually augmented, have, as previously shown, their size, hardiness,
and constitutional vigour generally increased. It is not a little remarkable
that an accession of vigour and size should thus arise under the opposite
contingencies of increased and diminished fertility.

It is a perfectly well ascertained fact (17/64. Gartner 'Bastarderzeugung' s.
430.) that hybrids invariably breed with either pure parent, and not rarely
with a distinct species, more readily than with one another. Herbert is
inclined to explain even this fact by the advantage derived from a cross; but
Gartner more justly accounts for it by the pollen of the hybrid, and probably
its ovules, being in some degree vitiated, whereas the pollen and ovules of
both pure parents and of any third species are sound. Nevertheless, there are
some well-ascertained and remarkable facts, which, as we shall presently see,
show that a cross by itself undoubtedly tends to increase or re-establish the
fertility of hybrids.

The same law, namely, that the crossed offspring both of varieties and species
are larger than the parent-forms, holds good in the most striking manner with
hybrid animals as well as with mongrels. Mr. Bartlett, who has had such large
experience says, "Among all hybrids of vertebrated animals there is a marked
increase of size." He then enumerates many cases with mammals, including
monkeys, and with various families of birds. (17/65. Quoted by Dr. Murie in
'Proc. Zoolog. Soc.' 1870 page 40.)]

ON CERTAIN HERMAPHRODITE PLANTS WHICH, EITHER NORMALLY OR ABNORMALLY, REQUIRE
TO BE FERTILISED BY POLLEN FROM A DISTINCT INDIVIDUAL OR SPECIES.

The facts now to be given differ from the foregoing, as self-sterility is not
here the result of long-continued close interbreeding. These facts are,
however, connected with our present subject, because a cross with a distinct
individual is shown to be either necessary or advantageous. Dimorphic and
trimorphic plants, though they are hermaphrodites, must be reciprocally
crossed, one set of forms by the other, in order to be fully fertile, and in
some cases to be fertile in any degree. But I should not have noticed these
plants, had it not been for the following cases given by Dr. Hildebrand
(17/66. 'Botanische Zeitung' January 1864 s. 3.):--

[Primula sinensis is a reciprocally dimorphic species: Dr. Hildebrand
fertilised twenty-eight flowers of both forms, each by pollen of the other
form, and obtained the full number of capsules containing on an average 42.7
seed per capsule; here we have complete and normal fertility. He then
fertilised forty-two flowers of both forms with pollen of the same form, but
taken from a distinct plant, and all produced capsules containing on an
average only 19.6 seed. Lastly, and here we come to our more immediate point,
he fertilised forty-eight flowers of both forms with pollen of the same form
and taken from the same flower, and now he obtained only thirty-two capsules,
and these contained on an average 18.6 seed, or one less per capsule than in
the former case. So that, with these illegitimate unions, the act of
impregnation is less assured, and the fertility slightly less, when the pollen
and ovules belong to the same flower, than when belonging to two distinct
individuals of the same form. Dr. Hildebrand has recently made analogous
experiments on the long-styled form of Oxalis rosea, with the same result.
(17/67. 'Monatsbericht Akad. Wissen.' Berlin 1866 s. 372.)]

It has recently been discovered that certain plants, whilst growing in their
native country under natural conditions, cannot be fertilised with pollen from
the same plant. They are sometimes so utterly self-impotent, that, though they
can readily be fertilised by the pollen of a distinct species or even distinct
genus, yet, wonderful as is the fact, they never produce a single seed by
their own pollen. In some cases, moreover, the plant's own pollen and stigma
mutually act on each other in a deleterious manner. Most of the facts to be
given relate to orchids, but I will commence with a plant belonging to a
widely different family.

[Sixty-three flowers of Corydalis cava, borne on distinct plants, were
fertilised by Dr. Hildebrand (17/68. International Hort. Congress, London
1866.) with pollen from other plants of the same species; and fifty-eight
capsules were obtained, including on an average 4.5 seed in each. He then
fertilised sixteen flowers produced by the same raceme, one with another, but
obtained only three capsules, one of which alone contained any good seeds,
namely, two in number. Lastly, he fertilised twenty-seven flowers, each with
its own pollen; he left also fifty-seven flowers to be spontaneously
fertilised, and this would certainly have ensued if it had been possible, for
the anthers not only touch the stigma, but the pollen-tubes were seen by Dr.
Hildebrand to penetrate it; nevertheless these eighty-four flowers did not
produce a single seed-capsule! This whole case is highly instructive, as it
shows how widely different the action of the same pollen is, according as it
is placed on the stigma of the same flower, or on that of another flower on
the same raceme, or on that of a distinct plant.

With exotic Orchids several analogous cases have been observed, chiefly by Mr.
John Scott. (17/69. 'Proc. Bot. Soc. of Edinburgh' May 1863: these
observations are given in abstract, and others are added, in the 'Journal of
Proc. of Linn. Soc.' volume 8 Bot. 1864 page 162.) Oncidium sphacelatum has
effective pollen, for Mr. Scott fertilised two distinct species with it; the
ovules are likewise capable of impregnation, for they were readily fertilised
by the pollen of O. divaricatum; nevertheless, between one and two hundred
flowers fertilised by their own pollen did not produce a single capsule,
though the stigmas were penetrated by the pollen-tubes. Mr. Robertson Munro,
of the Royal Botanic Gardens of Edinburgh, also informs me (1864) that a
hundred and twenty flowers of this same species were fertilised by him with
their own pollen, and did not produce a capsule, but eight flowers, fertilised
by the pollen of O. divaricatum, produced four fine capsules: again, between
two and three hundred flowers of O. divaricatum, fertilised by their own
pollen, did not set a capsule, but twelve flowers fertilised by O. flexuosum
produced eight fine capsules: so that here we have three utterly self-impotent
species, with their male and female organs perfect, as shown by their mutual
fertilisation. In these cases fertilisation was effected only by the aid of a
distinct species. But, as we shall presently see, distinct plants, raised from
seed, of Oncidium flexuosum, and probably of the other species, would have
been perfectly capable of fertilising each other, for this is the natural
process. Again, Mr. Scott found that the pollen of a plant of O. microchilum
was effective, for with it he fertilised two distinct species; he found its
ovules good, for they could be fertilised by the pollen of one of these
species, and by the pollen of a distinct plant of O. microchilum; but they
could not be fertilised by pollen of the same plant, though the pollen-tubes
penetrated the stigma. An analogous case has been recorded by M. Riviere
(17/70. Prof. Lecoq 'De la Fecondation' 2nd edition 1862 page 76.) with two
plants of O. cavendishianum, which were both self-sterile, but reciprocally
fertilised each other. All these cases refer to the genus Oncidium, but Mr.
Scott found that Maxillaria atro-rubens was "totally insusceptible of
fertilisation with its own pollen," but fertilised, and was fertilised by, a
widely distinct species, viz. M. squalens.

As these orchids had been grown under unnatural conditions in hot-houses, I
concluded that their self-sterility was due to this cause. But Fritz Muller
informs me that at Desterro, in Brazil, he fertilised above one hundred
flowers of the above-mentioned Oncidium flexuosum, which is there endemic,
with its own pollen, and with that taken from distinct plants: all the former
were sterile, whilst those fertilised by pollen from any OTHER PLANT of the
same species were fertile. During the first three days there was no difference
in the action of the two kinds of pollen: that placed on stigma of the same
plant separated in the usual manner into grains, and emitted tubes which
penetrated the column, and the stigmatic chamber shut itself; but only those
flowers which had been fertilised by pollen taken from a distinct plant
produced seed-capsules. On a subsequent occasion these experiments were
repeated on a large scale with the same result. Fritz Muller found that four
other endemic species of Oncidium were in like manner utterly sterile with
their own pollen, but fertile with that from any other plant: some of them
likewise produced seed-capsules when impregnated with pollen of widely
distinct genera, such as Cyrtopodium, and Rodriguezia. Oncidium crispum,
however, differs from the foregoing species in varying much in its self-
sterility; some plants producing fine pods with their own pollen, others
failing to do so in two or three instances, Fritz Muller observed that the
pods produced by pollen taken from a distinct flower on the same plant, were
larger than those produced by the flower's own pollen. In Epidendrum
cinnabarinum, an orchid belonging to another division of the family, fine pods
were produced by the plant's own pollen, but they contained by weight only
about half as much seed as the capsules which had been fertilised by pollen
from a distinct plant, and in one instance from a distinct species; moreover,
a very large proportion, and in some cases nearly all the seeds produced by
the plant's own pollen, were destitute of an embryo. Some self-fertilised
capsules of a Maxillaria were in a similar state.

Another observation made by Fritz Muller is highly remarkable, namely, that
with various orchids the plant's own pollen not only fails to impregnate the
flower, but acts on the stigma, and is acted on, in an injurious or poisonous
manner. This is shown by the surface of the stigma in contact with the pollen,
and by the pollen itself becoming in from three to five days dark brown, and
then decaying. The discoloration and decay are not caused by parasitic
cryptograms, which were observed by Fritz Muller in only a single instance.
These changes are well shown by placing on the same stigma, at the same time,
the plant's own pollen and that from a distinct plant of the same species, or
of another species, or even of another and widely remote genus. Thus, on the
stigma of Oncidium flexuosum, the plant's own pollen and that from a distinct
plant were placed side by side, and in five days' time the latter was
perfectly fresh, whilst the plant's own pollen was brown. On the other hand,
when the pollen of a distinct plant of the Oncidium flexuosum and of the
Epidendrum zebra (nov. spec.?) were placed together on the same stigma, they
behaved in exactly the same manner, the grains separating, emitting tubes, and
penetrating the stigma, so that the two pollen-masses, after an interval of
eleven days, could not be distinguished except by the difference of their
caudicles, which, of course, undergo no change. Fritz Muller has, moreover,
made a large number of crosses between orchids belonging to distinct species
and genera, and he finds that in all cases when the flowers are not fertilised
their footstalks first begin to wither; and the withering slowly spreads
upwards until the germens fall off, after an interval of one or two weeks, and
in one instance of between six and seven weeks; but even in this latter case,
and in most other cases, the pollen and stigma remained in appearance fresh.
Occasionally, however, the pollen becomes brownish, generally on the external
surface, and not in contact with the stigma, as is invariably the case when
the plant's own pollen is applied.

Fritz Muller observed the poisonous action of the plant's own pollen in the
above-mentioned Oncidium flexuosum, O. unicorne, pubes (?), and in two other
unnamed species. Also in two species of Rodriguezia, in two of Notylia, in one
of Burlingtonia, and of a fourth genus in the same group. In all these cases,
except the last, it was proved that the flowers were, as might have been
expected, fertile with pollen from a distinct plant of the same species.
Numerous flowers of one species of Notylia were fertilised with pollen from
the same raceme; in two days' time they all withered, the germens began to
shrink, the pollen-masses became dark brown, and not one pollen-grain emitted
a tube. So that in this orchid the injurious action of the plant's own pollen
is more rapid than with Oncidium flexuosum. Eight other flowers on the same
raceme were fertilised with pollen from a distinct plant of the same species:
two of these were dissected, and their stigmas were found to be penetrated by
numberless pollen-tubes; and the germens of the other six flowers became well
developed. On a subsequent occasion many other flowers were fertilised with
their own pollen, and all fell off dead in a few days; whilst some flowers on
the same raceme which had been left simply unfertilised adhered and long
remained fresh. We have seen that in cross-unions between extremely distinct
orchids the pollen long remains undecayed; but Notylia behaved in this respect
differently; for when its pollen was placed on the stigma of Oncidium
flexuosum, both the stigma and pollen quickly became dark brown, in the same
manner as if the plant's own pollen had been applied.

Fritz Muller suggests that, as in all these cases the plant's own pollen is
not only impotent (thus effectually preventing self-fertilisation), but
likewise prevents, as was ascertained in the case of the Notylia and Oncidium
flexuosum, the action of subsequently applied pollen from a distinct
individual, it would be an advantage to the plant to have its own pollen
rendered more and more deleterious; for the germens would thus quickly be
killed, and dropping off, there would be no further waste in nourishing a part
which ultimately could be of no avail.

The same naturalist found in Brazil three plants of a Bignonia growing near
together. He fertilised twenty-nine flowerets on one of them with their own
pollen, and they did not set a single capsule. Thirty flowers were then
fertilised with pollen from a distinct plant, one of the three, and they
yielded only two capsules. Lastly, five flowers were fertilised with pollen
from a fourth plant growing at a distance, and all five produced capsules.
Fritz Muller thinks that the three plants which grew near one another were
probably seedlings from the same parent, and that from being closely related,
they acted very feebly on one another. This view is extremely probable, for he
has since shown in a remarkable paper (17/71. 'Jenaische Zeitschrift fur
Naturwiss.' b. 7 page 22 1872 and page 441 1873. A large part of this paper
has been translated in the 'American Naturalist' 1874 page 223.), that in the
case of some Brazilian species of Abutilon, which are self-sterile, and
between which he raised some complex hybrids, that these, if near relatives,
were much less fertile inter se, than when not closely related.]

We now come to cases closely analogous with those just given, but different in
so far that only certain individuals of the species are self-sterile. This
self-impotence does not depend on the pollen or ovules being in an unfit state
for fertilisation, for both have been found effective in union with other
plants of the same or of a distinct species. The fact of plants having
acquired so peculiar a constitution, that they can be fertilised more readily
by the pollen of a distinct species than by their own, is exactly the reverse
of what occurs with all ordinary species. For in the latter the two sexual
elements of the same individual plant are of course capable of freely acting
on each other; but are so constituted that they are more or less impotent when
brought into union with the sexual elements of a distinct species, and produce
more or less sterile hybrids.

[Gartner experimented on two plants of Lobelia fulgens, brought from separate
places, and found (17/72. 'Bastarderzeugung' s. 64, 357.) that their pollen
was good, for he fertilised with it L. cardinalis and syphilitica; their
ovules were likewise good, for they were fertilised by the pollen of these
same two species; but these two plants of L. fulgens could not be fertilised
by their own pollen, as can generally be effected with perfect ease with this
species. Again, the pollen of a plant of Verbascum nigrum grown in a pot was
found by Gartner (17/73. Ibid s. 357.) capable of fertilising V. lychnitis and
V. austriacum; the ovules could be fertilised by the pollen of V. thapsus; but
the flowers could not be fertilised by their own pollen. Kolreuter, also
(17/74. 'Zweite Fortsetzung' s. 10; 'Dritte Forts.' s. 40. Mr. Scott likewise
fertilised fifty-four flowers of Verbascum phoeniceum, including two
varieties, with their own pollen, and not a single capsule was produced. Many
of the pollen-grains emitted their tubes, but only a few of them penetrated
the stigmas; some slight effect however was produced, as many of the ovaries
became somewhat developed: 'Journal Asiatic Soc. Bengal' 1867 page 150.),
gives the case of three garden plants of Verbascum phoeniceum, which bore
during two years many flowers; these he fertilised successfully with the
pollen of no less than four distinct species, but they produced not a seed
with their own apparently good pollen; subsequently these same plants, and
others raised from seed, assumed a strangely fluctuating condition, being
temporarily sterile on the male or female side, or on both sides, and
sometimes fertile on both sides; but two of the plants were perfectly fertile
throughout the summer.

With Reseda odorata I have found certain individuals quite sterile with their
own pollen, and so it is with the indigenous Reseda lutea. The self-sterile
plants of both species were perfectly fertile when crossed with pollen from
any other individual of the same species. These observations will hereafter be
published in another work, in which I shall also show that seeds sent to me by
Fritz Muller produced by plants of Eschscholtzia californica which were quite
self-sterile in Brazil, yielded in this country plants which were only
slightly self-sterile.

It appears (17/75. Duvernoy quoted by Gartner 'Bastarderzeugung' s. 334) that
certain flowers on certain plants of Lilium candidum can be fertilised more
freely by pollen from a distinct individual than by their own. So, again, with
the varieties of the potato. Tinzmann (17/76. 'Gardener's Chronicle' 1846 page
183.), who made many trials with this plant, says that pollen from another
variety sometimes "exerts a powerful influence, and I have found sorts of
potatoes which would not bear seed from impregnation with the pollen of their
own flowers would bear it when impregnated with other pollen." It does not,
however, appear to have been proved that the pollen which failed to act on the
flower's own stigma was in itself good.

In the genus Passiflora it has long been known that several species do not
produce fruit, unless fertilised by pollen taken from distinct species: thus,
Mr. Mowbray (17/77. 'Transact. Hort. Soc.' volume 7 1830 page 95.) found that
he could not get fruit from P. alata and racemosa except by reciprocally
fertilising them with each other's pollen; and similar facts have been
observed in Germany and France. (17/78. Prof. Lecoq 'De la Fecondation' 1845
page 70; Gartner 'Bastarderzeugung' s. 64.) I have received two accounts of P.
quadrangularis never producing fruit from its own pollen, but doing so freely
when fertilised in one case with the pollen of P. coerulea, and in another
case with that of P. edulis. But in three other cases this species fruited
freely when fertilised with its own pollen; and the writer in one case
attributed the favourable result to the temperature of the house having been
raised from 5 deg to 10 deg Fahr. above the former temperature, after the
flowers were fertilised. (17/79. 'Gardener's Chronicle' 1868 page 1341.) With
respect to P. laurifolia, a cultivator of much experience has recently
remarked (17/80. 'Gardener's Chronicle' 1866 page 1068.) that the flowers
"must be fertilised with the pollen of P. coerulea, or of some other common
kind, as their own pollen will not fertilise them." But the fullest details on
this subject have been given by Messrs. Scott and Robertson Munro (17/81.
'Journal of Proc. of Linn. Soc.' volume 8 1864 page 1168. Mr. Robertson Munro
in 'Trans. Bot. Soc.' of Edinburgh volume 9 page 399.): plants of Passiflora
racemosa, coerulea, and alata flowered profusely during many years in the
Botanic Gardens of Edinburgh, and, though repeatedly fertilised with their own
pollen, never produced any seed; yet this occurred at once with all three
species when they were crossed together in various ways. In the case of P.
coerulea three plants, two of which grew in the Botanic Gardens, were all
rendered fertile, merely by impregnating each with pollen of one of the
others. The same result was attained in the same manner with P. alata, but
with only one plant out of three. As so many self-sterile species of
Passiflora have been mentioned, it should be stated that the flowers of the
annual P. gracilis are nearly as fertile with their own pollen as with that
from a distinct plant; thus sixteen flowers spontaneously self-fertilised
produced fruit, each containing on an average 21.3 seed, whilst fruit from
fourteen crossed flowers contained 24.1 seed.

Returning to P. alata, I have received (1866) some interesting details from
Mr. Robertson Munro. Three plants, including one in England, have already been
mentioned which were inveterately self-sterile, and Mr. Munro informs me of
several others which, after repeated trials during many years, have been found
in the same predicament. At some other places, however, this species fruits
readily when fertilised with its own pollen. At Taymouth Castle there is a
plant which was formerly grafted by Mr. Donaldson on a distinct species, name
unknown, and ever since the operation it has produced fruit in abundance by
its own pollen; so that this small and unnatural change in the state of this
plant has restored its self-fertility! Some of the seedlings from the Taymouth
Castle plant were found to be not only sterile with their own pollen, but with
each other's pollen, and with the pollen of distinct species. Pollen from the
Taymouth plant failed to fertilise certain plants of the same species, but was
successful on one plant in the Edinburgh Botanic Gardens. Seedlings were
raised from this latter union, and some of their flowers were fertilised by
Mr. Munro with their own pollen; but they were found to be as self-impotent as
the mother-plant had always proved, except when fertilised by the grafted
Taymouth plant, and except, as we shall see, when fertilised by her own
seedlings. For Mr. Munro fertilised eighteen flowers on the self-impotent
mother-plant with pollen from these her own self-impotent seedlings, and
obtained, remarkable as the fact is, eighteen fine capsules full of excellent
seed! I have met with no case in regard to plants which shows so well as this
of P. alata, on what small and mysterious causes complete fertility or
complete sterility depends.]

The facts hitherto given relate to the much-lessened or completely destroyed
fertility of pure species when impregnated with their own pollen, in
comparison with their fertility when impregnated by distinct individuals or
distinct species; but closely analogous facts have been observed with hybrids.

[Herbert states (17/82. 'Amaryllidaceae' 1837 page 371; 'Journal of Hort.
Soc.' volume 2 1847 page 19.) that having in flower at the same time nine
hybrid Hippeastrums, of complicated origin, descended from several species, he
found that "almost every flower touched with pollen from another cross
produced seed abundantly, and those which were touched with their own pollen
either failed entirely, or formed slowly a pod of inferior size, with fewer
seeds." In the 'Horticultural Journal' he adds that "the admission of the
pollen of another cross-bred Hippeastrum (however complicated the cross) to
any one flower of the number, is almost sure to check the fructification of
the others." In a letter written to me in 1839, Dr. Herbert says that he had
already tried these experiments during five consecutive years, and he
subsequently repeated them, with the same invariable result. He was thus led
to make an analogous trial on a pure species, namely, on the Hippeastrum
aulicum, which he had lately imported from Brazil: this bulb produced four
flowers, three of which were fertilised by their own pollen, and the fourth by
the pollen of a triple cross between H. bulbulosum, reginae, and vittatum; the
result was, that "the ovaries of the three first flowers soon ceased to grow,
and after a few days perished entirely: whereas the pod impregnated by the
hybrid made vigorous and rapid progress to maturity, and bore good seed, which
vegetated freely." This is, indeed, as Herbert remarks, "a strange truth," but
not so strange as it then appeared.

As a confirmation of these statements, I may add that Mr. M. Mayes (17/83.
Loudon's 'Gardener's Magazine' volume 11 1835 page 260.) after much experience
in crossing the species of Amaryllis (Hippeastrum), says, "neither the species
nor the hybrids will, we are well aware, produce seed so abundantly from their
own pollen as from that of others." So, again, Mr. Bidwell, in New South Wales
(17/84. 'Gardener's Chronicle' 1850 page 470.) asserts that Amaryllis
belladonna bears many more seeds when fertilised by the pollen of Brunswigia
(Amaryllis of some authors) josephinae or of B. multiflora, than when
fertilised by its own pollen. Mr. Beaton dusted four flowers of a Cyrtanthus
with their own pollen, and four with the pollen of Vallota (Amaryllis)
purpurea; on the seventh day "those which received their own pollen slackened
their growth, and ultimately perished; those which were crossed with the
Vallota held on." (17/85. 'Journal Hort. Soc.' volume 5 page 135. The
seedlings thus raised were given to the Hort. Soc.; but I find, on inquiry,
that they unfortunately died the following winter.) These latter cases,
however, relate to uncrossed species, like those before given with respect to
Passiflora, Orchids, etc., and are here referred to only because the plants
belong to the same group of Amaryllidaceae.

In the experiments on the hybrid Hippeastrums, if Herbert had found that the
pollen of two or three kinds alone had been more efficient on certain kinds
than their own pollen, it might have been argued that these, from their mixed
parentage, had a closer mutual affinity than the others; but this explanation
is inadmissible, for the trials were made reciprocally backwards and forwards
on nine different hybrids; and a cross, whichever way taken, always proved
highly beneficial. I can add a striking and analogous case from experiments
made by the Rev. A. Rawson, of Bromley Common, with some complex hybrids of
Gladiolus. This skilful horticulturist possessed a number of French varieties,
differing from each other only in the colour and size of the flowers, all
descended from Gandavensis, a well-known old hybrid, said to be descended from
G. natalensis by the pollen of G. oppositiflorus. (17/86. Mr. D. Beaton in
'Journal of Hort.' 1861 page 453. Lecoq however ('De la Fecond.' 1862 page
369) states that this hybrid is descended from G. psittacinus and cardinalis;
but this is opposed to Herbert's experience, who found that the former species
could not be crossed.) Mr. Rawson, after repeated trials, found that none of
the varieties would set seed with their own pollen, although taken from
distinct plants of the same variety (which had, of course, been propagated by
bulbs), but that they all seeded freely with pollen from any other variety. To
give two examples: Ophir did not produce a capsule with its own pollen, but
when fertilised with that of Janire, Brenchleyensis, Vulcain and Linne, it
produced ten fine capsules; but the pollen of Ophir was good, for when Linne
was fertilised by it seven capsules were produced. This latter variety, on the
other hand, was utterly barren with its own pollen, which we have seen was
perfectly efficient on Ophir. Altogether, Mr. Rawson, in the year 1861
fertilised twenty-six flowers borne by four varieties with pollen taken from
other varieties, and every single flower produced a fine seed-capsule; whereas
fifty-two flowers on the same plants, fertilised at the same time with their
own pollen, did not yield a single seed-capsule. Mr. Rawson fertilised, in
some cases, the alternate flowers, and in other cases all those down one side
of the spike, with pollen of other varieties, and the remaining flowers with
their own pollen. I saw these plants when the capsules were nearly mature, and
their curious arrangement at once brought full conviction to the mind that an
immense advantage had been derived from crossing these hybrids.

Lastly, I have heard from Dr. E. Bornet, of Antibes, who has made numerous
experiments in crossing the species of Cistus, but has not yet published the
results, that, when any of these hybrids are fertile, they may be said to be,
in regard to function, dioecious; "for the flowers are always sterile when the
pistil is fertilised by pollen taken from the same flower or from flowers on
the same plant. But they are often fertile if pollen be employed from a
distinct individual of the same hybrid nature, or from a hybrid made by a
reciprocal cross."]

CONCLUSION.

That plants should be self-sterile, although both sexual elements are in a fit
state for reproduction, appears at first sight opposed to all analogy. With
respect to the species, all the individuals of which are in this state,
although living under their natural conditions, we may conclude that their
self-sterility has been acquired for the sake of effectually preventing self-
fertilisation. The case is closely analogous with that of dimorphic and
trimorphic or heterostyled plants, which can be fully fertilised only by
plants belonging to a different form, and not, as in the foregoing cases,
indifferently by any other individual of the species. Some of these hetero-
styled plants are completely sterile with pollen taken from the same plant or
from the same form. With respect to species living under their natural
conditions, of which only certain individuals are self-sterile (as with Reseda
lutea), it is probable that these have been rendered self-sterile to ensure
occasional cross-fertilisation, whilst other individuals have remained self-
fertile to ensure the propagation of the species. The case seems to be
parallel with that of plants which produce, as Hermann Muller has discovered,
two forms--one bearing more conspicuous flowers with their structure adapted
for cross-fertilisation by insects, and the other form with less conspicuous
flowers adapted for self-fertilisation. The self-sterility, however, of some
of the foregoing plants is incidental on the conditions to which they have
been subjected, as with the Eschscholtzia, the Verbascum phoeniceum (the
sterility of which varied according to the season), and with the Passiflora
alata, which recovered its self-fertility when grafted on a different stock.

It is interesting to observe in the above several cases the graduated series
from plants which, when fertilised by their own pollen, yield the full number
of seeds, but with the seedlings a little dwarfed in stature--to plants which
when self-fertilised yield few seeds--to those which yield none, but have
their ovaria somewhat developed--and, lastly, to those in which the plant's
own pollen and stigma mutually act on one another like poison. It is also
interesting to observe on how slight a difference in the nature of the pollen
or of the ovules complete self-sterility or complete self-fertility must
depend in some of the above cases. Every individual of the self-sterile
species appears to be capable of producing the full complement of seed when
fertilised by the pollen of any other individual (though judging from the
facts given with respect to Abutilon the nearest kin must be excepted); but
not one individual can be fertilised by its own pollen. As every organism
differs in some slight degree from every other individual of the same species,
so no doubt it is with their pollen and ovules; and in the above cases we must
believe that complete self-sterility and complete self-fertility depend on
such slight differences in the ovules and pollen, and not their having been
differentiated in some special manner in relation to one another; for it is
impossible that the sexual elements of many thousand individuals should have
been specialised in relation to every other individual. In some, however, of
the above cases, as with certain Passifloras, an amount of differentiation
between the pollen and ovules sufficient for fertilisation is gained only by
employing pollen from a distinct species; but this is probably the result of
such plants having been rendered somewhat sterile from the unnatural
conditions to which they have been exposed.

Exotic animals confined in menageries are sometimes in nearly the same state
as the above-described self-impotent plants; for, as we shall see in the
following chapter, certain monkeys, the larger carnivora, several finches,
geese, and pheasants, cross together, quite as freely as, or even more freely
than the individuals of the same species breed together. Cases will, also, be
given of sexual incompatibility between certain, male and female domesticated
animals, which, nevertheless, are fertile when matched with any other
individual of the same kind.

In the early part of this chapter it was shown that the crossing of
individuals belonging to distinct families of the same race, or to different
races or species, gives increased size and constitutional vigour to the
offspring, and, except in the case of crossed species, increased fertility.
The evidence rests on the universal testimony of breeders (for it should be
observed that I am not here speaking of the evil results of close
interbreeding), and is practically exemplified in the higher value of cross-
bred animals for immediate consumption. The good results of crossing have also
been demonstrated with some animals and with numerous plants, by actual weight
and measurement. Although animals of pure blood will obviously be deteriorated
by crossing, as far as their characteristic qualities are concerned, there
seems to be no exception to the rule that advantages of the kind just
mentioned are thus gained, even when there has not been any previous close
interbreeding; and the rule applies to such animals as cattle and sheep, which
can long resist breeding in-and-in between the nearest blood-relations.

In the case of crossed species, although size, vigour, precocity, and
hardiness are, with rare exceptions, gained, fertility, in a greater or less
degree, is lost; but the gain in the above respects can hardly be attributed
to the principle of compensation; for there is no close parallelism between
the increased size and vigour of hybrid offspring and their sterility.
Moreover, it has been clearly proved that mongrels which are perfectly fertile
gain these same advantages as well as sterile hybrids.

With the higher animals no special adaptations for ensuring occasional crosses
between distinct families seem to exist. The eagerness of the males, leading
to severe competition between them, is sufficient; for even with gregarious
animals, the old and dominant males will be dispossessed after a time and it
would be a mere chance if a closely related member of the same family were to
be the victorious successor. The structure of many of the lower animals, when
they are hermaphrodites, is such as to prevent the ovules being fertilised by
the male element of the same individual; so that the concourse of two
individuals is necessary. In other cases the access of the male element of a
distinct individual is at least possible. With plants, which are affixed to
the ground and cannot wander from place to place like animals, the numerous
adaptations for cross-fertilisation are wonderfully perfect, as has been
admitted by every one who has studied the subject.

The evil consequences of long-continued close interbreeding are not so easily
recognised as the good effects from crossing, for the deterioration is
gradual. Nevertheless, it is the general opinion of those who have had most
experience, especially with animals which propagate quickly, that evil does
inevitably follow sooner or later, but at different rates with different
animals. No doubt a false belief may, like a superstition, prevail widely; yet
it is difficult to suppose that so many acute observers have all been deceived
at the expense of much cost and trouble. A male animal may sometimes be paired
with his daughter, granddaughter, and so on, even for seven generations,
without any manifest bad result: but the experiment has never been tried of
matching brothers and sisters, which is considered the closest form of
interbreeding, for an equal number of generations. There is good reason to
believe that by keeping the members of the same family in distinct bodies,
especially if exposed to somewhat different conditions of life, and by
occasionally crossing these families, the evil results of interbreeding may be
much diminished or quite eliminated. These results are loss of constitutional
vigour, size, and fertility; but there is no necessary deterioration in the
general form of the body, or in other good qualities. We have seen that with
pigs first-rate animals have been produced after long-continued close
interbreeding, though they had become extremely infertile when paired with
their near relations. The loss of fertility, when it occurs, seems never to be
absolute, but only relative to animals of the same blood; so that this
sterility is to a certain extent analogous with that of self-impotent plants
which cannot be fertilised by their own pollen, but are perfectly fertile with
pollen of any other individual of the same species. The fact of infertility of
this peculiar nature being one of the results of long-continued interbreeding,
shows that interbreeding does not act merely by combining and augmenting
various morbid tendencies common to both parents; for animals with such
tendencies, if not at the time actually ill, can generally propagate their
kind. Although offspring descended from the nearest blood-relations are not
necessarily deteriorated in structure, yet some authors believe that they are
eminently liable to malformations; and this is not improbable, as everything
which lessens the vital powers acts in this manner. Instances of this kind
have been recorded in the case of pigs, bloodhounds, and some other animals.

Finally, when we consider the various facts now given which plainly show that
good follows from crossing, and less plainly that evil follows from close
interbreeding, and when we bear in mind that with very many organisms
elaborate provisions have been made for the occasional union of distinct
individuals, the existence of a great law of nature is almost proved; namely,
that the crossing of animals and plants which are not closely related to each
other is highly beneficial or even necessary, and that interbreeding prolonged
during many generations is injurious.


CHAPTER 2.XVIII.

ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE: STERILITY
FROM VARIOUS CAUSES.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE.
STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY AND IN
MENAGERIES.
MAMMALS, BIRDS, AND INSECTS.
LOSS OF SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS.
CAUSES OF STERILITY.
STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS.
SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS.
STERILITY OF PLANTS FROM CHANGED CONDITIONS OF LIFE.
CONTABESCENCE OF THE ANTHERS.
MONSTROSITIES AS A CAUSE OF STERILITY.
DOUBLE FLOWERS.
SEEDLESS FRUIT.
STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION.
FROM LONG-CONTINUED PROPAGATION BY BUDS.
INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS FRUIT.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE.

In considering whether any facts were known which might throw light on the
conclusion arrived at in the last chapter, namely, that benefits ensue from
crossing, and that it is a law of nature that all organic beings should
occasionally cross, it appeared to me probable that the good derived from
slight changes in the conditions of life, from being an analogous phenomenon,
might serve this purpose. No two individuals, and still less no two varieties,
are absolutely alike in constitution and structure; and when the germ of one
is fertilised by the male element of another, we may believe that it is acted
on in a somewhat similar manner as an individual when exposed to slightly
changed conditions. Now, every one must have observed the remarkable influence
on convalescents of a change of residence, and no medical man doubts the truth
of this fact. Small farmers who hold but little land are convinced that their
cattle derive great benefit from a change of pasture. In the case of plants,
the evidence is strong that a great advantage is derived from exchanging
seeds, tubers, bulbs, and cuttings from one soil or place to another as
different as possible.

[The belief that plants are thus benefited, whether or not well founded, has
been firmly maintained from the time of Columella, who wrote shortly after the
Christian era, to the present day; and it now prevails in England, France, and
Germany. (18/1. For England see below. For Germany see Metzger 'Getreidearten'
1841 s. 63. For France Loiseleur-Deslongchamps ('Consid. sur les Cereales'
1843 page 200) gives numerous references on this subject. For Southern France
see Godron 'Florula Juvenalis' 1854 page 28.) A sagacious observer, Bradley,
writing in 1724 (18/2. 'A General Treatise of Husbandry' volume 3 page 58.),
says, "When we once become Masters of a good Sort of Seed, we should at least
put it into Two or Three Hands, where the Soils and Situations are as
different as possible; and every Year the Parties should change with one
another; by which Means, I find the Goodness of the Seed will be maintained
for several Years. For Want of this Use many Farmers have failed in their
Crops and been great Losers." He then gives his own practical experience on
this head. A modern writer (18/3. 'Gardener's Chronicle and Agricult. Gazette'
1858 page 247; and for the second statement, Ibid 1850 page 702. On this same
subject see also Rev. D. Walker 'Prize Essay of Highland Agricult. Soc.'
volume 2 page 200. Also Marshall 'Minutes of Agriculture' November 1775.)
asserts, "Nothing can be more clearly established in agriculture than that the
continual growth of any one variety in the same district makes it liable to
deterioration either in quality or quantity." Another writer states that he
sowed close together in the same field two lots of wheat-seed, the product of
the same original stock, one of which had been grown on the same land and the
other at a distance, and the difference in favour of the crop from the latter
seed was remarkable. A gentleman in Surrey who has long made it his business
to raise wheat to sell for seed, and who has constantly realised in the market
higher prices than others, assures me that he finds it indispensable
continually to change his seed; and that for this purpose he keeps two farms
differing much in soil and elevation.

With respect to the tubers of the potato, I find that at the present day the
practice of exchanging sets is almost everywhere followed. The great growers
of potatoes in Lancashire formerly used to get tubers from Scotland, but they
found that "a change from the moss-lands, and vice versa, was generally
sufficient." In former times in France the crop of potatoes in the Vosges had
become reduced in the course of fifty or sixty years in the proportion from
120-150 to 30-40 bushels; and the famous Oberlin attributed the surprising
good which he effected in large part to changing the sets. (18/4. Oberlin
'Memoirs' English translation page 73. For Lancashire see Marshall 'Review of
Reports' 1808 page 295.)

A well-known practical gardener, Mr. Robson (18/5. 'Cottage Gardener' 1856
page 186. For Mr. Robson's subsequent statements see 'Journal of Horticulture'
February 18, 1866 page 121. For Mr. Abbey's remarks on grafting etc. Ibid July
18, 1865 page 44.) positively states that he has himself witnessed decided
advantage from obtaining bulbs of the onion, tubers of the potato, and various
seeds, all of the same kind, from different soils and distant parts of
England. He further states that with plants propagated by cuttings, as with
the Pelargonium, and especially the Dahlia, manifest advantage is derived from
getting plants of the same variety, which have been cultivated in another
place; or, "where the extent of the place allows, to take cuttings from one
description of soil to plant on another, so as to afford the change that seems
so necessary to the well-being of the plants." He maintains that after a time
an exchange of this nature is "forced on the grower, whether he be prepared
for it or not." Similar remarks have been made by another excellent gardener,
Mr. Fish, namely, that cuttings of the same variety of Calceolaria, which he
obtained from a neighbour, "showed much greater vigour than some of his own
that were "treated in exactly the same manner," and he attributed this solely
to his own plants having become "to a certain extent worn out or tired of
their quarters." Something of this kind apparently occurs in grafting and
budding fruit-trees; for, according to Mr. Abbey, grafts or buds generally
take with greater facility on a distinct variety or even species, or on a
stock previously grafted, than on stocks raised from seeds of the variety
which is to be grafted; and he believes this cannot be altogether explained by
the stocks in question being better adapted to the soil and climate of the
place. It should, however, be added, that varieties grafted or budded on very
distinct kinds, though they may take more readily and grow at first more
vigorously than when grafted on closely allied stocks, afterwards often become
unhealthy.

I have studied M. Tessier's careful and elaborate experiments (18/6. 'Mem. de
l'Acad. des Sciences' 1790 page 209.) made to disprove the common belief that
good is derived from a change of seed; and he certainly shows that the same
seed may with care be cultivated on the same farm (it is not stated whether on
exactly the same soil) for ten consecutive years without loss. Another
excellent observer, Colonel Le Couteur (18/7. 'On the Varieties of Wheat' page
52.) has come to the same conclusion; but then he expressly adds, if the same
seed be used, "that which is grown on land manured from the mixen one year
becomes seed for land prepared with lime, and that again becomes seed for land
dressed with ashes, then for land dressed with mixed manure, and so on." But
this in effect is a systematic exchange of seed, within the limits of the same
farm.]

On the whole the belief, which has long been held by many cultivators, that
good follows from exchanging seed, tubers, etc., seems to be fairly well
founded. It seems hardly credible that the advantage thus derived can be due
to the seeds, especially if very small ones, obtaining in one soil some
chemical element deficient in the other and in sufficient quantity to
influence the whole after-growth of the plant. As plants after once
germinating are fixed to the same spot, it might have been anticipated that
they would show the good effects of a change more plainly than do animals
which continually wander about; and this apparently is the case. Life
depending on, or consisting in, an incessant play of the most complex forces,
it would appear that their action is in some way stimulated by slight changes
in the circumstances to which each organism is exposed. All forces throughout
nature, as Mr. Herbert Spencer (18/8. Mr. Spencer has fully and ably discussed
this whole subject in his 'Principles of Biology' 1864 volume 2 chapter 10. In
the first edition of my 'Origin of Species' 1859 page 267, I spoke of the good
effects from slight changes in the conditions of life and from cross-breeding,
and of the evil effects from great changes in the conditions and from crossing
widely distinct forms, as a series of facts "connected together by some common
but unknown bond, which is essentially related to the principle of life.)
remarks, tend towards an equilibrium, and for the life of each organism it is
necessary that this tendency should be checked. These views and the foregoing
facts probably throw light, on the one hand, on the good effects of crossing
the breed, for the germ will be thus slightly modified or acted on by new
forces; and on the other hand, on the evil effects of close interbreeding
prolonged during many generations, during which the germ will be acted on by a
male having almost identically the same constitution.

STERILITY FROM CHANGED CONDITIONS OF LIFE.

I will now attempt to show that animals and plants, when removed from their
natural conditions, are often rendered in some degree infertile or completely
barren; and this occurs even when the conditions have not been greatly
changed. This conclusion is not necessarily opposed to that at which we have
just arrived, namely, that lesser changes of other kinds are advantageous to
organic beings. Our present subject is of some importance, from having an
intimate connection with the causes of variability. Indirectly it perhaps
bears on the sterility of species when crossed: for as, on the one hand,
slight changes in the conditions of life are favourable to plants and animals,
and the crossing of varieties adds to the size, vigour, and fertility of their
offspring; so, on the other hand, certain other changes in the conditions of
life cause sterility; and as this likewise ensues from crossing much-modified
forms or species, we have a parallel and double series of facts, which
apparently stand in close relation to each other.

It is notorious that many animals, though perfectly tamed, refuse to breed in
captivity. Isidore Geoffroy St.-Hilaire (18/9. 'Essais de Zoologie Generale'
1841 page 256. ) consequently has drawn a broad distinction between tamed
animals which will not breed under captivity, and truly domesticated animals
which breed freely--generally more freely, as shown in the sixteenth chapter,
than in a state of nature. It is possible and generally easy to tame most
animals; but experience has shown that it is difficult to get them to breed
regularly, or even at all. I shall discuss this subject in detail; but will
give only those cases which seem most illustrative. My materials are derived
from notices scattered through various works, and especially from a Report,
kindly drawn up for me by the officers of the Zoological Society of London,
which has especial value, as it records all the cases, during nine years from
1838-46, in which the animals were seen to couple but produced no offspring,
as well as the cases in which they never, as far as known, coupled. This MS.
Report I have corrected by the annual Reports subsequently published up to the
year 1865. (18/10. Since the appearance of the first edition of this work, Mr.
Sclater has published ('Proc. Zoolog. Soc.' 1868 page 623) a list of the
species of mammals which have bred in the gardens from 1848 to 1867 inclusive.
Of the Artiodactyla 85 species have been kept, and of these 1 species in 1.9
have bred at least once during the 20 years; of 28 Marsupialia, 1 in 2.5 have
bred; of 74 Carnivora, 1 in 3.0 have bred; of 52 Rodentia, 1 in 4.7 have bred;
and of Quadrumana 75 species have been kept, and 1 in 6.2 have bred.) Many
facts are given on the breeding of the animals in that magnificent work,
'Gleanings from the Menageries of Knowsley Hall' by Dr. Gray. I made, also,
particular inquiries from the experienced keeper of the birds in the old
Surrey Zoological Gardens. I should premise that a slight change in the
treatment of animals sometimes makes a great difference in their fertility;
and it is probable that the results observed in different menageries would
differ. Indeed, some animals in our Zoological Gardens have become more
productive since the year 1846. It is, also, manifest from F. Cuvier's account
of the Jardin des Plantes (18/11. Du Rut 'Annales du Museum' 1807 tome 9 page
120.) that the animals formerly bred much less freely there than with us; for
instance, in the Duck tribe, which is highly prolific, only one species had at
that period produced young.

[The most remarkable cases, however, are afforded by animals kept in their
native country, which, though perfectly tamed, quite healthy, and allowed some
freedom, are absolutely incapable of breeding. Rengger (18/12. 'Saugethiere
von Paraguay' 1830 s. 49, 106, 118, 124, 201, 208, 249, 265, 327.), who in
Paraguay particularly attended to this subject, specifies six quadrupeds in
this condition; and he mentions two or three others which most rarely breed.
Mr. Bates, in his admirable work on the Amazons, strongly insists on similar
cases (18/13. 'The Naturalist on the Amazons' 1863 volume 1 pages 99, 193;
volume 2 page 113.); and he remarks, that the fact of thoroughly tamed native
mammals and birds not breeding when kept by the Indians, cannot be wholly
accounted for by their negligence or indifference, for the turkey and fowl are
kept and bred by various remote tribes. In almost every part of the world--for
instance, in the interior of Africa, and in several of the Polynesian islands
--the natives are extremely fond of taming the indigenous quadrupeds and
birds; but they rarely or never succeed in getting them to breed.

The most notorious case of an animal not breeding in captivity is that of the
elephant. Elephants are kept in large numbers in their native Indian home,
live to old age, and are vigorous enough for the severest labour; yet, with a
very few exceptions, they have never been known even to couple, though both
males and females have their proper periodical seasons. If, however, we
proceed a little eastward to Ava, we hear from Mr. Crawfurd (18/14. 'Embassy
to the Court of Ava' volume 1 page 534.) that their "breeding in the domestic
state, or at least in the half-domestic state in which the female elephants
are generally kept, is of everyday occurrence;" and Mr. Crawfurd informs me
that he believes that the difference must be attributed solely to the females
being allowed to roam the forest with some degree of freedom. The captive
rhinoceros, on the other hand, seems from Bishop Heber's account (18/15.
'Journal' volume 1 page 213.) to breed in India far more readily than the
elephant. Four wild species of the horse genus have bred in Europe, though
here exposed to a great change in their natural habits of life; but the
species have generally been crossed one with another. Most of the members of
the pig family breed readily in our menageries; even the Red River hog
(Potamochoerus penicillatus), from the sweltering plains of West Africa, has
bred twice in the Zoological Gardens. Here also the Peccary (Dicotyles
torquatus) has bred several times; but another species, the D. labiatus,
though rendered so tame as to be half-domesticated, is said to breed so rarely
in its native country of Paraguay, that according to Rengger (18/16.
'Saugethiere' s. 327.) the fact requires confirmation. Mr. Bates remarks that
the tapir, though often kept tame in Amazonia by the Indians, never breeds.

Ruminants generally breed quite freely in England, though brought from widely
different climates, as may be seen in the Annual Reports of the Zoological
Gardens, and in the Gleanings from Lord Derby's menagerie.

The Carnivora, with the exception of the Plantigrade division, breed (though
with capricious exceptions) about half as freely as ruminants. Many species of
Felidae have bred in various menageries, although imported from diverse
climates and closely confined. Mr. Bartlett, the present superintendent of the
Zoological Gardens (18/17. On the Breeding of the Larger Felidae 'Proc.
Zoolog. Soc.' 1861 page 140.) remarks that the lion appears to breed more
frequently and to bring forth more young at a birth than any other species of
the family. He adds that the tiger has rarely bred; "but there are several
well-authenticated instances of the female tiger breeding with the lion."
Strange as the fact may appear, many animals under confinement unite with
distinct species and produce hybrids quite as freely as, or even more freely
than, with their own species. On inquiring from Dr. Falconer and others, it
appears that the tiger when confined in India does not breed, though it has
been known to couple. The chetah (Felis jubata) has never been known by Mr.
Bartlett to breed in England, but it has bred at Frankfort; nor does it breed
in India, where it is kept in large numbers for hunting; but no pains would be
taken to make them breed, as only those animals which have hunted for
themselves in a state of nature are serviceable and worth training. (18/18.
Sleeman's 'Rambles in India' volume 2 page 10.) According to Rengger, two
species of wild cats in Paraguay, though thoroughly tamed, have never bred.
Although so many of the Felidae breed readily in the Zoological Gardens, yet
conception by no means always follows union: in the nine-year Report, various
species are specified which were observed to couple seventy-three times, and
no doubt this must have passed many times unnoticed; yet from the seventy-
three unions only fifteen births ensued. The Carnivora in the Zoological
Gardens were formerly less freely exposed to the air and cold than at present,
and this change of treatment, as I was assured by the former superintendent,
Mr. Miller, greatly increased their fertility. Mr. Bartlett, and there cannot
be a more capable judge, says, "it is remarkable that lions breed more freely
in travelling collections than in the Zoological Gardens; probably the
constant excitement and irritation produced by moving from place to place, or
change of air, may have considerable influence in the matter."

Many members of the Dog family breed readily when confined. The Dhole is one
of the most untamable animals in India, yet a pair kept there by Dr. Falconer
produced young. Foxes, on the other hand, rarely breed, and I have never heard
of such an occurrence with the European fox: the silver fox of North America
(Canis argentatus), however, has bred several times in the Zoological Gardens.
Even the otter has bred there. Every one knows how readily the semi-
domesticated ferret breeds, though shut up in miserably small cages; but other
species of Viverra and Paradoxurus absolutely refuse to breed in the
Zoological Gardens. The Genetta has bred both here and in the Jardin des
Plantes, and produced hybrids. The Herpestes fasciatus has likewise bred; but
I was formerly assured that the H. griseus, though many were kept in the
Gardens, never bred.

The Plantigrade Carnivora breed under confinement much less freely than other
Carnivora, although no reason can be assigned for this fact. In the nine-year
Report it is stated that the bears had been seen in the Zoological Gardens to
couple freely, but previously to 1848 had most rarely conceived. In the
Reports published since this date three species have produced young (hybrids
in one case), and, wonderful to relate, the white Polar bear has produced
young. The badger (Meles taxus) has bred several times in the Gardens; but I
have not heard of this occurring elsewhere in England, and the event must be
very rare, for an instance in Germany has been thought worth recording.
(18/19. Wiegmann 'Archiv. fur Naturgesch.' 1837 s. 162.) In Paraguay the
native Nasua, though kept in pairs during many years and perfectly tamed, has
never been known, according to Rengger, to breed or show any sexual passion;
nor, as I hear from Mr. Bates, does this animal, or the Cercoleptes, breed in
Amazonia. Two other plantigrade genera, Procyon and Gulo, though often kept
tame in Paraguay, never breed there. In the Zoological Gardens species of
Nasua and Procyon have been seen to couple; but they did not produce young.

As domesticated rabbits, guinea-pigs, and white mice breed so abundantly when
closely confined under various climates, it might have been thought that most
other members of the Rodent order would have bred in captivity, but this is
not the case. It deserves notice, as showing how the capacity to breed
sometimes goes by affinity, that the one native rodent of Paraguay, which
there breeds FREELY and has yielded successive generations, is the Cavia
aperea; and this animal is so closely allied to the guinea-pig, that it has
been erroneously thought to be the parent form. (18/20. Rengger 'Saugethiere'
etc. s. 276. On the parentage of the guinea-pig, see also Isid. Geoffroy St.-
Hilaire 'Hist. Nat. Gen.' I sent to Mr. H. Denny of Leeds the lice which I
collected from the wild aperea in La Plata, and he informs me that they belong
to a genus distinct from those found on the guinea-pig. This is important
evidence that the aperea is not the parent of the guinea-pig; and is worth
giving, as some authors erroneously suppose that the guinea-pig since being
domesticated has become sterile when crossed with the aperea.) In the
Zoological Gardens, some rodents have coupled, but have never produced young;
some have neither coupled nor bred; but a few have bred, as the porcupine more
than once, the Barbary mouse, lemming, chinchilla, and agouti (Dasyprocta
aguti) several times. This latter animal has also produced young in Paraguay,
though they were born dead and ill-formed; but in Amazonia, according to Mr.
Bates, it never breeds, though often kept tame about the houses. Nor does the
paca (Coelogenys paca) breed there. The common hare when confined has, I
believe, never bred in Europe; though, according to a recent statement, it has
crossed with the rabbit. (18/21. Although the existence of the Leporides, as
described by Dr. Broca ('Journal de Phys.' tome 2 page 370), has been
positively denied, yet Dr. Pigeaux ('Annals and Mag. of Nat. Hist.' volume 20
1867 page 75) affirms that the hare and rabbit have produced hybrids.) I have
never heard of the dormouse breeding in confinement. But squirrels offer a
more curious case: with one exception, no species has bred in the Zoological
Gardens, yet as many as fourteen individuals of S. palmarum were kept together
during several years. The S. cinera has been seen to couple, but it did not
produce young; nor has this species, when rendered extremely tame in its
native country, North America, been ever known to breed. (18/22. 'Quadrupeds
of North America' by Audubon and Bachman 1846 page 268.) At Lord Derby's
menagerie squirrels of many kinds were kept in numbers, but Mr. Thompson, the
superintendent, told me that none had ever bred there, or elsewhere as far as
he knew. I have never heard of the English squirrel breeding in confinement.
But the species which has bred more than once in the Zoological Gardens is the
one which perhaps might have been least expected, namely, the flying squirrel
(Sciuropterus volucella): it has, also, bred several times near Birmingham;
but the female never produced more than two young at a birth, whereas in its
native American home she bears from three to six young. (18/23. Loudon's 'Mag.
of Nat. Hist.' volume 9 1836 page 571; Audubon and Bachman 'Quadrupeds of
North America' page 221.)

Monkeys, in the nine-year Report from the Zoological Gardens, are stated to
unite most freely, but during this period, though many individuals were kept,
there were only seven births. I have heard of only one American monkey, the
Ouistiti, breeding in Europe. (18/24. Flourens 'De l'Instinct' etc. 1845 page
88.) A Macacus, according to Flourens, bred in Paris; and more than one
species of this genus has produced young in London, especially the Macacus
rhesus, which everywhere shows a special capacity to breed under confinement.
Hybrids have been produced both in Paris and London from this same genus. The
Arabian baboon, or Cynocephalus hamadryas (18/25. See 'Annual Reports Zoolog.
Soc.' 1855, 1858, 1863, 1864; 'Times' newspaper August 10, 1847; Flourens 'De
l'Instinct' page 85.), and a Cercopithecus have bred in the Zoological
Gardens, and the latter species at the Duke of Northumberland's. Several
members of the family of Lemurs have produced hybrids in the Zoological
Gardens. It is much more remarkable that monkeys very rarely breed when
confined in their native country; thus the Cay (Cebus azara) is frequently and
completely tamed in Paraguay, but Rengger (18/26. 'Saugethiere' etc. s. 34,
49.) says that it breeds so rarely, that he never saw more than two females
which had produced young. A similar observation has been made with respect to
the monkeys which are frequently tamed by the aborigines in Brazil. (18/27.
Art. Brazil 'Penny Cyclop.' page 363.) In Amazonia, these animals are so often
kept in a tame state, that Mr. Bates in walking through the streets of Para
counted thirteen species; but, as he asserts, they have never been known to
breed in captivity. (18/28. 'The Naturalist on the Amazons' volume 1 page 99.)

BIRDS.

Birds offer in some respects better evidence than quadrupeds, from their
breeding more rapidly and being kept in greater numbers. (18/29. A list of the
species of birds which have bred in the Zoological Gardens from 1848 to 1867
inclusive has been published by Mr. Sclater in 'Proc. Zoolog. Soc.' 1869 page
626, since the first edition of this work appeared. Of Columbae 51 species
have been kept, and of Anseres 80 species, and in both these families 1
species in 2.6 have bred at least once in the 20 years. Of Gallinae 83 species
have been kept and 1 in 27 have bred; of 57 Grallae 1 in 9 have bred; of 110
Prehensores 1 in 22 have bred; of 178 Passeres 1 in 25.4 have bred; of 94
Accipitres 1 in 47 have bred; of 25 Picariae and of 35 Herodiones not one
species in either group has bred.) We have seen that carnivorous animals are
more fertile under confinement than most other mammals. The reverse holds good
with carnivorous birds. It is said (18/30. 'Encyclop. of Rural Sports' page
691.) that as many as eighteen species have been used in Europe for hawking,
and several others in Persia and India (18/31. According to Sir A. Burnes
'Cabool' etc. page 51, eight species are used for hawking in Sinde.); they
have been kept in their native country in the finest condition, and have been
flown during six, eight, or nine years (18/32. Loudon's 'Mag. of Nat. Hist.'
volume 6 1833 page 110.); yet there is no record of their having ever produced
young. As these birds were formerly caught whilst young, at great expense,
being imported from Iceland, Norway, and Sweden, there can be little doubt
that, if possible, they would have been propagated. In the Jardin des Plantes,
no bird of prey has been known to couple. (18/33. F. Cuvier 'Annal. du Museum'
tome 9 page 128.) No hawk, vulture, or owl has ever produced fertile eggs in
the Zoological Gardens, or in the old Surrey Gardens, with the exception, in
the former place on one occasion, of a condor and a kite (Milvus niger). Yet
several species, namely, the Aquila fusca, Haliaetus leucocephalus, Falco
tinnunculus, F. subbuteo, and Buteo vulgaris, have been seen to couple in the
Zoological Gardens. Mr. Morris (18/34. 'The Zoologist' volume 7-8 1849-50 page
2648.) mentions as a unique fact that a kestrel (Falco tinnunculus) bred in an
aviary. The one kind of owl which has been known to couple in the Zoological
Gardens was the Eagle Owl (Bubo maximus); and this species shows a special
inclination to breed in captivity; for a pair at Arundel Castle, kept more
nearly in a state of nature "than ever fell to the lot of an animal deprived
of its liberty" (18/35. Knox 'Ornithological Rambles in Sussex' page 91.),
actually reared their young. Mr. Gurney has given another instance of this
same owl breeding in confinement; and he records the case of a second species
of owl, the Strix passerina, breeding in captivity. (18/36. 'The Zoologist'
volume 7-8 1849-50 page 2566; volume 9-10 1851-2 page 3207.)

Of the smaller graminivorous birds, many kinds have been kept tame in their
native countries, and have lived long; yet, as the highest authority on cage-
birds (18/37. Bechstein 'Naturgesch. der Stubenvogel' 1840 s. 20.) remarks,
their propagation is "uncommonly difficult." The canary-bird shows that there
is no inherent difficulty in these birds breeding freely in confinement; and
Audubon says (18/38. 'Ornithological Biography' volume 5 page 517.) that the
Fringilla (Spiza) ciris of North America breeds as perfectly as the canary.
The difficulty with the many finches which have been kept in confinement is
all the more remarkable as more than a dozen species could be named which have
yielded hybrids with the canary; but hardly any of these, with the exception
of the siskin (Fringilla spinus), have reproduced their own kind. Even the
bullfinch (Loxia pyrrhula) has bred as frequently with the canary, though
belonging to a distinct genus, as with its own species. (18/39. A case is
recorded in 'The Zoologist' volume 1-2 1843-45 page 453. For the siskin
breeding, volume 3-4 1845-46 page 1075. Bechstein 'Stubenvogel' s. 139 speaks
of bullfinches making nests, but rarely producing young.) With respect to the
skylark (Alauda arvensis), I have heard of birds living for seven years in an
aviary, which never produced young; and a great London bird-fancier assured me
that he had never known an instance of their breeding; nevertheless one case
has been recorded. (18/40. Yarrell 'Hist. British Birds' 1839 volume 1 page
412.) In the nine-year Report from the Zoological Society, twenty-four
insessorial species are enumerated which had not bred, and of these only four
were known to have coupled.

Parrots are singularly long-lived birds; and Humboldt mentions the curious
fact of a parrot in South America, which spoke the language of an extinct
Indian tribe, so that this bird preserved the sole relic of a lost language.
Even in this country there is reason to believe (18/41. Loudon's 'Mag. of Nat.
History' volume 19 1836 page 347.) that parrots have lived to the age of
nearly one hundred years; yet they breed so rarely, though many have been kept
in Europe, that the event has been thought worth recording in the gravest
publications. (18/42. 'Memoires du Museum d'Hist. Nat.' tome 10 page 314: five
cases of parrots breeding in France are here recorded. See also 'Report Brit.
Assoc. Zoolog.' 1843.) Nevertheless, when Mr. Buxton turned out a large number
of parrots in Norfolk, three pairs bred and reared ten young birds in the
course of two seasons; and this success may be attributed to their free life.
(18/43. 'Annals and Mag. of Nat. Hist.' November 1868 page 311.) According to
Bechstein (18/44. 'Stubenvogel' s. 105, 83.) the African Psittacus erithacus
breeds oftener than any other species in Germany: the P. macoa occasionally
lays fertile eggs, but rarely succeeds in hatching them; this bird, however,
has the instinct of incubation sometimes so strongly developed, that it will
hatch the eggs of fowls or pigeons. In the Zoological Gardens and in the old
Surrey Gardens some few species have coupled, but, with the exception of three
species of parakeets, none have bred. It is a much more remarkable fact that
in Guiana parrots of two kinds, as I am informed by Sir R. Schomburgk, are
often taken from the nests by the Indians and reared in large numbers; they
are so tame that they fly freely about the houses, and come when called to be
fed, like pigeons; yet he has never heard of a single instance of their
breeding. (18/45. Dr. Hancock remarks ('Charlesworth's Mag. of Nat. Hist.'
volume 2 1838 page 492) "it is singular that, amongst the numerous useful
birds that are indigenous to Guiana, none are found to propagate among the
Indians; yet the common fowl is reared in abundance throughout the country.")
In Jamaica, a resident naturalist, Mr. R. Hill (18/46. 'A Week at Pert Royal'
1855 page 7.), says, "no birds more readily submit to human dependence than
the parrot-tribe, but no instance of a parrot breeding in this tame life has
been known yet." Mr. Hill specifies a number of other native birds kept tame
in the West Indies, which never breed in this state.

The great pigeon family offers a striking contrast with the parrots: in the
nine-year Report thirteen species are recorded as having bred, and, what is
more noticeable, only two were seen to couple without any result. Since the
above date every annual Report gives many cases of various pigeons breeding.
The two magnificent crowned pigeons (Goura coronata and victoriae) produced
hybrids; nevertheless, of the former species more than a dozen birds were
kept, as I am informed by Mr. Crawfurd, in a park at Penang, under a perfectly
well-adapted climate, but never once bred. The Columba migratoria in its
native country, North America, invariably lays two eggs, but in Lord Derby's
menagerie never more than one. The same fact has been observed with the C.
leucocephala. (18/47. Audubon 'American Ornithology' volume 5 pages 552, 557.)

Gallinaceous birds of many genera likewise show an eminent capacity for
breeding under captivity. This is particularly the case with pheasants, yet
our English species seldom lays more than ten eggs in confinement; whilst from
eighteen to twenty is the usual number in the wild state. (18/48. Mowbray on
'Poultry' 7th edition page 133.) With the Gallinaceae, as with all other
orders, there are marked and inexplicable exceptions in regard to the
fertility of certain species and genera under confinement. Although many
trials have been made with the common partridge, it has rarely bred, even when
reared in large aviaries; and the hen will never hatch her own eggs. (18/49.
Temminck 'Hist. Nat. Gen. des Pigeons' etc. 1813 tome 3 pages 288, 382;
'Annals and Mag. of Nat. Hist.' volume 12 1843 page 453. Other species of
partridge have occasionally bred; as the red-legged (P. rubra), when kept in a
large court in France (see Journal de Physique' tome 25 page 294), and in the
Zoological Gardens in 1856.) The American tribe of Guans or Cracidae are tamed
with remarkable ease, but are very shy breeders in this country (18/50. Rev.
E.S. Dixon 'The Dovecote' 1851 pages 243-252.); but with care various species
were formerly made to breed rather freely in Holland. (18/51. Temminck 'Hist.
Nat. Gen. des Pigeons' etc. tome 2 pages 456, 458; tome 3 pages 2, 13, 47.)
Birds of this tribe are often kept in a perfectly tamed condition in their
native country by the Indians, but they never breed. (18/52. Bates 'The
Naturalist on the Amazons' volume 1 page 193; volume 2 page 112.) It might
have been expected that grouse from their habits of life would not have bred
in captivity, more especially as they are said soon to languish and die.
(18/53. Temminck 'Hist. Nat. Gen.' etc. tome 2 page 125. For Tetrao urogallus
see L. Lloyd 'Field Sports of North of Europe' volume 1 pages 287, 314; and
Bull. de la Soc. d'Acclimat.' tome 7 1860 page 600. For T. scoticus Thompson
'Nat. Hist. of Ireland' volume 2 1850 page 49. For T. cupido 'Boston Journal
of Nat. Hist.' volume 3 page 199.) But many cases are recorded of their
breeding: the capercailzie (Tetrao urogallus) has bred in the Zoological
Gardens; it breeds without much difficulty when confined in Norway, and in
Russia five successive generations have been reared: Tetrao tetrix has
likewise bred in Norway; T. scoticus in Ireland; T. umbellus at Lord Derby's;
and T. cupido in North America.

It is scarcely possible to imagine a greater change in habits than that which
the members of the ostrich family must suffer, when cooped up in small
enclosures under a temperate climate, after freely roaming over desert and
tropical plains or entangled forests; yet almost all the kinds have frequently
produced young in the various European menageries, even the mooruk (Casuarius
bennetii) from New Ireland. The African ostrich, though perfectly healthy and
living long in the South of France, never lays more than from twelve to
fifteen eggs, though in its native country it lays from twenty-five to thirty.
(18/54. Marcel de Serres 'Annales des Sc. Nat.' 2nd series Zoolog. tome 13
page 175.) Here we have another instance of fertility impaired, but not lost,
under confinement, as with the flying squirrel, the hen-pheasant, and two
species of American pigeons.

Most Waders can be tamed, as the Rev. E.S. Dixon informs me, with remarkable
facility; but several of them are short-lived under confinement, so that their
sterility in this state is not surprising. The cranes breed more readily than
other genera: Grus montigresia has bred several times in Paris and in the
Zoological Gardens, as has G. cinerea at the latter place, and G. antigone at
Calcutta. Of other members of this great order, Tetrapteryx paradisea has bred
at Knowsley, a Porphyrio in Sicily, and the Gallinula chloropus in the
Zoological Gardens. On the other hand, several birds belonging to this order
will not breed in their native country, Jamaica; and the Psophia, though often
kept by the Indians of Guiana about their houses, "is seldom or never known to
breed." (18/55. Dr. Hancock in 'Charlesworth's Mag. of Nat. Hist.' volume 2
1838 page 491; R. Hill 'A Week at Port Royal' page 8; 'Guide to the Zoological
Gardens' by P.L. Sclater 1859 pages 11, 12; 'The Knowsley Menagerie' by D.
Gray 1846 p1. 14; E. Blyth 'Report Asiatic Soc. of Bengal' May 1855.)

The members of the great Duck family breed as readily in confinement as do the
Columbae and Gallinae and this, considering their aquatic and wandering
habits, and the nature of their food, could not have been anticipated. Even
some time ago above two dozen species had bred in the Zoological Gardens; and
M. Selys-Longchamps has recorded the production of hybrids from forty-four
different members of the family; and to these Professor Newton has added a few
more cases. (18/56. Prof. Newton in 'Proc. Zoolog. Soc.' 1860 page 336.)
"There is not," says Mr. Dixon (18/57. 'The Dovecote and Aviary' page 428.),
"in the wide world, a goose which is not in the strict sense of the word
domesticable;" that is, capable of breeding under confinement; but this
statement is probably too bold. The capacity to breed sometimes varies in
individuals of the same species; thus Audubon (18/58. 'Ornithological
Biography' volume 3 page 9.) kept for more than eight years some wild geese
(Anser canadensis), but they would not mate; whilst other individuals of the
same species produced young during the second year. I know of but one instance
in the whole family of a species which absolutely refuses to breed in
captivity, namely, the Dendrocygna viduata, although, according to Sir R.
Schomburgk (18/59. 'Geograph. Journal' volume 13 1844 page 32.), it is easily
tamed, and is frequently kept by the Indians of Guiana. Lastly, with respect
to Gulls, though many have been kept in the Zoological Gardens and in the old
Surrey Gardens, no instance was known before the year 1848 of their coupling
or breeding; but since that period the herring gull (Larus argentatus) has
bred many times in the Zoological Gardens and at Knowsley.

There is reason to believe that insects are affected by confinement like the
higher animals. It is well known that the Sphingidae rarely breed when thus
treated. An entomologist (18/60. Loudon's 'Mag. of Nat. Hist.' volume 5 1832
page 153.) in Paris kept twenty-five specimens of Saturnia pyri, but did not
succeed in getting a single fertile egg. A number of females of Orthosia munda
and of Mamestra suasa reared in confinement were unattractive to the males.
(18/61. 'Zoologist' volumes 5-6 1847-48 page 1660.) Mr. Newport kept nearly a
hundred individuals of two species of Vanessa, but not one paired; this,
however, might have been due to their habit of coupling on the wing. (18/62.
'Transact. Entomolog. Soc.' volume 4 1845 page 60.) Mr. Atkinson could never
succeed in India in making the Tarroo silk-moth breed in confinement. (18/63.
'Transact. Linn. Soc.' volume 7 page 40.) It appears that a number of moths,
especially the Sphingidae, when hatched in the autumn out of their proper
season, are completely barren; but this latter case is still involved in some
obscurity. (18/64. See an interesting paper by Mr. Newman in the 'Zoologist'
1857 page 5764; and Dr. Wallace in 'Proc. Entomolog. Soc.' June 4, 1860 page
119.)]

Independently of the fact of many animals under confinement not coupling, or,
if they couple, not producing young, there is evidence of another kind that
their sexual functions are disturbed. For many cases have been recorded of the
loss by male birds when confined of their characteristic plumage. Thus the
common linnet (Linota cannabina) when caged does not acquire the fine crimson
colour on its breast, and one of the buntings (Emberiza passerina) loses the
black on its head. A Pyrrhula and an Oriolus have been observed to assume the
quiet plumage of the hen-bird; and the Falco albidus returned to the dress of
an earlier age. (18/65. Yarrell 'British Birds' volume 1 page 506; Bechstein
'Stubenvogel' s. 185; 'Philosoph. Transact.' 1772 page 271. Bronn 'Geschichte
der Natur' b. 2 s. 96 has collected a number of cases. For the case of the
deer see 'Penny Cyclop.' volume 8 page 350.) Mr. Thompson, the superintendent
of the Knowsley menagerie, informed me that he had often observed analogous
facts. The horns of a male deer (Cervus canadensis) during the voyage from
America were badly developed; but subsequently in Paris perfect horns were
produced.

When conception takes place under confinement, the young are often born dead,
or die soon, or are ill-formed. This frequently occurs in the Zoological
Gardens, and, according to Rengger, with native animals confined in Paraguay.
The mother's milk often fails. We may also attribute to the disturbance of the
sexual functions the frequent occurrence of that monstrous instinct which
leads the mother to devour her own offspring,--a mysterious case of
perversion, as it at first appears.

Sufficient evidence has now been advanced to prove that animals when first
confined are eminently liable to suffer in their reproductive systems. We feel
at first naturally inclined to attribute the result to loss of health, or at
least to loss of vigour; but this view can hardly be admitted when we reflect
how healthy, long-lived, and vigorous many animals are under captivity, such
as parrots, and hawks when used for hawking, cheetahs when used for hunting,
and elephants. The reproductive organs themselves are not diseased; and the
diseases, from which animals in menageries usually perish, are not those which
in any way affect their fertility. No domestic animal is more subject to
disease than the sheep, yet it is remarkably prolific. The failure of animals
to breed under confinement has been sometimes attributed exclusively to a
failure in their sexual instincts: this may occasionally come into play, but
there is no obvious reason why this instinct should be especially liable to be
affected with perfectly tamed animals, except, indeed, indirectly through the
reproductive system itself being disturbed. Moreover, numerous cases have been
given of various animals which couple freely under confinement, but never
conceive; or, if they conceive and produce young, these are fewer in number
than is natural to the species. In the vegetable kingdom instinct of course
can play no part; and we shall presently see that plants when removed from
their natural conditions are affected in nearly the same manner as animals.
Change of climate cannot be the cause of the loss of fertility, for, whilst
many animals imported into Europe from extremely different climates breed
freely, many others when confined in their native land are completely sterile.
Change of food cannot be the chief cause; for ostriches, ducks, and many other
animals, which must have undergone a great change in this respect, breed
freely. Carnivorous birds when confined are extremely sterile, whilst most
carnivorous mammals, except plantigrades, are moderately fertile. Nor can the
amount of food be the cause; for a sufficient supply will certainly be given
to valuable animals; and there is no reason to suppose that much more food
would be given to them than to our choice domestic productions which retain
their full fertility. Lastly, we may infer from the case of the elephant,
cheetah, various hawks, and of many animals which are allowed to lead an
almost free life in their native land, that want of exercise is not the sole
cause.

It would appear that any change in the habits of life, whatever these habits
may be, if great enough, tends to affect in an inexplicable manner the powers
of reproduction. The result depends more on the constitution of the species
than on the nature of the change; for certain whole groups are affected more
than others; but exceptions always occur, for some species in the most fertile
groups refuse to breed, and some in the most sterile groups breed freely.
Those animals which usually breed freely under confinement, rarely breed, as I
was assured, in the Zoological Gardens, within a year or two after their first
importation. When an animal which is generally sterile under confinement
happens to breed, the young apparently do not inherit this power: for had this
been the case, various quadrupeds and birds, which are valuable for
exhibition, would have become common. Dr. Broca even affirms (18/66. 'Journal
de Physiologie' tome 2 page 347.) that many animals in the Jardin des Plantes,
after having produced young for three or four successive generations, become
sterile; but this may be the result of too close interbreeding. It is a
remarkable circumstance that many mammals and birds have produced hybrids
under confinement quite as readily as, or even more readily than, they have
procreated their own kind. Of this fact many instances have been given (18/67.
For additional evidence on this subject see F. Cuvier in 'Annales du Museum'
tome 12 page 119.); and we are thus reminded of those plants which when
cultivated refuse to be fertilised by their own pollen, but can easily be
fertilised by that of a distinct species. Finally, we must conclude, limited
as the conclusion is, that changed conditions of life have an especial power
of acting injuriously on the reproductive system. The whole case is quite
peculiar, for these organs, though not diseased, are thus rendered incapable
of performing their proper functions, or perform them imperfectly.

[STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS.

