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Title: The History of Creation, Vol. I (of 2) - Or the Development of the Earth and its Inhabitants by the - Action of Natural Causes
Author: Haeckel, Ernst, 1834-1919
Language: English
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| Transcriber’s note: |
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| This book was published in two volumes, of which this is the |
| |
| Numbers enclosed in square brackets, e.g. [1], relate to |
| footnotes, which have been placed at the end of the text. |
| Numbers enclosed in parentheses, e.g. (1), relate to works |
| referred to in the text and listed at the end of volume II. |
| |
| In the text versions of these two volumes, words in _italics_ |
| are enclosed in underscores, +bold+ words are enclosed in plus |
| signs, and words in =Gothic script= are enclosed in equal signs. |
| Curly brackets are used to represent subscripts, e.g. k{1}. |
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THE HISTORY OF CREATION.

[Illustration: Development of a Calcareous Sponge (Olynthus).]

THE
HISTORY OF CREATION:

_OR THE DEVELOPMENT OF THE EARTH AND ITS
INHABITANTS BY THE ACTION OF NATURAL CAUSES._

A POPULAR EXPOSITION OF
THE DOCTRINE OF EVOLUTION IN GENERAL, AND OF THAT OF
DARWIN, GOETHE, AND LAMARCK IN PARTICULAR.

FROM THE GERMAN OF
ERNST HAECKEL,
PROFESSOR IN THE UNIVERSITY OF JENA.

THE TRANSLATION REVISED BY
E. RAY LANKESTER, M.A., FELLOW OF EXETER COLLEGE, OXFORD.

_IN TWO VOLUMES._
VOL. I.

NEW YORK:
D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.
1880.

A sense sublime
Of something far more deeply interfused,
Whose dwelling is the light of setting suns,
And the round ocean, and the living air,
And the blue sky, and in the mind of man;
A motion and a spirit that impels
All thinking things, all objects of all thought,
And rolls through all things.

In all things, in all natures, in the stars
Of azure heaven, the unenduring clouds,
In flower and tree, in every pebbly stone
That paves the brooks, the stationary rocks,
The moving waters and the invisible air.

WORDSWORTH.

CONTENTS OF VOL. I.

CHAPTER I.

NATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION,
OR DESCENT-THEORY.
PAGE
General Importance and Essential Nature of the Theory of
Descent as reformed by Darwin.—Its Special Importance to
Biology (Zoology and Botany).—Its Special Importance to
the History of the Natural Development of the Human
Race.—The Theory of Descent as the Non-Miraculous History
of Creation.—Idea of Creation.—Knowledge and
Belief.—History of Creation and History of
Development.—The Connection between the History of
Individual and Palæontological Development.—The Theory of
Purposelessness, or the Science of Rudimentary
Organs.—Useless and Superfluous Arrangements in
Organisms.—Contrast between the two entirely Opposed
Views of Nature: the Monistic (mechanical, causal) and the
Dualistic (teleological, vital).—Proof of the former by
the Theory of Descent.—Unity of Organic and Inorganic
Nature, and the Identity of the Active Causes in
both.—The Importance of the Theory of Descent to the
Monistic Conception of all Nature 1

CHAPTER II.

SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT.
HISTORY OF CREATION ACCORDING TO LINNÆUS.

The Theory of Descent, or Doctrine of Filiation, as the
Monistic Explanation of Organic Natural Phenomena.—Its
Comparison with Newton’s Theory of Gravitation.—Limits of
Scientific Explanation and of Human Knowledge in
general.—All Knowledge founded originally on Sensuous
Experience, _à posteriori_.—Transition of _à posteriori_
knowledge, by inheritance, into _à priori_
knowledge.—Contrast between the Supernatural Hypotheses
of the Creation according to Linnæus, Cuvier, Agassiz,
and the Natural Theories of Development according to
Lamarck, Goethe, and Darwin.—Connection of the former
with the Monistic (mechanical), of the latter with the
Dualistic Conception of the Universe.—Monism and
Materialism.—Scientific and Moral Materialism.—The
History of Creation according to Moses.—Linnæus as the
Founder of the Systematic Description of Nature and
Distinction of Species.—Linnæus’ Classification and
Binary Nomenclature.—Meaning of Linnæus’ Idea of
Species.—His History of Creation.—Linnæus’ view of the
Origin of Species 24

CHAPTER III.

THE HISTORY OF CREATION ACCORDING TO CUVIER
AND AGASSIZ.

General Theoretical Meaning of the Idea of
Species.—Distinction between the Theoretical and
Practical Definition of the Idea of Species.—Cuvier’s
Definition of Species.—Merits of Cuvier as the Founder of
Comparative Anatomy.—Distinction of the Four Principal
Forms (types or branches) of the Animal Kingdom, by Cuvier
and Bär.—Cuvier’s Services to Palæontology.—His
Hypothesis of the Revolutions of our Globe, and the Epochs
of Creation separated by them.—Unknown Supernatural
Causes of the Revolutions, and the subsequent New
Creations.—Agassiz’s Teleological System of Nature.—His
Conception of the Plan of Creation, and its six Categories
(groups in classification).—Agassiz’s Views of the
Creation of Species.—Rude Conception of the Creator as a
man-like being in Agassiz’s Hypothesis of Creation.—Its
internal Inconsistency and Contradictions with the
important Palæontological Laws discovered by Agassiz 47

CHAPTER IV.

THEORY OF DEVELOPMENT ACCORDING TO GOETHE
AND OKEN.

Scientific Insufficiency of all Conceptions of a Creation
of Individual Species.—Necessity of the Counter Theories
of Development.—Historical Survey of the most Important
Theories of Development.—Aristotle.—His Doctrine of
Spontaneous Generation.—The Meaning of
Nature-philosophy.—Goethe.—His Merits as a
Naturalist.—His Metamorphosis of Plants.—His Vertebral
Theory of the Skull.—His Discovery of the Mid Jawbone in
Man.—Goethe’s Interest in the Dispute between Cuvier and
Geoffroy St. Hilaire.—Goethe’s Discovery of the two
Organic Formative Principles, of the Conservative
Principle of Specification (by Inheritance), and of the
Progressive Principle of Transformation (by
Adaptation).—Goethe’s Views of the Common Descent of all
Vertebrate Animals, including Man.—Theory of Development
according to Gottfried Reinhold Treviranus.—His Monistic
Conception of Nature.—Oken.—His
Nature-philosophy.—Oken’s Theory of Protoplasm.—Oken’s
Theory of Infusoria (Cell Theory).—Oken’s Theory of
Development 72

CHAPTER V.

THEORY OF DEVELOPMENT ACCORDING TO KANT AND
LAMARCK.

Kant’s Dualistic Biology.—His Conception of the Origin of
Inorganic Nature by Mechanical Causes, of Organic Nature
by Causes acting for a Definite Purpose.—Contradiction of
this Conception with his leaning towards the Theory of
Descent.—Kant’s Genealogical Theory of Development.—Its
Limitation by his Teleology.—Comparison of Genealogical
Biology with Comparative Philology.—Views in favour of
the Theory of Descent entertained by Leopold Buch, Bär,
Schleiden, Unger, Schaafhausen, Victor Carus,
Büchner.—French Nature-philosophy.—Lamarck’s Philosophic
Zoologique.—Lamarck’s Monistic (mechanical) System of
Nature.—His Views of the Interaction of the two Organic
Formative Tendencies of Inheritance and
Adaptation.—Lamarck’s Conception of Man’s Development
from Ape-like Mammals.—Geoffroy St. Hilaire’s, Naudin’s,
and Lecoq’s Defence of the Theory of Descent.—English
Nature-philosophy.—Views in favour of the Theory of
Descent entertained by Erasmus Darwin, W. Herbert, Grant,
Freke, Herbert Spencer, Hooker, Huxley.—The Double Merit
of Charles Darwin 100

CHAPTER VI.

THEORY OF DEVELOPMENT ACCORDING TO LYELL
AND DARWIN.

Charles Lyell’s Principles of Geology.—His Natural
History of the Earth’s Development.—Origin of the
Greatest Effects through the Multiplication of the
Smallest Causes.—Unlimited Extent of Geological
Periods.—Lyell’s Refutation of Cuvier’s History of
Creation.—The Establishment of the Uninterrupted
Connection of Historical Development by Lyell and
Darwin.—Biographical Notice of Charles Darwin.—His
Scientific Works.—His Theory of Coral
Reefs.—Development of the Theory of Selection.—A Letter
of Darwin’s.—The Contemporaneous Appearance of Darwin’s
and Alfred Wallace’s Theory of Selection.—Darwin’s Study
of Domestic Animals and Cultivated Plants.—Andreas
Wagner’s Notions as to the Special Creation of Cultivated
Organisms for the good of Man.—The Tree of Knowledge in
Paradise.—Comparison between Wild and Cultivated
Organisms.—Darwin’s Study of Domestic
Pigeons.—Importance of Pigeon Breeding.—Common Descent
of all Races of Pigeons 125

CHAPTER VII.

THE THEORY OF SELECTION (DARWINISM).

Darwinism (Theory of Selection) and Lamarckism (Theory of
Descent).—The Process of Artificial Breeding.—Selection
of the Different Individuals for After-breeding.—The
Active Causes of Transmutation.—Change connected with
Food and Transmission by Inheritance connected with
Propagation.—Mechanical Nature of these Two Physiological
Functions.—The Process of Natural Breeding: Selection in
the Struggle for Existence.—Malthus’ Theory of
Population.—The Proportion between the Numbers of
Potential and Actual Individuals of every Species of
Organisms.—General Struggle for Existence, or Competition
to attain the Necessaries of Life.—Transforming Force of
the Struggle for Existence.—Comparison of Natural and
Artificial Breeding.—Selection in the Life of
Man.—Military and Medical Selection 149

CHAPTER VIII.

TRANSMISSION BY INHERITANCE AND PROPAGATION.

Universality of Inheritance and Transmission by
Inheritance.—Special Evidences of the same.—Human Beings
with four, six, or seven Fingers and Toes.—Porcupine
Men.—Transmission of Diseases, especially Diseases of the
Mind.—Original Sin.—Hereditary Monarchies.—Hereditary
Aristocracy.—Hereditary Talents and Mental
Qualities.—Material Causes of Transmission by
Inheritance.—Connection between Transmission by
Inheritance and Propagation.—Spontaneous Generation and
Propagation.—Non-sexual or Monogonous
Propagation.—Propagation by Self-Division.—Monera and
Amœba.—Propagation by the formation of Buds, by the
formation of Germ-Buds, by the formation of
Germ-Cells.—Sexual or Amphigonous Propagation.—Formation
of Hermaphrodites.—Distinction of Sexes, or
Gonochorism.—Virginal Breeding, or
Parthenogenesis.—Material Transmission of Peculiarities
of both Parents to the Child by Sexual
Propagation.—Difference between Transmission by
Inheritance in Sexual and in Asexual Propagation 175

CHAPTER IX.

LAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND
NUTRITION.

Distinction between Conservative and Progressive
Transmission by Inheritance.—Laws of Conservative
Transmission: Transmission of Inherited
Characters.—Uninterrupted or Continuous
Transmission.—Interrupted or Latent
Transmission.—Alternation of
Generations.—Relapse.—Degeneracy.—Sexual
Transmission.—Secondary Sexual Characters.—Mixed or
Amphigonous Transmission.—Hybrids.—Abridged or
Simplified Transmission.—Laws of Progressive Inheritance:
Transmission of Acquired Characters.—Adapted or Acquired
Transmission.—Fixed or Established
Transmission.—Homochronous Transmission (Identity in
Epoch).—Homotopic Transmission (Identity in
Part).—Adaptation and Mutability.—Connection between
Adaptation and Nutrition.—Distinction between Indirect
and Direct Adaptation 203

CHAPTER X.

LAWS OF ADAPTATION.

Laws of Indirect or Potential Adaptation.—Individual
Adaptation.—Monstrous or Sudden Adaptation.—Sexual
Adaptation.—Laws of Direct or Actual
Adaptation.—Universal Adaptation.—Cumulative
Adaptation.—Cumulative Influence of External Conditions
of Existence and Cumulative Counter-Influence of the
Organism.—Free Will.—Use and Non-use of
Organs.—Practice and Habit.—Correlative
Adaptation.—Correlation of Development.—Correlation of
Organs.—Explanation of Indirect or Potential Adaptation
by the Correlation of the Sexual Organs and of the other
parts of the Body.—Divergent Adaptation.—Unlimited or
Infinite Adaptation 227

CHAPTER XI.

NATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION
OF LABOUR AND PROGRESS.

Interaction of the two Organic Formative Causes,
Inheritance and Adaptation.—Natural and Artificial
Selection.—Struggle for Existence, or Competition for the
Necessaries of Life.—Disproportion between the Number of
Possible or Potential, and the Number of Real or Actual
Individuals.—Complicated Correlations of all Neighbouring
Organisms.—Mode of Action in Natural
Selection.—Homochromic Selection as the Cause of
Sympathetic Colourings.—Sexual Selection as the Cause of
the Secondary Sexual Characters.—Law of Separation or
Division of Labour (Polymorphism, Differentiation,
Divergence of Characters).—Transition of Varieties into
Species.—Idea of Species.—Hybridism.—Law of Progress or
Perfecting (Progresses, Teleosis) 252

CHAPTER XII.

LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS.
PHYLOGENY AND ONTOGENY.

Laws of the Development of Mankind: Differentiation and
Perfecting.—Mechanical Cause of these two Fundamental
Laws.—Progress without Differentiation, and
Differentiation without Progress.—Origin of Rudimentary
Organs by Non-use and Discontinuance of
Habit.—Ontogenesis, or Individual Development of
Organisms.—Its General Importance.—Ontogeny, or the
Individual History of Development of Vertebrate Animals,
including Man.—The Fructification of the Egg.—Formation
of the Three Germ Layers.—History of the Development of
the Central Nervous System, of the Extremities, of the
Branchial Arches, and of the Tail of Vertebrate
Animals.—Causal Connection and Parallelism of Ontogenesis
and Phylogenesis, that is, of the Development of
Individuals and Tribes.—Causal Connection of the
Parallelism of Phylogenesis and of Systematic
Development.—Parallelism of the three Organic Series of
Development 280

CHAPTER XIII.

THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE
EARTH. SPONTANEOUS GENERATION. THE CARBON THEORY. THE
PLASTID THEORY.