With respect to domesticated animals, as their domestication mainly depends on
the accident of their breeding freely under captivity, we ought not to expect
that their reproductive system would be affected by any moderate degree of
change. Those orders of quadrupeds and birds, of which the wild species breed
most readily in our menageries, have afforded us the greatest number of
domesticated productions. Savages in most parts of the world are fond of
taming animals (18/68. Numerous instances could be given. Thus Livingstone
('Travels' page 217) states that the King of the Barotse, an inland tribe
which never had any communication with white men, was extremely fond of taming
animals, and every young antelope was brought to him. Mr. Galton informs me
that the Damaras are likewise fond of keeping pets. The Indians of South
America follow the same habit. Capt. Wilkes states that the Polynesians of the
Samoan Islands tamed pigeons; and the New Zealanders, as Mr. Mantell informs
me, kept various kinds of birds.); and if any of these regularly produced
young, and were at the same time useful, they would be at once domesticated.
If, when their masters migrated into other countries, they were in addition
found capable of withstanding various climates, they would be still more
valuable; and it appears that the animals which breed readily in captivity can
generally withstand different climates. Some few domesticated animals, such as
the reindeer and camel, offer an exception to this rule. Many of our
domesticated animals can bear with undiminished fertility the most unnatural
conditions; for instance, rabbits, guinea-pigs, and ferrets breed in miserably
confined hutches. Few European dogs of any kind withstand the climate of India
without degenerating, but as long as they survive, they retain, as I hear from
Dr. Falconer, their fertility; so it is, according to Dr. Daniell, with
English dogs taken to Sierra Leone. The fowl, a native of the hot jungles of
India, becomes more fertile than its parent-stock in every quarter of the
world, until we advance as far north as Greenland and Northern Siberia, where
this bird will not breed. Both fowls and pigeons, which I received during the
autumn direct from Sierra Leone, were at once ready to couple. (18/69. For
analogous cases with the fowl see Reaumur 'L'Art de faire Eclore' etc. 1749
page 243; and Col. Sykes in 'Proc. Zoolog. Soc.' 1832 etc. With respect to the
fowl not breeding in northern regions see Latham 'Hist. of Birds' volume 8
1823 page 169.) I have, also, seen pigeons breeding as freely as the common
kinds within a year after their importation from the upper Nile. The guinea-
fowl, an aboriginal of the hot and dry deserts of Africa, whilst living under
our damp and cool climate, produces a large supply of eggs.

Nevertheless, our domesticated animals under new conditions occasionally show
signs of lessened fertility. Roulin asserts that in the hot valleys of the
equatorial Cordillera sheep are not fully fecund (18/70. "Mem. par divers
Savans" 'Acad. des Sciences' tome 6 1835 page 347.); and according to Lord
Somerville (18/71. 'Youatt on Sheep' page 181.) the merino-sheep which he
imported from Spain were not at first perfectly fertile, it is said (18/72. J.
Mills 'Treatise on Cattle' 1776 page 72.) that mares brought up on dry food in
the stable, and turned out to grass, do not at first breed. The peahen, as we
have seen, is said not to lay so many eggs in England as in India. It was long
before the canary-bird was fully fertile, and even now first-rate breeding
birds are not common. (18/73. Bechstein 'Stubenvogel' s. 242.) In the hot and
dry province of Delhi, as I hear from Dr. Falconer, the eggs of the turkey,
though placed under a hen, are extremely liable to fail. According to Roulin,
geese taken to the lofty plateau of Bogota, at first laid seldom, and then
only a few eggs; of these scarcely a fourth were hatched, and half the young
birds died; in the second generation they were more fertile; and when Roulin
wrote they were becoming as fertile as our geese in Europe. With respect to
the valley of Quito, Mr. Orton says (18/74. 'The Andes and the Amazon' 1870
page 107.) "the only geese in the valley are a few imported from Europe, and
these refuse to propagate." In the Philippine Archipelago the goose, it is
asserted, will not breed or even lay eggs. (18/75. Crawford 'Descriptive Dict.
of the Indian Islands' 1856 page 145.) A more curious case is that of the
fowl, which, according to Roulin, when first introduced would not breed at
Cusco in Bolivia, but subsequently became quite fertile; and the English Game
fowl, lately introduced, had not as yet arrived at its full fertility, for to
raise two or three chickens from a nest of eggs was thought fortunate. In
Europe close confinement has a marked effect on the fertility of the fowl: it
has been found in France that with fowls allowed considerable freedom only
twenty per cent of the eggs failed; when allowed less freedom forty per cent
failed; and in close confinement sixty out of the hundred were not hatched.
(18/76. 'Bull. de la Soc. d'Acclimat.' tome 9 1862 pages 380, 384.) So we see
that unnatural and changed conditions of life produce some effect on the
fertility of our most thoroughly domesticated animals, in the same manner,
though in a far less degree, as with captive wild animals.

It is by no means rare to find certain males and females which will not breed
together, though both are known to be perfectly fertile with other males and
females. We have no reason to suppose that this is caused by these animals
having been subjected to any change in their habits of life; therefore such
cases are hardly related to our present subject. The cause apparently lies in
an innate sexual incompatibility of the pair which are matched. Several
instances have been communicated to me by Mr. W.C. Spooner (well known for his
essay on Cross-breeding), by Mr. Eyton of Eyton, by Mr. Wicksted and other
breeders, and especially by Mr. Waring of Chelsfield, in relation to horses,
cattle, pigs, foxhounds, other dogs, and pigeons. (18/77. For pigeons see Dr.
Chapuis 'Le Pigeon Voyageur Belge' 1865 page 66.) In these cases, females,
which either previously or subsequently were proved to be fertile, failed to
breed with certain males, with whom it was particularly desired to match them.
A change in the constitution of the female may sometimes have occurred before
she was put to the second male; but in other cases this explanation is hardly
tenable, for a female, known not to be barren, has been unsuccessfully paired
seven or eight times with the same male likewise known to be perfectly
fertile. With cart-mares, which sometimes will not breed with stallions of
pure blood, but subsequently have bred with cart-stallions, Mr. Spooner is
inclined to attribute the failure to the lesser sexual power of the racehorse.
But I have heard from the greatest breeder of racehorses at the present day,
through Mr. Waring, that "it frequently occurs with a mare to be put several
times during one or two seasons to a particular stallion of acknowledged
power, and yet prove barren; the mare afterwards breeding at once with some
other horse." These facts are worth recording, as they show, like so many
previous facts, on what slight constitutional differences the fertility of an
animal often depends.]

STERILITY OF PLANTS FROM CHANGED CONDITIONS OF LIFE, AND FROM OTHER CAUSES.

In the vegetable kingdom cases of sterility frequently occur, analogous with
those previously given in the animal kingdom. But the subject is obscured by
several circumstances, presently to be discussed, namely, the contabescence of
the anthers, as Gartner has named a certain affection--monstrosities--
doubleness of the flower--much-enlarged fruit--and long-continued or excessive
propagation by buds.

[It is notorious that many plants in our gardens and hot-houses, though
preserved in the most perfect health, rarely or never produce seed. I do not
allude to plants which run to leaves, from being kept too damp, or too warm,
or too much manured; for these do not flower, and the case may be wholly
different. Nor do I allude to fruit not ripening from want of heat or rotting
from too much moisture. But many exotic plants, with their ovules and pollen
appearing perfectly sound, will not set any seed. The sterility in many cases,
as I know from my own observation, is simply due to the absence of the proper
insects for carrying the pollen to the stigma. But after excluding the several
cases just specified, there are many plants in which the reproductive system
has been seriously affected by the altered conditions of life to which they
have been subjected.

It would be tedious to enter on many details. Linnaeus long ago observed
(18/78. 'Swedish Acts' volume 1 1739 page 3. Pallas makes the same remark in
his 'Travels' English translation volume 1 page 292.) that Alpine plants,
although naturally loaded with seed, produce either few or none when
cultivated in gardens. But exceptions often occur: the Draba sylvestris, one
of our most thoroughly Alpine plants, multiplies itself by seed in Mr. H.C.
Watson's garden, near London; and Kerner, who has particularly attended to the
cultivation of Alpine plants, found that various kinds, when cultivated,
spontaneously sowed themselves. (18/79. A. Kerner 'Die Cultur der
Alpenpflanzen' 1864 s. 139; Watson 'Cybele Britannica' volume 1 page 131; Mr.
D. Cameron also has written on the culture of Alpine plants in 'Gard.
Chronicle' 1848 pages 253, 268, and mentions a few which seed.) Many plants
which naturally grow in peat-earth are entirely sterile in our gardens. I have
noticed the same fact with several liliaceous plants, which nevertheless grew
vigorously.

Too much manure renders some kinds utterly sterile, as I have myself observed.
The tendency to sterility from this cause runs in families; thus, according to
Gartner (18/80. 'Beitrage zur Kenntniss der Befruchtung' 1844 s. 333.), it is
hardly possible to give too much manure to most Gramineae, Cruciferae, and
Leguminosae, whilst succulent and bulbous-rooted plants are easily affected.
Extreme poverty of soil is less apt to induce sterility; but dwarfed plants of
Trifolium minus and repens, growing on a lawn often mown and never manured,
were found by me not to produce any seed. The temperature of the soil, and the
season at which plants are watered, often have a marked effect on their
fertility, as was observed by Kolreuter in the case of Mirabilis. (18/81.
'Nova Acta Petrop.' 1793 page 391.) Mr. Scott, in the Botanic Gardens of
Edinburgh, observed that Oncidium divaricatum would not set seed when grown in
a basket in which it throve, but was capable of fertilisation in a pot where
it was a little damper. Pelargonium fulgidum, for many years after its
introduction, seeded freely; it then became sterile; now it is fertile (18/82.
'Cottage Gardener' 1856 pages 44, 109.) if kept in a dry stove during the
winter. Other varieties of pelargonium are sterile and others fertile without
our being able to assign any cause. Very slight changes in the position of a
plant, whether planted on a bank or at its base, sometimes make all the
difference in its producing seed. Temperature apparently has a much more
powerful influence on the fertility of plants than on that of animals.
Nevertheless it is wonderful what changes some few plants will withstand with
undiminished fertility: thus the Zephyranthes candida, a native of the
moderately warm banks of the Plata, sows itself in the hot dry country near
Lima, and in Yorkshire resists the severest frosts, and I have seen seeds
gathered from pods which had been covered with snow during three weeks.
(18/83. Dr. Herbert 'Amaryllidaceae' page 176.) Berberis wallichii, from the
hot Khasia range in India, is uninjured by our sharpest frosts, and ripens its
fruit under our cool summers. Nevertheless, I presume we must attribute to
change of climate the sterility of many foreign plants; thus, the Persian and
Chinese lilacs (Syringa persica and chinensis), though perfectly hardy here,
never produce a seed; the common lilac (S. vulgaris) seeds with us moderately
well, but in parts of Germany the capsules never contain seed. (18/84. Gartner
'Beitrage zur Kenntniss' etc. s. 560, 564.) Some few of the cases, given in
the last chapter, of self-impotent plants, might have been here introduced, as
their state seems due to the conditions to which they have been subjected.

The liability of plants to be affected in their fertility by slightly changed
conditions is the more remarkable, as the pollen when once in process of
formation is not easily injured; a plant may be transplanted, or a branch with
flower-buds be cut off and placed in water, and the pollen will be matured.
Pollen, also, when once mature, may be kept for weeks or even months. (18/85.
'Gardener's Chronicle' 1844 page 215; 1850 page 470. Faivre gives a good
resume on this subject in his 'La Variabilite des Especes' 1868 page 155.) The
female organs are more sensitive, for Gartner (18/86. 'Beitrage zur Kenntniss'
etc. s. 252, 338.) found that dicotyledonous plants, when carefully removed so
that they did not in the least flag, could seldom be fertilised; this occurred
even with potted plants if the roots had grown out of the hole at the bottom.
In some few cases, however, as with Digitalis, transplantation did not prevent
fertilisation; and according to the testimony of Mawz, Brassica rapa, when
pulled up by its roots and placed in water, ripened its seed. Flower-stems of
several monocotyledonous plants when cut off and placed in water likewise
produce seed. But in these cases I presume that the flowers had been already
fertilised, for Herbert (18/87. 'Journal of Hort. Soc.' volume 2 1847 page
83.) found with the Crocus that the plants might be removed or mutilated after
the act of fertilisation, and would still perfect their seeds; but that, if
transplanted before being fertilised, the application of pollen was powerless.

Plants which have been long cultivated can generally endure with undiminished
fertility various and great changes; but not in most cases so great a change
of climate as domesticated animals. It is remarkable that many plants under
these circumstances are so much affected that the proportion and the nature of
their chemical ingredients are modified, yet their fertility is unimpaired.
Thus, as Dr. Falconer informs me, there is a great difference in the character
of the fibre in hemp, in the quantity of oil in the seed of the Linum, in the
proportion of narcotin to morphine in the poppy, in gluten to starch in wheat,
when these plants are cultivated on the plains and on the mountains of India;
nevertheless, they all remain fully fertile.

CONTABESCENCE.

Gartner has designated by this term a peculiar condition of the anthers in
certain plants, in which they are shrivelled, or become brown and tough, and
contain no good pollen. When in this state they exactly resemble the anthers
of the most sterile hybrids. Gartner (18/88. 'Beitrage zur Kenntniss' etc. s.
117 et seq.; Kolreuter 'Zweite Fortsetzung' s. 10, 121; 'Dritte Fortsetzung'
s. 57. Herbert 'Amaryllidaceae' page 355. Wiegmann 'Ueber die
Bastarderzeugung' s. 27.), in his discussion on this subject, has shown that
plants of many orders are occasionally thus affected; but the Caryophyllaceae
and Liliaceae suffer most, and to these orders, I think, the Ericaceae may be
added. Contabescence varies in degree, but on the same plant all the flowers
are generally affected to nearly the same extent. The anthers are affected at
a very early period in the flower-bud, and remain in the same state (with one
recorded exception) during the life of the plant. The affection cannot be
cured by any change of treatment, and is propagated by layers, cuttings, etc.,
and perhaps even by seed. In contabescent plants the female organs are seldom
affected, or merely become precocious in their development. The cause of this
affection is doubtful, and is different in different cases. Until I read
Gartner's discussion I attributed it, as apparently did Herbert, to the
unnatural treatment of the plants; but its permanence under changed
conditions, and the female organs not being affected, seem incompatible with
this view. The fact of several endemic plants becoming contabescent in our
gardens seems, at first sight, equally incompatible with this view; but
Kolreuter believes that this is the result of their transplantation. The
contabescent plants of Dianthus and Verbascum, found wild by Wiegmann, grew on
a dry and sterile bank. The fact that exotic plants are eminently liable to
this affection also seems to show that it is in some manner caused by their
unnatural treatment. In some instances, as with Silene, Gartner's view seems
the most probable, namely, that it is caused by an inherent tendency in the
species to become dioecious. I can add another cause, namely, the illegitimate
unions of heterostyled plants, for I have observed seedlings of three species
of Primula and of Lythrum salicaria, which had been raised from plants
illegitimately fertilised by their own-form pollen, with some or all their
anthers in a contabescent state. There is perhaps an additional cause, namely,
self-fertilisation; for many plants of Dianthus and Lobelia, which had been
raised from self-fertilised seeds, had their anthers in this state; but these
instances are not conclusive, as both genera are liable from other causes to
this affection.

Cases of an opposite nature likewise occur, namely, plants with the female
organs struck with sterility, whilst the male organs remain perfect. Dianthus
japonicus, a Passiflora, and Nicotiana, have been described by Gartner (18/89.
'Bastarderzengung' s. 356.) as being in this unusual condition.

MONSTROSITIES AS A CAUSE OF STERILITY.

Great deviations of structure, even when the reproductive organs themselves
are not seriously affected, sometimes cause plants to become sterile. But in
other cases plants may become monstrous to an extreme degree and yet retain
their full fertility. Gallesio, who certainly had great experience (18/90.
'Teoria della Riproduzione' 1816 page 84; 'Traite du Citrus' 1811 page 67.),
often attributes sterility to this cause; but it may be suspected that in some
of his cases sterility was the cause, and not the result, of the monstrous
growths. The curious St. Valery apple, although it bears fruit, rarely
produces seed. The wonderfully anomalous flowers of Begonia frigida, formerly
described, though they appear fit for fructification, are sterile. (18/91. Mr.
C.W. Crocker in 'Gardener's Chronicle' 1861 page 1092.) Species of Primula in
which the calyx is brightly coloured are said (18/92. Verlot 'Des Varietes'
1865 page 80.) to be often sterile, though I have known them to be fertile. On
the other hand, Verlot gives several cases of proliferous flowers which can be
propagated by seed. This was the case with a poppy, which had become
monopetalous by the union of its petals. (18/93. Verlot ibid page 88.) Another
extraordinary poppy, with the stamens replaced by numerous small supplementary
capsules, likewise reproduces itself by seed. This has also occurred with a
plant of Saxifraga geum, in which a series of adventitious carpels, bearing
ovules on their margins, had been developed between the stamens and the normal
carpels (18/94. Prof. Allman, Brit. Assoc., quoted in the 'Phytologist' volume
2 page 483. Prof. Harvey, on the authority of Mr. Andrews, who discovered the
plant, informed me that this monstrosity could be propagated by seed. With
respect to the poppy see Prof. Goeppert as quoted in 'Journal of Horticulture'
July 1, 1863 page 171.) Lastly, with respect to peloric flowers, which depart
wonderfully from the natural structure,--those of Linaria vulgaris seem
generally to be more or less sterile, whilst those before described of
Antirrhinum majus, when artificially fertilised with their own pollen, are
perfectly fertile, though sterile when left to themselves, for bees are unable
to crawl into the narrow tubular flower. The peloric flowers of Corydalis
solida, according to Godron (18/95. 'Comptes Rendus' December 19, 1864 page
1039.), are sometimes barren and sometimes fertile; whilst those of Gloxinia
are well known to yield plenty of seed. In our greenhouse Pelargoniums, the
central flower of the truss is often peloric, and Mr. Masters informs me that
he tried in vain during several years to get seed from these flowers. I
likewise made many vain attempts, but sometimes succeeded in fertilising them
with pollen from a normal flower of another variety; and conversely I several
times fertilised ordinary flowers with peloric pollen. Only once I succeeded
in raising a plant from a peloric flower fertilised by pollen from a peloric
flower borne by another variety; but the plant, it may be added, presented
nothing particular in its structure. Hence we may conclude that no general
rule can be laid down; but any great deviation from the normal structure, even
when the reproductive organs themselves are not seriously affected, certainly
often leads to sexual impotence.

DOUBLE FLOWERS.

When the stamens are converted into petals, the plant becomes on the male side
sterile; when both stamens and pistils are thus changed, the plant becomes
completely barren. Symmetrical flowers having numerous stamens and petals are
the most liable to become double, as perhaps follows from all multiple organs
being the most subject to variability. But flowers furnished with only a few
stamens, and others which are asymmetrical in structure, sometimes become
double, as we see with the double gorse or Ulex, and Antirrhinum. The
Compositae bear what are called double flowers by the abnormal development of
the corolla of their central florets. Doubleness is sometimes connected with
prolification (18/96. 'Gardener's Chronicle' 1866 page 681.), or the continued
growth of the axis of the flower. Doubleness is strongly inherited. No one has
produced, as Lindley remarks (18/97. 'Theory of Horticulture' page 333.),
double flowers by promoting the perfect health of the plant. On the contrary,
unnatural conditions of life favour their production. There is some reason to
believe that seeds kept during many years, and seeds believed to be
imperfectly fertilised, yield double flowers more freely than fresh and
perfectly fertilised seed. (18/98. Mr. Fairweather 'Transact. Hort. Soc.'
volume 3 page 406: Bosse quoted by Bronn 'Geschichte der Natur' b. 2 s. 77. On
the effects of the removal of the anthers see Mr. Leitner in Silliman's 'North
American Journ. of Science' volume 23 page 47; and Verlot 'Des Varietes' 1865
page 84.) Long-continued cultivation in rich soil seems to be the commonest
exciting cause. A double narcissus and a double Anthemis nobilis, transplanted
into very poor soil, has been observed to become single (18/99. Lindley's
'Theory of Horticulture' page 3?3.); and I have seen a completely double white
primrose rendered permanently single by being divided and transplanted whilst
in full flower. It has been observed by Professor E. Morren that doubleness of
the flowers and variegation of the leaves are antagonistic states; but so many
exceptions to the rule have lately been recorded (18/100. 'Gardener's
Chronicle' 1865 page 626; 1866 pages 290, 730; and Verlot 'Des Varietes' page
75.), that, though general, it cannot be looked at as invariable. Variegation
seems generally to result from a feeble or atrophied condition of the plant,
and a large proportion of the seedlings raised from parents, if both are
variegated, usually perish at an early age; hence we may perhaps infer that
doubleness, which is the antagonistic state, commonly arises from a plethoric
condition. On the other hand, extremely poor soil sometimes, though rarely,
appears to cause doubleness: I formerly described (18/101. 'Gardener's
Chronicle' 1843 page 628. In this article I suggested the theory above given
on the doubleness of flowers. This view is adopted by Carriere 'Production et
Fix. des Varietes' 1865 page 67.) some completely double, bud-like, flowers
produced in large numbers by stunted wild plants of Gentiana amarella growing
on a poor chalky bank. I have also noticed a distinct tendency to doubleness
in the flowers of a Ranunculus, Horse-chestnut, and Bladder-nut (Ranunculus
repens, Aesculus pavia, and Staphylea), growing under very unfavourable
conditions. Professor Lehmann (18/102. Quoted by Gartner 'Bastarderzeugung' s.
567.) found several wild plants growing near a hot spring with double flowers.
With respect to the cause of doubleness, which arises, as we see, under widely
different circumstances, I shall presently attempt to show that the most
probable view is that unnatural conditions first give a tendency to sterility,
and that then, on the principle of compensation, as the reproductive organs do
not perform their proper functions, they either become developed into petals,
or additional petals are formed. This view has lately been supported by Mr.
Laxton (18/103. 'Gardener's Chronicle' 1866 page 901.) who advances the case
of some common peas, which, after long-continued heavy rain, flowered a second
time, and produced double flowers.

SEEDLESS FRUIT.

Many of our most valuable fruits, although consisting in a homological sense
of widely different organs, are either quite sterile, or produce extremely few
seeds. This is notoriously the case with our best pears, grapes, and figs,
with the pine-apple, banana, bread-fruit, pomegranate, azarole, date-palms,
and some members of the orange-tribe. Poorer varieties of these same fruits
either habitually or occasionally yield seed. (18/104. Lindley 'Theory of
Horticulture' pages 175-179; Godron 'De l'Espece' tome 2 page 106; Pickering
'Races of Man;' Gallesio 'Teoria della Riproduzione' l816 pages 101-110. Meyen
'Reise um Erde' Th. 2 s. 214 states that at Manilla one variety of the banana
is full of seeds: and Chamisso (Hooker's 'Bot. Misc.' volume 1 page 310)
describes a variety of the bread-fruit in the Mariana Islands with small
fruit, containing seeds which are frequently perfect. Burnes in his 'Travels
in Bokhara' remarks on the pomegranate seeding in Mazenderan, as a remarkable
peculiarity.) Most horticulturists look at the great size and anomalous
development of the fruit as the cause, and sterility as the result; but the
opposite view, as we shall presently see, is more probable.

STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF GROWTH OR
VEGETATION.

Plants which from any cause grow too luxuriantly, and produce leaves, stems,
runners, suckers, tubers, bulbs, etc., in excess, sometimes do not flower, or
if they flower do not yield seed. To make European vegetables under the hot
climate of India yield seed, it is necessary to check their growth; and, when
one-third grown, they are taken up, and their stems and tap-roots are cut or
mutilated. (18/105. Ingledew in 'Transact. of Agricult. and Hort. Soc. of
India' volume 2.) So it is with hybrids; for instance, Prof. Lecoq (18/106.
'De la Fecondation' 1862 page 308.) had three plants of Mirabilis, which,
though they grew luxuriantly and flowered, were quite sterile; but after
beating one with a stick until a few branches alone were left, these at once
yielded good seed. The sugar-cane, which grows vigorously and produces a large
supply of succulent stems, never, according to various observers, bears seed
in the West Indies, Malaga, India, Cochin China, Mauritius, or the Malay
Archipelago. (18/107. Hooker 'Bot. Misc.' volume 1 page 99; Gallesio 'Teoria
della Riproduzione' page 110. Dr. J. de Cordemoy in 'Transact. of the R. Soc.
of Mauritius' new series volume 6 1873 pages 60-67, gives a large number of
cases of plants which never seed, including several species indigenous in
Mauritius.) Plants which produce a large number of tubers are apt to be
sterile, as occurs, to a certain extent, with the common potato; and Mr.
Fortune informs me that the sweet potato (Convolvulus batatas) in China never,
as far as he has seen, yields seed. Dr. Royle remarks (18/108. 'Transact.
Linn. Soc.' volume 17 page 563.) that in India the Agave vivipara, when grown
in rich soil, invariably produces bulbs, but no seeds; whilst a poor soil and
dry climate lead to an opposite result. In China, according to Mr. Fortune, an
extraordinary number of little bulbs are developed in the axils of the leaves
of the yam, and this plant does not bear seed. Whether in these cases, as in
those of double flowers and seedless fruit, sexual sterility from changed
conditions of life is the primary cause which leads to the excessive
development of the organs of vegetation, is doubtful; though some evidence
might be advanced in favour of this view. It is perhaps a more probable view
that plants which propagate themselves largely by one method, namely by buds,
have not sufficient vital power or organised matter for the other method of
sexual generation.

Several distinguished botanists and good practical judges believe that long-
continued propagation by cuttings, runners, tubers, bulbs, etc., independently
of any excessive development of these parts, is the cause of many plants
failing to produce flowers, or producing only barren flowers,--it is as if
they had lost the habit of sexual generation. (18/109. Godron 'De l'Espece'
tome 2 page 106; Herbert on Crocus in 'Journal of Hort. Soc.' volume 1 1846
page 254: Dr. Wight, from what he has seen in India, believes in this view;
'Madras Journal of Lit. and Science' volume 4 1836 page 61.) That many plants
when thus propagated are sterile there can be no doubt, but as to whether the
long continuance of this form of propagation is the actual cause of their
sterility, I will not venture, from the want of sufficient evidence, to
express an opinion.

That plants may be propagated for long periods by buds, without the aid of
sexual generation, we may safely infer from this being the case with many
plants which must have long survived in a state of nature. As I have had
occasion before to allude to this subject, I will here give such cases as I
have collected. Many alpine plants ascend mountains beyond the height at which
they can produce seed. (18/110. Wahlenberg specifies eight species in this
state on the Lapland Alps: see Appendix to Linnaeus 'Tour in Lapland'
translated by Sir J.E. Smith volume 2 pages 274-280.) Certain species of Poa
and Festuca, when growing on mountain-pastures, propagate themselves, as I
hear from Mr. Bentham, almost exclusively by bulblets. Kalm gives a more
curious instance (18/111. 'Travels in North America' English translation
volume 3 page 175.) of several American trees, which grow so plentifully in
marshes or in thick woods, that they are certainly well adapted for these
stations, yet scarcely ever produce seeds; but when accidentally growing on
the outside of the marsh or wood, are loaded with seed. The common ivy is
found in Northern Sweden and Russia, but flowers and fruits only in the
southern provinces. The Acorus calamus extends over a large portion of the
globe, but so rarely perfects fruit that this has been seen only by a few
botanists; according to Caspary, all its pollen-grains are in a worthless
condition. (18/112. With respect to the ivy and Acorus see Dr. Broomfield in
the 'Phytologist' volume 3 page 376. Also Lindley and Vaucher on the Acorus
and see Caspary as below.) The Hypericum calycinum, which propagates itself so
freely in our shrubberies by rhizomes, and is naturalised in Ireland, blossoms
profusely, but rarely sets any seed, and this only during certain years; nor
did it set any when fertilised in my garden by pollen from plants growing at a
distance. The Lysimachia nummularia, which is furnished with long runners, so
seldom produces seed-capsules, that Prof. Decaisne (18/113. 'Annal. des Sc.
Nat.' 3rd series Zool. tome 4 page 280. Prof. Decaisne refers also to
analogous cases with mosses and lichens near Paris.), who has especially
attended to this plant, has never seen it in fruit. The Carex rigida often
fails to perfect its seed in Scotland, Lapland, Greenland, Germany, and New
Hampshire in the United States. (18/114. Mr. Tuckermann in Silliman's
'American Journal of Science' volume 65 page 1.) The periwinkle (Vinca minor),
which spreads largely by runners, is said scarcely ever to produce fruit in
England (18/115. Sir J.E. Smith 'English Flora' volume 1 page 339.); but this
plant requires insect-aid for its fertilisation, and the proper insects may be
absent or rare. The Jussiaea grandiflora has become naturalised in Southern
France, and has spread by its rhizomes so extensively as to impede the
navigation of the waters, but never produces fertile seed. (18/116. G.
Planchon 'Flora de Montpellier' 1864 page 20.) The horse-radish (Cochleria
armoracia) spreads pertinaciously and is naturalised in various parts of
Europe; though it bears flowers, these rarely produce capsules: Professor
Caspary informs me that he has watched this plant since 1851, but has never
seen its fruit; 65 per cent of its pollen-grains are bad. The common
Ranunculus ficaria rarely bears seed in England, France, or Switzerland; but
in 1863 I observed seeds on several plants growing near my house. (18/117. On
the non-production of seeds in England see Mr. Crocker in 'Gardener's Weekly
Magazine' 1852 page 70; Vaucher 'Hist. Phys. Plantes d'Europe' tome 1 page 33;
Lecoq 'Geograph. Bot. d'Europe' tome 4 page 466; Dr. D. Clos in 'Annal. des
Sc. Nat.' 3rd series Bot. tome 17 1852 page 129: this latter author refers to
other analogous cases. See more especially on this plant and on other allied
cases Prof. Caspary "Die Nuphar" 'Abhand. Naturw. Gesellsch. zu Halle' b. 11
1870 page 40, 78.) Other cases analogous with the foregoing could be given;
for instance, some kinds of mosses and lichens have never been seen to
fructify in France.

Some of these endemic and naturalised plants are probably rendered sterile
from excessive multiplication by buds, and their consequent incapacity to
produce and nourish seed. But the sterility of others more probably depends on
the peculiar conditions under which they live, as in the case of the ivy in
the northern part of Europe, and of the trees in the swamps of the United
States; yet these plants must be in some respects eminently well adapted for
the stations which they occupy, for they hold their places against a host of
competitors.]

Finally, the high degree of sterility which often accompanies the doubling of
flowers, or an excessive development of fruit, seldom supervenes at once. An
incipient tendency is observed, and continued selection completes the result.
The view which seems the most probable, and which connects together all the
foregoing facts and brings them within our present subject, is, that changed
and unnatural conditions of life first give a tendency to sterility; and in
consequence of this, the organs of reproduction being no longer able fully to
perform their proper functions, a supply of organised matter, not required for
the development of the seed, flows either into these organs and renders them
foliaceous, or into the fruit, stems, tubers, etc., increasing their size and
succulency. But it is probable that there exists, independently of any
incipient sterility, an antagonism between the two forms of reproduction,
namely, by seed and buds, when either is carried to an extreme degree. That
incipient sterility plays an important part in the doubling of flowers, and in
the other cases just specified, I infer chiefly from the following facts. When
fertility is lost from a wholly different cause, namely, from hybridism, there
is a strong tendency, as Gartner (18/118. 'Bastarderzeugung' s. 565. Kolreuter
'Dritte Fortsetzung' s. 73, 87, 119) also shows that when two species, one
single and the other double, are crossed, the hybrids are apt to be extremely
double.) affirms, for flowers to become double, and this tendency is
inherited. Moreover, it is notorious that with hybrids the male organs become
sterile before the female organs, and with double flowers the stamens first
become foliaceous. This latter fact is well shown by the male flowers of
dioecious plants, which, according to Gallesio (18/119. 'Teoria della
Riproduzione Veg.' 1816 page 73.) first become double. Again, Gartner (18/120.
'Bastarderzeugung' s. 573.) often insists that the flowers of even utterly
sterile hybrids, which do not produce any seed, generally yield perfect
capsules or fruit,--a fact which has likewise been repeatedly observed by
Naudin with the Cucurbitaceae; so that the production of fruit by plants
rendered sterile through any cause is intelligible. Kolreuter has also
expressed his unbounded astonishment at the size and development of the tubers
in certain hybrids; and all experimentalists (18/121. Ibid s. 527.) have
remarked on the strong tendency in hybrids to increase by roots, runners, and
suckers. Seeing that hybrid plants, which from their nature are more or less
sterile, thus tend to produce double flowers; that they have the parts
including the seed, that is the fruit, perfectly developed, even when
containing no seed; that they sometimes yield gigantic roots; that they almost
invariably tend to increase largely by suckers and other such means;--seeing
this, and knowing, from the many facts given in the earlier parts of this
chapter, that almost all organic beings when exposed to unnatural conditions
tend to become more or less sterile, it seems much the most probable view that
with cultivated plants sterility is the exciting cause, and double flowers,
rich seedless fruit, and in some cases largely-developed organs of vegetation,
etc., are the indirect results--these results having been in most cases
largely increased through continued selection by man.


CHAPTER 2.XIX.

SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.

ON THE EFFECTS OF CROSSING.
THE INFLUENCE OF DOMESTICATION ON FERTILITY.
CLOSE INTERBREEDING.
GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS OF LIFE.
VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE.
ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES.
CONCLUSIONS WITH RESPECT TO HYBRIDISM.
LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF HETEROSTYLED PLANTS.
STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE
SYSTEM.
NOT ACCUMULATED THROUGH NATURAL SELECTION.
REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE.
TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED
SPECIES AND CROSSED VARIETIES.
CONCLUSION.

It was shown in the fifteenth chapter that when individuals of the same
variety, or even of a distinct variety, are allowed freely to intercross,
uniformity of character is ultimately acquired. Some few characters, however,
are incapable of fusion, but these are unimportant, as they are often of a
semi-monstrous nature, and have suddenly appeared. Hence, to preserve our
domesticated breeds true, or to improve them by methodical selection, it is
obviously necessary that they should be kept separate. Nevertheless, a whole
body of individuals may be slowly modified, through unconscious selection, as
we shall see in a future chapter, without separating them into distinct lots.
Domestic races have often been intentionally modified by one or two crosses,
made with some allied race, and occasionally even by repeated crosses with
very distinct races; but in almost all such cases, long-continued and careful
selection has been absolutely necessary, owing to the excessive variability of
the crossed offspring, due to the principle of reversion. In a few instances,
however, mongrels have retained a uniform character from their first
production.

When two varieties are allowed to cross freely, and one is much more numerous
than the other, the former will ultimately absorb the latter. Should both
varieties exist in nearly equal numbers, it is probable that a considerable
period would elapse before the acquirement of a uniform character; and the
character ultimately acquired would largely depend on prepotency of
transmission and on the conditions of life; for the nature of these conditions
would generally favour one variety more than another, so that a kind of
natural selection would come into play. Unless the crossed offspring were
slaughtered by man without the least discrimination, some degree of
unmethodical selection would likewise come into action. From these several
considerations we may infer, that when two or more closely allied species
first came into the possession of the same tribe, their crossing will not have
influenced, in so great a degree as has often been supposed, the character of
the offspring in future times; although in some cases it probably has had a
considerable effect.

Domestication, as a general rule, increases the prolificness of animals and
plants. It eliminates the tendency to sterility which is common to species
when first taken from a state of nature and crossed. On this latter head we
have no direct evidence; but as our races of dogs, cattle, pigs etc., are
almost certainly descended from aboriginally distinct stocks, and as these
races are now fully fertile together, or at least incomparably more fertile
than most species when crossed, we may with entire confidence accept this
conclusion.

Abundant evidence has been given that crossing adds to the size, vigour, and
fertility of the offspring. This holds good when there has been no previous
close interbreeding. It applies to the individuals of the same variety but
belonging to different families, to distinct varieties, sub-species, and even
to species. In the latter case, though size is gained, fertility is lost; but
the increased size, vigour, and hardiness of many hybrids cannot be accounted
for solely on the principle of compensation from the inaction of the
reproductive system. Certain plants whilst growing under their natural
conditions, others when cultivated, and others of hybrid origin, are
completely self-impotent, though perfectly healthy; and such plants can be
stimulated to fertility only by being crossed with other individuals of the
same or of a distinct species.

On the other hand, long-continued close interbreeding between the nearest
relations diminishes the constitutional vigour, size, and fertility of the
offspring; and occasionally leads to malformations, but not necessarily to
general deterioration of form or structure. This failure of fertility shows
that the evil results of interbreeding are independent of the augmentation of
morbid tendencies common to both parents, though this augmentation no doubt is
often highly injurious. Our belief that evil follows from close interbreeding
rests to a certain extent on the experience of practical breeders, especially
of those who have reared many animals of quickly propagating kinds; but it
likewise rests on several carefully recorded experiments. With some animals
close interbreeding may be carried on for a long period with impunity by the
selection of the most vigorous and healthy individuals; but sooner or later
evil follows. The evil, however, comes on so slowly and gradually that it
easily escapes observation, but can be recognised by the almost instantaneous
manner in which size, constitutional vigour, and fertility are regained when
animals that have long been interbred are crossed with a distinct family.

These two great classes of facts, namely, the good derived from crossing, and
the evil from close interbreeding, with the consideration of the innumerable
adaptations throughout nature for compelling, or favouring, or at least
permitting, the occasional union of distinct individuals, taken together, lead
to the conclusion that it is a law of nature that organic beings shall not
fertilise themselves for perpetuity. This law was first plainly hinted at in
1799, with respect to plants, by Andrew Knight (19/1. 'Transactions Phil.
Soc.' 1799 page 202. For Kolreuter see 'Mem. de l'Acad. de St.-Petersbourg'
tome 3 1809 published 1811 page 197. In reading C.K. Sprengel's remarkable
work, 'Das entdeckte Geheimniss' etc. 1793, it is curious to observe how often
this wonderfully acute observer failed to understand the full meaning of the
structure of the flowers which he has so well described, from not always
having before his mind the key to the problem, namely, the good derived from
the crossing of distinct individual plants.) and, not long afterwards, that
sagacious observer Kolreuter, after showing how well the Malvaceae are adapted
for crossing, asks, "an id aliquid in recessu habeat, quod hujuscemodi flores
nunquam proprio suo pulvere, sed semper eo aliarum su speciei impregnentur,
merito quaritur? Certe natura nil facit frustra." Although we may demur to
Kolreuter's saying that nature does nothing in vain, seeing how many
rudimentary and useless organs there are, yet undoubtedly the argument from
the innumerable contrivances, which favour crossing, is of the greatest
weight. The most important result of this law is that it leads to uniformity
of character in the individuals of the same species. In the case of certain
hermaphrodites, which probably intercross only at long intervals of time, and
with unisexual animals inhabiting somewhat separated localities, which can
only occasionally come into contact and pair, the greater vigour and fertility
of the crossed offspring will ultimately tend to give uniformity of character.
But when we go beyond the limits of the same species, free intercrossing is
barred by the law of sterility.

In searching for facts which might throw light on the cause of the good
effects from crossing, and of the evil effects from close interbreeding, we
have seen that, on the one hand, it is a widely prevalent and ancient belief,
that animals and plants profit from slight changes in their condition of life;
and it would appear that the germ, in a somewhat analogous manner, is more
effectually stimulated by the male element, when taken from a distinct
individual, and therefore slightly modified in nature, than when taken from a
male having the same identical constitution. On the other hand, numerous facts
have been given, showing that when animals are first subjected to captivity,
even in their native land, and although allowed much liberty, their
reproductive functions are often greatly impaired or quite annulled. Some
groups of animals are more affected than others, but with apparently
capricious exceptions in every group. Some animals never or rarely couple
under confinement; some couple freely, but never or rarely conceive. The
secondary male characters, the maternal functions and instincts, are
occasionally affected. With plants, when first subjected to cultivation,
analogous facts have been observed. We probably owe our double flowers, rich
seedless fruits, and in some cases greatly developed tubers, etc., to
incipient sterility of the above nature combined with a copious supply of
nutriment. Animals which have long been domesticated, and plants which have
long been cultivated, can generally withstand, with unimpaired fertility,
great changes in their conditions of life; though both are sometimes slightly
affected. With animals the somewhat rare capacity of breeding freely under
confinement, together with their utility, mainly determine the kinds which
have been domesticated.

We can in no case precisely say what is the cause of the diminished fertility
of an animal when first captured, or of a plant when first cultivated; we can
only infer that it is caused by a change of some kind in the natural
conditions of life. The remarkable susceptibility of the reproductive system
to such changes,--a susceptibility not common to any other organ,--apparently
has an important bearing on Variability, as we shall see in a future chapter.

It is impossible not to be struck with the double parallelism between the two
classes of facts just alluded to. On the one hand, slight changes in the
conditions of life, and crosses between slightly modified forms or varieties,
are beneficial as far as prolificness and constitutional vigour are concerned.
On the other hand, changes in the conditions greater in degree, or of a
different nature, and crosses between forms which have been slowly and greatly
modified by natural means,--in other words, between species,--are highly
injurious, as far as the reproductive system is concerned, and in some few
instances as far as constitutional vigour is concerned. Can this parallelism
be accidental? Does it not rather indicate some real bond of connection? As a
fire goes out unless it be stirred up, so the vital forces are always tending,
according to Mr. Herbert Spencer, to a state of equilibrium, unless disturbed
and renovated through the action of other forces.

In some few cases varieties tend to keep distinct, by breeding at different
seasons, by great difference in size, or by sexual preference. But the
crossing of varieties, far from diminishing, generally adds to the fertility
of the first union and of the mongrel offspring. Whether all the more widely
distinct domestic varieties are invariably quite fertile when crossed, we do
not positively know; much time and trouble would be requisite for the
necessary experiments, and many difficulties occur, such as the descent of the
various races from aboriginally distinct species, and the doubts whether
certain forms ought to be ranked as species or varieties. Nevertheless, the
wide experience of practical breeders proves that the great majority of
varieties, even if some should hereafter prove not to be indefinitely fertile
inter se, are far more fertile when crossed, than the vast majority of closely
allied natural species. A few remarkable cases have, however, been given on
the authority of excellent observers, showing that with plants certain forms,
which undoubtedly must be ranked as varieties, yield fewer seeds when crossed
than is natural to the parent-species. Other varieties have had their
reproductive powers so far modified that they are either more or less fertile
than their parents, when crossed with a distinct species.

Nevertheless, the fact remains indisputable that domesticated varieties, of
animals and of plants, which differ greatly from one another in structure, but
which are certainly descended from the same aboriginal species, such as the
races of the fowl, pigeon, many vegetables, and a host of other productions,
are extremely fertile when crossed; and this seems to make a broad and
impassable barrier between domestic varieties and natural species. But, as I
will now attempt to show, the distinction is not so great and overwhelmingly
important as it at first appears.

ON THE DIFFERENCE IN FERTILITY BETWEEN VARIETIES AND SPECIES WHEN CROSSED.

This work is not the proper place for fully treating the subject of hybridism,
and I have already given in my 'Origin of Species' a moderately full abstract.
I will here merely enumerate the general conclusions which may be relied on,
and which bear on our present point.

FIRSTLY.

The laws governing the production of hybrids are identical, or nearly
identical, in the animal and vegetable kingdoms.

SECONDLY.

The sterility of distinct species when first united, and that of their hybrid
offspring, graduate, by an almost infinite number of steps, from zero, when
the ovule is never impregnated and a seed-capsule is never formed, up to
complete fertility. We can only escape the conclusion that some species are
fully fertile when crossed, by determining to designate as varieties all the
forms which are quite fertile. This high degree of fertility is, however,
rare. Nevertheless, plants, which have been exposed to unnatural conditions,
sometimes become modified in so peculiar a manner, that they are much more
fertile when crossed with a distinct species than when fertilised by their own
pollen. Success in effecting a first union between two species, and the
fertility of their hybrids, depend in an eminent degree on the conditions of
life being favourable. The innate sterility of hybrids of the same parentage
and raised from the same seed-capsule often differs much in degree.

THIRDLY.

The degree of sterility of a first cross between two species does not always
run strictly parallel with that of their hybrid offspring. Many cases are
known of species which can be crossed with ease, but yield hybrids excessively
sterile; and conversely some which can be crossed with great difficulty, but
produce fairly fertile hybrids. This is an inexplicable fact, on the view that
species have been specially endowed with mutual sterility in order to keep
them distinct.

FOURTHLY.

The degree of sterility often differs greatly in two species when reciprocally
crossed; for the first will readily fertilise the second; but the latter is
incapable, after hundreds of trials, of fertilising the former. Hybrids
produced from reciprocal crosses between the same two species likewise
sometimes differ in their degree of sterility. These cases also are utterly
inexplicable on the view of sterility being a special endowment.

FIFTHLY.

The degree of sterility of first crosses and of hybrids runs, to a certain
extent, parallel with the general or systematic affinity of the forms which
are united. For species belonging to distinct genera can rarely, and those
belonging to distinct families can never, be crossed. The parallelism,
however, is far from complete; for a multitude of closely allied species will
not unite, or unite with extreme difficulty, whilst other species, widely
different from one another, can be crossed with perfect facility. Nor does the
difficulty depend on ordinary constitutional differences, for annual and
perennial plants, deciduous and evergreen trees, plants flowering at different
seasons, inhabiting different stations, and naturally living under the most
opposite climates, can often be crossed with ease. The difficulty or facility
apparently depends exclusively on the sexual constitution of the species which
are crossed; or on their sexual elective affinity, i.e. Wahlverwandtschaft of
Gartner. As species rarely or never become modified in one character, without
being at the same time modified in many characters, and as systematic affinity
includes all visible similarities and dissimilarities, any difference in
sexual constitution between two species would naturally stand in more or less
close relation with their systematic position.

SIXTHLY.

The sterility of species when first crossed, and that of hybrids, may possibly
depend to a certain extent on distinct causes. With pure species the
reproductive organs are in a perfect condition, whilst with hybrids they are
often plainly deteriorated. A hybrid embryo which partakes of the constitution
of its father and mother is exposed to unnatural conditions, as long as it is
nourished within the womb, or egg, or seed of the mother-form; and as we know
that unnatural conditions often induce sterility, the reproductive organs of
the hybrid might at this early age be permanently affected. But this cause has
no bearing on the infertility of first unions. The diminished number of the
offspring from first unions may often result, as is certainly sometimes the
case, from the premature death of most of the hybrid embryos. But we shall
immediately see that a law of an unknown nature apparently exists, which leads
to the offspring from unions, which are infertile, being themselves more or
less infertile; and this at present is all that can be said.

SEVENTHLY.

Hybrids and mongrels present, with the one great exception of fertility, the
most striking accordance in all other respects; namely, in the laws of their
resemblance to their two parents, in their tendency to reversion, in their
variability, and in being absorbed through repeated crosses by either parent-
form.

After arriving at these conclusions, I was led to investigate a subject which
throws considerable light on hybridism, namely, the fertility of heterostyled
or dimorphic and trimorphic plants, when illegitimately united. I have had
occasion several times to allude to these plants, and I may here give a brief
abstract of my observations. Several plants belonging to distinct orders
present two forms, which exist in about equal numbers, and which differ in no
respect except in their reproductive organs; one form having a long pistil
with short stamens, the other a short pistil with long stamens; both with
differently sized pollen-grains. With trimorphic plants there are three forms
likewise differing in the lengths of their pistils and stamens, in the size
and colour of the pollen-grains, and in some other respects; and as in each of
the three forms there are two sets of stamens, there are altogether six sets
of stamens and three kinds of pistils. These organs are so proportioned in
length to one another that, in any two of the forms, half the stamens in each
stand on a level with the stigma of the third form. Now I have shown, and the
result has been confirmed by other observers, that, in order to obtain full
fertility with these plants, it is necessary that the stigma of the one form
should be fertilised by pollen taken from the stamens of corresponding height
in the other form. So that with dimorphic species two unions, which may be
called legitimate, are fully fertile, and two, which may be called
illegitimate, are more or less infertile. With trimorphic species six unions
are legitimate, or fully fertile, and twelve are illegitimate, or more or less
infertile. (19/2. My observations 'On the Character and hybrid-like nature of
the offspring from the illegitimate union of Dimorphic and Trimorphic Plants'
were published in the 'Journal of the Linnean Soc.' volume 10 page 393. The
abstract here given is nearly the same with that which appeared in the 6th
edition of my 'Origin of Species.')

The infertility which may be observed in various dimorphic and trimorphic
plants, when illegitimately fertilised, that is, by pollen taken from stamens
not corresponding in height with the pistil, differs much in degree, up to
absolute and utter sterility; just in the same manner as occurs in crossing
distinct species. As the degree of sterility in the latter case depends in an
eminent degree on the conditions of life being more or less favourable, so I
have found it with illegitimate unions. It is well known that if pollen of a
distinct species be placed on the stigma of a flower, and its own pollen be
afterwards, even after a considerable interval of time, placed on the same
stigma, its action is so strongly prepotent that it generally annihilates the
effect of the foreign pollen; so it is with the pollen of the several forms of
the same species, for legitimate pollen is strongly prepotent over
illegitimate pollen, when both are placed on the same stigma. I ascertained
this by fertilising several flowers, first illegitimately, and twenty-four
hours afterwards legitimately, with pollen taken from a peculiarly coloured
variety, and all the seedlings were similarly coloured; this shows that the
legitimate pollen, though applied twenty-four hours subsequently, had wholly
destroyed or prevented the action of the previously applied illegitimate
pollen. Again, as, in making reciprocal crosses between the same two species,
there is occasionally a great difference in the result, so the same thing
occurs with trimorphic plants; for instance, the mid-styled form of Lythrum
salicaria could be illegitimately fertilised with the greatest ease by pollen
from the longer stamens of the short-styled form, and yielded many seeds; but
the short-styled form did not yield a single seed when fertilised by the
longer stamens of the mid-styled form.

In all these respects the forms of the same undoubted species, when
illegitimately united, behave in exactly the same manner as do two distinct
species when crossed. This led me carefully to observe during four years many
seedlings, raised from several illegitimate unions. The chief result is that
these illegitimate plants, as they may be called, are not fully fertile. It is
possible to raise from dimorphic species, both long-styled and short-styled
illegitimate plants, and from trimorphic plants all three illegitimate forms.
These can then be properly united in a legitimate manner. When this is done,
there is no apparent reason why they should not yield as many seeds as did
their parents when legitimately fertilised. But such is not the case; they are
all infertile, but in various degrees; some being so utterly and incurably
sterile that they did not yield during four seasons a single seed or even
seed-capsule. These illegitimate plants, which are so sterile, although united
with each other in a legitimate manner, may be strictly compared with hybrids
when crossed inter se, and it is well known how sterile these latter generally
are. When, on the other hand, a hybrid is crossed with either pure parent-
species, the sterility is usually much lessened: and so it is when an
illegitimate plant is fertilised by a legitimate plant. In the same manner as
the sterility of hybrids does not always run parallel with the difficulty of
making the first cross between the two parent-species, so the sterility of
certain illegitimate plants was unusually great, whilst the sterility of the
union from which they were derived was by no means great. With hybrids raised
from the same seed-capsule the degree of sterility is innately variable, so it
is in a marked manner with illegitimate plants. Lastly, many hybrids are
profuse and persistent flowerers, whilst other and more sterile hybrids
produce few flowers, and are weak, miserable dwarfs; exactly similar cases
occur with the illegitimate offspring of various dimorphic and trimorphic
plants.

Although there is the closest identity in character and behaviour between
illegitimate plants and hybrids, it is hardly an exaggeration to maintain that
the former are hybrids, but produced within the limits of the same species by
the improper union of certain forms, whilst ordinary hybrids are produced from
an improper union between so-called distinct species. We have already seen
that there is the closest similarity in all respects between first
illegitimate unions, and first crosses between distinct species. This will
perhaps be made more fully apparent by an illustration:--we may suppose that a
botanist found two well-marked varieties (and such occur) of the long-styled
form of the trimorphic Lithrum salicaria, and that he determined to try by
crossing whether they were specifically distinct. He would find that they
yielded only about one-fifth of the proper number of seed, and that they
behaved in all the other above-specified respects as if they had been two
distinct species. But to make the case sure, he would raise plants from his
supposed hybridised seed, and he would find that the seedlings were miserably
dwarfed and utterly sterile, and that they behaved in all other respects like
ordinary hybrids, he might then maintain that he had actually proved, in
accordance with the common view, that his two varieties were as good and as
distinct species as any in the world; but he would be completely mistaken.

The facts now given on dimorphic and trimorphic plants are important, because
they show us, first, that the physiological test of lessened fertility, both
in first crosses and in hybrids, is no criterion of specific distinction;
secondly, because we may conclude that there is some unknown bond which
connects the infertility of illegitimate unions with that of their
illegitimate offspring, and we are led to extend the same view to first
crosses and hybrids; thirdly, because we find, and this seems to me of
especial importance, that two or three forms of the same species may exist and
may differ in no respect whatever, either in structure or in constitution,
relatively to external conditions, and yet be sterile when united in certain
ways. For we must remember that it is the union of the sexual elements of
individuals of the same form, for instance, of two long-styled forms, which
results in sterility; whilst it is the union of the sexual element proper to
two distinct forms which is fertile. Hence the case appears at first sight
exactly the reverse of what occurs in the ordinary unions of the individuals
of the same species, and with crosses between distinct species. It is,
however, doubtful whether this is really so; but I will not enlarge on this
obscure subject.

We may, however, infer as probable from the consideration of dimorphic and
trimorphic plants, that the sterility of distinct species when crossed, and of
their hybrid progeny, depends exclusively on the nature of their sexual
elements, and not on any difference in their structure or general
constitution. We are also led to this same conclusion by considering
reciprocal crosses, in which the male of one species cannot be united, or only
with great difficulty, with the female of a second species, whilst the
converse cross can be effected with perfect facility. That excellent observer,
Gartner, likewise concluded that species when crossed are sterile owing to
differences confined to their reproductive systems.

On the principle which makes it necessary for man, whilst he is selecting and
improving his domestic varieties, to keep them separate, it would clearly be
advantageous to varieties in a state of nature, that is to incipient species,
if they could be kept from blending, either through sexual aversion, or by
becoming mutually sterile. Hence it at one time appeared to me probable, as it
has to others, that this sterility might have been acquired through natural
selection. On this view we must suppose that a shade of lessened fertility
first spontaneously appeared, like any other modification, in certain
individuals of a species when crossed with other individuals of the same
species; and that successive slight degrees of infertility, from being
advantageous, were slowly accumulated. This appears all the more probable, if
we admit that the structural differences between the forms of dimorphic and
trimorphic plants, as the length and curvature of the pistil, etc., have been
co-adapted through natural selection; for if this be admitted, we can hardly
avoid extending the same conclusion to their mutual infertility. Sterility,
moreover, has been acquired through natural selection for other and widely
different purposes, as with neuter insects in reference to their social
economy. In the case of plants, the flowers on the circumference of the truss
in the guelder rose (Viburnum opulus) and those on the summit of the spike in
the feather-hyacinth (Muscari comosum) have been rendered conspicuous, and
apparently in consequence sterile, in order that insects might easily discover
and visit the perfect flowers. But when we endeavour to apply the principle of
natural selection to the acquirement by distinct species of mutual sterility,
we meet with great difficulties. In the first place, it may be remarked that
separate regions are often inhabited by groups of species or by single
species, which when brought together and crossed are found to be more or less
sterile; now it could clearly have been no advantage to such separated species
to have been rendered mutually sterile, and consequently this could not have
been effected through natural selection; but it may perhaps be argued, that,
if a species were rendered sterile with some one compatriot, sterility with
other species would follow as a necessary consequence. In the second place, it
is as much opposed to the theory of natural selection, as to the theory of
special creation, that in reciprocal crosses the male element of one form
should have been rendered utterly impotent on a second form, whilst at the
same time the male element of this second form is enabled freely to fertilise
the first form; for this peculiar state of the reproductive system could not
possibly have been advantageous to either species.

In considering the probability of natural selection having come into action in
rendering species mutually sterile, one of the greatest difficulties will be
found to lie in the existence of many graduated steps from slightly lessened
fertility to absolute sterility. It may be admitted, on the principle above
explained, that it would profit an incipient species if it were rendered in
some slight degree sterile when crossed with its parent-form or with some
other variety; for thus fewer bastardised and deteriorated offspring would be
produced to commingle their blood with the new species in process of
formation. But he who will take the trouble to reflect on the steps by which
this first degree of sterility could be increased through natural selection to
that higher degree which is common to so many species, and which is universal
with species which have been differentiated to a generic or family rank, will
find the subject extraordinarily complex. After mature reflection it seems to
me that this could not have been effected through natural selection. Take the
case of any two species which, when crossed, produce few and sterile
offspring; now, what is there which could favour the survival of those
individuals which happened to be endowed in a slightly higher degree with
mutual infertility, and which thus approached by one small step towards
absolute sterility? Yet an advance of this kind, if the theory of natural
selection be brought to bear, must have incessantly occurred with many
species, for a multitude are mutually quite barren. With sterile neuter
insects we have reason to believe that modifications in their structure and
fertility have been slowly accumulated by natural selection, from an advantage
having been thus indirectly given to the community to which they belonged over
other communities of the same species; but an individual animal not belonging
to a social community, if rendered slightly sterile when crossed with some
other variety, would not thus itself gain any advantage or indirectly give any
advantage to the other individuals of the same variety, thus leading to their
preservation.

But it would be superfluous to discuss this question in detail; for with
plants we have conclusive evidence that the sterility of crossed species must
be due to some principle, quite independent of natural selection. Both Gartner
and Kolreuter have proved that in general including numerous species, a series
can be formed from species which when crossed yield fewer and fewer seeds, to
species which never produce a single seed, but yet are affected by the pollen
of certain other species, for the germen swells. It is here manifestly
impossible to select the more sterile individuals, which have already ceased
to yield seeds; so that this acme of sterility, when the germen alone is
affected, cannot have been gained through selection; and from the laws
governing the various grades of sterility being so uniform throughout the
animal and vegetable kingdoms, we may infer that the cause, whatever it may
be, is the same or nearly the same in all cases.

As species have not been rendered mutually infertile through the accumulative
action of natural selection, and as we may safely conclude, from the previous
as well as from other and more general considerations, that they have not been
endowed through an act of creation with this quality, we must infer that it
has arisen incidentally during their slow formation in connection with other
and unknown changes in their organisation. By a quality arising incidentally,
I refer to such cases as different species of animals and plants being
differently affected by poisons to which they are not naturally exposed; and
this difference in susceptibility is clearly incidental on other and unknown
differences in their organisation. So again the capacity in different kinds of
trees to be grafted on each other, or on a third species, differs much, and is
of no advantage to these trees, but is incidental on structural or functional
differences in their woody tissues. We need not feel surprise at sterility
incidentally resulting from crosses between distinct species,--the modified
descendants of a common progenitor,--when we bear in mind how easily the
reproductive system is affected by various causes--often by extremely slight
changes in the conditions of life, by too close interbreeding, and by other
agencies. It is well to bear in mind such cases as that of the Passiflora
alata, which recovered its self-fertility from being grafted on a distinct
species--the cases of plants which normally or abnormally are self-impotent,
but can readily be fertilised by the pollen of a distinct species--and lastly
the cases of individual domesticated animals which evince towards each other
sexual incompatibility.

We now at last come to the immediate point under discussion: how is it that,
with some few exceptions in the case of plants, domesticated varieties, such
as those of the dog, fowl, pigeon, several fruit-trees, and culinary
vegetables, which differ from each other in external characters more than many
species, are perfectly fertile when crossed, or even fertile in excess, whilst
closely allied species are almost invariably in some degree sterile? We can,
to a certain extent, give a satisfactory answer to this question. Passing over
the fact that the amount of external difference between two species is no sure
guide to their degree of mutual sterility, so that similar differences in the
case of varieties would be no sure guide, we know that with species the cause
lies exclusively in differences in their sexual constitution. Now the
conditions to which domesticated animals and cultivated plants have been
subjected have had so little tendency towards modifying the reproductive
system in a manner leading to mutual sterility, that we have very good grounds
for admitting the directly opposite doctrine of Pallas, namely, that such
conditions generally eliminate this tendency; so that the domesticated
descendants of species, which in their natural state would have been in some
degree sterile when crossed, become perfectly fertile together. With plants,
so far is cultivation from giving a tendency towards mutual sterility, that in
several well-authenticated cases, already often alluded to, certain species
have been affected in a very different manner, for they have become self-
impotent, whilst still retaining the capacity of fertilising, and being
fertilised by, distinct species. If the Pallasian doctrine of the elimination
of sterility through long-continued domestication be admitted, and it can
hardly be rejected, it becomes in the highest degree improbable that similar
circumstances should commonly both induce and eliminate the same tendency;
though in certain cases, with species having a peculiar constitution,
sterility might occasionally be thus induced. Thus, as I believe, we can
understand why with domesticated animals varieties have not been produced
which are mutually sterile; and why with plants only a few such cases have
been observed, namely, by Gartner, with certain varieties of maize and
verbascum, by other experimentalists with varieties of the gourd and melon,
and by Kolreuter with one kind of tobacco.

With respect to varieties which have originated in a state of nature, it is
almost hopeless to expect to prove by direct evidence that they have been
rendered mutually sterile; for if even a trace of sterility could be detected,
such varieties would at once be raised by almost every naturalist to the rank
of distinct species. If, for instance, Gartner's statement were fully
confirmed, that the blue and red flowered forms of the pimpernel (Anagallis
arvensis) are sterile when crossed, I presume that all the botanists who now
maintain on various grounds that these two forms are merely fleeting
varieties, would at once admit that they were specifically distinct.

The real difficulty in our present subject is not, as it appears to me, why
domestic varieties have not become mutually infertile when crossed, but why
this has so generally occurred with natural varieties as soon as they have
been modified in a sufficient and permanent degree to take rank as species. We
are far from precisely knowing the cause; but we can see that the species,
owing to their struggle for existence with numerous competitors, must have
been exposed to more uniform conditions of life during long periods of time
than domestic varieties have been, and this may well make a wide difference in
the result. For we know how commonly wild animals and plants, when taken from
their natural conditions and subjected to captivity, are rendered sterile; and
the reproductive functions of organic beings which have always lived and been
slowly modified under natural conditions would probably in like manner be
eminently sensitive to the influence of an unnatural cross. Domesticated
productions, on the other hand, which, as shown by the mere fact of their
domestication, were not originally highly sensitive to changes in their
conditions of life, and which can now generally resist with undiminished
fertility repeated changes of conditions, might be expected to produce
varieties, which would be little liable to have their reproductive powers
injuriously affected by the act of crossing with other varieties which had
originated in a like manner.

Certain naturalists have recently laid too great stress, as it appears to me,
on the difference in fertility between varieties and species when crossed.
Some allied species of trees cannot be grafted on one another, whilst all
varieties can be so grafted. Some allied animals are affected in a very
different manner by the same poison, but with varieties no such case until
recently was known; whilst now it has been proved that immunity from certain
poisons sometimes stands in correlation with the colour of the individuals of
the same species. The period of gestation generally differs much in distinct
species, but with varieties until lately no such difference had been observed.
Here we have various physiological differences, and no doubt others could be
added, between one species and another of the same genus, which do not occur,
or occur with extreme rarity, in the case of varieties; and these differences
are apparently wholly or in chief part incidental on other constitutional
differences, just in the same manner as the sterility of crossed species is
incidental on differences confined to the sexual system. Why, then, should
these latter differences, however serviceable they may indirectly be in
keeping the inhabitants of the same country distinct, be thought of such
paramount importance, in comparison with other incidental and functional
differences? No sufficient answer to this question can be given. Hence the
fact that widely distinct domestic varieties are, with rare exceptions,
perfectly fertile when crossed, and produce fertile offspring, whilst closely
allied species are, with rare exceptions, more or less sterile, is not nearly
so formidable an objection as it appears at first to the theory of the common
descent of allied species.


CHAPTER 2.XX.

SELECTION BY MAN.

SELECTION A DIFFICULT ART.
METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION.
RESULTS OF METHODICAL SELECTION.
CARE TAKEN IN SELECTION.
SELECTION WITH PLANTS.
SELECTION CARRIED ON BY THE ANCIENTS AND BY SEMI-CIVILISED PEOPLE.
UNIMPORTANT CHARACTERS OFTEN ATTENDED TO.
UNCONSCIOUS SELECTION.
AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED
THROUGH THE ACTION OF UNCONSCIOUS SELECTION.
INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY.
PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION.
EFFECTS OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS
MOST VALUED BY MAN.

The power of Selection, whether exercised by man, or brought into play under
nature through the struggle for existence and the consequent survival of the
fittest, absolutely depends on the variability of organic beings. Without
variability nothing can be effected; slight individual differences, however,
suffice for the work, and are probably the chief or sole means in the
production of new species. Hence our discussion on the causes and laws of
variability ought in strict order to have preceded the present subject, as
well as inheritance, crossing, etc.; but practically the present arrangement
has been found the most convenient. Man does not attempt to cause variability;
though he unintentionally effects this by exposing organisms to new conditions
of life, and by crossing breeds already formed. But variability being granted,
he works wonders. Unless some degree of selection be exercised, the free
commingling of the individuals of the same variety soon obliterates, as we
have previously seen, the slight differences which arise, and gives uniformity
of character to the whole body of individuals. In separated districts, long-
continued exposure to different conditions of life may produce new races
without the aid of selection; but to this subject of the direct action of the
conditions of life I shall recur in a future chapter.

When animals or plants are born with some conspicuous and firmly inherited new
character, selection is reduced to the preservation of such individuals, and
to the subsequent prevention of crosses; so that nothing more need be said on
the subject. But in the great majority of cases a new character, or some
superiority in an old character, is at first faintly pronounced, and is not
strongly inherited; and then the full difficulty of selection is experienced.
Indomitable patience, the finest powers of discrimination, and sound judgment
must be exercised during many years. A clearly predetermined object must be
kept steadily in view. Few men are endowed with all these qualities,
especially with that of discriminating very slight differences; judgment can
be acquired only by long experience; but if any of these qualities be wanting,
the labour of a life may be thrown away. I have been astonished when
celebrated breeders, whose skill and judgment have been proved by their
success at exhibitions, have shown me their animals, which appeared all alike,
and have assigned their reasons for matching this and that individual. The
importance of the great principle of Selection mainly lies in this power of
selecting scarcely appreciable differences, which nevertheless are found to be
transmissible, and which can be accumulated until the result is made manifest
to the eyes of every beholder.

The principle of selection may be conveniently divided into three kinds.
METHODICAL SELECTION is that which guides a man who systematically endeavours
to modify a breed according to some predetermined standard. UNCONSCIOUS
SELECTION is that which follows from men naturally preserving the most valued
and destroying the less valued individuals, without any thought of altering
the breed; and undoubtedly this process slowly works great changes.
Unconscious selection graduates into methodical, and only extreme cases can be
distinctly separated; for he who preserves a useful or perfect animal will
generally breed from it with the hope of getting offspring of the same
character; but as long as he has not a predetermined purpose to improve the
breed, he may be said to be selecting unconsciously. (20/1. The term
"unconscious selection" has been objected to as a contradiction; but see some
excellent observations on this head by Prof. Huxley ('Nat. Hist. Review'
October 1864 page 578) who remarks that when the wind heaps up sand-dunes it
sifts and UNCONSCIOUSLY SELECTS from the gravel on the beach grains of sand of
equal size.) Lastly, we have NATURAL SELECTION, which implies that the
individuals which are best fitted for the complex, and in the course of ages
changing conditions to which they are exposed, generally survive and procreate
their kind. With domestic productions, natural selection comes to a certain
extent into action, independently of, and even in opposition to, the will of
man.

METHODICAL SELECTION.

What man has effected within recent times in England by methodical selection
is clearly shown by our exhibitions of improved quadrupeds and fancy birds.
With respect to cattle, sheep, and pigs, we owe their great improvement to a
long series of well-known names--Bakewell, Coiling, Ellman, Bates, Jonas Webb,
Lords Leicester and Western, Fisher Hobbs, and others. Agricultural writers
are unanimous on the power of selection: any number of statements to this
effect could be quoted; a few will suffice. Youatt, a sagacious and
experienced observer, writes (20/2. 'On Sheep' 1838 page 60.) the principle of
selection is "that which enables the agriculturist, not only to modify the
character of his flock, but to change it altogether." A great breeder of
Shorthorns (20/3. Mr. J. Wright on Shorthorn Cattle in 'Journal of Royal
Agricult. Soc.' volume 7 pages 208, 209.) says, "In the anatomy of the
shoulder modern breeders have made great improvement on the Ketton shorthorns
by correcting the defect in the knuckle or shoulder-joint, and by laying the
top of the shoulder more snugly in the crop, and thereby filling up the hollow
behind it...The eye has its fashion at different periods: at one time the eye
high and outstanding from the head, and at another time the sleepy eye sunk
into the head; but these extremes have merged into the medium of a full, clear
and prominent eye with a placid look."

Again, hear what an excellent judge of pigs (20/4. H.D. Richardson 'On Pigs'
1847 page 44.) says: "The legs should be no longer than just to prevent the
animal's belly from trailing on the ground. The leg is the least profitable
portion of the hog, and we therefore require no more of it than is absolutely
necessary for the support of the rest." Let any one compare the wild-boar with
any improved breed, and he will see how effectually the legs have been
shortened.

Few persons, except breeders, are aware of the systematic care taken in
selecting animals, and of the necessity of having a clear and almost prophetic
vision into futurity. Lord Spencer's skill and judgment were well known; and
he writes (20/5. 'Journal of Royal Agricult. Soc.' volume 1 page 24.), "It is
therefore very desirable, before any man commences to breed either cattle or
sheep, that he should make up his mind to the shape and qualities he wishes to
obtain, and steadily pursue this object." Lord Somerville, in speaking of the
marvellous improvement of the New Leicester sheep, effected by Bakewell and
his successors, says, "It would seem as if they had first drawn a perfect
form, and then given it life." Youatt (20/6. 'On Sheep' pages 520, 319.) urges
the necessity of annually drafting each flock, as many animals will certainly
degenerate "from the standard of excellence which the breeder has established
in his own mind." Even with a bird of such little importance as the canary,
long ago (1780-1790) rules were established, and a standard of perfection was
fixed according to which the London fanciers tried to breed the several sub-
varieties. (20/7. Loudon's 'Mag. of Nat. Hist.' volume 8 1835 page 618.) A
great winner of prizes at the Pigeon-shows (20/8. 'A treatise on the Art of
Breeding the Almond Tumbler' 1851 page 9.), in describing the short-faced
Almond Tumbler, says, "There are many first-rate fanciers who are particularly
partial to what is called the goldfinch-beak, which is very beautiful; others
say, take a full-size round cherry then take a barleycorn, and judiciously
placing and thrusting it into the cherry, form as it were your beak; and that
is not all, for it will form a good head and beak, provided, as I said before,
it is judiciously done; others take an oat; but as I think the goldfinch-beak
the handsomest, I would advise the inexperienced fancier to get the head of a
goldfinch, and keep it by him for his observation." Wonderfully different as
are the beaks of the rock pigeon and goldfinch, the end has undoubtedly been
nearly gained, as far as external shape and proportions are concerned.

Not only should our animals be examined with the greatest care whilst alive,
but, as Anderson remarks (20/9. 'Recreations in Agriculture' volume 2 page
409.) their carcases should be scrutinised, "so as to breed from the
descendants of such only as, in the language of the butcher, cut up well." The
"grain of the meat" in cattle, and its being well marbled with fat (20/10.
'Youatt on Cattle' pages 191, 227.), and the greater or less accumulation of
fat in the abdomen of our sheep, have been attended to with success. So with
poultry, a writer (20/11. Ferguson 'Prize Poultry' 1854 page 208.), speaking
of Cochin-China fowls, which are said to differ much in the quality of their
flesh, says, "the best mode is to purchase two young brother-cocks, kill,
dress, and serve up one; if he be indifferent, similarly dispose of the other,
and try again; if, however, he be fine and well-flavoured, his brother will
not be amiss for breeding purposes for the table."

The great principle of the division of labour has been brought to bear on
selection. In certain districts (20/12. Wilson in 'Transact. Highland
Agricult. Soc.' quoted in 'Gardener's Chronicle' 1844 page 29.) "the breeding
of bulls is confined to a very limited number of persons, who by devoting
their whole attention to this department, are able from year to year to
furnish a class of bulls which are steadily improving the general breed of the
district." The rearing and letting of choice rams has long been, as is well
known, a chief source of profit to several eminent breeders. In parts of
Germany this principle is carried with merino sheep to an extreme point.
(20/13. Simmonds quoted in 'Gardener's Chronicle' 1855 page 637. And for the
second quotation see 'Youatt on Sheep' page 171.) So "important is the proper
selection of breeding animals considered, that the best flock-masters do not
trust to their own judgment or to that of their shepherds, but employ persons
called 'sheep-classifiers' who make it their special business to attend to
this part of the management of several flocks, and thus to preserve, or if
possible to improve, the best qualities of both parents in the lambs." In
Saxony, "when the lambs are weaned, each in his turn is placed upon a table
that his wool and form may be minutely observed. The finest are selected for
breeding and receive a first mark. When they are one year old, and prior to
shearing them, another close examination of those previously marked takes
place: those in which no defect can be found receive a second mark, and the
rest are condemned. A few months afterwards a third and last scrutiny is made;
the prime rams and ewes receive a third and final mark, but the slightest
blemish is sufficient to cause the rejection of the animal." These sheep are
bred and valued almost exclusively for the fineness of their wool; and the
result corresponds with the labour bestowed on their selection. Instruments
have been invented to measure accurately the thickness of the fibres; and "an
Austrian fleece has been produced of which twelve hairs equalled in thickness
one from a Leicester sheep."

Throughout the world, wherever silk is produced, the greatest care is bestowed
on selecting the cocoons from which the moths for breeding are to be reared. A
careful cultivator (20/14. Robinet 'Vers a Soie' 1848 page 271.) likewise
examines the moths themselves, and destroys those that are not perfect. But
what more immediately concerns us is that certain families in France devote
themselves to raising eggs for sale. (20/15. Quatrefages 'Les Maladies du Ver
a Soie' 1859 page 101.) In China, near Shanghai, the inhabitants of two small
districts have the privilege of raising eggs for the whole surrounding
country, and that they may give up their whole time to this business, they are
interdicted by law from producing silk. (20/16. M. Simon in 'Bull. de la Soc.
d'Acclimat.' tome 9 1862 page 221.)