History of the Development of the Earth.—Kant’s Theory of
the Development of the Universe, or the Cosmological Gas
Theory.—Development of Suns, Planets, and Moons.—First
Origin of Water.—Comparison of Organisms and
Anorgana.—Organic and Inorganic Substances.—Degrees of
Density, or Conditions of Aggregation.—Albuminous
Combinations of Carbon.—Organic and Inorganic
Forms.—Crystals and Formless Organisms without
Organs.Stereometrical Fundamental Forms of Crystals and
of Organisms.—Organic and Inorganic Forces.—Vital
Force.—Growth and Adaptation in Crystals and in
Organisms.—Formative Tendencies of Crystals.—Unity of
Organic and Inorganic Nature.—Spontaneous Generation, or
Archigony.—Autogony and Plasmogony.—Origin of Monera by
Spontaneous Generation.—Origin of Cells from Monera.—The
Cell Theory.—The Plastid Theory.—Plastids, or
Structural-Units.—Cytods and Cells.—Four Different Kinds
of Plastids 316

CHAPTER XIV.

MIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE
ICE-PERIOD OF THE EARTH.

Chorological Facts and Causes.—Origin of most Species in
one Single Locality.—“Centres of Creation.”—Distribution
by Migration.—Active and Passive Migrations of Animals
and Plants.—Means of Transport.—Transport of Germs by
Water and by Wind.—Continual Change of the Area of
Distribution by Elevations and Depressions of the
Ground.—Chorological Importance of Geological
Processes.—Influence of the Change of Climate.—Ice or
Glacial Period.—Its Importance to Chorology.—Importance
of Migrations for the Origin of New Species.—Isolation of
Colonists.—Wagner’s Law of Migration.—Connection between
the Theory of Migration and the Theory of
Selection.—Agreement of its Results with the Theory of
Descent 350

LIST OF ILLUSTRATIONS.

PLATES.
PAGE

Development of a Calcareous Sponge (Olynthus) _Frontispiece_

I.—Life History of a Simplest Organism _To face page_ 184

II., III.—Germs or Embryos of Four Vertebrates ” 306

FIGURES.

1.—Propagation of Moneron 186

2.—Propagation of Amœba 188

3.—Egg of Mammal 189

4.—First Development of Mammal’s Egg 190

5.—The Human Egg Enlarged 297

6.—Development of Mammal’s Egg 299

7.—Embryo of a Mammal or Bird 304

AUTHOR’S PREFACE TO THE ENGLISH EDITION.

I am desirous of prefacing the English edition of the “History of
Creation” with a few remarks which may serve to explain the origin and
object of this book. In the year 1866 I published, under the title
“Generelle Morphologie,” a somewhat comprehensive work, which
constituted the first attempt to apply the general doctrine of
development to the whole range of organic morphology (Anatomy and
Biogenesis), and thus to make use of the vast march onwards which the
genius of Charles Darwin has effected in all biological science by his
reform of the Descent Theory and its establishment through the doctrine
of selection. At the same time, in the “Generelle Morphologie,” the
first attempt was made to introduce the Descent Theory into the
systematic classification of animals and plants, and to found a “natural
system” on the basis of genealogy; that is, to construct hypothetical
pedigrees for the various species of organisms.

The “Generelle Morphologie” found but few readers, for which the
voluminous and unpopular style of treatment, and its too extensive Greek
terminology, may be chiefly to blame. But a proportionately large
measure of approval has met the “Natürliche Schöpfungsgeschichte” in
Germany. This book took its origin in the shorthand notes of a course of
lectures which treated, before a mixed audience and in a popular form,
the most important topics discussed in the “Generelle Morphologie.” The
notes were subsequently revised, and received considerable additions.
The book appeared first in 1868, its fourth edition in 1873, and has
been translated into several languages. I hope that it may also find
sympathy in the fatherland of Darwin, the more so since it contains
special morphological evidence in favour of many of the important
doctrines with which this greatest naturalist of our century has
enriched science. Proud as England may be to be called the fatherland of
Newton, who, with his law of gravitation, brought inorganic nature under
the dominion of natural laws of cause and effect, yet may she with even
greater pride reckon Charles Darwin among her sons—he who solved the
yet harder problem of bringing the complicated phenomena of organic
nature under the sway of the same natural laws.

The reproach which is now oftenest made against the Descent Theory is
that it is not securely founded, not sufficiently proven. Not only its
distinct opponents maintain that there is a want of satisfactory proofs,
but even faint-hearted and wavering adherents declare that Darwin’s
hypothesis is still wanting fundamental proof. Neither the former nor
the latter estimate rightly the immeasurable weight which the great
series of phenomena of comparative anatomy and ontogeny, palæontology
and taxonomy, chorology and œcology, cast into the scale in favour of
the doctrine of filiation. Darwin’s Theory of Selection, which
completely explains the origin of species through the combined action of
Inheritance and Adaptation in the struggle for existence, also appears
to these persons not sufficient. They demand, over and above, that the
descent of species from common ancestral forms shall be proved in a
particular case; that, in contradistinction to the _synthetic_ proofs
adduced for the Descent Theory, the _analytic_ proof of the genealogical
continuity of the several species shall be brought forward.

This “analytical solution of the problem of the origin of species” I
have myself endeavoured to afford in my recently published “Monograph of
the Calcareous Sponges.” For five consecutive years I have investigated
this small but highly instructive group of animals in all its forms in
the most careful manner, and I venture to maintain that the monograph,
which is the result of those studies, is the most complete and accurate
morphological analysis of an entire organic group which has up to this
time been made. Provided with the whole of the material for study as yet
brought together, and assisted by numerous contributions from all parts
of the world, I was able to work over the whole group of organic forms
known as the Calcareous Sponges in that greatest possible degree of
fulness which appeared indispensable for the proof of the common origin
of its species. This particular animal group is especially fitted for
the analytical solution of the species problem, because it presents
exceedingly simple conditions of organisation, because in it the
morphological conditions possess a greatly superior, and the
physiological conditions an inferior, import, and because all species of
Calcispongiæ are remarkable for the fluidity and plasticity of their
form. With a view to these facts, I made two journeys to the sea-coast
(1869 to Norway, 1871 to Dalmatia), in order to study as large a number
of individuals as possible in their natural circumstances, and to
collect specimens for comparison. Of many species, I compared several
hundred individuals in the most careful way. I examined with the
microscope and measured in the most accurate manner the details of form
of all the species. As the final result of these exhaustive and almost
endless examinations and measurements it appeared that “good species,”
in the ordinary dogmatic sense of the systematists, have no existence at
all among the Calcareous Sponges; that the most different forms are
connected one with another by numberless gradational transition forms;
and that all the different species of Calcareous Sponges are derived
from a single exceedingly simple ancestral form, the Olynthus. A drawing
of the Olynthus and its earliest stages of development (observe
especially the highly important Gastrula) is given in the frontispiece
of the present edition. Illustrations of the various structural details
which establish the derivation of all Calcareous Sponges from the
Olynthus, are given in the atlas of sixty plates which accompanies my
monograph of the group. In the gastrula, moreover, is now also found the
common ancestral form from which all the tribes of animals (the lowest
group, that of the protozoa, alone being excepted) can without
difficulty be derived. It is one of the most ancient and important
ancestors of the human race!

If we take for the limitation of genus and species an average standard,
derived from the actual practice of systematists, and apply this to the
whole of the Calcareous Sponges at present known, we can distinguish
about twenty-one genera, with one hundred and eleven species (as I have
done in the second volume of the Monograph). I have, however, shown that
we may draw up, in addition to this, another systematic arrangement
(more nearly agreeing with the arrangement of the Calcispongiæ hitherto
in vogue) which gives thirty-nine genera and two hundred and eighty-nine
species. A systematist who gives a more limited extension to the “ideal
species” might arrange the same series of forms in forty-three genera
and three hundred and eighty-one species, or even in one hundred and
thirteen genera and five hundred and ninety species; another systematist
on the other hand, who takes a wider limit for the “abstract species,”
would use in arranging the same series of forms only three genera, with
twenty-one species, or might even satisfy himself with one genus and
seven species. The delimitation of species and genera appears to be so
arbitrary a matter, on account of endless varieties and transitional
forms in this group, that their number is entirely left to the
subjective taste of the individual systematist. In truth, from the point
of view of the theory of descent, it appears altogether an unimportant
question as to whether we give a wider or a narrower signification to
allied groups of forms—whether we choose, that is to say, to call them
genera or species, varieties or sub-species. The main fact remains
undeniable, viz., the common origin of all the species from one
ancestral form. The many-shaped Calcareous Sponges furnish, in the very
remarkable conditions of their varieties of aggregation (metrocormy), a
body of evidence in favour of this view which could hardly be more
convincing. Not unfrequently the case occurs of several different forms
growing out from a single “stock” or “cormus”—forms which until now
have been regarded by systematists, not only as belonging to different
species, but even to different genera. Fig. 10 in the frontispiece
represents such a composite stock. This solid and tangible piece of
evidence in favour of the common descent of different species ought, one
would think, to satisfy the most determined sceptic!

In point of fact, I have a right to expect of my opponents that they
shall carefully consider the “exact empirical proof” here brought
forward for them, as they have so eagerly demanded. The opponents of the
doctrine of filiation, who have too little power of weighing evidence,
or possess too little knowledge to appreciate the overpowering weight of
proof afforded by the synthetical argument (comparative anatomy,
ontogeny, taxonomy, etc.), may yet be able to follow me along the path
of analytical proof, and attempt to upset the conclusion as to the
common origin of all species of all Calcareous Sponges which I have
given in my Monograph. I must, however, repeat that this conclusion is
based on the most minute investigation of an extraordinarily rich mass
of material,—that it is securely established by thousands of the most
careful microscopical observations, measurements, and comparisons of
every single part, and that thousands of collected microscopic
preparations render, at any moment, the most searching criticism of my
results confirmatory of their correctness. One may hope, then, that
opponents will endeavour to confront me on the ground of this “exact
empiricism,” instead of trying to damn my “nature-philosophical
speculations.” One may hope that they will endeavour to bring forward
some evidence to show that the latter do not follow as the legitimate
consequences of the former. May they, however, spare me the
empty—though by even respectable naturalists oft-repeated—phrase, that
the monistic nature-philosophy, as expounded in the “General
Morphology,” and in the “History of Creation,” is wanting in actual
proofs. The proofs are there. Of course those who turn their eyes away
from them will not see them. Precisely that “exact” form of analytical
proof which the opponents of the descent theory demand is to be found,
by anybody who wishes to find it, in the “Monograph of the Calcareous
Sponges.”

ERNST HEINRICH HAECKEL.

_Jena, June 24th, 1873._

NOTE.

Feeling sure that such a book as Professor Haeckel’s
“Schöpfungsgeschichte” would do a great deal of good, if placed in the
hands of the English reading public, and of commencing students of
Natural History, I gladly undertook to revise for the publishers the
present translation, which was made by a young lady. I have not
attempted to escape a difficulty by ignoring the German names made use
of by Professor Haeckel for classes, orders, and genera, but have
adopted English equivalents. I do not submit these names as a maturely
considered English nomenclature, they appear here simply as necessary
parts of a close rendering of the German work. I do, however, hold that
some such series of English terms is both possible and useful, and do
not doubt—in spite of the pretended hostility of the genius of our
language, and the curious sentimental objection that English names are
_unscientific_—that we shall before long make use of plain English in
speaking of the various groups of plants and animals—much to the gain
of the larger public, and without detriment to the latinized
nomenclature established for the purposes of the professional student.

E. R. L.

_Oxford, October, 1874._

THE HISTORY OF CREATION.

CHAPTER I.

NATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION, OR DESCENT-THEORY.

General Importance and Essential Nature of the Theory of
Descent as reformed by Darwin.—Its Special Importance to
Biology (Zoology and Botany).—Its Special Importance to
the History of the Natural Development of the Human
Race.—The Theory of Descent as the Non-Miraculous
History of Creation.—Idea of Creation.—Knowledge and
Belief.—History of Creation and History of
Development.—The Connection between the History of
Individual and Palæontological Development.—The Theory
of Purposelessness, or the Science of Rudimentary
Organs.—Useless and Superfluous Arrangements in
Organisms.—Contrast between the two entirely opposed
Views of Nature: the Monistic (mechanical, causal) and
the Dualistic (teleological, vital).—Proof of the former
by the Theory of Descent.—Unity of Organic and Inorganic
Nature, and the Identity of the Active Causes in
both.—The Importance of the Theory of Descent to the
Monistic Conception of all Nature.

The intellectual movement to which the impulse was given, thirteen years
ago, by the English naturalist, Charles Darwin, in his celebrated work,
“On the Origin of Species,”(1) has, within this short period, assumed
dimensions which cannot but excite the most universal interest. It is
true the scientific theory set forth in that work, which is commonly
called briefly Darwinism, is only a small fragment of a far more
comprehensive doctrine—a part of the universal Theory of Development,
which embraces in its vast range the whole domain of human knowledge.

But the manner in which Darwin has firmly established the latter by the
former is so convincing, and the direction which has been given by the
unavoidable conclusions of that theory to all our views of the universe,
must appear to every thinking man of such deep significance, that its
general importance cannot be over estimated. There is no doubt that this
immense extension of our intellectual horizon must be looked upon as by
far the most important, and rich in results, among all the numerous and
grand advances which natural science has made in our day.

When our century, with justice, is called the age of natural science,
when we look with pride upon the immensely important progress made in
all its branches, we are generally in the habit of thinking more of
immediate practical results, and less of the extension of our general
knowledge of nature. We call to mind the complete reform, so infinitely
rich in consequences to human intercourse, which has been effected by
the development of machinery, by railways, steamships, telegraphs, and
other inventions of physics. Or we think of the enormous influence which
chemistry has brought to bear upon medicine, agriculture, and upon all
arts and trades.

But much as we may value this influence of modern science upon practical
life, still it must, estimated from a higher and more general point of
view, stand most assuredly below the enormous influence which the
theoretical progress of modern science will have on the entire range of
human knowledge, on our conception of the universe, and on the
perfecting of man’s culture.

Think of the immense revolutions in all our theoretical views which we
owe to the general application of the microscope. Think of the cell
theory, which explains the apparent unity of the human organism as the
combined result of the union of a mass of elementary vital units. Or
consider the immense extension of our theoretical horizon which we owe
to spectral analysis and to the mechanical theory of heat. But among all
these wonderful theoretical advances, the theory wrought out by Darwin
occupies by far the highest rank.

Every one of my readers has heard of the name of Darwin. But most
persons have probably only an imperfect idea of the real value of his
theory. If a reader estimates as of equal value all that has been
written upon Darwin’s memorable work since its appearance, the value of
the theory will appear very doubtful to him, supposing that he has not
been engaged in the organic natural sciences, and has not penetrated
into the inner secrets of zoology and botany. The criticisms of it are
so full of contradictions, and for the most part so defective, that we
ought not to be at all astonished that even now, after the lapse of
thirteen years since the appearance of Darwin’s work, it has not gained
half that importance which is justly due to it, and which sooner or
later it certainly will attain.

Most of the innumerable writings which have been published during these
years, both for and against Darwinism, are the productions of persons
who are entirely wanting in the necessary amount of biological, and
especially of zoological, knowledge. Although almost all of the more
celebrated naturalists of the present day are adherents of the theory,
yet only a few of them have endeavoured to procure its acceptance and
recognition in larger circles. Hence the odd contradictions and the
strange opinions which may still be heard everywhere about Darwinism.
This is the reason which induces me to make Darwin’s theory, and those
further doctrines which are connected with it, the subject of these
pages, which, I hope, will be generally intelligible. I hold it to be
the duty of naturalists, not merely to meditate upon improvements and
discoveries in the narrow circle to which their speciality confines
them, not merely to pore over their one study with love and care, but
also to seek to make the important general results of it fruitful to the
mass, and to assist in spreading the knowledge of physical science among
the people. The highest triumph of the human mind, the true knowledge of
the most general laws of nature, ought not to remain the private
possession of a privileged class of savans, but ought to become the
common property of all mankind.

The theory which, through Darwin, has been placed at the head of all our
knowledge of nature, is usually called the Doctrine of Filiation, or the
Theory of Descent. Others term it the Transmutation Theory. Both
designations are correct. For this doctrine affirms, that _all
organisms_ (viz., all species of animals, all species of plants, which
have ever existed or still exist on the earth) _are derived from one
single, or from a few simple original forms, and that they have
developed themselves from these in the natural course of a gradual
change_. Although this theory of development had already been brought
forward and defended by several great naturalists, and especially by
Lamarck and Goethe, in the beginning of our century, still it was
through Darwin, thirteen years ago, that it received its complete
demonstration and causal foundation; and this is the reason why now it
is commonly and exclusively (though not quite correctly) designated as
_Darwin’s Theory_.

The great and really inestimable value of the Theory of Descent appears
in a different light, accordingly as we merely consider its more
immediate connection with organic natural science, or its larger
influence upon the whole range of man’s knowledge of the universe.
Organic natural science, or Biology, which as Zoology treats of animals,
as Botany of plants, is completely reformed and founded anew by the
Theory of Descent. For by this theory we are made acquainted with the
active causes of organic forms, while up to the present time Zoology and
Botany have simply been occupied with the facts of these forms. We may
therefore also term the theory of descent a _mechanical explanation of
organic forms_, or the science of the true causes of Organic Nature.

As I cannot take for granted that my readers are all familiar with the
terms “organic and inorganic nature,” and as the contrast of both these
natural bodies will, in future, occupy much of our attention, I must say
a few words in explanation of them. We designate as _Organisms_, or
_Organic bodies_, all _living creatures_ or _animated bodies_; therefore
all plants and animals, man included; for in them we can almost always
prove a combination of various parts (instruments or organs) which work
together for the purpose of producing the phenomena of life. Such a
combination we do not find in _Anorgana_, or inorganic natural
bodies—the so-called dead or _inanimate bodies_, such as minerals or
stones, water, the atmospheric air, etc. Organisms always contain
albuminous combinations of carbon in a semi-fluid condition of
aggregation, which are always wanting in the Anorgana. Upon this
important distinction rests the division of all natural history into two
great and principal parts—_Biology_, or the science of Organisms
(Zoology and Botany), and _Anorganology_, or the science of Anorgana
(Mineralogy, Geology, Meteorology, etc.).

The great value of the Theory of Descent in regard to Biology consists,
as I have already remarked, in its explaining to us the origin of
organic forms in a mechanical way, and pointing out their active causes.
But however highly and justly this service of the Theory of Descent may
be valued, yet it is almost eclipsed by the immense importance which a
single necessary inference from it claims for itself alone. This
necessary and unavoidable inference is the theory of the _animal descent
of the human race_.

The determination of the position of man in nature, and of his relations
to the totality of things—this question of all questions for mankind,
as Huxley justly calls it—is finally solved by the knowledge that man
is descended from animals. In consequence of Darwin’s reformed Theory of
Descent, we are now in a position to establish scientifically the
groundwork of a _non-miraculous history of the development of the human
race_. All those who have defended Darwin’s theory, as well as all its
thoughtful opponents, have acknowledged that, as a matter of necessity,
it follows from his theory that the human race, in the first place, must
be traced to ape-like mammals, and further back to the lower vertebrate
animals.

It is true Darwin himself did not express at first this most important
of all the inferences from his theory. In his work, “On the Origin of
Species,” not a word is found about the animal descent of man. The
courageous but cautious naturalist was at that time purposely silent on
the subject, for he anticipated that this most important of all the
conclusions of the Theory of Descent was at the same time the greatest
obstacle to its being generally accepted and acknowledged. Certain it is
that Darwin’s book would have created, from the beginning, even much
more opposition and offence, if this most important inference had at
once been clearly expressed. It was not till twelve years later, in his
work on “The Descent of Man, and Selection in Relation to Sex,” that
Darwin openly acknowledged that far-reaching conclusion, and expressly
declared his entire agreement with those naturalists who had, in the
meantime, themselves formed that conclusion. Manifestly the effect of
this conclusion is immense, and _no_ science will be able to escape from
the consequences. Anthropology, or the science of man, and consequently
all philosophy, are thereby thoroughly reformed in all their various
branches.

It will be a later task in these pages to discuss this special point. I
shall not treat of the theory of the animal descent of man till I have
spoken of Darwin’s theory, and its general foundation and importance. To
express it in one word, that most important, but (to most men) at first
repulsive, conclusion is nothing more than a special deduction, which we
must draw from the general inductive law of the descent theory (now
firmly established), according to the stern commands of inexorable
logic.

Perhaps nothing will make the full meaning of the theory of descent
clearer than calling it the “_non-miraculous history of creation_.” I
have therefore chosen that name for this work. It is, however, correct
only in a certain sense, and it must be borne in mind that, strictly
speaking, the expression “non-miraculous history of creation” contains a
“_contradictio in adjecto_.”

In order to understand this, let us for a moment examine somewhat more
closely what we understand by _creation_. If we understand the creation
to mean the _coming into existence of a body_ by a creative power or
force, we may then either think of the _coming into existence of its
substance_ (corporeal matter), or of the _coming into existence of its
form_ (the corporeal form).

Creation in the former sense, as the _coming into existence of matter_,
does not concern us here at all. This process, if indeed it ever took
place, is completely beyond human comprehension, and can therefore never
become a subject of scientific inquiry. Natural science teaches that
matter is eternal and imperishable, for experience has never shown us
that even the smallest particle of matter has come into existence or
passed away. Where a natural body seems to disappear, as for example by
burning, decaying, evaporation, etc., it merely changes its form, its
physical composition or chemical combination. In like manner the coming
into existence of a natural body, for example, of a crystal, a fungus,
an infusorium, depends merely upon the different particles, which had
before existed in a certain form or combination, assuming a new form or
combination in consequence of changed conditions of existence. But never
yet has an instance been observed of even the smallest particle of
matter having vanished, or even of an atom being added to the already
existing mass. Hence a naturalist can no more imagine the coming into
existence of matter, than he can imagine its disappearance, and he
therefore looks upon the existing quantity of matter in the universe as
a given fact. If any person feels the necessity of conceiving the coming
into existence of this matter as the work of a supernatural creative
power, of the creative force of something outside of matter, we have
nothing to say against it. But we must remark, that thereby not even the
smallest advantage is gained for a scientific knowledge of nature. Such
a conception of an immaterial force, which at the first creates matter,
is an article of faith which has nothing whatever to do with human
science. _Where faith commences, science ends._ Both these arts of the
human mind must be strictly kept apart from each other. Faith has its
origin in the poetic imagination; knowledge, on the other hand,
originates in the reasoning intelligence of man. Science has to pluck
the blessed fruits from the tree of knowledge, unconcerned whether these
conquests trench upon the poetical imaginings of faith or not.

If, therefore, science makes the “history of creation” its highest, most
difficult, and most comprehensive problem, it must accept as its idea of
creation the second explanation of the word, viz., _the coming into
being of the form_ of natural bodies. In this way geology, which tries
to investigate the origin of the inorganic surface of the earth as it
now appears, and the manifold historical changes in the form of the
solid crust of the earth, may be called the history of the creation of
the earth. In like manner, the history of the development of animals and
plants, which investigates the origin of living forms, and the manifold
historical changes in animal and vegetable forms, may be termed the
history of the creation of organisms. As, however, in the idea of
creation, although used in this sense, the unscientific idea of a
creator existing outside of matter, and changing it, may easily creep
in, it will perhaps be better in future to substitute for it the more
accurate term, _development_.

The great value which the _History of Development_ possesses for the
scientific understanding of animal and vegetable forms, has now been
generally acknowledged for many years, and without it it would be
impossible to make any sure progress in organic morphology, or the
theory of forms. But by the history of development, only one part of
this science has generally been understood, namely, that of organic
individuals, usually called Embryology, but more correctly and
comprehensively, _Ontogeny_. But, besides this, there is another history
of development of organic species, genera, and tribes (phyla), which has
the most important relations to the former.

The subject of this is furnished to us by the science of petrifactions,
or palæontology, which shows us that each tribe of animals and plants,
during different periods of the earth’s history, has been represented by
a series of entirely different genera and species. Thus, for example,
the tribe of vertebrated animals was represented by classes of fish,
amphibious animals, reptiles, birds, and mammals, and each of these
groups, at different periods, by quite different kinds. This
palæontological history of the development of organisms, which we may
term _Phylogeny_, stands in the most important and remarkable relation
to the other branch of organic history of development, I mean that of
individuals, or Ontogeny. On the whole, the one runs parallel to the
other. In fact, the history of individual development, or Ontogeny, is a
short and quick recapitulation of palæontological development, or
Phylogeny, dependent on the laws of Inheritance and Adaptation.

As I shall have, later, to explain this most interesting and important
coincidence more fully, I shall not dwell further upon it here, and
merely call attention to the fact that it can only be explained and its
causes understood by the Theory of Descent, while without that theory it
remains completely incomprehensible and inexplicable. The Theory of
Descent in the same way shows us _why_ individual animals and plants
must develop at all, and why they do not come into life at once in a
perfect and developed state. No supernatural history of creation can in
any way explain to us the great mystery of organic development. To this
most weighty question, as well as to all other biological questions, the
Theory of Descent gives us perfectly satisfactory answers—and always
answers which refer to purely mechanical causes, and point to purely
physico-chemical forces as the causes of phenomena which we were
formerly accustomed to ascribe to the direct action of supernatural,
creative forces. Hence, by our theory the mystic veil of the miraculous
and supernatural, which has hitherto been allowed to hide the
complicated phenomena of this branch of natural knowledge, is removed.
All the departments of Botany and Zoology, and especially the most
important portion of the latter, Anthropology, become reasonable. The
dimming mirage of mythological fiction can no longer exist in the clear
sunlight of scientific knowledge.

Of special interest among general biological phenomena are those which
are quite irreconcilable with the usual supposition, that every organism
is the product of a creative power, acting for a definite object.
Nothing in this respect caused the earlier naturalists greater
difficulty than the explanation of the so-called “_rudimentary
organs_,”—those parts in animal and vegetable bodies which really have
no function, which have no physiological importance, and yet exist in
form. These parts deserve the most careful attention, although most
unscientific men know little or nothing about them. Almost every
organism, almost every animal and plant possesses, besides the obviously
useful arrangements of its organization, other arrangements the purpose
of which it is utterly impossible to make out.

Examples of this are found everywhere. In the embryos of many ruminating
animals—among others, in our common cattle—fore-teeth, or incisors,
are placed in the mid-bone of the upper jaw, which never fully develop,
and therefore serve no purpose. The embryos of many whales—which
afterwards possess the well-known whalebone instead of teeth—yet have
before they are born, and while they take no nourishment, teeth in their
jaws, which set of teeth never comes into use. Moreover, most of the
higher animals possess muscles which are never employed; even man has
such rudimentary muscles. Most of us are incapable of moving our ears as
we wish, although the muscles for this movement exist, and although
individual persons who have taken the trouble to exercise these muscles
do succeed in moving their ears. It is still possible, by special
exercise, by the persevering influence of the will upon the nervous
system, to reanimate the almost extinct activity in the existing but
imperfect organs, which are on the road to complete disappearance. On
the other hand, we can no longer do this with another set of small
rudimentary muscles, which still exist in the cartilage of the outer
ear, but which are always perfectly inactive. Our long-eared ancestors
of the tertiary period—apes, semi-apes, and pouched animals, like most
other mammals, moved their large ear-flaps freely and actively; their
muscles were much more strongly developed and of great importance. In a
similar way, many varieties of dogs and rabbits, under the influence of
civilized life, have left off “pricking up” their ears, and thereby have
acquired imperfect auricular muscles and loose-hanging ears, although
their wild ancestors moved their stiff ears in many ways.

Man has also these rudimentary organs on other parts of his body; they
are of no importance to life, and never perform any function. One of the
most remarkable, although the smallest organ of this kind, is the little
crescent-like fold, the so-called “plica semilunaris,” which we have in
the inner corner of the eye, near the root of the nose. This
insignificant fold of skin, which is quite useless to our eye, is the
imperfect remnant of a third inner eyelid which, besides the upper and
under eyelid, is highly developed in other mammals, and in birds and
reptiles. Even our very remote ancestors of the Silurian period, the
Primitive Fishes, seem to have possessed this third eyelid, the
so-called nictitating membrane. For many of their nearest kin, who still
exist in our day but little changed in form, viz., many sharks, possess
a very strong nictitating membrane, which they can draw right across the
whole eyeball, from the inner corner of the eye.

Eyes which do not see form the most striking example of rudimentary
organs. These are found in very many animals, which live in the dark, as
in caves or underground. Their eyes often exist in a well-developed
condition, but they are covered by membrane, so that no ray of light
can enter, and they can never see. Such eyes, without the function of
sight, are found in several species of moles and mice which live
underground, in serpents and lizards, in amphibious animals (Proteus,
Cæcilia), and in fishes; also in numerous invertebrate animals, which
pass their lives in the dark, as do many beetles, crabs, snails, worms,
etc.

An abundance of the most interesting examples of rudimentary organs is
furnished by Comparative Osteology, or the study of the skeletons of
vertebrate animals, one of the most attractive branches of Comparative
Anatomy. In most of the vertebrate animals we find two pairs of limbs on
the body, a pair of fore-legs and a pair of hind-legs. Very often,
however, one or the other pair is imperfect; it is seldom that both are,
as in the case of serpents and some varieties of eel-like fish. But some
serpents, viz., the giant serpents (Boa, Python), have still in the
hinder portion of the body some useless little bones, which are the
remains of lost hind-legs.

In like manner the mammals of the whale tribe (Cetacea), which have only
fore-legs fully developed (breast-fins,), have further back in their
body another pair of utterly superfluous bones, which are remnants of
undeveloped hind-legs. The same thing occurs in many genuine fishes, in
which the hind-legs have in like manner been lost.

Again, in our slow-worm (Anguis), and in some other lizards, no
fore-legs exist, although they have a perfect shoulder apparatus within
their bodies, which should serve as a means of affixing the legs.
Moreover, in various vertebrate animals, the single bones of both pairs
of legs are found in all the different stages of imperfection, and often
the degenerate bones and those muscles belonging to them are partially
preserved, without their being able in any way to perform any function.
The instrument is still there, but it can no longer play.