The care which successful breeders take in matching their birds is surprising.
Sir John Sebright, whose fame is perpetuated by the "Sebright Bantam," used to
spend "two and three days in examining, consulting, and disputing with a
friend which were the best of five or six birds." (20/17. 'The Poultry
Chronicle' volume 1 1854 page 607.) Mr. Bult, whose pouter-pigeons won so many
prizes, and were exported to North America under the charge of a man sent on
purpose, told me that he always deliberated for several days before he matched
each pair. Hence we can understand the advice of an eminent fancier, who
writes (20/18. J.M. Eaton 'A Treatise on Fancy Pigeons' 1852 page 14 and 'A
Treatise on the Almond Tumbler' 1851 page 11.) "I would here particularly
guard you against having too great a variety of pigeons, otherwise you will
know a little of all, but nothing about one as it ought to be known."
Apparently it transcends the power of the human intellect to breed all kinds:
"it is possible that there may be a few fanciers that have a good general
knowledge of fancy pigeons; but there are many more who labour under the
delusion of supposing they know what they do not." The excellence of one sub-
variety, the Almond Tumbler, lies in the plumage, carriage, head, beak, and
eye; but it is too presumptuous in the beginner to try for all these points.
The great judge above quoted says, "There are some young fanciers who are
over-covetous, who go for all the above five properties at once; they have
their reward by getting nothing." We thus see that breeding even fancy pigeons
is no simple art: we may smile at the solemnity of these precepts, but he who
laughs will win no prizes.

What methodical selection has effected for our animals is sufficiently proved,
as already remarked, by our Exhibitions. So greatly were the sheep belonging
to some of the earlier breeders, such as Bakewell and Lord Western, changed,
that many persons could not be persuaded that they had not been crossed. Our
pigs, as Mr. Corringham remarks (20/19. 'Journal Royal Agricultural Soc.'
volume 6 page 22.) during the last twenty years have undergone, through
rigorous selection together with crossing, a complete metamorphosis. The first
exhibition for poultry was held in the Zoological Gardens in 1845; and the
improvement effected since that time has been great. As Mr. Bailey, the great
judge, remarked to me, it was formerly ordered that the comb of the Spanish
cock should be upright, and in four or five years all good birds had upright
combs; it was ordered that the Polish cock should have no comb or wattles, and
now a bird thus furnished would be at once disqualified; beards were ordered,
and out of fifty-seven pens lately (1860) exhibited at the Crystal Palace, all
had beards. So it has been in many other cases. But in all cases the judges
order only what is occasionally produced and what can be improved and rendered
constant by selection. The steady increase in weight during the last few years
in our fowls, turkeys, ducks, and geese is notorious; "six-pound ducks are now
common, whereas four pounds was formerly the average." As the time required to
make a change has not often been recorded, it may be worth mentioning that it
took Mr. Wicking thirteen years to put a clean white head on an almond
tumbler's body, "a triumph," says another fancier, "of which he may be justly
proud." (20/20. 'Poultry Chronicle' volume 2 1855 page 596.)

Mr. Tollet, of Betley Hall, selected cows, and especially bulls, descended
from good milkers, for the sole purpose of improving his cattle for the
production of cheese; he steadily tested the milk with the lactometer, and in
eight years he increased, as I was informed by him, the product in proportion
of four to three. Here is a curious case (20/21. Isid. Geoffroy St.-Hilaire
'Hist. Nat. Gen.' tome 3 page 254.) of steady but slow progress, with the end
not as yet fully attained: in 1784 a race of silkworms was introduced into
France, in which one hundred in the thousand failed to produce white cocoons;
but now after careful selection during sixty-five generations, the proportion
of yellow cocoons has been reduced to thirty-five in the thousand.

With plants selection has been followed with the same good result as with
animals. But the process is simpler, for plants in the great majority of cases
bear both sexes. Nevertheless, with most kinds it is necessary to take as much
care to prevent crosses as with animals or unisexual plants; but with some
plants, such as peas, this care is not necessary. With all improved plants,
excepting of course those which are propagated by buds, cuttings, etc., it is
almost indispensable to examine the seedlings and destroy those which depart
from the proper type. This is called "roguing," and is, in fact, a form of
selection, like the rejection of inferior animals. Experienced horticulturists
and agriculturists incessantly urge every one to preserve the finest plants
for the production of seed.

Although plants often present much more conspicuous variations than animals,
yet the closest attention is generally requisite to detect each slight and
favourable change. Mr. Masters relates (20/22. 'Gardener's Chronicle' 1850
page 198.) how "many a patient hour was devoted," whilst he was young, to the
detection of differences in peas intended for seed. Mr. Barnet (20/23.
'Transact. Hort. Soc.' volume 6 page 152.) remarks that the old scarlet
American strawberry was cultivated for more than a century without producing a
single variety; and another writer observes how singular it was that when
gardeners first began to attend to this fruit it began to vary; the truth no
doubt being that it had always varied, but that, until slight variations were
selected and propagated by seed, no conspicuous result was obtained. The
finest shades of difference in wheat have been discriminated and selected with
almost as much care as, in the case of the higher animals, for instance by
Col. Le Couteur and more especially by Major Hallett.

It may be worth while to give a few examples of methodical selection with
plants; but in fact the great improvement of all our anciently cultivated
plants may be attributed to selection long carried on, in part methodically,
and in part unconsciously. I have shown in a former chapter how the weight of
the gooseberry has been increased by systematic selection and culture. The
flowers of the Heartsease have been similarly increased in size and regularity
of outline. With the Cineraria, Mr. Glenny (20/24. 'Journal of Horticulture'
1862 page 369.) "was bold enough when the flowers were ragged and starry and
ill defined in colour, to fix a standard which was then considered
outrageously high and impossible, and which, even if reached, it was said, we
should be no gainers by, as it would spoil the beauty of the flowers. He
maintained that he was right; and the event has proved it to be so." The
doubling of flowers has several times been effected by careful selection: the
Rev. W. Williamson (20/25 'Transact. Hort. Soc.' volume 4 page 381.), after
sowing during several years seed of Anemone coronaria, found a plant with one
additional petal; he sowed the seed of this, and by perseverance in the same
course obtained several varieties with six or seven rows of petals. The single
Scotch rose was doubled, and yielded eight good varieties in nine or ten
years. (20/26. 'Transact. Hort. Soc.' volume 4 page 285.) The Canterbury bell
(Campanula medium) was doubled by careful selection in four generations.
(20/27. Rev. W. Bromehead in 'Gardener's Chronicle' 1857 page 550.) In four
years Mr. Buckman (20/28. 'Gardener's Chronicle' 1862 page 721.), by culture
and careful selection, converted parsnips, raised from wild seed, into a new
and good variety. By selection during a long course of years, the early
maturity of peas has been hastened by between ten and twenty-one days. (20/29.
Dr. Anderson in 'The Bee' volume 6 page 96; Mr. Barnes in 'Gardener's
Chronicle' 1844 page 476.) A more curious case is offered by the beet plant,
which since its cultivation in France, has almost exactly doubled its yield of
sugar. This has been effected by the most careful selection; the specific
gravity of the roots being regularly tested, and the best roots saved for the
production of seed. (20/30. Godron 'De l'Espece' 1859 tome 2 page 69;
'Gardener's Chronicle' 1854 page 258.)

SELECTION BY ANCIENT AND SEMI-CIVILISED PEOPLE.

In attributing so much importance to the selection of animals and plants, it
may be objected, that methodical selection would not have been carried on
during ancient times. A distinguished naturalist considers it as absurd to
suppose that semi-civilised people should have practised selection of any
kind. Undoubtedly the principle has been systematically acknowledged and
followed to a far greater extent within the last hundred years than at any
former period, and a corresponding result has been gained; but it would be a
greater error to suppose, as we shall immediately see, that its importance was
not recognised and acted on during the most ancient times, and by semi-
civilised people. I should premise that many facts now to be given only show
that care was taken in breeding; but when this is the case, selection is
almost sure to be practised to a certain extent. We shall hereafter be enabled
better to judge how far selection, when only occasionally carried on, by a few
of the inhabitants of a country, will slowly produce a great effect.

In a well-known passage in the thirtieth chapter of Genesis, rules are given
for influencing, as was then thought possible, the colour of sheep; and
speckled and dark breeds are spoken of as being kept separate. By the time of
David the fleece was likened to snow. Youatt (20/31. 'On Sheep' page 18.), who
has discussed all the passages in relation to breeding in the Old Testament,
concludes that at this early period "some of the best principles of breeding
must have been steadily and long pursued." It was ordered, according to Moses,
that "Thou shalt not let thy cattle gender with a diverse kind;" but mules
were purchased (20/32. Volz 'Beitrage zur Kulturgeschichte' 1852 s. 47.) so
that at this early period other nations must have crossed the horse and ass.
It is said (20/33. Mitford 'History of Greece' volume 1 page 73.) that
Erichthonius, some generations before the Trojan war, had many brood-mares,
"which by his care and judgment in the choice of stallions produced a breed of
horses superior to any in the surrounding countries." Homer (Book 5) speaks of
Aeneas' horses as bred from mares which were put to the steeds of Laomedon.
Plato, in his 'Republic' says to Glaucus, "I see that you raise at your house
a great many dogs for the chase. Do you take care about breeding and pairing
them? Among animals of good blood, are there not always some which are
superior to the rest?" To which Glaucus answers in the affirmative. (20/34.
Dr. Dally translated in 'Anthropological Review' May 1864 page 101.) Alexander
the Great selected the finest Indian cattle to send to Macedonia to improve
the breed. (20/35. Volz 'Beitrage' etc. 1852 s. 80.) According to Pliny (20/36
'History of the World' chapter 45.), King Pyrrhus had an especially valuable
breed of oxen: and he did not suffer the bulls and cows to come together till
four years old, that the breed might not degenerate. Virgil, in his Georgics
(lib. 3), gives as strong advice as any modern agriculturist could do,
carefully to select the breeding stock; "to note the tribe, the lineage, and
the sire; whom to reserve for husband of the herd;"--to brand the progeny;--to
select sheep of the purest white, and to examine if their tongues are swarthy.
We have seen that the Romans kept pedigrees of their pigeons, and this would
have been a senseless proceeding had not great care been taken in breeding
them. Columella gives detailed instructions about breeding fowls: "Let the
breeding hens therefore be of a choice colour, a robust body, square-built,
full-breasted, with large heads, with upright and bright-red combs. Those are
believed to be the best bred which have five toes." (20/37. 'Gardener's
Chronicle' 1848 page 323.) According to Tacitus, the Celts attended to the
races of their domestic animals; and Caesar states that they paid high prices
to merchants for fine imported horses. (20/38. Reynier 'De l'Economie des
Celtes' 1818 pages 487, 503.) In regard to plants, Virgil speaks of yearly
culling the largest seeds; and Celsus says, "where the corn and crop is but
small, we must pick out the best ears of corn, and of them lay up our seed
separately by itself." (20/39. Le Couteur on 'Wheat' page 15.)

Coming down the stream of time, we may be brief. At about the beginning of the
ninth century Charlemagne expressly ordered his officers to take great care of
his stallions; and if any proved bad or old, to forewarn him in good time
before they were put to the mares. (20/40. Michel 'Des Haras' 1861 page 84.)
Even in a country so little civilised as Ireland during the ninth century, it
would appear from some ancient verses (20/41. Sir W. Wilde an 'Essay on
Unmanufactured Animal Remains' etc. 1860 page 11.), describing a ransom
demanded by Cormac, that animals from particular places, or having a
particular character, were valued. Thus it is said,--

Two pigs of the pigs of Mac Lir,
A ram and ewe both round and red,
I brought with me from Aengus.
I brought with me a stallion and a mare
From the beautiful stud of Manannan,
A bull and a white cow from Druim Cain.

Athelstan, in 930, received running-horses as a present from Germany; and he
prohibited the exportation of English horses. King John imported "one hundred
chosen stallions from Flanders." (20/42. Col. Hamilton Smith 'Nat. Library'
volume 12 Horses, pages 135, 140.) On June 16th, 1305, the Prince of Wales
wrote to the Archbishop of Canterbury, begging for the loan of any choice
stallion, and promising its return at the end of the season. (20/43. Michel
'Des Haras' page 90.) There are numerous records at ancient periods in English
history of the importation of choice animals of various kinds, and of foolish
laws against their exportation. In the reigns of Henry VII. and VIII. it was
ordered that the magistrates, at Michaelmas, should scour the heaths and
commons, and destroy all mares beneath a certain size. (20/44. Mr. Baker
'History of the Horse' 'Veterinary' volume 13 page 423.) Some of our earlier
kings passed laws against the slaughtering rams of any good breed before they
were seven years old, so that they might have time to breed. In Spain Cardinal
Ximenes issued, in 1509, regulations on the SELECTION of good rams for
breeding. (20/45. M. l'Abbe Carlier in 'Journal de Physique' volume 24 1784
page 181; this memoir contains much information on the ancient selection of
sheep; and is my authority for rams not being killed young in England.)

The Emperor Akbar Khan before the year l600 is said to have "wonderfully
improved" his pigeons by crossing the breeds; and this necessarily implies
careful selection. About the same period the Dutch attended with the greatest
care to the breeding of these birds. Belon in 1555 says that good managers in
France examined the colour of their goslings in order to get geese of a white
colour and better kinds. Markham in 1631 tells the breeder "to elect the
largest and goodliest conies," and enters into minute details. Even with
respect to seeds of plants for the flower-garden, Sir J. Hanmer writing about
the year 1660 (20/46. 'Gardener's Chronicle' 1843 page 389.) says, in
"choosing seed, the best seed is the most weighty, and is had from the
lustiest and most vigorous stems;" and he then gives rules about leaving only
a few flowers on plants for seed; so that even such details were attended to
in our flower-gardens two hundred years ago. In order to show that selection
has been silently carried on in places where it would not have been expected,
I may add that in the middle of the last century, in a remote part of North
America, Mr. Cooper improved by careful selection all his vegetables, "so that
they were greatly superior to those of any other person. When his radishes,
for instance, are fit for use, he takes ten or twelve that he most approves,
and plants them at least 100 yards from others that blossom at the same time.
In the same manner he treats all his other plants, varying the circumstances
according to their nature." (20/47. 'Communications to Board of Agriculture'
quoted in Dr. Darwin 'Phytologia' 1800 page 451.)

In the great work on China published in the last century by the Jesuits, and
which is chiefly compiled from ancient Chinese encyclopaedias, it is said that
with sheep "improving the breed consists in choosing with particular care the
lambs which are destined for propagation, in nourishing them well, and in
keeping the flocks separate." The same principles were applied by the Chinese
to various plants and fruit-trees. (20/48. 'Memoire sur les Chinois' 1786 tome
11 page 55; tome 5 page 507.) An imperial edict recommends the choice of seed
of remarkable size; and selection was practised even by imperial hands, for it
is said that the Ya-mi, or imperial rice, was noticed at an ancient period in
a field by the Emperor Khang-hi, was saved and cultivated in his garden, and
has since become valuable from being the only kind which will grow north of
the Great Wall. (20/49. 'Recherches sur l'Agriculture des Chinois' par L.
D'Hervey Saint-Denys 1850 page 229. With respect to Khang-hi see Huc's
'Chinese Empire' page 311.) Even with flowers, the tree paeony (P. moutan) has
been cultivated, according to Chinese traditions, for 1400 years; between 200
and 300 varieties have been raised, which are cherished like tulips formerly
were by the Dutch. (20/50. Anderson in 'Linn. Transact.' volume 12 page 253.)

Turning now to semi-civilised people and to savages: it occurred to me, from
what I had seen of several parts of South America, where fences do not exist,
and where the animals are of little value, that there would be absolutely no
care in breeding or selecting them; and this to a large extent is true. Roulin
(20/51. 'Mem. de l'Acad.' (divers savants), tome 6 1835 page 333.), however,
describes in Columbia a naked race of cattle, which are not allowed to
increase, on account of their delicate constitution. According to Azara
(20/52. 'Des Quadrupedes du Paraguay' 1801 tome 2 pages 333, 371.) horses are
often born in Paraguay with curly hair; but, as the natives do not like them,
they are destroyed. On the other hand, Azara states that a hornless bull, born
in 1770, was preserved and propagated its race. I was informed of the
existence in Banda Oriental of a breed with reversed hair; and the
extraordinary niata cattle first appeared and have since been kept distinct in
La Plata. Hence certain conspicuous variations have been preserved, and others
have been habitually destroyed, in these countries, which are so little
favourable for careful selection. We have also seen that the inhabitants
sometimes introduce fresh cattle on their estates to prevent the evil effects
of close interbreeding. On the other hand, I have heard on reliable authority
that the Gauchos of the Pampas never take any pains in selecting the best
bulls or stallions for breeding; and this probably accounts for the cattle and
horses being remarkably uniform in character throughout the immense range of
the Argentine republic.

Looking to the Old World, in the Sahara Desert "The Touareg is as careful in
the selection of his breeding Mahari (a fine race of the dromedary) as the
Arab is in that of his horse. The pedigrees are handed down, and many a
dromedary can boast a genealogy far longer than the descendants of the Darley
Arabian." (20/53. 'The Great Sahara' by the Rev. H.B. Tristram 1860 page 238.)
According to Pallas the Mongolians endeavour to breed the Yaks or horse-tailed
buffaloes with white tails, for these are sold to the Chinese mandarins as
fly-flappers; and Moorcroft, about seventy years after Pallas, found that
white-tailed animals were still selected for breeding. (20/54. Pallas 'Act.
Acad. St. Petersburg' 1777 page 249. Moorcroft and Trebeck 'Travels in the
Himalayan Provinces' 1841.)

We have seen in the chapter on the Dog that savages in different parts of
North America and in Guiana cross their dogs with wild Canidae, as did the
ancient Gauls, according to Pliny. This was done to give their dogs strength
and vigour, in the same way as the keepers in large warrens now sometimes
cross their ferrets (as I have been informed by Mr. Yarrell) with the wild
polecat, "to give them more devil." According to Varro, the wild ass was
formerly caught and crossed with the tame animal to improve the breed, in the
same manner as at the present day the natives of Java sometimes drive their
cattle into the forests to cross with the wild Banteng (Bos sondaicus).
(20/55. Quoted from Raffles in the 'Indian Field' 1859 page 196: for Varro see
Pallas ut supra.) In Northern Siberia, among the Ostyaks, the dogs vary in
markings in different districts, but in each place they are spotted black and
white in a remarkably uniform manner (20/56. Erman 'Travels in Siberia'
English translation volume 1 page 453.); and from this fact alone we may infer
careful breeding, more especially as the dogs of one locality are famed
throughout the country for their superiority. I have heard of certain tribes
of Esquimaux who take pride in their teams of dogs being uniformly coloured.
In Guiana, as Sir H. Schomburgk informs me (20/57. See also 'Journal of R.
Geograph. Soc.' volume 13 part 1 page 65.), the dogs of the Turuma Indians are
highly valued and extensively bartered: the price of a good one is the same as
that given for a wife: they are kept in a sort of cage, and the Indians "take
great care when the female is in season to prevent her uniting with a dog of
an inferior description." The Indians told Sir Robert that, if a dog proved
bad or useless, he was not killed, but was left to die from sheer neglect.
Hardly any nation is more barbarous than the Fuegians, but I hear from Mr.
Bridges, the Catechist to the Mission, that, "when these savages have a large,
strong, and active bitch, they take care to put her to a fine dog, and even
take care to feed her well, that her young may be strong and well favoured."

In the interior of Africa, negroes, who have not associated with white men,
show great anxiety to improve their animals; they "always choose the larger
and stronger males for stock;" the Malakolo were much pleased at Livingstone's
promise to send them a bull, and some Bakalolo carried a live cock all the way
from Loanda into the interior. (20/58. Livingstone 'First Travels' pages 191,
439, 565; see also 'Expedition to the Zambesi' 1865 page 495, for an analogous
case respecting a good breed of goats.) At Falaba Mr. Winwood Reade noticed an
unusually fine horse, and the negro King informed him that "the owner was
noted for his skill in breeding horses." Further south on the same continent,
Andersson states that he has known a Damara give two fine oxen for a dog which
struck his fancy. The Damaras take great delight in having whole droves of
cattle of the same colour, and they prize their oxen in proportion to the size
of their horns. "The Namaquas have a perfect mania for a uniform team; and
almost all the people of Southern Africa value their cattle next to their
women, and take a pride in possessing animals that look high-bred. They rarely
or never make use of a handsome animal as a beast of burden." (20/59.
Andersson 'Travels in South Africa' pages 232, 318, 319.) The power of
discrimination which these savages possess is wonderful, and they can
recognise to which tribe any cattle belong. Mr. Andersson further informs me
that the natives frequently match a particular bull with a particular cow.

The most curious case of selection by semi-civilised people, or indeed by any
people, which I have found recorded, is that given by Garcilazo de la Vega, a
descendant of the Incas, as having been practised in Peru before the country
was subjugated by the Spaniards. (20/60. Dr. Vavasseur in 'Bull. de La Soc.
d'Acclimat.' tome 8 1861 page 136.) The Incas annually held great hunts, when
all the wild animals were driven from an immense circuit to a central point.
The beasts of prey were first destroyed as injurious. The wild Guanacos and
Vicunas were sheared; the old males and females killed, and the others set at
liberty. The various kinds of deer were examined; the old males and females
were likewise killed, "but the young females, with a certain number of males,
selected from the most beautiful and strong," were given their freedom. Here,
then, we have selection by man aiding natural selection. So that the Incas
followed exactly the reverse system of that which our Scottish sportsman are
accused of following, namely, of steadily killing the finest stags, thus
causing the whole race to degenerate. (20/61. 'The Natural History of Dee
Side' 1855 page 476.) In regard to the domesticated llamas and alpacas, they
were separated in the time of the Incas according to colour: and if by chance
one in a flock was born of the wrong colour, it was eventually put into
another flock.

In the genus Auchenia there are four forms,--the Guanaco and Vicuna, found
wild and undoubtedly distinct species; the Llama and Alpaca, known only in a
domesticated condition. These four animals appear so different, that most
naturalists, especially those who have studied these animals in their native
country, maintain that they are specifically distinct, notwithstanding that no
one pretends to have seen a wild llama or alpaca. Mr. Ledger, however, who has
closely studied these animals both in Peru and during their exportation to
Australia, and who has made many experiments on their propagation, adduces
arguments (20/62. 'Bull. de la Soc. d'Acclimat.' tome 7 1860 page 457.) which
seem to me conclusive, that the llama is the domesticated descendant of the
guanaco, and the alpaca of the vicuna. And now that we know that these animals
were systematically bred and selected many centuries ago, there is nothing
surprising in the great amount of change which they have undergone.

It appeared to me at one time probable that, though ancient and semi-civilised
people might have attended to the improvement of their more useful animals in
essential points, yet that they would have disregarded unimportant characters.
But human nature is the same throughout the world: fashion everywhere reigns
supreme, and man is apt to value whatever he may chance to possess. We have
seen that in South America the niata cattle, which certainly are not made
useful by their shortened faces and upturned nostrils, have been preserved.
The Damaras of South Africa value their cattle for uniformity of colour and
enormously long horns. And I will now show that there is hardly any
peculiarity in our most useful animals which, from fashion, superstition, or
some other motive, has not been valued, and consequently preserved. With
respect to cattle, "an early record," according to Youatt (20/63. 'Cattle'
page 48.) "speaks of a hundred white cows with red ears being demanded as a
compensation by the princes of North and South Wales. If the cattle were of a
dark or black colour, 150 were to be presented." So that colour was attended
to in Wales before its subjugation by England. In Central Africa, an ox that
beats the ground with its tail is killed; and in South Africa some of the
Damaras will not eat the flesh of a spotted ox. The Kaffirs value an animal
with a musical voice; and "at a sale in British Kaffraria the low "of a heifer
excited so much admiration that a sharp competition sprung up for her
possession, and she realised a considerable price." (20/64. Livingstone
'Travels' page 576; Andersson 'Lake Ngami' 1856 page 222. With respect to the
sale in Kaffraria see 'Quarterly Review' 1860 page 139.) With respect to
sheep, the Chinese prefer rams without horns; the Tartars prefer them with
spirally wound horns, because the hornless are thought to lose courage.
(20/65. 'Memoire sur les Chinois' by the Jesuits 1786 tome 11 page 57.) Some
of the Damaras will not eat the flesh of hornless sheep. In regard to horses,
at the end of the fifteenth century animals of the colour described as liart
pomme were most valued in France. The Arabs have a proverb, "Never buy a horse
with four white feet, for he carries his shroud with him" (20/66. F. Michel
'Des Haras' pages 47, 50.); the Arabs also, as we have seen, despise dun-
coloured horses. So with dogs, Xenophon and others at an ancient period were
prejudiced in favour of certain colours; and "white or slate-coloured hunting
dogs were not esteemed." (20/67. Col. Hamilton Smith 'Dogs' in 'Nat. Lib.'
volume 10 page 103.)

Turning to poultry, the old Roman gourmands thought that the liver of a white
goose was the most savoury. In Paraguay black-skinned fowls are kept because
they are thought to be more productive, and their flesh the most proper for
invalids. (20/68. Azara 'Quadrupedes du Paraguay' tome 2 page 324.) In Guiana,
as I am informed by Sir R. Schomburgk, the aborigines will not eat the flesh
or eggs of the fowl, but two races are kept distinct merely for ornament. In
the Philippines, no less than nine sub-varieties of the game-cock are kept and
named, so that they must be separately bred.

At the present time in Europe, the smallest peculiarities are carefully
attended to in our most useful animals, either from fashion, or as a mark of
purity of blood. Many examples could be given; two will suffice. "In the
Western counties of England the prejudice against a white pig is nearly as
strong as against a black one in Yorkshire." In one of the Berkshire sub-
breeds, it is said, "the white should be confined to four white feet, a white
spot between the eyes, and a few white hairs behind each shoulder." Mr.
Saddler possessed three hundred pigs, every one of which was marked in this
manner." (20/69. Sidney's edition of Youatt 1860 pages 24, 25.) Marshall,
towards the close of the last century, in speaking of a change in one of the
Yorkshire breeds of cattle, says the horns have been considerably modified, as
"a clean, small, sharp horn has been FASHIONABLE for the last twenty years."
(20/70. 'Rural Economy of Yorkshire' volume 2 page 182.) In a part of Germany
the cattle of the Race de Gfoehl are valued for many good qualities, but they
must have horns of a particular curvature and tint, so much so that mechanical
means are applied if they take a wrong direction; but the inhabitants
"consider it of the highest importance that the nostrils of the bull should be
flesh-coloured, and the eyelashes light; this is an indispensable condition. A
calf with blue nostrils would not be purchased, or purchased at a very low
price." (20/71. Moll et Gayot 'Du Boeuf' 1860 page 547.) Therefore let no man
say that any point or character is too trifling to be methodically attended to
and selected by breeders.

UNCONSCIOUS SELECTION.

By this term I mean, as already more than once explained, the preservation by
man of the most valued, and the destruction of the least valued individuals,
without any conscious intention on his part of altering the breed. It is
difficult to offer direct proofs of the results which follow from this kind of
selection; but the indirect evidence is abundant. In fact, except that in the
one case man acts intentionally, and in the other unintentionally, there is
little difference between methodical and unconscious selection. In both cases
man preserves the animals which are most useful or pleasing to him, and
destroys or neglects the others. But no doubt a far more rapid result follows
from methodical than from unconscious selection. The "roguing" of plants by
gardeners, and the destruction by law in Henry VIII.'s reign of all under-
sized mares, are instances of a process the reverse of selection in the
ordinary sense of the word, but leading to the same general result. The
influence of the destruction of individuals having a particular character is
well shown by the necessity of killing every lamb with a trace of black about
it, in order to keep the flock white; or again, by the effects on the average
height of the men of France of the destructive wars of Napoleon, by which many
tall men were killed, the short ones being left to be the fathers of families.
This at least is the conclusion of some of those who have closely studied the
effects of the conscription; and it is certain that since Napoleon's time the
standard for the army has been lowered two or three times.

Unconscious selection blends with methodical, so that it is scarcely possible
to separate them. When a fancier long ago first happened to notice a pigeon
with an unusually short beak, or one with the tail-feathers unusually
developed, although he bred from these birds with the distinct intention of
propagating the variety, yet he could not have intended to make a short-faced
tumbler or a fantail, and was far from knowing that he had made the first step
towards this end. If he could have seen the final result, he would have been
struck with astonishment, but, from what we know of the habits of fanciers,
probably not with admiration. Our English carriers, barbs, and short-faced
tumblers have been greatly modified in the same manner, as we may infer both
from the historical evidence given in the chapters on the Pigeon, and from the
comparison of birds brought from distant countries.

So it has been with dogs; our present fox-hounds differ from the old English
hound; our greyhounds have become lighter: the Scotch deer-hound has been
modified, and is now rare. Our bulldogs differ from those which were formerly
used for baiting bulls. Our pointers and Newfoundlands do not closely resemble
any native dog now found in the countries whence they were brought. These
changes have been effected partly by crosses; but in every case the result has
been governed by the strictest selection. Nevertheless, there is no reason to
suppose that man intentionally and methodically made the breeds exactly what
they now are. As our horses became fleeter, and the country more cultivated
and smoother, fleeter fox-hounds were desired and produced, but probably
without any one distinctly foreseeing what they would become. Our pointers and
setters, the latter almost certainly descended from large spaniels, have been
greatly modified in accordance with fashion and the desire for increased
speed. Wolves have become extinct, and so has the wolf-dog; deer have become
rarer, bulls are no longer baited, and the corresponding breeds of the dog
have answered to the change. But we may feel almost sure that when, for
instance, bulls were no longer baited, no man said to himself, I will now
breed my dogs of smaller size, and thus create the present race. As
circumstances changed, men unconsciously and slowly modified their course of
selection.

With racehorses selection for swiftness has been followed methodically, and
our horses now easily surpass their progenitors. The increased size and
different appearance of the English racehorse led a good observer in India to
ask," Could any one in this year of 1856, looking at our racehorses, conceive
that they were the result of the union of the Arab horse and the African
mare?" (20/72. 'The India Sporting Review' volume 2 page 181; 'The Stud Farm'
by Cecil page 58.) This change has, it is probable, been largely effected
through unconscious selection, that is, by the general wish to breed as fine
horses as possible in each generation, combined with training and high
feeding, but without any intention to give to them their present appearance.
According to Youatt (20/73. 'The Horse' page 22.), the introduction in Oliver
Cromwell's time of three celebrated Eastern stallions speedily affected the
English breed; "so that Lord Harleigh, one of the old school, complained that
the great horse was fast disappearing." This is an excellent proof how
carefully selection must have been attended to; for without such care, all
traces of so small an infusion of Eastern blood would soon have been absorbed
and lost. Notwithstanding that the climate of England has never been esteemed
particularly favourable to the horse, yet long-continued selection, both
methodical and unconscious, together with that practised by the Arabs during a
still longer and earlier period, has ended in giving us the best breed of
horses in the world. Macaulay (20/74. 'History of England' volume 1 page 316.)
remarks, "Two men whose authority on such subjects was held in great esteem,
the Duke of Newcastle and Sir John Fenwick, pronounced that the meanest hack
ever imported from Tangier would produce a finer progeny than could be
expected from the best sire of our native breed. They would not readily have
believed that a time would come when the princes and nobles of neighbouring
lands would be as eager to obtain horses from England as ever the English had
been to obtain horses from Barbary."

The London dray-horse, which differs so much in appearance from any natural
species, and which from its size has so astonished many Eastern princes, was
probably formed by the heaviest and most powerful animals having been selected
during many generations in Flanders and England, but without the least
intention or expectation of creating a horse such as we now see. If we go back
to an early period of history, we behold in the antique Greek statues, as
Schaaffhausen has remarked (20/75. 'Ueber Bestandigkeit der Arten.'), a horse
equally unlike a race or dray horse, and differing from any existing breed.

The results of unconscious selection, in an early stage, are well shown in the
difference between the flocks descended from the same stock, but separately
reared by careful breeders. Youatt gives an excellent instance of this fact in
the sheep belonging to Messrs. Buckley and Burgess, which "have been purely
bred from the original stock of Mr. Bakewell for upwards of fifty years. There
is not a suspicion existing in the mind of any one at all acquainted with the
subject that the owner of either flock has deviated in any one instance from
the pure blood of Mr. Bakewell's flock; yet the difference between the sheep
possessed by these two gentlemen is so great, that they have the appearance of
being quite different varieties." (20/76. 'Youatt on Sheep' page 315.) I have
seen several analogous and well marked cases with pigeons: for instance, I had
a family of barbs descended from those long bred by Sir J. Sebright, and
another family long bred by another fancier, and the two families plainly
differed from each other. Nathusius--and a more competent witness could not be
cited--observes that, though the Shorthorns are remarkably uniform in
appearance (except in colour), yet the individual character and wishes of each
breeder become impressed on his cattle, so that different herds differ
slightly from one another. (20/77. 'Ueber Shorthorn Rindvieh' 1857 s. 51.) The
Hereford cattle assumed their present well-marked character soon after the
year 1769, through careful selection by Mr. Tomkins (20/78. Low 'Domesticated
Animals' 1845 page 363.) and the breed has lately split into two strains--one
strain having a white face, and differing slightly, it is said (20/79.
'Quarterly Review' 1849 page 392.), in some other points: but there is no
reason to believe that this split, the origin of which is unknown, was
intentionally made; it may with much more probability be attributed to
different breeders having attended to different points. So again, the
Berkshire breed of swine in the year 1810 had greatly changed from what it was
in 1780; and since 1810 at least two distinct sub-breeds have arisen bearing
the same name. (20/80. H. von Nathusius 'Vorstudien...Schweineschadel' 1864 s
140.) Keeping in mind how rapidly all animals increase, and that some must be
annually slaughtered and some saved for breeding, then, if the same breeder
during a long course of years deliberately settles which shall be saved and
which shall be killed, it is almost inevitable that his individual turn of
mind will influence the character of his stock, without his having had any
intention to modify the breed.

Unconscious selection in the strictest sense of the word, that is, the saving
of the more useful animals and the neglect or slaughter of the less useful,
without any thought of the future, must have gone on occasionally from the
remotest period and amongst the most barbarous nations. Savages often suffer
from famines, and are sometimes expelled by war from their own homes. In such
cases it can hardly be doubted that they would save their most useful animals.
When the Fuegians are hard pressed by want, they kill their old women for food
rather than their dogs; for, as we were assured, "old women no use--dogs catch
otters." The same sound sense would surely lead them to preserve their more
useful dogs when still harder pressed by famine. Mr. Oldfield, who has seen so
much of the aborigines of Australia, informs me that "they are all very glad
to get a European kangaroo dog, and several instances have been known of the
father killing his own infant that the mother might suckle the much-prized
puppy." Different kinds of dogs would be useful to the Australian for hunting
opossums and kangaroos, and to the Fuegian for catching fish and otters; and
the occasional preservation in the two countries of the most useful animals
would ultimately lead to the formation of two widely distinct breeds.

With plants, from the earliest dawn of civilisation, the best variety which
was known would generally have been cultivated at each period and its seeds
occasionally sown; so that there will have been some selection from an
extremely remote period, but without any prefixed standard of excellence or
thought of the future. We at the present day profit by a course of selection
occasionally and unconsciously carried on during thousands of years. This is
proved in an interesting manner by Oswald Heer's researches on the lake-
inhabitants of Switzerland, as given in a former chapter; for he shows that
the grain and seed of our present varieties of wheat, barley, oats, peas,
beans, lentils, and poppy, exceed in size those which were cultivated in
Switzerland during the Neolithic and Bronze periods. These ancient people,
during the Neolithic period, possessed also a crab considerably larger than
that now growing wild on the Jura. (20/81. See also Dr. Christ in Rutimeyer's
'Pfahlbauten' 1861 s. 226.) The pears described by Pliny were evidently
extremely inferior in quality to our present pears. We can realise the effects
of long-continued selection and cultivation in another way, for would any one
in his senses expect to raise a first-rate apple from the seed of a truly wild
crab, or a luscious melting pear from the wild pear? Alphonse de Candolle
informs me that he has lately seen on an ancient mosaic at Rome a
representation of the melon; and as the Rotnans, who were such gourmands, are
silent on this fruit, he infers that the melon has been greatly ameliorated
since the classical period.

Coming to later times, Buffon (20/82. The passage is given 'Bull. Soc.
d'Acclimat.' 1858 page 11.) on comparing the flowers, fruit, and vegetables
which were then cultivated with some excellent drawings made a hundred and
fifty years previously, was struck with surprise at the great improvement
which had been effected; and remarks that these ancient flowers and vegetables
would now be rejected, not only by a florist but by a village gardener. Since
the time of Buffon the work of improvement has steadily and rapidly gone on.
Every florist who compares our present flowers with those figured in books
published not long since, is astonished at the change. A well-known amateur
(20/83. 'Journal of Horticulture' 1862 page 394.), in speaking of the
varieties of Pelargonium raised by Mr. Garth only twenty-two years before,
remarks, "What a rage they excited: surely we had attained perfection, it was
said; and now not one of the flowers of those days will be looked at. But none
the less is the debt of gratitude which we owe to those who saw what was to be
done, and did it." Mr. Paul, the well-known horticulturist, in writing of the
same flower (20/84. 'Gardener's Chronicle' 1857 page 85.), says he remembers
when young being delighted with the portraits in Sweet's work; "but what are
they in point of beauty compared with the Pelargoniums of this day? Here again
nature did not advance by leaps; the improvement was gradual, and if we had
neglected those very gradual advances, we must have foregone the present grand
results." How well this practical horticulturist appreciates and illustrates
the gradual and accumulative force of selection! The Dahlia has advanced in
beauty in a like manner; the line of improvement being guided by fashion, and
by the successive modifications which the flower slowly underwent. (20/85. See
Mr. Wildman's address to the Floricult. Soc. in 'Gardener's Chronicle' 1843
page 86.) A steady and gradual change has been noticed in many other flowers:
thus an old florist (20/86. 'Journal of Horticulture' October 24, 1865 page
239.), after describing the leading varieties of the Pink which were grown in
1813 adds, "the pinks of those days would now be scarcely grown as border-
flowers." The improvement of so many flowers and the number of the varieties
which have been raised is all the more striking when we hear that the earliest
known flower-garden in Europe, namely at Padua, dates only from the year 1545.
(20/87. Prescott 'Hist. of Mexico' volume 2 page 61.)

EFFECTS OF SELECTION, AS SHOWN BY THE PARTS MOST VALUED BY MAN PRESENTING THE
GREATEST AMOUNT OF DIFFERENCE.

The power of long-continued selection, whether methodical or unconscious, or
both combined, is well shown in a general way, namely, by the comparison of
the differences between the varieties of distinct species, which are valued
for different parts, such as for the leaves, or stems, or tubers, the seed, or
fruit, or flowers. Whatever part man values most, that part will be found to
present the greatest amount of difference. With trees cultivated for their
fruit, Sageret remarks that the fruit is larger than in the parent-species,
whilst with those cultivated for the seed, as with nuts, walnuts, almonds,
chestnuts, etc., it is the seed itself which is larger; and he accounts for
this fact by the fruit in the one case, and by the seed in the other, having
been carefully attended to and selected during many ages. Gallesio has made
the same observation. Godron insists on the diversity of the tuber in the
potato, of the bulb in the onion, and of the fruit in the melon; and on the
close similarity of the other parts in these same plants. (20/88. Sagaret
'Pomologie Physiologique' 1830 page 47; Gallesio 'Teoria della Riproduzione'
1816 page 88; Godron 'De l'Espece' 1859 tome 2 pages 63, 67, 70. In my tenth
and eleventh chapters I have given details on the potato; and I can confirm
similar remarks with respect to the onion. I have also shown how far Naudin
concurs in regard to the varieties of the melon.)

In order to judge how far my own impression on this subject was correct, I
cultivated numerous varieties of the same species close to one another. The
comparison of the amount of difference between widely different organs is
necessarily vague; I will therefore give the results in only a few cases. We
have previously seen in the ninth chapter how greatly the varieties of the
cabbage differ in their foliage and stems, which are the selected parts, and
how closely they resemble one another in their flowers, capsules, and seeds.
In seven varieties of the radish, the roots differed greatly in colour and
shape, but no difference whatever could be detected in their foliage, flowers,
or seeds. Now what a contrast is presented, if we compare the flowers of the
varieties of these two plants with those of any species cultivated in our
flower-gardens for ornament; or if we compare their seeds with those of the
varieties of maize, peas, beans, etc., which are valued and cultivated for
their seeds. In the ninth chapter it was shown that the varieties of the pea
differ but little except in the tallness of the plant, moderately in the shape
of the pod, and greatly in the pea itself, and these are all selected points.
The varieties, however, of the Pois sans parchemin differ much more in their
pods, and these are eaten and valued. I cultivated twelve varieties of the
common bean; one alone, the Dwarf Fan, differed considerably in general
appearance; two differed in the colour of their flowers, one being an albino,
and the other being wholly instead of partially purple; several differed
considerably in the shape and size of the pod, but far more in the bean
itself, and this is the valued and selected part. Toker's bean, for instance,
is twice-and-a-half as long and broad as the horse-bean, and is much thinner
and of a different shape.

The varieties of the gooseberry, as formerly described, differ much in their
fruit, but hardly perceptibly in their flowers or organs of vegetation. With
the plum, the differences likewise appear to be greater in the fruit than in
the flowers or leaves. On the other hand, the seed of the strawberry, which
corresponds with the fruit of the plum, differs hardly at all; whilst every
one knows how greatly the fruit--that is, the enlarged receptacle--differs in
several varieties. In apples, pears, and peaches the flowers and leaves differ
considerably, but not, as far as I can judge, in proportion with the fruit.
The Chinese double-flowering peaches, on the other hand, show that varieties
of this tree have been formed, which differ more in flower than in fruit. If,
as is highly probable, the peach is the modified descent of the almond, a
surprising amount of change has been effected in the same species, in the
fleshy covering of the former and in the kernels of the latter.

When parts stand in close relationship to each other, such as the seed and the
fleshy covering of the fruit (whatever its homological nature may be), changes
in the one are usually accompanied by modifications in the other, though not
necessarily to the same degree. With the plum-tree, for instance, some
varieties produce plums which are nearly alike, but include stones extremely
dissimilar in shape; whilst conversely other varieties produce dissimilar
fruit with barely distinguishable stones; and generally the stones, though
they have never been subjected to selection, differ greatly in the several
varieties of the plum. In other cases organs which are not manifestly related,
through some unknown bond vary together, and are consequently liable, without
any intention on man's part, to be simultaneously acted on by selection. Thus
the varieties of the stock (Matthiola) have been selected solely for the
beauty of their flowers, but the seeds differ greatly in colour and somewhat
in size. Varieties of the lettuce have been selected solely on account of
their leaves, yet produce seeds which likewise differ in colour. Generally,
through the law of correlation, when a variety differs greatly from its
fellow-varieties in any one character, it differs to a certain extent in
several other characters. I observed this fact when I cultivated together many
varieties of the same species, for I used first to make a list of the
varieties which differed most from each other in their foliage and manner of
growth, afterwards of those that differed most in their flowers, then in their
seed-capsules, and lastly in their mature seed; and I found that the same
names generally occurred in two, three, or four of the successive lists.
Nevertheless the greatest amount of difference between the varieties was
always exhibited, as far as I could judge, by that part or organ for which the
plant was cultivated.

When we bear in mind that each plant was at first cultivated because useful to
man, and that its variation was a subsequent, often a long subsequent, event,
we cannot explain the greater amount of diversity in the valuable parts by
supposing that species endowed with an especial tendency to vary in any
particular manner were originally chosen. We must attribute the result to the
variations in these parts having been successively preserved, and thus
continually augmented; whilst other variations, excepting such as inevitably
appeared through correlation, were neglected and lost. We may therefore infer
that most plants might be made, through long-continued selection, to yield
races as different from one another in any character as they now are in those
parts for which they are valued and cultivated.

With animals we see nothing of the same kind; but a sufficient number of
species have not been domesticated for a fair comparison. Sheep are valued for
their wool, and the wool differs much more in the several races than the hair
in cattle. Neither sheep, goats, European cattle, nor pigs are valued for
their fleetness or strength; and we do not possess breeds differing in these
respects like the racehorse and dray-horse. But fleetness and strength are
valued in camels and dogs; and we have with the former the swift dromedary and
heavy camel; with the latter the greyhound and mastiff. But dogs are valued
even in a higher degree for their mental qualities and senses; and every one
knows how greatly the races differ in these respects. On the other hand, where
the dog is kept solely to serve for food, as in the Polynesian islands and
China, it is described as an extremely stupid animal. (20/89. Godron 'De
l'Espece' tome 2 page 27.) Blumenbach remarks that "many dogs, such as the
badger-dog, have a build so marked and so appropriate for particular purposes,
that I should find it very difficult to persuade myself that this astonishing
figure was an accidental consequence of degeneration." (20/90. 'The
Anthropological Treatises of Blumenbach' 1856 page 292.) Had Blumenbach
reflected on the great principle of selection, he would not have used the term
degeneration, and he would not have been astonished that dogs and other
animals should become excellently adapted for the service of man.

On the whole we may conclude that whatever part or character is most valued--
whether the leaves, stems, tubers, bulbs, flowers, fruit, or seed of plants,
or the size, strength, fleetness, hairy covering, or intellect of animals--
that character will almost invariably be found to present the greatest amount
of difference both in kind and degree. And this result may be safely
attributed to man having preserved during a long course of generations the
variations which were useful to him, and neglected the others.

I will conclude this chapter by some remarks on an important subject. With
animals such as the giraffe, of which the whole structure is admirably co-
ordinated for certain purposes, it has been supposed that all the parts must
have been simultaneously modified; and it has been argued that, on the
principle of natural selection, this is scarcely possible. But in thus
arguing, it has been tacitly assumed that the variations must have been abrupt
and great. No doubt, if the neck of a ruminant were suddenly to become greatly
elongated, the fore limbs and back would have to be simultaneously
strengthened and modified; but it cannot be denied that an animal might have
its neck, or head, or tongue, or fore-limbs elongated a very little without
any corresponding modification in other parts of the body; and animals thus
slightly modified would, during a dearth, have a slight advantage, and be
enabled to browse on higher twigs, and thus survive. A few mouthfuls more or
less every day would make all the difference between life and death. By the
repetition of the same process, and by the occasional intercrossing of the
survivors, there would be some progress, slow and fluctuating though it would
be, towards the admirably coordinated structure of the giraffe. If the short-
faced tumbler-pigeon, with its small conical beak, globular head, rounded
body, short wings, and small feet--characters which appear all in harmony--had
been a natural species, its whole structure would have been viewed as well
fitted for its life; but in this case we know that inexperienced breeders are
urged to attend to point after point, and not to attempt improving the whole
structure at the same time. Look at the greyhound, that perfect image of
grace, symmetry, and vigour; no natural species can boast of a more admirably
co-ordinated structure, with its tapering head, slim body, deep chest, tucked-
up abdomen, rat-like tail, and long muscular limbs, all adapted for extreme
fleetness, and for running down weak prey. Now, from what we see of the
variability of animals, and from what we know of the method which different
men follow in improving their stock--some chiefly attending to one point,
others to another point, others again correcting defects by crosses, and so
forth--we may feel assured that if we could see the long line of ancestors of
a first-rate greyhound up to its wild wolf-like progenitor, we should behold
an infinite number of the finest gradations, sometimes in one character and
sometimes in another, but all leading towards our present perfect type. By
small and doubtful steps such as these, nature, as we may confidently believe,
has progressed, on her grand march of improvement and development.

A similar line of reasoning is as applicable to separate organs as to the
whole organisation. A writer (20/91. Mr. J.J. Murphy in his opening address to
the Belfast Nat. Hist. Soc. as given in the 'Belfast Northern Whig' November
19, 1866. Mr. Murphy here follows the line of argument against my views
previously and more cautiously given by the Rev. C. Pritchard, Pres. Royal
Astronomical Soc., in his sermon Appendix page 33 preached before the British
Association at Nottingham 1866.) has recently maintained that "it is probably
no exaggeration to suppose that in order to improve such an organ as the eye
at all, it must be improved in ten different ways at once. And the
improbability of any complex organ being produced and brought to perfection in
any such way is an improbability of the same kind and degree as that of
producing a poem or a mathematical demonstration by throwing letters at random
on a table." If the eye were abruptly and greatly modified, no doubt many
parts would have to be simultaneously altered, in order that the organ should
remain serviceable.

But is this the case with smaller changes? There are persons who can see
distinctly only in a dull light, and this condition depends, I believe, on the
abnormal sensitiveness of the retina, and is known to be inherited. Now if a
bird, for instance, receive some great advantage from seeing well in the
twilight, all the individuals with the most sensitive retina would succeed
best and be the most likely to survive; and why should not all those which
happened to have the eye itself a little larger, or the pupil capable of
greater dilatation, be likewise preserved, whether or not these modifications
were strictly simultaneous? These individuals would subsequently intercross
and blend their respective advantages. By such slight successive changes, the
eye of a diurnal bird would be brought into the condition of that of an owl,
which has often been advanced as an excellent instance of adaptation. Short-
sight, which is often inherited, permits a person to see distinctly a minute
object at so near a distance that it would be indistinct to ordinary eyes; and
here we have a capacity which might be serviceable under certain conditions,
abruptly gained. The Fuegians on board the Beagle could certainly see distant
objects more distinctly than our sailors with all their long practice; I do
not know whether this depends upon sensitiveness or on the power of adjustment
in the focus; but this capacity for distant vision might, it is probable, be
slightly augmented by successive modifications of either kind. Amphibious
animals which are enabled to see both in the water and in the air, require and
possess, as M. Plateau has shown (20/92. On the Vision of Fishes and Amphibia,
translated in 'Annals and Mag. of Nat. Hist.' volume 18 1866 page 469.), eyes
constructed on the following plan: "the cornea is always flat, or at least
much flattened in the front of the crystalline and over a space equal to the
diameter of that lens, whilst the lateral portions may be much curved." The
crystalline is very nearly a sphere, and the humours have nearly the same
density as water. Now as a terrestrial animal became more and more aquatic in
its habits, very slight changes, first in the curvature of the cornea or
crystalline, and then in the density of the humours, or conversely, might
successively occur, and would be advantageous to the animal whilst under
water, without serious detriment to its power of vision in the air. It is of
course impossible to conjecture by what steps the fundamental structure of the
eye in the Vertebrata was originally acquired, for we know nothing about this
organ in the first progenitors of the class. With respect to the lowest
animals in the scale, the transitional states through which the eye at first
probably passed, can by the aid of analogy be indicated, as I have attempted
to show in my 'Origin of Species.' (20/93. Sixth edition 1872 page 144.)


CHAPTER 2.XXI.

SELECTION, continued.

NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS.
CHARACTERS WHICH APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE.
CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN.
FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE CONDITIONS.
CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE.
THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE.
WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE NOT FORMED.
HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION.
TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT,
LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE.
CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE
ALREADY VARIED.
DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE VARIETIES, LEADS
TO DISTINCTNESS IN OUR DOMESTIC RACES.
LIMIT TO THE POWER OF SELECTION.
LAPSE OF TIME IMPORTANT.
MANNER IN WHICH DOMESTIC RACES HAVE ORIGINATED.
SUMMARY.

NATURAL SELECTION, OR THE SURVIVAL OF THE FITTEST, AS AFFECTING DOMESTIC
PRODUCTIONS.

We know little on this head. But as animals kept by savages have to provide
throughout the year their own food either entirely or to a large extent, it
can hardly be doubted that in different countries, varieties differing in
constitution and in various characters would succeed best, and so be naturally
selected. Hence perhaps it is that the few domesticated animals kept by
savages partake, as has been remarked by more than one writer, of the wild
appearance of their masters, and likewise resemble natural species. Even in
long-civilised countries, at least in the wilder parts, natural selection must
act on our domestic races. It is obvious that varieties having very different
habits, constitution, and structure, would succeed best on mountains and on
rich lowland pastures. For example, the improved Leicester sheep were formerly
taken to the Lammermuir Hills; but an intelligent sheep-master reported that
"our coarse lean pastures were unequal to the task of supporting such heavy-
bodied sheep; and they gradually dwindled away into less and less bulk: each
generation was inferior to the preceding one; and when the spring was severe,
seldom more than two-thirds of the lambs survived the ravages of the storms."
(21/1. Quoted by Youatt on 'Sheep' page 325. See also Youatt on 'Cattle' pages
62, 69.) So with the mountain cattle of North Wales and the Hebrides, it has
been found that they could not withstand being crossed with the larger and
more delicate lowland breeds. Two French naturalists, in describing the horses
of Circassia, remark that, subjected as they are to extreme vicissitudes of
climate, having to search for scanty pasture, and exposed to constant danger
from wolves, the strongest and most vigorous alone survive. (21/2. MM.
Lherbette and De Quatrefages in 'Bull. Soc. d'Acclimat.' tome 8 1861 page
311.)

Every one must have been struck with the surpassing grace, strength, and
vigour of the Game-cock, with its bold and confident air, its long, yet firm
neck, compact body, powerful and closely pressed wings, muscular thighs,
strong beak massive at the base, dense and sharp spurs set low on the legs for
delivering the fatal blow, and its compact, glossy, and mail-like plumage
serving as a defence. Now the English game-cock has not only been improved
during many years by man's careful selection, but in addition, as Mr.
Tegetmeier has remarked (21/3. 'The Poultry Book' 1866 page 123. Mr.
Tegetmeier, 'The Homing or Carrier Pigeon' 1871 pages 45-58.), by a kind of
natural selection, for the strongest, most active and courageous birds have
stricken down their antagonists in the cockpit, generation after generation,
and have subsequently served as the progenitors of their race. The same kind
of double selection has come into play with the carrier pigeon, for during
their training the inferior birds fail to return home and are lost, so that
even without selection by man only the superior birds propagate their race.

In Great Britain, in former times, almost every district had its own breed of
cattle and sheep; "they were indigenous to the soil, climate, and pasturage of
the locality on which they grazed: they seemed to have been formed for it and
by it." (21/4. 'Youatt on Sheep' page 312.) But in this case we are quite
unable to disentangle the effects of the direct action of the conditions of
life,--of use or habit--of natural selection--and of that kind of selection
which we have seen is occasionally and unconsciously followed by man even
during the rudest periods of history.

Let us now look to the action of natural selection on special characters.
Although nature is difficult to resist, yet man often strives against her
power, and sometimes with success. From the facts to be given, it will also be
seen that natural selection would powerfully affect many of our domestic
productions if left unprotected. This is a point of much interest, for we thus
learn that differences apparently of very slight importance would certainly
determine the survival of a form when forced to struggle for its own
existence. It may have occurred to some naturalists, as it formerly did to me,
that, though selection acting under natural conditions would determine the
structure of all important organs, yet that it could not affect characters
which are esteemed by us of little importance; but this is an error to which
we are eminently liable, from our ignorance of what characters are of real
value to each living creature.

When man attempts to make a breed with some serious defect in structure, or in
the mutual relation of the several parts, he will partly or completely fail,
or encounter much difficulty; he is in fact resisted by a form of natural
selection. We have seen that an attempt was once made in Yorkshire to breed
cattle with enormous buttocks, but the cows perished so often in bringing
forth their calves, that the attempt had to be given up. In rearing short-
faced tumblers, Mr. Eaton says (21/5. 'Treatise on the Almond Tumbler' 1851
page 33.), "I am convinced that better head and beak birds have perished in
the shell than ever were hatched; the reason being that the amazingly short-
faced bird cannot reach and break the shell with its beak, and so perishes."
Here is a more curious case, in which natural selection comes into play only
at long intervals of time: during ordinary seasons the Niata cattle can graze
as well as others, but occasionally, as from 1827 to 1830 the plains of La
Plata suffer from long-continued droughts and the pasture is burnt up; at such
times common cattle and horses perish by the thousand, but many survive by
browsing on twigs, reeds, etc.; this the Niata cattle cannot so well effect
from their upturned jaws and the shape of their lips; consequently, if not
attended to, they perish before the other cattle. In Columbia, according to
Roulin, there is a breed of nearly hairless cattle, called Pelones; these
succeed in their native hot district, but are found too tender for the
Cordillera; in this case, however, natural selection determines only the range
of the variety. It is obvious that a host of artificial races could never
survive in a state of nature;--such as Italian greyhounds,--hairless and
almost toothless Turkish dogs,--fantail pigeons, which cannot fly well against
a strong wind,--barbs and Polish fowls, with their vision impeded by their eye
wattles and great topknots,--hornless bulls and rams, which consequently
cannot cope with other males, and thus have a poor chance of leaving
offspring,--seedless plants, and many other such cases.

Colour is generally esteemed by the systematic naturalist as unimportant: let
us, therefore, see how far it indirectly affects our domestic productions, and
how far it would affect them if they were left exposed to the full force of
natural selection. In a future chapter I shall have to show that
constitutional peculiarities of the strangest kind, entailing liability to the
action of certain poisons, are correlated with the colour of the skin. I will
here give a single case, on the high authority of Professor Wyman; he informs
me that, being surprised at all the pigs in a part of Virginia being black, he
made inquiries, and ascertained that these animals feed on the roots of the
Lachnanthes tinctoria, which colours their bones pink, and, excepting in the
case of the black varieties, causes the hoofs to drop off. Hence, as one of
the squatters remarked, "we select the black members of the litter for
raising, as they alone have a good chance of living." So that here we have
artificial and natural selection working hand in hand. I may add that in the
Tarentino the inhabitants keep black sheep alone, because the Hypericum
crispum abounds there; and this plant does not injure black sheep, but kills
the white ones in about a fortnight's time. (21/6. Dr. Heusinger
'Wochenschrift fur die Hei1kunde' Berlin 1846 s. 279.)

Complexion, and liability to certain diseases, are believed to run together in
man and the lower animals. Thus white terriers suffer more than those of any
other colour from the fatal distemper. (21/7. Youatt on the 'Dog' page 232.)
In North America plum-trees are liable to a disease which Downing (21/8. 'The
Fruit-trees of America' 1845 page 270: for peaches page 466.) believes is not
caused by insects; the kinds bearing purple fruit are most affected, "and we
have never known the green or yellow fruited varieties infected until the
other sorts had first become filled with the knots." On the other hand,
peaches in North America suffer much from a disease called the "yellows,"
which seems to be peculiar to that continent, and more than nine-tenths of the
victims, "when the disease first appeared, were the yellow-fleshed peaches.
The white-fleshed kinds are much more rarely attacked; in some parts of the
country never." In Mauritius, the white sugar-canes have of late years been so
severely attacked by a disease, that many planters have been compelled to give
up growing this variety (although fresh plants were imported from China for
trial), and cultivate only red canes. (21/9. 'Proc. Royal Soc. of Arts and
Sciences of Mauritius' 1852 page 135.) Now, if these plants had been forced to
struggle with other competing plants and enemies, there cannot be a doubt that
the colour of the flesh or skin of the fruit, unimportant as these characters
are considered, would have rigorously determined their existence.

Liability to the attacks of parasites is also connected with colour. White
chickens are certainly more subject than dark-coloured chickens to the
"gapes," which is caused by a parasitic worm in the trachea. (21/10.
'Gardener's Chronicle' 1856 page 379.) On the other hand, experience has shown
that in France the caterpillars which produce white cocoons resist the deadly
fungus better than those producing yellow cocoons. (21/11. Quatrefages
'Maladies Actuelles du Ver a Soie' 1859 pages 12, 214.) Analogous facts have
been observed with plants: a new and beautiful white onion, imported from
France, though planted close to other kinds, was alone attacked by a parasitic
fungus. (21/12. 'Gardener's Chronicle' 1851 page 595.) White verbenas are
especially liable to mildew. (21/13. 'Journal of Horticulture' 1862 page 476.)
Near Malaga, during an early period of the vine-disease, the green sorts
suffered most; "and red and black grapes, even when interwoven with the sick
plants, suffered not at all." In France whole groups of varieties were
comparatively free, and others, such as the Chasselas, did not afford a single
fortunate exception; but I do not know whether any correlation between colour
and liability to disease was here observed. (21/14. 'Gardener's Chronicle'
1852 pages 435, 691.) In a former chapter it was shown how curiously liable
one variety of the strawberry is to mildew.

It is certain that insects regulate in many cases the range and even the
existence of the higher animals, whilst living under their natural conditions.
Under domestication light-coloured animals suffer most: in Thuringia (21/15.
Bechstein 'Naturgesch. Deutschlands' 1801 b. 1 s. 310.) the inhabitants do not
like grey, white, or pale cattle, because they are much more troubled by
various kinds of flies than the brown, red, or black cattle. An Albino negro,
it has been remarked (21/16. Prichard 'Phys. Hist. of Mankind' 1851 volume 1
page 224.), was peculiarly sensitive to the bites of insects. In the West
Indies (21/17. G. Lewis 'Journal of Residence in West Indies' 'Home and Col.
Library' page 100.) it is said that "the only horned cattle fit for work are
those which have a good deal of black in them. The white are terribly
tormented by the insects; and they are weak and sluggish in proportion to the
white."

In Devonshire there is a prejudice against white pigs, because it is believed
that the sun blisters them when turned out (21/18. Sidney's edition of Youatt
on the 'Pig' page 24. I have given analogous facts in the case of mankind in
my 'Descent of Man' 2nd edition page 195.); and I knew a man who would not
keep white pigs in Kent, for the same reason. The scorching of flowers by the
sun seems likewise to depend much on colour; thus, dark pelargoniums suffer
most; and from various accounts it is clear that the cloth-of-gold variety
will not withstand a degree of exposure to sunshine which other varieties
enjoy. Another amateur asserts that not only all dark-coloured verbenas, but
likewise scarlets, suffer from the sun: "the paler kinds stand better, and
pale blue is perhaps the best of all." So again with the heartsease (Viola
tricolor); hot weather suits the blotched sorts, whilst it destroys the
beautiful markings of some other kinds. (21/19. 'Journal of Horticulture' 1862
pages 476, 498; 1865 page 460. With respect to the heartsease 'Gardener's
Chronicle' 1863 page 628.) During one extremely cold season in Holland all
red-flowered hyacinths were observed to be very inferior in quality. It is
believed by many agriculturists that red wheat is hardier in northern climates
than white wheat. (21/20. 'Des Jacinthes, de leur Culture' 1768 page 53: on
wheat 'Gardener's Chronicle' 1846 page 653.)

With animals, white varieties from being conspicuous are the most liable to be
attacked by beasts and birds of prey. In parts of France and Germany where
hawks abound, persons are advised not to keep white pigeons; for, as
Parmentier says, "it is certain that in a flock the white always first fall
victims to the kite." In Belgium, where so many societies have been
established for the flight of carrier-pigeons, white is the one colour which
for the same reason is disliked. (20/21. W.B. Tegetmeier 'The Field' February
25, 1865. With respect to black fowls see a quotation in Thompson 'Nat. Hist.
of Ireland' 1849 volume 1 page 22.) Prof. G. Jaeger (21/22. 'In Sachen
Darwin's contra Wigand' 1874 page 70.) whilst fishing found four pigeons which
had been killed by hawks, and all were white; on another occasion he examined
the eyrie of a hawk, and the feathers of the pigeons which had been caught
were all of a white or yellow colour. On the other hand, it is said that the
sea-eagle (Falco ossifragus, Linn.) on the west coast of Ireland picks out the
black fowls, so that "the villagers avoid as much as possible rearing birds of
that colour." M. Daudin (20/23. 'Bull. de la Soc. d'Acclimat.' tome 7 1860
page 359.), speaking of white rabbits kept in warrens in Russia, remarks that
their colour is a great disadvantage, as they are thus more exposed to attack,
and can be seen during bright nights from a distance. A gentleman in Kent, who
failed to stock his woods with a nearly white and hardy kind of rabbit,
accounted in the same manner for their early disappearance. Any one who will
watch a white cat prowling after her prey will soon perceive under what a
disadvantage she lies.

The white Tartarian cherry, "owing either to its colour being so much like
that of the leaves, or to the fruit always appearing from a distance unripe,"
is not so readily attacked by birds as other sorts. The yellow-fruited
raspberry, which generally comes nearly true by seed, "is very little molested
by birds, who evidently are not fond of it; so that nets may be dispensed with
in places where nothing else will protect the red fruit." (21/24. 'Transact.
Hort. Soc.' volume 1 2nd series 1835 page 275. For raspberries see 'Gardener's
Chronicle' 1855 page 154 and 1863 page 245.) This immunity, though a benefit
to the gardener, would be a disadvantage in a state of nature both to the
cherry and raspberry, as dissemination depends on birds. I noticed during
several winters that some trees of the yellow-berried holly, which were raised
from seed from a tree found wild by my father remained covered with fruit,
whilst not a scarlet berry could be seen on the adjoining trees of the common
kind. A friend informs me that a mountain-ash (Pyrus aucuparia) growing in his
garden bears berries which, though not differently coloured, are always
devoured by birds before those on the other trees. This variety of the
mountain-ash would thus be more freely disseminated, and the yellow-berried
variety of the holly less freely, than the common varieties of these two
trees.

Independently of colour, trifling differences are sometimes found to be of
importance to plants under cultivation, and would be of paramount importance
if they had to fight their own battle and to struggle with many competitors.
The thin-shelled peas, called pois sans parchemin, are attacked by birds
(21/25. 'Gardener's Chronicle' 1843 page 806.) much more commonly than
ordinary peas. On the other hand, the purple-podded pea, which has a hard
shell, escaped the attacks of tomtits (Parus major) in my garden far better
than any other kind. The thin-shelled walnut likewise suffers greatly from the
tomtit. (21/26. Ibid 1850 page 732.) These same birds have been observed to
pass over and thus favour the filbert, destroying only the other kinds of nuts
which grew in the same orchard. (21/27. Ibid 1860 page 956.)

Certain varieties of the pear have soft bark, and these suffer severely from
wood-boring beetles; whilst other varieties are known to resist their attacks
much better. (21/28. J. De Jonghe in 'Gardener's Chronicle' 1860 page 120.) In
North America the smoothness, or absence of down on the fruit, makes a great
difference in the attacks of the weevil, "which is the uncompromising foe of
all smooth stone-fruits;" and the cultivator "has the frequent mortification
of seeing nearly all, or indeed often the whole crop, fall from the trees when
half or two-thirds grown." Hence the nectarine suffers more than the peach. A
particular variety of the Morello cherry, raised in North America, is, without
any assignable cause, more liable to be injured by this same insect than other
cherry-trees. (21/29. Downing 'Fruit-trees of North America' pages 266, 501:
in regard to the cherry page 198.) From some unknown cause, certain varieties
of the apple enjoy, as we have seen, the great advantage in various parts of
the world of not being infested by the coccus. On the other hand, a particular
case has been recorded in which aphides confined themselves to the Winter
Nelis pear and touched no other kind in an extensive orchard. (21/30.
'Gardener's Chronicle' 1849 page 755.) The existence of minute glands on the
leaves of peaches, nectarines, and apricots, would not be esteemed by
botanists as a character of the least importance for they are present or
absent in closely-related sub-varieties, descended from the same parent-tree;
yet there is good evidence (21/31. 'Journal of Horticulture' September 26,
1865 page 254; see other references given in chapter 10.) that the absence of
glands leads to mildew, which is highly injurious to these trees.

A difference either in flavour or in the amount of nutriment in certain
varieties causes them to be more eagerly attacked by various enemies than
other varieties of the same species. Bullfinches (Pyrrhula vulgaris) injure
our fruit-trees by devouring the flower-buds, and a pair of these birds have
been seen "to denude a large plum-tree in a couple of days of almost every
bud;" but certain varieties (21/32. Mr. Selby in 'Mag. of Zoology and Botany'
Edinburgh volume 2 1838 page 393.) of the apple and thorn (Crataegus
oxyacantha) are more especially liable to be attacked. A striking instance of
this was observed in Mr. Rivers's garden, in which two rows of a particular
variety of plum (21/33. The Reine Claude de Bavay 'Journal of Horticulture'
December 27, 1864 page 511.) had to be carefully protected, as they were
usually stripped of all their buds during the winter, whilst other sorts
growing near them escaped. The root (or enlarged stem) of Laing's Swedish
turnip is preferred by hares, and therefore suffers more than other varieties.
Hares and rabbits eat down common rye before St. John's-day-rye, when both
grow together. (21/34. Mr. Pusey in 'Journal of R. Agricult. Soc.' volume 6
page 179. For Swedish turnips see 'Gardener's Chronicle' 1847 page 91.) In the
south of France, when an orchard of almond-trees is formed, the nuts of the
bitter variety are sown, "in order that they may not be devoured by field-
mice" (21/35. Godron 'De l'Espece' tome 2 page 98.); so we see the use of the
bitter principle in almonds.

Other slight differences, which would be thought quite unimportant, are no
doubt sometimes of great service both to plants and animals. The Whitesmith's
gooseberry, as formerly stated, produces its leaves later than other
varieties, and, as the flowers are thus left unprotected, the fruit often
fails. In one variety of the cherry, according to Mr. Rivers (21/36.
'Gardener's Chronicle' 1866 page 732.), the petals are much curled backwards,
and in consequence of this the stigmas were observed to be killed by a severe
frost; whilst at the same time, in another variety with incurved petals, the
stigmas were not in the least injured. The straw of the Fenton wheat is
remarkably unequal in height; and a competent observer believes that this
variety is highly productive, partly because the ears from being distributed
at various heights above the ground are less crowded together. The same
observer maintains that in the upright varieties the divergent awns are
serviceable by breaking the shocks when the ears are dashed together by the
wind. (21/37. 'Gardener's Chronicle' 1862 pages 820, 821.) If several
varieties of a plant are grown together, and the seed is indiscriminately
harvested, it is clear that the hardier and more productive kinds will, by a
sort of natural selection, gradually prevail over the others; this takes
place, as Colonel Le Couteur believes (21/38. 'On the Varieties of Wheat' page
59.), in our wheat-fields, for, as formerly shown, no variety is quite uniform
in character. The same thing, as I am assured by nurserymen, would take place
in our flower-gardens, if the seed of the different varieties were not
separately saved. When the eggs of the wild and tame duck are hatched
together, the young wild ducks almost invariably perish, from being of smaller
size and not getting their fair share of food. (21/39. Mr. Hewitt and others,
in 'Journal of Hort.' 1862 page 773.)

Facts in sufficient number have now been given showing that natural selection
often checks, but occasionally favours, man's power of selection. These facts
teach us, in addition, a valuable lesson, namely, that we ought to be
extremely cautious in judging what characters are of importance in a state of
nature to animals and plants, which have to struggle for existence from the
hour of their birth to that of their death,--their existence depending on
conditions, about which we are profoundly ignorant.

CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN.

The possibility of selection rests on variability, and this, as we shall see
in the following chapters, mainly depends on changed conditions of life, but
is governed by infinitely complex and unknown laws. Domestication, even when
long continued, occasionally causes but a small amount of variability, as in
the case of the goose and turkey. The slight differences, however, which
characterise each individual animal and plant would in most, probably in all,
cases suffice for the production of distinct races through careful and
prolonged selection. We see what selection, though acting on mere individual
differences, can effect when families of cattle, sheep, pigeons, etc., of the
same race, have been separately bred during a number of years by different men
without any wish on their part to modify the breed. We see the same fact in
the difference between hounds bred for hunting in different districts (21/40.
'Encyclop. of Rural Sports' page 405.), and in many other such cases.

In order that selection should produce any result, it is manifest that the
crossing of distinct races must be prevented; hence facility in pairing, as
with the pigeon, is highly favourable for the work; and difficulty in pairing,
as with cats, prevents the formation of distinct breeds. On nearly the same
principle the cattle of the small island of Jersey have been improved in their
milking qualities "with a rapidity that could not have been obtained in a
widely extended country like France." (21/41. Col. Le Couteur 'Journal Roy.
Agricult. Soc.' volume 4 page 43.) Although free crossing is a danger on the
one side which every one can see, too close interbreeding is a hidden danger
on the other side. Unfavourable conditions of life overrule the power of
selection. Our improved heavy breeds of cattle and sheep could not have been
formed on mountainous pastures; nor could dray-horses have been raised on a
barren and inhospitable land, such as the Falkland Islands, where even the
light horses of La Plata rapidly decrease in size. It seems impossible to
preserve several English breeds of sheep in France; for as soon as the lambs
are weaned their vigour decays as the heat of the summer increases (21/42.
Malingie-Nouel 'Journal R. Agricult. Soc.' volume 14 1853 pages 215, 217.): it
would be impossible to give great length of wool to sheep within the tropics;
yet selection has kept the Merino breed nearly true under diversified and
unfavourable conditions. The power of selection is so great, that breeds of
the dog, sheep, and poultry, of the largest and smallest size, long and short
beaked pigeons, and other breeds with opposite characters, have had their
characteristic qualities augmented, though treated in every way alike, being
exposed to the same climate and fed on the same food. Selection, however, is
either checked or favoured by the effects of use or habit. Our wonderfully-
improved pigs could never have been formed if they had been forced to search
for their own food; the English racehorse and greyhound could not have been
improved up to their present high standard of excellence without constant
training.