Moreover, we can, almost as generally, find rudimentary organs in the
blossoms of plants, inasmuch as one part or another of the male organs
of propagation—the stamen and anther, or of the female organs of
propagation—the style, germ, etc.—is more or less imperfect or
abortive. Among these we can trace, in various closely connected species
of plants, the organ in all stages of degeneration. Thus, for example,
the great natural family of lip-blossomed plants (Labiatæ), to which the
balm, peppermint, marjoram, ground-ivy, thyme, etc., belong, are
distinguished by the fact that their mouth-like, two-lipped flower
contains two long and two short stamens. But in many exceptional plants
of this family, _e.g._ in different species of sage, and in the
rosemary, only one pair of stamens is developed; the other pair is more
or less imperfect, or has quite disappeared. Sometimes stamens exist,
but without the anthers, so that they are utterly useless. Less
frequently the rudiment or imperfect remnant of a fifth stamen is found,
physiologically (for the functions of life) quite useless, but
morphologically (for the knowledge of the form and of the natural
relationship) a most valuable organ. In my “General Morphology of
Organisms,”(4) in the chapter on “Purposelessness, or Dysteleology,” I
have given a great number of other examples (Gen. Morph. ii. 226).

No biological phenomenon has perhaps ever placed zoologists or botanists
in greater embarrassment than these rudimentary or abortive organs. They
are instruments without employment, parts of the body which exist
without performing any service—adapted for a purpose, but without in
reality fulfilling that purpose. When we consider the attempts which the
earlier naturalists have made in order to explain this mystery, we can
scarcely help smiling at the strange ideas to which they were led. Being
unable to find a true explanation, they came, for example, to the
conclusion that the Creator had placed these organs there “for the sake
of symmetry,” or they believed that it had appeared unwise and
unsuitable to the Creator (seeing that their nearest kin did possess
such organs) that these organs should be completely wanting in
creatures, where they are incapable of performing a function, and where
it cannot be otherwise from the special mode of life. In compensation
for the non-existing function, he had at least furnished them with the
outward but empty form; nearly in the same manner as civil officers, in
uniform, are furnished with an innocent sword, which is never drawn from
the scabbard. I scarcely believe, however, that any of my readers will
be content with such an explanation.

Now, it is precisely this widely spread and mysterious phenomenon of
rudimentary organs, in regard to which all other attempts at explanation
fail, which is perfectly explained, and indeed in the simplest and
clearest way, by Darwin’s _Theory of Inheritance_ and _Adaptation_. We
can trace the important laws of inheritance and adaptation in the
domestic animals which we breed, and the plants which we cultivate; and
a series of such laws of inheritance have already been established.
Without going further into this at present, I will only remark that some
of them perfectly explain, in a mechanical way, the coming into
existence of rudimentary organs, so that we must look upon the
appearance of such structures as an entirely natural process, arising
from the _disuse of the organs_.

By _adaptation_ to special conditions of life, the formerly active and
really working organs have gradually ceased to be used or employed. In
consequence of their not being exercised they have become more and more
imperfect, but in spite of this have always been handed down from one
generation to another by _inheritance_, until at last they vanish
partially or entirely. Now, if we admit that all the vertebrate animals
mentioned above are derived from one common ancestor, possessing two
seeing eyes and two well developed pairs of legs, the different stages
of suppression and degeneration of these organs are easily accounted for
in such of the descendants as could no longer use them. In like manner
the various stages of suppression of the stamens, originally existing to
the number of five (in the flower-bud), among the Labiatæ is explained,
if we admit that all the plants of this family sprung from one common
ancestor, provided with five stamens.

I have here spoken somewhat fully of the phenomena of rudimentary
organs, because they are of the utmost general importance, and because
they lead us to the great, general, and fundamental questions in
philosophy and natural science, for the solution of which the Theory of
Descent has now become the indispensable guide. As soon, in fact, as,
according to this theory, we acknowledge the exclusive activity of
physico-chemical causes in living (organic) bodies, as well as in
so-called inanimate (inorganic) nature, we concede exclusive dominion to
that view of the universe, which we may designate as the _mechanical_,
and which is opposed to the _teleological_ conception. If we compare
all the ideas of the universe prevalent among different nations at
different times, we can divide them all into two sharply contrasted
groups—a _causal_ or _mechanical_, and a _teleological_ or
_vitalistic_. The latter has prevailed generally in Biology until now,
and accordingly the animal and vegetable kingdoms have been considered
as the products of a creative power, acting for a definite purpose. In
the contemplation of every organism the unavoidable conviction seemed to
press itself upon us, that such a wonderful machine, so complicated an
apparatus for motion as exists in the organism, could only be produced
by a power analogous to, but infinitely more perfect than, the power of
man in the construction of his machines.

However sublime the former idea of a Creator, and his creative power,
may have been; however much it may be attempted to divest it of all
human analogy, yet in the end this analogy still remains unavoidable and
necessary in the teleological conception of nature. In reality the
Creator must himself be conceived of as an organism, that is, as a being
who, analogous to man, even though in an infinitely more perfect form,
reflects on his constructive power, lays down a plan of his mechanisms,
and then, by the application of suitable materials, makes them answer
their purpose. Such conceptions necessarily suffer from the fundamental
error of _anthropomorphism_, or man-likening. In such a view, however
exalted the Creator may be imagined, we assign to him the human
attributes of designing a plan, and therefrom suitably constructing the
organism. This is, in fact, quite clearly expressed in that view which
is most sharply opposed to Darwin’s theory, and which has found among
naturalists its most distinguished representative in Agassiz. His
celebrated work, “An Essay on Classification,”(5) which is entirely
opposed to Darwin’s, and appeared almost at the same time, has
elaborated quite consistently, and to the utmost extent, these
anthropomorphic conceptions of the Creator.

I maintain with regard to the much-talked-of “purpose in nature,” that
it really has no existence but for those persons who observe phenomena
in animals and plants in the most superficial manner. Without going more
deeply into the matter, we can see at once that the rudimentary organs
are a formidable obstacle to this theory. And, indeed, everyone who
makes a really close study of the organization and mode of life of the
various animals and plants, and becomes familiar with the reciprocity or
interaction of the phenomena of life, and the so-called “economy of
nature,” must necessarily come to the conclusion that this
“purposiveness” no more exists than the much-talked-of “beneficence” of
the Creator. These optimistic views have, unfortunately, as little real
foundation as the favourite phrase, the “moral order of the universe,”
which is illustrated in an ironical way by the history of all nations.
The dominion of the “moral” popes, and their pious inquisition, in the
mediæval times, is not less significant of this than the present
prevailing militarism, with its “moral” apparatus of needle-guns and
other refined instruments of murder.

If we contemplate the common life and the mutual relations between
plants and animals (man included), we shall find everywhere, and at all
times, the very opposite of that kindly and peaceful social life which
the goodness of the Creator ought to have prepared for his creatures—we
shall rather find everywhere a pitiless, most embittered _Struggle of
All against All_. Nowhere in nature, no matter where we turn our eyes,
does that idyllic peace, celebrated by the poets, exist; we find
everywhere a struggle and a striving to annihilate neighbours and
competitors. Passion and selfishness—conscious or unconscious—is
everywhere the motive force of life. The well-known words of the German
poet—

“Die Welt ist vollkommen überall
Wo der Mensch nicht hinkommt mit seiner Qual.”[1]

are beautiful, but, unfortunately, not true. Man in this respect
certainly forms no exception to the rest of the animal world. The
remarks which we shall have to make on the theory of “Struggle for
Existence” will sufficiently justify this assertion. It is, in fact,
Darwin who has placed this important point, in its high and general
significance, very clearly before our eyes, and the chapter in his
theory which he himself calls “Struggle for Existence” is one of the
most important parts of it.

Whilst, then, we emphatically oppose the vital or teleological view of
animate nature which presents animal and vegetable forms as the
productions of a kind Creator, acting for a definite purpose, or of a
creative, natural force acting for a definite purpose, we must, on the
other hand, decidedly adopt that view of the universe which is called
the _mechanical_ or _causal_. It may also be called the _monistic_, or
_single-principle_ theory, as opposed to the _twofold principle_, or
_dualistic_ theory, which is necessarily implied in the teleological
conception of the universe. The mechanical view of nature has for many
years been so firmly established in certain domains of natural science,
that it is here unnecessary to say much about it. It no longer occurs to
physicists, chemists, mineralogists, or astronomers, to seek to find in
the phenomena which continually appear before them in their scientific
domain the action of a Creator acting for a definite purpose. They
universally, and without hesitation, look upon the phenomena which
appear in their different departments of study as the necessary and
invariable effects of physical and chemical forces which are inherent in
matter. Thus far their view is purely _materialistic_, in a certain
sense of that “word of many meanings.”

When a physicist traces the phenomena of motion in electricity or
magnetism, the fall of a heavy body, or the undulations in the waves of
light, he never, in the whole course of his research, thinks of looking
for the interference of a supernatural power. In this respect, Biology,
as the science of so-called “_animated_” natural bodies, was formerly
placed in sharp opposition to the above-mentioned inorganic natural
sciences (Anorganology). It is true modern Physiology, the science of
the phenomena of motion in animals and plants, has completely adopted
the mechanical view; but Morphology, the science of the forms of animals
and plants, has not been affected at all by it. Morphologists, in spite
of the position of physiology, have continued, as before, in opposition
to the mechanical view of functions, to look upon the forms of animals
and plants as something which cannot be at all explained mechanically,
but which must owe its origin necessarily to a higher, supernatural
creative power, acting for a definite purpose.

In this general view it is quite indifferent whether the creative power
be worshipped as a personal god, or whether it be termed the power of
life (vis vitalis), or final cause (causa finalis). In any case, to
express it in one word, its supporters have recourse to a _miracle_ for
an explanation. They throw themselves into the arms of a poetic faith,
which as such can have no value in the domain of scientific knowledge.

All that was done before Darwin, to establish a natural mechanical
conception of the origin of animals and plants, has been in vain, and
until his time no theory gained a general recognition. Darwin’s theory
first succeeded in doing this, and thus has rendered an immense service.
For the idea of the _unity of organic and inorganic nature_ is now
firmly established; and that branch of natural science which had longest
and most obstinately opposed mechanical conception and explanation,
viz., the science of the structure of animate forms, is launched on to
identically the same road towards perfection as that along which all the
rest of the natural sciences are travelling. The unity of _all_ natural
phenomena is by Darwin’s theory finally established.

This unity of all nature, the animating of all matter, the
inseparability of mental power and corporeal substance, Goethe has
asserted in the words: “Matter can never exist and be active without
mind, nor can mind without matter.” These first principles of the
mechanical conception of the universe have been taught by the great
monistic philosophers of all ages. Even Democritus of Abdera, the
immortal founder of the Atomic theory, clearly expressed them about 500
years before Christ; but the great Dominican friar, Giordano Bruno, did
so even more explicitly. For this he was burnt at the stake, by the
Christian inquisition in Rome, on the 17th of Feb., 1600, on the same
day on which, 36 years before, Galileo, his great fellow-countryman and
fellow-worker, was born. Such men, who live and die for a great idea,
are usually stigmatized as “materialists”; but their opponents, whose
arguments were torture and the stake, are praised as “spiritualists.”

By the Theory of Descent we are for the first time enabled to conceive
of the unity of nature in such a manner that a mechanico-causal
explanation of even the most intricate organic phenomena, for example,
the origin and structure of the organs of sense, is no more difficult
(in a general way) than is the mechanical explanation of any physical
process; as, for example, earthquakes, the courses of the wind, or the
currents of the ocean. We thus arrive at the extremely important
conviction that _all natural bodies_ which are known to us are _equally
animated_, that the distinction which has been made between animate and
inanimate bodies does _not_ exist. When a stone is thrown into the air,
and falls to earth according to definite laws, or when in a solution of
salt a crystal is formed, the phenomenon is neither more nor less a
mechanical manifestation of life than the growth and flowering of
plants, than the propagation of animals or the activity of their senses,
than the perception or the formation of thought in man. This final
triumph of the monistic conception of nature constitutes the highest and
most general merit of the Theory of Descent, as reformed by Darwin.

CHAPTER II.

SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT.
HISTORY OF CREATION ACCORDING TO LINNÆUS.

The Theory of Descent, or Doctrine of Filiation, as the
Monistic Explanation of Organic Natural Phenomena.—Its
Comparison with Newton’s Theory of Gravitation.—Limits
of Scientific Explanation and of Human Knowledge in
general.—All Knowledge founded originally on Sensuous
Experience, _a posteriori_.—Transition of _a posteriori_
knowledge, by Inheritance, into _a priori_
knowledge.—Contrast between the Supernatural Hypotheses
of the Creation according to Linnæus, Cuvier, Agassiz,
and the Natural Theories of Development according to
Lamarck, Goethe, and Darwin.—Connection of the former
with the Monistic (mechanical), of the latter with the
Dualistic Conception of the Universe.—Monism and
Materialism.—Scientific and Moral Materialism.—The
History of Creation according to Moses.—Linnæus as the
Founder of the Systematic Description of Nature and
Distinction of Species.—Linnæus’ Classification and
Binary Nomenclature.—Meaning of Linnæus’ Idea of
Species.—His History of Creation.—Linnæus’ view of the
Origin of Species.

The value which every scientific theory possesses is measured by the
number and importance of the objects which can be explained by it, as
well as by the simplicity and universality of the causes which are
employed in it as grounds of explanation. On the one hand, the greater
the number and the more important the meaning of the phenomena explained
by the theory, and the simpler, on the other hand, and the more general
the causes which the theory assigns as explanations, the greater is its
scientific value, the more safely we are guided by it, and the more
strongly are we bound to adopt it.

Let us call to mind, for example, that theory which has ranked up to the
present time as the greatest achievement of the human mind—the Theory
of Gravitation, which Newton, two hundred years ago, established in his
Mathematical Principles of Natural Philosophy. Here we find that the
object to be explained is as large as one can well imagine. He undertook
to reduce the phenomena of the motion of the planets, and the structure
of the universe, to mathematical laws. As the most simple cause of these
intricate phenomena of motion, Newton established the law of weight or
attraction, the same law which is the cause of the fall of bodies, of
adhesion, cohesion, and many other phenomena.