As conspicuous deviations of structure occur rarely, the improvement of each
breed is generally the result of the selection of slight individual
differences. Hence the closest attention, the sharpest powers of observation,
and indomitable perseverance, are indispensable. It is, also, highly important
that many individuals of the breed which is to be improved should be raised;
for thus there will be a better chance of the appearance of variations in the
right direction, and individuals varying in an unfavourable manner may be
freely rejected or destroyed. But that a large number of individuals should be
raised, it is necessary that the conditions of life should favour the
propagation of the species. Had the peacock been reared as easily as the fowl,
we should probably ere this have had many distinct races. We see the
importance of a large number of plants, from the fact of nursery gardeners
almost always beating amateurs in the exhibition of new varieties. In 1845 it
was estimated (21/43. Gardener's Chronicle' 1845 page 273.) that between 4000
and 5000 pelargoniums were annually raised from seed in England, yet a
decidedly improved variety is rarely obtained. At Messrs. Carter's grounds, in
Essex, where such flowers as the Lobelia, Nemophila, Mignonette, etc., are
grown by the acre for seed, "scarcely a season passes without some new kinds
being raised, or some improvement effected on old kinds." (21/44. 'Journal of
Horticulture' 1862 page 157.) At Kew, as Mr. Beaton remarks, where many
seedlings of common plants are raised, "you see new forms of Laburnums,
Spiraeas, and other shrubs." (21/45. 'Cottage Gardener' 1860 page 368.) So
with animals: Marshall (21/46. 'A Review of Reports' 1808 page 406.), in
speaking of the sheep in one part of Yorkshire, remarks, "as they belong to
poor people, and are mostly in small lots, they never can be improved." Lord
Rivers, when asked how he succeeded in always having first-rate greyhounds,
answered, "I breed many, and hang many." This, as another man remarks, "was
the secret of his success; and the same will be found in exhibiting fowls,--
successful competitors breed largely, and keep the best." (21/47. 'Gardener's
Chronicle' 1853 page 45.)

It follows from this that the capacity of breeding at an early age and at
short intervals, as with pigeons, rabbits, etc., facilitates selection; for
the result is thus soon made visible, and perseverance in the work encouraged.
It can hardly be an accident that the great majority of the culinary and
agricultural plants which have yielded numerous races are annuals or
biennials, which therefore are capable of rapid propagation, and thus of
improvement. Sea-kale, asparagus, common and Jerusalem artichokes, potatoes,
and onions, must be excepted, as they are perennials: but onions are
propagated like annuals, and of the other plants just specified, none, with
the exception of the potato, have yielded in this country more than one or two
varieties. In the Mediterranean region, where artichokes are often raised from
seed, there are several kinds, as I hear from Mr. Bentham. No doubt fruit-
trees, which cannot be propagated quickly by seed, have yielded a host of
varieties, though not permanent races; but these, judging from prehistoric
remains, have been produced at a comparatively late period.

A species may be highly variable, but distinct races will not be formed, if
from any cause selection be not applied. It would be difficult to select
slight variations in fishes from their place of habitation; and though the
carp is extremely variable and is much attended to in Germany, only one well-
marked race has been formed, as I hear from Lord A. Russell, namely the
spiegel-carpe; and this is carefully secluded from the common scaly kind. On
the other hand, a closely allied species, the gold-fish, from being reared in
small vessels, and from having been carefully attended to by the Chinese, has
yielded many races. Neither the bee, which has been semi-domesticated from an
extremely remote period, nor the cochineal insect, which was cultivated by the
aboriginal Mexicans (21/48. Isidore Geoffroy Saint-Hilaire 'Hist. Nat. Gen.'
tome 3 page 49. 'On the Cochineal Insect' page 46.), has yielded races; and it
would be impossible to match the queen-bee with any particular drone, and most
difficult to match cochineal insects. Silk-moths, on the other hand, have been
subjected to rigorous selection, and have produced a host of races. Cats,
which from their nocturnal habits cannot be selected for breeding, do not, as
formerly remarked, yield distinct races within the same country. Dogs are held
in abomination in the East, and their breeding is neglected; consequently, as
Prof. Moritz Wagner (21/49. 'Die Darwin'sche Theorie und das Migrationsgesetz
der Organismen' 1868 page 19.) remarks, one kind alone exists there. The ass
in England varies much in colour and size; but as it is an animal of little
value and bred by poor people, there has been no selection, and distinct races
have not been formed. We must not attribute the inferiority of our asses to
climate, for in India they are of even smaller size than in Europe. But when
selection is brought to bear on the ass, all is changed. Near Cordova, as I am
informed (February 1860) by Mr. W.E. Webb, C.E., they are carefully bred, as
much as 200 pounds having been paid for a stallion ass, and they have been
immensely improved. In Kentucky, asses have been imported (for breeding mules)
from Spain, Malta, and France; these "seldom averaged more than fourteen hands
high: but the Kentuckians, by great care, have raised them up to fifteen
hands, and sometimes even to sixteen. The prices paid for these splendid
animals, for such they really are, will prove how much they are in request.
One male, of great celebrity, was sold for upwards of one thousand pounds
sterling." These choice asses are sent to cattle-shows, a day being given for
their exhibition. (21/50. Capt. Marryat quoted by Blyth in 'Journ. Asiatic
Soc. of Bengal' volume 28 page 229.)

Analogous facts have been observed with plants: the nutmeg-tree in the Malay
archipelago is highly variable, but there has been no selection, and there are
no distinct races. (21/51. Mr. Oxley 'Journal of the Indian Archipelago'
volume 2 1848 page 645.) The common mignonette (Reseda odorata), from bearing
inconspicuous flowers, valued solely for their fragrance, "remains in the same
unimproved condition as when first introduced." (21/52. Mr. Abbey 'Journal of
Horticulture' December 1, 1863 page 430.) Our common forest-trees are very
variable, as may be seen in every extensive nursery-ground; but as they are
not valued like fruit-trees, and as they seed late in life, no selection has
been applied to them; consequently, as Mr. Patrick Matthews remarks (21/53.
'On Naval Timber' 1831 page 107.), they have not yielded distinct races,
leafing at different periods, growing to different sizes, and producing timber
fit for different purposes. We have gained only some fanciful and semi-
monstrous varieties, which no doubt appeared suddenly as we now see them.

Some botanists have argued that plants cannot have so strong a tendency to
vary as is generally supposed, because many species long grown in botanic
gardens, or unintentionally cultivated year after year mingled with our corn
crops, have not produced distinct races; but this is accounted for by slight
variations not having been selected and propagated. Let a plant which is now
grown in a botanic garden, or any common weed, be cultivated on a large scale,
and let a sharp-sighted gardener look out for each slight variety and sow the
seed, and then, if distinct races are not produced, the argument will be
valid.

The importance of selection is likewise shown by considering special
characters. For instance, with most breeds of fowls the form of the comb and
the colour of the plumage have been attended to, and are eminently
characteristic of each race; but in Dorkings fashion has never demanded
uniformity of comb or colour; and the utmost diversity in these respects
prevails. Rose-combs, double-combs, cup-combs, etc., and colours of all kinds,
may be seen in purely bred and closely related Dorking fowls, whilst other
points, such as the general form of body, and the presence of an additional
toe, have been attended to, and are invariably present. It has also been
ascertained that colour can be fixed in this breed, as well as in any other.
(21/54. Mr. Baily in 'The Poultry Chronicle' volume 2 1854 page 150. Also
volume 1 page 342; volume 3 page 245.)

During the formation or improvement of a breed, its members will always be
found to vary much in those characters to which especial attention is
directed, and of which each slight improvement is eagerly sought and selected.
Thus, with short-faced tumbler-pigeons, the shortness of the beak, shape of
head and plumage,--with carriers, the length of the beak and wattle,--with
fantails, the tail and carriage,--with Spanish fowls, the white face and
comb,--with long-eared rabbits, the length of ear, are all points which are
eminently variable. So it is in every case; and the large price paid for
first-rate animals proves the difficulty of breeding them up to the highest
standard of excellence. This subject has been discussed by fanciers (21/55.
'Cottage Gardener' 1855 December page 171; 1856 January pages 248, 323.), and
the greater prizes given for highly improved breeds, in comparison with those
given for old breeds which are not now undergoing rapid improvement, have been
fully justified. Nathusius makes (21/56. 'Ueber Shorthorn Rindvieh' 1857 s.
51.) a similar remark when discussing the less uniform character of improved
Shorthorn cattle and of the English horse, in comparison, for example, with
the unennobled cattle of Hungary, or with the horses of the Asiatic steppes.
This want of uniformity in the parts which at the time are undergoing
selection chiefly depends on the strength of the principle of reversion; but
it likewise depends to a certain extent on the continued variability of the
parts which have recently varied. That the same parts do continue varying in
the same manner we must admit, for if it were not so, there could be no
improvement beyond an early standard of excellence, and we know that such
improvement is not only possible, but is of general occurrence.

As a consequence of continued variability, and more especially of reversion,
all highly improved races, if neglected or not subjected to incessant
selection, soon degenerate. Youatt gives a curious instance of this in some
cattle formerly kept in Glamorganshire; but in this case the cattle were not
fed with sufficient care. Mr. Baker, in his memoir on the Horse, sums up: "It
must have been observed in the preceding pages that, whenever there has been
neglect, the breed has proportionally deteriorated." (21/57. 'The Veterinary'
volume 13 page 720. For the Glamorganshire cattle see Youatt on 'Cattle' page
51.) If a considerable number of improved cattle, sheep, or other animals of
the same race, were allowed to breed freely together, with no selection, but
with no change in their condition of life, there can be no doubt that after a
score or hundred generations they would be very far from excellent of their
kind; but, from what we see of the many common races of dogs, cattle, fowls,
pigeons, etc., which without any particular care have long retained nearly the
same character, we have no grounds for believing that they would altogether
depart from their type.

It is a general belief amongst breeders that characters of all kinds become
fixed by long-continued inheritance. But I have attempted to show in the
fourteenth chapter that this belief apparently resolves itself into the
following proposition, namely, that all characters whatever, whether recently
acquired or ancient, tend to be transmitted, but that those which have already
long withstood all counteracting influences, will, as a general rule, continue
to withstand them, and consequently be faithfully transmitted.

TENDENCY IN MAN TO CARRY THE PRACTICE OF SELECTION TO AN EXTREME POINT.

It is an important principle that in the process of selection man almost
invariably wishes to go to an extreme point. Thus, there is no limit to his
desire to breed certain kinds of horses and dogs as fleet as possible, and
others as strong as possible; certain kinds of sheep for extreme fineness, and
others for extreme length of wool; and he wishes to produce fruit, grain,
tubers, and other useful parts of plants, as large and excellent as possible.
With animals bred for amusement, the same principle is even more powerful; for
fashion, as we see in our dress, always runs to extremes. This view has been
expressly admitted by fanciers. Instances were given in the chapters on the
pigeon, but here is another: Mr. Eaton, after describing a comparatively new
variety, namely, the Archangel, remarks, "What fanciers intend doing with this
bird I am at a loss to know, whether they intend to breed it down to the
tumbler's head and beak, or carry it out to the carrier's head and beak;
leaving it as they found it, is not progressing." Ferguson, speaking of fowls,
says, "their peculiarities, whatever they may be, must necessarily be fully
developed: a little peculiarity forms nought but ugliness, seeing it violates
the existing laws of symmetry." So Mr. Brent, in discussing the merits of the
sub-varieties of the Belgian canary-bird, remarks, "Fanciers always go to
extremes; they do not admire indefinite properties." (21/58. J.M. Eaton 'A
Treatise on Fancy Pigeons' page 82; Ferguson on 'Rare and Prize Poultry' page
162; Mr. Brent in 'Cottage Gardener' October 1860 page 13.)

This principle, which necessarily leads to divergence of character, explains
the present state of various domestic races. We can thus see how it is that
racehorses and dray-horses, greyhounds and mastiffs, which are opposed to each
other in every character,--how varieties so distinct as Cochin-china fowls and
bantams, or carrier-pigeons with very long beaks, and tumblers with
excessively short beaks, have been derived from the same stock. As each breed
is slowly improved, the inferior varieties are first neglected and finally
lost. In a few cases, by the aid of old records, or from intermediate
varieties still existing in countries where other fashions have prevailed, we
are enabled partially to trace the graduated changes through which certain
breeds have passed. Selection, whether methodical or unconscious, always
tending towards an extreme point, together with the neglect and slow
extinction of the intermediate and less-valued forms, is the key which unlocks
the mystery of how man has produced such wonderful results.

In a few instances selection, guided by utility for a single purpose, has led
to convergence of character. All the improved and different races of the pig,
as Nathusius has well shown (21/59. 'Die Racen des Schweines' 1860 s. 48.),
closely approach each other in character, in their shortened legs and muzzles,
their almost hairless, large, rounded bodies, and small tusks. We see some
degree of convergence in the similar outline of the body in well-bred cattle
belonging to distinct races. (21/60. See some good remarks on this head by M.
de Quatrefages 'Unite de l'Espece Humaine' 1861 page 119.) I know of no other
such cases.

Continued divergence of character depends on, and is indeed a clear proof, as
previously remarked, of the same parts continuing to vary in the same
direction. The tendency to mere general variability or plasticity of
organisation can certainly be inherited, even from one parent, as has been
shown by Gartner and Kolreuter, in the production of varying hybrids from two
species, of which one alone was variable. It is in itself probable that, when
an organ has varied in any manner, it will again vary in the same manner, if
the conditions which first caused the being to vary remain, as far as can be
judged, the same. This is either tacitly or expressly admitted by all
horticulturists: if a gardener observes one or two additional petals in a
flower, he feels confident that in a few generations he will be able to raise
a double flower, crowded with petals. Some of the seedlings from the weeping
Moccas oak were so prostrate that they only crawled along the ground. A
seedling from the fastigiate or upright Irish yew is described as differing
greatly from the parent-form "by the exaggeration of the fastigiate habit of
its branches." (21/61. Verlot 'Des Varietes' 1865 page 94.) Mr. Shirreff, who
has been highly successful in raising new kinds of wheat, remarks, "A good
variety may safely be regarded as the forerunner of a better one." (21/62. Mr.
Patrick Shirreff 'Gardener's Chronicle' 1858 page 771.) A great rose-grower,
Mr. Rivers, has made the same remark with respect to roses. Sageret (21/63.
'Pomologie Physiolog.' 1830 page 106.), who had large experience, in speaking
of the future progress of fruit-trees, observes that the most important
principle is "that the more plants have departed from their original type, the
more they tend to depart from it." There is apparently much truth in this
remark; for we can in no other way understand the surprising amount of
difference between varieties in the parts or qualities which are valued,
whilst other parts retain nearly their original character.

The foregoing discussion naturally leads to the question, what is the limit to
the possible amount of variation in any part or quality, and, consequently, is
there any limit to what selection can effect? Will a racehorse ever be reared
fleeter than Eclipse? Can our prize-cattle and sheep be still further
improved? Will a gooseberry ever weigh more than that produced by "London" in
1852? Will the beet-root in France yield a greater percentage of sugar? Will
future varieties of wheat and other grain produce heavier crops than our
present varieties? These questions cannot be positively answered; but it is
certain that we ought to be cautious in answering them by a negative. In some
lines of variation the limit has probably been reached. Youatt believes that
the reduction of bone in some of our sheep has already been carried so far
that it entails great delicacy of constitution. (21/64. Youatt on 'Sheep' page
521.) But seeing the great improvement within recent times in our cattle and
sheep, and especially in our pigs; seeing the wonderful increase in weight in
our poultry of all kinds during the last few years; he would be a bold man who
would assert that perfection has been reached. It has often been said that
Eclipse never was, and never will be, beaten in speed by any other horse; but
on making inquiries I find that the best judges believe that our present
racehorses are fleeter. (21/65. See also Stonehenge 'British Rural Sports'
edition of 1871 page 384.) The attempt to raise a new variety of wheat more
productive than the many old kinds, might have been thought until lately quite
hopeless; but this has been effected by Major Hallett, by careful selection.
With respect to almost all our animals and plants, those who are best
qualified to judge do not believe that the extreme point of perfection has yet
been reached even in the characters which have already been carried to a high
standard. For instance, the short-faced tumbler-pigeon has been greatly
modified; nevertheless, according to Mr. Eaton (21/66. 'A Treatise on the
Almond Tumbler' page 1.) "the field is still as open for fresh competitors as
it was one hundred years ago." Over and over again it has been said that
perfection had been attained with our flowers, but a higher standard has soon
been reached. Hardly any fruit has been more improved than the strawberry, yet
a great authority remarks (21/67. M. J. de Jonghe in 'Gardener's Chronicle'
1858 page 173.), "it must not be concealed that we are far from the extreme
limits at which we may arrive."

No doubt there is a limit beyond which the organisation cannot be modified
compatibly with health or life. The extreme degree of fleetness, for instance,
of which a terrestrial animal is capable, may have been acquired by our
present racehorses; but as Mr. Wallace has well remarked (21/68.
'Contributions to the Theory of Natural Selection' 2nd edition 1871 page
292.), the question that interests us, "is not whether indefinite and
unlimited change in any or all directions is possible, but whether such
differences as do occur in nature could have been produced by the accumulation
of varieties by selection." And in the case of our domestic productions, there
can be no doubt that many parts of the organisation, to which man has
attended, have been thus modified to a greater degree than the corresponding
parts in the natural species of the same genera or even families. We see this
in the form and size of our light and heavy dogs or horses,--in the beak and
many other characters of our pigeons,--in the size and quality of many
fruits,--in comparison with the species belonging to the same natural groups.

Time is an important element in the formation of our domestic races, as it
permits innumerable individuals to be born, and these when exposed to
diversified conditions are rendered variable. Methodical selection has been
occasionally practised from an ancient period to the present day, even by
semi-civilised people, and during former times will have produced some effect.
Unconscious selection will have been still more effective; for during a
lengthened period the more valuable individual animals will occasionally have
been saved, and the less valuable neglected. In the course of time, different
varieties, especially in the less civilised countries, will also have been
more or less modified through natural selection. It is generally believed,
though on this head we have little or no evidence, that new characters in time
become fixed; and after having long remained fixed it seems possible that
under new conditions they might again be rendered variable.

How great the lapse of time has been since man first domesticated animals and
cultivated plants, we begin dimly to see. When the lake-dwellings of
Switzerland were inhabited during the Neolithic period, several animals were
already domesticated and various plants cultivated. The science of language
tells us that the art of ploughing and sowing the land was followed, and the
chief animals had been already domesticated, at an epoch so immensely remote,
that the Sanskrit, Greek, Latin, Gothic, Celtic, and Sclavonic languages had
not as yet diverged from their common parent-tongue. (21/69. Max Muller
'Science of Language' 1861 page 223.)

It is scarcely possible to overrate the effects of selection occasionally
carried on in various ways and places during thousands of generations. All
that we know, and, in a still stronger degree, all that we do not know (21/70.
'Youatt on Cattle' pages 116, 128.), of the history of the great majority of
our breeds, even of our more modern breeds, agrees with the view that their
production, through the action of unconscious and methodical selection, has
been almost insensibly slow. When a man attends rather more closely than is
usual to the breeding of his animals, he is almost sure to improve them to a
slight extent. They are in consequence valued in his immediate neighbourhood,
and are bred by others; and their characteristic features, whatever these may
be, will then slowly but steadily be increased, sometimes by methodical and
almost always by unconscious selection. At last a strain, deserving to be
called a sub-variety, becomes a little more widely known, receives a local
name, and spreads. The spreading will have been extremely slow during ancient
and less civilised times, but now is rapid. By the time that the new breed had
assumed a somewhat distinct character, its history, hardly noticed at the
time, will have been completely forgotten; for, as Low remarks (21/71.
'Domesticated Animals' page 188.), "we know how quickly the memory of such
events is effaced."

As soon as a new breed is thus formed, it is liable through the same process
to break up into new strains and sub-varieties. For different varieties are
suited for, and are valued under, different circumstances. Fashion changes,
but, should a fashion last for even a moderate length of time, so strong is
the principle of inheritance, that some effect will probably be impressed on
the breed. Thus varieties go on increasing in number, and history shows us how
wonderfully they have increased since the earliest records. (21/72. Volz
'Beitrage zur Kulturgeschichte' 1852 s. 99 et passim.) As each new variety is
produced, the earlier, intermediate, and less valuable forms will be
neglected, and perish. When a breed, from not being valued, is kept in small
numbers, its extinction almost inevitably follows sooner or later, either from
accidental causes of destruction or from close interbreeding; and this is an
event which, in the case of well-marked breeds, excites attention. The birth
or production of a new domestic race is so slow a process that it escapes
notice; its death or destruction is comparatively sudden, is often recorded,
and when too late sometimes regretted.

Several authors have drawn a wide distinction between artificial and natural
races. The latter are more uniform in character, possessing in a high degree
the appearance of natural species, and are of ancient origin. They are
generally found in less civilised countries, and have probably been largely
modified by natural selection, and only to a small extent by man's unconscious
and methodical selection. They have, also, during a long period, been directly
acted on by the physical conditions of the countries which they inhabit. The
so-called artificial races, on the other hand, are not so uniform in
character; some have a semi-monstrous character, such as "the wry-legged
terriers so useful in rabbit-shooting" (21/73. Blaine 'Encyclop. of Rural
Sports' page 213.), turnspit dogs, ancon sheep, niata oxen, Polish fowls,
fantail-pigeons, etc.; their characteristic features have generally been
acquired suddenly, though subsequently increased by careful selections in many
cases. Other races, which certainly must be called artificial, for they have
been largely modified by methodical selection and by crossing, as the English
racehorse, terrier-dogs, the English game-cock, Antwerp carrier-pigeons, etc.,
nevertheless cannot be said to have an unnatural appearance; and no distinct
line, as it seems to me, can be drawn between natural and artificial races.

It is not surprising that domestic races should generally present a different
aspect from natural species. Man selects and propagates modifications solely
for his own use or fancy, and not for the creature's own good. His attention
is struck by strongly marked modifications, which have appeared suddenly, due
to some great disturbing cause in the organisation. He attends almost
exclusively to external characters; and when he succeeds in modifying internal
organs,--when for instance he reduces the bones and offal, or loads the
viscera with fat, or gives early maturity, etc.-the chances are strong that he
will at the same time weaken the constitution. On the other hand, when an
animal has to struggle throughout its life with many competitors and enemies,
under circumstances inconceivably complex and liable to change, modifications
of the most varied nature in the internal organs as well as in external
characters, in the functions and mutual relations of parts, will be rigorously
tested, preserved, or rejected. Natural selection often checks man's
comparatively feeble and capricious attempts at improvement; and if it were
not so, the result of his work, and of nature's work, would be even still more
different. Nevertheless, we must not overrate the amount of difference between
natural species and domestic races; the most experienced naturalists have
often disputed whether the latter are descended from one or from several
aboriginal stocks, and this clearly shows that there is no palpable difference
between species and races.

Domestic races propagate their kind far more truly, and endure for munch
longer periods, than most naturalists are willing to admit. Breeders feel no
doubt on this head: ask a man who has long reared Shorthorn or Hereford
cattle, Leicester or Southdown sheep, Spanish or Game poultry, tumbler or
carrier-pigeons, whether these races may not have been derived from common
progenitors, and he will probably laugh you to scorn. The breeder admits that
he may hope to produce sheep with finer or longer wool and with better
carcases, or handsomer fowls, or carrier-pigeons with beaks just perceptibly
longer to the practised eye, and thus be successful at an exhibition. Thus far
he will go, but no farther. He does not reflect on what follows from adding up
during a long course of time many slight, successive modifications; nor does
he reflect on the former existence of numerous varieties, connecting the links
in each divergent line of descent. He concludes, as was shown in the earlier
chapters, that all the chief breeds to which he has long attended are
aboriginal productions. The systematic naturalist, on the other hand, who
generally knows nothing of the art of breeding, who does not pretend to know
how and when the several domestic races were formed, who cannot have seen the
intermediate gradations, for they do not now exist, nevertheless feels no
doubt that these races are sprung from a single source. But ask him whether
the closely allied natural species which he has studied may not have descended
from a common progenitor, and he in his turn will perhaps reject the notion
with scorn. Thus the naturalist and breeder may mutually learn a useful lesson
from each other.

SUMMARY ON SELECTION BY MAN.

There can be no doubt that methodical selection has effected and will effect
wonderful results. It was occasionally practised in ancient times, and is
still practised by semi-civilised people. Characters of the highest
importance, and others of trifling value, have been attended to, and modified.
I need not here repeat what has been so often said on the part which
unconscious selection has played: we see its power in the difference between
flocks which have been separately bred, and in the slow changes, as
circumstances have slowly changed, which many animals have undergone in the
same country, or when transported into a foreign land. We see the combined
effects of methodical and unconscious selection, in the great amount of
difference in those parts or qualities which are valued by man in comparison
with the parts which are not valued, and consequently have not been attended
to. Natural selection often determines man's power of selection. We sometimes
err in imagining that characters, which are considered as unimportant by the
systematic naturalist, could not be affected by the struggle for existence,
and could not be acted on by natural selection; but striking cases have been
given, showing how great an error this is.

The possibility of selection coming into action rests on variability; and this
is mainly caused, as we shall hereafter see, by changes in the conditions of
life. Selection is sometimes rendered difficult, or even impossible, by the
conditions being opposed to the desired character or quality. It is sometimes
checked by the lessened fertility and weakened constitution which follow from
long-continued close interbreeding. That methodical selection may be
successful, the closest attention and discernment, combined with unwearied
patience, are absolutely necessary; and these same qualities, though not
indispensable, are highly serviceable in the case of unconscious selection. It
is almost necessary that a large number of individuals should be reared; for
thus there will be a fair chance of variations of the desired nature arising,
and of every individual with the slightest blemish or in any degree inferior
being freely rejected. Hence length of time is an important element of
success. Thus, also, reproduction at an early age and at short intervals
favours the work. Facility in pairing animals, or their inhabiting a confined
area, is advantageous as a check to free crossing. Whenever and wherever
selection is not practised, distinct races are not formed within the same
country. When any one part of the body or one quality is not attended to, it
remains either unchanged or varies in a fluctuating manner, whilst at the same
time other parts and other qualities may become permanently and greatly
modified. But from the tendency to reversion and to continued variability,
those parts or organs which are now undergoing rapid improvement through
selection, are likewise found to vary much. Consequently highly-bred animals
when neglected soon degenerate; but we have no reason to believe that the
effects of long-continued selection would, if the conditions of life remained
the same, be soon and completely lost.

Man always tends to go to an extreme point in the selection, whether
methodical or unconscious, of all useful and pleasing qualities. This is an
important principle, as it leads to continued divergence, and in some rare
cases to convergence of character. The possibility of continued divergence
rests on the tendency in each part or organ to go on varying in the same
manner in which it has already varied; and that this occurs, is proved by the
steady and gradual improvement of many animals and plants during lengthened
periods. The principle of divergence of character, combined with the neglect
and final extinction of all previous, less-valued, and intermediate varieties,
explains the amount of difference and the distinctness of our several races.
Although we may have reached the utmost limit to which certain characters can
be modified, yet we are far from having reached, as we have good reason to
believe, the limit in the majority of cases. Finally, from the difference
between selection as carried on by man and by nature, we can understand how it
is that domestic races often, though by no means always, differ in general
aspect from closely allied natural species.

Throughout this chapter and elsewhere I have spoken of selection as the
paramount power, yet its action absolutely depends on what we in our ignorance
call spontaneous or accidental variability. Let an architect be compelled to
build an edifice with uncut stones, fallen from a precipice. The shape of each
fragment may be called accidental; yet the shape of each has been determined
by the force of gravity, the nature of the rock, and the slope of the
precipice,--events and circumstances, all of which depend on natural laws; but
there is no relation between these laws and the purpose for which each
fragment is used by the builder. In the same manner the variations of each
creature are determined by fixed and immutable laws; but these bear no
relation to the living structure which is slowly built up through the power of
selection, whether this be natural or artificial selection.

If our architect succeeded in rearing a noble edifice, using the rough wedge-
shaped fragments for the arches, the longer stones for the lintels, and so
forth, we should admire his skill even in a higher degree than if he had used
stones shaped for the purpose. So it is with selection, whether applied by man
or by nature; for although variability is indispensably necessary, yet, when
we look at some highly complex and excellently adapted organism, variability
sinks to a quite subordinate position in importance in comparison with
selection, in the same manner as the shape of each fragment used by our
supposed architect is unimportant in comparison with his skill.


CHAPTER 2.XXII.

CAUSES OF VARIABILITY.

VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION.
CAUSES ASSIGNED BY VARIOUS AUTHORS.
INDIVIDUAL DIFFERENCES.
VARIABILITY OF EVERY KIND DUE TO CHANGED CONDITIONS OF LIFE.
ON THE NATURE OF SUCH CHANGES.
CLIMATE, FOOD, EXCESS OF NUTRIMENT.
SLIGHT CHANGES SUFFICIENT.
EFFECTS OF GRAFTING ON THE VARIABILITY OF SEEDLING-TREES.
DOMESTIC PRODUCTIONS BECOME HABITUATED TO CHANGED CONDITIONS.
ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS.
CLOSE INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE
VARIABILITY.
CROSSING AS A CAUSE OF THE APPEARANCE OF NEW CHARACTERS.
VARIABILITY FROM THE COMMINGLING OF CHARACTERS AND FROM REVERSION.
ON THE MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH EITHER DIRECTLY, OR
INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE VARIABILITY.

We will now consider, as far as we can, the causes of the almost universal
variability of our domesticated productions. The subject is an obscure one;
but it may be useful to probe our ignorance. Some authors, for instance Dr.
Prosper Lucas, look at variability as a necessary contingent on reproduction,
and as much an aboriginal law as growth or inheritance. Others have of late
encouraged, perhaps unintentionally, this view by speaking of inheritance and
variability as equal and antagonistic principles. Pallas maintained, and he
has had some followers, that variability depends exclusively on the crossing
of primordially distinct forms. Other authors attribute variability to an
excess of food, and with animals to an excess relatively to the amount of
exercise taken, or again to the effects of a more genial climate. That these
causes are all effective is highly probable. But we must, I think, take a
broader view, and conclude that organic beings, when subjected during several
generations to any change whatever in their conditions, tend to vary; the kind
of variation which ensues depending in most cases in a far higher degree on
the nature or constitution of the being, than on the nature of the changed
conditions.

Those authors who believe that it is a law of nature that each individual
should differ in some slight degree from every other, may maintain, apparently
with truth, that this is the fact, not only with all domesticated animals and
cultivated plants, but likewise with all organic beings in a state of nature.
The Laplander by long practice knows and gives a name to each reindeer,
though, as Linnaeus remarks, "to distinguish one from another among such
multitudes was beyond my comprehension, for they were like ants on an
anthill." In Germany shepherds have won wagers by recognising each sheep in a
flock of a hundred, which they had never seen until the previous fortnight.
This power of discrimination, however, is as nothing compared to that which
some florists have acquired. Verlot mentions a gardener who could distinguish
150 kinds of camellia, when not in flower; and it has been positively asserted
that the famous old Dutch florist Voorhelm, who kept above 1200 varieties of
the hyacinth, was hardly ever deceived in knowing each variety by the bulb
alone. Hence we must conclude that the bulbs of the hyacinth and the branches
and leaves of the camellia, though appearing to an unpractised eye absolutely
undistinguishable, yet really differ. (22/1. 'Des Jacinthes' etc. Amsterdam
1768 page 43; Verlot 'Des Varietes' etc. page 86. On the reindeer see Linnaeus
'Tour in Lapland' translated by Sir J.E. Smith volume 1 page 314. The
statement in regard to German shepherds is given on the authority of Dr.
Weinland.)

As Linnaeus has compared the reindeer in number to ants, I may add that each
ant knows its fellow of the same community. Several times I carried ants of
the same species (Formica rufa) from one ant-hill to another, inhabited
apparently by tens of thousands of ants; but the strangers were instantly
detected and killed. I then put some ants taken from a very large nest into a
bottle strongly perfumed with assafoetida, and after an interval of twenty-
four hours returned them to their home; they were at first threatened by their
fellows, but were soon recognised and allowed to pass. Hence each ant
certainly recognised, independently of odour, its fellow; and if all the ants
of the same community have not some countersign or watchword, they must
present to each other's senses some distinguishable character.

The dissimilarity of brothers or sisters of the same family, and of seedlings
from the same capsule, may be in part accounted for by the unequal blending of
the characters of the two parents, and by the more or less complete recovery
through reversion of ancestral characters on either side; but we thus only
push the difficulty further back in time, for what made the parents or their
progenitors different? Hence the belief (22/2. Muller 'Physiology' English
translation, volume 2 page 1662. With respect to the similarity of twins in
constitution, Dr. William Ogle has given me the following extract from
Professor Trousseau's Lectures 'Clinique Medicale' tome 1 page 523, in which a
curious case is recorded:--"J'ai donne mes soins a deux freres jumeaux, tous
deux si extraordinairement ressemblants qu'il m'etait impossible de les
reconnaitre, a moin de les voir l'un a cote de l'autre. Cette ressemblance
physique s'etendait plus loin: ils avaient, permettez-moi l'expression, une
similitude pathologique plus remarquable encore. Ainsi l'un d'eux que je
voyais aux neothermes a Paris malade d'une ophthalmie rhumatismale me disait,
'En ce moment mon frere doit avoir une ophthalmie comme la mienne;' et comme
je m'etais recrie, il me montrait quelques jours apres une lettre qu'il venait
de recevoir de ce frere alors a Vienne, et qui lui ecrivait en effet--'J'ai
mon ophthalmie, tu dois avoir la tienne.' Quelque singulier que ceci puisse
paraitre, le fait n'en est pas moins exact: on ne me l'a pas raconte, je l'ai
vu, et j'en ai vu d'autres analogues dans ma pratique. Ces deux jumeaux
etaient aussi tous deux asthmatiques, et asthmatiques a un effroyable degre.
Originaires de Marseille, ils n'ont jamais pu demeurer dans cette ville, ou
leurs interets les appelaient souvent, sans etre pris de leurs acces; jamais
ils n'en eprouvaient a Paris. Bien mieux, il leur suffisait de gagner Toulon
pour etre gueris de leurs attaques de Marseille. Voyageant sans cesse et dans
tous pays pour leurs affaires, ils avaient remarque que certaines localites
leur etaient funestes, que dans d'autres ils etaient exempts de tout phenomene
d'oppression.") that an innate tendency to vary exists, independently of
external differences, seems at first sight probable. But even the seeds
nurtured in the same capsule are not subjected to absolutely uniform
conditions, as they draw their nourishment from different points; and we shall
see in a future chapter that this difference sometimes suffices to affect the
character of the future plant. The greater dissimilarity of the successive
children of the same family in comparison with twins, which often resemble
each other in external appearance, mental disposition, and constitution, in so
extraordinary a manner, apparently proves that the state of the parents at the
exact period of conception, or the nature of the subsequent embryonic
development, has a direct and powerful influence on the character of the
offspring. Nevertheless, when we reflect on the individual differences between
organic beings in a state of nature, as shown by every wild animal knowing its
mate; and when we reflect on the infinite diversity of the many varieties of
our domesticated productions, we may well be inclined to exclaim, though
falsely as I believe, that Variability must be looked at as an ultimate fact,
necessarily contingent on reproduction.

Those authors who adopt this latter view would probably deny that each
separate variation has its own proper exciting cause. Although we can seldom
trace the precise relation between cause and effect, yet the considerations
presently to be given lead to the conclusion that each modification must have
its own distinct cause, and is not the result of what we blindly call
accident. The following striking case has been communicated to me by Dr.
William Ogle. Two girls, born as twins, and in all respects extremely alike,
had their little fingers on both hands crooked; and in both children the
second bicuspid tooth of the second dentition on the right side in the upper
jaw was misplaced; for, instead of standing in a line with the others, it grew
from the roof of the mouth behind the first bicuspid. Neither the parents nor
any other members of the family were known to have exhibited any similar
peculiarity; but a son of one of these girls had the same tooth similarly
misplaced. Now, as both the girls were affected in exactly the same manner,
the idea of accident is at once excluded: and we are compelled to admit that
there must have existed some precise and sufficient cause which, if it had
occurred a hundred times, would have given crooked fingers and misplaced
bicuspid teeth to a hundred children. It is of course possible that this case
may have been due to reversion to some long-forgotten progenitor, and this
would much weaken the value of the argument. I have been led to think of the
probability of reversion, from having been told by Mr. Galton of another case
of twin girls born with their little fingers slightly crooked, which they
inherited from their maternal grandmother.

We will now consider the general arguments, which appear to me to have great
weight, in favour of the view that variations of all kinds and degrees are
directly or indirectly caused by the conditions of life to which each being,
and more especially its ancestors, have been exposed.

No one doubts that domesticated productions are more variable than organic
beings which have never been removed from their natural conditions.
Monstrosities graduate so insensibly into mere variations that it is
impossible to separate them; and all those who have studied monstrosities
believe that they are far commoner with domesticated than with wild animals
and plants (22/3. Isid. Geoffroy St.-Hilaire 'Hist. des Anomalies' tome 3 page
352; Moquin-Tandon 'Teratologie Vegetale' 1841 page 115.); and in the case of
plants, monstrosities would be equally noticeable in the natural as in the
cultivated state. Under nature, the individuals of the same species are
exposed to nearly uniform conditions, for they are rigorously kept to their
proper places by a host of competing animals and plants; they have, also, long
been habituated to their conditions of life; but it cannot be said that they
are subject to quite uniform conditions, and they are liable to a certain
amount of variation. The circumstances under which our domestic productions
are reared are widely different: they are protected from competition; they
have not only been removed from their natural conditions and often from their
native land, but they are frequently carried from district to district, where
they are treated differently, so that they rarely remain during any
considerable length of time exposed to closely similar conditions. In
conformity with this, all our domesticated productions, with the rarest
exceptions, vary far more than natural species. The hive-bee, which feeds
itself and follows in most respects its natural habits of life, is the least
variable of all domesticated animals, and probably the goose is the next least
variable; but even the goose varies more than almost any wild bird, so that it
cannot be affiliated with perfect certainty to any natural species. Hardly a
single plant can be named, which has long been cultivated and propagated by
seed, that is not highly variable; common rye (Secale cereale) has afforded
fewer and less marked varieties than almost any other cultivated plant (22/4.
Metzger 'Die Getreidarten' 1841 s. 39.); but it may be doubted whether the
variations of this, the least valuable of all our cereals, have been closely
observed.

Bud-variation, which was fully discussed in a former chapter, shows us that
variability may be quite independent of seminal reproduction, and likewise of
reversion to long-lost ancestral characters. No one will maintain that the
sudden appearance of a moss-rose on a Provence-rose is a return to a former
state, for mossiness of the calyx has been observed in no natural species; the
same argument is applicable to variegated and laciniated leaves; nor can the
appearance of nectarines on peach-trees be accounted for on the principle of
reversion. But bud-variations more immediately concern us, as they occur far
more frequently on plants which have been highly cultivated during a length of
time, than on other and less highly cultivated plants; and very few well-
marked instances have been observed with plants growing under strictly natural
conditions. I have given one instance of an ash-tree growing in a gentleman's
pleasure-grounds; and occasionally there may be seen, on beech and other
trees, twigs leafing at a different period from the other branches. But our
forest trees in England can hardly be considered as living under strictly
natural conditions; the seedlings are raised and protected in nursery-grounds,
and must often be transplanted into places where wild trees of the kind would
not naturally grow. It would be esteemed a prodigy if a dog-rose growing in a
hedge produced by bud-variation a moss-rose, or a wild bullace or wild cherry-
tree yielded a branch bearing fruit of a different shape and colour from the
ordinary fruit. The prodigy would be enhanced if these varying branches were
found capable of propagation, not only by grafts, but sometimes by seed; yet
analogous cases have occurred with many of our highly cultivated trees and
herbs.

These several considerations alone render it probable that variability of
every kind is directly or indirectly caused by changed conditions of life. Or,
to put the case under another point of view, if it were possible to expose all
the individuals of a species during many generations to absolutely uniform
conditions of life, there would be no variability.

ON THE NATURE OF THE CHANGES IN THE CONDITIONS OF LIFE WHICH INDUCE
VARIABILITY.

From a remote period to the present day, under climates and circumstances as
different as it is possible to conceive, organic beings of all kinds, when
domesticated or cultivated, have varied. We see this with the many domestic
races of quadrupeds and birds belonging to different orders, with goldfish and
silkworms, with plants of many kinds, raised in various quarters of the world.
In the deserts of northern Africa the date-palm has yielded thirty-eight
varieties; in the fertile plains of India it is notorious how many varieties
of rice and of a host of other plants exist; in a single Polynesian island,
twenty-four varieties of the bread-fruit, the same number of the banana, and
twenty-two varieties of the arum, are cultivated by the natives; the mulberry-
tree in India and Europe has yielded many varieties serving as food for the
silkworm; and in China sixty-three varieties of the bamboo are used for
various domestic purposes. (22/5. On the date-palm see Vogel 'Annals and Mag.
of Nat. Hist.' 1854 page 460. On Indian varieties Dr. F. Hamilton 'Transact.
Linn. Soc.' volume 14 page 296. On the varieties cultivated in Tahiti see Dr.
Bennett in Loudon's 'Mag. of N. Hist.' volume 5 1832 page 484. Also Ellis
'Polynesian Researches' volume 1 pages 370, 375. On twenty varieties of the
Pandanus and other trees in the Marianne Island see 'Hooker's Miscellany'
volume 1 page 308. On the bamboo in China see Huc 'Chinese Empire' volume 2
page 307.) These facts, and innumerable others which could be added, indicate
that a change of almost any kind in the conditions of life suffices to cause
variability--different changes acting on different organisms.

Andrew Knight (22/6. 'Treatise on the Culture of the Apple' etc. page 3.)
attributed the variation of both animals and plants to a more abundant supply
of nourishment, or to a more favourable climate, than that natural to the
species. A more genial climate, however, is far from necessary; the kidney-
bean, which is often injured by our spring frosts, and peaches, which require
the protection of a wall, have varied much in England, as has the orange-tree
in northern Italy, where it is barely able to exist. (22/7. Gallesio 'Teoria
della Riproduzione Veg.' page 125.) Nor can we overlook the fact, though not
immediately connected with our present subject, that the plants and shells of
the Arctic regions are eminently variable. (22/8. See Dr. Hooker's Memoir on
Arctic Plants in 'Linn. Transact.' volume 23 part 2. Mr. Woodward, and a
higher authority cannot be quoted, speaks of the Arctic mollusca in his
'Rudimentary Treatise' 1856 page 355 as remarkably subject to variation.)
Moreover, it does not appear that a change of climate, whether more or less
genial, is one of the most potent causes of variability; for in regard to
plants Alph. De Candolle, in his 'Geographie Botanique' repeatedly shows that
the native country of a plant, where in most cases it has been longest
cultivated, is that where it has yielded the greatest number of varieties.

It is doubtful whether a change in the nature of the food is a potent cause of
variability. Scarcely any domesticated animal has varied more than the pigeon
or the fowl, but their food, especially that of highly-bred pigeons, is
generally the same. Nor can our cattle and sheep have been subjected to any
great change in this respect. But in all these cases the food probably is much
less varied in kind than that which was consumed by the species in its natural
state. (22/9. Bechstein in his 'Naturgeschichte der Stubenvogel' 1840 s. 238,
has some good remarks on this subject. He states that his canary-birds varied
in colour, though kept on uniform food.)

Of all the causes which induce variability, excess of food, whether or not
changed in nature, is probably the most powerful. This view was held with
regard to plants by Andrew Knight, and is now held by Schleiden, more
especially in reference to the inorganic elements of the food. (22/10. 'The
Plant' by Schleiden translated by Henfrey 1848 page 169. See also Alex. Braun
in 'Bot. Memoirs' Ray Soc. 1853 page 313.) In order to give a plant more food
it suffices in most cases to grow it separately, and thus prevent other plants
robbing its roots. It is surprising, as I have often seen, how vigorously our
common wild species flourish when planted by themselves, though not in highly
manured land; separate growth is, in fact, the first step in cultivation. We
see the converse of the belief that excess of food induces variability in the
following statement by a great raiser of seeds of all kinds (22/11. Messrs.
Hardy and Son of Maldon in 'Gardener's Chronicle' 1856 page 458. Carriere
'Production et Fixation des Varietes' 1865 page 31.): "It is a rule invariably
with us, when we desire to keep a true stock of any one kind of seed, to grow
it on poor land without dung; but when we grow for quantity, we act contrary,
and sometimes have dearly to repent of it." According also to Carriere, who
has had great experience with flower-garden seeds, "On remarque en general les
plantes de vigeur moyenne sont celles qui conservent le mieux leurs
caracteres."

In the case of animals the want of a proper amount of exercise, as Bechstein
remarked, has perhaps played, independently of the direct effects of the
disuse of any particular organ, an important part in causing variability. We
can see in a vague manner that, when the organised and nutrient fluids of the
body are not used during growth, or by the wear and tear of the tissues, they
will be in excess; and as growth, nutrition, and reproduction are intimately
allied processes, this superfluity might disturb the due and proper action of
the reproductive organs, and consequently affect the character of the future
offspring. But it may be argued that neither an excess of food nor a
superfluity in the organised fluids of the body necessarily induces
variability. The goose and the turkey have been well fed for many generations,
yet have varied very little. Our fruit-trees and culinary plants, which are so
variable, have been cultivated from an ancient period, and, though they
probably still receive more nutriment than in their natural state, yet they
must have received during many generations nearly the same amount; and it
might be thought that they would have become habituated to the excess.
Nevertheless, on the whole, Knight's view, that excess of food is one of the
most potent causes of variability, appears, as far as I can judge, probable.

Whether or not our various cultivated plants have received nutriment in
excess, all have been exposed to changes of various kinds. Fruit-trees are
grafted on different stocks, and grown in various soils. The seeds of culinary
and agricultural plants are carried from place to place; and during the last
century the rotation of our crops and the manures used have been greatly
changed.

Slight changes of treatment often suffice to induce variability. The simple
fact of almost all our cultivated plants and domesticated animals having
varied in all places and at all times, leads to this conclusion. Seeds taken
from common English forest-trees, grown under their native climate, not highly
manured or otherwise artificially treated, yield seedlings which vary much, as
may be seen in every extensive seed-bed. I have shown in a former chapter what
a number of well-marked and singular varieties the thorn (Crataegus oxycantha)
has produced: yet this tree has been subjected to hardly any cultivation. In
Staffordshire I carefully examined a large number of two British plants,
namely Geranium phaeum and pyrenaicum, which have never been highly
cultivated. These plants had spread spontaneously by seed from a common garden
into an open plantation; and the seedlings varied in almost every single
character, both in their flower and foliage, to a degree which I have never
seen exceeded; yet they could not have been exposed to any great change in
their conditions.

With respect to animals, Azara has remarked with much surprise (22/12.
'Quadrupedes du Paraguay' 1801 tome 2 page 319.) that, whilst the feral horses
on the Pampas are always of one of three colours, and the cattle always of a
uniform colour, yet these animals, when bred on the unenclosed estancias,
though kept in a state which can hardly be called domesticated, and apparently
exposed to almost identically the same conditions as when they are feral,
nevertheless display a great diversity of colour. So again in India several
species of fresh-water fish are only so far treated artificially, that they
are reared in great tanks; but this small change is sufficient to induce much
variability. (22/13. M'Clelland on Indian Cyprinidae 'Asiatic Researches'
volume 19 part 2 1839 pages 266, 268, 313.)

Some facts on the effects of grafting, in regard to the variability of trees,
deserve attention. Cabanis asserts that when certain pears are grafted on the
quince, their seeds yield a greater number of varieties than do the seeds of
the same variety of pear when grafted on the wild pear. (22/14. Quoted by
Sageret 'Pom. Phys.' 1830 page 43. This statement, however, is not believed by
Decaisne.) But as the pear and quince are distinct species, though so closely
related that the one can be readily grafted and succeeds admirably on the
other, the fact of variability being thus caused is not surprising; as we are
here enabled to see the cause, namely, the very different nature of the stock
and graft. Several North American varieties of the plum and peach are well
known to reproduce themselves truly by seed; but Downing asserts (22/15. 'The
Fruits of America' 1845 page 5.), "that when a graft is taken from one of
these trees and placed upon another stock, this grafted tree is found to lose
its singular property of producing the same variety by seed, and becomes like
all other worked trees;"--that is, its seedlings become highly variable.
Another case is worth giving: the Lalande variety of the walnut-tree leafs
between April 20th and May 15th, and its seedlings invariably inherit the same
habit; whilst several other varieties of the walnut leaf in June. Now, if
seedlings are raised from the May-leafing Lalande variety, grafted on another
May-leafing variety, though both stock and graft have the same early habit of
leafing, yet the seedlings leaf at various times, even as late as the 5th of
June. (22/16. M. Cardan in 'Comptes Rendus' December 1848 quoted in
'Gardener's Chronicle' 1849 page 101.) Such facts as these are well fitted to
show on what obscure and slight causes variability depends.

[I may here just allude to the appearance of new and valuable varieties of
fruit-trees and of wheat in woods and waste places, which at first sight seems
a most anomalous circumstance. In France a considerable number of the best
pears have been discovered in woods; and this has occurred so frequently, that
Poiteau asserts that "improved varieties of our cultivated fruits rarely
originate with nurserymen." (22/17. M. Alexis Jordan mentions four excellent
pears found in woods in France, and alludes to others ('Mem. Acad. de Lyon'
tome 2 1852 page 159). Poiteau's remark is quoted in 'Gardener's Mag.' volume
4 1828 page 385. See 'Gardener's Chronicle' 1862 page 335, for another case of
a new variety of the pear found in a hedge in France. Also for another case,
see Loudon's 'Encyclop. of Gardening' page 901. Mr. Rivers has given me
similar information.) In England, on the other hand, no instance of a good
pear having been found wild has been recorded; and Mr. Rivers informs me that
he knows of only one instance with apples, namely, the Bess Poole, which was
discovered in a wood in Nottinghamshire. This difference between the two
countries may be in part accounted for by the more favourable climate of
France, but chiefly from the great number of seedlings which spring up there
in the woods. I infer that this is the case from a remark made by a French
gardener (22/18. Duval 'Hist. du Poirier' 1849 page 2.), who regards it as a
national calamity that such a number of pear-trees are periodically cut down
for firewood, before they have borne fruit. The new varieties which thus
spring up in the woods, though they cannot have received any excess of
nutriment, will have been exposed to abruptly changed conditions, but whether
this is the cause of their production is very doubtful. These varieties,
however, are probably all descended (22/19. I infer that this is the fact from
Van Mons' statement ('Arbres Fruitiers' 1835 tome 1 page 446) that he finds
in the woods seedlings resembling all the chief cultivated races of both the
pear and apple. Van Mons, however, looked at these wild varieties as
aboriginal species.) from old cultivated kinds growing in adjoining orchards--
a circumstance which will account for their variability; and out of a vast
number of varying trees there will always be a good chance of the appearance
of a valuable kind. In North America, where fruit-trees frequently spring up
in waste places, the Washington pear was found in a hedge, and the Emperor
peach in a wood. (22/20. Downing 'Fruit-trees of North America' page 422;
Foley in 'Transact. Hort. Soc.' volume 6 page 412.)

With respect to wheat, some writers have spoken (22/21. 'Gardener's Chronicle'
1847 page 244.) as if it were an ordinary event for new varieties to be found
in waste places; the Fenton wheat was certainly discovered growing on a pile
of basaltic detritus in a quarry, but in such a situation the plant would
probably receive a sufficient amount of nutriment. The Chidham wheat was
raised from an ear found ON a hedge; and Hunter's wheat was discovered BY the
roadside in Scotland, but it is not said that this latter variety grew where
it was found. (22/22. 'Gardener's Chronicle' 1841 page 383; 1850 page 700;
1854 page 650.)]

Whether our domestic productions would ever become so completely habituated to
the conditions under which they now live, as to cease varying, we have no
sufficient means for judging. But, in fact, our domestic productions are never
exposed for a great length of time to uniform conditions, and it is certain
that our most anciently cultivated plants, as well as animals, still go on
varying, for all have recently undergone marked improvement. In some few
cases, however, plants have become habituated to new conditions. Thus,
Metzger, who cultivated in Germany during many years numerous varieties of
wheat, brought from different countries (22/23. 'Die Getreidearten' 1843 s.
66, 116, 117.), states that some kinds were at first extremely variable, but
gradually, in one   instance after an interval of twenty-five years, became
constant; and it does not appear that this resulted from the selection of the
more constant forms.

ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS OF LIFE.

We have good grounds for believing that the influence of changed conditions
accumulates, so that no effect is produced on a species until it has been
exposed during several generations to continued cultivation or domestication.
Universal experience shows us that when new flowers are first introduced into
our gardens they do not vary; but ultimately all, with the rarest exceptions,
vary to a greater or less extent. In a few cases the requisite number of
generations, as well as the successive steps in the progress of variation,
have been recorded, as in the often quoted instance of the Dahlia. (22/24.
Sabine in 'Hort. Transact.' volume 3 page 225; Bronn 'Geschichte der Natur' b.
2 s. 119.) After several years' culture the Zinnia has only lately (1860)
begun to vary in any great degree. "In the first seven or eight years of high
cultivation, the Swan River daisy (Brachycome iberidifolia) kept to its
original colour; it then varied into lilac and purple and other minor shades."
(22/25. 'Journal of Horticulture' 1861 page 112; on Zinnia 'Gardener's
Chronicle' 1860 page 852.) Analogous facts have been recorded with the Scotch
rose. In discussing the variability of plants several experienced
horticulturists have spoken to the same general effect. Mr. Salter (22/26.
'The Chrysanthemum, its History, etc.' 1865 page 3.) remarks, "Every one knows
that the chief difficulty is in breaking through the original form and colour
of the species, and every one will be on the look-out for any natural sport,
either from seed or branch; that being once obtained, however trifling the
change may be, the result depends upon himself." M. de Jonghe, who has had so
much success in raising new varieties of pears and strawberries (22/27.
'Gardener's Chronicle' 1855 page 54; 'Journal of Horticulture' May 9, 1865
page 363.), remarks with respect to the former, "There is another principle,
namely, that the more a type has entered into a state of variation, the
greater is its tendency to continue doing so; and the more it has varied from
the original type, the more it is disposed to vary still farther." We have,
indeed, already discussed this latter point when treating of the power which
man possesses, through selection, of continually augmenting in the same
direction each modification; for this power depends on continued variability
of the same general kind. The most celebrated horticulturist in France,
namely, Vilmorin (22/28. Quoted by Verlot 'Des Varietes' etc. 1865 page 28.),
even maintains that, when any particular variation is desired, the first step
is to get the plant to vary in any manner whatever, and to go on selecting the
most variable individuals, even though they vary in the wrong direction; for
the fixed character of the species being once broken, the desired variation
will sooner or later appear.

As nearly all our animals were domesticated at an extremely remote epoch, we
cannot, of course, say whether they varied quickly or slowly when first
subjected to new conditions. But Dr. Bachman (22/29. 'Examination of the
Characteristics of Genera and Species' Charleston 1855 page 14.) states that
he has seen turkeys raised from the eggs of the wild species lose their
metallic tints and become spotted with white in the third generation. Mr.
Yarrell many years ago informed me that the wild ducks bred on the ponds in
St. James's Park, which had never been crossed, as it is believed, with
domestic ducks, lost their true plumage after a few generations. An excellent
observer (22/30. Mr. Hewitt 'Journal of Hort.' 1863 page 39.), who has often
reared ducks from the eggs of the wild bird, and who took precautions that
there should be no crossing with domestic breeds, has given, as previously
stated, full details on the changes which they gradually undergo. He found
that he could not breed these wild ducks true for more than five or six
generations, "as they then proved so much less beautiful. The white collar
round the neck of the mallard became much broader and more irregular, and
white feathers appeared in the ducklings' wings." They increased also in size
of body; their legs became less fine, and they lost their elegant carriage.
Fresh eggs were then procured from wild birds; but again the same result
followed. In these cases of the duck and turkey we see that animals, like
plants, do not depart from their primitive type until they have been subjected
during several generations to domestication. On the other hand, Mr. Yarrell
informed me that the Australian dingos, bred in the Zoological Gardens, almost
invariably produced in the first generation puppies marked with white and
other colours; but, these introduced dingos had probably been procured from
the natives, who keep them in a semi-domesticated state. It is certainly a
remarkable fact that changed conditions should at first produce, as far as we
can see, absolutely no effect; but that they should subsequently cause the
character of the species to change. In the chapter on pangenesis I shall
attempt to throw a little light on this fact.

Returning now to the causes which are supposed to induce variability. Some
authors (22/31. Devay 'Mariages Consanguins' pages 97, 125. In conversation I
have found two or three naturalists of the same opinion.) believe that close
interbreeding gives this tendency, and leads to the production of
monstrosities. In the seventeenth chapter some few facts were advanced,
showing that monstrosities are, as it appears, occasionally thus induced; and
there can be no doubt that close interbreeding causes lessened fertility and a
weakened constitution; hence it may lead to variability: but I have not
sufficient evidence on this head. On the other hand, close interbreeding, if
not carried to an injurious extreme, far from causing variability, tends to
fix the character of each breed.

It was formerly a common belief, still held by some persons, that the
imagination of the mother affects the child in the womb. (22/32. Muller has
conclusively argued against this belief, 'Elements of Phys.' English
translation volume 2 1842 page 1405.) This view is evidently not applicable to
the lower animals, which lay unimpregnated eggs, or to plants. Dr. William
Hunter, in the last century, told my father that during many years every woman
in a large London Lying-in Hospital was asked before her confinement whether
anything had specially affected her mind, and the answer was written down; and
it so happened that in no one instance could a coincidence be detected between
the woman's answer and any abnormal structure; but when she knew the nature of
the structure, she frequently suggested some fresh cause. The belief in the
power of the mother's imagination may perhaps have arisen from the children of
a second marriage resembling the previous father, as certainly sometimes
occurs, in accordance with the facts given in the eleventh chapter.

CROSSING AS A CAUSE OF VARIABILITY.

In an early part of this chapter it was stated that Pallas (22/33. 'Act. Acad.
St. Petersburg' 1780 part 2 page 84 etc.) and a few other naturalists maintain
that variability is wholly due to crossing. If this means that new characters
never spontaneously appear in our domestic races, but that they are all
directly derived from certain aboriginal species, the doctrine is little less
than absurd; for it implies that animals like Italian greyhounds, pug-dogs,
bull-dogs, pouter and fantail pigeons, etc., were able to exist in a state of
nature. But the doctrine may mean something widely different, namely, that the
crossing of distinct species is the sole cause of the first appearance of new
characters, and that without this aid man could not have formed his various
breeds. As, however, new characters have appeared in certain cases by bud-
variation, we may conclude with certainty that crossing is not necessary for
variability. It is, moreover, certain that the breeds of various animals, such
as of the rabbit, pigeon, duck, etc., and the varieties of several plants, are
the modified descendants of a single wild species. Nevertheless, it is
probable that the crossing of two forms, when one or both have long been
domesticated or cultivated, adds to the variability of the offspring,
independently of the commingling of the characters derived from the two
parent-forms; and this implies that new characters actually arise. But we must
not forget the facts advanced in the thirteenth chapter, which clearly prove
that the act of crossing often leads to the reappearance or reversion of long-
lost characters; and in most cases it would be impossible to distinguish
between the reappearance of ancient characters and the first appearance of
absolutely new characters. Practically, whether new or old, they would be new
to the breed in which they reappeared.

[Gartner declares (22/34. 'Bastarderzeugung' s. 249, 255, 295.), and his
experience is of the highest value on such a point, that, when he crossed
native plants which had not been cultivated, he never once saw in the
offspring any new character; but that from the odd manner in which the
characters derived from the parents were combined, they sometimes appeared as
if new. When, on the other hand, he crossed cultivated plants, he admits that
new characters occasionally appeared, but he is strongly inclined to attribute
their appearance to ordinary variability, not in any way to the cross. An
opposite conclusion, however, appears to me the more probable. According to
Kolreuter, hybrids in the genus Mirabilis vary almost infinitely, and he
describes new and singular characters in the form of the seeds, in the colour
of the anthers, in the cotyledons being of immense size, in new and highly
peculiar odours, in the flowers expanding early in the season, and in their
closing at night. With respect to one lot of these hybrids, he remarks that
they presented characters exactly the reverse of what might have been expected
from their parentage. (22/35. 'Nova Acta, St. Petersburg' 1794 page 378; 1795
pages 307, 313, 316; 1787 page 407.)

Prof. Lecoq (22/36. 'De la Fecondation' 1862 page 311.) speaks strongly to the
same effect in regard to this same genus, and asserts that many of the hybrids
from Mirabilis jalapa and multiflora might easily be mistaken for distinct
species, and adds that they differed in a greater degree than the other
species of the genus, from M. jalapa. Herbert, also, has described (22/37.
'Amaryllidaceae' 1837 page 362.) certain hybrid Rhododendrons as being "as
UNLIKE ALL OTHERS in foliage, as if they had been a separate species." The
common experience of floriculturists proves that the crossing and recrossing
of distinct but allied plants, such as the species of Petunia, Calceolaria,
Fuchsia, Verbena, etc., induces excessive variability; hence the appearance of
quite new characters is probable. M. Carriere (22/38. Abstracted in
'Gardener's Chronicle' 1860 page 1081.) has lately discussed this subject: he
states that Erythrina cristagalli had been multiplied by seed for many years,
but had not yielded any varieties: it was then crossed with the allied E.
herbacea, and "the resistance was now overcome, and varieties were produced
with flowers of extremely different size, form, and colour."

From the general and apparently well-founded belief that the crossing of
distinct species, besides commingling their characters, adds greatly to their
variability, it has probably arisen that some botanists have gone so far as to
maintain (22/39. This was the opinion of the elder De Candolle, as quoted in
'Dic. Class. d'Hist. Nat.' tome 8 page 405. Puvis in his work 'De la
Degeneration' 1837 page 37, has discussed this same point.) that, when a genus
includes only a single species, this when cultivated never varies. The
proposition made so broadly cannot be admitted; but it is probably true that
the variability of monotypic genera when cultivated is generally less than
that of genera including numerous species, and this quite independently of the
effects of crossing. I have shown in my 'Origin of Species' that the species
belonging to small genera generally yield a less number of varieties in a
state of nature than those belonging to large genera. Hence the species of
small genera would, it is probable, produce fewer varieties under cultivation
than the already variable species of larger genera.

Although we have not at present sufficient evidence that the crossing of
species, which have never been cultivated, leads to the appearance of new
characters, this apparently does occur with species which have been already
rendered in some degree variable through cultivation. Hence crossing, like any
other change in the conditions of life, seems to be an element, probably a
potent one, in causing variability. But we seldom have the means of
distinguishing, as previously remarked, between the appearance of really new
characters and the reappearance of long-lost characters, evoked through the
act of crossing. I will give an instance of the difficulty in distinguishing
such cases. The species of Datura may be divided into two sections, those
having white flowers with green stems, and those having purple flowers with
brown stems: now Naudin (22/40. 'Comptes Rendus' Novembre 21, 1864 page 838.)
crossed Datura laevis and ferox, both of which belong to the white section,
and raised from them 205 hybrids. Of these hybrids, every one had brown stems
and bore purple flowers; so that they resembled the species of the other
section of the genus, and not their own two parents. Naudin was so much
astonished at this fact, that he was led carefully to observe both parent-
species, and he discovered that the pure seedlings of D. ferox, immediately
after germination, had dark purple stems, extending from the young roots up to
the cotyledons, and that this tint remained ever afterwards as a ring round
the base of the stem of the plant when old. Now I have shown in the thirteenth
chapter that the retention or exaggeration of an early character is so
intimately related to reversion, that it evidently comes under the same
principle. Hence probably we ought to look at the purple flowers and brown
stems of these hybrids, not as new characters due to variability, but as a
return to the former state of some ancient progenitor.

Independently of the appearance of new characters from crossing, a few words
may be added to what has been said in former chapters on the unequal
combination and transmission of the characters proper to the two parent-forms.
When two species or races are crossed, the offspring of the first generation
are generally uniform, but those subsequently produced display an almost
infinite diversity of character. He who wishes, says Kolreuter (22/41. 'Nova
Acta, St. Petersburg' 1794 page 391.), to obtain an endless number of
varieties from hybrids should cross and recross them. There is also much
variability when hybrids or mongrels are reduced or absorbed by repeated
crosses with either pure parent-form: and a still higher degree of variability
when three distinct species, and most of all when four species, are blended
together by successive crosses. Beyond this point Gartner (22/42.
'Bastarderzeugung' s. 507, 516, 572.), on whose authority the foregoing
statements are made, never succeeded in effecting a union; but Max Wichura
(22/43. 'Die Bastardbefruchtung' etc. 1865 s. 24.) united six distinct species
of willows into a single hybrid. The sex of the parent species affects in an
inexplicable manner the degree of variability of hybrids; for Gartner (22/44.
'Bastarderzeugung' s. 452, 507.) repeatedly found that when a hybrid was used
as a father and either one of the pure parent-species, or a third species, was
used as the mother, the offspring were more variable than when the same hybrid
was used as the mother, and either pure parent or the same third species as
the father: thus seedlings from Dianthus barbatus crossed by the hybrid D.
chinensi-barbatus were more variable than those raised from this latter hybrid
fertilised by the pure D. barbatus. Max Wichura (22/45. 'Die
Bastardbefruchtung' s. 56.) insists strongly on an analogous result with his
hybrid willows. Again Gartner (22/46. 'Bastarderzeugung' s. 423.) asserts that
the degree of variability sometimes differs in hybrids raised from reciprocal
crosses between the same two species; and here the sole difference is, that
the one species is first used as the father and then as the mother. On the
whole we see that, independently of the appearance of new characters, the
variability of successive crossed generations is extremely complex, partly
from the offspring partaking unequally of the characters of the two parent-
forms, and more especially from their unequal tendency to revert to such
characters or to those of more ancient progenitors.]

ON THE MANNER AND ON THE PERIOD OF ACTION OF THE CAUSES WHICH INDUCE
VARIABILITY.

This is an extremely obscure subject, and we need here only consider, whether
inherited variations are due to certain parts being acted on after they have
been formed, or through the reproductive system being affected before their
formation; and in the former case at what period of growth or development the
effect is produced. We shall see in the two following chapters that various
agencies, such as an abundant supply of food, exposure to a different climate,
increased use or disuse of parts, etc., prolonged during several generations,
certainly modify either the whole organisation or certain organs; and it is
clear at least in the case of bud-variation that the action cannot have been
through the reproductive system.

[With respect to the part which the reproductive system takes in causing
variability, we have seen in the eighteenth chapter that even slight changes
in the conditions of life have a remarkable power in causing a greater or less
degree of sterility. Hence it seems not improbable that beings generated
through a system so easily affected should themselves be affected, or should
fail to inherit, or inherit in excess, characters proper to their parents. We
know that certain groups of organic beings, but with exceptions in each group,
have their reproductive systems much more easily affected by changed
conditions than other groups; for instance, carnivorous birds, more readily
than carnivorous mammals, and parrots more readily than pigeons; and this fact
harmonises with the apparently capricious manner and degree in which various
groups of animals and plants vary under domestication.

Kolreuter (22/47. 'Dritte Fortsetzung' etc. 1766 s. 85.) was struck with the
parallelism between the excessive variability of hybrids when crossed and
recrossed in various ways,--these hybrids having their reproductive powers
more or less affected,--and the variability of anciently cultivated plants.
Max Wichura (22/48. 'Die Bastardbefruchtung' etc. 1865 s. 92: see also the
Rev. M.J. Berkeley on the same subject in 'Journal of Royal Hort. Soc.' 1866
page 80.) has gone one step farther, and shows that with many of our highly
cultivated plants, such as the hyacinth, tulip, auricula, snapdragon, potato,
cabbage, etc., which there is no reason to believe have been hybridised, the
anthers contain many irregular pollen-grains in the same state as in hybrids.
He finds also in certain wild forms, the same coincidence between the state of
the pollen and a high degree of variability, as in many species of Rubus; but
in R. caesius and idaeus, which are not highly variable species, the pollen is
sound. It is also notorious that many cultivated plants, such as the banana,
pineapple, bread-fruit, and others previously mentioned, have their
reproductive organs so seriously affected as to be generally quite sterile;
and when they do yield seed, the seedlings, judging from the large number of
cultivated races which exist, must be variable in an extreme degree. These
facts indicate that there is some relation between the state of the
reproductive organs and a tendency to variability; but we must not conclude
that the relation is strict. Although many of our highly cultivated plants may
have their pollen in a deteriorated condition, yet, as we have previously
seen, they yield more seeds, and our anciently domesticated animals are more
prolific, than the corresponding species in a state of nature. The peacock is
almost the only bird which is believed to be less fertile under domestication
than in its native state, and it has varied in a remarkably small degree. From
these considerations it would seem that changes in the conditions of life lead
either to sterility or to variability, or to both; and not that sterility
induces variability. On the whole it is probable that any cause affecting the
organs of reproduction would likewise affect their product,--that is, the
offspring thus generated.

The period of life at which the causes that induce variability act, is
likewise an obscure subject, which has been discussed by various authors.
(22/49. Dr. P. Lucas has given a history of opinion on this subject 'Hered.
Nat.' 1847 tome 1 page 175.) In some of the cases, to be given in the
following chapter, of modifications from the direct action of changed
conditions, which are inherited, there can be no doubt that the causes have
acted on the mature or nearly mature animal. On the other hand, monstrosities,
which cannot be distinctly separated from lesser variations, are often caused
by the embryo being injured whilst in the mother's womb or in the egg. Thus I.
Geoffroy Saint-Hilaire (22/50. 'Hist. des Anomalies' tome 3 page 499.) asserts
that poor women who work hard during their pregnancy, and the mothers of
illegitimate children troubled in their minds and forced to conceal their
state, are far more liable to give birth to monsters than women in easy
circumstances. The eggs of the fowl when placed upright or otherwise treated
unnaturally frequently produce monstrous chickens. It would, however, appear
that complex monstrosities are induced more frequently during a rather late
than during a very early period of embryonic life; but this may partly result
from some one part, which has been injured during an early period, affecting
by its abnormal growth other parts subsequently developed; and this would be
less likely to occur with parts injured at a later period. (22/51. Ibid tome 3
pages 392, 502. The several memoirs by M. Dareste hereafter referred to are of
special value on this whole subject.) When any part or organ becomes monstrous
through abortion, a rudiment is generally left, and this likewise indicates
that its development had already commenced.

Insects sometimes have their antennae or legs in a monstrous condition, the
larvae of which do not possess either antennae or legs; and in these cases, as
Quatrefages (22/52. See his interesting work 'Metamorphoses de l'Homme' etc.
1862 page 129.) believes, we are enabled to see the precise period at which
the normal progress of development was troubled. But the nature of the food
given to a caterpillar sometimes affects the colours of the moth, without the
caterpillar itself being affected; therefore it seems possible that other
characters in the mature insect might be indirectly modified through the
larvae. There is no reason to suppose that organs which have been rendered
monstrous have always been acted on during their development; the cause may
have acted on the organisation at a much earlier stage. It is even probable
that either the male or female sexual elements, or both, before their union,
may be affected in such a manner as to lead to modifications in organs
developed at a late period of life; in nearly the same manner as a child may
inherit from his father a disease which does not appear until old age.

In accordance with the facts above given, which prove that in many cases a
close relation exists between variability and the sterility following from
changed conditions, we may conclude that the exciting cause often acts at the
earliest possible period, namely, on the sexual elements, before impregnation
has taken place. That an affection of the female sexual element may induce
variability we may likewise infer as probable from the occurrence of bud-
variations; for a bud seems to be the analogue of an ovule. But the male
element is apparently much oftener affected by changed conditions, at least in
a visible manner, than the female element or ovule and we know from Gartner's
and Wichura's statements that a hybrid used as the father and crossed with a
pure species gives a greater degree of variability to the offspring, than does
the same hybrid when used as the mother. Lastly, it is certain that
variability may be transmitted through either sexual element, whether or not
originally excited in them, for Kolreuter and Gartner (22/53. 'Dritte
Fortsetzung' etc. s. 123; 'Bastarderzeugung' s. 249.) found that when two
species were crossed, if either one was variable, the offspring were rendered
variable.]

SUMMARY.

From the facts given in this chapter, we may conclude that the variability of
organic beings under domestication, although so general, is not an inevitable
contingent on life, but results from the conditions to which the parents have
been exposed. Changes of any kind in the conditions of life, even extremely
slight changes, often suffice to cause variability. Excess of nutriment is
perhaps the most efficient single exciting cause. Animals and plants continue
to be variable for an immense period after their first domestication; but the
conditions to which they are exposed never long remain quite constant. In the
course of time they can be habituated to certain changes, so as to become less
variable; and it is possible that when first domesticated they may have been
even more variable than at present. There is good evidence that the power of
changed conditions accumulates; so that two, three, or more generations must
be exposed to new conditions before any effect is visible. The crossing of
distinct forms, which have already become variable, increases in the offspring
the tendency to further variability, by the unequal commingling of the
characters of the two parents, by the reappearance of long-lost characters,
and by the appearance of absolutely new characters. Some variations are
induced by the direct action of the surrounding conditions on the whole
organisation, or on certain parts alone; other variations appear to be induced
indirectly through the reproductive system being affected, as we know is often
the case with various beings, which when removed from their natural conditions
become sterile. The causes which induce variability act on the mature
organism, on the embryo, and, probably, on the sexual elements before
impregnation has been effected.


CHAPTER 2.XXIII.

DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE.

SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS,
IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES.
LOCAL DISEASES.
CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC.
PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF
POISON.
LAND-SHELLS.
MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE
ACTION OF EXTERNAL CONDITIONS.
COMPARISON OF AMERICAN AND EUROPEAN TREES.
GALLS.
EFFECTS OF PARASITIC FUNGI.
CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT INFLUENCE OF CHANGED
EXTERNAL CONDITIONS.
PARALLEL SERIES OF VARIETIES.
AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF CHANGE IN THE
CONDITIONS.
BUD-VARIATION.
MONSTROSITIES PRODUCED BY UNNATURAL TREATMENT.
SUMMARY.

If we ask ourselves why this or that character has been modified under
domestication, we are, in most cases, lost in utter darkness. Many
naturalists, especially of the French school, attribute every modification to
the "monde ambiant," that is, to changed climate, with all its diversities of
heat and cold, dampness and dryness, light and electricity, to the nature of
the soil, and to varied kinds and amount of food. By the term definite action,
as used in this chapter, I mean an action of such a nature that, when many
individuals of the same variety are exposed during several generations to any
particular change in their conditions of life, all, or nearly all the
individuals, are modified in the same manner. The effects of habit, or of the
increased use and disuse of various organs, might have been included under
this head; but it will be convenient to discuss this subject in a separate
chapter. By the term indefinite action I mean an action which causes one
individual to vary in one way and another individual in another way, as we
often see with plants and animals after they have been subjected for some
generations to changed conditions of life. But we know far too little of the
causes and laws of variation to make a sound classification. The action of
changed conditions, whether leading to definite or indefinite results, is a
totally distinct consideration from the effects of selection; for selection
depends on the preservation by man of certain individuals, or on their
survival under various and complex natural circumstances, and has no relation
whatever to the primary cause of each particular variation.