If we apply the same standard of valuation to Darwin’s theory, we must
arrive at the conclusion that this theory, also, is one of the greatest
achievements of the human mind, and that it may be placed quite on a
level with Newton’s Theory of Gravitation. Perhaps this opinion will
seem a little exaggerated, or at any rate very bold, but I hope in the
course of this treatise to convince the reader that this estimate is not
too high. In the preceding chapter, some of the most important and most
general phenomena in organic nature, which have been explained by
Darwin’s theory, have been named. Among them are the variations in form
which accompany the individual development of organisms, most varied and
complicated phenomena, which until now presented the greatest
difficulties in the way of mechanical explanation, that is, in the
tracing of them to active causes. We have mentioned the _rudimentary
organs_, those exceedingly remarkable structures in animals and plants
which have no object and refute every teleological explanation seeking
for the final purpose of the organism. A great number of other phenomena
might have been mentioned, which are no less important, and are
explained in the simplest manner by Darwin’s reformed Theory of Descent.
For the present I will only mention the phenomena presented to us by the
_geographical distribution of animals and plants_ on the surface of our
planet, as well as the _geological distribution of the extinct and
petrified organisms_ in the different strata of the earth’s crust. These
important palæontological and geographical phenomena, which were
formerly only known to us as _facts_, are now traced to their active
_causes_ by the Theory of Descent.

The same statement applies further to all the general laws of
_Comparative Anatomy_, especially to the great law of _division of
labour_ or _separation_ (polymorphism, or differentiation), a law which
determines the form or structure of human society, as well as the
organization of individual animals and plants. It is this law which
necessitates an ever _increasing variety_, as well as a _progressive
development_ of organic forms. This law of the division of labour has,
up to the present time, been only recognized as a fact, and it, like the
law of progressive development, or the law of progress which we perceive
active everywhere in the history of nations (as also in that of animals
and plants), is explained by Darwin’s Doctrine of Descent. Then, if we
turn our attention to the great whole of organic nature, if we compare
all the individual groups of phenomena of this immense domain of life,
it cannot fail to appear, in the light of the Doctrine of Descent, no
longer as the ingeniously designed work of a Creator building up
according to a definite purpose, but as the necessary consequence of
active causes, which are inherent in the chemical combination of matter
itself, and in its physical properties.

In fact, we can most positively assert, and I shall justify this
assertion in the course of these pages, that by the Doctrine of
Filiation, or Descent, we are enabled for the first time to reduce all
organic phenomena to a single law, and to discover a single active cause
for the infinitely intricate mechanism of the whole of this rich world
of phenomena. In this respect, Darwin’s theory stands quite on a level
with Newton’s Theory of Gravitation; indeed, it even rises higher than
Newton’s theory!

The grounds of explanation are equally simple in the two theories. In
explaining this most intricate world of phenomena, Darwin does not make
use of new or hitherto unknown properties of matter, nor does he, as one
might suppose, make use of discoveries of new combinations of matter or
of new forces of organization; but it is simply by extremely ingenious
combination, by the synthetic comprehension, and by the thoughtful
comparison of a number of well-known facts, that Darwin has solved the
“holy mystery” of the living world of forms. The consideration of the
interchanging relations which exist between two general properties of
organisms, viz., _Inheritance and Adaptation_, is what has here been of
the first importance. Merely by considering the relations between these
two vital actions or physiological functions of organisms, also further
by considering the reciprocal interaction which all animals and plants,
living in one and the same place, necessarily exert on one
another—solely by the correct estimate of these simple facts, and by
skilfully combining them, Darwin has succeeded in finding the true
active causes (causæ efficientes) of the immensely intricate world of
forms in organic nature.

In any case we are in duty bound to accept this theory till a better one
be found, which will undertake to explain the same amount of facts in an
equally simple manner. Until now we have been in utter want of such a
theory. The fundamental idea that all different animal and vegetable
forms must be descended from a few or even from one single, most simple
primary form, was indeed not new. This idea was long since distinctly
formulated—first by the great Lamarck, at the beginning of our century.
But Lamarck in reality only expressed the hypothesis of the Doctrine of
Filiation, without establishing it by an explanation of the active
causes. And it is just the demonstration of these causes which marks the
extraordinary progress which Darwin’s theory has made beyond that of
Lamarck. In the physiological properties of Inheritance and Adaptation
of organic matter, Darwin discovered the true cause of the genealogical
relationship of organisms. It was not possible for the genius of Lamarck
in his day to command that colossal material of biological facts which
has been collected by the patient zoological and botanical
investigations of the last fifty years, and which has been used by
Darwin as an overpowering apparatus of evidence.

Darwin’s theory is therefore not what his opponents frequently represent
it as being—an unwarranted hypothesis taken up at random. It is not for
zoologists or botanists to accept or reject this as an explanatory
theory, as they please; they are rather compelled and obliged to accept
it, according to the general principle observed in all natural sciences,
that we must accept and retain for the explanation of phenomena any
theory which, though it has only a feeble basis, is compatible with the
actual facts—until it is replaced by a better one. If we do not adopt
it, we renounce a scientific explanation of phenomena, and this is, in
fact, the position which many biologists still maintain. They look upon
the whole domain of animate nature as a perfect mystery, and upon the
origin of animals and plants, the phenomena of their development and
affinities, as quite inexplicable and miraculous; in fact, they will not
allow that there _can_ be a true understanding of them.

Those opponents of Darwin who do not exactly wish to renounce a
scientific explanation are in the habit of saying, “Darwin’s theory of
the common origin of the different species is only _one_ hypothesis; we
oppose to it _another_, the hypothesis that the individual animal and
vegetable species have not developed one from another by descent, but
that they have come into existence independently of one another, by a
still undiscovered law of nature.” But as long as it is not shown how
this coming into existence is to be conceived of, and what that “law of
nature” is—as long as not even _probable_ grounds of explanation can be
brought forward to account for the independent coming into existence of
animal and vegetable species, so long this counter-hypothesis is in fact
no hypothesis, but an empty unmeaning phrase. Darwin’s theory ought,
moreover, not to be called an hypothesis. For a scientific hypothesis is
a supposition, postulating the existence of unknown properties or
motional phenomena of natural bodies, which properties have not as yet
been observed by the experience of the senses. But Darwin’s theory does
not assume such unknown conditions; it is based upon general properties
of organisms that have long been recognized, and—as has been
remarked—it is the exceedingly ingenious and comprehensive combination
of a number of phenomena which had hitherto stood isolated, which gives
the theory its extraordinarily great and intrinsic value. By it we are
for the first time in a position to demonstrate an active cause for all
the known morphological phenomena in the animal and vegetable kingdoms;
and, in fact, this cause is always one and the same, viz., the alternate
action of Adaptation and Inheritance, therefore a physiological, that
is, a physico-chemical or mechanical, relationship. For these reasons
the acceptance of the Doctrine of Filiation, as mechanically established
by Darwin, is a binding and unavoidable necessity for the whole domain
of zoology and botany.

As, therefore, in my opinion the immense importance of Darwin’s theory
lies in the fact that it has _mechanically explained those organic
phenomena of forms_ which had hitherto been unexplained, it is perhaps
necessary that I should here say a few words about the different ideas
connected with the word “explanation.” It is very frequently said, in
opposition to Darwin’s theory, that it does indeed explain those
phenomena by Inheritance and Adaptation, but that it does not at the
same time explain those properties of organic matter, and that therefore
we do not arrive at first causes. This objection is quite correct, but
it applies equally to _all_ explanations of phenomena. We _nowhere_
arrive at a knowledge of first causes. The origin of every simple salt
crystal, which we obtain by evaporating its mother liquor, is no less
mysterious to us, as far as concerns its first cause, and in itself no
less incomprehensible than the origin of every animal which is developed
out of a simple cell. In explaining the most simple physical or chemical
phenomena, as the falling of a stone, or the formation of a chemical
combination, we arrive, by discovering and establishing the active
causes—for example, the gravitation or the chemical affinity—at other
remoter phenomena, which in themselves are mysterious. This arises from
the limitation or relativity of our powers of understanding. We must not
forget that human knowledge is absolutely limited, and possesses only a
relative extension. It is, in its essence, limited by the very nature of
our senses and of our brains.

All knowledge springs from sensuous perceptions. In opposition to this
statement, the innate, _à priori_ knowledge of man may be brought up;
but we can see that the so-called _à priori_ knowledge can by Darwin’s
theory be proved to have been acquired _à posteriori_, being based on
experience as its first cause. Knowledge which is based originally upon
purely empirical observations, and which is therefore a purely sensuous
experience, but has then been transmitted from generation to generation
by inheritance, appears in later generations as if it were independent,
innate, and _à priori_. In our late animal ancestors, all our so-called
“_à priori_ knowledge” was originally acquired _à posteriori_, and only
gradually became _à priori_ by inheritance. It is based in the first
instance upon experiences, and by the laws of Inheritance and Adaptation
we can positively prove that knowledge _à priori_ and knowledge _à
posteriori_ cannot rightly be placed in opposition, as is usually done.
On the contrary, sensuous experience is the original source of _all_
knowledge. For this reason alone, all our knowledge is limited, and we
can never apprehend the _first causes_ of any phenomena. The force of
crystallization, the force of gravitation, and chemical affinity remain
in themselves just as incomprehensible as do Adaptation and Inheritance.

Seeing that Darwin’s theory explains from a single point of view the
totality of all those phenomena of which we have given a brief survey,
that it demonstrates one and the same quality of the organism as the
active cause in all cases, we must allow that it gives us for the
present _all_ that we can desire. Moreover, we have good reason to hope
that at some future time we shall learn to explain the first causes at
which Darwin has arrived, namely, the properties of Adaptation and
Inheritance; and that we shall succeed in discovering in the composition
of albuminous matter certain molecular relations as the remoter, simpler
causes of these phenomena. There is indeed no prospect of this in the
immediate future, and we content ourselves for the present with the
tracing back of organic phenomena to two mysterious properties, just as
in the case of Newton’s theory we are satisfied with tracing the
planetary motions to the force of gravitation, which itself is likewise
a mystery to us and not cognizable in itself.

Before commencing our principal task, which is the careful discussion of
the Doctrine of Descent, and the consequences that arise out of it, let
us take an historical retrospect of the most important and most widely
spread of those views, which before Darwin men had elaborated
concerning organic creation, and the coming into existence of the many
animal and vegetable species. In doing this I have no intention of
entertaining the reader with a statement of all the innumerable stories
about the creation which have been current among the different human
species, races, or tribes. However interesting and gratifying this task
would be, from an ethnographical point of view, as well as in a history
of civilization, it would lead us here much too far from our subject.
Besides, the great majority of all these legends about creation bear too
clearly the stamp of arbitrary fiction, and of a want of a close
observance of nature, to be of interest in a scientific treatment of the
history of creation. I shall therefore only select the Mosaic history
from among those that are not founded on scientific investigation, on
account of the unparalleled influence which it has gained in the western
civilized world; and then I shall immediately take up the scientific
hypothesis about creation, which originated with Linnæus as late as the
commencement of last century.

All the different conceptions which man has ever formed about the coming
into existence of the different animal and vegetable species may
conveniently be divided into two great contrasted groups—the natural
and supernatural histories of creation.

These two groups, on the whole, correspond with the two different
principal forms of the human notions of the universe which we have
already contrasted as the _monistic and the dualistic_ conception of
nature. In the usual dualistic or teleological (vital) conception of the
universe, organic nature is regarded as the purposely executed
production of a Creator working according to a definite plan. Its
adherents see in every individual species of animal and plant an
“embodied creative thought,” the material expression of a _definite
first cause_ (causa finalis) acting for a set purpose. They must
necessarily assume supernatural (not mechanical) processes for the
origin of organisms. With justice, we may therefore designate their
scheme of the world’s growth as the _Supernatural History of Creation_.
Among all such teleological histories of creation, that of Moses has
gained the greatest influence, since even so distinguished a naturalist
as Linnæus has claimed admittance for it in Natural Science. Cuvier’s
and Agassiz’s views of creation also belong to this group, as do in fact
those of the great majority of both scientific and unscientific men.

On the other hand, the theory of development carried out by Darwin,
which we shall have to treat of here as the _Non-miraculous_ or _Natural
History of Creation_, and which has already been put forward by Goethe
and Lamarck, must, if carried out logically, lead to the monistic or
mechanical (causal) conception of the universe. In opposition to the
dualistic or teleological conception of nature, our theory considers
organic, as well as inorganic, bodies to be the necessary products of
natural forces. It does not see in every individual species of animal
and plant the embodied thought of a personal Creator, but the expression
for the time being of a mechanical process of development of matter, the
expression of a necessarily active cause, that is, of a mechanical cause
(causa efficiens). Where teleological Dualism seeks the arbitrary
thoughts of a capricious Creator in the miracles of creation, causal
Monism finds in the process of development the necessary effects of
eternal immutable laws of nature.

The Monism here maintained by us is often considered identical with
Materialism. Now, as Darwinism, and in fact the whole theory of
development, has been designated as “_materialistic_,” I cannot avoid
here at once guarding myself against this ambiguous word, and against
the malice with which, in certain quarters, it is employed to stigmatize
our doctrine.

By the word “_Materialism_,” two completely different things are very
frequently confounded and mixed up, which in reality have nothing
whatever to do with each other, namely, scientific and moral
materialism. Scientific materialism, which is identical with our Monism,
affirms in reality no more than that everything in the world goes on
naturally—that every effect has its cause, and every cause its effect.
It therefore assigns to causal law—that is, the law of a necessary
connection between cause and effect—its place over the entire series of
phenomena that can be known. At the same time, scientific materialism
positively rejects every belief in the miraculous, and every conception,
in whatever form it appears, of supernatural processes. Accordingly,
nowhere in the whole domain of human knowledge does it recognize real
metaphysics, but throughout only physics; through it the inseparable
connection between matter, form, and force becomes self evident. This
scientific materialism has long since been so universally acknowledged
in the wide domain of inorganic science, in Physics and Chemistry, in
Mineralogy and Geology, that no one now doubts its sole authority. But
in Biology, or Organic science, the case is very different; here its
value is still continually a matter of dispute in many quarters. There
is, however, nothing else which can be set up against it, excepting the
metaphysical spectre of a vital power, or empty theological dogma. If we
can prove that all nature, so far as it can be known, is only _one_,
that the same “great, eternal, iron laws” are active in the life of
animals and plants, as in the growth of crystals and in the force of
steam, we may with reason maintain the monistic or mechanical view of
things throughout the domain of Biology—in Zoology and Botany—whether
it be stigmatized as “materialism” or not. In such a sense all exact
science, and the law of cause and effect at its head, is purely
materialistic.

_Moral_, or _ethical Materialism_, is something quite distinct from
scientific materialism, and has nothing whatever in common with the
latter. This real materialism proposes no other aim to man in the course
of his life than the most refined possible gratification of his senses.
It is based on the delusion that purely material enjoyment can alone
give satisfaction to man; but as he can find that satisfaction in no one
form of sensuous pleasure, he dashes on weariedly from one to another.
The profound truth that the real value of life does not lie in material
enjoyment, but in moral action—that true happiness does not depend upon
external possessions, but only in a virtuous course of life—this is
unknown to ethical materialism. We therefore look in vain for such
materialism among naturalists and philosophers, whose highest happiness
is the intellectual enjoyment of Nature, and whose highest aim is the
knowledge of her laws. We find it in the palaces of ecclesiastical
princes, and in those hypocrites who, under the outward mask of a pious
worship of God, solely aim at hierarchical tyranny over, and material
spoliation of, their fellow-men. Blind to the infinite grandeur of the
so-called “raw material,” and the glorious world of phenomena arising
from it—insensible to the inexhaustible charms of Nature, and without a
knowledge of her laws—they stigmatize all natural science, and the
culture arising from it, as sinful “materialism,” while really it is
this which they themselves exhibit in a most shocking form. Satisfactory
proofs of this are furnished, not only by the whole history of the
Catholic Popes, with their long series of crimes, but also by the
history of the morals of orthodoxy in every form of religion.

In order, then, to avoid in future the usual confusion of this utterly
objectionable Moral Materialism with our Scientific Materialism, we
think it necessary to call the latter either _Monism_ or _Realism_. The
principle of this _Monism_ is the same as what Kant terms the
“principle of mechanism,” and of which he expressly asserts, that
_without it there can be no natural science at all_. This principle is
quite inseparable from our Non-miraculous History of Creation, and
characterizes it as opposed to the teleological belief in the miracles
of a Supernatural History of Creation.

Let us now first of all glance at the most important of all the
supernatural histories of creation, I mean that of Moses, as it has been
handed down to us in the Bible, the ancient document of the history and
laws of the Jewish people. The Mosaic history of creation, since in the
first chapter of Genesis it forms the introduction to the Old Testament,
has enjoyed, down to the present day, general recognition in the whole
Jewish and Christian world of civilization. Its extraordinary success is
explained not only by its close connection with Jewish and Christian
doctrines, but also by the simple and natural chain of ideas which runs
through it, and which contrasts favourably with the confused mythology
of creation current among most of the other ancient nations. First the
Lord God creates the earth as an inorganic body; then he separates light
from darkness, then water from the dry land. Now the earth has become
inhabitable for organisms, and plants are first created, animals
later—and among the latter the inhabitants of the water and the air
first, afterwards the inhabitants of the dry land. Finally God creates
man, the last of all organisms, in his own image, and as the ruler of
the earth.

Two great and fundamental ideas, common also to the non-miraculous
theory of development, meet us in this Mosaic hypothesis of creation,
with surprising clearness and simplicity—the idea of separation or
_differentiation_, and the idea of progressive development or
_perfecting_. Although Moses looks upon the results of the great laws of
organic development (which we shall later point out as the necessary
conclusions of the Doctrine of Descent) as the direct actions of a
constructing Creator, yet in his theory there lies hidden the ruling
idea of a progressive development and a differentiation of the
originally simple matter. We can therefore bestow our just and sincere
admiration on the Jewish lawgiver’s grand insight into nature, and his
simple and natural hypothesis of creation, without discovering in it a
so-called “divine revelation.” That it cannot be such is clear from the
fact that two great fundamental errors are asserted in it, namely,
first, the _geocentric_ error that the earth is the fixed central point
of the whole universe, round which the sun, moon, and stars move; and
secondly, the _anthropocentric_ error, that man is the premeditated aim
of the creation of the earth, for whose service alone all the rest of
nature is said to have been created. The former of these errors was
demolished by Copernicus’ System of the Universe in the beginning of the
16th century, the latter by Lamarck’s Doctrine of Descent in the
beginning of the 19th century.

Although the geocentric error of the Mosaic history was demonstrated by
Copernicus, and thereby its authority as an absolutely perfect divine
revelation was destroyed, yet it has maintained, down to the present
day, such influence, that it forms in many wide circles the principle
obstacle to the adoption of a natural theory of development. Even in our
century, many naturalists, especially geologists, have tried to bring
the Mosaic theory into harmony with the recent results of natural
science, and have, for example, interpreted Moses’ seven days of
creation as seven great geological periods. However, all these ingenious
attempts at interpretation have so utterly failed, that they require no
refutation here. The Bible is no scientific book, but consists of
records of the history, the laws, and the religion of the Jewish people,
the high merit of which, as a history of civilization, is not impaired
by the fact that in all scientific questions it has no commanding
importance, and is full of gross errors.

We may now make a great stride over more than three thousand years, from
Moses, who died about the year 1480 before Christ, to Linnæus, who was
born in the year 1707 after Christ. During this whole period no history
of creation was brought forward that gained any lasting importance, or
the closer examination of which would here be of any interest. Indeed,
during the last fifteen hundred years, since Christianity gained its
supremacy, the Mosaic history of creation, together with the dogmas
connected with it, has become so generally predominant, that the 19th
century is the first that has dared positively to rise against it. Even
the great Swedish naturalist, Linnæus, the founder of modern natural
history, linked his System of Nature most closely to the Mosaic history
of creation.

The extraordinary progress which Charles Linnæus made in the so-called
descriptive natural sciences, consists, as is well known, in his having
established a system of nomenclature of animals and plants, which he
carried out in a manner so perfectly logical and consistent, that down
to the present day it has remained in many respects the standard for all
succeeding naturalists engaged in the study of the forms of animals and
plants. Although Linnæus’ system was artificial, although in classifying
animal and vegetable species he only sought and employed single parts as
the foundation for his divisions, it has, nevertheless, gained the
greatest success; firstly, in consequence of its being carried out
consistently, and secondly, by its nomenclature of natural bodies, which
has become extremely important, and at which we must here briefly
glance.

Before Linnæus’ time, many vain attempts had been made to throw light
upon the endless chaos of different animal and vegetable forms (then
known) by adopting for them suitable names and groupings; but Linnæus,
by a happy hit, succeeded in accomplishing this important and difficult
task, when he established the so-called “_binary nomenclature_.” The
binary nomenclature, or the twofold designation, as Linnæus first
established it, is still universally applied by all zoologists and
botanists, and will, no doubt, maintain itself, for a long time to come,
with undiminished authority. It consists in this, that every species of
animal and plant is designated by two names, which stand to each other
in the same relation as do the christian and surnames of a man. The
special name which corresponds with the christian name, and expresses
the idea of “a species,” serves as the common designation of all
individual animals or plants, which are equal in all essential matters
of form, and are only distinguished by quite subordinate features. The
more general name, on the other hand, corresponding with the surname,
and which expresses the idea of a genus, serves for the common
designation of all the most nearly similar kinds or species.

According to Linnæus’ plan, the more general and comprehensive generic
name is written first; the special subordinate name of the species
follows it. Thus, for example, the common cat is called Felis domestica;
the wild cat, Felis catus; the panther, Felis pardus; the jaguar, Felis
onca; the tiger, Felis tigris; the lion, Felis leo. All these six kinds
of animals of prey are different species of one and the same
genus—Felis. Or, to add an example from the vegetable kingdom,
according to Linnæus’ designation the pine is Pinus abies; the fir,
Pinus picea; the larch, Pinus larix; the Italian pine, Pinus pinea; the
Siberian stone pine, Pinus cembra; the knee timber, Pinus mughus; the
common pine, Pinus silvestris. All these seven kinds of pines are
different species of one and the same genus—Pinus.

Perhaps this advance made by Linnæus may seem to some only of
subordinate importance in the practical distinction and designation of
the variously formed organisms. But in reality it was of the very
greatest importance, both from a practical and theoretical point of
view. For now, for the first time, it became possible to arrange the
immense mass of different organic forms according to their greater or
less degree of resemblance, and to obtain an easy survey of the general
outlines of such a “system.” Linnæus facilitated the tabulation and
survey of this “system” of plants and animals still more by placing
together the most nearly similar genera into so-called orders (ordines);
and by uniting the most nearly similar orders into still more
comprehensive main divisions or classes. Thus, according to Linnæus,
each of the two organic kingdoms were broken up into a number of
classes, the vegetable kingdom into twenty-four, and the animal kingdom
into six. Each class again contains several orders. Every single order
may contain a number of genera, and, again, every single genus several
species.

Valuable as was Linnæus’ binary nomenclature in a _practical_ way, in
bringing about a comprehensive systematic distinction, designation,
arrangement, and division of the organic world of forms, yet the
incalculable _theoretical_ influence which it gained forthwith in
relation to the history of creation was no less important. Even now all
the important fundamental questions as to the history of creation turn
finally upon the decision of the very remote and unimportant question,
_What really are kinds or species?_ Even now the _idea of organic
species_ may be termed the central point of the whole question of
creation, the disputed centre, about the different conceptions of which
Darwinists and Anti-Darwinists fight.

According to Darwin’s opinion, and that of his adherents, the different
species of one and the same genus of animals and plants are nothing else
than differently developed descendants of one and the same original
primary form. The different kinds of pine mentioned above would
accordingly have originated from a single primæval form of pine. In like
manner the origin of all the species of cat mentioned above would be
traced to a single common form of Felis, the ancestor of the whole
genus. But further, in accordance with the Doctrine of Descent, all the
different genera of one and the same order ought also to be descended
from one common primary ancestor, and so, in like manner, all orders of
a class from a single primary form.

On the other hand, according to the idea of Darwin’s opponents, all
species of animals and plants are quite independent of each other, and
only the individuals of each species have originated from a single
primary form. But if we ask them how they conceive these original
primary forms of each species to have come into existence, they answer
with a leap into the incomprehensible, “They were created.”

Linnæus himself defined the idea of species in this manner by saying,
“There are as many different species as there were different forms
created in the beginning by the infinite Being.” (“Species tot sunt
diversæ, quot diversas formas ab initio creavit infinitum ens.”) In this
respect, therefore, he follows most closely the Mosaic history of
creation, which in the same way maintains that animals and plants were
created “each one after its kind.” Linnæus, accepting this, held that
originally of each species of animals and plants either a single
individual or a pair had been created; in fact a pair, or, as Moses
says, “a male and a female” of those species which have separate sexes,
but of those species in which each individual combines both sexual
organs (hermaphrodites), as for instance the earthworm, the garden and
vineyard snails, as well as the great majority of plants, a single
individual.

Linnæus further follows the Mosaic legend in regard to the flood, by
supposing that the great general flood destroyed all existing organisms,
except those few individuals of each species (seven pairs of the birds
and of clean animals, one pair of unclean animals) which Noah saved in
the ark, and which were placed again on land, on Mount Ararat, after the
flood had subsided. He tried to explain the geographical difficulty of
the living together of the most different animals and plants, as
follows: Mount Ararat, in Armenia, being situated in a warm climate, and
rising over 16,000 feet in height, combines in itself the conditions for
a temporary common abode of such animals as live in different zones.
Accordingly, animals accustomed to the polar regions could climb up the
cold mountain ridges, those accustomed to a warm climate could go down
to the foot of the mountain, and the inhabitants of a temperate zone
could remain midway up the mountain. From this point it was possible for
them to spread north and south over the earth.

It is scarcely necessary to remark that this Linnæan hypothesis of
creation, which evidently was intended to harmonize most closely with
the prevailing belief in the Bible, requires no serious refutation. When
we consider Linnæus’ clearness and sagacity in other matters, we may
doubt whether he believed it himself. As to the simultaneous origin of
all individuals of each species from one pair of ancestors respectively
(or in the case of the hermaphrodite species, from one original
hermaphrodite), it is clearly quite untenable; for, apart from other
reasons, in the first days after the creation, the few animals of prey
would have sufficed to have utterly demolished all the herbivorous
animals, as the herbivorous animals must have destroyed the few
individuals of the different species of plants. The existence of such an
equilibrium in the economy of nature as obtains at present cannot
possibly be conceived, if only one individual of each species, or only
one pair, had originally and simultaneously been created.

Moreover, how little importance Linnæus himself attached to this
untenable hypothesis of creation is clear, among other things, from the
fact that he recognized _Hybridism_ (crossing) as a source of the
production of new species. He assumed that a great number of independent
new species had originated by the interbreeding of two different
species. Indeed, such hybrids are not at all rare in nature, and it is
now proved that a great number of species, for example, of the genus
Rubus (bramble), mullen (Verbascum), willow (Salix), thistle (Cirsium),
are hybrids of different species of these genera. We also know of
hybrids between hares and rabbits (two species of the genus Lepus),
further of hybrids between different species of dog (genus Canis), etc.,
which can be propagated as independent species.

It is certainly very remarkable that Linnæus asserted the physiological
(therefore mechanical) origin of new species in this process of
hybridism. It clearly stands in direct opposition to the supernatural
origin of the other species by creation, which he accepted as put
forward in the Mosaic account. The one set of species would therefore
have originated by dualistic (teleological) creation, the other by
monistic (mechanical) development.

The great and well merited authority which Linnæus gained by his
systematic classification and by his other services to Biology, was
clearly the reason why his views of creation also remained, throughout
the whole of the last century, undisputed and generally recognized. If
throughout systematic Zoology and Botany the distinctions,
classification, and designations of species, introduced by Linnæus, and
the dogmatic ideas connected therewith had not been maintained—more or
less unaltered—we should be at a loss to understand how his idea of an
independent creation of single species could have stood, by itself down
to the present day. It is only owing to his great authority, and through
his attaching himself to the prevailing Biblical belief, that his
hypothesis of creation has retained its position so long.

CHAPTER III.

THE HISTORY OF CREATION ACCORDING TO CUVIER AND AGASSIZ.

General Theoretical Meaning of the Idea of
Species.—Distinction between the Theoretical and
Practical Definition of the Idea of Species.—Cuvier’s
Definition of Species.—Merits of Cuvier as the Founder
of Comparative Anatomy.—Distinction of the Four
Principal Forms (types or branches) of the Animal
Kingdom, by Cuvier and Bär.—Cuvier’s Services to
Palæontology.—His Hypothesis of the Revolutions of our
Globe, and the Epochs of Creation separated by
them.—Unknown Supernatural Causes of the Revolutions,
and the subsequent New Creations.—Agassiz’s Teleological
System of Nature.—His Conception of the Plan of
Creation, and its six Categories (groups in
classification).—Agassiz’s Views of the Creation of
Species.—Rude Conception of the Creator as a man-like
being in Agassiz’s Hypothesis of Creation.—Its internal
Inconsistency and Contradictions with the important
Palæontological Laws discovered by Agassiz.

The real matter of dissension in the contest carried on by naturalists
as to the origin of organisms, their creation and development, lies in
the conceptions which are entertained about the _nature of species_.
Naturalists either agree with Linnæus, and look upon the different
species as distinct forms of creation, independent of one another, or
they assume with Darwin their blood-relationship. If we share Linnæus’
view (which was discussed in our last chapter), that the different
organic species came into existence independently—that they have no
blood-relationship—we are forced to admit that they were created
independently, and we must either suppose that every single organic
individual was a special act of creation (to which surely no naturalist
will agree), or we must derive all individuals of every species from a
single individual, or from a single pair, which did not arise in a
natural manner, but was called into being by command of a Creator. In so
doing, however, we turn aside from the safe domain of a rational
knowledge of nature, and take refuge in the mythological belief in
miracles.