I will first give in detail all the facts which I have been able to collect,
rendering it probable that climate, food, etc., have acted so definitely and
powerfully on the organisation of our domesticated productions, that new sub-
varieties or races have been thus formed without the aid of selection by man
or nature. I will then give the facts and considerations opposed to this
conclusion, and finally we will weigh, as fairly as we can, the evidence on
both sides.

When we reflect that distinct races of almost all our domesticated animals
exist in each kingdom of Europe, and formerly even in each district of
England, we are at first strongly inclined to attribute their origin to the
definite action of the physical conditions of each country; and this has been
the conclusion of many authors. But we should bear in mind that man annually
has to choose which animals shall be preserved for breeding, and which shall
be slaughtered. We have also seen that both methodical and unconscious
selection were formerly practised, and are now occasionally practised by the
most barbarous races, to a much greater extent than might have been
anticipated. Hence it is difficult to judge how far differences in the
conditions between, for instance, the several districts in England, have
sufficed to modify the breeds which have been reared in each. It may be argued
that, as numerous wild animals and plants have ranged during many ages
throughout Great Britain, and still retain the same character, the difference
in conditions between the several districts could not have modified in a
marked manner the various native races of cattle, sheep, pigs, and horses. The
same difficulty of distinguishing between the effects of natural selection and
the definite action of external conditions is encountered in a still higher
degree when we compare closely allied species inhabiting two countries, such
as North America and Europe, which do not differ greatly in climate, nature of
soil, etc., for in this case natural selection will inevitably and rigorously
have acted during a long succession of ages.

Prof. Weismann has suggested (23/1. 'Ueber den Einfluss der Isolirung auf die
Artbildung' 1872.) that when a variable species enters a new and isolated
country, although the variations may be of the same general nature as before,
yet it is improbable that they should occur in the same proportional numbers.
After a longer or shorter period, the species will tend to become nearly
uniform in character from the incessant crossing of the varying individuals;
but owing to the proportion of the individuals varying in different ways not
being the same in the two cases, the final result will be the production of
two forms somewhat different from one another. In cases of this kind it would
falsely appear as if the conditions had induced certain definite
modifications, whereas they had only excited indefinite variability, but with
the variations in slightly different proportional numbers. This view may throw
some light on the fact that the domestic animals which formerly inhabited the
several districts in Great Britain, and the half wild cattle lately kept in
several British parks, differed slightly from one another; for these animals
were prevented from wandering over the whole country and intercrossing, but
would have crossed freely within each district or park.

[From the difficulty of judging how far changed conditions have caused
definite modifications of structure, it will be advisable to give as large a
body of facts as possible, showing that extremely slight differences within
the same country, or during different seasons, certainly produce an
appreciable effect, at least on varieties which are already in an unstable
condition. Ornamental flowers are good for this purpose, as they are highly
variable, and are carefully observed. All floriculturists are unanimous that
certain varieties are affected by very slight differences in the nature of the
artificial compost in which they are grown, and by the natural soil of the
district, as well as by the season. Thus, a skilful judge, in writing on
Carnations and Picotees (23/2. 'Gardener's Chronicle' 1853 page 183.) asks
"where can Admiral Curzon be seen possessing the colour, size, and strength
which it has in Derbyshire? Where can Flora's Garland be found equal to those
at Slough? Where do high-coloured flowers revel better than at Woolwich and
Birmingham? Yet in no two of these districts do the same varieties attain an
equal degree of excellence, although each may be receiving the attention of
the most skilful cultivators." The same writer then recommends every
cultivator to keep five different kinds of soil and manure, "and to endeavour
to suit the respective appetites of the plants you are dealing with, for
without such attention all hope of general success will be vain." So it is
with the Dahlia (23/3. Mr. Wildman 'Floricultural Soc.' February 7, 1843
reported in 'Gardener's Chronicle' 1843 page 86.): the Lady Cooper rarely
succeeds near London, but does admirably in other districts; the reverse holds
good with other varieties; and again, there are others which succeed equally
well in various situations. A skilful gardener (23/4. Mr. Robson in 'Journal
of Horticulture' February 13, 1866 page 122.) states that he procured cuttings
of an old and well-known variety (pulchella) of Verbena, which from having
been propagated in a different situation presented a slightly different shade
of colour; the two varieties were afterwards multiplied by cuttings, being
carefully kept distinct; but in the second year they could hardly be
distinguished, and in the third year no one could distinguish them.

The nature of the season has an especial influence on certain varieties of the
Dahlia: in 1841 two varieties were pre-eminently good, and the next year these
same two were pre-eminently bad. A famous amateur (23/5. 'Journal of
Horticulture' 1861 page 24.) asserts that in 1861 many varieties of the Rose
came so untrue in character, "that it was hardly possible to recognise them,
and the thought was not seldom entertained that the grower had lost his
tally." The same amateur (23/6. Ibid 1862 page 83.) states that in 1862 two-
thirds of his Auriculas produced central trusses of flowers, and such trusses
are liable not to keep true; and he adds that in some seasons certain
varieties of this plant all prove good, and the next season all prove bad;
whilst exactly the reverse happens with other varieties. In 1845 the editor of
the 'Gardener's Chronicle' (23/7. 'Gardener's Chronicle' 1845 page 660.)
remarked how singular it was that this year many Calceolarias tended to assume
a tubular form. With Heartsease (23/8. Ibid 1863 page 628.) the blotched sorts
do not acquire their proper character until hot weather sets in; whilst other
varieties lose their beautiful marks as soon as this occurs.

Analogous facts have been observed with leaves: Mr. Beaton asserts (23/9.
'Journal of Hort.' 1861 pages 64, 309.) that he raised at Shrubland, during
six years, twenty thousand seedlings from the Punch Pelargonium, and not one
had variegated leaves; but at Surbiton, in Surrey, one-third, or even a
greater proportion, of the seedlings from this same variety were more or less
variegated. The soil of another district in Surrey has a strong tendency to
cause variegation, as appears from information given me by Sir F. Pollock.
Verlot (23/10. 'Des Varietes' etc. page 76.) states that the variegated
strawberry retains its character as long as grown in a dryish soil, but soon
loses it when planted in fresh and humid soil. Mr. Salter, who is well known
for his success in cultivating variegated plants, informs me that rows of
strawberries were planted in his garden in 1859, in the usual way; and at
various distances in one row, several plants simultaneously became variegated;
and what made the case more extraordinary, all were variegated in precisely
the same manner. These plants were removed, but during the three succeeding
years other plants in the same row became variegated, and in no instance were
the plants in any adjoining row affected.

The chemical qualities, odours, and tissues of plants are often modified by a
change which seems to us slight. The Hemlock is said not to yield conicine in
Scotland. The root of the Aconitum napellus becomes innocuous in frigid
climates. The medicinal properties of the Digitalis are easily affected by
culture. As the Pistacia lentiscus grows abundantly in the South of France,
the climate must suit it, but it yields no mastic. The Laurus sassafras in
Europe loses the odour proper to it in North America. (23/11. Engel 'Sur les
Prop. Medicales des Plantes' 1860 pages 10, 25. On changes in the odours of
plants see Dalibert's Experiments quoted by Beckman 'Inventions' volume 2 page
344; and Nees in Ferussac 'Bull. des Sc. Nat.' 1824 tome 1 page 60. With
respect to the rhubarb etc. see also 'Gardener's Chronicle' 1849 page 355;
1862 page 1123.) Many similar facts could be given, and they are remarkable
because it might have been thought that definite chemical compounds would have
been little liable to change either in quality or quantity.

The wood of the American Locust-tree (Robinia) when grown in England is nearly
worthless, as is that of the Oak-tree when grown at the Cape of Good Hope.
(23/12. Hooker 'Flora Indica' page 32.) Hemp and flax, as I hear from Dr.
Falconer, flourish and yield plenty of seed on the plains of India, but their
fibres are brittle and useless. Hemp, on the other hand, fails to produce in
England that resinous matter which is so largely used in India as an
intoxicating drug.

The fruit of the Melon is greatly influenced by slight differences in culture
and climate. Hence it is generally a better plan, according to Naudin, to
improve an old kind than to introduce a new one into any locality. The seed of
the Persian Melon produces near Paris fruit inferior to the poorest market
kinds, but at Bordeaux yields delicious fruit. (23/13. Naudin 'Annales des Sc.
Nat.' 4th series, Bot. tome 11 1859 page 81. 'Gardener's Chronicle' 1859 page
464.) Seed is annually brought from Thibet to Kashmir (23/14. Moorcroft
'Travels' etc. volume 2 page 143.) and produces fruit weighing from four to
ten pounds, but plants raised next year from seed saved in Kashmir give fruit
weighing only from two to three pounds. It is well known that American
varieties of the Apple produce in their native land magnificent and brightly-
coloured fruit, but these in England are of poor quality and a dull colour. In
Hungary there are many varieties of the kidney-bean, remarkable for the beauty
of their seeds, but the Rev. M.J. Berkeley (23/15. 'Gardener's Chronicle' 1861
page 1113.) found that their beauty could hardly ever be preserved in England,
and in some cases the colour was greatly changed. We have seen in the ninth
chapter, with respect to wheat, what a remarkable effect transportal from the
north to the south of France, and conversely, produced on the weight of the
grain.]

When man can perceive no change in plants or animals which have been exposed
to a new climate or to different treatment, insects can sometimes perceive a
marked change. A cactus has been imported into India from Canton, Manilla
Mauritius, and from the hot-houses of Kew, and there is likewise a so-called
native kind which was formerly introduced from South America; all these plants
belong to the same species and are alike in appearance, but the cochineal
insect flourishes only on the native kind, on which it thrives prodigiously.
(23/16. Royle 'Productive Resources of India' page 59.) Humboldt remarks
(23/17. 'Personal Narrative' English translation volume 5 page 101. This
statement has been confirmed by Karsten 'Beitrag zur Kenntniss der
Rhynchoprion' Moscow 1864 s. 39 and by others.) that white men "born in the
torrid zone walk barefoot with impunity in the same apartment where a
European, recently landed, is exposed to the attacks of the Pulex penetrans."
This insect, the too well-known chigoe, must therefore be able to perceive
what the most delicate chemical analysis fails to discover, namely, a
difference between the blood or tissues of a European and those of a white man
born in the tropics. But the discernment of the chigoe is not so surprising as
it at first appears; for according to Liebig (23/18. 'Organic Chemistry'
English translation 1st edition page 369.) the blood of men with different
complexions, though inhabiting the same country, emits a different odour.

[Diseases peculiar to certain localities, heights, or climates, may be here
briefly noticed, as showing the influence of external circumstances on the
human body. Diseases confined to certain races of man do not concern us, for
the constitution of the race may play the more important part, and this may
have been determined by unknown causes. The Plica Polonica stands, in this
respect, in a nearly intermediate position; for it rarely affects Germans, who
inhabit the neighbourhood of the Vistula, where so many Poles are grievously
affected; neither does it affect Russians, who are said to belong to the same
original stock as the Poles. (23/19. Prichard 'Phys. Hist. of Mankind' 1851
volume 1 page 155.) The elevation of a district often governs the appearance
of diseases; in Mexico the yellow fever does not extend above 924 metres; and
in Peru, people are affected with the verugas only between 600 and 1600 metres
above the sea; many other such cases could be given. A peculiar cutaneous
complaint, called the Bouton d'Alep, affects in Aleppo and some neighbouring
districts almost every native infant, and some few strangers; and it seems
fairly well established that this singular complaint depends on drinking
certain waters. In the healthy little island of St. Helena the scarlet-fever
is dreaded like the Plague; analogous facts have been observed in Chili and
Mexico. (23/20. Darwin 'Journal of Researches' 1845 page 434.) Even in the
different departments of France it is found that the various infirmities which
render the conscript unfit for serving in the army, prevail with remarkable
inequality, revealing, as Boudin observes, that many of them are endemic,
which otherwise would never have been suspected. (23/21. These statements on
disease are taken from Dr. Boudin 'Geographie et Statistique Medicale' 1857
tome 1 pages 44 and 52; tome 2 page 315.) Any one who will study the
distribution of disease will be struck with surprise at what slight
differences in the surrounding circumstances govern the nature and severity of
the complaints by which man is at least temporarily affected.

The modifications as yet referred to are extremely slight, and in most cases
have been caused, as far as we can judge, by equally slight differences in the
conditions. But such conditions acting during a series of generations would
perhaps produce a marked effect.

With plants, a considerable change of climate sometimes produces a conspicuous
result. I have given in the ninth chapter the most remarkable case known to
me, namely, that of varieties of maize, which were greatly modified in the
course of only two or three generations when taken from a tropical country to
a cooler one, or conversely. Dr. Falconer informs me that he has seen the
English Ribston-pippin apple, a Himalayan oak, Prunus and Pyrus, all assume in
the hotter parts of India a fastigiate or pyramidal habit; and this fact is
the more interesting, as a Chinese tropical species of Pyrus naturally grows
thus. Although in these cases the changed manner of growth seems to have been
directly caused by the great heat, we know that many fastigiate trees have
originated in their temperate homes. In the Botanic Gardens of Ceylon the
apple-tree (23/22. 'Ceylon' by Sir J.E. Tennent volume 1 1859 page 89.) "sends
out numerous runners under ground, which continually rise into small stems,
and form a growth around the parent-tree.) The varieties of the cabbage which
produce heads in Europe fail to do so in certain tropical countries (23/23.
Godron 'De l'Espece' tome 2 page 52.) The Rhododendron ciliatum produced at
Kew flowers so much larger and paler-coloured than those which it bears on its
native Himalayan mountain, that Dr. Hooker (23/24. 'Journal of Horticultural
Soc.' volume 7 1852 page 117.) would hardly have recognised the species by the
flowers alone. Many similar facts with respect to the colour and size of
flowers could be given.

The experiments of Vilmorin and Buckman on carrots and parsnips prove that
abundant nutriment produces a definite and inheritable effect on the roots,
with scarcely any change in other parts of the plant. Alum directly influences
the colour of the flowers of the Hydrangea. (23/25. 'Journal of Hort. Soc.'
volume 1 page 160.) Dryness seems generally to favour the hairiness or
villosity of plants. Gartner found that hybrid Verbascums became extremely
woolly when grown in pots. Mr. Masters, on the other hand, states that the
Opuntia leucotricha "is well clothed with beautiful white hairs when grown in
a damp heat, but in a dry heat exhibits none of this peculiarity." (23/26. See
Lecoq on the Villosity of Plants 'Geograph. Bot.' tome 3 pages 287, 291;
Gartner 'Bastarderz.' s. 261; Mr. Masters on the Opuntia in 'Gardener's
Chronicle' 1846 page 444.) Slight variations of many kinds, not worth
specifying in detail, are retained only as long as plants are grown in certain
soils, of which Sageret (23/27. 'Pom. Phys.' page 136.) gives some instances
from his own experience. Odart, who insists strongly on the permanence of the
varieties of the grape, admits (23/28. 'Ampelographie' 1849 page 19.) that
some varieties, when grown under a different climate or treated differently,
vary in a slight degree, as in the tint of the fruit and in the period of
ripening. Some authors have denied that grafting causes even the slightest
difference in the scion; but there is sufficient evidence that the fruit is
sometimes slightly affected in size and flavour, the leaves in duration, and
the flowers in appearance. (23/29. Gartner 'Bastarderz.' s. 606, has collected
nearly all recorded facts. Andrew Knight in 'Transact. Hort. Soc.' volume 2
page 160, goes so far as to maintain that few varieties are absolutely
permanent in character when propagated by buds or grafts.)

There can be no doubt, from the facts given in the first chapter, that
European dogs deteriorate in India, not only in their instincts but in
structure; but the changes which they undergo are of such a nature, that they
may be partly due to reversion to a primitive form, as in the case of feral
animals. In parts of India the turkey becomes reduced in size, "with the
pendulous appendage over the beak enormously developed." (23/30. Mr. Blyth
'Annals and Mag of Nat. Hist.' volume 20 1847 page 391.) We have seen how soon
the wild duck, when domesticated, loses its true character, from the effects
of abundant or changed food, or from taking little exercise. From the direct
action of a humid climate and poor pasture the horse rapidly decreases in size
in the Falkland Islands. From information which I have received, this seems
likewise to be the case to a certain extent with sheep in Australia.

Climate definitely influences the hairy covering of animals; in the West
Indies a great change is produced in the fleece of sheep, in about three
generations. Dr. Falconer states (23/31. 'Natural History Review' 1862 page
113.) that the Thibet mastiff and goat, when brought down from the Himalaya to
Kashmir, lose their fine wool. At Angora not only goats, but shepherd-dogs and
cats, have fine fleecy hair, and Mr. Ainsworth (23/32. 'Journal of Roy.
Geographical Soc.' volume 9 1839 page 275.) attributes the thickness of the
fleece to the severe winters, and its silky lustre to the hot summers. Burnes
states positively (23/33. 'Travels in Bokhara' volume 3 page 151.) that the
Karakool sheep lose their peculiar black curled fleeces when removed into any
other country. Even within the limits of England, I have been assured that the
wool of two breeds of sheep was slightly changed by the flocks being pastured
in different localities. (23/34. See also on the influence of marshy pastures
on the wool Godron 'L'Espece' tome 2 page 22.) It has been asserted on good
authority (23/35. Isidore Geoffroy Saint-Hilaire 'Hist. Nat. Gen.' tome 3 page
438.) that horses kept during several years in the deep coal-mines of Belgium
become covered with velvety hair, almost like that on the mole. These cases
probably stand in close relation to the natural change of coat in winter and
summer. Naked varieties of several domestic animals have occasionally
appeared; but there is no reason to believe that this is in any way related to
the nature of the climate to which they have been exposed. (23/36. Azara has
made some good remarks on this subject 'Quadrupedes du Paraguay' tome 2 page
337. See an account of a family of naked mice produced in England 'Proc.
Zoolog. Soc.' 1856 page 38.)

It appears at first sight probable that the increased size, the tendency to
fatten, the early maturity and altered forms of our improved cattle, sheep,
and pigs, have directly resulted from their abundant supply of food. This is
the opinion of many competent judges, and probably is to a great extent true.
But as far as form is concerned, we must not overlook the more potent
influence of lessened use on the limbs and lungs. We see, moreover, as far as
size is concerned, that selection is apparently a more powerful agent than a
large supply of food, for we can thus only account for the existence, as
remarked to me by Mr. Blyth, of the largest and smallest breeds of sheep in
the same country, of Cochin-China fowls and Bantams, of small Tumbler and
large Runt pigeons, all kept together and supplied with abundant nourishment.
Nevertheless there can be little doubt that our domesticated animals have been
modified, independently of the increased or lessened use of parts, by the
conditions to which they have been subjected, without the aid of selection.
For instance, Prof. Rutimeyer (23/37. 'Die Fauna der Pfahlbauten' 1861 s. 15.)
shows that the bones of domesticated quadrupeds can be distinguished from
those of wild animals by the state of their surface and general appearance. It
is scarcely possible to read Nathusius's excellent 'Vorstudien' (23/38.
'Schweineschadel' 1864 s. 99.) and doubt that, with the highly improved races
of the pig, abundant food has produced a conspicuous effect on the general
form of the body, on the breadth of the head and face, and even on the teeth.
Nathusius rests much on the case of a purely bred Berkshire pig, which when
two months old became diseased in its digestive organs, and was preserved for
observation until nineteen months old; at this age it had lost several
characteristic features of the breed, and had acquired a long, narrow head, of
large size relatively to its small body, and elongated legs. But in this case
and in some others we ought not to assume that, because certain characters are
lost, perhaps through reversion, under one course of treatment, therefore that
they were at first directly produced by an opposite treatment.

In the case of the rabbit, which has become feral on the island of Porto
Santo, we are at first strongly tempted to attribute the whole change--the
greatly reduced size, the altered tints of the fur, and the loss of certain
characteristic marks--to the definite action of the new conditions to which it
has been exposed. But in all such cases we have to consider in addition the
tendency to reversion to progenitors more or less remote, and the natural
selection of the finest shades of difference.

The nature of the food sometimes either definitely induces certain
peculiarities, or stands in some close relation with them. Pallas long ago
asserted that the fat-tailed sheep of Siberia degenerate and lose their
enormous tails when removed from certain saline pastures; and recently Erman
(23/39. 'Travels in Siberia' English translation volume 1 page 228.) states
that this occurs with the Kirgisian sheep when brought to Orenburgh.

It is well known that hemp-seed causes bullfinches and certain other birds to
become black. Mr. Wallace has communicated to me some much more remarkable
facts of the same nature. The natives of the Amazonian region feed the common
green parrot (Chrysotis festiva, Linn.) with the fat of large Siluroid fishes,
and the birds thus treated become beautifully variegated with red and yellow
feathers. In the Malayan archipelago, the natives of Gilolo alter in an
analogous manner the colours of another parrot, namely, the Lorius garrulus,
Linn., and thus produce the Lori rajah or King-Lory. These parrots in the
Malay Islands and South America, when fed by the natives on natural vegetable
food, such as rice and plaintains, retain their proper colours. Mr. Wallace
has, also, recorded (23/40. A.R. Wallace 'Travels on the Amazon and Rio Negro'
page 294.) a still more singular fact. "The Indians (of S. America) have a
curious art by which they change the colours of the feathers of many birds.
They pluck out those from the part they wish to paint, and inoculate the fresh
wound with the milky secretion from the skin of a small toad. The feathers
grow of a brilliant yellow colour, and on being plucked out, it is said, grow
again of the same colour without any fresh operation."

Bechstein (23/41. 'Naturgeschichte der Stubenvogel' 1840 s. 262, 308.) does
not entertain any doubt that seclusion from light affects, at least
temporarily, the colours of cage-birds.

It is well known that the shells of land-mollusca are affected by the
abundance of lime in different districts. Isidore Geoffroy Saint-Hilaire
(23/42. 'Hist. Nat Gen.' tome 3 page 402.) gives the case of Helix lactea,
which has recently been carried from Spain to the South of France and to the
Rio Plata, and in both countries now presents a distinct appearance, but
whether this has resulted from food or climate is not known. With respect to
the common oyster, Mr. F. Buckland informs me that he can generally
distinguish the shells from different districts; young oysters brought from
Wales and laid down in beds where "natives" are indigenous, in the short space
of two months begin to assume the "native" character. M. Costa (23/43. 'Bull.
de La Soc. Imp. d'Acclimat.' tome 8 page 351.) has recorded a much more
remarkable case of the same nature, namely, that young shells taken from the
shores of England and placed in the Mediterranean, at once altered their
manner of growth and formed prominent diverging rays, like those on the shells
of the proper Mediterranean oyster. The same individual shell, showing both
forms of growth, was exhibited before a society in Paris. Lastly, it is well
known that caterpillars fed on different food sometimes either themselves
acquire a different colour or produce moths differing in colour. (23/44. See
an account of Mr. Gregson's experiments on the Abraxus grossulariata 'Proc.
Entomolog. Soc.' January 6, 1862: these experiments have been confirmed by Mr.
Greening in 'Proc. of the Northern Entomolog. Soc.' July 28, 1862. For the
effects of food on caterpillars see a curious account by M. Michely in 'Bull.
De La Soc. Imp. d'Acclimat.' tome 8 page 563. For analogous facts from Dahlbom
on Hymenoptera see Westwood 'Modern Class. of Insects' volume 2 page 98. See
also Dr. L. Moller 'Die Abhangigkeit der Insecten' 1867 s. 70.)

It would be travelling beyond my proper limits here to discuss how far organic
beings in a state of nature are definitely modified by changed conditions. In
my 'Origin of Species' I have given a brief abstract of the facts bearing on
this point, and have shown the influence of light on the colours of birds, and
of residence near the sea on the lurid tints of insects, and on the succulency
of plants. Mr. Herbert Spencer (23/45. 'The Principles of Biology' volume 2
1866. The present chapters were written before I had read Mr. Herbert
Spencer's work, so that I have not been able to make so much use of it as I
should otherwise probably have done.) has recently discussed with much ability
this whole subject on general grounds. He argues, for instance, that with all
animals the external and internal tissues are differently acted on by the
surrounding conditions, and they invariably differ in intimate structure. So
again the upper and lower surfaces of true leaves, as well as of stems and
petioles, when these assume the function and occupy the position of leaves,
are differently circumstanced with respect to light, etc., and apparently in
consequence differ in structure. But, as Mr. Herbert Spencer admits, it is
most difficult in all such cases to distinguish between the effects of the
definite action of physical conditions and the accumulation through natural
selection of inherited variations which are serviceable to the organism, and
which have arisen independently of the definite action of these conditions.]

Although we are not here concerned with the definite action of the conditions
of life on organisms in a state of nature, I may state that much evidence has
been gained during the last few years on this subject. In the United States,
for instance, it has been clearly proved, more especially by Mr. J.A. Allen,
that, with birds, many species differ in tint, size of body and of beak, and
in length of tail, in proceeding from the North to the South; and it appears
that these differences must be attributed to the direct action of temperature.
(23/46. Professor Weismann comes to the same conclusion with respect to
certain European butterflies in his valuable essay 'Ueber den Saison-
Dimorphismus' 1875. I might also refer to the recent works of several other
authors on the present subject; for instance to Kerner's 'Gute und schlechte
Arten' 1866.) With respect to plants I will give a somewhat analogous case:
Mr. Meehan (23/47. 'Proc. Acad. Nat. Soc. of Philadelphia' January 28, 1862.),
has compared twenty-nine kinds of American trees with their nearest European
allies, all grown in close proximity and under as nearly as possible the same
conditions. In the American species he finds, with the rarest exceptions, that
the leaves fall earlier in the season, and assume before their fall a brighter
tint; that they are less deeply toothed or serrated; that the buds are
smaller; that the trees are more diffuse in growth and have fewer branchlets;
and, lastly, that the seeds are smaller--all in comparison with the
corresponding European species. Now considering that these corresponding trees
belong to several distinct orders, and that they are adapted to widely
different stations, it can hardly be supposed that their differences are of
any special service to them in the New and Old worlds; and if so such
differences cannot have been gained through natural selection, and must be
attributed to the long continued action of a different climate.

GALLS.

Another class of facts, not relating to cultivated plants, deserves attention.
I allude to the production of galls. Every one knows the curious, bright-red,
hairy productions on the wild rose-tree, and the various different galls
produced by the oak. Some of the latter resemble fruit, with one face as rosy
as the rosiest apple. These bright colours can be of no service either to the
gall-forming insect or to the tree, and probably are the direct result of the
action of the light, in the same manner as the apples of Nova Scotia or Canada
are brighter coloured than English apples. According to Osten Sacken's latest
revision, no less than fifty-eight kinds of galls are produced on the several
species of oak, by Cynips with its sub-genera; and Mr. B.D. Walsh (23/48. See
Mr. B.D. Walsh's excellent papers in 'Proc. Entomolog. Soc. Philadelphia'
December 1866 page 284. With respect to the willow see ibid 1864 page 546.)
states that he can add many others to the list. One American species of
willow, the Salix humilis, bears ten distinct kinds of galls. The leaves which
spring from the galls of various English willows differ completely in shape
from the natural leaves. The young shoots of junipers and firs, when punctured
by certain insects, yield monstrous growths resembling flowers and fir-cones;
and the flowers of some plants become from the same cause wholly changed in
appearance. Galls are produced in every quarter of the world; of several sent
to me by Mr. Thwaites from Ceylon, some were as symmetrical as a composite
flower when in bud, others smooth and spherical like a berry; some protected
by long spines, others clothed with yellow wool formed of long cellular hairs,
others with regularly tufted hairs. In some galls the internal structure is
simple, but in others it is highly complex; thus M. Lacaze-Duthiers (23/49.
See his admirable 'Histoire des Galles' in 'Annal. des Sc. Nat. Bot.' 3rd
series tome 19 1853 page 273.) has figured in the common ink-gall no less than
seven concentric layers, composed of distinct tissue, namely, the epidermic,
sub-epidermic, spongy, intermediate, and the hard protective layer formed of
curiously thickened woody cells, and, lastly, the central mass, abounding with
starch-granules on which the larvae feed.

Galls are produced by insects of various orders, but the greater number by
species of Cynips. It is impossible to read M. Lacaze-Duthiers' discussion and
doubt that the poisonous secretion of the insect causes the growth of the
gall; and every one knows how virulent is the poison secreted by wasps and
bees, which belong to the same group with Cynips. Galls grow with
extraordinary rapidity, and it is said that they attain their full size in a
few days (23/50. Kirby and Spence 'Entomology' 1818 volume 1 page 450; Lacaze-
Duthiers ibid page 284.); it is certain that they are almost completely
developed before the larvae are hatched. Considering that many gall-insects
are extremely small, the drop of secreted poison must be excessively minute;
it probably acts on one or two cells alone, which, being abnormally
stimulated, rapidly increase by a process of self-division. Galls, as Mr.
Walsh (23/51. 'Proc. Entomolog. Soc. Philadelphia' 1864 page 558.) remarks,
afford good, constant, and definite characters, each kind keeping as true to
form as does any independent organic being. This fact becomes still more
remarkable when we hear that, for instance, seven out of the ten different
kinds of galls produced on Salix humilis are formed by gall-gnats
(Cecidomyidae) which "though essentially distinct species, yet resemble one
another so closely that in almost all cases it is difficult, and in most cases
impossible, to distinguish the full-grown insects one from the other." (23/52.
Mr. B.D. Walsh ibid page 633 and December 1866 page 275.) For in accordance
with a wide-spread analogy we may safely infer that the poison secreted by
insects so closely allied would not differ much in nature; yet this slight
difference is sufficient to induce widely different results. In some few cases
the same species of gall-gnat produces on distinct species of willows galls
which cannot be distinguished; the Cynips fecundatrix, also, has been known to
produce on the Turkish oak, to which it is not properly attached, exactly the
same kind of gall as on the European oak. (23/53. Mr. B.D. Walsh ibid 1864
pages 545, 411, 495; and December 1866 page 278. See also Lacaze-Duthiers.)
These latter facts apparently prove that the nature of the poison is a more
powerful agent in determining the form of the gall than the specific character
of the tree which is acted on.

As the poisonous secretion of insects belonging to various orders has the
special power of affecting the growth of various plants; as a slight
difference in the nature of the poison suffices to produce widely different
results; and lastly, as we know that the chemical compounds secreted by plants
are eminently liable to be modified by changed conditions of life, we may
believe it possible that various parts of a plant might be modified through
the agency of its own altered secretions. Compare, for instance, the mossy and
viscid calyx of a moss-rose, which suddenly appears through bud-variation on a
Provence-rose, with the gall of red moss growing from the inoculated leaf of a
wild rose, with each filament symmetrically branched like a microscopical
spruce-fir, bearing a glandular tip and secreting odoriferous gummy matter.
(23/54. Lacaze-Duthiers ibid pages 325, 328.) Or compare, on the one hand, the
fruit of the peach, with its hairy skin, fleshy covering, hard shell and
kernel, and on the other hand one of the more complex galls with its
epidermic, spongy, and woody layers, surrounding tissue loaded with starch
granules. These normal and abnormal structures manifestly present a certain
degree of resemblance. Or, again, reflect on the cases above given of parrots
which have had their plumage brightly decorated through some change in their
blood, caused by having been fed on certain fishes, or locally inoculated with
the poison of a toad. I am far from wishing to maintain that the moss-rose or
the hard shell of the peach-stone or the bright colours of birds are actually
due to any chemical change in the sap or blood; but these cases of galls and
of parrots are excellently adapted to show us how powerfully and singularly
external agencies may affect structure. With such facts before us, we need
feel no surprise at the appearance of any modification in any organic being.

[I may, also, here allude to the remarkable effects which parasitic fungi
sometimes produce on plants. Reissek (23/55. 'Linnaea' volume 17 1843; quoted
by Dr. M.T. Masters, Royal Institution, March 16, 1860.) has described a
Thesium, affected by an Oecidium, which was greatly modified, and assumed some
of the characteristic features of certain allied species, or even genera.
Suppose, says Reissek, "the condition originally caused by the fungus to
become constant in the course of time, the plant would, if found growing wild,
be considered as a distinct species or even as belonging to a new genus." I
quote this remark to show how profoundly, yet in how natural a manner, this
plant must have been modified by the parasitic fungus. Mr. Meehan (23/56.
'Proc. Acad. Nat. Sc., Philadelphia' June 16, 1874 and July 23, 1875.) also
states that three species of Euphorbia and Portulaca olereacea, which
naturally grow prostrate, become erect when they are attacked by the Oecidium.
Euphorbia maculata in this case also becomes nodose, with the branchlets
comparatively smooth and the leaves modified in shape, approaching in these
respects to a distinct species, namely, the E. hypericifolia.]

FACTS AND CONSIDERATIONS OPPOSED TO THE BELIEF THAT THE CONDITIONS OF LIFE ACT
IN A POTENT MANNER IN CAUSING DEFINITE MODIFICATIONS OF STRUCTURE.

I have alluded to the slight differences in species naturally living in
distinct countries under different conditions; and such differences we feel at
first inclined to attribute, probably often with justice, to the definite
action of the surrounding conditions. But it must be borne in mind that there
exist many animals and plants which range widely and have been exposed to
great diversities of climate, yet remain uniform in character. Some authors,
as previously remarked, account for the varieties of our culinary and
agricultural plants by the definite action of the conditions to which they
have been exposed in the different parts of Great Britain; but there are about
200 plants (23/57. Hewett C. Watson 'Cybele Britannica' volume 1 1847 page
11.) which are found in every single English county; and these plants must
have been exposed for an immense period to considerable differences of climate
and soil, yet do not differ. So, again,, some animals and plants range over a
large portion of the world, yet retain the same character.

[Notwithstanding the facts previously given on the occurrence of highly
peculiar local diseases and on the strange modifications of structure in
plants caused by the inoculated poison of insects, and other analogous cases;
still there are a multitude of variations--such as the modified skull of the
niata ox and bulldog, the long horns of Caffre cattle, the conjoined toes of
the solid-hoofed swine, the immense crest and protuberant skull of Polish
fowls, the crop of the pouter-pigeon, and a host of other such cases--which we
can hardly attribute to the definite action, in the sense before specified, of
the external conditions of life. No doubt in every case there must have been
some exciting cause; but as we see innumerable individuals exposed to nearly
the same conditions, and one alone is affected, we may conclude that the
constitution of the individual is of far higher importance than the conditions
to which it has been exposed. It seems, indeed, to be a general rule that
conspicuous variations occur rarely, and in one individual alone out of
millions, though all may have been exposed, as far as we can judge, to nearly
the same conditions. As the most strongly marked variations graduate
insensibly into the most trifling, we are led by the same train of thought to
attribute each slight variation much more to innate differences of
constitution, however caused, than to the definite action of the surrounding
conditions.

We are led to the same conclusion by considering the cases, formerly alluded
to, of fowls and pigeons, which have varied and will no doubt go on varying in
directly opposite ways, though kept during many generations under nearly the
same conditions. Some, for instance, are born with their beaks, wings, tails,
legs, etc., a little longer, and others with these same parts a little
shorter. By the long-continued selection of such slight individual differences
which occur in birds kept in the same aviary, widely different races could
certainly be formed; and long-continued selection, important as is the result,
does nothing but preserve the variations which arise, as it appears to us,
spontaneously.

In these cases we see that domesticated animals vary in an indefinite number
of particulars, though treated as uniformly as is possible. On the other hand,
there are instances of animals and plants, which, though they have been
exposed to very different conditions, both under nature and domestication,
have varied in nearly the same manner. Mr. Layard informs me that he has
observed amongst the Caffres of South Africa a dog singularly like an arctic
Esquimaux dog. Pigeons in India present nearly the same wide diversities of
colour as in Europe; and I have seen chequered and simply barred pigeons, and
pigeons with blue and white loins, from Sierra Leone, Madeira, England, and
India. New varieties of flowers are continually raised in different parts of
Great Britain, but many of these are found by the judges at our exhibitions to
be almost identical with old varieties. A vast number of new fruit-trees and
culinary vegetables have been produced in North America: these differ from
European varieties in the same general manner as the several varieties raised
in Europe differ from one another; and no one has ever pretended that the
climate of America has given to the many American varieties any general
character by which they can be recognised. Nevertheless, from the facts
previously advanced on the authority of Mr. Meehan with respect to American
and European forest-trees it would be rash to affirm that varieties raised in
the two countries would not in the course of ages assume a distinctive
character. Dr. M. Masters has recorded a striking fact (23/58. 'Gardener's
Chronicle' 1857 page 629.) bearing on this subject: he raised numerous plants
of Hybiscus syriacus from seed collected in South Carolina and the Holy Land,
where the parent-plants must have been exposed to considerably different
conditions; yet the seedlings from both localities broke into two similar
strains, one with obtuse leaves and purple or crimson flowers, and the other
with elongated leaves and more or less pink flowers.

We may, also, infer the prepotent influence of the constitution of the
organism over the definite action of the conditions of life, from the several
cases given in the earlier chapters of parallel series of varieties,--an
important subject, hereafter to be more fully discussed. Sub-varieties of the
several kinds of wheat, gourds, peaches, and other plants, and to a limited
extent sub-varieties of the fowl, pigeon, and dog, have been shown either to
resemble or to differ from one another in a closely corresponding or parallel
manner. In other cases, a variety of one species resembles a distinct species;
or the varieties of two distinct species resemble one another. Although these
parallel resemblances no doubt often result from reversion to the former
characters of a common progenitor; yet in other cases, when new characters
first appear, the resemblance must be attributed to the inheritance of a
similar constitution, and consequently to a tendency to vary in the same
manner. We see something of a similar kind in the same monstrosity appearing
and reappearing many times in the same species of animal, and, as Dr. Maxwell
Masters has remarked to me, in the same species of plant.]

We may at least conclude, that the amount of modification which animals and
plants have undergone under domestication does not correspond with the degree
to which they have been subjected to changed circumstances. As we know the
parentage of domesticated birds far better than of most quadrupeds, we will
glance through the list. The pigeon has varied in Europe more than almost any
other bird; yet it is a native species, and has not been exposed to any
extraordinary change of conditions. The fowl has varied equally, or almost
equally, with the pigeon, and is a native of the hot jungles of India. Neither
the peacock, a native of the same country, nor the guinea-fowl, an inhabitant
of the dry deserts of Africa, has varied at all, or only in colour. The
turkey, from Mexico, has varied but little. The duck, on the other hand, a
native of Europe, has yielded some well-marked races; and as this is an
aquatic bird, it must have been subjected to a far more serious change in its
habits than the pigeon or even the fowl, which nevertheless have varied in a
much higher degree. The goose, a native of Europe and aquatic like the duck,
has varied less than any other domesticated bird, except the peacock.

Bud-variation is, also, important under our present point of view, in some few
cases, as when all the eyes on the same tuber of the potato, or all the fruit
on the same plum-tree, or all the flowers on the same plant, have suddenly
varied in the same manner, it might be argued that the variation had been
definitely caused by some change in the conditions to which the plants had
been exposed; yet, in other cases, such an admission is extremely difficult.
As new characters sometimes appear by bud-variation, which do not occur in the
parent-species or in any allied species, we may reject, at least in these
cases, the idea that they are due to reversion. Now it is well worth while to
reflect maturely on some striking case of bud-variation, for instance that of
the peach. This tree has been cultivated by the million in various parts of
the world, has been treated differently, grown on its own roots and grafted on
various stocks, planted as a standard, trained against a wall, or under glass;
yet each bud of each sub-variety keeps true to its kind. But occasionally, at
long intervals of time, a tree in England, or under the widely different
climate of Virginia, produces a single bud, and this yields a branch which
ever afterwards bears nectarines. Nectarines differ, as every one knows, from
peaches in their smoothness, size, and flavour; and the difference is so great
that some botanists have maintained that they are specifically distinct. So
permanent are the characters thus suddenly acquired, that a nectarine produced
by bud-variation has propagated itself by seed. To guard against the
supposition that there is some fundamental distinction between bud and seminal
variation, it is well to bear in mind that nectarines have likewise been
produced from the stone of the peach; and, reversely, peaches from the stone
of the nectarine. Now is it possible to conceive external conditions more
closely alike than those to which the buds on the same tree are exposed? Yet
one bud alone, out of the many thousands borne by the same tree, has suddenly,
without any apparent cause, produced a nectarine. But the case is even
stronger than this, for the same flower-bud has yielded a fruit, one-half or
one-quarter a nectarine, and the other half or three-quarters a peach. Again,
seven or eight varieties of the peach have yielded by bud-variation
nectarines: the nectarines thus produced, no doubt, differ a little from one
another; but still they are nectarines. Of course there must be some cause,
internal or external, to excite the peach-bud to change its nature; but I
cannot imagine a class of facts better adapted to force on our minds the
conviction that what we call the external conditions of life are in many cases
quite insignificant in relation to any particular variation, in comparison
with the organisation or constitution of the being which varies.

It is known from the labours of Geoffroy Saint-Hilaire, and recently from
those of Dareste and others, that eggs of the fowl, if shaken, placed upright,
perforated, covered in part with varnish, etc., produce monstrous chickens.
Now these monstrosities may be said to be directly caused by such unnatural
conditions, but the modifications thus induced are not of a definite nature.
An excellent observer, M. Camille Dareste (23/59. 'Memoire sur la Production
Artificielle des Monstruosites' 1862 pages 8-12; 'Recherches sur les
Conditions, etc., chez les Monstres' 1863 page 6. An abstract is given of
Geoffroy's Experiments by his son, in his 'Vie, Travaux' etc. 1847 page 290.),
remarks "that the various species of monstrosities are not determined by
specific causes; the external agencies which modify the development of the
embryo act solely in causing a perturbation--a perversion in the normal course
of development." He compares the result to what we see in illness: a sudden
chill, for instance, affects one individual alone out of many, causing either
a cold, or sore-throat, rheumatism, or inflammation of the lungs or pleura.
Contagious matter acts in an analogous manner. (23/60. Paget 'Lectures on
Surgical Pathology' 1853 volume 1 page 483.) We may take a still more specific
instance: seven pigeons were struck by rattle-snakes (23/61. 'Researches upon
the Venom of the Rattle-snake' January 1861 by Dr. Mitchell page 67.): some
suffered from convulsions; some had their blood coagulated, in others it was
perfectly fluid; some showed ecchymosed spots on the heart, others on the
intestines, etc.; others again showed no visible lesion in any organ. It is
well known that excess in drinking causes different diseases in different men;
but in the tropics the effects of intemperance differ from those caused in a
cold climate (23/62. Mr. Sedgwick 'British and Foreign Medico-Chirurg. Review'
July 1863 page 175.); and in this case we see the definite influence of
opposite conditions. The foregoing facts apparently give us as good an idea as
we are likely for a long time to obtain, how in many cases external conditions
act directly, though not definitely, in causing modifications of structure.

SUMMARY.

There can be no doubt, from the facts given in this chapter, that extremely
slight changes in the conditions of life sometimes, probably often, act in a
definite manner on our domesticated productions; and, as the action of changed
conditions in causing indefinite variability is accumulative, so it may be
with their definite action. Hence considerable and definite modifications of
structure probably follow from altered conditions acting during a long series
of generations. In some few instances a marked effect has been produced
quickly on all, or nearly all, the individuals which have been exposed to a
marked change of climate, food, or other circumstance. This has occurred with
European men in the United States, with European dogs in India, with horses in
the Falkland Islands, apparently with various animals at Angora, with foreign
oysters in the Mediterranean, and with maize transported from one climate to
another. We have seen that the chemical compounds of some plants and the state
of their tissues are readily affected by changed conditions. A relation
apparently exists between certain characters and certain conditions, so that
if the latter be changed the character is lost--as with the colours of
flowers, the state of some culinary plants, the fruit of the melon, the tail
of fat-tailed sheep, and the peculiar fleeces of other sheep.

The production of galls, and the change of plumage in parrots when fed on
peculiar food or when inoculated by the poison of a toad, prove to us what
great and mysterious changes in structure and colour, may be the definite
result of chemical changes in the nutrient fluids or tissues.

We now almost certainly know that organic beings in a state of nature may be
modified in various definite ways by the conditions to which they have been
long exposed, as in the case of the birds and other animals in the northern
and southern United States, and of American trees in comparison with their
representatives in Europe. But in many cases it is most difficult to
distinguish between the definite result of changed conditions, and the
accumulation through natural selection of indefinite variations which have
proved serviceable. If it profited a plant to inhabit a humid instead of an
arid station, a fitting change in its constitution might possibly result from
the direct action of the environment, though we have no grounds for believing
that variations of the right kind would occur more frequently with plants
inhabiting a station a little more humid than usual, than with other plants.
Whether the station was unusually dry or humid, variations adapting the plant
in a slight degree for directly opposite habits of life would occasionally
arise, as we have good reason to believe from what we actually see in other
cases.

The organisation or constitution of the being which is acted on, is generally
a much more important element than the nature of the changed conditions, in
determining the nature of the variation. We have evidence of this in the
appearance of nearly similar modifications under different conditions, and of
different modifications under apparently nearly the same conditions. We have
still better evidence of this in closely parallel varieties being frequently
produced from distinct races, or even distinct species; and in the frequent
recurrence of the same monstrosity in the same species. We have also seen that
the degree to which domesticated birds have varied, does not stand in any
close relation with the amount of change to which they have been subjected.

To recur once again to bud-variations. When we reflect on the millions of buds
which many trees have produced, before some one bud has varied, we are lost in
wonder as to what the precise cause of each variation can be. Let us recall
the case given by Andrew Knight of the forty-year-old tree of the yellow
magnum bonum plum, an old variety which has been propagated by grafts on
various stocks for a very long period throughout Europe and North America, and
on which a single bud suddenly produced the red magnum bonum. We should also
bear in mind that distinct varieties, and even distinct species,--as in the
case of peaches, nectarines, and apricots,--of certain roses and camellias,--
although separated by a vast number of generations from any progenitor in
common, and although cultivated under diversified conditions, have yielded by
bud-variation closely analogous varieties. When we reflect on these facts we
become deeply impressed with the conviction that in such cases the nature of
the variation depends but little on the conditions to which the plant has been
exposed, and not in any especial manner on its individual character, but much
more on the inherited nature or constitution of the whole group of allied
beings to which the plant in question belongs. We are thus driven to conclude
that in most cases the conditions of life play a subordinate part in causing
any particular modification; like that which a spark plays, when a mass of
combustibles bursts into flame--the nature of the flame depending on the
combustible matter, and not on the spark. (23/63. Professor Weismann argues
strongly in favour of this view in his 'Saison-Dimorphismus der
Schmetterlinge' 1875 pages 40-43.)

No doubt each slight variation must have its efficient cause; but it is as
hopeless an attempt to discover the cause of each, as to say why a chill or a
poison affects one man differently from another. Even with modifications
resulting from the definite action of the conditions of life, when all or
nearly all the individuals, which have been similarly exposed, are similarly
affected, we can rarely see the precise relation between cause and effect. In
the next chapter it will be shown that the increased use or disuse of various
organs produces an inherited effect. It will further be seen that certain
variations are bound together by correlation as well as by other laws. Beyond
this we cannot at present explain either the causes or nature of the
variability of organic beings.


CHAPTER 2.XXIV.

LAWS OF VARIATION--USE AND DISUSE, ETC.

NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION.
ON THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS.
CHANGED HABITS OF LIFE.
ACCLIMATISATION WITH ANIMALS AND PLANTS.
VARIOUS METHODS BY WHICH THIS CAN BE EFFECTED.
ARRESTS OF DEVELOPMENT.
RUDIMENTARY ORGANS.

In this and the two following chapters I shall discuss, as well as the
difficulty of the subject permits, the several laws which govern Variability.
These may be grouped under the effects of use and disuse, including changed
habits and acclimatisation--arrest of development--correlated variation--the
cohesion of homologous parts-the variability of multiple parts--compensation
of growth--the position of buds with respect to the axis of the plant--and
lastly, analogous variation. These several subjects so graduate into one
another that their distinction is often arbitrary.

It may be convenient first briefly to discuss that coordinating and reparative
power which is common, in a higher or lower degree, to all organic beings, and
which was formerly designated by physiologists as nisus formativus.

[Blumenbach and others (24/1. 'An Essay on Generation' English translation
page 18; Paget 'Lectures on Surgical Pathology' 1853 volume 1 page 209.) have
insisted that the principle which permits a Hydra, when cut into fragments, to
develop itself into two or more perfect animals, is the same with that which
causes a wound in the higher animals to heal by a cicatrice. Such cases as
that of the Hydra are evidently analogous to the spontaneous division or
fissiparous generation of the lowest animals, and likewise to the budding of
plants. Between these extreme cases and that of a mere cicatrice we have every
gradation. Spallanzani (24/2. 'An Essay on Animal Reproduction' English
translation 1769 page 79.) by cutting off the legs and tail of a Salamander,
got in the course of three months six crops of these members; so that 687
perfect bones were reproduced by one animal during one season. At whatever
point the limb was cut off, the deficient part, and no more, was exactly
reproduced. When a diseased bone has been removed, a new one sometimes
"gradually assumes the regular form, and all the attachments of muscles,
ligaments, etc., become as complete as before." (24/3. Carpenter 'Principles
of Comp. Physiology' 1854 page 479.)

This power of regrowth does not, however, always act perfectly; the reproduced
tail of a lizard differs in the form of the scales from the normal tail: with
certain Orthopterous insects the large hind legs are reproduced of smaller
size (24/4. Charlesworth 'Mag. of Nat. Hist.' volume 1 1837 page 145.): the
white cicatrice which in the higher animals unites the edges of a deep wound
is not formed of perfect skin, for elastic tissue is not produced till long
afterwards. (24/5. Paget 'Lectures on Surgical Pathology' volume 1 page 239.)
"The activity of the nisus formativus," says Blumenbach, "is in an inverse
ratio to the age of the organised body." Its power is also greater with
animals, the lower they stand in the scale of organisation; and animals low in
the scale correspond with the embryos of higher animals belonging to the same
class. Newport's observations (24/6. Quoted by Carpenter 'Comp. Phys.' page
479.) afford a good illustration of this fact, for he found that "myriapods,
whose highest development scarcely carries them beyond the larva of perfect
insects, can regenerate limbs and antennae up to the time of their last
moult;" and so can the larvae of true insects, but, except in one order, not
in the mature insect. Salamanders correspond in development with the tadpoles
or larvae of the tailless Batrachians, and both possess to a large extent the
power of regrowth; but not so the mature tailless Batrachians.

Absorption often plays an important part in the repair of injuries. When a
bone is broken and does not unite, the ends are absorbed and rounded, so that
a false joint is formed; or if the ends unite, but overlap, the projecting
parts are removed. (24/7. Prof. Marey's discussion on the power of co-
adaptation in all parts of the organisation is excellent. 'La Machine Animale'
1873 chapter 9. See also Paget 'Lectures' etc. page 257.) A dislocated bone
will form for itself a new socket. Displaced tendons and varicose veins
excavate new channels in the bones against which they press. But absorption
comes into action, as Virchow remarks, during the normal growth of bones;
parts which are solid during youth become hollowed out for the medullary
tissue as the bone increases in size. In trying to understand the many well-
adapted cases of regrowth when aided by absorption, we should remember that
almost all parts of the organisation, even whilst retaining the same form,
undergo constant renewal; so that a part which is not renewed would be liable
to absorption.

Some cases, usually classed under the so-called nisus formativus, at first
appear to come under a distinct head; for not only are old structures
reproduced, but new structures are formed. Thus, after inflammation "false
membranes," furnished with blood-vessels, lymphatics, and nerves, are
developed; or a foetus escapes from the Fallopian tubes, and falls into the
abdomen, "nature pours out a quantity of plastic lymph, which forms itself
into organised membrane, richly supplied with blood-vessels," and the foetus
is nourished for a time. In certain cases of hydrocephalus the open and
dangerous spaces in the skull are filled up with new bones, which interlock by
perfect serrated sutures. (24/8. These cases are given by Blumenbach in his
'Essay on Generation' pages 52, 54.) But most physiologists, especially on the
Continent, have now given up the belief in plastic lymph or blastema, and
Virchow (24/9. 'Cellular Pathology' translation by Dr. Chance 1860 pages 27,
441.) maintains that every structure, new or old, is formed by the
proliferation of pre-existing cells. On this view false membranes, like
cancerous or other tumours, are merely abnormal developments of normal
growths; and we can thus understand how it is that they resemble adjoining
structures; for instance, that a "false membrane in the serous cavities
acquires a covering of epithelium exactly like that which covers the original
serous membrane; adhesions of the iris may become black apparently from the
production of pigment-cells like those of the uvea." (24/10. Paget 'Lectures
on Pathology' volume 1 1853 page 357.)

No doubt the power of reparation, though not always perfect, is an admirable
provision, ready for various emergencies, even for such as occur only at long
intervals of time. (24/11. Paget ibid page 150.) Yet this power is not more
wonderful than the growth and development of every single creature, more
especially of those which are propagated by fissiparous generation. This
subject has been here noticed, because we may infer that, when any part or
organ is either greatly increased in size or wholly suppressed through
variation and continued selection, the co-ordinating power of the organisation
will continually tend to bring again all the parts into harmony with one
another.]

ON THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS.

It is notorious, and we shall immediately adduce proofs, that increased use or
action strengthens muscles, glands, sense-organs, etc.; and that disuse, on
the other hand, weakens them. It has been experimentally proved by Ranke
(24/12. 'Die Blutvertheilung, etc. der Organe' 1871 as quoted by Jaeger 'In
Sachen Darwin's' 1874 page 48. See also H. Spencer 'The Principles of Biology'
volume 2 1866 chapters 3-5.) that the flow of blood is greatly increased
towards any part which is performing work, and sinks again when the part is at
rest. Consequently, if the work is frequent, the vessels increase in size and
the part is better nourished. Paget (24/13. 'Lectures on Pathology' 1853
volume 1 page 71.) also accounts for the long, thick, dark-coloured hairs
which occasionally grow, even in young children, near old-standing inflamed
surfaces or fractured bones by an increased flow of blood to the part. When
Hunter inserted the spur of a cock into the comb, which is well supplied with
blood-vessels, it grew in one case spirally to a length of six inches, and in
another case forward, like a horn, so that the bird could not touch the ground
with its beak. According to the interesting observations of M. Sedillot
(24/14. 'Comptes Rendus' September 26, 1864 page 539.), when a portion of one
of the bones of the leg of an animal is removed, the associated bone enlarges
till it attains a bulk equal to that of the two bones, of which it has to
perform the functions. This is best exhibited in dogs in which the tibia has
been removed; the companion bone, which is naturally almost filiform and not
one-fifth the size of the other, soon acquires a size equal to or greater than
that of the tibia. Now, it is at first difficult to believe that increased
weight acting on a straight bone could, by alternately increasing and
diminishing the pressure, cause the blood to flow more freely in the vessels
which permeate the periosteum and thus supply more nutriment to the bone.
Nevertheless the observations adduced by Mr. Spencer (24/15. H. Spencer 'The
Principles of Biology' volume 2 page 243.), on the strengthening of the bowed
bones of rickety children, along their concave sides, leads to the belief that
this is possible.

The rocking of the stem of a tree increases in a marked manner the growth of
the woody tissue in the parts which are strained. Prof. Sachs believes, from
reasons which he assigns, that this is due to the pressure of the bark being
relaxed in such parts, and not as Knight and H. Spencer maintain, to an
increased flow of sap caused by the movement of the trunk. (24/16. Ibid volume
2 page 269. Sachs 'Text-book of Botany' 1875 page 734.) But hard woody tissue
may be developed without the aid of any movement, as we see with ivy closely
attached to an old wall. In all such cases, it is very difficult to
distinguish between the effects of long-continued selection and those which
follow from the increased action of the part, or directly from some other
cause. Mr. H. Spencer (24/17. Ibid volume 2 page 273.) acknowledges this
difficulty, and gives as an instance the thorns on trees and the shells of
nuts. Here we have extremely hard woody tissue without the possibility of any
movement, and without, as far as we can see, any other directly exciting
cause; and as the hardness of these parts is of manifest service to the plant,
we may look at the result as probably due to the selection of so-called
spontaneous variations. Every one knows that hard work thickens the epidermis
on the hands; and when we hear that with infants, long before birth, the
epidermis is thicker on the palms and soles of the feet than on any other part
of the body, as was observed with admiration by Albinus (24/18. Paget
'Lectures on Pathology' volume 2 page 209.), we are naturally inclined to
attribute this to the inherited effects of long-continued use or pressure. We
are tempted to extend the same view even to the hoofs of quadrupeds; but who
will pretend to determine how far natural selection may have aided in the
formation of structures of such obvious importance to the animal?

[That use strengthens the muscles may be seen in the limbs of artisans who
follow different trades; and when a muscle is strengthened, the tendons, and
the crests of bone to which they are attached, become enlarged; and this must
likewise be the case with the blood-vessels and nerves. On the other hand,
when a limb is not used, as by Eastern fanatics, or when the nerve supplying
it with nervous power is effectually destroyed, the muscles wither. So again,
when the eye is destroyed the optic nerve becomes atrophied, sometimes even in
the course of a few months. (24/19. Muller 'Phys.' English translation pages
54, 791. Prof. Reed has given ('Physiological and Anat. Researches' page 10) a
curious account of the atrophy of the limbs of rabbits after the destruction
of the nerve.) The Proteus is furnished with branchiae as well as with lungs:
and Schreibers (24/20. Quoted by Lecoq in 'Geograph. Bot.' tome 1 1854 page
182.) found that when the animal was compelled to live in deep water, the
branchiae were developed to thrice their ordinary size, and the lungs were
partially atrophied. When, on the other hand, the animal was compelled to live
in shallow water, the lungs became larger and more vascular, whilst the
branchiae disappeared in a more or less complete degree. Such modifications as
these are, however, of comparatively little value for us, as we do not
actually know that they tend to be inherited.

In many cases there is reason to believe that the lessened use of various
organs has affected the corresponding parts in the offspring. But there is no
good evidence that this ever follows in the course of a single generation. It
appears, as in the case of general or indefinite variability, that several
generations must be subjected to changed habits for any appreciable result.
Our domestic fowls, ducks, and geese have almost lost, not only in the
individual but in the race, their power of flight; for we do not see a young
fowl, when frightened, take flight like a young pheasant. Hence I was led
carefully to compare the limb-bones of fowls, ducks, pigeons, and rabbits,
with the same bones in the wild parent-species. As the measurements and
weights were fully given in the earlier chapters I need here only recapitulate
the results. With domestic pigeons, the length of the sternum, the prominence
of its crest, the length of the scapulae and furculum, the length of the wings
as measured from tip to tip of the radii, are all reduced relatively to the
same parts in the wild pigeon. The wing and tail feathers, however, are
increased in length, but this may have as little connection with the use of
the wings or tail, as the lengthened hair on a dog with the amount of exercise
which it has habitually taken. The feet of pigeons, except in the long-beaked
races, are reduced in size. With fowls the crest of the sternum is less
prominent, and is often distorted or monstrous; the wing-bones have become
lighter relatively to the leg-bones, and are apparently a little shorter in
comparison with those of the parent-form, the Gallus bankiva. With ducks, the
crest of the sternum is affected in the same manner as in the foregoing cases:
the furculum, coracoids, and scapulae are all reduced in weight relatively to
the whole skeleton: the bones of the wings are shorter and lighter, and the
bones of the legs longer and heavier, relatively to each other, and relatively
to the whole skeleton, in comparison with the same bones in the wild-duck. The
decreased weight and size of the bones, in the foregoing cases, is probably
the indirect result of the reaction of the weakened muscles on the bones. I
failed to compare the feathers of the wings of the tame and wild duck; but
Gloger (24/21. 'Das Abandern der Vogel' 1833 s. 74.) asserts that in the wild
duck the tips of the wing-feathers reach almost to the end of the tail, whilst
in the domestic duck they often hardly reach to its base. He remarks also on
the greater thickness of the legs, and says that the swimming membrane between
the toes is reduced; but I was not able to detect this latter difference.

With the domesticated rabbit the body, together with the whole skeleton, is
generally larger and heavier than in the wild animal, and the leg-bones are
heavier in due proportion; but whatever standard of comparison be taken,
neither the leg-bones nor the scapulae have increased in length proportionally
with the increased dimensions of the rest of the skeleton. The skull has
become in a marked manner narrower, and, from the measurements of its capacity
formerly given, we may conclude, that this narrowness results from the
decreased size of the brain, consequent on the mentally inactive life led by
these closely-confined animals.

We have seen in the eighth chapter that silk-moths, which have been kept
during many centuries closely confined, emerge from their cocoons with their
wings distorted, incapable of flight, often greatly reduced in size, or even,
according to Quatrefages, quite rudimentary. This condition of the wings may
be largely owing to the same kind of monstrosity which often affects wild
Lepidoptera when artificially reared from the cocoon; or it may be in part due
to an inherent tendency, which is common to the females of many Bombycidae, to
have their wings in a more or less rudimentary state; but part of the effect
may be attributed to long-continued disuse.]

From the foregoing facts there can be no doubt that with our anciently
domesticated animals, certain bones have increased or decreased in size and
weight owing to increased or decreased use; but they have not been modified,
as shown in the earlier chapters, in shape or structure. With animals living a
free life and occasionally exposed to severe competition the reduction would
tend to be greater, as it would be an advantage to them to have the
development of every superfluous part saved. With highly-fed domesticated
animals, on the other hand, there seems to be no economy of growth, nor any
tendency to the elimination of superfluous details. But to this subject I
shall recur.

Turning now to more general observations, Nathusius has shown that with the
improved races of the pig, the shortened legs and snout, the form of the
articular condyles of the occiput, and the position of the jaws with the upper
canine teeth projecting in a most anomalous manner in front of the lower
canines, may be attributed to these parts not having been fully exercised. For
the highly-cultivated races do not travel in search of food, nor root up the
ground with their ringed muzzles. (24/22. Nathusius 'Die Racen des Schweines'
1860 s. 53, 57; 'Vorstudien...Schweineschadel' 1864 s. 103, 130, 133. Prof.
Lucae supports and extends the conclusions of Von Nathusius: 'Der Schadel des
Maskenschweines' 1870.) These modifications of structure, which are all
strictly inherited, characterise several improved breeds, so that they cannot
have been derived from any single domestic stock. With respect to cattle,
Professor Tanner has remarked that the lungs and liver in the improved breeds
"are found to be considerably reduced in size when compared with those
possessed by animals having perfect liberty" (24/23. 'Journal of Agriculture
of Highland Soc.' July 1860 page 321.); and the reduction of these organs
affects the general shape of the body. The cause of the reduced lungs in
highly-bred animals which take little exercise is obvious; and perhaps the
liver may be affected by the nutritious and artificial food on which they
largely subsist. Again, Dr. Wilckens asserts (24/24. 'Landwirth. Wochenblatt'
No. 10.) that various parts of the body certainly differ in Alpine and lowland
breeds of several domesticated animals, owing to their different habits of
life; for instance, the neck and fore-legs in length, and the hoofs in shape.

[It is well known that, when an artery is tied, the anastomosing branches,
from being forced to transmit more blood, increase in diameter; and this
increase cannot be accounted for by mere extension, as their coats gain in
strength. With respect to glands, Sir J. Paget observes that "when one kidney
is destroyed the other often becomes much larger, and does double work."
(24/25. 'Lectures on Surgical Pathology' 1853 volume 1 page 27.) If we compare
the size of the udders and their power of secretion in cows which have been
long domesticated, and in certain breeds of the goat in which the udders
nearly touch the ground, with these organs in wild or half-domesticated
animals, the difference is great. A good cow with us daily yields more than
five gallons, or forty pints of milk, whilst a first-rate animal, kept, for
instance, by the Damaras of South Africa (24/26. Andersson 'Travels in South
Africa' page 318. For analogous cases in South America see Aug. St.-Hilaire
'Voyage dans la Province de Goyaz' tome 1 page 71.), "rarely gives more than
two or three pints of milk daily, and, should her calf be taken from her, she
absolutely refuses to give any." We may attribute the excellence of our cows
and of certain goats, partly to the continued selection of the best milking
animals, and partly to the inherited effects of the increased action, through
man's art, of the secreting glands.

It is notorious that short-sight is inherited; and we have seen in the twelfth
chapter from the statistical researches of M. Giraud-Teulon, that the habit of
viewing near objects gives a tendency to short-sight. Veterinarians are
unanimous that horses are affected with spavins, splints, ringbones, etc.,
from being shod and from travelling on hard roads, and they are almost equally
unanimous that a tendency to these malformations is transmitted. Formerly
horses were not shod in North Carolina, and it has been asserted that they did
not then suffer from these diseases of the legs and feet. (24/27. Brickell
'Nat. Hist. of North Carolina' 1739 page 53.)]

Our domesticated quadrupeds are all descended, as far as is known, from
species having erect ears; yet few kinds can be named, of which at least one
race has not drooping ears. Cats in China, horses in parts of Russia, sheep in
Italy and elsewhere, the guinea-pig formerly in Germany, goats and cattle in
India, rabbits, pigs, and dogs in all long-civilised countries have dependent
ears. With wild animals, which constantly use their ears like funnels to catch
every passing sound, and especially to ascertain the direction whence it
comes, there is not, as Mr. Blyth has remarked, any species with drooping ears
except the elephant. Hence the incapacity to erect the ears is certainly in
some manner the result of domestication; and this incapacity has been
attributed by various authors (24/28. Livingstone quoted by Youatt on 'Sheep'
page 142. Hodgson in 'Journal of Asiatic Soc. of Bengal' volume 16 1847 page
1006 etc. etc. On the other hand Dr. Wilckens argues strongly against the
belief that the drooping of the ears is the result of disuse: 'Jahrbuch der
deutschen Viehzucht' 1866.) to disuse, for animals protected by man are not
compelled habitually to use their ears. Col. Hamilton Smith (24/29.
'Naturalist's Library' Dogs volume 2 1840 page 104.) states that in ancient
effigies of the dog, "with the exception of one Egyptian instance, no
sculpture of the earlier Grecian era produces representations of hounds with
completely drooping ears; those with them half pendulous are missing in the
most ancient; and this character increases, by degrees, in the works of the
Roman period." Godron also has remarked "that the pigs of the ancient
Egyptians had not their ears enlarged and pendent." (24/30. 'De l'Espece' tome
1 1859 page 367.) But it is remarkable that the drooping of the ear is not
accompanied by any decrease in size; on the contrary, animals so different as
fancy rabbits, certain Indian breeds of the goat, our petted spaniels, blood-
hounds, and other dogs, have enormously elongated ears, so that it would
appear as if their weight had caused them to droop, aided perhaps by disuse.
With rabbits, the drooping of the much elongated ears has affected even the
structure of the skull.

The tail of no wild animal, as remarked to me by Mr. Blyth, is curled; whereas
pigs and some races of dogs have their tails much curled. This deformity,
therefore, appears to be the result of domestication, but whether in any way
connected with the lessened use of the tail is doubtful.

The epidermis on our hands is easily thickened, as every one knows, by hard
work. In a district of Ceylon the sheep have "horny callosities that defend
their knees, and which arise from their habit of kneeling down to crop the
short herbage, and this distinguishes the Jaffna flocks from those of other
portions of the island;" but it is not stated whether this peculiarity is
inherited. (24/31. 'Ceylon' by Sir J.E. Tennent 1859 volume 2 page 531.)

The mucous membrane which lines the stomach is continuous with the external
skin of the body; therefore it is not surprising that its texture should be
affected by the nature of the food consumed, but other and more interesting
changes likewise follow. Hunter long ago observed that the muscular coat of
the stomach of a gull (Larus tridactylus) which had been fed for a year
chiefly on grain was thickened; and, according to Dr. Edmondston, a similar
change periodically occurs in the Shetland Islands in the stomach of the Larus
argentatus, which in the spring frequents the cornfields and feeds on the
seed. The same careful observer has noticed a great change in the stomach of a
raven which had been long fed on vegetable food. In the case of an owl (Strix
grallaria), similarly treated, Menetries states that the form of the stomach
was changed, the inner coat became leathery, and the liver increased in size.
Whether these modifications in the digestive organs would in the course of
generations become inherited is not known. (24/32. For the foregoing
statements see Hunter 'Essays and Observations' 1861 volume 2 page 329; Dr.
Edmondston, as quoted in Macgillivray 'British Birds' volume 5 page 550:
Menetries as quoted in Bronn 'Geschichte der Natur' b. 2 s. 110.)

The increased or diminished length of the intestines, which apparently results
from changed diet, is a more remarkable case, because it is characteristic of
certain animals in their domesticated condition, and therefore must be
inherited. The complex absorbent system, the blood-vessels, nerves, and
muscles, are necessarily all modified together with the intestines. According
to Daubenton, the intestines of the domestic cat are one-third longer than
those of the wild cat of Europe; and although this species is not the parent-
stock of the domestic animal, yet, as Isidore Geoffroy has remarked, the
several species of cats are so closely allied that the comparison is probably
a fair one. The increased length appears to be due to the domestic cat being
less strictly carnivorous in its diet than any wild feline species; for
instance, I have seen a French kitten eating vegetables as readily as meat.
According to Cuvier, the intestines of the domesticated pig exceed greatly in
proportionate length those of the wild boar. In the tame and wild rabbit the
change is of an opposite nature, and probably results from the nutritious food
given to the tame rabbit. (24/33. These statements on the intestines are taken
from Isidore Geoffroy Saint-Hilaire 'Hist. Nat. Gen.' tome 3 pages 427, 441.)

CHANGED AND INHERITED HABITS OF LIFE.

This subject, as far as the mental powers of animals are concerned, so blends
into instinct, that I will here only remind the reader of such cases as the
tameness of our domesticated animals--the pointing or retrieving of dogs--
their not attacking the smaller animals kept by man--and so forth. How much of
these changes ought to be attributed to mere habit, and how much to the
selection of individuals which have varied in the desired manner,
irrespectively of the special circumstances under which they have been kept,
can seldom be told.

We have already seen that animals may be habituated to a changed diet; but
some additional instances may be given. In the Polynesian Islands and in China
the dog is fed exclusively on vegetable matter, and the taste for this kind of
food is to a certain extent inherited. (24/34. Gilbert White 'Nat. Hist.
Selborne' 1825 volume 2 page 121.) Our sporting dogs will not touch the bones
of game birds, whilst most other dogs devour them with greediness. In some
parts of the world sheep have been largely fed on fish. The domestic hog is
fond of barley, the wild boar is said to disdain it; and the disdain is
partially inherited, for some young wild pigs bred in captivity showed an
aversion for this grain, whilst others of the same brood relished it. (24/35.
Burdach 'Traite de Phys.' tome 2 page 267 as quoted by Dr. P. Lucas 'L'Hered.
Nat.' tome 1 page 388.) One of my relations bred some young pigs from a
Chinese sow by a wild Alpine boar; they lived free in the park, and were so
tame that they came to the house to be fed; but they would not touch swill,
which was devoured by the other pigs. An animal when once accustomed to an
unnatural diet, which can generally be effected only during youth, dislikes
its proper food, as Spallanzani found to be the case with a pigeon which had
been long fed on meat. Individuals of the same species take to new food with
different degrees of readiness; one horse, it is stated, soon learned to eat
meat, whilst another would have perished from hunger rather than have partaken
of it. (24/36. This and several other cases are given by Colin 'Physiologie
Comp. des Animaux Dom.' 1854 tome 1 page 426.) The caterpillars of the Bombyx
hesperus feed in a state of nature on the leaves of the Cafe diable, but,
after having been reared on the Ailanthus, they would not touch the Cafe
diable, and actually died of hunger. (24/37. M. Michely de Cayenne in 'Bull.
Soc. d'Acclimat.' tome 8 1861 page 563.)

It has been found possible to accustom marine fish to live in fresh water; but
as such changes in fish and other marine animals have been chiefly observed in
a state of nature, they do not properly belong to our present subject. The
period of gestation and of maturity, as shown in the earlier chapters,--the
season and the frequency of the act of breeding,--have all been greatly
modified under domestication. With the Egyptian goose the rate of change with
respect to the season has been recorded. (24/38. Quatrefages 'Unite de
l'Espece Humaine' 1861 page 79.) The wild drake pairs with one female, the
domestic drake is polygamous. Certain breeds of fowls have lost the habit of
incubation. The paces of the horse, and the manner of flight of certain breeds
of the pigeon, have been modified and are inherited. Cattle, horses, and pigs
have learnt to browse under water in the St. John's River, East Florida, where
the Vallisneria has been largely naturalised. The cows were observed by Prof.
Wyman to keep their heads immersed for "a period varying from fifteen to
thirty-five seconds." (24/39. 'The American Naturalist' April 1874 page 237.)
The voice differs much in certain kinds of fowls and pigeons. Some varieties
are clamorous and others silent, as the Call and common duck, or the Spitz and
pointer dog. Every one knows how the breeds of the dog differ from one another
in their manner of hunting, and in their ardour after different kinds of game
or vermin.

With plants the period of vegetation is easily changed and is inherited, as in
the case of summer and winter wheat, barley, and vetches; but to this subject
we shall immediately return under acclimatisation. Annual plants sometimes
become perennial under a new climate, as I hear from Dr. Hooker is the case
with the stock and mignonette in Tasmania. On the other hand, perennials
sometimes become annuals, as with the Ricinus in England, and as, according to
Captain Mangles, with many varieties of the heartsease. Von Berg (24/40.
'Flora' 1835 b. 2 page 504.) raised from seed of Verbascum phoeniceum, which
is usually a biennial, both annual and perennial varieties. Some deciduous
bushes become evergreen in hot countries. (24/41. Alph. de Candolle 'Geograph.
Bot.' tome 2 page 1078.) Rice requires much water, but there is one variety in
India which can be grown without irrigation. (24/42. Royle 'Illustrations of
the Botany of the Himalaya' page 19.) Certain varieties of the oat and of our
other cereals are best fitted for certain soils. (24/43. 'Gardener's
Chronicle' 1850 pages 204, 219.) Endless similar facts could be given in the
animal and vegetable kingdoms. They are noticed here because they illustrate
analogous differences in closely allied natural species, and because such
changed habits of life, whether due to habit, or to the direct action of
external conditions, or to so-called spontaneous variability, would be apt to
lead to modifications of structure.