If, on the other hand, with Darwin, we refer the similarity of form of
the different species to real blood-relationship, we must consider all
the different species of animals and plants as the altered descendants
of one or a few most simple original forms. Viewed in this way, the
Natural System of organisms (that is, their tree-like and branching
arrangement and division into classes, orders, families, genera, and
species) acquires the significance of a real genealogical tree, whose
root is formed by those original archaic forms which have long since
disappeared. But a truly natural and consistent view of organisms can
assume no supernatural act of creation for even those simplest original
forms, but only a coming into existence by _spontaneous generation_[2]
(archigony, or generatio spontanea). From Darwin’s view of the nature of
species, we arrive therefore at a _natural theory of development_; but
from Linnæus’ conception of the idea of species, we must assume a
_supernatural dogma of creation_.

Most naturalists after Linnæus, whose great services in
systematic and descriptive natural history won for him such high
authority, followed in his footsteps, and without further inquiry into
the origin of organization, they assumed, in the sense of Linnæus, an
independent creation of individual species, in conformity with the
Mosaic account of creation. The foundation of their conception was based
upon Linnæus’ words: “There are as many different species as there were
different forms created in the beginning by the Infinite Being.” We must
here remark at once, without going further into the definition of
species, that all zoologists and botanists in their classificatory
systems, in the practical distinction and designation of species of
animals and plants, never troubled, or even could trouble, themselves in
the slightest degree about this assumed creation of the parent forms. In
reference to this, one of our first zoologists, the ingenious Fritz
Müller, makes the following striking observation: “Just as in Christian
countries there is a catechism of morals, which every one knows by
heart, but which no one considers it his duty to follow, or expects to
see followed by others,—so zoology also has its dogmas, which are just
as generally professed as they are denied in practice.” (Für Darwin, p.
71.)(16)

Linnæus’ venerated dogma of species is just such an irrational dogma,
and for that very reason it is powerful. Although most naturalists
blindly submitted to it, yet they were, of course, never in a position
to demonstrate the descent of individuals belonging to one species from
the common, originally created, primitive form. Zoologists and
botanists, in their systems of nomenclature, confined themselves
entirely to the similarity of forms, in order to distinguish and name
the different species. They placed in one species all organic
individuals which were very similar, or almost identical in form, and
which could only be distinguished from one another by very unimportant
differences. On the other hand, they considered as different species
those individuals which presented more essential or more striking
differences in the formation of their bodies. But of course this opened
the flood-gates to the most arbitrary proceedings in the systematic
distinctions of species. For as all the individuals of one species are
never completely alike in all their parts, but as every species varies
more or less, no one could point out which degree of variation
constituted a really “good species,” or which degree indicated a “mere
variety.”

This dogmatic conception of the idea of species, and the arbitrary
proceedings connected with it, necessarily led to the most perplexing
contradictions, and to the most untenable suppositions. This is clearly
demonstrable in the case of the celebrated Cuvier (born in 1769), who
next to Linnæus has exercised the greatest influence on the study of
zoology. In his conception and definition of the idea of species, he
agreed on the whole with Linnæus, and shared also his belief in an
independent creation of individual species. Cuvier considered their
immutability of such importance that he was led to the foolish
assertion—“The immutability of species is a necessary condition of the
existence of scientific natural history.” As Linnæus’ definition of
species did not satisfy him, he made an attempt to give a more exact
and, for systematic practice, a more useful definition, in the following
words: “All those individual animals and plants belong to one species
which can be proved to be either descended from one another, or from
common ancestors, or which are as similar to these as the latter are
among themselves.”

In dealing with this matter, Cuvier reasoned in the following
manner:—“In those organic individuals, of which we know that they are
descended from one and the same common form of ancestors—in which,
therefore, their common ancestry is empirically proved—there can be no
doubt that they belong to one species, whether they differ much or
little from one another, or whether they are almost alike or very
unlike. Moreover, all those individuals also belong to this species
which differ no more from the latter (those proved to be derived from a
common stock) than these differ from one another.” In a closer
examination of this definition of species given by Cuvier, it becomes at
once evident that it is neither theoretically satisfactory nor
practically applicable. Cuvier, with this definition, began to move in
the same circle in which almost all subsequent definitions of species
have moved, through the assumption of their immutability.

Considering the extraordinary authority which George Cuvier has gained
in the science of organic nature, and in consequence of the almost
unlimited supremacy which his views exercised in zoology, during the
first half of our century, it seems appropriate here to examine his
influence a little more closely. This is all the more necessary as we
have to combat, in Cuvier, the most formidable opponent to the Theory of
Descent and the monistic conception of nature.

One of the many and great merits of Cuvier is that he stands forth as
the founder of Comparative Anatomy. While Linnæus established the
distinction of species, genera, orders, and classes mostly upon external
characters, and upon separate and easily discoverable signs in the
number, size, place, and form of individual organic parts of the body,
Cuvier penetrated much more deeply into the essence of organization. He
demonstrated great and wide differences in the inner structure of
animals, as the real foundation of a scientific knowledge and
classification of them. He distinguished natural families in the classes
of animals, and established his natural system of the animal kingdom on
their comparative anatomy.

The progress from Linnæus’ artificial system to Cuvier’s natural system
was exceedingly important. Linnæus had arranged all animals in a single
series, which he divided into six classes, two classes of Invertebrate,
and four classes of Vertebrate animals. He distinguished these
artificially, according to the nature of their blood and heart. Cuvier,
on the other hand, showed that in the animal kingdom there were four
great natural divisions to be distinguished, which he termed Principal
Forms, or General Plans, or Branches of the animal kingdom
(Embranchments), namely—1. The Vertebrate animals (Vertebrata); 2. The
Articulate animals (Articulata); 3. The Molluscous animals (Mollusca);
and 4. The Radiate animals (Radiata). He further demonstrated that in
each of these four branches a peculiar plan of structure or type was
discernible, distinguishing each branch from the three others. In the
Vertebrate animals it is distinctly expressed by the form of the
skeleton, or bony framework, as also by the structure and position of
the dorsal nerve-chord, apart from many other peculiarities. The
Articulate animals are characterized by their ventral nerve-chord and
their dorsal heart. In Molluscs the sack-shaped and non-articulate body
is the distinguishing feature. The Radiate animals, finally, differ
from the three other principal forms by their body being the combination
of four or more main sections united in the form of radii (antimera).

The distinction of these four principal forms of animals, which has
become extremely productive in the development of zoology, is commonly
ascribed entirely to Cuvier. However, the same thought was expressed
almost simultaneously, and independently of Cuvier, by Bär, one of the
greatest naturalists, and still living, who did the most eminent service
in the study of animal development. Bär showed that in the development
of animals, also, four different main forms (or types) must be
distinguished.(20) These correspond with the four plans of structure in
animals, which Cuvier distinguished on the ground of comparative
anatomy. Thus, for example, the individual development of all Vertebrate
animals agrees, from the commencement, so much in its fundamental
features that the germs or embryos of different Vertebrate animals (for
example, of reptiles, birds, and mammals) in their earlier stages cannot
be distinguished at all. It is only at a late stage of development that
there gradually appear the more marked differences of form which
separate those different classes and orders from one another. The plan
of structure, which shows itself in the individual development of
Articulate animals (insects, spiders, crabs), is from the beginning
essentially the same in all Articulate animals, but different from that
of all Vertebrate animals. The same holds good, with certain
limitations, in Molluscous and Radiated animals.

Neither Bär, who arrived at the distinction of the four animal types or
principal forms through the history of the individual development
(Embryology), nor Cuvier, who arrived at the same conclusion by means
of comparative anatomy, recognized the true cause of this difference.
This is disclosed to us by the Theory of Descent. The wonderful and
astonishing similarity in the inner organization and in the anatomical
relations of structure, and the still more remarkable agreement in the
embryonic development of all animals belonging to one and the same type
(for example, to the branch of the Vertebrate animals), is explained in
the simplest manner by the supposition of their common descent from a
single primary original form. If this view is not accepted, then the
complete agreement of the most different Vertebrate animals, in their
inner structure and their manner of development, remains perfectly
inexplicable. In fact it can only be explained by the law of
_inheritance_.

Next to the comparative anatomy of animals and the systematic zoology
founded anew by it, it was specially to the science of petrifactions, or
Palæontology, that Cuvier rendered great service. We must draw special
attention to this, because these very palæontological views, and the
geological ideas connected with them, were held almost universally in
the highest esteem during the first half of the present century, and
caused the greatest hindrance to the working out of a truly natural
history of creation.

Petrifactions, the scientific study of which Cuvier promoted at the
beginning of our century in a most extensive manner, and established
quite anew for the Vertebrate animals, play one of the most important
parts in the “non-miraculous history of creation.” For these remains and
impressions of extinct animals and plants, preserved to us in a
petrified condition, are the true “monuments of the creation,” the
infallible and indisputable records which fix the correct history of
organisms upon an irrefragable foundation. All petrified or fossil
remains and impressions tell us of the forms and structure of such
animals and plants as are either the progenitors and ancestors of the
present living organisms, or they are the representatives of extinct
collateral lines, which, together with the present living organisms,
branched off from a common stem.

These inestimable records of the history of creation throughout a long
period played a subordinate part in science. Their true nature was
indeed correctly understood, even more than five hundred years before
Christ, by the great Greek philosopher, Xenophanes of Colophon, the same
who founded the so-called Eleatic philosophy, and who was the first to
demonstrate with convincing precision that all conceptions of personal
gods result in more or less rude anthropomorphism.

Xenophanes for the first time, asserted that the fossil impressions of
animals and plants were real remains of formerly living creatures, and
that the mountains in whose rocks they were found must at an earlier
date have stood under water. But although other great philosophers of
antiquity, and among them Aristotle, also possessed this true knowledge,
yet throughout the illiterate Middle Ages, and even with some
naturalists of the last century, the idea prevailed that petrifactions
were so-called freaks of nature (lusus naturæ), or products of an
unknown formative power or instinct of nature (nisus formativus, vis
plastica). Respecting the nature of this mysterious and mystic creative
power, the strangest ideas were formed. Some believed that this
constructive power—the same to which they also ascribed the coming
into existence of the present species of animals and plants—had made
numerous attempts to create organisms of different forms, but that these
attempts had only partially succeeded, had often failed, and that
petrifactions were nothing more than such unsuccessful attempts.
According to others, petrifactions originated from the influence of the
stars upon the interior of the earth.

Others, again, had the still cruder notion that the Creator had first
made models (out of mineral substances—for example, of gypsum or clay)
of those forms of animals and plants which he afterwards executed in
organic substances, and into which he breathed his living breath;
petrifactions were accordingly such rude inorganic models. Even as late
as the last century these crude ideas prevailed, and it was assumed, for
example, that there existed a special “seminal air,” which was said to
penetrate into the earth with the water, and by fructifying the stones
formed petrifactions or “stony flesh” (caro fossilis).

It took a very long time before the simple and natural view was
accepted, namely, that petrifactions are in reality nothing but what
they appear to simple observation—the indestructible remains of extinct
organisms. It is true the celebrated painter, Leonardo da Vinci, in the
15th century, ventured to assert that the mud which was constantly
deposited by water was the cause of petrifactions, as it surrounded the
indestructible shells of mussels and snails which lay at the bottom of
the waters, and gradually turned them into solid stone. The same idea
was maintained in the 16th century by a Parisian potter, Palissy by
name, who became celebrated on account of his invention of china.
However, the so-called “professional men” were very far from paying any
regard to these correct assertions of a simple and healthy human
understanding; it was not till the end of the last century that it was
generally accepted, in consequence of the foundation of the Neptunian
geology by Werner.

The foundation of a more strictly scientific palæontology, however,
belongs to the beginning of our century, when Cuvier published his
classic researches on petrified Vertebrate animals, and when his great
opponent, Lamarck, made known his remarkable investigations on fossil
Invertebrate animals, especially on petrified snails and clams. In
Cuvier’s celebrated work “On the Fossil Bones” of Vertebrate
animals—principally of mammals and reptiles—we see that he had already
arrived at the knowledge of some very important and general
palæontological laws, which are of great consequence to the history of
creation. Foremost among them stands the assertion that the extinct
species of animals, whose remains we find petrified in the different
strata of the earth’s crust, lying one above another, differ all the
more strikingly from the still living kindred species of animals the
deeper those strata lie—in other words, the earlier the animals lived
in past ages. In fact, in every perpendicular section of the stratified
crust of the earth we find that the different strata, deposited by the
water in a certain historical succession, are characterized by different
petrifactions, and that these extinct organisms become more like those
of the present day the higher the strata lie; in other words, the more
recent the period in the earth’s history in which they lived, died, and
became encrusted by the deposited and hardened strata of mud.

However important this general observation of Cuvier’s was in one
sense, yet in another it became to him the source of a very serious
error. For as he considered the characteristic petrifactions of each
individual group of strata (which had been deposited during one main
period of the earth’s history) to be entirely different from those of
the strata lying above or below, and as he erroneously believed that one
and the same species of animal was never found in two succeeding groups
of strata, he arrived at the false idea, which was accepted as a law by
most subsequent naturalists, that a series of quite distinct periods of
creation had succeeded one another. Each period was supposed to have had
its special animal and vegetable world, each its peculiar specific Fauna
and Flora.

Cuvier imagined that the whole history of the earth’s crust, since the
time when living creatures had first appeared on the surface, must be
divided into a number of perfectly distinct periods, or divisions of
time, and that the individual periods must have been separated from one
another by peculiar revolutions of an unknown nature (cataclysms, or
catastrophes). Each revolution was followed by the utter annihilation of
the till then existing animals and plants, and after its termination a
completely new creation of organic forms took place. A new world of
animals and plants, absolutely and specifically distinct from those of
the preceding historical periods, was called into existence at once, and
now again peopled the globe for thousands of years, till it again
perished suddenly in the crash of a new revolution.

About the nature and causes of these revolutions, Cuvier expressly said
that no idea could be formed, and that the present active forces in
nature were not sufficient for their explanation. Cuvier points out four
active causes as the natural forces, or mechanical agents, at present
constantly but slowly at work in changing the earth’s surface: first,
_rain_, which washes down the steep mountain slopes and heaps up débris
at their foot; secondly, _flowing waters_, which carry away this débris
and deposit it as mud in stagnant waters; thirdly, the sea, whose
breakers gnaw at the steep _sea_ coasts, and throw up “dunes” on the
flat sea margins; finally and fourthly, _volcanos_, which break through
and heave up the strata of the earth’s hardened crust, and pile up and
scatter about the products of their eruptions. Whilst Cuvier recognizes
the constant slow transformation of the present surface of the earth by
these four mighty causes, he asserts at the same time that they would
not have sufficed to effect the revolutions of the remote ages, and that
the anatomical structure of the earth’s surface cannot be explained by
the necessary action of those mechanical agents: the great and
marvellous revolutions of the whole earth’s surface must, according to
him, have been rather the effects of very peculiar causes, completely
unknown to us; the usual thread of development was broken by them, and
the course of nature altered.