ACCLIMATISATION.

From the previous remarks we are naturally led to the much disputed subject of
acclimatisation. There are two distinct questions: Do varieties descended from
the same species differ in their power of living under different climates? And
secondly, if they so differ, how have they become thus adapted? We have seen
that European dogs do not succeed well in India, and it is asserted (24/44.
Rev. R. Everest 'Journal As. Soc. of Bengal' volume 3 page 19.), that no one
has there succeeded in keeping the Newfoundland long alive; but then it may be
argued, and probably with truth, that these northern breeds are specifically
distinct from the native dogs which flourish in India. The same remark may be
made with respect to different breeds of sheep, of which, according to Youatt
(24/45. Youatt on 'Sheep' 1838 page 491.), not one brought "from a torrid
climate lasts out the second year," in the Zoological Gardens. But sheep are
capable of some degree of acclimatisation, for Merino sheep bred at the Cape
of Good Hope have been found far better adapted for India than those imported
from England. (24/46. Royle 'Prod. Resources of India' page 153.) It is almost
certain that all the breeds of the fowl are descended from one species; but
the Spanish breed, which there is good reason to believe originated near the
Mediterranean (24/47. Tegetmeier 'Poultry Book' 1866 page 102.), though so
fine and vigorous in England, suffers more from frost than any other breed.
The Arrindy silk moth introduced from Bengal, and the Ailanthus moth from the
temperate province of Shan Tung, in China, belong to the same species, as we
may infer from their identity in the caterpillar, cocoon, and mature states
(24/48. Dr. R. Paterson in a paper communicated to Bot. Soc. of Canada quoted
in the 'Reader' 1863 November 13.); yet they differ much in constitution: the
Indian form "will flourish only in warm latitudes," the other is quite hardy
and withstands cold and rain.

[Plants are more strictly adapted to climate than are animals. The latter when
domesticated withstand such great diversities of climate, that we find nearly
the same species in tropical and temperate countries; whilst the cultivated
plants are widely dissimilar. Hence a larger field is open for inquiry in
regard to the acclimatisation of plants than of animals. It is no exaggeration
to say that with almost every plant which has long been cultivated, varieties
exist which are endowed with constitutions fitted for very different climates;
I will select only a few of the more striking cases, as it would be tedious to
give all. In North America numerous fruit-trees have been raised, and in
horticultural publications,--for instance, in that by Downing,--lists are
given of the varieties which are best able to withstand the severe climate of
the northern States and Canada. Many American varieties of the pear, plum, and
peach are excellent in their own country, but until recently, hardly one was
known that succeeded in England; and with apples (24/49. See remarks by Editor
in 'Gardener's Chronicle' 1848 page 5.), not one succeeds. Though the American
varieties can withstand a severer winter than ours, the summer here is not hot
enough. Fruit-trees have also originated in Europe with different
constitutions, but they are not much noticed, because nurserymen here do not
supply wide areas. The Forelle pear flowers early, and when the flowers have
just set, and this is the critical period, they have been observed, both in
France and England, to withstand with complete impunity a frost of 18 deg and
even 14 deg Fahr., which killed the flowers, whether fully expanded or in bud,
of all other kinds of pears. (24/50. 'Gardener's Chronicle' 1860 page 938.
Remarks by Editor and quotation from Decaisne.) This power in the flower of
resisting cold and afterwards producing fruit does not invariably depend, as
we know on good authority (24/51. J. de Jonghe of Brussels in 'Gardener's
Chronicle' 1857 page 612.), on general constitutional vigour. In proceeding
northward, the number of varieties which are found capable of resisting the
climate rapidly decreases, as may be seen in the list of the varieties of the
cherry, apple, and pear, which can be cultivated in the neighbourhood of
Stockholm. (24/52. Ch. Martius 'Voyage Bot. Cotes Sept. de la Norvege' page
26.) Near Moscow, Prince Troubetzkoy planted for experiment in the open ground
several varieties of the pear, but one alone, the Poire sans Pepins, withstood
the cold of winter. (24/53. 'Journal de l'Acad. Hort. de Gand' quoted in
'Gardener's Chronicle' 1859 page 7.) We thus see that our fruit-trees, like
distinct species of the same genus, certainly differ from each other in their
constitutional adaptation to different climates.

With the varieties of many plants, the adaptation to climate is often very
close. Thus it has been proved by repeated trials "that few if any of the
English varieties of wheat are adapted for cultivation in Scotland" (24/54.
'Gardener's Chronicle' 1851 page 396.); but the failure in this case is at
first only in the quantity, though ultimately in the quality, of the grain
produced. The Rev. M.J. Berkeley sowed wheat-seed from India, and got "the
most meagre ears," on land which would certainly have yielded a good crop from
English wheat. (24/55. Ibid 1862 page 235.) In these cases varieties have been
carried from a warmer to a cooler climate; in the reverse case, as "when wheat
was imported directly from France into the West Indian Islands, it produced
either wholly barren spikes or furnished with only two or three miserable
seeds, while West Indian seed by its side yielded an enormous harvest."
(24/56. On the authority of Labat quoted in 'Gardener's Chronicle' 1862 page
235.) Here is another case of close adaptation to a slightly cooler climate; a
kind of wheat which in England may be used indifferently either as a winter or
summer variety, when sown under the warmer climate of Grignan, in France,
behaved exactly as if it had been a true winter wheat. (24/57. MM. Edwards and
Colin 'Annal. des Sc. Nat.' 2nd series Bot. tome 5 page 22.)

Botanists believe that all the varieties of maize belong to the same species;
and we have seen that in North America, in proceeding northward, the varieties
cultivated in each zone produce their flowers and ripen their seed within
shorter and shorter periods. So that the tall, slowly maturing southern
varieties do not succeed in New England, and the New English varieties do not
succeed in Canada. I have not met with any statement that the southern
varieties are actually injured or killed by a degree of cold which the
northern varieties can withstand with impunity, though this is probable; but
the production of early flowering and early seeding varieties deserves to be
considered as one form of acclimatisation. Hence it has been found possible,
according to Kalm, to cultivate maize further and further northwards in
America. In Europe, also, as we learn from the evidence given by Alph. De
Candolle, the culture of maize has extended since the end of the last century
thirty leagues north of its former boundary. (24/58. 'Geograph. Bot.' page
337.) On the authority of Linnaeus (24/59. 'Swedish Acts' English translation
1739-40 volume 1. Kalm in his 'Travels' volume 2 page 166 gives an analogous
case with cotton-plants raised in New Jersey from Carolina seed.), I may quote
an analogous case, namely, that in Sweden tobacco raised from home-grown seed
ripens its seed a month sooner and is less liable to miscarry than plants
raised from foreign seed.

With the Vine, differently from the maize, the line of practical culture has
retreated a little southward since the middle ages (24/60. De Candolle
'Geograph. Bot.' page 339.); but this seems due to commerce being now easier,
so that it is better to import wine from the south than to make it in northern
districts. Nevertheless the fact of the vine not having spread northward shows
that acclimatisation has made no progress during several centuries. There is,
however, a marked difference in the constitution of the several varieties,--
some being hardy, whilst others, like the muscat of Alexandria, require a very
high temperature to come to perfection. According to Labat (24/61. 'Gardener's
Chronicle' 1862 page 235.), vines taken from France to the West Indies succeed
with extreme difficulty, whilst those imported from Madeira or the Canary
Islands thrive admirably.

Gallesio gives a curious account of the naturalisation of the Orange in Italy.
During many centuries the sweet orange was propagated exclusively by grafts,
and so often suffered from frosts, that it required protection. After the
severe frost of 1709, and more especially after that of 1763, so many trees
were destroyed, that seedlings from the sweet orange were raised, and, to the
surprise of the inhabitants, their fruit was found to be sweet. The trees thus
raised were larger, more productive, and hardier than the old kinds; and
seedlings are now continually raised. Hence Gallesio concludes that much more
was effected for the naturalisation of the orange in Italy by the accidental
production of new kinds during a period of about sixty years, than had been
effected by grafting old varieties during many ages. (24/62. Gallesio 'Teoria
della Riproduzione Veg.' 1816 page 125; and 'Traite du Citrus' 1811 page 359.)
I may add that Risso (24/63. 'Essai sur l'Hist. des Orangers' 1813 page 20
etc.) describes some Portuguese varieties of the orange as extremely sensitive
to cold, and as much tenderer than certain other varieties.

The peach was known to Theophrastus, 322 B.C. (24/64. Alph. de Candolle
'Geograph. Bot.' page 882.) According to the authorities quoted by Dr. F.
Rolle (24/65. 'Ch. Darwin's Lehre von der Entstehung' etc. 1862 s. 87.), it
was tender when first introduced into Greece, and even in the island of Rhodes
only occasionally bore fruit. If this be correct, the peach, in spreading
during the last two thousand years over the middle parts of Europe, must have
become much hardier. At the present day different varieties differ much in
hardiness: some French varieties will not succeed in England; and near Paris,
the Pavie de Bonneuil does not ripen its fruit till very late in the season,
even when grown on a wall; "it is, therefore, only fit for a very hot southern
climate." (24/66. Decaisne quoted in 'Gardener's Chronicle' 1865 page 271.)

I will briefly give a few other cases. A variety of Magnolia grandiflora,
raised by M. Roy, withstands a temperature several degrees lower than that
which any other variety can resist. With camellias there is much difference in
hardiness. One particular variety of the Noisette rose withstood the severe
frost of 1860 "untouched and hale amidst a universal destruction of other
Noisettes." In New York the "Irish yew is quite hardy, but the common yew is
liable to be cut down." I may add that there are varieties of the sweet potato
(Convolvulus batatas) which are suited for warmer, as well as for colder,
climates. (24/67. For the magnolia see Loudon's 'Gardener's Mag.' volume 13
1837 page 21. For camellias and roses see 'Gardener's Chronicle' 1860 page
384. For the yew 'Journal of Hort.' March 3, 1863 p 174. For sweet potatoes
see Col. von Siebold in 'Gardener's Chronicle' 1855 page 822.)]

The plants as yet mentioned have been found capable of resisting an unusual
degree of cold or heat, when fully grown. The following cases refer to plants
whilst young. In a large bed of young Araucarias of the same age, growing
close together and equally exposed, it was observed (24/68. The Editor
'Gardener's Chronicle' 1861 page 239.), after the unusually severe winter of
1860-61, that, "in the midst of the dying, numerous individuals remained on
which the frost had absolutely made no kind of impression." Dr. Lindley, after
alluding to this and other similar cases, remarks, "Among the lessons which
the late formidable winter has taught us, is that, even in their power of
resisting cold, individuals of the same species of plants are remarkably
different." Near Salisbury, there was a sharp frost on the night of May 24,
1836, and all the French beans (Phaseolus vulgaris) in a bed were killed
except about one in thirty, which completely escaped. (24/69. Loudon's
'Gardener's Mag.' volume 12 1836 page 378.) On the same day of the month, but
in the year 1864, there was a severe frost in Kent, and two rows of scarlet-
runners (P. multiflorus) in my garden, containing 390 plants of the same age
and equally exposed, were all blackened and killed except about a dozen
plants. In an adjoining row of "Fulmer's dwarf bean" (P. vulgaris), one single
plant escaped. A still more severe frost occurred four days afterwards, and of
the dozen plants which had previously escaped only three survived; these were
not taller or more vigorous than the other young plants, but they escaped
completely, with not even the tips of their leaves browned. It was impossible
to behold these three plants, with their blackened, withered, and dead
brethren all around, and not see at a glance that they differed widely in
constitutional power of resisting frost.

This work is not the proper place to show that wild plants of the same
species, naturally growing at different altitudes or under different
latitudes, become to a certain extent acclimatised, as is proved by the
different behaviour of their seedlings when raised in another country. In my
'Origin of Species' I have alluded to some cases, and I could add many others.
One instance must suffice: Mr. Grigor, of Forres (24/70. 'Gardener's
Chronicle' 1865 page 699. Mr. G. Maw gives ('Gardener's Chronicle' 1870 page
895) a number of striking cases; he brought home from southern Spain and
northern Africa several plants, which he cultivated in England alongside
specimens from northern districts; and he found a great difference not only in
their hardiness during the winter, but in the behaviour of some of them during
the summer.), states that seedlings of the Scotch fir (Pinus sylvestris),
raised from seed from the Continent and from the forests of Scotland, differ
much. "The difference is perceptible in one-year-old, and more so in two-year-
old seedlings; but the effects of the winter on the second year's growth
almost uniformly make those from the Continent quite brown, and so damaged,
that by the month of March they are quite unsaleable, while the plants from
the native Scotch pine, under the same treatment, and standing alongside,
although considerably shorter, are rather stouter and quite green, so that the
beds of the one can be known from the other when seen from the distance of a
mile." Closely similar facts have been observed with seedling larches.

[Hardy varieties would alone be valued or noticed in Europe; whilst tender
varieties, requiring more warmth, would generally be neglected; but such
occasionally arise. Thus Loudon (24/71. 'Arboretum et Fruticetum' volume 3
page 1376.) describes a Cornish variety of the elm which is almost an
evergreen, and of which the shoots are often killed by the autumnal frosts, so
that its timber is of little value. Horticulturists know that some varieties
are much more tender than others: thus all the varieties of the broccoli are
more tender than cabbages; but there is much difference in this respect in the
sub-varieties of the broccoli; the pink and purple kinds are a little hardier
than the white Cape broccoli, "but they are not to be depended on after the
thermometer falls below 24 deg Fahr.;" the Walcheren broccoli is less tender
than the Cape, and there are several varieties which will stand much severer
cold than the Walcheren. (24/72. Mr. Robson in 'Journal of Horticulture' 1861
page 23.) Cauliflowers seed more freely in India than cabbages. (24/73. Dr.
Bonavia 'Report of the Agri.-Hort. Soc. of Oudh' 1866.) To give one instance
with flowers: eleven plants raised from a hollyhock, called the Queen of the
Whites (24/74. 'Cottage Gardener' 1860 April 24 page 57.) were found to be
much more tender than various other seedlings. It may be presumed that all
tender varieties would succeed better under a climate warmer than ours. With
fruit-trees, it is well known that certain varieties, for instance of the
peach, stand forcing in a hot-house better than others; and this shows either
pliability of organisation or some constitutional difference. The same
individual cherry-tree, when forced, has been observed during successive years
gradually to change its period of vegetation. (24/75. 'Gardener's Chronicle'
1841 page 291.) Few pelargoniums can resist the heat of a stove, but Alba
Multiflora will, as a most skilful gardener asserts, "stand pine-apple top and
bottom heat the whole winter; without looking any more drawn than if it had
stood in a common greenhouse; and Blanche Fleur seems as if it had been made
on purpose for growing in winter, like many bulbs, and to rest all summer."
(24/76. Mr. Beaton in 'Cottage Gardener' March 20, 1860 page 377. Queen Mab
will also stand stove heat. See 'Gardener's Chronicle' 1845 page 226.) There
can hardly be a doubt that the Alba Multiflora pelargonium must have a widely
different constitution from that of most other varieties of this plant; it
would probably withstand even an equatorial climate.

We have seen that according to Labat the vine and wheat require
acclimatisation in order to succeed in the West Indies. Similar facts have
been observed at Madras: "two parcels of mignonette-seed, one direct from
Europe, the other saved at Bangalore (of which the mean temperature is much
below that of Madras), were sown at the same time: they both vegetated equally
favourably, but the former all died off a few days after they appeared above
ground; the latter still survive, and are vigorous, healthy plants." "So
again, turnip and carrot seed saved at Hyderabad are found to answer better at
Madras than seed from Europe or from the Cape of Good Hope." (24/77.
'Gardener's Chronicle' 1841 page 439.) Mr. J. Scott of the Calcutta Botanic
Gardens, informs me that seeds of the sweet-pea (Lathyrus odoratus) imported
from England produce plants, with thick, rigid stems and small leaves, which
rarely blossom and never yield seed; plants raised from French seed blossom
sparingly, but all the flowers are sterile; on the other hand, plants raised
from sweet-peas grown near Darjeeling in Upper India, but originally derived
from England, can be successfully cultivated on the plains of India; for they
flower and seed profusely, and their stems are lax and scandent. In some of
the foregoing cases, as Dr. Hooker has remarked to me, the greater success may
perhaps be attributed to the seeds having been more fully ripened under a more
favourable climate; but this view can hardly be extended to so many cases,
including plants, which, from being cultivated under a climate hotter than
their native one, become fitted for a still hotter climate. We may therefore
safely conclude that plants can to a certain extent become accustomed to a
climate either hotter or colder than their own; although the latter cases have
been more frequently observed.]

We will now consider the means by which acclimatisation may be effected,
namely, through the appearance of varieties having a different constitution,
and through the effects of habit. In regard to new varieties, there is no
evidence that a change in the constitution of the offspring necessarily stands
in any direct relation with the nature of the climate inhabited by the
parents. On the contrary, it is certain that hardy and tender varieties of the
same species appear in the same country. New varieties thus spontaneously
arising become fitted to slightly different climates in two different ways;
firstly, they may have the power, either as seedlings or when full-grown, of
resisting intense cold, as with the Moscow pear, or of resisting intense heat,
as with some kinds of Pelargonium, or the flowers may withstand severe frost,
as with the Forelle pear. Secondly, plants may become adapted to climates
widely different from their own, from flowering and fruiting either earlier or
later in the season. In both these cases the power of acclimatisation by man
consists simply in the selection and preservation of new varieties. But
without any direct intention on his part of securing a hardier variety,
acclimatisation may be unconsciously effected by merely raising tender plants
from seed, and by occasionally attempting their cultivation further and
further northwards, as in the case of maize, the orange and the peach.

How much influence ought to be attributed to inherited habit or custom in the
acclimatisation of animals and plants is a much more difficult question. In
many cases natural selection can hardly have failed to have come into play and
complicated the result. It is notorious that mountain sheep resist severe
weather and storms of snow which would destroy lowland breeds; but then
mountain sheep have been thus exposed from time immemorial, and all delicate
individuals will have been destroyed, and the hardiest preserved. So with the
Arrindy silk-moths of China and India; who can tell how far natural selection
may have taken a share in the formation of the two races, which are now fitted
for such widely different climates? It seems at first probable that the many
fruit-trees which are so well fitted for the hot summers and cold winters of
North America, in contrast with their poor success under our climate, have
become adapted through habit; but when we reflect on the multitude of
seedlings annually raised in that country, and that none would succeed unless
born with a fitting constitution, it is possible that mere habit may have done
nothing towards their acclimatisation. On the other hand, when we hear that
Merino sheep, bred during no great number of generations at the Cape of Good
Hope--that some European plants raised during only a few generations in the
cooler parts of India, withstand the hotter parts of that country much better
than the sheep or seeds imported directly from England, we must attribute some
influence to habit. We are led to the same conclusion when we hear from Naudin
(24/78. Quoted by Asa Gray in 'Am. Journ. of Sc.' 2nd series January 1865 page
106.) that the races of melons, squashes, and gourds, which have long been
cultivated in Northern Europe, are comparatively more precocious, and need
much less heat for maturing their fruit, than the varieties of the same
species recently brought from tropical regions. In the reciprocal conversion
of summer and winter wheat, barley, and vetches into each other, habit
produces a marked effect in the course of a very few generations. The same
thing apparently occurs with the varieties of maize, which, when carried from
the Southern States of America, or into Germany, soon became accustomed to
their new homes. With vine-plants taken to the West Indies from Madeira, which
are said to succeed better than plants brought directly from France, we have
some degree of acclimatisation in the individual, independently of the
production of new varieties by seed.

The common experience of agriculturists is of some value, and they often
advise persons to be cautious in trying the productions of one country in
another. The ancient agricultural writers of China recommend the preservation
and cultivation of the varieties peculiar to each country. During the
classical period, Columella wrote, "Vernaculum pecus peregrino longe
praestantius est." (24/79. For China see 'Memoire sur les Chinois' tome 11
1786 page 60. Columella is quoted by Carlier in 'Journal de Physique' tome 24
1784.)

I am aware that the attempt to acclimatise either animals or plants has been
called a vain chimera. No doubt the attempt in most cases deserves to be thus
called, if made independently of the production of new varieties endowed with
a different constitution. With plants propagated by buds, habit rarely
produces any effect; it apparently acts only through successive seminal
generations. The laurel, bay, laurestinus, etc., and the Jerusalem artichoke,
which are propagated by cuttings or tubers, are probably now as tender in
England as when first introduced; and this appears to be the case with the
potato, which until recently was seldom multiplied by seed. With plants
propagated by seed, and with animals, there will be little or no
acclimatisation unless the hardier individuals are either intentionally or
unconsciously preserved. The kidney-bean has often been advanced as an
instance of a plant which has not become hardier since its first introduction
into Britain. We hear, however, on excellent authority (24/80. Messrs. Hardy
and Son in 'Gardener's Chronicle' 1856 page 589.) that some very fine seed,
imported from abroad, produced plants "which blossomed most profusely, but
were nearly all but abortive, whilst plants grown alongside from English seed
podded abundantly;" and this apparently shows some degree of acclimatisation
in our English plants. We have also seen that seedlings of the kidney-bean
occasionally appear with a marked power of resisting frost; but no one, as far
as I can hear, has ever separated such hardy seedlings, so as to prevent
accidental crossing, and then gathered their seed, and repeated the process
year after year. It may, however, be objected with truth that natural
selection ought to have had a decided effect on the hardiness of our kidney-
beans; for the tenderest individuals must have been killed during every severe
spring, and the hardier preserved. But it should be borne in mind that the
result of increased hardiness would simply be that gardeners, who are always
anxious for as early a crop as possible, would sow their seed a few days
earlier than formerly. Now, as the period of sowing depends much on the soil
and elevation of each district, and varies with the season; and as new
varieties have often been imported from abroad, can we feel sure that our
kidney-beans are not somewhat hardier? I have not been able, by searching old
horticultural works, to answer this question satisfactorily.

On the whole the facts now given show that, though habit does something
towards acclimatisation, yet that the appearance of constitutionally different
individuals is a far more effective agent. As no single instance has been
recorded either with animals or plants of hardier individuals having been long
and steadily selected, though such selection is admitted to be indispensable
for the improvement of any other character, it is not surprising that man has
done little in the acclimatisation of domesticated animals and cultivated
plants. We need not, however, doubt that under nature new races and new
species would become adapted to widely different climates, by variation, aided
by habit, and regulated by natural selection.

[ARRESTS OF DEVELOPMENT: RUDIMENTARY AND ABORTED ORGANS.

Modifications of structure from arrested development, so great or so serious
as to deserve to be called monstrosities, are not infrequent with domesticated
animals, but, as they differ much from any normal structure, they require only
a passing notice. Thus the whole head may be represented by a soft nipple-like
projection, and the limbs by mere papillae. These rudiments of limbs are
sometimes inherited, as has been observed in a dog. (24/81. Isid. Geoffroy
Saint-Hilaire 'Hist. Nat. des Anomalies' 1836 tome 2 pages 210, 223, 224, 395;
'Philosoph. Transact.' 1775 page 313.)

Many lesser anomalies appear to be due to arrested development. What the cause
of the arrest may be, we seldom know, except in the case of direct injury to
the embryo. That the cause does not generally act at an extremely early
embryonic period we may infer from the affected organ seldom being wholly
aborted,--a rudiment being generally preserved. The external ears are
represented by mere vestiges in a Chinese breed of sheep; and in another
breed, the tail is reduced "to a little button, suffocated in a manner, by
fat." (24/82. Pallas quoted by Youatt on 'Sheep' page 25.) In tailless dogs
and cats a stump is left. In certain breeds of fowls the comb and wattles are
reduced to rudiments; in the Cochin-China breed scarcely more than rudiments
of spurs exist. With polled Suffolk cattle, "rudiments of horns can often be
felt at an early age" (24/83. Youatt on 'Cattle' 1834 page 174.); and with
species in a state of nature, the relatively great development of rudimentary
organs at an early period of life is highly characteristic of such organs.
With hornless breeds of cattle and sheep, another and singular kind of
rudiment has been observed, namely, minute dangling horns attached to the skin
alone, and which are often shed and grow again. With hornless goats, according
to Desmarest (24/84. 'Encyclop. Method.' 1820 page 483: see page 500, on the
Indian zebu casting its horns. Similar cases in European cattle were given in
the third chapter.), the bony protuberance which properly supports the horn
exists as a mere rudiment.

With cultivated plants it is far from rare to find the petals, stamens, and
pistils represented by rudiments, like those observed in natural species. So
it is with the whole seed in many fruits; thus, near Astrakhan there is a
grape with mere traces of seeds, "so small and lying so near the stalk that
they are not perceived in eating the grape." (24/85. Pallas 'Travels' English
Translat. volume 1 page 243.) In certain varieties of the gourd, the tendrils,
according to Naudin, are represented by rudiments or by various monstrous
growths. In the broccoli and cauliflower the greater number of the flowers are
incapable of expansion, and include rudimentary organs. In the Feather
hyacinth (Muscari comosum) in its natural state the upper and central flowers
are brightly coloured but rudimentary; under cultivation the tendency to
abortion travels downwards and outwards, and all the flowers become
rudimentary; but the abortive stamens and pistils are not so small in the
lower as in the upper flowers. In the Viburnum opulus, on the other hand, the
outer flowers naturally have their organs of fructification in a rudimentary
state, and the corolla is of large size; under cultivation, the change spreads
to the centre, and all the flowers become affected. In the compositae, the so-
called doubling of the flowers consists in the greater development of the
corolla of the central florets, generally accompanied with some degree of
sterility; and it has been observed (24/86. Mr. Beaton in 'Journal of
Horticulture' May 21, 1861 page 133.) that the progressive doubling invariably
spreads from the circumference to the centre,--that is, from the ray florets,
which so often include rudimentary organs, to those of the disc. I may add, as
bearing on this subject, that with Asters, seeds taken from the florets of the
circumference have been found to yield the greatest number of double flowers.
(24/87. Lecoq 'De la Fecondation' 1862 page 233.) In the above cases we have a
natural tendency in certain parts to be rudimentary, and this under culture
spreads either to, or from, the axis of the plant. It deserves notice, as
showing how the same laws govern the changes which natural species and
artificial varieties undergo, that in the species of Carthamus, one of the
Compositae, a tendency to the abortion of the pappus may be traced extending
from the circumference to the centre of the disc as in the so-called doubling
of the flowers in the members of the same family. Thus, according to A. de
Jussieu (24/88. 'Annales du Museum' tome 6 page 319.), the abortion is only
partial in Carthamus creticus, but more extended in C. lanatus; for in this
species only two or three of the central seeds are furnished with a pappus,
the surrounding seeds being either quite naked or furnished with a few hairs;
and lastly in C. tinctorius, even the central seeds are destitute of pappus,
and the abortion is complete.

With animals and plants under domestication, when an organ disappears, leaving
only a rudiment, the loss has generally been sudden, as with hornless and
tailless breeds; and such cases may be ranked as inherited monstrosities. But
in some few cases the loss has been gradual, and has been effected partly by
selection, as with the rudimentary combs and wattles of certain fowls. We have
also seen that the wings of some domesticated birds have been slightly reduced
by disuse, and the great reduction of the wings in certain silk-moths, with
mere rudiments left, has probably been aided by disuse.]

With species in a state of nature, rudimentary organs are extremely common.
Such organs are generally variable, as several naturalists have observed; for,
being useless, they are not regulated by natural selection, and they are more
or less liable to reversion. The same rule certainly holds good with parts
which have become rudimentary under domestication. We do not know through what
steps under nature rudimentary organs have passed in being reduced to their
present condition; but we so incessantly see in species of the same group the
finest gradations between an organ in a rudimentary and perfect state, that we
are led to believe that the passage must have been extremely gradual. It may
be doubted whether a change of structure so abrupt as the sudden loss of an
organ would ever be of service to a species in a state of nature; for the
conditions to which all organisms are closely adapted usually change very
slowly. Even if an organ did suddenly disappear in some one individual by an
arrest of development, intercrossing with the other individuals of the same
species would tend to cause its partial reappearance; so that its final
reduction could only be effected by some other means. The most probable view
is, that a part which is now rudimentary, was formerly, owing to changed
habits of life, used less and less, being at the same time reduced in size by
disuse, until at last it became quite useless and superfluous. But as most
parts or organs are not brought into action during an early period of life,
disuse or decreased action will not lead to their reduction until the organism
arrives at a somewhat advanced age; and from the principle of inheritance at
corresponding ages the reduction will be transmitted to the offspring at the
same advanced stage of growth. The part or organ will thus retain its full
size in the embryo, as we know to be the case with most rudiments. As soon as
a part becomes useless, another principle, that of economy of growth, will
come into play, as it would be an advantage to an organism exposed to severe
competition to save the development of any useless part; and individuals
having the part less developed will have a slight advantage over others. But,
as Mr. Mivart has justly remarked, as soon as a part is much reduced, the
saving from its further reduction will be utterly insignificant; so that this
cannot be effected by natural selection. This manifestly holds good if the
part be formed of mere cellular tissue, entailing little expenditure of
nutriment. How then can the further reduction of an already somewhat reduced
part be effected? That this has occurred repeatedly under Nature is shown by
the many gradations which exist between organs in a perfect state and the
merest vestiges of them. Mr. Romanes (24/89. I suggested in 'Nature' (volume 8
pages 432, 505) that with organisms subjected to unfavourable conditions all
the parts would tend towards reduction, and that under such circumstances any
part which was not kept up to its standard size by natural selection would,
owing to intercrossing, slowly but steadily decrease. In three subsequent
communications to 'Nature' (March 12, April 9, and July 2, 1874), Mr. Romanes
gives his improved view.) has, I think, thrown much light on this difficult
problem. His view, as far as it can be given in a few words, is as follows:
all parts are somewhat variable and fluctuate in size round an average point.
Now, when a part has already begun from any cause to decrease, it is very
improbable that the variations should be as great in the direction of increase
as of diminution; for the previous reduction shows that circumstances have not
been favourable for its development; whilst there is nothing to check
variations in the opposite direction. If this be so, the long continued
crossing of many individuals furnished with an organ which fluctuates in a
greater degree towards decrease than towards increase, will slowly but
steadily lead to its diminution. With respect to the complete and absolute
abortion of a part, a distinct principle, which will be discussed in the
chapter on pangenesis, probably comes into action.

With animals and plants reared by man there is no severe or recurrent struggle
for existence, and the principle of economy will not come into action, so that
the reduction of an organ will not thus be aided. So far, indeed, is this from
being the case, that in some few instances organs, which are naturally
rudimentary in the parent-species, become partially redeveloped in the
domesticated descendants. Thus cows, like most other ruminants, properly have
four active and two rudimentary mamma; but in our domesticated animals, the
latter occasionally become considerably developed and yield milk. The
atrophied mammae, which, in male domesticated animals, including man, have in
some rare cases grown to full size and secreted milk, perhaps offer an
analogous case. The hind feet of dogs naturally include rudiments of a fifth
toe, and in certain large breeds these toes, though still rudimentary, become
considerably developed and are furnished with claws. In the common Hen, the
spurs and comb are rudimentary, but in certain breeds these become,
independently of age or disease of the ovaria, well developed. The stallion
has canine teeth, but the mare has only traces of the alveoli, which, as I am
informed by the eminent veterinarian Mr. G.T. Brown, frequently contain minute
irregular nodules of bone. These nodules, however, sometimes become developed
into imperfect teeth, protruding through the gums and coated with enamel; and
occasionally they grow to a fourth or even a third of the length of the
canines in the stallion. With plants I do not know whether the redevelopment
of rudimentary organs occurs more frequently under culture than under nature.
Perhaps the pear-tree may be a case in point, for when wild it bears thorns,
which consist of branches in a rudimentary condition and serve as a
protection, but, when the tree is cultivated, they are reconverted into
branches.


CHAPTER 2.XXV.

LAWS OF VARIATION, continued.--CORRELATED VARIABILITY.

EXPLANATION OF TERM CORRELATION.
CONNECTED WITH DEVELOPMENT.
MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZE
OF PARTS.
CORRELATED VARIATION OF HOMOLOGOUS PARTS.
FEATHERED FEET IN BIRDS ASSUMING THE STRUCTURE OF THE WINGS.
CORRELATION BETWEEN THE HEAD AND THE EXTREMITIES.
BETWEEN THE SKIN AND DERMAL APPENDAGES.
BETWEEN THE ORGANS OF SIGHT AND HEARING.
CORRELATED MODIFICATIONS IN THE ORGANS OF PLANTS.
CORRELATED MONSTROSITIES.
CORRELATION BETWEEN THE SKULL AND EARS.
SKULL AND CREST OF FEATHERS.
SKULL AND HORNS.
CORRELATION OF GROWTH COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL
SELECTION.
COLOUR AS CORRELATED WITH CONSTITUTIONAL PECULIARITIES.

All parts of the organisation are to a certain extent connected together; but
the connection may be so slight that it hardly exists, as with compound
animals or the buds on the same tree. Even in the higher animals various parts
are not at all closely related; for one part may be wholly suppressed or
rendered monstrous without any other part of the body being affected. But in
some cases, when one part varies, certain other parts always, or nearly
always, simultaneously vary; they are then subject to the law of correlated
variation. The whole body is admirably co-ordinated for the peculiar habits of
life of each organic being, and may be said, as the Duke of Argyll insists in
his 'Reign of Law' to be correlated for this purpose. Again, in large groups
of animals certain structures always co-exist: for instance, a peculiar form
of stomach with teeth of peculiar form, and such structures may in one sense
be said to be correlated. But these cases have no necessary connection with
the law to be discussed in the present chapter; for we do not know that the
initial or primary variations of the several parts were in any way related:
slight modifications or individual differences may have been preserved, first
in one and then in another part, until the final and perfectly co-adapted
structure was acquired; but to this subject I shall presently recur. Again, in
many groups of animals the males alone are furnished with weapons, or are
ornamented with gay colours; and these characters manifestly stand in some
sort of correlation with the male reproductive organs, for when the latter are
destroyed these characters disappear. But it was shown in the twelfth chapter
that the very same peculiarity may become attached at any age to either sex,
and afterwards be exclusively transmitted to the same sex at a corresponding
age. In these cases we have inheritance limited by both sex and age; but we
have no reason for supposing that the original cause of the variation was
necessarily connected with the reproductive organs, or with the age of the
affected being.

In cases of true correlated variation, we are sometimes able to see the nature
of the connection; but in most cases it is hidden from us, and certainly
differs in different cases. We can seldom say which of two correlated parts
first varies, and induces a change in the other; or whether the two are the
effects of some common cause. Correlated variation is an important subject for
us; for when one part is modified through continued selection, either by man
or under nature, other parts of the organisation will be unavoidably modified.
From this correlation it apparently follows that with our domesticated animals
and plants, varieties rarely or never differ from one another by a single
character alone.

One of the simplest cases of correlation is that a modification which arises
during an early stage of growth tends to influence the subsequent development
of the same part, as well as of other and intimately connected parts. Isidore
Geoffroy Saint-Hilaire states (25/1. 'Hist. des Anomalies' tome 3 page 392.
Prof. Huxley applies the same principle in accounting for the remarkable,
though normal, differences in the arrangement of the nervous system in the
Mollusca, in his paper on the Morphology of the Cephalous Mollusca in 'Phil.
Transact.' 1853 page 56.) that this may constantly be observed with
monstrosities in the animal kingdom; and Moquin-Tandon (25/2. 'Elements de
Teratologie Veg.' 1841 page 13.) remarks, that, as with plants the axis cannot
become monstrous without in some way affecting the organs subsequently
produced from it, so axial anomalies are almost always accompanied by
deviations of structure in the appended parts. We shall presently see that
with short-muzzled races of the dog certain histological changes in the basal
elements of the bones arrest their development and shorten them, and this
affects the position of the subsequently developed molar teeth. It is probable
that certain modifications in the larvae of insects would affect the structure
of the mature insects. But we must be careful not to extend this view too far,
for during the normal course of development, certain species pass through an
extraordinary course of change, whilst other and closely allied species arrive
at maturity with little change of structure.

Another simple case of correlation is that with the increased or decreased
dimensions of the whole body, or of any particular part, certain organs are
increased or diminished in number, or are otherwise modified. Thus pigeon
fanciers have gone on selecting pouters for length of body, and we have seen
that their vertebrae are generally increased not only in size but in number,
and their ribs in breadth. Tumblers have been selected for their small bodies,
and their ribs and primary wing-feathers are generally lessened in number.
Fantails have been selected for their large widely-expanded tails, with
numerous tail-feathers, and the caudal vertebrae are increased in size and
number. Carriers have been selected for length of beak, and their tongues have
become longer, but not in strict accordance with the length of beak. In this
latter breed and in others having large feet, the number of the scutellae on
the toes is greater than in the breeds with small feet. Many similar cases
could be given. In Germany it has been observed that the period of gestation
is longer in large than in small breeds of cattle. With our highly-improved
breeds of all kinds, the periods of maturity and of reproduction have advanced
with respect to the age of the animal; and, in correspondence with this, the
teeth are now developed earlier than formerly, so that, to the surprise of
agriculturists, the ancient rules for judging of the age of an animal by the
state of its teeth are no longer trustworthy. (25/3. Prof. J.B. Simonds on the
Age of the Ox, Sheep, etc. quoted in 'Gardener's Chronicle' 1854 page 588.)

CORRELATED VARIATION OF HOMOLOGOUS PARTS.

Parts which are homologous tend to vary in the same manner; and this is what
might have been expected, for such parts are identical in form and structure
during an early period of embryonic development, and are exposed in the egg or
womb to similar conditions. The symmetry, in most kinds of animals, of the
corresponding or homologous organs on the right and left sides of the body, is
the simplest case in point; but this symmetry sometimes fails, as with rabbits
having only one ear, or stags with one horn, or with many-horned sheep which
sometimes carry an additional horn on one side of their heads. With flowers
which have regular corollas, all the petals generally vary in the same manner,
as we see in the complicated and symmetrical pattern, on the flowers, for
instance, of the Chinese pink; but with irregular flowers, though the petals
are of course homologous, this symmetry often fails, as with the varieties of
the Antirrhinum or snapdragon, or that variety of the kidney-bean (Phaseolus)
which has a white standard-petal.

In the Vertebrata the front and hind limbs are homologous, and they tend to
vary in the same manner, as we see in long and short legged, or in thick and
thin legged races of the horse and dog. Isidore Geoffroy (25/4. 'Hist. des
Anomalies' tome 1 page 674.) has remarked on the tendency of supernumerary
digits in man to appear, not only on the right and left sides, but on the
upper and lower extremities. Meckel has insisted (25/5. Quoted by Isid.
Geoffroy ibid tome 1 page 635.) that, when the muscles of the arm depart in
number or arrangement from their proper type, they almost always imitate those
of the leg; and so conversely the varying muscles of the leg imitate the
normal muscles of the arm.

In several distinct breeds of the pigeon and fowl, the legs and the two outer
toes are heavily feathered, so that in the trumpeter pigeon they appear like
little wings. In the feather-legged bantam the "boots" or feathers, which grow
from the outside of the leg and generally from the two outer toes, have,
according to the excellent authority of Mr. Hewitt (25/6. 'The Poultry Book'
by W.B. Tegetmeier 1866 page 250.), been seen to exceed the wing-feathers in
length, and in one case were actually nine and a half inches long! As Mr.
Blyth has remarked to me, these leg-feathers resemble the primary wing-
feathers, and are totally unlike the fine down which naturally grows on the
legs of some birds, such as grouse and owls. Hence it may be suspected that
excess of food has first given redundancy to the plumage, and then that the
law of homologous variation has led to the development of feathers on the
legs, in a position corresponding with those on the wing, namely, on the
outside of the tarsi and toes. I am strengthened in this belief by the
following curious case of correlation, which for a long time seemed to me
utterly inexplicable, namely, that in pigeons of any breed, if the legs are
feathered, the two outer toes are partially connected by skin. These two outer
toes correspond with our third and fourth toes. (25/7. Naturalists differ with
respect to the homologies of the digits of birds; but several uphold the view
above advanced. See on this subject Dr. E.S. Morse in 'Annals of the Lyceum of
Nat. Hist. of New York' volume 10 1872 page 16.) Now, in the wing of the
pigeon or of any other bird, the first and fifth digits are aborted; the
second is rudimentary and carries the so-called "bastard-wing;" whilst the
third and fourth digits are completely united and enclosed by skin, together
forming the extremity of the wing. So that in feather-footed pigeons, not only
does the exterior surface support a row of long feathers, like wing-feathers,
but the very same digits which in the wing are completely united by skin
become partially united by skin in the feet; and thus by the law of the
correlated variation of homologous parts we can understand the curious
connection of feathered legs and membrane between the two outer toes.

Andrew Knight (24/8. A. Walker on 'Intermarriage' 1838 page 160.) has remarked
that the face or head and the limbs usually vary together in general
proportions. Compare, for instance, the limbs of a dray and race horse, or of
a greyhound and mastiff. What a monster a greyhound would appear with the head
of a mastiff! The modern bulldog, however, has fine limbs, but this is a
recently-selected character. From the measurements given in the sixth chapter,
we see that in several breeds of the pigeon the length of the beak and the
size of the feet are correlated. The view which, as before explained, seems
the most probable is, that disuse in all cases tends to diminish the feet, the
beak becoming at the same time shorter through correlation; but that in some
few breeds in which length of beak has been a selected point, the feet,
notwithstanding disuse, have increased in size through correlation. In the
following case some kind of correlation is seen to exist between the feet and
beak: several specimens have been sent to Mr. Bartlett at different times, as
hybrids between ducks and fowls, and I have seen one; these were, as might be
expected, ordinary ducks in a semi-monstrous condition, and in all of them the
swimming-web between the toes was quite deficient or much reduced, and in all
the beak was narrow and ill-shaped.

With the increased length of the beak in pigeons, not only the tongue
increases in length, but likewise the orifice of the nostrils. But the
increased length of the orifice of the nostrils perhaps stands in closer
correlation with the development of the corrugated skin or wattle at the base
of the beak, for when there is much wattle round the eyes, the eyelids are
greatly increased or even doubled in length.

There is apparently some correlation even in colour between the head and the
extremities. Thus with horses a large white star or blaze on the forehead is
generally accompanied by white feet. (25/9. 'The Farrier and Naturalist'
volume 1 1828 page 456. A gentleman who has attended to this point, tells me
that about three-fourths of white-faced horses have white legs.) With white
rabbits and cattle, dark marks often co-exist on the tips of the ears and on
the feet. In black and tan dogs of different breeds, tan-coloured spots over
the eyes and tan-coloured feet almost invariably go together. These latter
cases of connected colouring may be due either to reversion or to analogous
variation,--subjects to which I shall hereafter return,--but this does not
necessarily determine the question of their original correlation. Mr. H.W.
Jackson informs me that he has observed many hundred white-footed cats, and he
finds that all are more or less conspicuously marked with white on the front
of the neck or chest.

The lopping forwards and downwards of the immense ears of fancy rabbits seems
partly due to the disuse of the muscles, and partly to the weight and length
of the ears, which have been increased by selection during many generations.
Now, with the increased size and changed direction of the ears not only has
the bony auditory meatus become changed in outline, direction, and greatly in
size, but the whole skull has been slightly modified. This could be clearly
seen in "half-lops"--that is, in rabbits with only one ear lopping forward--
for the opposite sides of their skulls were not strictly symmetrical. This
seems to me a curious instance of correlation, between hard bones and organs
so soft and flexible, as well as so unimportant under a physiological point of
view, as the external ears. The result no doubt is largely due to mere
mechanical action, that is, to the weight of the ears, on the same principle
that the skull of a human infant is easily modified by pressure.

The skin and the appendages of hair, feathers, hoofs, horns, and teeth, are
homologous over the whole body. Every one knows that the colour of the skin
and that of the hair usually vary together; so that Virgil advises the
shepherd to look whether the mouth and tongue of the ram are black, lest the
lambs should not be purely white. The colour of the skin and hair, and the
odour emitted by the glands of the skin, are said (25/10. Godron 'Sur
l'Espece' tome 2 page 217.) to be connected, even in the same race of men.
Generally the hair varies in the same way all over the body in length,
fineness, and curliness. The same rule holds good with feathers, as we see
with the laced and frizzled breeds both of fowls and pigeons. In the common
cock the feathers on the neck and loins are always of a particular shape,
called hackles: now in the Polish breed, both sexes are characterised by a
tuft of feathers on the head, and through correlation these feathers in the
male always assume the form of hackles. The wing and tail-feathers, though
arising from parts not homologous, vary in length together; so that long or
short winged pigeons generally have long or short tails. The case of the
Jacobin-pigeon is more curious, for the wing and tail feathers are remarkably
long; and this apparently has arisen in correlation with the elongated and
reversed feathers on the back of the neck, which form the hood.

The hoofs and hair are homologous appendages; and a careful observer, namely
Azara (25/11. 'Quadrupedes du Paraguay' tome 2 page 333.), states that in
Paraguay horses of various colours are often born with their hair curled and
twisted like that on the head of a negro. This peculiarity is strongly
inherited. But what is remarkable is that the hoofs of these horses "are
absolutely like those of a mule." The hair also of their manes and tails is
invariably much shorter than usual, being only from four to twelve inches in
length; so that curliness and shortness of the hair are here, as with the
negro, apparently correlated.

With respect to the horns of sheep, Youatt (25/12. 'On Sheep' page 142.)
remarks that "multiplicity of horns is not found in any breed of much value;
it is generally accompanied by great length and coarseness of the fleece."
Several tropical breeds of sheep which are clothed with hair instead of wool,
have horns almost like those of a goat. Sturm (25/13. 'Ueber Racen,
Kreuzungen' etc. 1825 s. 24.) expressly declares that in different races the
more the wool is curled the more the horns are spirally twisted. We have seen
in the third chapter, where other analogous facts have been given, that the
parent of the Mauchamp breed, so famous for its fleece, had peculiarly shaped
horns. The inhabitants of Angora assert (25/14. Quoted from Conolly in 'The
Indian Field' February 1859 volume 2 page 266.) that "only the white goats
which have horns wear the fleece in the long curly locks that are so much
admired; those which are not horned having a comparatively close coat." From
these cases we may infer that the hair or wool and the horns tend to vary in a
correlated manner. (25/15. In the third chapter I have said that "the hair and
horns are so closely related to each other, that they are apt to vary
together." Dr. Wilckens ("Darwin's Theorie" 'Jahrbuch der Deutschen Viehzucht'
1866 1. Heft) translates my words into "lang- und grobhaarige Thiere sollen
geneigter sein, lange und viele Horner zu bekommen" and he then justly
disputes this proposition; but what I have really said, in accordance with the
authorities just quoted, may, I think, be trusted.) Those who have tried
hydropathy are aware that the frequent application of cold water stimulates
the skin; and whatever stimulates the skin tends to increase the growth of the
hair, as is well shown in the abnormal growth of hair near old inflamed
surfaces. Now, Professor Low (25/16. 'Domesticated Animals of the British
Islands' pages 307, 368. Dr. Wilckens argues ('Landwirth. Wochenblatt' Nr. 10
1869) to the same effect with respect to domestic animals in Germany.) is
convinced that with the different races of British cattle thick skin and long
hair depend on the humidity of the climate which they inhabit. We can thus see
how a humid climate might act on the horns--in the first place directly on the
skin and hair, and secondly by correlation on the horns. The presence or
absence of horns, moreover, both in the case of sheep and cattle, acts, as
will presently be shown, by some sort of correlation on the skull.

With respect to hair and teeth, Mr. Yarrell (25/17. 'Proceedings Zoolog. Soc.'
1833 page 113.) found many of the teeth deficient in three hairless "Egyptian
dogs," and in a hairless terrier. The incisors, canines, and the premolars
suffered most, but in one case all the teeth, except the large tubercular
molar on each side, were deficient. With man several striking cases have been
recorded (25/18. Sedgwick 'Brit. and Foreign Medico-Chirurg. Review' April
1863 page 453.) of inherited baldness with inherited deficiency, either
complete or partial, of the teeth. I may give an analogous case, communicated
to me by Mr. W. Wedderburn, of a Hindoo family in Scinde, in which ten men, in
the course of four generations, were furnished, in both jaws taken together,
with only four small and weak incisor teeth and with eight posterior molars.
The men thus affected have very little hair on the body, and become bald early
in life. They also suffer much during hot weather from excessive dryness of
the skin. It is remarkable that no instance has occurred of a daughter being
thus affected; and this fact reminds us how much more liable men are in
England to become bald than women. Though the daughters in the above family
are never affected, they transmit the tendency to their sons; and no case has
occurred of a son transmitting it to his sons. The affection thus appears only
in alternate generations, or after longer intervals. There is a similar
connection between hair and teeth, according to Mr. Sedgwick, in those rare
cases in which the hair has been renewed in old age, for this has "usually
been accompanied by a renewal of the teeth." I have remarked in a former part
of this volume that the great reduction in the size of the tusks in domestic
boars probably stands in close relation with their diminished bristles, due to
a certain amount of protection; and that the reappearance of the tusks in
boars, which have become feral and are fully exposed to the weather, probably
depends on the reappearance of the bristles. I may add, though not strictly
connected with our present point, that an agriculturist (25/19. 'Gardener's
Chronicle' 1849 page 205.) asserts that "pigs with little hair on their bodies
are most liable to lose their tails, showing a weakness of the tegumental
structure. It may be prevented by crossing with a more hairy breed."

In the previous cases deficient hair, and teeth deficient in number or size,
are apparently connected. In the following cases abnormally redundant hair,
and teeth either deficient or redundant, are likewise connected. Mr. Crawfurd
(25/20. 'Embassy to the Court of Ava' volume 1 page 320.) saw at the Burmese
Court a man, thirty years old, with his whole body, except the hands and feet,
covered with straight silky hair, which on the shoulders and spine was five
inches in length. At birth the ears alone were covered. He did not arrive at
puberty, or shed his milk teeth, until twenty years old; and at this period he
acquired five teeth in the upper jaw, namely, four incisors and one canine,
and four incisor teeth in the lower jaw; all the teeth were small. This man
had a daughter who was born with hair within her ears; and the hair soon
extended over her body. When Captain Yule (25/21. 'Narrative of a Mission to
the Court of Ava in 1855' page 94.) visited the Court, he found this girl
grown up; and she presented a strange appearance with even her nose densely
covered with soft hair. Like her father, she was furnished with incisor teeth
alone. The King had with difficulty bribed a man to marry her, and of her two
children, one, a boy fourteen months old, had hair growing out of his ears,
with a beard and moustache. This strange peculiarity has, therefore, been
inherited for three generations, with the molar teeth deficient in the
grandfather and mother; whether these teeth would likewise fail in the infant
could not then be told.

A parallel case of a man fifty-five years old, and of his son, with their
faces covered with hair, has recently occurred in Russia. Dr. Alex. Brandt has
sent me an account of this case, together with specimens of the extremely fine
hair from the cheeks. The man is deficient in teeth, possessing only four
incisors in the lower and two in the upper jaw. His son, about three years
old, has no teeth except four lower incisors. The case, as Dr. Brandt remarks
in his letter, no doubt is due to an arrest of development in the hair and
teeth. We here see how independent of the ordinary conditions of existence
such arrests must be, for the lives of a Russian peasant and of a native of
Burmah are as different as possible. (25/22. I owe to the kindness of M.
Chauman, of St. Petersburg, excellent photographs of this man and his son,
both of whom have since been exhibited in Paris and London.)

Here is another and somewhat different case communicated to me by Mr. Wallace
on the authority of Dr. Purland, a dentist: Julia Pastrana, a Spanish dancer,
was a remarkably fine woman, but she had a thick masculine beard and a hairy
forehead; she was photographed, and her stuffed skin was exhibited as a show;
but what concerns us is, that she had in both the upper and lower jaw an
irregular double set of teeth, one row being placed within the other, of which
Dr. Purland took a cast. From the redundancy of teeth her mouth projected, and
her face had a gorilla-like appearance. These cases and those of the hairless
dogs forcibly call to mind the fact, that the two orders of mammals--namely,
the Edentata and Cetacea--which are the most abnormal in their dermal
covering, are likewise the most abnormal either by deficiency or redundancy of
teeth.

The organs of sight and hearing are generally admitted to be homologous with
one another and with various dermal appendages; hence these parts are liable
to be abnormally affected in conjunction. Mr. White Cowper says "that in all
cases of double microphthalmia brought under his notice he has at the same
time met with defective development of the dental system." Certain forms of
blindness seem to be associated with the colour of the hair; a man with black
hair and a woman with light-coloured hair, both of sound constitution, married
and had nine children, all of whom were born blind; of these children, five
"with dark hair and brown iris were afflicted with amaurosis; the four others,
with light-coloured hair and blue iris, had amaurosis and cataract conjoined."
Several cases could be given, showing that some relation exists between
various affections of the eyes and ears; thus Liebreich states that out of 241
deaf-mutes in Berlin, no less than fourteen suffered from the rare disease
called pigmentary retinitis. Mr. White Cowper and Dr. Earle have remarked that
inability to distinguish different colours, or colour-blindness, "is often
associated with a corresponding inability to distinguish musical sounds."
(25/23. These statements are taken from Mr. Sedgwick in the 'Medico-Chirurg.
Review' July 1861 page 198; April 1863 pages 455 and 458. Liebreich is quoted
by Professor Devay in his 'Mariages Consanguins' 1862 page 116.)

Here is a more curious case: white cats, if they have blue eyes, are almost
always deaf. I formerly thought that the rule was invariable, but I have heard
of a few authentic exceptions. The first two notices were published in 1829
and relate to English and Persian cats: of the latter, the Rev. W.T. Bree
possessed a female, and he states, "that of the offspring produced at one and
the same birth, such as, like the mother, were entirely white (with blue eyes)
were, like her, invariably deaf; while those that had the least speck of
colour on their fur, as invariably possessed the usual faculty of hearing."
(25/24. Loudon's 'Mag. of Nat. Hist.' volume 1 1829 pages 66, 178. See also
Dr. P. Lucas 'L'Hered. Nat.' tome 1 page 428 on the inheritance of deafness in
cats. Mr. Lawson Tait states ('Nature' 1873 page 323) that only male cats are
thus affected; but this must be a hasty generalisation. The first case
recorded in England by Mr. Bree related to a female, and Mr. Fox informs me
that he has bred kittens from a white female with blue eyes, which was
completely deaf; he has also observed other females in the same condition.)
The Rev. W. Darwin Fox informs me that he has seen more than a dozen instances
of this correlation in English, Persian, and Danish cats; but he adds "that,
if one eye, as I have several times observed, be not blue, the cat hears. On
the other hand, I have never seen a white cat with eyes of the common colour
that was deaf." In France Dr. Sichel (25/25. 'Annales des Sc. Nat.' Zoolog.
3rd series 1847 tome 8 page 239.) has observed during twenty years similar
facts; he adds the remarkable case of the iris beginning, at the end of four
months, to grow dark-coloured, and then the cat first began to hear.

This case of correlation in cats has struck many persons as marvellous. There
is nothing unusual in the relation between blue eyes and white fur; and we
have already seen that the organs of sight and hearing are often
simultaneously affected. In the present instance the cause probably lies in a
slight arrest of development in the nervous system in connection with the
sense-organs. Kittens during the first nine days, whilst their eyes are
closed, appear to be completely deaf; I have made a great clanging noise with
a poker and shovel close to their heads, both when they were asleep and awake,
without producing any effect. The trial must not be made by shouting close to
their ears, for they are, even when asleep, extremely sensitive to a breath of
air. Now, as long as the eyes continue closed, the iris is no doubt blue, for
in all the kittens which I have seen this colour remains for some time after
the eyelids open. Hence, if we suppose the development of the organs of sight
and hearing to be arrested at the stage of the closed eyelids, the eyes would
remain permanently blue and the ears would be incapable of perceiving sound;
and we should thus understand this curious case. As, however, the colour of
the fur is determined long before birth, and as the blueness of the eyes and
the whiteness of the fur are obviously connected, we must believe that some
primary cause acts at a much earlier period.

The instances of correlated variability hitherto given have been chiefly drawn
from the animal kingdom, and we will now turn to plants. Leaves, sepals,
petals, stamens, and pistils are all homologous. In double flowers we see that
the stamens and pistils vary in the same manner, and assume the form and
colour of the petals. In the double columbine (Aquilegia vulgaris), the
successive whorls of stamens are converted into cornucopias, which are
enclosed within one another and resemble the true petals. In hose-in-hose
flowers the sepals mock the petals. In some cases the flowers and leaves vary
together in tint: in all the varieties of the common pea, which have purple
flowers, a purple mark may be seen on the stipules.

M. Faivre states that with the varieties of Primula sinensis the colour of the
flower is evidently correlated with the colour of the under side of the
leaves; and he adds that the varieties with fimbriated flowers almost always
have voluminous, balloon-like calyces. (25/26. 'Revue des Cours Scientifiques'
June 5, 1869 page 430.) With other plants the leaves and fruit or seeds vary
together in colour, as in a curious pale-leaved variety of the sycamore, which
has recently been described in France (25/27. 'Gardener's Chronicle' 1864 page
1202.), and as in the purple-leaved hazel, in which the leaves, the husk of
the nut, and the pellicle round the kernel are all coloured purple. (25/28.
Verlot gives several other instances 'Des Varietes' 1865 page 72.) Pomologists
can predict to a certain extent, from the size and appearance of the leaves of
their seedlings, the probable nature of the fruit; for, as Van Mons remarks
(25/29. 'Arbres Fruitiers' 1836 tome 2 pages 204, 226.) variations in the
leaves are generally accompanied by some modification in the flower, and
consequently in the fruit. In the Serpent melon, which has a narrow tortuous
fruit above a yard in length, the stem of the plant, the peduncle of the
female flower, and the middle lobe of the leaf, are all elongated in a
remarkable manner. On the other hand, several varieties of Cucurbita, which
have dwarfed stems, all produce, as Naudin remarks, leaves of the same
peculiar shape. Mr. G. Maw informs me that all the varieties of the scarlet
Pelargoniums which have contracted or imperfect leaves have contracted
flowers: the difference between "Brilliant" and its parent "Tom Thumb" is a
good instance of this. It may be suspected that the curious case described by
Risso (25/30. 'Annales du Museum' tome 20 page 188.), of a variety of the
Orange which produces on the young shoots rounded leaves with winged petioles,
and afterwards elongated leaves on long but wingless petioles, is connected
with the remarkable change in form and nature which the fruit undergoes during
its development.

In the following instance we have the colour and the form of the petals
apparently correlated, and both dependent on the nature of the season. An
observer, skilled in the subject, writes (25/31. 'Gardener's Chronicle' 1843
page 877.), "I noticed, during the year 1842, that every Dahlia of which the
colour had any tendency to scarlet, was deeply notched--indeed, to so great an
extent as to give the petals the appearance of a saw; the indentures were, in
some instances, more than a quarter of an inch deep." Again, Dahlias which
have their petals tipped with a different colour from the rest of the flower
are very inconstant, and during certain years some, or even all the flowers,
become uniformly coloured; and it has been observed with several varieties
(25/32. Ibid 1845 page 102.) that when this happens the petals grow much
elongated and lose their proper shape. This, however, may be due to reversion,
both in colour and form, to the aboriginal species.

In this discussion on correlation, we have hitherto treated of cases in which
we can partly understand the bond of connection; but I will now give cases in
which we cannot even conjecture, or can only very obscurely see, the nature of
the bond. Isidore Geoffroy Saint-Hilaire, in his work on Monstrosities,
insists (25/33. 'Hist. des Anomalies' tome 3 page 402. See also M. Camille
Dareste 'Recherches sur les Conditions' etc. 1863 pages 16, 48.), "que
certaines anomalies coexistent rarement entr'elles, d'autres frequemment,
d'autres enfin presque constamment, malgre la difference tres-grande de leur
nature, et quoiqu'elles puissent paraitre COMPLETEMENT INDEPENDANTES les unes
des autres." We see something analogous in certain diseases: thus in a rare
affection of the renal capsules (of which the functions are unknown), the skin
becomes bronzed; and in hereditary syphilis, as I hear from Sir J. Paget, both
the milk and the second teeth assume a peculiar and characteristic form.
Professor Rolleston, also, informs me that the incisor teeth are sometimes
furnished with a vascular rim in correlation with intra-pulmonary deposition
of tubercles. In other cases of phthisis and of cyanosis the nails and finger-
ends become clubbed like acorns. I believe that no explanation has been
offered of these and of many other cases of correlated disease.

What can be more curious and less intelligible than the fact previously given,
on the authority of Mr. Tegetmeier, that young pigeons of all breeds, which
when mature have white, yellow, silver-blue, or dun-coloured plumage, come out
of the egg almost naked; whereas pigeons of other colours when first born are
clothed with plenty of down? White Pea-fowls, as has been observed both in
England and France (25/34. Rev. E.S. Dixon 'Ornamental Poultry' 1848 page 111;
Isidore Geoffroy 'Hist. Anomalies' tome 1 page 211.), and as I have myself
seen, are inferior in size to the common coloured kind; and this cannot be
accounted for by the belief that albinism is always accompanied by
constitutional weakness; for white or albino moles are generally larger than
the common kind.

To turn to more important characters: the niata cattle of the Pampas are
remarkable from their short foreheads, upturned muzzles, and curved lower
jaws. In the skull the nasal and premaxillary bones are much shortened, the
maxillaries are excluded from any junction with the nasals, and all the bones
are slightly modified, even to the plane of the occiput. From the analogous
case of the dog, hereafter to be given, it is probable that the shortening of
the nasal and adjoining bones is the proximate cause of the other
modifications in the skull, including the upward curvature of the lower jaw,
though we cannot follow out the steps by which these changes have been
effected.

Polish fowls have a large tuft of feathers on their heads; and their skulls
are perforated by numerous holes, so that a pin can be driven into the brain
without touching any bone. That this deficiency of bone is in some way
connected with the tuft of feathers is clear from tufted ducks and geese
likewise having perforated skulls. The case would probably be considered by
some authors as one of balancement or compensation. In the chapter on Fowls, I
have shown that with Polish fowls the tuft of feathers was probably at first
small; by continued selection it became larger, and then rested on a fibrous
mass; and finally, as it became still larger, the skull itself became more and
more protuberant until it acquired its present extraordinary structure.
Through correlation with the protuberance of the skull, the shape and even the
relative connection of the premaxillary and nasal bones, the shape of the
orifice of the nostrils, the breadth of the frontal bone, the shape of the
post-lateral processes of the frontal and squamosal bones, and the direction
of the bony cavity of the ear, have all been modified. The internal
configuration of the skull and the whole shape of the brain have likewise been
altered in a truly marvellous manner.

After this case of the Polish fowl it would be superfluous to do more than
refer to the details previously given on the manner in which the changed form
of the comb has affected the skull, in various breeds of the fowl, causing by
correlation crests, protuberances, and depressions on its surface.

With our cattle and sheep the horns stand in close connection with the size of
the skull, and with the shape of the frontal bones; thus Cline (25/35. 'On the
Breeding of Domestic Animals' 1829 page 6.) found that the skull of a horned
ram weighed five times as much as that of a hornless ram of the same age. When
cattle become hornless, the frontal bones are "materially diminished in
breadth towards the poll;" and the cavities between the bony plates "are not
so deep, nor do they extend beyond the frontals." (25/36. Youatt on 'Cattle'
1834 page 283.)

It may be well here to pause and observe how the effects of correlated
variability, of the increased use of parts, and of the accumulation of so-
called spontaneous variations through natural selection, are in many cases
inextricably commingled. We may borrow an illustration from Mr. Herbert
Spencer, who remarks that, when the Irish elk acquired its gigantic horns,
weighing above one hundred pounds, numerous co-ordinated changes of structure
would have been indispensable,--namely, a thickened skull to carry the horns;
strengthened cervical vertebrae, with strengthened ligaments; enlarged dorsal
vertebrae to support the neck, with powerful fore-legs and feet; all these
parts being supplied with proper muscles, blood-vessels, and nerves. How then
could these admirably co-ordinated modifications of structure have been
acquired? According to the doctrine which I maintain, the horns of the male
elk were slowly gained through sexual selection,--that is, by the best-armed
males conquering the worse-armed, and leaving a greater number of descendants.
But it is not at all necessary that the several parts of the body should have
simultaneously varied. Each stag presents individual characteristics, and in
the same district those which had slightly heavier horns, or stronger necks,
or stronger bodies, or were the most courageous, would secure the greater
number of does, and consequently have a greater number of offspring. The
offspring would inherit, in a greater or less degree, these same qualities,
would occasionally intercross with one another, or with other individuals
varying in some favourable manner; and of their offspring, those which were
the best endowed in any respect would continue multiplying; and so onwards,
always progressing, sometimes in one direction, and sometimes in another,
towards the excellently co-ordinated structure of the male elk. To make this
clear, let us reflect on the probable steps, as shown in the twentieth
chapter, by which our race and dray horses have arrived at their present state
of excellence; if we could view the whole series of intermediate forms between
one of these animals and an early unimproved progenitor, we should behold a
vast number of animals, not equally improved in each generation throughout
their entire structure, but sometimes a little more in one point, and
sometimes in another, yet on the whole gradually approaching in character to
our present race or dray horses, which are so admirably fitted in the one case
for fleetness and in the other for draught.

Although natural selection would thus (25/37. Mr. Herbert Spencer 'Principles
of Biology' 1864 volume 1 pages 452, 468 takes a different view; and in one
place remarks: "We have seen reason to think that, as fast as essential
faculties multiply, and as fast as the number of organs that co-operate in any
given function increases, indirect equilibration through natural selection
becomes less and less capable of producing specific adaptations; and remains
fully capable only of maintaining the general fitness of constitution to
conditions." This view that natural selection can do little in modifying the
higher animals surprises me, seeing that man's selection has undoubtedly
effected much with our domesticated quadrupeds and birds.) tend to give to the
male elk its present structure, yet it is probable that the inherited effects
of use, and of the mutual action of part on part, have been equally or more
important. As the horns gradually increased in weight the muscles of the neck,
with the bones to which they are attached, would increase in size and
strength; and these parts would react on the body and legs. Nor must we
overlook the fact that certain parts of the skull and the extremities would,
judging by analogy, tend from the first to vary in a correlated manner. The
increased weight of the horns would also act directly on the skull, in the
same manner as when one bone is removed in the leg of a dog, the other bone,
which has to carry the whole weight of the body, increases in thickness. But
from the fact given with respect to horned and hornless cattle, it is probable
that the horns and skull would immediately act on each other through the
principle of correlation. Lastly, the growth and subsequent wear and tear of
the augmented muscles and bones would require an increased supply of blood,
and consequently increased supply of food; and this again would require
increased powers of mastication, digestion, respiration, and excretion.

COLOUR AS CORRELATED WITH CONSTITUTIONAL PECULIARITIES.

It is an old belief that with man there is a connection between complexions
and constitution; and I find that some of the best authorities believe in this
to the present day. (25/38. Dr. Prosper Lucas apparently disbelieves in any
such connection; 'L'Hered. Nat.' tome 2 pages 88-94.) Thus Dr. Beddoe by his
tables shows (25/39. 'British Medical Journal' 1862 page 433.) that a relation
exists between liability to consumption and the colour of the hair, eyes, and
skin. It has been affirmed (25/40. Boudin 'Geograph. Medicale' tome 1 page
406.) that, in the French army which invaded Russia, soldiers having a dark
complexion from the southern parts of Europe, withstood the intense cold
better than those with lighter complexions from the north; but no doubt such
statements are liable to error.

In the second chapter on Selection I have given several cases proving that
with animals and plants differences in colour are correlated with
constitutional differences, as shown by greater or less immunity from certain
diseases, from the attacks of parasitic plants and animals, from scorching by
the sun, and from the action of certain poisons. When all the individuals of
any one variety possess an immunity of this nature, we do not know that it
stands in any sort of correlation with their colour; but when several
similarly coloured varieties of the same species are thus characterised,
whilst other coloured varieties are not thus favoured, we must believe in the
existence of a correlation of this kind. Thus, in the United States purple-
fruited plums of many kinds are far more affected by a certain disease than
green or yellow-fruited varieties. On the other hand, yellow-fleshed peaches
of various kinds suffer from another disease much more than the white-fleshed
varieties. In the Mauritius red sugar-canes are much less affected by a
particular disease than the white canes. White onions and verbenas are the
most liable to mildew; and in Spain the green-fruited grapes suffered from the
vine-disease more than other coloured varieties. Dark-coloured pelargoniums
and verbenas are more scorched by the sun than varieties of other colours. Red
wheats are believed to be hardier than white; and red-flowered hyacinths were
more injured during one particular winter in Holland than other coloured
varieties. With animals, white terriers suffer most from the distemper, white
chickens from a parasitic worm in their tracheae, white pigs from scorching by
the sun, and white cattle from flies; but the caterpillars of the silk-moth
which yield white cocoons suffered in France less from the deadly parasitic
fungus than those producing yellow silk.

The cases of immunity from the action of certain vegetable poisons, in
connexion with colour, are more interesting, and are at present wholly
inexplicable. I have already given a remarkable instance, on the authority of
Professor Wyman, of all the hogs, excepting those of a black colour, suffering
severely in Virginia from eating the root of the Lachnanthes tinctoria.
According to Spinola and others (25/41. This fact and the following cases,
when not stated to the contrary, are taken from a very curious paper by Prof.
Heusinger in 'Wochenschrift fur Heilkunde' May 1846 s. 277. Settegast 'Die
Thierzucht' 1868 page 39 says that white or white-spotted sheep suffer like
pigs, or even die from eating buckwheat; whilst black or dark-woolled
individuals are not in the least affected.), buckwheat (Po1ygonum fagopyrum),
when in flower, is highly injurious to white or white-spotted pigs, if they
are exposed to the heat of the sun, but is quite innocuous to black pigs.
According to two accounts, the Hypericum crispum in Sicily is poisonous to
white sheep alone; their heads swell, their wool falls off, and they often
die; but this plant, according to Lecce, is poisonous only when it grows in
swamps; nor is this improbable, as we know how readily the poisonous principle
in plants is influenced by the conditions under which they grow.

Three accounts have been published in Eastern Prussia, of white and white-
spotted horses being greatly injured by eating mildewed and honeydewed
vetches; every spot of skin bearing white hairs becoming inflamed and
gangrenous. The Rev. J. Rodwell informs me that his father turned out about
fifteen cart-horses into a field of tares which in parts swarmed with black
aphides, and which no doubt were honeydewed, and probably mildewed; the
horses, with two exceptions, were chestnuts and bays with white marks on their
faces and pasterns, and the white parts alone swelled and became angry scabs.
The two bay horses with no white marks entirely escaped all injury. In
Guernsey, when horses eat fool's parsley (Aethusa cynapium) they are sometimes
violently purged; and this plant "has a peculiar effect on the nose and lips,
causing deep cracks and ulcers, particularly on horses with white muzzles."
(25/42. Mr. Mogford in the 'Veterinarian' quoted in 'The Field' January 22,
1861 page 545.) With cattle, independently of the action of any poison, cases
have been published by Youatt and Erdt of cutaneous diseases with much
constitutional disturbance (in one instance after exposure to a hot sun)
affecting every single point which bore a white hair, but completely passing
over other parts of the body. Similar cases have been observed with horses.
(25/43. 'Edinburgh Veterinary Journal' October 1860 page 347.)

We thus see that not only do those parts of the skin which bear white hair
differ in a remarkable manner from those bearing hair of any other colour, but
that some great constitutional difference must be correlated with the colour
of the hair; for in the above-mentioned cases, vegetable poisons caused fever,
swelling of the head, as well as other symptoms, and even death, to all the
white, or white-spotted animals.


CHAPTER 2.XXVI.

LAWS OF VARIATION, continued.--SUMMARY.

THE FUSION OF HOMOLOGOUS PARTS.
THE VARIABILITY OF MULTIPLE AND HOMOLOGOUS PARTS.
COMPENSATION OF GROWTH.
MECHANICAL PRESSURE.
RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS, AND OF SEEDS IN THE
OVARY, AS INDUCING VARIATION.
ANALOGOUS OR PARALLEL VARIETIES.
SUMMARY OF THE THREE LAST CHAPTERS.

THE FUSION OF HOMOLOGOUS PARTS.

Geoffroy Saint-Hilaire formerly propounded what he called la loi de l'affinite
de soi pour soi, which has been discussed and illustrated by his son, Isidore,
with respect to monsters in the animal kingdom (26/1. 'Hist. des Anomalies'
1832 tome 1 pages 22, 537-556; tome 3 page 462.), and by Moquin-Tandon, with
respect to monstrous plants.

This law seems to imply that homologous parts actually attract one another and
then unite. No doubt there are many wonderful cases, in which such parts
become intimately fused together. This is perhaps best seen in monsters with
two heads, which are united, summit to summit, or face to face, or Janus-like,
back to back, or obliquely side to side. In one instance of two heads united
almost face to face, but a little obliquely, four ears were developed, and on
one side a perfect face, which was manifestly formed by the fusion of two
half-faces. Whenever two bodies or two heads are united, each bone, muscle,
vessel, and nerve on the line of junction appears as if it had sought out its
fellow, and had become completely fused with it. Lereboullet (26/2. 'Comptes
Rendus' 1855 pages 855, 1039.), who carefully studied the development of
double monsters in fishes, observed in fifteen instances the steps by which
two heads gradually became united into one. In all such cases it is now
thought by the greater number of capable judges that the homologous parts do
not attract each other, but that in the words of Mr. Lowne (26/3. 'Catalogue
of the Teratological Series in the Museum of the R. Coll. of Surgeons' 1872
page 16.): "As union takes place before the differentiation of distinct organs
occurs, these are formed in continuity with each other." He adds that organs
already differentiated probably in no case become united to homologous ones.
M. Dareste does not speak (26/4. 'Archives de Zoolog. Exper.' January 1874
page 78.) quite decisively against the law of soi pour soi, but concludes by
saying, "On se rend parfaitement compte de la formation des monstres, si l'on
admet que les embryons qui se soudent appartiennent a un meme oeuf; qu'ils
s'unissent en meme temps qu'ils se forment, et que la soudure ne se produit
que pendant la premiere periode de la vie embryonnaire, celle ou les organes
ne sont encore constitues que par des blastemes homogenes."

By whatever means the abnormal fusion of homologous parts is effected, such
cases throw light on the frequent presence of organs which are double during
an embryonic period (and throughout life in other and lower members of the
same class) but which afterwards unite by a normal process into a single
medial organ. In the vegetable kingdom Moquin-Tandon (26/5. 'Teratologie Veg.'
1841 livre 3.) gives a long list of cases, showing how frequently homologous
parts, such as leaves, petals, stamens, and pistils, flowers, and aggregates
of homologous parts, such as buds, as well as fruit, become blended, both
normally and abnormally, with perfect symmetry into one another.

THE VARIABILITY OF MULTIPLE AND HOMOLOGOUS PARTS.

Isidore Geoffroy (26/6. 'Hist. des Anomalies' tome 3 pages 4, 5, 6.) insists
that, when any part or organ is repeated many times in the same animal, it is
particularly liable to vary both in number and structure. With respect to
number, the proposition may, I think, be considered as fully established; but
the evidence is chiefly derived from organic beings living under their natural
conditions, with which we are not here concerned. Whenever such parts as the
vertebrae or teeth, the rays in the fins of fishes, or the feathers in the
tails of birds, or petals, stamens, pistils, or seeds, are very numerous, the
number is generally variable. With respect to the structure of multiple parts,
the evidence of variability is not so decisive; but the fact, as far as it may
be trusted, probably depends on multiple parts being of less physiological
importance than single parts; consequently their structure has been less
rigorously guarded by natural selection.

COMPENSATION OF GROWTH, OR BALANCEMENT.

This law, as applied to natural species, was propounded by Goethe and Geoffroy
Saint-Hilaire at nearly the same time. It implies that, when much organised
matter is used in building up some one part, other parts are starved and
become reduced. Several authors, especially botanists, believe in this law;
others reject it. As far as I can judge, it occasionally holds good; but its
importance has probably been exaggerated. It is scarcely possible to
distinguish between the supposed effects of such compensation, and the effects
of long-continued selection which may lead to the augmentation of one part,
and simultaneously to the diminution of another. Anyhow, there can be no doubt
that an organ may be greatly increased without any corresponding diminution of
an adjoining part. To recur to our former illustration of the Irish elk, it
may be asked what part has suffered in consequence of the immense development
of the horns?

It has already been observed that the struggle for existence does not bear
hard on our domesticated productions, and consequently the principle of
economy of growth will seldom come into play, so that we ought not to expect
to find with them frequent evidence of compensation. We have, however, some
such cases. Moquin-Tandon describes a monstrous bean (26/7. 'Teratologie Veg.'
page 156. See also my book on 'The Movements and Habits of Climbing Plants'
2nd edition 1875 page 202.), in which the stipules were enormously developed,
and the leaflets apparently in consequence completely aborted; this case is
interesting, as it represents the natural condition of Lathyrus aphaca, with
its stipules of great size, and its leaves reduced to mere threads, which act
as tendrils. De Candolle (26/8. 'Memoires du Museum' etc. tome 8 page 178.)
has remarked that the varieties of Raphanus sativus which have small roots
yield numerous seed containing much oil, whilst those with large roots are not
productive in oil; and so it is with Brassica asperifolia. The varieties of
Cucurbita pepo which bear large fruit yield a small crop, according to Naudin;
whilst those producing small fruit yield a vast number. Lastly, I have
endeavoured to show in the eighteenth chapter that with many cultivated plants
unnatural treatment checks the full and proper action of the reproductive
organs, and they are thus rendered more or less sterile; consequently, in the
way of compensation, the fruit becomes greatly enlarged, and, in double
flowers, the petals are greatly increased in number.

With animals, it has been found difficult to produce cows which yield much
milk, and are afterwards capable of fattening well. With fowls which have
large top-knots and beards the comb and wattles are generally much reduced in
size; though there are exceptions to this rule. Perhaps the entire absence of
the oil-gland in fantail pigeons may be connected with the great development
of their tails.

MECHANICAL PRESSURE AS A CAUSE OF MODIFICATIONS.

In some few cases there is reason to believe that mere mechanical pressure has
affected certain structures. Vrolik and Weber (26/9. Prichard 'Phys. Hist. of
Mankind' 1851 volume 1 page 324.) maintain that the shape of the human head is
influenced by the shape of the mother's pelvis. The kidneys in different birds
differ much in form, and St. Ange (26/10. 'Annales des Sc. Nat.' 1st series
tome 19 page 327.) believes that this is determined by the form of the pelvis,
which again, no doubt, stands in close relation with their power of
locomotion. In snakes, the viscera are curiously displaced, in comparison with
their position in other vertebrates; and this has been attributed by some
authors to the elongation of their bodies; but here, as in so many previous
cases, it is impossible to disentangle a direct result of this kind from that
consequent on natural selection. Godron has argued (26/11. 'Comptes Rendus'
December 1864 page 1039.) that the abortion of the spur on the inner side of
the flowers in Corydalis, is caused by the buds at a very early period of
growth whilst underground being closely pressed against one another and
against the stem. Some botanists believe that the singular difference in the
shape both of the seed and corolla, in the interior and exterior florets in
certain Compositous and Umbelliferous plants, is due to the pressure to which
the inner florets are subjected; but this conclusion is doubtful.

The facts just given do not relate to domesticated productions, and therefore
do not strictly concern us. But here is a more appropriate case: H. Muller
(26/12. "Ueber fotale Rachites" 'Wurzburger Medicin. Zeitschrift' 1860 b. 1 s.
265.) has shown that in shortfaced races of the dog some of the molar teeth
are placed in a slightly different position to that which they occupy in other
dogs, especially in those having elongated muzzles; and as he remarks, any
inherited change in the arrangement of the teeth deserves notice, considering
their classificatory importance. This difference in position is due to the
shortening of certain facial bones and the consequent want of space; and the
shortening results from a peculiar and abnormal state of the embryonal
cartilages of the bones.

[RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE AXIS, AND OF SEEDS IN THE
OVARY, AS INDUCING VARIATION.

In the thirteenth chapter various peloric flowers were described, and their
production was shown to be due either to arrested development, or to reversion
to a primordial condition. Moquin-Tandon has remarked that the flowers which
stand on the summit of the main stem or of a lateral branch are more liable to
become peloric than those on the sides (26/13. 'Teratologie Veg.' page 192.);
and he adduces, amongst other instances, that of Teucrium campanulatum. In
another Labiate plant grown by me, viz., the Galeobdolon luteum, the peloric
flowers were always produced on the summit of the stem, where flowers are not
usually borne. In Pelargonium, a SINGLE flower in the truss is frequently
peloric, and when this occurs I have during several years invariably observed
it to be the central flower. This is of such frequent occurrence that one
observer (26/14. 'Journal of Horticulture' July 2, 1861 page 253.) gives the
names of ten varieties flowering at the same time, in every one of which the
central flower was peloric. Occasionally more than one flower in the truss is
peloric, and then of course the additional ones must be lateral. These flowers
are interesting as showing how the whole structure is correlated. In the
common Pelargonium the upper sepal is produced into a nectary which coheres
with the flower-peduncle; the two upper petals differ a little in shape from
the three lower ones, and are marked with dark shades of colour; the stamens
are graduated in length and upturned. In the peloric flowers, the nectary
aborts; all the petals become alike both in shape and colour; the stamens are
generally reduced in number and become straight, so that the whole flower
resembles that of the allied genus Erodium. The correlation between these
changes is well shown when one of the two upper petals alone loses its dark
mark, for in this case the nectary does not entirely abort, but is usually
much reduced in length. (26/15. It would be worth trial to fertilise with the
same pollen the central and lateral flowers of the pelargonium, or of other
highly cultivated plants, protecting them of course from insects: then to sow
the seed separately, and observe whether the one or the other lot of seedlings
varied the most.)

Morren has described (26/16. Quoted in 'Journal of Horticulture' February 24,
1863 page 152.) a marvellous flask-shaped flower of the Calceolaria, nearly
four inches in length, which was almost completely peloric; it grew on the
summit of the plant, with a normal flower on each side; Prof. Westwood also
has described (26/17. 'Gardener's Chronicle' 1866 page 612. For the
Phalaenopsis see ibid 1867 page 211.) three similar peloric flowers, which all
occupied a central position on the flower-branches. In the Orchideous genus,
Phalaenopsis, the terminal flower has been seen to become peloric.

In a Laburnum-tree I observed that about a fourth part of the racemes produced
terminal flowers which had lost their papilionaceous structure. These were
produced after almost all the other flowers on the same racemes had withered.
The most perfectly pelorised examples had six petals, each marked with black
striae like those on the standard-petal. The keel seemed to resist the change
more than the other petals. Dutrochet has described (26/18. 'Memoires...des
Vegetaux' 1837 tome 2 page 170.) an exactly similar case in France, and I
believe these are the only two instances of pelorism in the laburnum which
have been recorded. Dutrochet remarks that the racemes on this tree do not
properly produce a terminal flower, so that (as in the case of the
Galeobdolon) their position as well as structure are both anomalies, which no
doubt are in some manner related. Dr. Masters has briefly described another
leguminous plant (26/19. 'Journal of Horticulture' July 23, 1861 page 311.),
namely, a species of clover, in which the uppermost and central flowers were
regular or had lost their papilionaceous structure. In some of these plants
the flower-heads were also proliferous.

Lastly, Linaria produces two kinds of peloric flowers, one having simple
petals, and the other having them all spurred. The two forms, as Naudin
remarks (26/20. 'Nouvelles Archives du Museum' tome 1 page 137.), not rarely
occur on the same plant, but in this case the spurred form almost invariably
stands on the summit of the spike.

The tendency in the terminal or central flower to become peloric more
frequently than the other flowers, probably results from "the bud which stands
on the end of a shoot receiving the most sap; it grows out into a stronger
shoot than those situated lower down." (26/21. Hugo von Mohl 'The Vegetable
Cell' English translation 1852 page 76.) I have discussed the connection
between pelorism and a central position, partly because some few plants are
known normally to produce a terminal flower different in structure from the
lateral ones; but chiefly on account of the following case, in which we see a
tendency to variability or to reversion connected with the same position. A
great judge of Auriculas (26/22. The Rev. H.H. Dombrain in 'Journal of
Horticulture' 1861 June 4 page 174; and June 25 page 234; 1862 April 29 page
83.) states that when one throws up a side bloom it is pretty sure to keep its
character; but that if it grows from the centre or heart of the plant,
whatever the colour of the edging ought to be, "it is just as likely to come
in any other class as in the one to which it properly belongs." This is so
notorious a fact, that some florists regularly pinch off the central trusses
of flowers. Whether in the highly improved varieties the departure of the
central trusses from their proper type is due to reversion, I do not know. Mr.
Dombrain insists that, whatever may be the commonest kind of imperfection in
each variety, this is generally exaggerated in the central truss. Thus one
variety "sometimes has the fault of producing a little green floret in the
centre of the flower," and in central blooms these become excessive in size.
In some central blooms, sent to me by Mr. Dombrain, all the organs of the
flower were rudimentary in structure, of minute size, and of a green colour,
so that by a little further change all would have been converted into small
leaves. In this case we clearly see a tendency to prolification--a term which
I may explain, for those who have never attended to botany, to mean the
production of a branch or flower, or head of flowers, out of another flower.
Now Dr. Masters (26/23. 'Transact. Linn. Soc.' volume 23 1861 page 360.)
states that the central or uppermost flower on a plant is generally the most
liable to prolification. Thus, in the varieties of the Auricula, the loss of
their proper character and a tendency to prolification, also a tendency to
prolification with pelorism, are all connected together, and are due either to
arrested development, or to reversion to a former condition.

The following is a more interesting case; Metzger (26/24. 'Die Getreidearten'
1845 s. 208, 209.) cultivated in Germany several kinds of maize brought from
the hotter parts of America, and he found, as previously described, that in
two or three generations the grains became greatly changed in form, size, and
colour; and with respect to two races he expressly states that in the first
generation, whilst the lower grains on each head retained their proper
character, the uppermost grains already began to assume that character which
in the third generation all the grains acquired. As we do not know the
aboriginal parent of the maize, we cannot tell whether these changes are in
any way connected with reversion.

In the two following cases, reversion comes into play and is determined by the
position of the seed in the capsule. The Blue Imperial pea is the offspring of
the Blue Prussian, and has larger seed and broader pods than its parent. Now
Mr. Masters, of Canterbury, a careful observer and a raiser of new varieties
of the pea, states (26/25. 'Gardener's Chronicle' 1850 page 198.) that the
Blue Imperial always has a strong tendency to revert to its parent-stock, and
the reversion "occurs in this manner: the last (or uppermost) pea in the pod
is frequently much smaller than the rest; and if these small peas are
carefully collected and sown separately, very many more, in proportion, will
revert to their origin, than those taken from the other parts of the pod."
Again, M. Chate (26/26. Quoted in 'Gardener's Chronicle' 1866 page 74.) says
that in raising seedling stocks he succeeds in getting eighty per cent to bear
double flowers, by leaving only a few of the secondary branches to seed; but
in addition to this, "at the time of extracting the seeds, the upper portion
of the pod is separated and placed aside, because it has been ascertained that
the plants coming from the seeds situated in this portion of the pod, give
eighty per cent of single flowers." Now the production of single-flowering
plants from the seed of double-flowering plants is clearly a case of
reversion. These latter facts, as well as the connection between a central
position and pelorism and prolification, show in an interesting manner how
small a difference--namely, a little greater or less freedom in the flow of
sap towards one part of the plant--determines important changes of structure.]

ANALOGOUS OR PARALLEL VARIATION.

By this term I mean that similar characters occasionally make their appearance
in the several varieties or races descended from the same species, and more
rarely in the offspring of widely distinct species. We are here concerned, not
as hitherto with the causes of variation, but with the results; but this
discussion could not have been more conveniently introduced elsewhere. The
cases of analogous variation, as far as their origin is concerned, may be
grouped, disregarding minor subdivisions, under two main heads; firstly, those
due to unknown causes acting on similarly constituted organisms, and which
consequently have varied in a similar manner; and secondly, those due to the
reappearance of characters which were possessed by a more or less remote
progenitor. But these two main divisions can often be separated only
conjecturally, and graduate, as we shall presently see, into each other.

[Under the first head of analogous variations, not due to reversion, we have
the many cases of trees belonging to quite different orders which have
produced pendulous and fastigiate varieties. The beech, hazel, and barberry
have given rise to purple-leaved varieties; and, as Bernhardi remarks (26/27.
'Ueber den Begriff der Pflanzenart' 1834 s. 14.), a multitude of plants, as
distinct as possible, have yielded varieties with deeply-cut or laciniated
leaves. Varieties descended from three distinct species of Brassica have their
stems, or so-called roots, enlarged into globular masses. The nectarine is the
offspring of the peach; and the varieties of peaches and nectarines offer a
remarkable parallelism in the fruit being white, red, or yellow fleshed--in
being clingstones or freestones--in the flowers being large or small--in the
leaves being serrated or crenated, furnished with globose or reniform glands,
or quite destitute of glands. It should be remarked that each variety of the
nectarine has not derived its character from a corresponding variety of the
peach. The several varieties also of a closely allied genus, namely the
apricot, differ from one another in nearly the same parallel manner. There is
no reason to believe that any of these varieties have merely reacquired long-
lost characters; and in most of them this certainly is not the case.

Three species of Cucurbita have yielded a multitude of races which correspond
so closely in character that, as Naudin insists, they may be arranged in
almost strictly parallel series. Several varieties of the melon are
interesting from resembling, in important characters, other species, either of
the same genus or of allied genera; thus, one variety has fruit so like, both
externally and internally, the fruit of a perfectly distinct species, namely,
the cucumber, as hardly to be distinguished from it; another has long
cylindrical fruit twisting about like a serpent; in another the seeds adhere
to portions of the pulp; in another the fruit, when ripe, suddenly cracks and
falls into pieces; and all these highly remarkable peculiarities are
characteristic of species belonging to allied genera. We can hardly account
for the appearance of so many unusual characters by reversion to a single
ancient form; but we must believe that all the members of the family have
inherited a nearly similar constitution from an early progenitor. Our cereal
and many other plants offer similar cases.

With animals we have fewer cases of analogous variation, independently of
direct reversion. We see something of the kind in the resemblance between the
short-muzzled races of the dog, such as the pug and bull-dog; in feather-
footed races of the fowl, pigeon, and canary-bird; in horses of the most
different races presenting the same range of colour; in all black-and-tan dogs
having tan-coloured eye-spots and feet, but in this latter case reversion may
possibly have played a part. Low has remarked (26/28. 'Domesticated Animals'
1845 page 351.) that several breeds of cattle are "sheeted,"--that is, have a
broad band of white passing round their bodies like a sheet; this character is
strongly inherited, and sometimes originates from a cross; it may be the first
step in reversion to an early type, for, as was shown in the third chapter,
white cattle with dark ears, dark feet and tip of tail, formerly existed, and
now exist in feral or semi-feral condition in several quarters of the world.

Under our second main division, namely, of analogous variations due to
reversion, the best cases are afforded by pigeons. In all the most distinct
breeds, sub-varieties occasionally appear coloured exactly like the parent
rock-pigeon, with black wing-bars, white loins, banded tail, etc.; and no one
can doubt that these characters are due to reversion. So with minor details;
turbits properly have white tails, but occasionally a bird is born with a
dark-coloured and banded tail; pouters properly have their primary wing-
feathers white, but not rarely a "sword-flighted" bird appears, that is, one
with the few first primaries dark-coloured; and in these cases we have
characters proper to the rock-pigeon, but new to the breed, evidently
appearing from reversion. In some domestic varieties the wing-bars, instead of
being simply black, as in the rock-pigeon, are beautifully edged with
different zones of colour, and they then present a striking analogy with the
wing-bars in certain natural species of the same family, such as Phaps
chalcoptera; and this may probably be accounted for by all the species of the
family being descended from the same remote progenitor and having a tendency
to vary in the same manner. Thus, also, we can perhaps understand the fact of
some Laugher-pigeons cooing almost like turtle-doves, and for several races
having peculiarities in their flight, since certain natural species (viz., C.
torquatrix and palumbus), display singular vagaries in this respect. In other
cases a race, instead of imitating a distinct species, resembles some other
race; thus, certain runts tremble and slightly elevate their tails, like
fantails; and turbits inflate the upper part of their oesophagus, like pouter-
pigeons.

It is a common circumstance to find certain coloured marks persistently
characterising all the species of a genus, but differing much in tint; and the
same thing occurs with the varieties of the pigeon: thus, instead of the
general plumage being blue, with the wing-bars black, there are snow-white
varieties with red bars, and black varieties with white bars; in other
varieties the wing-bars, as we have seen, are elegantly zoned with different
tints. The Spot pigeon is characterised by the whole plumage being white,
excepting a spot on the forehead and the tail; but these parts may be red,
yellow, or black. In the rock-pigeon and in many varieties the tail is blue,
with the outer edges of the outer feathers white; but in the sub-variety of
the monk-pigeon we have a reversed style of coloration, for the tail is white,
except the outer edges of the outer feathers, which are black. (26/29.
Bechstein 'Naturgeschichte Deutschlands' b. 4 1795 s. 31.)

With some species of birds, for instance with gulls, certain coloured parts
appear as if almost washed out, and I have observed exactly the same
appearance in the terminal dark tail-bar in certain pigeons, and in the whole
plumage of certain varieties of the duck. Analogous facts in the vegetable
kingdom could be given.

Many sub-varieties of the pigeon have reversed and somewhat lengthened
feathers on the back part of their heads, and this is certainly not due to
reversion to the parent-species, which shows no trace of such structure: but
when we remember that sub-varieties of the fowl, turkey, canary-bird, duck,
and goose, all have either topknots or reversed feathers on their heads; and
when we remember that scarcely a single large natural group of birds can be
named, in which some members have not a tuft of feathers on their heads, we
may suspect that reversion to some extremely remote form has come into action.

Several breeds of the fowl have either spangled or pencilled feathers; and
these cannot be derived from the parent-species, the Gallus bankiva; though of
course it is possible that one early progenitor of this species may have been
spangled, and another pencilled. But, as many gallinaceous birds are either
spangled or pencilled, it is a more probable view that the several domestic
breeds of the fowl have acquired this kind of plumage from all the members of
the family inheriting a tendency to vary in a like manner. The same principle
may account for the ewes in certain breeds of sheep being hornless, like the
females of some other hollow-horned ruminants; it may account for certain
domestic cats having slightly-tufted ears, like those of the lynx; and for the
skulls of domestic rabbits often differing from one another in the same
characters by which the skulls of the various species of the genus Lepus
differ.

I will only allude to one other case, already discussed. Now that we know that
the wild parent of the ass commonly has striped legs, we may feel confident
that the occasional appearance of stripes on the legs of the domestic ass is
due to reversion; but this will not account for the lower end of the shoulder-
stripe being sometimes angularly bent or slightly forked. So, again, when we
see dun and other coloured horses with stripes on the spine, shoulders, and
legs, we are led, from reasons formerly given, to believe that they reappear
through reversion to the wild parent-horse. But when horses have two or three
shoulder-stripes, with one of them occasionally forked at the lower end, or
when they have stripes on their faces, or are faintly striped as foals over
nearly their whole bodies, with the stripes angularly bent one under the other
on the forehead, or irregularly branched in other parts, it would be rash to
attribute such diversified characters to the reappearance of those proper to
the aboriginal wild horse. As three African species of the genus are much
striped, and as we have seen that the crossing of the unstriped species often
leads to the hybrid offspring being conspicuously striped--bearing also in
mind that the act of crossing certainly causes the reappearance of long-lost
characters--it is a more probable view that the above-specified stripes are
due to reversion, not to the immediate wild parent-horse, but to the striped
progenitor of the whole genus.]

I have discussed this subject of analogous variation at considerable length,
because it is well known that the varieties of one species frequently resemble
distinct species--a fact in perfect harmony with the foregoing cases, and
explicable on the theory of descent. Secondly, because these facts are
important from showing, as remarked in a former chapter, that each trifling
variation is governed by law, and is determined in a much higher degree by the
nature of the organisation, than by the nature of the conditions to which the
varying being has been exposed. Thirdly, because these facts are to a certain
extent related to a more general law, namely, that which Mr. B.D. Walsh
(26/30. 'Proc. Entomolog. Soc. of Philadelphia' October 1863 page 213.) has
called the "Law of EQUABLE VARIABILITY," or, as he explains it, "if any given
character is very variable in one species of a group, it will tend to be
variable in allied species; and if any given character is perfectly constant
in one species of a group, it will tend to be constant in allied species."

This leads me to recall a discussion in the chapter on Selection, in which it
was shown that with domestic races, which are now undergoing rapid
improvement, those parts or characters vary the most, which are the most
valued. This naturally follows from recently selected characters continually
tending to revert to their former less improved standard, and from their being
still acted on by the same agencies, whatever these may be, which first caused
the characters in question to vary. The same principle is applicable to
natural species, for, as stated in my 'Origin of Species' generic characters
are less variable than specific characters; and the latter are those which
have been modified by variation and natural selection, since the period when
all the species belonging to the genus branched off from a common progenitor,
whilst generic characters are those which have remained unaltered from a much
more remote epoch, and accordingly are now less variable. This statement makes
a near approach to Mr. Walsh's law of Equable Variability. Secondary sexual
characters, it may be added, rarely serve to characterise distinct genera, for
they usually differ much in the species of the same genus, and they are highly
variable in the individuals of the same species; we have also seen in the
earlier chapters of this work how variable secondary sexual characters become
under domestication.

SUMMARY OF THE THREE PREVIOUS CHAPTERS ON THE LAWS OF VARIATION.

In the twenty-third chapter we saw that changed conditions occasionally, or
even often, act in a definite manner on the organisation, so that all, or
nearly all, the individuals thus exposed become modified in the same manner.
But a far more frequent result of changed conditions, whether acting directly
on the organisation or indirectly through the reproductive system, is
indefinite and fluctuating variability. In the three last chapters, some of
the laws by which such variability is regulated have been discussed.

Increased use adds to the size of muscles, together with the blood-vessels,
nerves, ligaments, the crests of bone and the whole bones, to which they are
attached. Increased functional activity increases the size of various glands,
and strengthens the sense-organs. Increased and intermittent pressure thickens
the epidermis. A change in the nature of the food sometimes modifies the coats
of the stomach, and augments or decreases the length of the intestines.
Continued disuse, on the other hand, weakens and diminishes all parts of the
organisation. Animals which during many generations have taken but little
exercise, have their lungs reduced in size, and as a consequence the bony
fabric of the chest and the whole form of the body become modified. With our
anciently domesticated birds, the wings have been little used, and they are
slightly reduced; with their decrease, the crest of the sternum, the scapulae,
coracoids, and furculum, have all been reduced.

With domesticated animals, the reduction of a part from disuse is never
carried so far that a mere rudiment is left; whereas we have reason to believe
that this has often occurred under nature; the effects of disuse in this
latter case being aided by economy of growth, together with the intercrossing
of many varying individuals. The cause of this difference between organisms in
a state of nature, and under domestication, probably is that in the latter
case there has not been time sufficient for any very great change, and that
the principle of economy of growth does not come into action. On the contrary,
structures which are rudimentary in the parent-species, sometimes become
partially redeveloped in our domesticated productions. Such rudiments as
occasionally make their appearance under domestication, seem always to be the
result of a sudden arrest of development; nevertheless they are of interest,
as showing that rudiments are the relics of organs once perfectly developed.

Corporeal, periodical, and mental habits, though the latter have been almost
passed over in this work, become changed under domestication, and the changes
are often inherited. Such changed habits in an organic being, especially when
living a free life, would often lead to the augmented or diminished use of
various organs, and consequently to their modification. From long-continued
habit, and more especially from the occasional birth of individuals with a
slightly different constitution, domestic animals and cultivated plants become
to a certain extent acclimatised or adapted to a climate different from that
proper to the parent-species.

Through the principle of correlated variability, taken in its widest sense,
when one part varies other parts vary, either simultaneously, or one after the
other. Thus, an organ modified during an early embryonic period affects other
parts subsequently developed. When an organ, such as the beak, increases or
decreases in length, adjoining or correlated parts, as the tongue and the
orifice of the nostrils, tend to vary in the same manner. When the whole body
increases or decreases in size, various parts become modified; thus, with
pigeons the ribs increase or decrease in number and breadth. Homologous parts
which are identical during their early development and are exposed to similar
conditions, tend to vary in the same or in some connected manner,--as in the
case of the right and left sides of the body, and of the front and hind limbs.
So it is with the organs of sight and hearing; for instance, white cats with
blue eyes are almost always deaf. There is a manifest relation throughout the
body between the skin and various dermal appendages, such as hair, feathers,
hoofs, horns, and teeth. In Paraguay, horses with curly hair have hoofs like
those of a mule; the wool and the horns of sheep often vary together; hairless
dogs are deficient in their teeth; men with redundant hair have abnormal
teeth, either by deficiency or excess. Birds with long wing-feathers usually
have long tail-feathers. When long feathers grow from the outside of the legs
and toes of pigeons, the two outer toes are connected by membrane; for the
whole leg tends to assume the structure of the wing. There is a manifest
relation between a crest of feathers on the head and a marvellous amount of
change in the skull of various fowls; and in a lesser degree, between the
greatly elongated, lopping ears of rabbits and the structure of their skulls.
With plants, the leaves, various parts of the flower, and the fruit, often
vary together to a correlated manner.

In some cases we find correlation without being able even to conjecture what
is the nature of the connection, as with various monstrosities and diseases.
This is likewise the case with the colour of the adult pigeon, in connection
with the presence of down on the young bird. Numerous curious instances have
been given of peculiarities of constitution, in correlation with colour, as
shown by the immunity of individuals of one colour from certain diseases, from
the attacks of parasites and from the action of certain vegetable poisons.

Correlation is an important subject; for with species, and in a lesser degree
with domestic races, we continually find that certain parts have been greatly
modified to serve some useful purpose; but we almost invariably find that
other parts have likewise been more or less modified, without our being able
to discover any advantage in the change. No doubt great caution is necessary
with respect to this latter point, for it is difficult to overrate our
ignorance on the use of various parts of the organisation; but from what we
have seen, we may believe that many modifications are of no direct service,
having arisen in correlation with other and useful changes.

Homologous parts during their early development often become fused together.
Multiple and homologous organs are especially liable to vary in number and
probably in form. As the supply of organised matter is not unlimited, the
principle of compensation sometimes comes into action; so that, when one part
is greatly developed, adjoining parts are apt to be reduced; but this
principle is probably of much less importance than the more general one of the
economy of growth. Through mere mechanical pressure hard parts occasionally
affect adjoining parts. With plants the position of the flowers on the axis,
and of the seeds in the ovary, sometimes leads, through a more or less free
flow of sap, to changes of structure; but such changes are often due to
reversion. Modifications, in whatever manner caused, will be to a certain
extent regulated by that co-ordinating power, or so-called nisus formativus,
which is in fact a remnant of that simple form of reproduction, displayed by
many lowly organised beings in their power of fissiparous generation and
budding. Finally, the effects of the laws which directly or indirectly govern
variability, may be largely regulated by man's selection, and will so far be
determined by natural selection that changes advantageous to any race will be
favoured, and disadvantageous changes will be checked.

Domestic races descended from the same species, or from two or more allied
species, are liable to revert to characters derived from their common
progenitor; and, as they inherit a somewhat similar constitution, they are
liable to vary in the same manner. From these two causes analogous varieties
often arise. When we reflect on the several foregoing laws, imperfectly as we
understand them, and when we bear in mind how much remains to be discovered,
we need not be surprised at the intricate and to us unintelligible manner in
which our domestic productions have varied, and still go on varying.


CHAPTER 2.XXVII.

PROVISIONAL HYPOTHESIS OF PANGENESIS.

PRELIMINARY REMARKS.
FIRST PART:
THE FACTS TO BE CONNECTED UNDER A SINGLE POINT OF VIEW, NAMELY, THE VARIOUS
KINDS OF REPRODUCTION.
REGROWTH OF AMPUTATED PARTS.
GRAFT-HYBRIDS.
THE DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE.
DEVELOPMENT.
THE FUNCTIONAL INDEPENDENCE OF THE UNITS OF THE BODY.
VARIABILITY.
INHERITANCE.
REVERSION.

SECOND PART:
STATEMENT OF THE HYPOTHESIS.
HOW FAR THE NECESSARY ASSUMPTIONS ARE IMPROBABLE.
EXPLANATION BY AID OF THE HYPOTHESIS OF THE SEVERAL CLASSES OF FACTS SPECIFIED
IN THE FIRST PART.
CONCLUSION.

In the previous chapters large classes of facts, such as those bearing on bud-
variation, the various forms of inheritance, the causes and laws of variation,
have been discussed; and it is obvious that these subjects, as well as the
several modes of reproduction, stand in some sort of relation to one another.
I have been led, or rather forced, to form a view which to a certain extent
connects these facts by a tangible method. Every one would wish to explain to
himself, even in an imperfect manner, how it is possible for a character
possessed by some remote ancestor suddenly to reappear in the offspring; how
the effects of increased or decreased use of a limb can be transmitted to the
child; how the male sexual element can act not solely on the ovules, but
occasionally on the mother-form; how a hybrid can be produced by the union of
the cellular tissue of two plants independently of the organs of generation;
how a limb can be reproduced on the exact line of amputation, with neither too
much nor too little added; how the same organism may be produced by such
widely different processes, as budding and true seminal generation; and,
lastly, how of two allied forms, one passes in the course of its development
through the most complex metamorphoses, and the other does not do so, though
when mature both are alike in every detail of structure. I am aware that my
view is merely a provisional hypothesis or speculation; but until a better one
be advanced, it will serve to bring together a multitude of facts which are at
present left disconnected by any efficient cause. As Whewell, the historian of
the inductive sciences, remarks:--"Hypotheses may often be of service to
science, when they involve a certain portion of incompleteness, and even of
error." Under this point of view I venture to advance the hypothesis of
Pangenesis, which implies that every separate part of the whole organisation
reproduces itself. So that ovules, spermatozoa, and pollen-grains,--the
fertilised egg or seed, as well as buds,--include and consist of a multitude
of germs thrown off from each separate part or unit. (27/1. This hypothesis
has been severely criticised by many writers, and it will be fair to give
references to the more important articles. The best essay which I have seen is
by Prof. Delpino, entitled 'Sulla Darwiniana Teoria della Pangenesi, 1869' of
which a translation appeared in 'Scientific Opinion' September 29, 1869 and
the succeeding numbers. He rejects the hypothesis, but criticises it fairly,
and I have found his criticisms very useful. Mr. Mivart ('Genesis of Species'
1871 chapter 10.) follows Delpino, but adds no new objections of any weight.
Dr. Bastian ('The Beginnings of Life' 1872 volume 2 page 98) says that the
hypothesis "looks like a relic of the old rather than a fitting appanage of
the new evolution philosophy." He shows that I ought not to have used the term
"pangenesis," as it had been previously used by Dr. Gros in another sense. Dr.
Lionel Beale ('Nature' May 11, 1871 page 26) sneers at the whole doctrine with
much acerbity and some justice. Prof. Wigand ('Schriften der Gesell. der
gesammt. Naturwissen. zu Marburg' b. 9 1870) considers the hypothesis as
unscientific and worthless. Mr. G.H. Lewes ('Fortnightly Review' November 1,
1868 page 503) seems to consider that it may be useful: he makes many good
criticisms in a perfectly fair spirit. Mr. F. Galton, after describing his
valuable experiments ('Proc. Royal Soc.' volume 19 page 393) on the
intertransfusion of the blood of distinct varieties of the rabbit, concludes
by saying that in his opinion the results negative beyond all doubt the
doctrine of Pangenesis. He informs me that subsequently to the publication of
his paper he continued his experiments on a still larger scale for two more
generations, without any sign of mongrelism showing itself in the very
numerous offspring. I certainly should have expected that gemmules would have
been present in the blood, but this is no necessary part of the hypothesis,
which manifestly applies to plants and the lowest animals. Mr. Galton, in a
letter to 'Nature' (April 27, 1871 page 502), also criticises various
incorrect expressions used by me. On the other hand, several writers have
spoken favourably of the hypothesis, but there would be no use in giving
references to their articles. I may, however, refer to Dr. Ross' work, 'The
Graft Theory of Disease; being an application of Mr. Darwin's hypothesis of
Pangenesis' 1872 as he gives several original and ingenious discussions.)

In the First Part I will enumerate as briefly as I can the groups of facts
which seem to demand connection; but certain subjects, not hitherto discussed,
must be treated at disproportionate length. In the Second Part the hypothesis
will be given; and after considering how far the necessary assumptions are in
themselves improbable, we shall see whether it serves to bring under a single
point of view the various facts.

PART I.

Reproduction may be divided into two main classes, namely, sexual and asexual.
The latter is effected in many ways--by the formation of buds of various
kinds, and by fissiparous generation, that is by spontaneous or artificial
division. It is notorious that some of the lower animals, when cut into many
pieces, reproduce so many perfect individuals: Lyonnet cut a Nais or
freshwater worm into nearly forty pieces, and these all reproduced perfect
animals. (27/2. Quoted by Paget 'Lectures on Pathology' 1853 page 159.) It is
probable that segmentation could be carried much further in some of the
protozoa; and with some of the lowest plants each cell will reproduce the
parent-form. Johannes Muller thought that there was an important distinction
between gemmation and fission; for in the latter case the divided portion,
however small, is more fully developed than a bud, which also is a younger
formation; but most physiologists are now convinced that the two processes are
essentially alike. (27/3. Dr. Lachmann also observes ('Annals and Mag. of Nat.
History' 2nd series volume 19 1857 page 231) with respect to infusoria, that
"fissation and gemmation pass into each other almost imperceptibly." Again,
Mr. W.C. Minor ('Annals and Mag. of Nat. Hist.' 3rd series volume 11 page 328)
shows that with Annelids the distinction that has been made between fission
and budding is not a fundamental one. See also Professor Clark's work 'Mind in
Nature' New York 1865 pages 62, 94.) Prof. Huxley remarks, "fission is little
more than a peculiar mode of budding," and Prof. H.J. Clark shows in detail
that there is sometimes "a compromise between self-division and budding." When
a limb is amputated, or when the whole body is bisected, the cut extremities
are said to bud forth (27/4. See Bonnet 'Oeuvres d'Hist. Nat.' tome 5 1781
page 339 for remarks on the budding-out of the amputated limbs of
Salamanders.); and as the papilla, which is first formed, consists of
undeveloped cellular tissue like that forming an ordinary bud, the expression
is apparently correct. We see the connection of the two processes in another
way; for Trembley observed with the hydra, that the reproduction of the head
after amputation was checked as soon as the animal put forth reproductive
gemmae. (27/5. Paget 'Lectures on Pathology' 1853 page 158.)

Between the production, by fissiparous generation, of two or more complete
individuals, and the repair of even a very slight injury, there is so perfect
a gradation, that it is impossible to doubt that the two processes are
connected. As at each stage of growth an amputated part is replaced by one in
the same state of development, we must also follow Sir J. Paget in admitting,
"that the powers of development from the embryo, are identical with those
exercised for the restoration from injuries: in other words, that the powers
are the same by which perfection is first achieved, and by which, when lost,
it is recovered." (27/6. Ibid pages 152, 164.) Finally, we may conclude that
the several forms of budding, fissiparous generation, the repair of injuries,
and development, are all essentially the results of one and the same power.

SEXUAL GENERATION.

The union of the two sexual elements seems at first sight to make a broad
distinction between sexual and asexual generation. But the conjugation of
algae, by which process the contents of two cells unite into a single mass
capable of development, apparently gives us the first step towards sexual
union: and Pringsheim, in his memoir on the pairing of Zoospores (27/7.
Translated in 'Annals and Mag. of Nat. Hist.' April 1870 page 272.), shows
that conjugation graduates into true sexual reproduction. Moreover, the now
well-ascertained cases of Parthenogenesis prove that the distinction between
sexual and asexual generation is not nearly so great as was formerly thought;
for ova occasionally, and even in some cases frequently, become developed into
perfect beings, without the concourse of the male. With most of the lower
animals and even with mammals, the ova show a trace of parthenogenetic power,
for without being fertilised they pass through the first stages of
segmentation. (27/8. Bischoff as quoted by von Siebold "Ueber Parthenogenesis"
'Sitzung der math. phys. Classe.' Munich November 4, 1871 page 240. See also
Quatrefages 'Annales des Sc. Nat. Zoolog.' 3rd series 1850 page 138.) Nor can
pseudova which do not need fertilisation, be distinguished from true ova, as
was first shown by Sir J. Lubbock, and is now admitted by Siebold. So, again,
the germ-balls in the larvae of Cecidomyia are said by Leuckart (27/9. 'On the
Asexual Reproduction of Cecidomyide Larvae' translated in 'Annals and Mag. of
Nat. Hist.' March 1866 pages 167, 171.) to be formed within the ovarium, but
they do not require to be fertilised. It should also be observed that in
sexual generation, the ovules and the male element have equal power of
transmitting every single character possessed by either parent to their
offspring. We see this clearly when hybrids are paired inter se, for the
characters of both grandparents often appear in the progeny, either perfectly
or by segments. It is an error to suppose that the male transmits certain
characters and the female other characters; although no doubt, from unknown
causes, one sex sometimes has a much stronger power of transmission than the
other.

It has, however, been maintained by some authors that a bud differs
essentially from a fertilised germ, in always reproducing the perfect
character of the parent-stock; whilst fertilised germs give birth to variable
beings. But there is no such broad distinction as this. In the eleventh
chapter numerous cases were advanced showing that buds occasionally grow into
plants having quite new characters; and the varieties thus produced can be
propagated for a length of time by buds, and occasionally by seed.
Nevertheless, it must be admitted that beings produced sexually are much more
liable to vary than those produced asexually; and of this fact a partial
explanation will hereafter be attempted. The variability in both cases is
determined by the same general causes, and is governed by the same laws. Hence
new varieties arising from buds cannot be distinguished from those arising
from seed. Although bud-varieties usually retain their character during
successive bud-generations, yet they occasionally revert, even after a long
series of bud-generations, to their former character. This tendency to
reversion in buds, is one of the most remarkable of the several points of
agreement between the offspring from bud and seminal reproduction.

But there is one difference between organisms produced sexually and asexually,
which is very general. The former pass in the course of their development from
a very low stage to their highest stage, as we see in the metamorphoses of
insects and of many other animals, and in the concealed metamorphoses of the
vertebrata. Animals propagated asexually by buds or fission, on the other
hand, commence their development at that stage at which the budding or self-
dividing animal may happen to be, and therefore do not pass through some of
the lower developmental stages. (27/10. Prof. Allman speaks ('Transact. R.
Soc. of Edinburgh' volume 26 1870 page 102) decisively on this head with
respect to the Hydroida: he says, "It is a universal law in the succession of
zooids, that no retrogression ever takes place in the series.") Afterwards,
they often advance in organisation, as we see in the many cases of "alternate
generation." In thus speaking of alternate generation, I follow those
naturalists who look at this process as essentially one of internal budding or
of fissiparous generation. Some of the lower plants, however, such as mosses
and certain algae, according to Dr. L. Radlkofer (27/11. 'Annals and Mag. of
Nat. Hist.' 2nd series volume 20 1857 pages 153-455), when propagated
asexually, do undergo a retrogressive metamorphosis. As far as the final cause
is concerned, we can to a certain extent understand why beings propagated by
buds should not pass through all the early stages of development; for with
each organism the structure acquired at each stage must be adapted to its
peculiar habits; and if there are places for the support of many individuals
at some one stage, the simplest plan will be that they should be multiplied at
this stage, and not that they should first retrograde in their development to
an earlier or simpler structure, which might not be fitted for the then
surrounding conditions.

From the several foregoing considerations we may conclude that the difference
between sexual and asexual generation is not nearly so great as at first
appears; the chief difference being that an ovule cannot continue to live and
to be fully developed unless it unites with the male element; but even this
difference is far from invariable, as shown by the many cases of
parthenogenesis. We are therefore naturally led to inquire what the final
cause can be of the necessity in ordinary generation for the concourse of the
two sexual elements.

Seeds and ova are often highly serviceable as the means of disseminating
plants and animals, and of preserving them during one or more seasons in a
dormant state; but unimpregnated seeds or ova, and detached buds, would be
equally serviceable for both purposes. We can, however, indicate two important
advantages gained by the concourse of the two sexes, or rather of two
individuals belonging to opposite sexes; for, as I have shown in a former
chapter, the structure of every organism appears to be especially adapted for
the concurrence, at least occasionally, of two individuals. When species are
rendered highly variable by changed conditions of life, the free intercrossing
of the varying individuals tends to keep each form fitted for its proper place
in nature; and crossing can be effected only by sexual generation; but whether
the end thus gained is of sufficient importance to account for the first
origin of sexual intercourse is extremely doubtful. Secondly, I have shown
from a large body of facts, that, as a slight change in the conditions of life
is beneficial to each creature, so, in an analogous manner, is the change
effected in the germ by sexual union with a distinct individual; and I have
been led, from observing the many widely-extended provisions throughout nature
for this purpose, and from the greater vigour of crossed organisms of all
kinds, as proved by direct experiments, as well as from the evil effects of
close interbreeding when long continued, to believe that the advantage thus
gained is very great.

Why the germ, which before impregnation undergoes a certain amount of
development, ceases to progress and perishes, unless it be acted on by the
male element; and why conversely the male element, which in the case of some
insects is enabled to keep alive for four or five years, and in the case of
some plants for several years, likewise perishes, unless it acts on or unites
with the germ, are questions which cannot be answered with certainty. It is,
however, probable that both sexual elements perish, unless brought into union,
simply from including too little formative matter for independent development.
Quatrefages has shown in the case of the Teredo (27/12. 'Annales des Sc. Nat.'
3rd series 1850 tome 13.), as did formerly Prevost and Dumas with other
animals, that more than one spermatozoon is requisite to fertilise an ovum.
This has likewise been shown by Newport (27/13. 'Transact. Phil. Soc.' 1851
pages 196, 208, 210; 1853 pages 245, 247.), who proved by numerous
experiments, that, when a very small number of spermatozoa are applied to the
ova of Batrachians, they are only partially impregnated, and an embryo is
never fully developed. The rate also of the segmentation of the ovum is
determined by the number of the spermatozoa. With respect to plants, nearly
the same results were obtained by Kolreuter and Gartner. This last careful
observer, after making successive trials on a Malva with more and more pollen-
grains, found (27/14. 'Beitrage zur Kenntniss' etc. 1844 s. 345.), that even
thirty grains did not fertilise a single seed; but when forty grains were
applied to the stigma, a few seeds of small size were formed. In the case of
Mirabilis the pollen grains are extraordinarily large, and the ovarium
contains only a single ovule; and these circumstances led Naudin (27/15.
'Nouvelles Archives du Museum' tome 1 page 27.) to make the following
experiments: a flower was fertilised by three grains and succeeded perfectly;
twelve flowers were fertilised by two grains, and seventeen flowers by a
single grain, and of these one flower alone in each lot perfected its seed:
and it deserves especial notice that the plants produced by these two seeds
never attained their proper dimensions, and bore flowers of remarkably small
size. From these facts we clearly see that the quantity of the peculiar
formative matter which is contained within the spermatozoa and pollen-grains
is an all-important element in the act of fertilisation, not only for the full
development of the seed, but for the vigour of the plant produced from such
seed. We see something of the same kind in certain cases of parthenogenesis,
that is, when the male element is wholly excluded; for M. Jourdan (27/16. As
quoted by Sir J. Lubbock in 'Nat. Hist. Review' 1862 page 345. Weijenbergh
also raised ('Nature' December 21, 1871 page 149) two successive generations
from unimpregnated females of another lepidopterous insect, Liparis dispar.
These females did not produce at most one-twentieth of their full complement
of eggs, and many of the eggs were worthless. Moreover the caterpillars raised
from these unfertilised eggs "possessed far less vitality" than those from
fertilised eggs. In the third parthenogenetic generation not a single egg
yielded a caterpillar.) found that, out of about 58,000 eggs laid by
unimpregnated silk-moths, many passed through their early embryonic stages,
showing that they were capable of self-development, but only twenty-nine out
of the whole number produced caterpillars. The same principle of quantity
seems to hold good even in artificial fissiparous reproduction, for Hackel
(27/17. 'Entwickelungsgeschichte der Siphonophora' 1869 page 73.) found that
by cutting the segmented and fertilised ova or larva of Siphonophorae (jelly-
fishes) into pieces, the smaller the pieces were, the slower was the rate of
development, and the larvae thus produced were by so much the more imperfect
and inclined to monstrosity. It seems, therefore, probable that with the
separate sexual elements deficient quantity of formative matter is the main
cause of their not having the capacity for prolonged existence and
development, unless they combine and thus increase each other's bulk. The
belief that it is the function of the spermatozoa to communicate life to the
ovule seems a strange one, seeing that the unimpregnated ovule is already
alive and generally undergoes a certain amount of independent development.
Sexual and asexual reproduction are thus seen not to differ essentially; and
we have already shown that asexual reproduction, the power of regrowth and
development are all parts of one and the same great law.

REGROWTH OF AMPUTATED PARTS.

This subject deserves a little further discussion. A multitude of the lower
animals and some vertebrates possess this wonderful power. For instance,
Spallanzani cut off the legs and tail of the same salamander six times
successively, and Bonnet (27/18. Spallanzani 'An Essay on Animal Reproduction'
translated by Dr. Maty 1769 page 79. Bonnet 'Oeuvres d'Hist. Nat.' tome 5 part
1 4to. edition 1781 pages 343, 350.) did so eight times; and on each occasion
the limbs were reproduced on the exact line of amputation, with no part
deficient or in excess. An allied animal, the axolotl, had a limb bitten off,
which was reproduced in an abnormal condition, but when this was amputated it
was replaced by a perfect limb. (27/19. Vulpian as quoted by Prof. Faivre 'La
Variabilite des Especes' 1868 page 112.) The new limbs in these cases bud
forth, and are developed in the same manner as during the regular development
of a young animal. For instance, with the Amblystoma lurida, three toes are
first developed, then the fourth, and on the hind-feet the fifth, and so it is
with a reproduced limb. (27/20. Dr. P. Hoy 'The American Naturalist' September
1871 page 579.)

The power of regrowth is generally much greater during the youth of an animal
or during the earlier stages of its development than during maturity. The
larvae or tadpoles of the Batrachians are capable of reproducing lost members,
but not so the adults. (27/21. Dr. Gunther in Owen 'Anatomy of Vertebrates'
volume 1 1866 page 567. Spallanzani has made similar observations.) Mature
insects have no power of regrowth, excepting in one order, whilst the larvae
of many kinds have this power. Animals low in the scale are able, as a general
rule, to reproduce lost parts far more easily than those which are more highly
organised. The myriapods offer a good illustration of this rule; but there are
some strange exceptions to it--thus Nemerteans, though lowly organised, are
said to exhibit little power of regrowth. With the higher vertebrata, such as
birds and mammals, the power is extremely limited. (27/22. A thrush was
exhibited before the British Association at Hull in 1853 which had lost its
tarsus, and this member, it was asserted, had been thrice reproduced; having
been lost, I presume, each time by disease. Sir J. Paget informs me that he
feels some doubt about the facts recorded by Sir J. Simpson ('Monthly Journal
of Medical Science' Edinburgh 1848 new series volume 2 page 890) of the
regrowth of limbs in the womb in the case of man.)

In the case of those animals which may be bisected or chopped into pieces, and
of which every fragment will reproduce the whole, the power of regrowth must
be diffused throughout the whole body. Nevertheless there seems to be much
truth in the view maintained by Prof. Lessona (27/23. 'Atti della Soc. Ital.
di Sc. Nat.' volume 11 1869 page 493.), that this capacity is generally a
localised and special one, serving to replace parts which are eminently liable
to be lost in each particular animal. The most striking case in favour of this
view, is that the terrestrial salamander, according to Lessona, cannot
reproduce lost parts, whilst another species of the same genus, the aquatic
salamander, has extraordinary powers of regrowth, as we have just seen; and
this animal is eminently liable to have its limbs, tail, eyes and jaws bitten
off by other tritons. (27/24. Lessona states that this is so in the paper just
referred to. See also 'The American Naturalist' September 1871 page 579.) Even
with the aquatic salamander the capacity is to a certain extent localised, for
when M. Philipeaux (27/25. 'Comptes Rendus' October 1, 1866 and June 1867.)
extirpated the entire fore limb together with the scapula, the power of
regrowth was completely lost. It is also a remarkable fact, standing in
opposition to a very general rule, that the young of the aquatic salamander do
not possess the power of repairing their limbs in an equal degree with the
adults (27/26. Bonnet 'Oeuvres Hist. Nat.' volume 5 page 294, as quoted by
Prof. Rolleston in his remarkable address to the 36th annual meeting of the
British Medical Association.) but I do not know that they are more active, or
can otherwise better escape the loss of their limbs, than the adults. The
walking-stick insect, Diapheromera femorata, like other insects of the same
order, can reproduce its legs in the mature state, and these from their great
length must be liable to be lost: but the capacity is localised (as in the
case of the salamander), for Dr. Scudder found (27/27. 'Proc. Boston Soc. of
Nat. Hist.' volume 12 1868-69 page 1.), that if the limb was removed within
the trochanto-femoral articulation, it was never renewed. When a crab is
seized by one of its legs, this is thrown off at the basal joint, being
afterwards replaced by a new leg; and it is generally admitted that this is a
special provision for the safety of the animal. Lastly, with gasteropod
molluscs, which are well known to have the power of reproducing their heads,
Lessona shows that they are very liable to have their heads bitten off by
fishes; the rest of the body being protected by the shell. Even with plants we
see something of the same kind, for non-deciduous leaves and young stems have
no power of regrowth, these parts being easily replaced by growth from new
buds; whilst the bark and subjacent tissues of the trunks of trees have great
power of regrowth, probably on account of their increase in diameter, and of
their liability to injury from being gnawed by animals.

GRAFT-HYBRIDS.

It is well known from innumerable trials made in all parts of the world, that
buds may be inserted into a stock, and that the plants thus raised are not
affected in a greater degree than can be accounted for by changed nutrition.
Nor do the seedlings raised from such inserted buds partake of the character
of the stock, though they are more liable to vary than are seedlings from the
same variety growing on its own roots. A bud, also, may sport into a new and
strongly-marked variety without any other bud on the same plant being in the
least degree affected. We may therefore infer, in accordance with the common
view, that each bud is a distinct individual, and that its formative elements
do not spread beyond the parts subsequently developed from it. Nevertheless,
we have seen in the abstract on graft-hybridisation in the eleventh chapter
that buds certainly include formative matter, which can occasionally combine
with that included in the tissues of a distinct variety or species; a plant
intermediate between the two parent-forms being thus produced. In the case of
the potato we have seen that the tubers produced from a bud of one kind
inserted into another are intermediate in colour, size, shape and state of
surface; that the stems, foliage, and even certain constitutional
peculiarities, such as precocity, are likewise intermediate. With these well-
established cases, the evidence that graft-hybrids have also been produced
with the laburnum, orange, vine, rose, etc., seems sufficient. But we do not
know under what conditions this rare form of reproduction is possible. From
these several cases we learn the important fact that formative elements
capable of blending with those of a distinct individual (and this is the chief
characteristic of sexual generation), are not confined to the reproductive
organs, but are present in the buds and cellular tissue of plants; and this is
a fact of the highest physiological importance.

DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE.

In the eleventh chapter, abundant proofs were given that foreign pollen
occasionally affects in a direct manner the mother-plant. Thus, when Gallesio
fertilised an orange-flower with pollen from the lemon, the fruit bore stripes
of perfectly characterised lemon-peel. With peas, several observers have seen
the colour of the seed-coats and even of the pod directly affected by the
pollen of a distinct variety. So it has been with the fruit of the apple,
which consists of the modified calyx and upper part of the flower-stalk. In
ordinary cases these parts are wholly formed by the mother-plant. We here see
that the formative elements included within the male element or pollen of one
variety can affect and hybridise, not the part which they are properly adapted
to affect, namely, the ovules, but the partially-developed tissues of a
distinct variety or species. We are thus brought half-way towards a graft-
hybrid, in which the formative elements included within the tissues of one
individual combine with those included in the tissues of a distinct variety or
species, thus giving rise to a new and intermediate form, independently of the
male or female sexual organs.

With animals which do not breed until nearly mature, and of which all the
parts are then fully developed, it is hardly possible that the male element
should directly affect the female. But we have the analogous and perfectly
well-ascertained case of the male element affecting (as with the quagga and
Lord Morton's mare) the female or her ova, in such a manner that when she is
impregnated by another male her offspring are affected and hybridised by the
first male. The explanation would be simple if the spermatozoa could keep
alive within the body of the female during the long interval which has
sometimes elapsed between the two acts of impregnation; but no one will
suppose that this is possible with the higher animals.

DEVELOPMENT.

The fertilised germ reaches maturity by a vast number of changes: these are
either slight and slowly effected, as when the child grows into the man, or
are great and sudden, as with the metamorphoses of most insects. Between these
extremes we have every gradation, even within the same class; thus, as Sir J.
Lubbock has shown (27/28. 'Transact. Linn. Soc.' volume 24 1863 page 62.)
there is an Ephemerous insect which moults above twenty times, undergoing each
time a slight but decided change of structure; and these changes, as he
further remarks, probably reveal to us the normal stages of development, which
are concealed and hurried through or suppressed in most other insects. In
ordinary metamorphoses, the parts and organs appear to become changed into the
corresponding parts in the next stage of development; but there is another
form of development, which has been called by Professor Owen metagenesis. In
this case "the new parts are not moulded upon the inner surface of the old
ones. The plastic force has changed its course of operation. The outer case,
and all that gave form and character to the precedent individual, perish and
are cast off; they are not changed into the corresponding parts of the new
individual. These are due to a new and distinct developmental process," etc.
(27/29. 'Parthenogenesis' 1849 pages 25, 26. Prof. Huxley has some excellent
remarks ('Medical Times' 1856 page 637) on this subject in reference to the
development of star-fishes, and shows how curiously metamorphosis graduates
into gemmation or zoid-formation, which is in fact the same as metagenesis.)
Metamorphosis, however, graduates so insensibly, into metagenesis, that the
two processes cannot be distinctly separated. For instance, in the last change
which Cirripedes undergo, the alimentary canal and some other organs are
moulded on pre-existing parts; but the eyes of the old and the young animal
are developed in entirely different parts of the body; the tips of the mature
limbs are formed within the larval limbs, and may be said to be metamorphosed
from them; but their basal portions and the whole thorax are developed in a
plane at right angles to the larval limbs and thorax; and this may be called
metagenesis. The metagenetic process is carried to an extreme point in the
development of some Echinoderms, for the animal in the second stage of
development is formed almost like a bud within the animal of the first stage,
the latter being then cast off like an old vestment, yet sometimes maintaining
for a short period an independent vitality. (27/30. Prof. J. Reay Greene in
Gunther's 'Record of Zoolog. Lit.' 1865 page 625.) If, instead of a single
individual, several were to be thus developed metagenetically within a pre-
existing form, the process would be called one of alternate generation. The
young thus developed may either closely resemble the encasing parent-form, as
with the larvae of Cecidomyia, or may differ to an astonishing degree, as with
many parasitic worms and jelly-fishes; but this does not make any essential
difference in the process, any more than the greatness or abruptness of the
change in the metamorphoses of insects.

The whole question of development is of great importance for our present
subject. When an organ, the eye, for instance, is metagenetically formed in a
part of the body where during the previous stage of development no eye
existed, we must look at it as a new and independent growth. The absolute
independence of new and old structures, although corresponding in structure
and function, is still more obvious when several individuals are formed within
a previous form, as in the cases of alternate generation. The same important
principle probably comes largely into play even in the case of apparently
continuous growth, as we shall see when we consider the inheritance of
modifications at corresponding ages.

We are led to the same conclusion, namely, the independence of parts
successively developed, by another and quite distinct group of facts. It is
well known that many animals belonging to the same order, and therefore not
differing widely from each other, pass through an extremely different course
of development. Thus certain beetles, not in any way remarkably different from
others of the same order, undergo what has been called a hyper-metamorphosis--
that is, they pass through an early stage wholly different from the ordinary
grub-like larva. In the same sub-order of crabs, namely, the Macroura, as
Fritz Muller remarks, the river cray-fish is hatched under the same form which
it ever afterwards retains; the young lobster has divided legs, like a Mysis;
the Palaemon appears under the form of a Zoea, and Peneus under the Nauplius-
form; and how wonderfully these larval forms differ from one another, is known
to every naturalist. (27/31. Fritz Muller 'Fur Darwin' 1864 s. 65, 71. The
highest authority on crustaceans, Prof. Milne-Edwards, insists ('Annal. des
Sci. Nat.' 2nd series Zoolog. tome 3 page 322) on the difference in the
metamorphosis of closely-allied genera.) Some other crustaceans, as the same
author observes, start from the same point and arrive at nearly the same end,
but in the middle of their development are widely different from one another.
Still more striking cases could be given with respect to the Echinodermata.
With the Medusae or jelly-fishes Professor Allman observes, "The
classification of the Hydroida would be a comparatively simple task if, as has
been erroneously asserted, generically-identical medusoids always arose from
generically-identical polypoids; and, on the other hand, that generically-
identical polypoids always gave origin to generically-identical medusoids." So
again, Dr. Strethill Wright remarks, "In the life-history of the Hydroidae any
phase, planuloid, polypoid, or medusoid, may be absent." (27/32. Prof. Allman
'Annals and Mag. of Nat. Hist.' 3rd series volume 13 1864 page 348; Dr. S.
Wright ibid volume 8 1861 page 127. See also page 358 for analogous statements
by Sars.)

According to the belief now generally accepted by our best naturalists, all
the members of the same order or class, for instance, the Medusae or the
Macrourous crustaceans, are descended from a common progenitor. During their
descent they have diverged much in structure, but have retained much in
common; and this has occurred, though they have passed through and still pass
through marvellously different metamorphoses. This fact well illustrates how
independent each structure is from that which precedes and that which follows
it in the course of development.

THE FUNCTIONAL INDEPENDENCE OF THE ELEMENTS OR UNITS OF THE BODY.

Physiologists agree that the whole organism consists of a multitude of
elemental parts, which are to a great extent independent of one another. Each
organ, says Claude Bernard (27/33. 'Tissus Vivants' 1866 page 22.), has its
proper life, its autonomy; it can develop and reproduce itself independently
of the adjoining tissues. A great German authority, Virchow (27/34. 'Cellular
Pathology' translated by Dr. Chance 1860 pages 14, 18, 83, 460.), asserts
still more emphatically that each system consists of an "enormous mass of
minute centres of action...Every element has its own special action, and even
though it derive its stimulus to activity from other parts, yet alone effects
the actual performance of duties...Every single epithelial and muscular fibre-
cell leads a sort of parasitical existence in relation to the rest of the
body...Every single bone-corpuscle really possesses conditions of nutrition
peculiar to itself." Each element, as Sir J. Paget remarks, lives its
appointed time and then dies, and is replaced after being cast off or
absorbed. (27/35. Paget 'Surgical Pathology' volume 1 1853 pages 12-14.) I
presume that no physiologist doubts that, for instance, each bone-corpuscle of
the finger differs from the corresponding corpuscle in the corresponding joint
of the toe; and there can hardly be a doubt that even those on the
corresponding sides of the body differ, though almost identical in nature.
This near approach to identity is curiously shown in many diseases in which
the same exact points on the right and left sides of the body are similarly
affected; thus Sir J. Paget (27/36. Ibid page 19.) gives a drawing of a
diseased pelvis, in which the bone has grown into a most complicated pattern,
but "there is not one spot or line on one side which is not represented, as
exactly as it would be in a mirror, on the other."

Many facts support this view of the independent life of each minute element of
the body. Virchow insists that a single bone-corpuscle or a single cell in the
skin may become diseased. The spur of a cock, after being inserted into the
ear of an ox, lived for eight years, and acquired a weight of 396 grammes
(nearly fourteen ounces), and the astonishing length of twenty-four
centimetres, or about nine inches; so that the head of the ox appeared to bear
three horns. (27/37. See Prof. Mantegazza's interesting work 'Degli innesti
Animali' etc. Milano 1865 page 51 tab. 3.) The tail of a pig has been grafted
into the middle of its back, and reacquired sensibility. Dr. Ollier (27/38.
'De la Production Artificielle des Os' page 8.) inserted a piece of periosteum
from the bone of a young dog under the skin of a rabbit, and true bone was
developed. A multitude of similar facts could be given. The frequent presence
of hairs and of perfectly developed teeth, even teeth of the second dentition,
in ovarian tumours (27/39. Isidore Geoffroy Saint-Hilaire 'Hist. des
Anomalies' tome 2 pages 549, 560, 562; Virchow ibid page 484. Lawson Tait 'The
Pathology of Diseases of the Ovaries' 1874 pages 61, 62.), are facts leading
to the same conclusion. Mr. Lawson Tait refers to a tumour in which "over 300
teeth were found, resembling in many respects milk-teeth;" and to another
tumour, "full of hair which had grown and been shed from one little spot of
skin not bigger than the tip of my little finger. The amount of hair in the
sac, had it grown from a similarly sized area of the scalp, would have taken
almost a lifetime to grow and be shed."

Whether each of the innumerable autonomous elements of the body is a cell or
the modified product of a cell, is a more doubtful question, even if so wide a
definition be given to the term, as to include cell-like bodies without walls
and without nuclei. (27/40. For the most recent classification of cells, see
Ernst Hackel 'Generelle Morpholog.' b. 2 1866 s. 275.) The doctrine of omnis
cellula e cellula is admitted for plants, and widely prevails with respect to
animals. (27/41. Dr. W. Turner 'The Present Aspect of Cellular Pathology'
'Edinburgh Medical Journal' April 1863.) Thus Virchow, the great supporter of
the cellular theory, whilst allowing that difficulties exist, maintains that
every atom of tissue is derived from cells, and these from pre-existing cells,
and these primarily from the egg, which he regards as a great cell. That
cells, still retaining the same nature, increase by self-division or
proliferation, is admitted by every one. But when an organism undergoes great
changes of structure during development, the cells, which at each stage are
supposed to be directly derived from previously existing cells, must likewise
be greatly changed in nature; this change is attributed by the supporters of
the cellular doctrine to some inherent power which the cells possess, and not
to any external agency. Others maintain that cells and tissues of all kinds
may be formed, independently of pre-existing cells, from plastic lymph or
blastema. Whichever view may be correct, every one admits that the body
consists of a multitude of organic units, all of which possess their own
proper attributes, and are to a certain extent independent of all others.
Hence it will be convenient to use indifferently the terms cells or organic
units, or simply units.

VARIABILITY AND INHERITANCE.

We have seen in the twenty-second chapter that variability is not a principle
co-ordinate with life or reproduction, but results from special causes,
generally from changed conditions acting during successive generations. The
fluctuating variability thus induced is apparently due in part to the sexual
system being easily affected, so that it is often rendered impotent; and when
not so seriously affected, it often fails in its proper function of
transmitting truly the characters of the parents to the offspring. But
variability is not necessarily connected with the sexual system, as we see in
the cases of bud-variation. Although we are seldom able to trace the nature of
the connection, many deviations of structure no doubt result from changed
conditions acting directly on the organisation, independently of the
reproductive system. In some instances we may feel sure of this, when all, or
nearly all the individuals which have been similarly exposed are similarly and
definitely affected, of which several instances have been given. But it is by
no means clear why the offspring should be affected by the exposure of the
parents to new conditions, and why it is necessary in most cases that several
generations should have been thus exposed.

How, again, can we explain the inherited effects of the use or disuse of
particular organs? The domesticated duck flies less and walks more than the
wild duck, and its limb-bones have become diminished and increased in a
corresponding manner in comparison with those of the wild duck. A horse is
trained to certain paces, and the colt inherits similar consensual movements.
The domesticated rabbit becomes tame from close confinement; the dog,
intelligent from associating with man; the retriever is taught to fetch and
carry; and these mental endowments and bodily powers are all inherited.
Nothing in the whole circuit of physiology is more wonderful. How can the use
or disuse of a particular limb or of the brain affect a small aggregate of
reproductive cells, seated in a distant part of the body, in such a manner
that the being developed from these cells inherits the characters of either
one or both parents? Even an imperfect answer to this question would be
satisfactory.

In the chapters devoted to inheritance it was shown that a multitude of newly
acquired characters, whether injurious or beneficial, whether of the lowest or
highest vital importance, are often faithfully transmitted--frequently even
when one parent alone possesses some new peculiarity; and we may on the whole
conclude that inheritance is the rule, and non-inheritance the anomaly. In
some instances a character is not inherited, from the conditions of life being
directly opposed to its development; in many instances, from the conditions
incessantly inducing fresh variability, as with grafted fruit-trees and
highly-cultivated flowers. In the remaining cases the failure may be
attributed to reversion, by which the child resembles its grandparents or more
remote progenitors, instead of its parents.

Inheritance is governed by various laws. Characters which first appear at any
particular age tend to reappear at a corresponding age. They often become
associated with certain seasons of the year, and reappear in the offspring at
a corresponding season. If they appear rather late in life in one sex, they
tend to reappear exclusively in the same sex at the same period of life.

The principle of reversion, recently alluded to, is one of the most wonderful
of the attributes of Inheritance. It proves to us that the transmission of a
character and its development, which ordinarily go together and thus escape
discrimination, are distinct powers; and these powers in some cases are even
antagonistic, for each acts alternately in successive generations. Reversion
is not a rare event, depending on some unusual or favourable combination of
circumstances, but occurs so regularly with crossed animals and plants, and so
frequently with uncrossed breeds, that it is evidently an essential part of
the principle of inheritance. We know that changed conditions have the power
of evoking long-lost characters, as in the case of animals becoming feral. The
act of crossing in itself possesses this power in a high degree. What can be
more wonderful than that characters, which have disappeared during scores, or
hundreds, or even thousands of generations, should suddenly reappear perfectly
developed, as in the case of pigeons and fowls, both when purely bred and
especially when crossed; or as with the zebrine stripes on dun-coloured
horses, and other such cases? Many monstrosities come under this same head, as
when rudimentary organs are redeveloped, or when an organ which we must
believe was possessed by an early progenitor of the species, but of which not
even a rudiment is left, suddenly reappears, as with the fifth stamen in some
Scrophulariaceae. We have already seen that reversion acts in bud-
reproduction; and we know that it occasionally acts during the growth of the
same individual animal, especially, but not exclusively, if of crossed
parentage,--as in the rare cases described of fowls, pigeons, cattle, and
rabbits, which have reverted to the colours of one of their parents or
ancestors as they advanced in years.

We are led to believe, as formerly explained, that every character which
occasionally reappears is present in a latent form in each generation, in
nearly the same manner as in male and female animals the secondary characters
of the opposite sex lie latent and ready to be evolved when the reproductive
organs are injured. This comparison of the secondary sexual characters which
lie latent in both sexes, with other latent characters, is the more
appropriate from the case recorded of a Hen, which assumed some of the
masculine characters, not of her own race, but of an early progenitor; she
thus exhibited at the same time the redevelopment of latent characters of both
kinds. In every living creature we may feel assured that a host of long-lost
characters lie ready to be evolved under proper conditions. How can we make
intelligible and connect with other facts, this wonderful and common capacity
of reversion,--this power of calling back to life long-lost characters?

PART II.

I have now enumerated the chief facts which every one would desire to see
connected by some intelligible bond. This can be done, if we make the
following assumptions, and much may be advanced in favour of the chief one.
The secondary assumptions can likewise be supported by various physiological
considerations. It is universally admitted that the cells or units of the body
increase by self-division or proliferation, retaining the same nature, and
that they ultimately become converted into the various tissues and substances
of the body. But besides this means of increase I assume that the units throw
off minute granules which are dispersed throughout the whole system; that
these, when supplied with proper nutriment, multiply by self-division, and are
ultimately developed into units like those from which they were originally
derived. These granules may be called gemmules. They are collected from all
parts of the system to constitute the sexual elements, and their development
in the next generation forms a new being; but they are likewise capable of
transmission in a dormant state to future generations and may then be
developed. Their development depends on their union with other partially
developed or nascent cells which precede them in the regular course of growth.
Why I use the term union, will be seen when we discuss the direct action of
pollen on the tissues of the mother-plant. Gemmules are supposed to be thrown
off by every unit, not only during the adult state, but during each stage of
development of every organism; but not necessarily during the continued
existence of the same unit. Lastly, I assume that the gemmules in their
dormant state have a mutual affinity for each other, leading to their
aggregation into buds or into the sexual elements. Hence, it is not the
reproductive organs or buds which generate new organisms, but the units of
which each individual is composed. These assumptions constitute the
provisional hypothesis which I have called Pangenesis. Views in many respects
similar have been propounded by various authors. (27/42. Mr. G.H. Lewes
('Fortnightly Review' November 1, 1868 page 506) remarks on the number of
writers who have advanced nearly similar views. More than two thousand years
ago Aristotle combated a view of this kind, which, as I hear from Dr. W. Ogle,
was held by Hippocrates and others. Ray, in his 'Wisdom of God' (2nd edition
1692 page 68), says that "every part of the body seems to club and contribute
to the seed." The "organic molecules" of Buffon ('Hist. Nat. Gen.' edition of
1749 tome 2 pages 54, 62, 329, 333, 420, 425) appear at first sight to be the
same as the gemmules of my hypothesis, but they are essentially different.
Bonnet ('Oeuvres d'Hist. Nat.' tome 5 part 1 1781 4to edition page 334) speaks
of the limbs having germs adapted for the reparation of all possible losses;
but whether these germs are supposed to be the same with those within buds and
the sexual organs is not clear. Prof. Owen says ('Anatomy of Vertebrates'
volume 3 1868 page 813) that he fails to see any fundamental difference
between the views which he propounded in his 'Parthenogenesis' (1849 pages 5-
8), and which he now considers as erroneous, and my hypothesis of pangenesis:
but a reviewer ('Journal of Anat. and Phys.' May 1869 page 441) shows how
different they really are. I formerly thought that the "physiological units"
of Herbert Spencer ('Principles of Biology' volume 1 chapters 4 and 8 1863-64)
were the same as my gemmules, but I now know that this is not the case.
Lastly, it appears from a review of the present work by Prof. Mantegazza
('Nuova Antologia, Maggio' 1868), that he (in his 'Elementi di Igiene' Ediz. 3
page 540) clearly foresaw the doctrine of pangenesis.)

Before proceeding to show, firstly, how far these assumptions are in
themselves probable, and secondly, how far they connect and explain the
various groups of facts with which we are concerned, it may be useful to give
an illustration, as simple as possible, of the hypothesis. If one of the
Protozoa be formed, as it appears under the microscope, of a small mass of
homogeneous gelatinous matter, a minute particle or gemmule thrown off from
any part and nourished under favourable circumstances would reproduce the
whole; but if the upper and lower surfaces were to differ in texture from each
other and from the central portion, then all three parts would have to throw
off gemmules, which when aggregated by mutual affinity would form either buds
or the sexual elements, and would ultimately be developed into a similar
organism. Precisely the same view may be extended to one of the higher
animals; although in this case many thousand gemmules must be thrown off from
the various parts of the body at each stage of development; these gemmules
being developed in union with pre-existing nascent cells in due order of
succession.

Physiologists maintain, as we have seen, that each unit of the body, though to
a large extent dependent on others, is likewise to a certain extent
independent or autonomous, and has the power of increasing by self-division. I
go one step further, and assume that each unit casts off free gemmules which
are dispersed throughout the system, and are capable under proper conditions
of being developed into similar units. Nor can this assumption be considered
as gratuitous and improbable. It is manifest that the sexual elements and buds
include formative matter of some kind, capable of development; and we now know
from the production of graft-hybrids that similar matter is dispersed
throughout the tissues of plants, and can combine with that of another and
distinct plant, giving rise to a new being, intermediate in character. We know
also that the male element can act directly on the partially developed tissues
of the mother-plant, and on the future progeny of female animals. The
formative matter which is thus dispersed throughout the tissues of plants, and
which is capable of being developed into each unit or part, must be generated
there by some means; and my chief assumption is that this matter consists of
minute particles or gemmules cast off from each unit or cell. (27/43. Mr.
Lowne has observed ('Journal of Queckett Microscopical Club' September 23,
1870) certain remarkable changes in the tissues of the larva of a fly, which
makes him believe "it possible that organs and organisms are sometimes
developed by the aggregation of excessively minute gemmules, such as those
which Mr. Darwin's hypothesis demands.")

But I have further to assume that the gemmules in their undeveloped state are
capable of largely multiplying themselves by self-division, like independent
organisms. Delpino insists that to "admit of multiplication by fissiparity in
corpuscles, analogous to seeds or buds...is repugnant to all analogy." But
this seems a strange objection, as Thuret (27/44. 'Annales des Sc. Nat.' 3rd
series Bot. tome 14 1850 page 244.) has seen the zoospore of an alga divide
itself, and each half germinated. Haeckel divided the segmented ovum of a
siphonophora into many pieces, and these were developed. Nor does the extreme
minuteness of the gemmules, which can hardly differ much in nature from the
lowest and simplest organisms, render it improbable that they should grow and
multiply. A great authority, Dr. Beale (27/45. 'Disease Germs' page 20.), says
"that minute yeast cells are capable of throwing off buds or gemmules, much
less than the 1/100000 of an inch in diameter;" and these he thinks are
"capable of subdivision practically ad infinitum."

A particle of small-pox matter, so minute as to be borne by the wind, must
multiply itself many thousandfold in a person thus inoculated; and so with the
contagious matter of scarlet fever. (27/46. See some very interesting papers
on this subject by Dr. Beale in 'Medical Times and Gazette' September 9, 1865
pages 273, 330.) It has recently been ascertained (27/47. Third Report of the
R. Comm. on the Cattle Plague as quoted in 'Gardener's Chronicle' 1866 page
446.) that a minute portion of the mucous discharge from an animal affected
with rinderpest, if placed in the blood of a healthy ox, increases so fast
that in a short space of time "the whole mass of blood, weighing many pounds,
is infected, and every small particle of that blood contains enough poison to
give, within less than forty-eight hours, the disease to another animal."

The retention of free and undeveloped gemmules in the same body from early
youth to old age will appear improbable, but we should remember how long seeds
lie dormant in the earth and buds in the bark of a tree. Their transmission
from generation to generation will appear still more improbable; but here
again we should remember that many rudimentary and useless organs have been
transmitted during an indefinite number of generations. We shall presently see
how well the long-continued transmission of undeveloped gemmules explains many
facts.

As each unit, or group of similar units, throughout the body, casts off its
gemmules, and as all are contained within the smallest ovule, and within each
spermatozoon or pollen-grain, and as some animals and plants produce an
astonishing number of pollen-grains and ovules (27/48. Mr. F. Buckland found
6,867,840 eggs in a cod-fish ('Land and Water' 1868 page 62). An Ascaris
produces about 64,000,000 eggs (Carpenter's 'Comp. Phys.' 1854 page 590). Mr.
J. Scott, of the Royal Botanic Garden of Edinburgh, calculated, in the same
manner as I have done for some British Orchids ('Fertilisation of Orchids'
page 344), the number of seeds in a capsule of an Acropera and found the
number to be 371,250. Now this plant produces several flowers on a raceme, and
many racemes during a season. In an allied genus, Gongora, Mr. Scott has seen
twenty capsules produced on a single raceme; ten such racemes on the Acropera
would yield above seventy-four millions of seed.), the number and minuteness
of the gemmules must be something inconceivable. But considering how minute
the molecules are, and how many go to the formation of the smallest granule of
any ordinary substance, this difficulty with respect to the gemmules is not
insuperable. From the data arrived at by Sir W. Thomson, my son George finds
that a cube of 1/10000 of an inch of glass or water must consist of between 16
million millions, and 131 thousand million million molecules. No doubt the
molecules of which an organism is formed are larger, from being more complex,
than those of an inorganic substance, and probably many molecules go to the
formation of a gemmule; but when we bear in mind that a cube of 1/10000 of an
inch is much smaller than any pollen-grain, ovule or bud, we can see what a
vast number of gemmules one of these bodies might contain.

The gemmules derived from each part or organ must be thoroughly dispersed
throughout the whole system. We know, for instance, that even a minute
fragment of a leaf of a Begonia will reproduce the whole plant; and that if a
fresh-water worm is chopped into small pieces, each will reproduce the whole
animal. Considering also the minuteness of the gemmules and the permeability
of all organic tissues, the thorough dispersion of the gemmules is not
surprising. That matter may be readily transferred without the aid of vessels
from part to part of the body, we have a good instance in a case recorded by
Sir J. Paget of a lady, whose hair lost its colour at each successive attack
of neuralgia and recovered it again in the course of a few days. With plants,
however, and probably with compound animals, such as corals, the gemmules do
not ordinarily spread from bud to bud, but are confined to the parts developed
from each separate bud; and of this fact no explanation can be given.

The assumed elective affinity of each gemmule for that particular cell which
precedes it in due order of development is supported by many analogies. In all
ordinary cases of sexual reproduction, the male and female elements certainly
have a mutual affinity for each other: thus, it is believed that about ten
thousand species of Compositae exist, and there can be no doubt that if the
pollen of all these species could be simultaneously or successively placed on
the stigma of any one species, this one would elect with unerring certainty
its own pollen. This elective capacity is all the more wonderful, as it must
have been acquired since the many species of this great group of plants
branched off from a common progenitor. On any view of the nature of sexual
reproduction, the formative matter of each part contained within the ovules
and the male element act on each other by some law of special affinity, so
that corresponding parts affect one another; thus, a calf produced from a
short-horned cow by a long-horned bull has its horns affected by the union of
the two forms, and the offspring from two birds with differently coloured
tails have their tails affected.

The various tissues of the body plainly show, as many physiologists have
insisted (27/49. Paget 'Lectures on Pathology' page 27; Virchow 'Cellular
Pathology' translated by Dr. Chance pages 123, 126, 294. Claude Bernard 'Des
Tissus Vivants' pages 177, 210, 337; Muller 'Physiology' English translation
page 290.), an affinity for special organic substances, whether natural or
foreign to the body. We see this in the cells of the kidneys attracting urea
from the blood; in curare affecting certain nerves; Lytta vesicatoria the
kidneys; and the poisonous matter of various diseases, as small-pox, scarlet-
fever, hooping-cough, glanders, and hydrophobia, affecting certain definite
parts of the body. It has also been assumed that the development of each
gemmule depends on its union with another cell or unit which has just
commenced its development, and which precedes it in due order of growth. That
the formative matter within the pollen of plants, which by our hypothesis
consists of gemmules, can unite with and modify the partially developed cells
of the mother-plant, we have clearly seen in the section devoted to this
subject. As the tissues of plants are formed, as far as is known, only by the
proliferation of pre-existing cells, we must conclude that the gemmules
derived from the foreign pollen do not become developed into new and separate
cells, but penetrate and modify the nascent cells of the mother-plant. This
process may be compared with what takes place in the act of ordinary
fertilisation, during which the contents of the pollen-tubes penetrate the
closed embryonic sac within the ovule, and determine the development of the
embryo. According to this view, the cells of the mother-plant may almost
literally be said to be fertilised by the gemmules derived from the foreign
pollen. In this case and in all others the proper gemmules must combine in due
order with pre-existing nascent cells, owing to their elective affinities. A
slight difference in nature between the gemmules and the nascent cells would
be far from interfering with their mutual union and development, for we well
know in the case of ordinary reproduction that such slight differentiation in
the sexual elements favours in a marked manner their union and subsequent
development, as well as the vigour of the offspring thus produced.

Thus far we have been able by the aid of our hypothesis to throw some obscure
light on the problems which have come before us; but it must be confessed that
many points remain altogether doubtful. Thus it is useless to speculate at
what period of development each unit of the body casts off its gemmules, as
the whole subject of the development of the various tissues is as yet far from
clear. We do not know whether the gemmules are merely collected by some
unknown means at certain seasons within the reproductive organs, or whether
after being thus collected they rapidly multiply there, as the flow of blood
to these organs at each breeding season seems to render probable. Nor do we
know why the gemmules collect to form buds in certain definite places, leading
to the symmetrical growth of trees and corals. We have no means of deciding
whether the ordinary wear and tear of the tissues is made good by means of
gemmules, or merely by the proliferation of pre-existing cells. If the
gemmules are thus consumed, as seems probable from the intimate connection
between the repair of waste, regrowth, and development, and more especially
from the periodical changes which many male animals undergo in colour and
structure, then some light would be thrown on the phenomena of old age, with
its lessened power of reproduction and of the repair of injuries, and on the
obscure subject of longevity. The fact of castrated animals, which do not cast
off innumerable gemmules in the act of reproduction, not being longer-lived
than perfect males, seems opposed to the belief that gemmules are consumed in
the ordinary repair of wasted tissues; unless indeed the gemmules after being
collected in small numbers within the reproductive organs are there largely
multiplied. (27/50. Prof. Ray Lankester has discussed several of the points
here referred to as bearing on pangenesis, in his interesting essay, 'On
Comparative Longevity in Man and the Lower Animals' 1870 pages 33, 77, etc.)

That the same cells or units may live for a long period and continue
multiplying without being modified by their union with free gemmules of any
kind, is probable from such cases as that of the spur of a cock which grew to
an enormous size when grafted into the ear of an ox. How far units are
modified during their normal growth by absorbing peculiar nutriment from the
surrounding tissues, independently of their union with gemmules of a distinct
nature, is another doubtful point. (27/51. Dr. Ross refers to this subject in
his 'Graft Theory of Disease' 1872 page 53.) We shall appreciate this
difficulty by calling to mind what complex yet symmetrical growths the cells
of plants yield when inoculated by the poison of a gall-insect. With animals
various polypoid excrescences and tumours are generally admitted (27/52.
Virchow 'Cellular Pathology' translated by Dr. Chance 1860 pages 60, 162, 245,
441, 454.) to be the direct product, through proliferation, of normal cells
which have become abnormal. In the regular growth and repair of bones, the
tissues undergo, as Virchow remarks (27/53. Ibid pages 412-426.), a whole
series of permutations and substitutions. "The cartilage cells may be
converted by a direct transformation into marrow-cells, and continue as such;
or they may first be converted into osseous and then into medullary tissue; or
lastly, they may first be converted into marrow and then into bone. So
variable are the permutations of these tissues, in themselves so nearly
allied, and yet in their external appearance so completely distinct." But as
these tissues thus change their nature at any age, without any obvious change
in their nutrition, we must suppose in accordance with our hypothesis that
gemmules derived from one kind of tissue combine with the cells of another
kind, and cause the successive modifications.

We have good reason to believe that several gemmules are requisite for the
development of one and the same unit or cell; for we cannot otherwise
understand the insufficiency of a single or even of two or three pollen-grains
or spermatozoa. But we are far from knowing whether the gemmules of all the
units are free and separate from one another, or whether some are from the
first united into small aggregates. A feather, for instance, is a complex
structure, and, as each separate part is liable to inherited variations, I
conclude that each feather generates a large number of gemmules; but it is
possible that these may be aggregated into a compound gemmule. The same remark
applies to the petals of flowers, which are sometimes highly complex
structures, with each ridge and hollow contrived for a special purpose, so
that each part must have been separately modified, and the modifications
transmitted; consequently, separate gemmules, according to our hypothesis,
must have been thrown off from each cell or unit. But, as we sometimes see
half an anther or a small portion of a filament becoming petali-form, or parts
or mere stripes of the calyx assuming the colour and texture of the corolla,
it is probable that with petals the gemmules of each cell are not aggregated
together into a compound gemmule, but are free and separate. Even in so simple
a case as that of a perfect cell, with its protoplasmic contents, nucleus,
nucleolus, and walls, we do not know whether or not its development depends on
a compound gemmule derived from each part. (27/54. See some good criticisms on
this head by Delpino and by Mr. G.H. Lewes in the 'Fortnightly Review'
November 1, 1868 page 509.)

Having now endeavoured to show that the several foregoing assumptions are to a
certain extent supported by analogous facts, and having alluded to some of the
most doubtful points, we will consider how far the hypothesis brings under a
single point of view the various cases enumerated in the First Part. All the
forms of reproduction graduate into one another and agree in their product;
for it is impossible to distinguish between organisms produced from buds, from
self-division, or from fertilised germs; such organisms are liable to
variations of the same nature and to reversions of the same kind; and as,
according to our hypothesis, all the forms of reproduction depend on the
aggregation of gemmules derived from the whole body, we can understand this
remarkable agreement. Parthenogenesis is no longer wonderful, and if we did
not know that great good followed from the union of the sexual elements
derived from two distinct individuals, the wonder would be that
parthenogenesis did not occur much oftener than it does. On any ordinary
theory of reproduction the formation of graft-hybrids, and the action of the
male element on the tissues of the mother-plant, as well as on the future
progeny of female animals, are great anomalies; but they are intelligible on
our hypothesis. The reproductive organs do not actually create the sexual
elements; they merely determine the aggregation and perhaps the multiplication
of the gemmules in a special manner. These organs, however, together with
their accessory parts, have high functions to perform. They adapt one or both
elements for independent temporary existence, and for mutual union. The
stigmatic secretion acts on the pollen of a plant of the same species in a
wholly different manner to what it does on the pollen of one belonging to a
distinct genus or family. The spermatophores of the Cephalopoda are
wonderfully complex structures, which were formerly mistaken for parasitic
worms; and the spermatozoa of some animals possess attributes which, if
observed in an independent animal, would be put down to instinct guided by
sense-organs,--as when the spermatozoa of an insect find their way into the
minute micropyle of the egg.

The antagonism which has long been observed (27/55. Mr. Herbert Spencer
('Principles of Biology' volume 2 page 430) has fully discussed this
antagonism.), with certain exceptions, between growth and the power of sexual
reproduction (27/56. The male salmon is known to breed at a very early age.
The Triton and Siredon, whilst retaining their larval branchiae, according to
Filippi and Dumeril ('Annals and Mag. of Nat. Hist.' 3rd series 1866 page 157)
are capable of reproduction. Ernst Haeckel has recently ('Monatsbericht Akad.
Wiss. Berlin' February 2, 1865) observed the surprising case of a medusa, with
its reproductive organs active, which produces by budding a widely different
form of medusa; and this latter also has the power of sexual reproduction.
Krohn has shown ('Annals and Mag. of Nat. Hist.' 3rd series volume 19 1862
page 6) that certain other medusae, whilst sexually mature, propagate by
gemmae. See also Kolliker 'Morphologie und Entwickelungsgeschichte des
Pennatulidenstammes' 1872 page 12.)--between the repair of injuries and
gemmation--and with plants, between rapid increase by buds, rhizomes, etc.,
and the production of seed, is partly explained by the gemmules not existing
in sufficient numbers for these processes to be carried on simultaneously.

Hardly any fact in physiology is more wonderful than the power of regrowth;
for instance, that a snail should be able to reproduce its head, or a
salamander its eyes, tail, and legs, exactly at the points where they have
been cut off. Such cases are explained by the presence of gemmules derived
from each part, and disseminated throughout the body. I have heard the process
compared with that of the repair of the broken angles of a crystal by re-
crystallisation; and the two processes have this much in common, that in the
one case the polarity of the molecules is the efficient cause, and in the
other the affinity of the gemmules for particular nascent cells. But we have
here to encounter two objections which apply not only to the regrowth of a
part, or of a bisected individual, but to fissiparous generation and budding.
The first objection is that the part which is reproduced is in the same stage
of development as that of the being which has been operated on or bisected;
and in the case of buds, that the new beings thus produced are in the same
stage as that of the budding parent. Thus a mature salamander, of which the
tail has been cut off, does not reproduce a larval tail; and a crab does not
reproduce a larval leg. In the case of budding it was shown in the first part
of this chapter that the new being thus produced does not retrograde in
development,--that is, does not pass through those earlier stages, which the
fertilised germ has to pass through. Nevertheless, the organisms operated on
or multiplying themselves by buds must, by our hypothesis, include innumerable
gemmules derived from every part or unit of the earlier stages of development;
and why do not such gemmules reproduce the amputated part or the whole body at
a corresponding early stage of development?

The second objection, which has been insisted on by Delpino, is that the
tissues, for instance, of a mature salamander or crab, of which a limb has
been removed, are already differentiated and have passed through their whole
course of development; and how can such tissues in accordance with our
hypothesis attract and combine with the gemmules of the part which is to be
reproduced? In answer to these two objections we must bear in mind the
evidence which has been advanced, showing that at least in a large number of
cases the power of regrowth is a localised faculty, acquired for the sake of
repairing special injuries to which each particular creature is liable; and in
the case of buds or fissiparous generation, for the sake of quickly
multiplying the organism at a period of life when it can be supported in large
numbers. These considerations lead us to believe that in all such cases a
stock of nascent cells or of partially developed gemmules are retained for
this special purpose either locally or throughout the body, ready to combine
with the gemmules derived from the cells which come next in due succession. If
this be admitted we have a sufficient answer to the above two objections.
Anyhow, pangenesis seems to throw a considerable amount of light on the
wonderful power of regrowth.

It follows, also, from the view just given, that the sexual elements differ
from buds in not including nascent cells or gemmules in a somewhat advanced
stage of development, so that only the gemmules belonging to the earliest
stages are first developed. As young animals and those which stand low in the
scale generally have a much greater capacity for regrowth than older and
higher animals, it would also appear that they retain cells in a nascent
state, or partially developed gemmules, more readily than do animals which
have already passed through a long series of developmental changes. I may here
add that although ovules can be detected in most or all female animals at an
extremely early age, there is no reason to doubt that gemmules derived from
parts modified during maturity can pass into the ovules.

With respect to hybridism, pangenesis agrees well with most of the ascertained
facts. We must believe, as previously shown, that several gemmules are
requisite for the development of each cell or unit. But from the occurrence of
parthenogenesis, more especially from those cases in which an embryo is only
partially formed, we may infer that the female element generally includes
gemmules in nearly sufficient number for independent development, so that when
united with the male element the gemmules are superabundant. Now, when two
species or races are crossed reciprocally, the offspring do not commonly
differ, and this shows that the sexual elements agree in power, in accordance
with the view that both include the same gemmules. Hybrids and mongrels are
also generally intermediate in character between the two parent-forms, yet
occasionally they closely resemble one parent in one part and the other parent
in another part, or even in their whole structure: nor is this difficult to
understand on the admission that the gemmules in the fertilised germ are
superabundant in number, and that those derived from one parent may have some
advantage in number, affinity, or vigour over those derived from the other
parent. Crossed forms sometimes exhibit the colour or other characters of
either parent in stripes or blotches; and this occurs in the first generation,
or through reversion in succeeding bud and seminal generations, of which fact
several instances were given in the eleventh chapter. In these cases we must
follow Naudin (27/57. See his excellent discussion on this subject in
'Nouvelles Archives du Museum' tome 1 page 151.) and admit that the "essence"
or "element" of the two species,--terms which I should translate into the
gemmules,--have an affinity for their own kind, and thus separate themselves
into distinct stripes or blotches; and reasons were given, when discussing in
the fifteenth chapter the incompatibility of certain characters to unite, for
believing in such mutual affinity. When two forms are crossed, one is not
rarely found to be prepotent in the transmission of its characters over the
other; and this we can explain by again assuming that the one form has some
advantage over the other in the number, vigour, or affinity of its gemmules.
In some cases, however, certain characters are present in the one form and
latent in the other; for instance, there is a latent tendency in all pigeons
to become blue, and, when a blue pigeon is crossed with one of any other
colour, the blue tint is generally prepotent. The explanation of this form of
prepotency will be obvious when we come to the consideration of Reversion.

When two distinct species are crossed, it is notorious that they do not yield
the full or proper number of offspring; and we can only say on this head that,
as the development of each organism depends on such nicely-balanced affinities
between a host of gemmules and nascent cells, we need not feel at all
surprised that the commixture of gemmules derived from two distinct species
should lead to partial or complete failure of development. With respect to the
sterility of hybrids produced from the union of two distinct species, it was
shown in the nineteenth chapter that this depends exclusively on the
reproductive organs being specially affected; but why these organs should be
thus affected we do not know, any more than why unnatural conditions of life,
though compatible with health, should cause sterility; or why continued close
interbreeding, or the illegitimate unions of heterostyled plants, induce the
same result. The conclusion that the reproductive organs alone are affected,
and not the whole organisation, agrees perfectly with the unimpaired or even
increased capacity in hybrid plants for propagation by buds; for this implies,
according to our hypothesis, that the cells of the hybrids throw off
hybridised gemmules, which become aggregated into buds, but fail to become
aggregated within the reproductive organs, so as to form the sexual elements.
In a similar manner many plants, when placed under unnatural conditions, fail
to produce seed, but can readily be propagated by buds. We shall presently see
that pangenesis agrees well with the strong tendency to reversion exhibited by
all crossed animals and plants.

Each organism reaches maturity through a longer or shorter course of growth
and development: the former term being confined to mere increase of size, and
development to changed structure. The changes may be small and insensibly
slow, as when a child grows into a man, or many, abrupt, and slight, as in the
metamorphoses of certain ephemerous insects, or, again, few and strongly-
marked, as with most other insects. Each newly formed part may be moulded
within a previously existing and corresponding part, and in this case it will
appear, falsely as I believe, to be developed from the old part; or it may be
formed within a distinct part of the body, as in the extreme cases of
metagenesis. An eye, for instance, may be developed at a spot where no eye
previously existed. We have also seen that allied organic beings in the course
of their metamorphoses sometimes attain nearly the same structure after
passing through widely different forms; or conversely, after passing through
nearly the same early forms, arrive at widely different mature forms. In these
cases it is very difficult to accept the common view that the first-formed
cells or units possess the inherent power, independently of any external
agency, of producing new structures wholly different in form, position, and
function. But all these cases become plain on the hypothesis of pangenesis.
The units, during each stage of development, throw off gemmules, which,
multiplying, are transmitted to the offspring. In the offspring, as soon as
any particular cell or unit becomes partially developed, it unites with (or,
to speak metaphorically, is fertilised by) the gemmule of the next succeeding
cell, and so onwards. But organisms have often been subjected to changed
conditions of life at a certain stage of their development, and in consequence
have been slightly modified; and the gemmules cast off from such modified
parts will tend to reproduce parts modified in the same manner. This process
may be repeated until the structure of the part becomes greatly changed at one
particular stage of development, but this will not necessarily affect other
parts, whether previously or subsequently formed. In this manner we can
understand the remarkable independence of structure in the successive
metamorphoses, and especially in the successive metageneses of many animals.
In the case, however, of diseases which supervene during old age, subsequently
to the ordinary period of procreation, and which, nevertheless, are sometimes
inherited, as occurs with brain and heart complaints, we must suppose that the
organs were affected at an early age and threw off at this period affected
gemmules; but that the affection became visible or injurious only after the
prolonged growth, in the strict sense of the word, of the part. In all the
changes of structure which regularly supervene during old age, we probably see
the effects of deteriorated growth, and not of true development.

The principle of the independent formation of each part, owing to the union of
the proper gemmules with certain nascent cells, together with the
superabundance of the gemmules derived from both parents, and the subsequent
self-multiplication of the gemmules, throws light on a widely different group
of facts, which on any ordinary view of development appears very strange. I
allude to organs which are abnormally transposed or multiplied. For instance,
a curious case has been recorded by Dr. Elliott Coues (27/58. 'Proc. Boston
Soc. of Nat. Hist.' republished in 'Scientific Opinion' November 10, 1869 page
488.) of a monstrous chicken with a perfect additional RIGHT leg articulated
to the LEFT side of the pelvis. Gold-fish often have supernumerary fins placed
on various parts of their bodies. When the tail of a lizard is broken off, a
double tail is sometimes reproduced; and when the foot of the salamander was
divided longitudinally by Bonnet, additional digits were occasionally formed.
Valentin injured the caudal extremity of an embryo, and three days afterwards
it produced rudiments of a double pelvis and of double hind-limbs. (27/59.
Todd 'Cyclop. of Anat. and Phys.' volume 4 1849-52 page 975.) When frogs,
toads, etc., are born with their limbs doubled, as sometimes happens, the
doubling, as Gervais remarks (27/60. 'Compte Rendus' November 14, 1865 page
800.), cannot be due to the complete fusion of two embryos, with the exception
of the limbs, for the larvae are limbless. The same argument is applicable
(27/61. As previously remarked by Quatrefages in his 'Metamorphoses de
l'Homme' etc. 1862 page 129.) to certain insects produced with multiple legs
or antennae, for these are metamorphosed from apodal or antennae-less larvae.
Alphonse Milne-Edwards (27/62. Gunther 'Zoological Record' 1864 page 279.) has
described the curious case of a crustacean in which one eye-peduncle
supported, instead of a complete eye, only an imperfect cornea, and out of the
centre of this a portion of an antenna was developed. A case has been recorded
(27/63. Sedgwick 'Medico-Chirurg. Review' April 1863 page 454.) of a man who
had during both dentitions a double tooth in place of the left second incisor,
and he inherited this peculiarity from his paternal grandfather. Several cases
are known (27/64. Isid. Geoffroy Saint-Hilaire 'Hist. des Anomalies' tome 1
1832 pages 435, 657; and tome 2 page 560.) of additional teeth having been
developed in the orbit of the eye, and, more especially with horses, in the
palate. Hairs occasionally appear in strange situations, as "within the
substance of the brain." (27/65. Virchow 'Cellular Pathology' 1860 page 66.)
Certain breeds of sheep bear a whole crowd of horns on their foreheads. As
many as five spurs have been seen on both legs of certain Game-fowls. In the
Polish fowl the male is ornamented with a topknot of hackles like those on his
neck, whilst the female has a top-knot formed of common feathers. In feather-
footed pigeons and fowls, feathers like those on the wing arise from the outer
side of the legs and toes. Even the elemental parts of the same feather may be
transposed; for in the Sebastopol goose, barbules are developed on the divided
filaments of the shaft. Imperfect nails sometimes appear on the stumps of the
amputated fingers of man (27/66. Muller 'Phys.' English Translation volume 1
1833 page 407. A case of this kind has lately been communicated to me.) and it
is an interesting fact that with the snake-like Saurians, which present a
series with more and more imperfect limbs, the terminations of the phalanges
first disappear, "the nails becoming transferred to their proximal remnants,
or even to parts which are not phalanges." (27/67. Dr. Furbringer 'Die Knochen
etc. bei den schlangenahnlichen Sauriern' as reviewed in 'Journal of Anat. and
Phys.' May 1870 page 286.)

Analogous cases are of such frequent occurrence with plants that they do not
strike us with sufficient surprise. Supernumerary petals, stamens, and
pistils, are often produced. I have seen a leaflet low down in the compound
leaf of Vicia sativa replaced by a tendril; and a tendril possesses many
peculiar properties, such as spontaneous movement and irritability. The calyx
sometimes assumes, either wholly or by stripes, the colour and texture of the
corolla. Stamens are so frequently converted into petals, more or less
completely, that such cases are passed over as not deserving notice; but as
petals have special functions to perform, namely, to protect the included
organs, to attract insects, and in not a few cases to guide their entrance by
well-adapted contrivances, we can hardly account for the conversion of stamens
into petals merely by unnatural or superfluous nourishment. Again, the edge of
a petal may occasionally be found including one of the highest products of the
plant, namely, pollen; for instance, I have seen the pollen-mass of an Ophrys,
which is a very complex structure, developed in the edge of an upper petal.
The segments of the calyx of the common pea have been observed partially
converted into carpels, including ovules, and with their tips converted into
stigmas. Mr. Salter and Dr. Maxwell Masters have found pollen within the
ovules of the passion-flower and of the rose. Buds may be developed in the
most unnatural positions, as on the petal of a flower. Numerous analogous
facts could be given. (27/68. Moquin-Tandon 'Teratologie Veg.' 1841 pages 218,
220, 353. For the case of the pea see 'Gardener's Chronicle' 1866 page 897.
With respect to pollen within ovules see Dr. Masters in 'Science Review'
October 1873 page 369. The Rev. J.M. Berkeley describes a bud developed on a
petal of a Clarkia in 'Gardener's Chronicle' April 28, 1866.)

I do not know how physiologists look at such facts as the foregoing. According
to the doctrine of pangenesis, the gemmules of the transposed organs become
developed in the wrong place, from uniting with wrong cells or aggregates of
cells during their nascent state; and this would follow from a slight
modification in their elective affinities. Nor ought we to feel much surprise
at the affinities of cells and gemmules varying, when we remember the many
curious cases given in the seventeenth chapter, of plants which absolutely
refuse to be fertilised by their own pollen, though abundantly fertile with
that of any other individual of the same species, and in some cases only with
that of a distinct species. It is manifest that the sexual elective affinities
of such plants--to use the term employed by Gartner--have been modified. As
the cells of adjoining or homologous parts will have nearly the same nature,
they will be particularly liable to acquire by variation each other's elective
affinities; and we can thus understand to a certain extent such cases as a
crowd of horns on the heads of certain sheep, of several spurs on the legs of
fowls, hackle-like feathers on the heads of the males of other fowls, and with
the pigeon wing-like feathers on their legs and membrane between their toes,
for the leg is the homologue of the wing. As all the organs of plants are
homologous and spring from a common axis, it is natural that they should be
eminently liable to transposition. It ought to be observed that when any
compound part, such as an additional limb or an antenna, springs from a false
position, it is only necessary that the few first gemmules should be wrongly
attached; for these whilst developing would attract other gemmules in due
succession, as in the regrowth of an amputated limb. When parts which are
homologous and similar in structure, as the vertebrae of snakes or the stamens
of polyandrous flowers, etc., are repeated many times in the same organism,
closely allied gemmules must be extremely numerous, as well as the points to
which they ought to become united; and, in accordance with the foregoing
views, we can to a certain extent understand Isid. Geoffroy Saint-Hilaire's
law, that parts, which are already multiple, are extremely liable to vary in
number.

Variability often depends, as I have attempted to show, on the reproductive
organs being injuriously affected by changed conditions; and in this case the
gemmules derived from the various parts of the body are probably aggregated in
an irregular manner, some superfluous and others deficient. Whether a
superabundance of gemmules would lead to the increased size of any part cannot
be told; but we can see that their partial deficiency, without necessarily
leading to the entire abortion of the part, might cause considerable
modifications; for in the same manner as plants, if their own pollen be
excluded, are easily hybridised, so, in the case of cells, if the properly
succeeding gemmules were absent, they would probably combine easily with other
and allied gemmules, as we have just seen with transposed parts.

In variations caused by the direct action of changed conditions, of which
several instances have been given, certain parts of the body are directly
affected by the new conditions, and consequently throw off modified gemmules,
which are transmitted to the offspring. On any ordinary view it is
unintelligible how changed conditions, whether acting on the embryo, the young
or the adult, can cause inherited modifications. It is equally or even more
unintelligible on any ordinary view, how the effects of the long-continued use
or disuse of a part, or of changed habits of body or mind, can be inherited. A
more perplexing problem can hardly be proposed; but on our view we have only
to suppose that certain cells become at last structurally modified; and that
these throw off similarly modified gemmules. This may occur at any period of
development, and the modification will be inherited at a corresponding period;
for the modified gemmules will unite in all ordinary cases with the proper
preceding cells, and will consequently be developed at the same period at
which the modification first arose. With respect to mental habits or
instincts, we are so profoundly ignorant of the relation between the brain and
the power of thought that we do not know positively whether a fixed habit
induces any change in the nervous system, though this seems highly probable;
but when such habit or other mental attribute, or insanity, is inherited, we
must believe that some actual modification is transmitted (27/69. See some
remarks to this effect by Sir H. Holland in his 'Medical Notes' 1839 page
32.); and this implies, according to our hypothesis, that gemmules derived
from modified nerve-cells are transmitted to the offspring.

It is generally necessary that an organism should be exposed during several
generations to changed conditions or habits, in order that any modification
thus acquired should appear in the offspring. This may be partly due to the
changes not being at first marked enough to catch attention, but this
explanation is insufficient; and I can account for the fact only by the
assumption, which we shall see under the head of reversion is strongly
supported, that gemmules derived from each unmodified unit or part are
transmitted in large numbers to successive generations, and that the gemmules
derived from the same unit after it has been modified go on multiplying under
the same favourable conditions which first caused the modification, until at
last they become sufficiently numerous to overpower and supplant the old
gemmules.

A difficulty may be here noticed; we have seen that there is an important
difference in the frequency, though not in the nature, of the variations in
plants propagated by sexual and asexual generation. As far as variability
depends on the imperfect action of the reproductive organs under changed
conditions, we can at once see why plants propagated asexually should be far
less variable than those propagated sexually. With respect to the direct
action of changed conditions, we know that organisms produced from buds do not
pass through the earlier phases of development; they will therefore not be
exposed, at that period of life when structure is most readily modified, to
the various causes inducing variability in the same manner as are embryos and
young larval forms; but whether this is a sufficient explanation I know not.

With respect to variations due to reversion, there is a similar difference
between plants propagated from buds and seeds. Many varieties can be
propagated securely by buds, but generally or invariably revert to their
parent-forms by seed. So, also, hybridised plants can be multiplied to any
extent by buds, but are continually liable to reversion by seed,--that is, to
the loss of their hybrid or intermediate character. I can offer no
satisfactory explanation of these facts. Plants with variegated leaves,
phloxes with striped flowers, barberries with seedless fruit, can all be
securely propagated by buds taken from the stem or branches; but buds from the
roots of these plants almost invariably lose their character and revert to
their former condition. This latter fact is also inexplicable, unless buds
developed from the roots are as distinct from those on the stem, as is one bud
on the stem from another, and we know that these latter behave like
independent organisms.

Finally, we see that on the hypothesis of pangenesis variability depends on at
least two distinct groups of causes. Firstly, the deficiency, superabundance,
and transposition of gemmules, and the redevelopment of those which have long
been dormant; the gemmules themselves not having undergone any modification;
and such changes will amply account for much fluctuating variability.
Secondly, the direct action of changed conditions on the organisation, and of
the increased use or disuse of parts; and in this case the gemmules from the
modified units will be themselves modified, and, when sufficiently multiplied,
will supplant the old gemmules and be developed into new structures.

Turning now to the laws of Inheritance. If we suppose a homogeneous gelatinous
protozoon to vary and assume a reddish colour, a minute separated particle
would naturally, as it grew to full size, retain the same colour; and we
should have the simplest form of inheritance. (27/70. This is the view taken
by Prof. Hackel in his 'Generelle Morphologie' b. 2 s. 171, who says:
"Lediglich die partielle Identitat der specifisch constituirten Materie im
elterlichen und im kindlichen Organismus, die Theilung dieser Materie bei der
Fortpflanzung, ist die Ursache der Erblichkeit.") Precisely the same view may
be extended to the infinitely numerous and diversified units of which the
whole body of one of the higher animals is composed; the separated particles
being our gemmules. We have already sufficiently discussed by implication, the
important principle of inheritance at corresponding ages. Inheritance as
limited by sex and by the season of the year (for instance with animals
becoming white in winter) is intelligible if we may believe that the elective
affinities of the units of the body are slightly different in the two sexes,
especially at maturity, and in one or both sexes at different seasons, so that
they unite with different gemmules. It should be remembered that, in the
discussion on the abnormal transposition of organs, we have seen reason to
believe that such elective affinities are readily modified. But I shall soon
have to recur to sexual and seasonal inheritance. These several laws are
therefore explicable to a large extent through pangenesis, and on no other
hypothesis which has as yet been advanced.

But it appears at first sight a fatal objection to our hypothesis that a part
or organ may be removed during several successive generations, and if the
operation be not followed by disease, the lost part reappears in the
offspring. Dogs and horses formerly had their tails docked during many
generations without any inherited effect; although, as we have seen, there is
some reason to believe that the tailless condition of certain sheep-dogs is
due to such inheritance. Circumcision has been practised by the Jews from a
remote period, and in most cases the effects of the operation are not visible
in the offspring; though some maintain that an inherited effect does
occasionally appear. If inheritance depends on the presence of disseminated
gemmules derived from all the units of the body, why does not the amputation
or mutilation of a part, especially if effected on both sexes, invariably
affect the offspring? The answer in accordance with our hypothesis probably is
that gemmules multiply and are transmitted during a long series of
generations--as we see in the reappearance of zebrine stripes on the horse--in
the reappearance of muscles and other structures in man which are proper to
his lowly organised progenitors, and in many other such cases. Therefore the
long-continued inheritance of a part which has been removed during many
generations is no real anomaly, for gemmules formerly derived from the part
are multiplied and transmitted from generation to generation.

We have as yet spoken only of the removal of parts, when not followed by
morbid action: but when the operation is thus followed, it is certain that the
deficiency is sometimes inherited. In a former chapter instances were given,
as of a cow, the loss of whose horn was followed by suppuration, and her
calves were destitute of a horn on the same side of their heads. But the
evidence which admits of no doubt is that given by Brown-Sequard with respect
to guinea-pigs, which after their sciatic nerves had been divided, gnawed off
their own gangrenous toes, and the toes of their offspring were deficient in
at least thirteen instances on the corresponding feet. The inheritance of the
lost part in several of these cases is all the more remarkable as only one
parent was affected; but we know that a congenital deficiency is often
transmitted from one parent alone--for instance, the offspring of hornless
cattle of either sex, when crossed with perfect animals, are often hornless.
How, then, in accordance with our hypothesis can we account for mutilations
being sometimes strongly inherited, if they are followed by diseased action?
The answer probably is that all the gemmules of the mutilated or amputated
part are gradually attracted to the diseased surface during the reparative
process, and are there destroyed by the morbid action.

A few words must be added on the complete abortion of organs. When a part
becomes diminished by disuse prolonged during many generations, the principle
of economy of growth, together with intercrossing, will tend to reduce it
still further as previously explained, but this will not account for the
complete or almost complete obliteration of, for instance, a minute papilla of
cellular tissue representing a pistil, or of a microscopically minute nodule
of bone representing a tooth. In certain cases of suppression not yet
completed, in which a rudiment occasionally reappears through reversion,
dispersed gemmules derived from this part must, according to our view, still
exist; we must therefore suppose that the cells, in union with which the
rudiment was formerly developed, fail in their affinity for such gemmules,
except in the occasional cases of reversion. But when the abortion is complete
and final, the gemmules themselves no doubt perish; nor is this in any way
improbable, for, though a vast number of active and long-dormant gemmules are
nourished in each living creature, yet there must be some limit to their
number; and it appears natural that gemmules derived from reduced and useless
parts would be more liable to perish than those freshly derived from other
parts which are still in full functional activity.

The last subject that need be discussed, namely, Reversion, rests on the
principle that transmission and development, though generally acting in
conjunction, are distinct powers; and the transmission of gemmules with their
subsequent development shows us how this is possible. We plainly see the
distinction in the many cases in which a grandfather transmits to his
grandson, through his daughter, characters which she does not, or cannot,
possess. But before proceeding, it will be advisable to say a few words about
latent or dormant characters. Most, or perhaps all, of the secondary
characters, which appertain to one sex, lie dormant in the other sex; that is,
gemmules capable of development into the secondary male sexual characters are
included within the female; and conversely female characters in the male: we
have evidence of this in certain masculine characters, both corporeal and
mental, appearing in the female, when her ovaria are diseased or when they
fail to act from old age. In like manner female characters appear in castrated
males, as in the shape of the horns of the ox, and in the absence of horns in
castrated stags. Even a slight change in the conditions of life due to
confinement sometimes suffices to prevent the development of masculine
characters in male animals, although their reproductive organs are not
permanently injured. In the many cases in which masculine characters are
periodically renewed, these are latent at other seasons; inheritance as
limited by sex and season being here combined. Again, masculine characters
generally lie dormant in male animals until they arrive at the proper age for
reproduction. The curious case formerly given of a Hen which assumed the
masculine characters, not of her own breed but of a remote progenitor,
illustrates the close connection between latent sexual characters and ordinary
reversion.

With those animals and plants which habitually produce several forms, as with
certain butterflies described by Mr. Wallace, in which three female forms and
one male form co-exist, or, as with the trimorphic species of Lythrum and
Oxalis, gemmules capable of reproducing these different forms must be latent
in each individual.

Insects are occasionally produced with one side or one quarter of their bodies
like that of the male, with the other half or three-quarters like that of the
female. In such cases the two sides are sometimes wonderfully different in
structure, and are separated from each other by a sharp line. As gemmules
derived from every part are present in each individual of both sexes, it must
be the elective affinities of the nascent cells which in these cases differ
abnormally on the two sides of the body. Almost the same principle comes into
play with those animals, for instance, certain gasteropods and Verruca amongst
cirripedes, which normally have the two sides of the body constructed on a
very different plan; and yet a nearly equal number of individuals have either
side modified in the same remarkable manner.

Reversion, in the ordinary sense of the word, acts so incessantly, that it
evidently forms an essential part of the general law of inheritance. It occurs
with beings, however propagated, whether by buds or seminal generation, and
sometimes may be observed with advancing age even in the same individual. The
tendency to reversion is often induced by a change of conditions, and in the
plainest manner by crossing. Crossed forms of the first generation are
generally nearly intermediate in character between their two parents; but in
the next generation the offspring commonly revert to one or both of their
grandparents, and occasionally to more remote ancestors. How can we account
for these facts? Each unit in a hybrid must throw off, according to the
doctrine of pangenesis, an abundance of hybridised gemmules, for crossed
plants can be readily and largely propagated by buds; but by the same
hypothesis dormant gemmules derived from both pure parent-forms are likewise
present; and as these gemmules retain their normal condition, they would, it
is probable, be enabled to multiply largely during the lifetime of each
hybrid. Consequently the sexual elements of a hybrid will include both pure
and hybridised gemmules; and when two hybrids pair, the combination of pure
gemmules derived from the one hybrid with the pure gemmules of the same parts
derived from the other, would necessarily lead to complete reversion of
character; and it is, perhaps, not too bold a supposition that unmodified and
undeteriorated gemmules of the same nature would be especially apt to combine.
Pure gemmules in combination with hybridised gemmules would lead to partial
reversion. And lastly, hybridised gemmules derived from both parent-hybrids
would simply reproduce the original hybrid form. (27/71. In these remarks I,
in fact, follow Naudin, who speaks of the elements or essences of the two
species which are crossed. See his excellent memoir in the 'Nouvelles Archives
du Museum' tome 1 page 151.) All these cases and degrees of reversion
incessantly occur.

It was shown in the fifteenth chapter that certain characters are antagonistic
to each other or do not readily blend; hence, when two animals with
antagonistic characters are crossed, it might well happen that a sufficiency
of gemmules in the male alone for the reproduction of his peculiar characters,
and in the female alone for the reproduction of her peculiar characters, would
not be present; and in this case dormant gemmules derived from the same part
in some remote progenitor might easily gain the ascendancy, and cause the
reappearance of the long-lost character. For instance, when black and white
pigeons, or black and white fowls, are crossed,--colours which do not readily
blend,--blue plumage in the one case, evidently derived from the rock-pigeon,
and red plumage in the other case, derived from the wild jungle-cock,
occasionally reappear. With uncrossed breeds the same result follows, under
conditions which favour the multiplication and development of certain dormant
gemmules, as when animals become feral and revert to their pristine character.
A certain number of gemmules being requisite for the development of each
character, as is known to be the case from several spermatozoa or pollen-
grains being necessary for fertilisation, and time favouring their
multiplication, will perhaps account for the curious cases, insisted on by Mr.
Sedgwick, of certain diseases which regularly appear in alternate generations.
This likewise holds good, more or less strictly, with other weakly inherited
modifications. Hence, as I have heard it remarked, certain diseases appear to
gain strength by the intermission of a generation. The transmission of dormant
gemmules during many successive generations is hardly in itself more
improbable, as previously remarked, than the retention during many ages of
rudimentary organs, or even only of a tendency to the production of a
rudiment; but there is no reason to suppose that dormant gemmules can be
transmitted and propagated for ever. Excessively minute and numerous as they
are believed to be, an infinite number derived, during a long course of
modification and descent, from each unit of each progenitor, could not be
supported or nourished by the organism. But it does not seem improbable that
certain gemmules, under favourable conditions, should be retained and go on
multiplying for a much longer period than others. Finally, on the view here
given, we certainly gain some insight into the wonderful fact that the child
may depart from the type of both its parents, and resemble its grandparents,
or ancestors removed by many hundreds of generations.

CONCLUSION.

The hypothesis of Pangenesis, as applied to the several great classes of facts
just discussed, no doubt is extremely complex, but so are the facts. The chief
assumption is that all the units of the body, besides having the universally
admitted power of growing by self-division, throw off minute gemmules which
are dispersed through the system. Nor can this assumption be considered as too
bold, for we know from the cases of graft-hybridisation that formative matter
of some kind is present in the tissues of plants, which is capable of
combining with that included in another individual, and of reproducing every
unit of the whole organism. But we have further to assume that the gemmules
grow, multiply, and aggregate themselves into buds and the sexual elements;
their development depending on their union with other nascent cells or units.
They are also believed to be capable of transmission in a dormant state, like
seeds in the ground, to successive generations.

In a highly-organised animal, the gemmules thrown off from each different unit
throughout the body must be inconceivably numerous and minute. Each unit of
each part, as it changes during development, and we know that some insects
undergo at least twenty metamorphoses, must throw off its gemmules. But the
same cells may long continue to increase by self-division, and even become
modified by absorbing peculiar nutriment, without necessarily throwing off
modified gemmules. All organic beings, moreover, include many dormant gemmules
derived from their grandparents and more remote progenitors, but not from all
their progenitors. These almost infinitely numerous and minute gemmules are
contained within each bud, ovule, spermatozoon, and pollen-grain. Such an
admission will be declared impossible; but number and size are only relative
difficulties. Independent organisms exist which are barely visible under the
highest powers of the microscope, and their germs must be excessively minute.
Particles of infectious matter, so small as to be wafted by the wind or to
adhere to smooth paper, will multiply so rapidly as to infect within a short
time the whole body of a large animal. We should also reflect on the admitted
number and minuteness of the molecules composing a particle of ordinary
matter. The difficulty, therefore, which at first appears insurmountable, of
believing in the existence of gemmules so numerous and small as they must be
according to our hypothesis, has no great weight.

The units of the body are generally admitted by physiologists to be
autonomous. I go one step further and assume that they throw off reproductive
gemmules. Thus an organism does not generate its kind as a whole, but each
separate unit generates its kind. It has often been said by naturalists that
each cell of a plant has the potential capacity of reproducing the whole
plant; but it has this power only in virtue of containing gemmules derived
from every part. When a cell or unit is from some cause modified, the gemmules
derived from it will be in like manner modified. If our hypothesis be
provisionally accepted, we must look at all the forms of asexual reproduction,
whether occurring at maturity or during youth, as fundamentally the same, and
dependent on the mutual aggregation and multiplication of the gemmules. The
regrowth of an amputated limb and the healing of a wound is the same process
partially carried out. Buds apparently include nascent cells, belonging to
that stage of development at which the budding occurs, and these cells are
ready to unite with the gemmules derived from the next succeeding cells. The
sexual elements, on the other hand, do not include such nascent cells; and the
male and female elements taken separately do not contain a sufficient number
of gemmules for independent development, except in the cases of
parthenogenesis. The development of each being, including all the forms of
metamorphosis and metagenesis, depends on the presence of gemmules thrown off
at each period of life, and on their development, at a corresponding period,
in union with preceding cells. Such cells may be said to be fertilised by the
gemmules which come next in due order of development. Thus the act of ordinary
impregnation and the development of each part in each being are closely
analogous processes. The child, strictly speaking, does not grow into the man,
but includes germs which slowly and successively become developed and form the
man. In the child, as well as in the adult, each part generates the same part.
Inheritance must be looked at as merely a form of growth, like the self-
division of a lowly-organised unicellular organism. Reversion depends on the
transmission from the forefather to his descendants of dormant gemmules, which
occasionally become developed under certain known or unknown conditions. Each
animal and plant may be compared with a bed of soil full of seeds, some of
which soon germinate, some lie dormant for a period, whilst others perish.
When we hear it said that a man carries in his constitution the seeds of an
inherited disease, there is much truth in the expression. No other attempt, as
far as I am aware, has been made, imperfect as this confessedly is, to connect
under one point of view these several grand classes of facts. An organic being
is a microcosm--a little universe, formed of a host of self-propagating
organisms, inconceivably minute and numerous as the stars in heaven.


CHAPTER 2.XXVIII.

CONCLUDING REMARKS.

DOMESTICATION.
NATURE AND CAUSES OF VARIABILITY.
SELECTION.
DIVERGENCE AND DISTINCTNESS OF CHARACTER.
EXTINCTION OF RACES.
CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN.
ANTIQUITY OF CERTAIN RACES.
THE QUESTION WHETHER EACH PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED.

As summaries have been added to nearly all the chapters, and as, in the
chapter on pangenesis, various subjects, such as the forms of reproduction,
inheritance, reversion, the causes and laws of variability, etc., have been
recently discussed, I will here only make a few general remarks on the more
important conclusions which may be deduced from the multifarious details given
throughout this work.

Savages in all parts of the world easily succeed in taming wild animals; and
those inhabiting any country or island, when first visited by man, would
probably have been still more easily tamed. Complete subjugation generally
depends on an animal being social in its habits, and on receiving man as the
chief of the herd or family. In order that an animal should be domesticated it
must be fertile under changed conditions of life, and this is far from being
always the case. An animal would not have been worth the labour of
domestication, at least during early times, unless of service to man. From
these circumstances the number of domesticated animals has never been large.
With respect to plants, I have shown in the ninth chapter how their varied
uses were probably first discovered, and the early steps in their cultivation.
Man could not have known, when he first domesticated an animal or plant,
whether it would flourish and multiply when transported to other countries,
therefore he could not have been thus influenced in his choice. We see that
the close adaptation of the reindeer and camel to extremely cold and hot
countries has not prevented their domestication. Still less could man have
foreseen whether his animals and plants would vary in succeeding generations
and thus give birth to new races; and the small capacity of variability in the
goose has not prevented its domestication from a remote epoch.

With extremely few exceptions, all animals and plants which have been long
domesticated have varied greatly. It matters not under what climate, or for
what purpose they are kept, whether as food for man or beast, for draught or
hunting, for clothing or mere pleasure,--under all these circumstances races
have been produced which differ more from one another than do the forms which
in a state of nature are ranked as different species. Why certain animals and
plants have varied more under domestication than others we do not know, any
more than why some are rendered more sterile than others under changed
conditions of life. But we have to judge of the amount of variation which our
domestic productions have undergone, chiefly by the number and amount of
difference between the races which have been formed, and we can often clearly
see why many and distinct races have not been formed, namely, because slight
successive variations have not been steadily accumulated; and such variations
will never be accumulated if an animal or plant be not closely observed, much
valued, and kept in large numbers.

The fluctuating, and, as far as we can judge, never-ending variability of our
domesticated productions,--the plasticity of almost their whole organisation,-
-is one of the most important lessons which we learn from the numerous details
given in the earlier chapters of this work. Yet domesticated animals and
plants can hardly have been exposed to greater changes in their conditions of
life than have many natural species during the incessant geological,
geographical, and climatal changes to which the world has been subject; but
domesticated productions will often have been exposed to more sudden changes
and to less continuously uniform conditions. As man has domesticated so many
animals and plants belonging to widely different classes, and as he certainly
did not choose with prophetic instinct those species which would vary most, we
may infer that all natural species, if exposed to analogous conditions, would,
on an average, vary to the same degree. Few men at the present day will
maintain that animals and plants were created with a tendency to vary, which
long remained dormant, in order that fanciers in after ages might rear, for
instance, curious breeds of the fowl, pigeon, or canary-bird.

From several causes it is difficult to judge of the amount of modification
which our domestic productions have undergone. In some cases the primitive
parent-stock has become extinct; or it cannot be recognised with certainty,
owing to its supposed descendants having been so much modified. In other cases
two or more closely-allied forms, after being domesticated, have crossed; and
then it is difficult to estimate how much of the character of the present
descendants ought to be attributed to variation, and how much to the influence
of the several parent-stocks. But the degree to which our domesticated breeds
have been modified by the crossing of distinct species has probably been much
exaggerated by some authors. A few individuals of one form would seldom
permanently affect another form existing in greater numbers; for, without
careful selection, the stain of the foreign blood would soon be obliterated,
and during early and barbarous times, when our animals were first
domesticated, such care would seldom have been taken.

There is good reason to believe in the case of the dog, ox, pig, and of some
other animals, that several of our races are descended from distinct wild
prototypes; nevertheless the belief in the multiple origin of our domesticated
animals has been extended by some few naturalists and by many breeders to an
unauthorised extent. Breeders refuse to look at the whole subject under a
single point of view; I have heard it said by a man, who maintained that our
fowls were descended from at least half-a-dozen aboriginal species, that the
evidence of the common origin of pigeons, ducks and rabbits, was of no avail
with respect to fowls. Breeders overlook the improbability of many species
having been domesticated at an early and barbarous period. They do not
consider the improbability of species having existed in a state of nature
which, if they resembled our present domestic breeds, would have been highly
abnormal in comparison with all their congeners. They maintain that certain
species, which formerly existed, have become extinct, or are now unknown,
although formerly known. The assumption of so much recent extinction is no
difficulty in their eyes; for they do not judge of its probability by the
facility or difficulty of the extinction of other closely-allied wild forms.
Lastly, they often ignore the whole subject of geographical distribution as
completely as if it were the result of chance.

Although from the reasons just assigned it is often difficult to judge
accurately of the amount of change which our domesticated productions have
undergone, yet this can be ascertained in the cases in which all the breeds
are known to be descended from a single species,--as with the pigeon, duck,
rabbit, and almost certainly with the fowl; and by the aid of analogy this can
be judged of to a certain extent with domesticated animals descended from
several wild stocks. It is impossible to read the details given in the earlier
chapters and in many published works, or to visit our various exhibitions,
without being deeply impressed with the extreme variability of our
domesticated animals and cultivated plants. No part of the organisation
escapes the tendency to vary. The variations generally affect parts of small
vital or physiological importance, but so it is with the differences which
exist between closely-allied species. In these unimportant characters there is
often a greater difference between the breeds of the same species than between
the natural species of the same genus, as Isidore Geoffroy has shown to be the
case with size, and as is often the case with the colour, texture, form, etc.,
of the hair, feathers, horns, and other dermal appendages.

It has often been asserted that important parts never vary under
domestication, but this is a complete error. Look at the skull of the pig in
any one of the highly improved breeds, with the occipital condyles and other
parts greatly modified; or look at that of the niata ox. Or, again, in the
several breeds of the rabbit, observe the elongated skull, with the
differently shaped occipital foramen, atlas, and other cervical vertebrae. The
whole shape of the brain, together with the skull, has been modified in Polish
fowls; in other breeds of the fowl the number of the vertebrae and the forms
of the cervical vertebrae have been changed. In certain pigeons the shape of
the lower jaw, the relative length of the tongue, the size of the nostrils and
eyelids, the number and shape of the ribs, the form and size of the
oesophagus, have all varied. In certain quadrupeds the length of the
intestines has been much increased or diminished. With plants we see wonderful
differences in the stones of various fruits. In the Cucurbitaceae several
highly important characters have varied, such as the sessile position of the
stigmas on the ovarium, the position of the carpels, and the projection of the
ovarium out of the receptacle. But it would be useless to run through the many
facts given in the earlier chapters.

It is notorious how greatly the mental disposition, tastes, habits, consensual
movements, loquacity or silence, and tone of voice have varied and been
inherited in our domesticated animals. The dog offers the most striking
instance of changed mental attributes, and these differences cannot be
accounted for by descent from distinct wild types.

New characters may appear and old ones disappear at any stage of development,
being inherited at a corresponding stage. We see this in the difference
between the eggs, the down on the chickens and the first plumage of the
various breeds of the fowl; and still more plainly in the differences between
the caterpillars and cocoons of the various breeds of the silk-moth. These
facts, simple as they appear, throw light on the differences between the
larval and adult states of allied natural species, and on the whole great
subject of embryology. New characters first appearing late in life are apt to
become attached exclusively to that sex in which they first arose, or they may
be developed in a much higher degree in this than in the other sex; or again,
after having become attached to one sex, they may be transferred to the
opposite sex. These facts, and more especially the circumstance that new
characters seem to be particularly liable, from some unknown cause, to become
attached to the male sex, have an important bearing on the acquirement of
secondary sexual characters by animals in a state of nature.

It has sometimes been said that our domestic races do not differ in
constitutional peculiarities, but this cannot be maintained. In our improved
cattle, pigs, etc., the period of maturity, including that of the second
dentition, has been much hastened. The period of gestation varies much, and
has been modified in a fixed manner in one or two cases. In some breeds of
poultry and pigeons the period at which the down and the first plumage are
acquired, differs. The number of moults through which the larvae of silk-moths
pass, varies. The tendency to fatten, to yield much milk, to produce many
young or eggs at a birth or during life, differs in different breeds. We find
different degrees of adaptation to climate, and different tendencies to
certain diseases, to the attacks of parasites, and to the action of certain
vegetable poisons. With plants, adaptation to certain soils, the power of
resisting frost, the period of flowering and fruiting, the duration of life,
the period of shedding the leaves or of retaining them throughout the winter,
the proportion and nature of certain chemical compounds in the tissues or
seeds, all vary.

There is, however, one important constitutional difference between domestic
races and species; I refer to the sterility which almost invariably follows,
in a greater or less degree, when species are crossed, and to the perfect
fertility of the most distinct domestic races, with the exception of a very
few plants, when similarly crossed. It is certainly a most remarkable fact
that many closely-allied species, which in appearance differ extremely little,
should yield when crossed only a few more or less sterile offspring, or none
at all; whilst domestic races which differ conspicuously from each other are,
when united, remarkably fertile, and yield perfectly fertile offspring. But
this fact is not in reality so inexplicable as it at first appears. In the
first place, it was clearly shown in the nineteenth chapter that the sterility
of crossed species does not depend chiefly on differences in their external
structure or general constitution, but on differences in the reproductive
system, analogous to those which cause the lessened fertility of the
illegitimate unions of dimorphic and trimorphic plants. In the second place,
the Pallasian doctrine, that species after having been long domesticated lose
their natural tendency to sterility when crossed, has been shown to be highly
probable or almost certain. We cannot avoid this conclusion when we reflect on
the parentage and present fertility of the several breeds of the dog, of the
Indian or humped and European cattle, and of the two chief kinds of pigs.
Hence it would be unreasonable to expect that races formed under domestication
should acquire sterility when crossed, whilst at the same time we admit that
domestication eliminates the normal sterility of crossed species. Why with
closely-allied species their reproductive systems should almost invariably
have been modified in so peculiar a manner as to be mutually incapable of
acting on each other--though in unequal degrees in the two sexes, as shown by
the difference in fertility between reciprocal crosses of the same species--we
do not know, but may with much probability infer the cause to be as follows.
Most natural species have been habituated to nearly uniform conditions of life
for an incomparably longer time than have domestic races; and we positively
know that changed conditions exert an especial and powerful influence on the
reproductive system. Hence this difference may well account for the difference
in the power of reproduction between domestic races when crossed and species
when crossed. It is probably in chief part owing to the same cause that
domestic races can be suddenly transported from one climate to another, or
placed under widely different conditions, and yet retain in most cases their
fertility unimpaired; whilst a multitude of species subjected to lesser
changes are rendered incapable of breeding.

The offspring of crossed domestic races and of crossed species resemble each
other in most respects, with the one important exception of fertility; they
often partake in the same unequal degree of the characters of their parents,
one of which is often prepotent over the other; and they are liable to
reversion of the same kind. By successive crosses one species may be made to
absorb completely another, and so it notoriously is with races. The latter
resemble species in many other ways. They sometimes inherit their newly-
acquired characters almost or even quite as firmly as species. The conditions
leading to variability and the laws governing its nature appear to be the same
in both. Varieties can be classed in groups under groups, like species under
genera, and these under families and orders; and the classification may be
either artificial,--that is, founded on any arbitrary character,--or natural.
With varieties a natural classification is certainly founded, and with species
is apparently founded, on community of descent, together with the amount of
modification which the forms have undergone. The characters by which domestic
varieties differ from one another are more variable than those distinguishing
species, though hardly more so than with certain polymorphic species; but this
greater degree of variability is not surprising, as varieties have generally
been exposed within recent times to fluctuating conditions of life, and are
much more liable to have been crossed; they are also in many cases still
undergoing, or have recently undergone, modification by man's methodical or
unconscious selection.

Domestic varieties as a general rule certainly differ from one another in less
important parts than do species; and when important differences occur, they
are seldom firmly fixed; but this fact is intelligible, if we consider man's
method of selection. In the living animal or plant he cannot observe internal
modifications in the more important organs; nor does he regard them as long as
they are compatible with health and life. What does the breeder care about any
slight change in the molar teeth of his pigs, or for an additional molar tooth
in the dog; or for any change in the intestinal canal or other internal organ?
The breeder cares for the flesh of his cattle being well marbled with fat, and
for an accumulation of fat within the abdomen of his sheep, and this he has
effected. What would the floriculturist care for any change in the structure
of the ovarium or of the ovules? As important internal organs are certainly
liable to numerous slight variations, and as these would probably be
transmitted, for many strange monstrosities are inherited, man could
undoubtedly effect a certain amount of change in these organs. When he has
produced any modification in an important part, he has generally done so
unintentionally, in correlation with some other conspicuous part. For
instance, he has given ridges and protuberances to the skulls of fowls, by
attending to the form of the comb, or to the plume of feathers on the head. By
attending to the external form of the pouter-pigeon, he has enormously
increased the size of the oesophagus, and has added to the number of the ribs,
and given them greater breadth. With the carrier-pigeon, by increasing through
steady selection the wattles on the upper mandible, he has greatly modified
the form of the lower mandible; and so in many other cases. Natural species,
on the other hand, have been modified exclusively for their own good, to fit
them for infinitely diversified conditions of life, to avoid enemies of all
kinds, and to struggle against a host of competitors. Hence, under such
complex conditions, it would often happen that modifications of the most
varied kinds, in important as well as in unimportant parts, would be
advantageous or even necessary; and they would slowly but surely be acquired
through the survival of the fittest. Still more important is the fact that
various indirect modifications would likewise arise through the law of
correlated variation.

Domestic breeds often have an abnormal or semi-monstrous character, as amongst
dogs, the Italian greyhound, bulldog, Blenheim spaniel, and bloodhound,--some
breeds of cattle and pigs,--several breeds of the fowl,--and the chief breeds
of the pigeon. In such abnormal breeds, parts which differ but slightly or not
at all in the allied natural species, have been greatly modified. This may be
accounted for by man's often selecting, especially at first, conspicuous and
semi-monstrous deviations of structure. We should, however, be cautious in
deciding what deviations ought to be called monstrous: there can hardly be a
doubt that, if the brush of horse-like hair on the breast of the turkey-cock
had first appeared in the domesticated bird, it would have been considered as
a monstrosity; the great plume of feathers on the head of the Polish cock has
been thus designated, though plumes are common on the heads of many kinds of
birds; we might call the wattle or corrugated skin round the base of the beak
of the English carrier-pigeon a monstrosity, but we do not thus speak of the
globular fleshy excrescence at the base of the beak of the Carpophaga
oceanica.

Some authors have drawn a wide distinction between artificial and natural
breeds; although in extreme cases the distinction is plain, in many other
cases it is arbitrary; the difference depending chiefly on the kind of
selection which has been applied. Artificial breeds are those which have been
intentionally improved by man; they frequently have an unnatural appearance,
and are especially liable to lose their characters through reversion and
continued variability. The so-called natural breeds, on the other hand, are
those which are found in semi-civilised countries, and which formerly
inhabited separate districts in nearly all the European kingdoms. They have
been rarely acted on by man's intentional selection; more frequently by
unconscious selection, and partly by natural selection, for animals kept in
semi-civilised countries have to provide largely for their own wants. Such
natural breeds will also have been directly acted on by the differences,
though slight, in the surrounding conditions.

There is a much more important distinction between our several breeds, namely,
in some having originated from a strongly-marked or semi-monstrous deviation
of structure, which, however, may subsequently have been augmented by
selection; whilst others have been formed in so slow and insensible a manner,
that if we could see their early progenitors we should hardly be able to say
when or how the breed first arose. From the history of the racehorse,
greyhound, gamecock, etc., and from their general appearance, we may feel
nearly confident that they were formed by a slow process of improvement; and
we know that this has been the case with the carrier-pigeon, as well as with
some other pigeons. On the other hand, it is certain that the ancon and
mauchamp breeds of sheep, and almost certain that the niata cattle, turnspit,
and pug-dogs, jumper and frizzled fowls, short-faced tumbler pigeons, hook-
billed ducks, etc., suddenly appeared in nearly the same state as we now see
them. So it has been with many cultivated plants. The frequency of these cases
is likely to lead to the false belief that natural species have often
originated in the same abrupt manner. But we have no evidence of the
appearance, or at least of the continued procreation, under nature, of abrupt
modifications of structure; and various general reasons could be assigned
against such a belief.

On the other hand, we have abundant evidence of the constant occurrence under
nature of slight individual differences of the most diversified kinds; and we
are thus led to conclude that species have generally originated by the natural
selection of extremely slight differences. This process may be strictly
compared with the slow and gradual improvement of the racehorse, greyhound,
and gamecock. As every detail of structure in each species has to be closely
adapted to its habits of life, it will rarely happen that one part alone will
be modified; but, as was formerly shown, the co-adapted modifications need not
be absolutely simultaneous. Many variations, however, are from the first
connected by the law of correlation. Hence it follows that even closely-allied
species rarely or never differ from one another by one character alone; and
the same remark is to a certain extent applicable to domestic races; for
these, if they differ much, generally differ in many respects.

Some naturalists boldly insist (28/1. Godron 'De l'Espece' 1859 tome 2 page 44
etc.) that species are absolutely distinct productions, never passing by
intermediate links into one another; whilst they maintain that domestic
varieties can always be connected either with one another or with their
parent-forms. But if we could always find the links between the several breeds
of the dog, horse, cattle, sheep, pigs, etc., there would not have been such
incessant doubts whether they were descended from one or several species. The
greyhound genus, if such a term may be used, cannot be closely connected with
any other breed, unless, perhaps, we go back to the ancient Egyptian
monuments. Our English bulldog also forms a very distinct breed. In all these
cases crossed breeds must of course be excluded, for distinct natural species
can thus be likewise connected. By what links can the Cochin fowl be closely
united with others? By searching for breeds still preserved in distant lands,
and by going back to historical records, tumbler-pigeons, carriers, and barbs
can be closely connected with the parent rock-pigeon; but we cannot thus
connect the turbit or the pouter. The degree of distinctness between the
various domestic breeds depends on the amount of modification which they have
undergone, and more especially on the neglect and final extinction of
intermediate and less-valued forms.

It has often been argued that no light is thrown on the changes which natural
species are believed to undergo from the admitted changes of domestic races,
as the latter are said to be mere temporary productions, always reverting, as
soon as they become feral, to their pristine form. This argument has been well
combated by Mr. Wallace (28/2. 'Journal Proc. Linn. Soc.' 1858 volume 3 page
60.) and full details were given in the thirteenth chapter, showing that the
tendency to reversion in feral animals and plants has been greatly
exaggerated, though no doubt it exists to a certain extent. It would be
opposed to all the principles inculcated in this work, if domestic animals,
when exposed to new conditions and compelled to struggle for their own wants
against a host of foreign competitors, were not modified in the course of
time. It should also be remembered that many characters lie latent in all
organic beings, ready to be evolved under fitting conditions; and in breeds
modified within recent times, the tendency to reversion is particularly
strong. But the antiquity of some of our breeds clearly proves that they
remain nearly constant as long as their conditions of life remain the same.

It has been boldly maintained by some authors that the amount of variation to
which our domestic productions are liable is strictly limited; but this is an
assertion resting on little evidence. Whether or not the amount of change in
any particular direction is limited, the tendency to general variability is,
as far as we can judge, unlimited. Cattle, sheep, and pigs have varied under
domestication from the remotest period, as shown by the researches of
Rutimeyer and others; yet these animals have been improved to an unparalleled
degree, within quite recent times, and this implies continued variability of
structure. Wheat, as we know from the remains found in the Swiss lake-
dwellings, is one of the most anciently cultivated plants, yet at the present
day new and better varieties frequently arise. It may be that an ox will never
be produced of larger size and finer proportions, or a racehorse fleeter, than
our present animals, or a gooseberry larger than the London variety; but he
would be a bold man who would assert that the extreme limit in these respects
has been finally attained. With flowers and fruit it has repeatedly been
asserted that perfection has been reached, but the standard has soon been
excelled. A breed of pigeons may never be produced with a beak shorter than
that of the present short-faced tumbler, or with one longer than that of the
English carrier, for these birds have weak constitutions and are bad breeders;
but shortness and length of beak are the points which have been steadily
improved during the last 150 years, and some of the best judges deny that the
goal has yet been reached. From reasons which could be assigned, it is
probable that parts which have now reached their maximum development, might,
after remaining constant during a long period, vary again in the direction of
increase under new conditions of life. But there must be, as Mr. Wallace has
remarked with much truth (28/3. 'The Quarterly Journal of Science' October
1867 page 486.), a limit to change in certain directions both with natural and
domestic productions; for instance, there must be a limit to the fleetness of
any terrestrial animal, as this will be determined by the friction to be
overcome, the weight to be carried, and the power of contraction in the
muscular fibres. The English racehorse may have reached this limit; but it
already surpasses in fleetness its own wild progenitor and all other equine
species. The short-faced tumbler-pigeon has a beak shorter, and the carrier a
beak longer, relatively to the size of their bodies, than that of any natural
species of the family. Our apples, pears and gooseberries bear larger fruit
than those of any natural species of the same genera; and so in many other
cases.

It is not surprising, seeing the great difference between many domestic
breeds, that some few naturalists have concluded that each is descended from a
distinct aboriginal stock, more especially as the principle of selection has
been ignored, and the high antiquity of man, as a breeder of animals, has only
recently become known. Most naturalists, however, freely admit that our
various breeds, however dissimilar, are descended from a single stock,
although they do not know much about the art of breeding, cannot show the
connecting links, nor say where and when the breeds arose. Yet these same
naturalists declare, with an air of philosophical caution, that they will
never admit that one natural species has given birth to another until they
behold all the transitional steps. Fanciers use exactly the same language with
respect to domestic breeds; thus, an author of an excellent treatise on
pigeons says he will never allow that the carrier and fantail are the
descendants of the wild rock-pigeon, until the transitions have "actually been
observed, and can be repeated whenever man chooses to set about the task." No
doubt it is difficult to realise that slight changes added up during long
centuries can produce such great results; but he who wishes to understand the
origin of domestic breeds or of natural species must overcome this difficulty.

The causes which excite and the laws which govern variability have been
discussed so lately, that I need here only enumerate the leading points. As
domesticated organisms are much more liable to slight deviations of structure
and to monstrosities than species living under their natural conditions, and
as widely-ranging species generally vary more than those which inhabit
restricted areas, we may infer that variability mainly depends on changed
conditions of life. We must not overlook the effects of the unequal
combination of the characters derived from both parents, or reversion to
former progenitors. Changed conditions have an especial tendency to render the
reproductive organs more or less impotent, as shown in the chapter devoted to
this subject; and these organs consequently often fail to transmit faithfully
the parental characters. Changed conditions also act directly and definitely
on the organisation, so that all or nearly all the individuals of the same
species thus exposed become modified in the same manner; but why this or that
part is especially affected we can seldom or ever say. In most cases, however,
a change in the conditions seems to act indefinitely, causing diversified
variations in nearly the same manner as exposure to cold or the absorption of
the same poison affects different individuals in different ways. We have
reason to suspect that an habitual excess of highly-nutritious food, or an
excess relatively to the wear and tear of the organisation from exercise, is a
powerful exciting cause of variability. When we see the symmetrical and
complex outgrowths, caused by a minute drop of the poison of a gall-insect, we
may believe that slight changes in the chemical nature of the sap or blood
would lead to extraordinary modifications of structure.

The increased use of a muscle with its various attached parts, and the
increased activity of a gland or other organ, lead to their increased
development. Disuse has a contrary effect. With domesticated productions,
although their organs sometimes become rudimentary through abortion, we have
no reason to suppose that this has ever followed solely from disuse. With
natural species, on the contrary, many organs appear to have been rendered
rudimentary through disuse, aided by the principle of the economy of growth
together with intercrossing. Complete abortion can be accounted for only by
the hypothesis given in the last chapter, namely, the final destruction of the
germs or gemmules of useless parts. This difference between species and
domestic varieties may be partly accounted for by disuse having acted on the
latter for an insufficient length of time, and partly from their exemption
from any severe struggle for existence entailing rigid economy in the
development of each part, to which all species under nature are subjected.
Nevertheless the law of compensation or balancement, which likewise depends on
the economy of growth, apparently has affected to a certain extent our
domesticated productions.

As almost every part of the organisation becomes highly variable under
domestication, and as variations are easily selected both consciously and
unconsciously, it is very difficult to distinguish between the effects of the
selection of indefinite variations and the direct action of the conditions of
life. For instance, it is possible that the feet of our water-dogs and of the
American dogs which have to travel much over the snow, may have become
partially webbed from the stimulus of widely extending their toes; but it is
more probable that the webbing, like the membrane between the toes of certain
pigeons, spontaneously appeared and was afterwards increased by the best
swimmers and the best snow-travellers being preserved durin