These views Cuvier explained in a special work “On the Revolutions of
the Earth’s Surface, and the Changes which they have wrought in the
Animal World.” They were maintained, and generally accepted for a long
time, and became the greatest obstacle to the development of a natural
history of the creation. For if such all-destructive revolutions had
actually occurred, of course a continuity of the development of species,
a connecting thread in the organic history of the earth, could not be
admitted at all, and we should be obliged to have recourse to the
action of supernatural forces; that is, to the interference of miracles
in the natural course of things. It is only through miracles that these
revolutions of the earth could have been brought about, and it is only
through miracles that, after their cessation and at the commencement of
each new period, a new animal and vegetable kingdom could have been
created. But science has no room for miracles, for by miracles we
understand an interference of supernatural forces in the natural course
of development of matter.

Just as the great authority which Linnæus gained by his system of
distinguishing and naming organic species led his successors to a
complete ossification, as it were, of the dogmatic idea of species and
to a real abuse of the systematic distinction implied by it, so the
great services which Cuvier had rendered to the knowledge and
distinction of extinct species became the cause of a general adoption of
his theory of revolutions and catastrophes, and of the false views of
creation connected therewith. The consequence of this was that, during
the first half of our century, most zoologists and botanists clung to
the opinion that a series of independent periods in the organic history
of the earth had existed; that each period was distinguished by distinct
and peculiar kinds of animal and vegetable species; that these were
annihilated at the termination of the period by a general revolution;
and that, after the cessation of the latter, a new world of different
species of animals and plants was created.

It is true some independent thinkers, above all the great physical
philosopher, Lamarck, even at an early period, set forth a series of
weighty reasons which refuted Cuvier’s theory of cataclysms, and
pointed to a perfectly continuous and uninterrupted developmental
history of all the organic inhabitants of the earth through all ages.
They maintained that the animal and vegetable species of each period
were derived from those of the preceding period, and were only the
altered descendants of the former. This true conception, however, being
opposed to Cuvier’s great authority, was then unable to make way. Nay,
even after Cuvier’s theory of catastrophes had been completely cast out
from the domain of geology by Lyell’s classic Principles of Geology,
which appeared in 1830, still his idea of the specific distinctness of a
series of organic creations maintained its influence, in many ways, in
the science of Palæontology. (Gen. Morph. ii. 312.)

By a curious coincidence, thirteen years ago, almost at the same time
that Cuvier’s History of Creation received its death-blow by Darwin’s
book, another celebrated naturalist made an attempt to re-establish it,
and to adopt it in the roughest manner, as a part of a
teleologico-theological system of nature. This was the Swiss geologist,
Louis Agassiz, who attained a great reputation by his theory of glaciers
and the ice-period, borrowed from Schimper and Charpentier, and who has
been living in North America for many years. He commenced in 1858 to
publish a work planned on a very large scale, which bears the title of
“Contributions to the Natural History of the United States of North
America.” The first volume of this work, although large and costly,
owing to the patriotism of the Americans, had an unprecedented sale; its
title is, “An Essay on Classification.”(5)

In this essay Agassiz not only discusses the natural series of
organisms, and the different attempts of naturalists at classification,
but also all the general biological phenomena which have reference to
it. The history of the development of organisms, both the embryonal and
the palæontological, comparative anatomy, the general economy of nature,
the geographical and topographical distribution of animals and
plants—in short, almost all the general phenomena of organic nature are
discussed in Agassiz’s Essay on Classification, and are explained in a
sense and from a point of view which is thoroughly opposed to that of
Darwin. While Darwin’s chief merit lies in the fact that he demonstrates
natural causes for the coming into existence of animal and vegetable
species, and thereby establishes the mechanical or monistic view of the
universe as regards this most difficult branch of the history of
creation, Agassiz, on the contrary, strives to exclude every mechanical
hypothesis from the subject, and to put the supernatural interference of
a personal Creator in the place of the natural forces of matter;
consequently, to establish a thoroughly teleological or dualistic view
of the universe. It will not be out of place if I examine a little more
closely Agassiz’s biological views, and especially his ideas of
creation, because no other work of our opponents treats the important
fundamental questions with equal minuteness, and because the utter
untenableness of the dualistic conception of nature becomes very evident
from the failure of this attempt.

The organic _species_, the various conceptions of which we have above
designated as the real centre of dispute in the opposed views of
creation, is looked upon by Agassiz, as by Cuvier and Linnæus, as a form
unchangeable in all its essential characteristics. The species may
indeed change and vary within certain narrow limits; never in essential
qualities, but only in unessential points. No new species could ever
proceed from the changes or varieties of a species. Not one of all
organic species, therefore, is ever derived from another, but each
individual species has been separately created by God. Each individual
species, as Agassiz expresses it, is “an embodied creative thought” of
God.

In direct opposition to the fact established by palæontological
experience, that the duration of the individual organic species is most
unequal, and that many species continue unchanged through several
successive periods of the earth’s history, while others only existed
during a small portion of such a period, Agassiz maintains that one and
the same species never occurs in two different periods, but that each
individual period is characterized by species of animals and plants
which are quite peculiar, and belong to it exclusively. He further
shares Cuvier’s opinion that the whole of these inhabitants were
annihilated by the great and universal revolutions of the earth’s
surface, which divide two successive periods, and that after its
destruction a new and specifically different assemblage of organisms was
created. This new creation Agassiz supposes to have taken place in this
manner: viz., that at each creation all the inhabitants of the earth, in
their full average number of individuals, and in the peculiar relations
corresponding to the economy of nature, were, as a whole, suddenly
placed upon the earth by the Creator. In saying this he puts himself in
opposition to one of the most firmly established and most important laws
of animal and vegetable geography—namely, to the law that each species
has a single original locality of origin, or a so-called “centre of
creation,” from which it has gradually spread over the rest of the
earth. Instead of this, Agassiz assumes each species to have been
created at several points of the earth’s surface, and that in each case
a large number of individuals was created.

The “natural system” of organisms, the different groups and categories
of which arranged above one another—namely, the branches, classes,
orders, families, genera, and species—we consider, in accordance with
the Theory of Descent, as different branches and twigs of the organic
family-tree, is, according to Agassiz, the direct expression of the
divine plan of creation, and the naturalist, while investigating the
natural system, repeats the creative thoughts of God. In this Agassiz
finds the strongest proof that man is the image and child of God. The
different stages of groups or categories of the natural system
correspond with the different stages of development which the divine
plan of creation had attained. The Creator, in projecting and carrying
out this plan, starting from the most general ideas of creation, plunged
more and more into specialities. For instance, when creating the animal
kingdom, God had in the first place four totally distinct ideas of
animal bodies, which he embodied in the different structures of the four
great, principal forms, types, or branches of the animal kingdom;
namely, vertebrate animals, articulate animals, molluscous animals, and
radiate animals. The Creator then, having reflected in what manner he
might vary these four different plans of structure, next created within
each of the four principal forms, several different classes—for
example, in the vertebrate animal form, the classes of mammals, birds,
reptiles, amphibious animals, and fishes. Then God further reflected
upon the individual classes, and by various modifications in the
structure of each class, he produced the individual orders. By further
variation in the order, he created natural families. As the Creator
further varied the peculiarities of structure of individual parts in
each family, genera arose. In further meditation on his plan of
creation, he entered so much into detail that individual species came
into existence, which, consequently, are embodied creative thoughts of
the most special kind. It is only to be regretted that the Creator
expressed these most special and most deeply considered “creative
thoughts” in so very indistinct and loose a manner, and that he
imprinted so vague a stamp upon them, and permitted them to vary so
freely that not one naturalist is able to distinguish the “good” from
the “bad species,” or a genuine species from varieties, races, etc.
(Gen. Morph. ii. 373.)

We see, then, according to Agassiz’s conception, that the Creator, in
producing organic forms, goes to work exactly as a human architect, who
has taken upon himself the task of devising and producing as many
different buildings as possible, for the most manifold purposes, in the
most different styles, in various degrees of simplicity, splendour,
greatness, and perfection. This architect would perhaps at first choose
four different styles for all these buildings, say the Gothic,
Byzantine, Chinese, and Rococo styles. In each of these styles he would
build a number of churches, palaces, garrisons, prisons, and
dwelling-houses. Each of these different buildings he would execute in
ruder and more perfect, in greater and smaller, in simpler and grander
fashion, etc. However, the human architect would perhaps, in this
respect, be better off than the divine Creator, as he would have perfect
liberty in the number of graduated subordinate groups. The Creator,
however, according to Agassiz, can only move within six groups or
categories: the species, genus, family, order, class, and type. More
than these six categories do not exist for him.

When we read Agassiz’s book on classification, and see how he carries
out and establishes these strange ideas, we can scarcely understand how,
with all the appearance of scientific earnestness, he can persevere in
his idea of the divine Creator as a man-like being (anthropomorphism),
for by his explanation of details he produces a picture of the most
absurd nonsense. In the whole series of these suppositions the Creator
is nothing but an all-mighty man, who, plagued with _ennui_, amuses
himself with planning and constructing most varied toys in the shape of
organic species. After having diverted himself with these for thousands
of years, they become tiresome to him, he destroys them by a general
revolution of the earth’s surface, and thus throws the whole of the
useless toys in heaps together; then, in order to while away his time
with something new and better, he calls a new and more perfect animal
and vegetable world into existence. But in order not to have the trouble
of beginning the work of creation over again, he keeps, in the main, to
his original plan of creation, and creates merely new species, or at
most only new genera, and much more rarely new families, new orders, or
classes. He never succeeds in producing a new style or type, and always
keeps strictly within the six categories or graduated groups.

When, according to Agassiz, the Creator has thus amused himself for
thousands of millions of years with constructing and destroying a series
of different creations, at last (but very late) he is struck with the
happy thought of creating something like himself, and so makes man in
his own image. The end of all the history of creation is thus arrived at
and the series of revolutions of the earth is closed. Man, the child and
image of God, gives him so much to do, causes him so much pleasure and
trouble, that he is wearied no longer, and therefore need not undertake
a new creation. It is clear that if, according to Agassiz, we once
assign to the Creator entirely human attributes and qualities, and
regard his work of creation as entirely analogous to human creative
activity, we are necessarily obliged to admit such utterly absurd
inferences as those just stated.

The many intrinsic contradictions and perversities in Agassiz’s view of
creation—a view which necessarily led him to the most decided
opposition to the Theory of Descent—must excite our astonishment all
the more because, in his earlier scientific works, he had in many
respects actually paved the way for Darwin, especially by his researches
in Palæontology. Among the numerous investigations which created general
interest in the then young science of Palæontology, those of Agassiz,
especially his celebrated work on “Fossil Fish,” rank next in importance
to Cuvier’s work, which formed the foundation of the science. The
petrified fish, with which Agassiz has made us acquainted, have not only
an extremely great importance for the understanding of all groups of
Vertebrate animals, and their historical development, but we have
arrived through them at a sure knowledge of important general laws of
development, some of which were first discovered by Agassiz. He it was
who drew special attention to the remarkable parallelism between the
embryonal and the palæontological development—between ontogeny and
phylogeny, which I have already (p. 10) claimed as one of the strongest
pillars of the Theory of Descent. No one before had so distinctly stated
as Agassiz did, that, of the Vertebrate animals, fishes alone existed,
at first, that amphibious animals came later, and that birds and mammals
appeared only at a much later period, further, that among mammals, as
among fishes, imperfect and lower orders had appeared first, but more
perfect and higher orders at a later period. Agassiz, therefore, showed
that the palæontological development of the whole Vertebrate group was
not only parallel with the embryonic, but also with the systematic
development, that is, with the graduated series which we see everywhere
in the system, ascending from the lower to the higher classes, orders,
etc.

In the earth’s history lower forms appeared first, the higher forms
later. This important fact, as well as the agreement of the embryonic
and palæontological development, is explained quite simply and naturally
by the Doctrine of Descent, and without it is perfectly inexplicable.
This cause holds good also in the great law of _progressive
development_, that is, of the historical progress of organization, which
is traceable, broadly and as a whole, in the historical succession of
all organisms, as well as in the special perfecting of individual parts
of animal bodies. Thus, for example, the skeleton of Vertebrate animals
acquired at first slowly, and by degrees, that high degree of perfection
which it now possesses in man and the other higher Vertebrate animals.
This progress, acknowledged in point of fact by Agassiz, necessarily
follows from Darwin’s Doctrine of Descent, which demonstrates its active
causes. If this doctrine is correct, the perfecting and diversification
of animal and vegetable species must of necessity have gradually
increased in the course of the organic history of the earth, and could
only attain its highest perfection in most recent times.

The above-mentioned laws of development, together with some other
general ones, which have been expressly admitted and justly emphasized
by Agassiz, and some of which have first been set forth by him, are, as
we shall see later, only explicable by the Theory of Descent, and
without it remain perfectly incomprehensible. The conjoint action of
Inheritance and Adaptation, as explained by Darwin, can alone be their
true cause. But they all stand in sharp and irreconcilable opposition to
the hypothesis of creation maintained by Agassiz, as well as to the idea
of a personal Creator who acts for a definite purpose. If we seriously
wish to explain those remarkable phenomena and their inter-connection by
Agassiz’s theory, then we are necessarily driven to the curious
supposition that the Creator himself has developed, together with the
organic nature which he created and modelled. We can, in that case, no
longer rid ourselves of the idea that the Creator himself, like a human
being, designed, improved, and finally, with many alterations, carried
out his plans. “Man grows as higher grow his aims,” and the same
supposition, so unworthy of a God, must be applied to him. Although,
from the reverence with which, in every page, Agassiz speaks of the
Creator, it might appear that, on his theory, we attain to the sublimest
conception of the divine activity in nature, yet the contrary is in
truth the case. The divine Creator is degraded to the level of an
idealized man, of an organism progressing in development!

Considering the wide popularity and great authority which Agassiz’s work
has gained, and which is perhaps justified on account of earlier
scientific services rendered by the author, I have thought it my duty
here to show the utter untenableness of his general conceptions. So far
as this work pretends to be a scientific history of creation, it is
undoubtedly a complete failure. But still it has great value, being the
only detailed attempt, adorned with scientific arguments, which an
eminent naturalist of our day has made to found a teleological or
dualistic history of creation. The utter impossibility of such a history
has thus been made obvious to every one. No opponent of Agassiz could
have refuted the dualistic conception of organic nature and its origin
more strikingly than he himself has done by the intrinsic contradictions
which present themselves everywhere in his theory.

The opponents of the monistic or mechanical conception of the world have
welcomed Agassiz’s work with delight, and find in it a perfect proof of
the direct creative action of a personal God. But they overlook the fact
that this personal Creator is only an idealized organism, endowed with
human attributes. This low dualistic conception of God corresponds with
a low animal stage of development of the human organism. The more
developed man of the present day is capable of, and justified in,
conceiving that infinitely nobler and sublimer idea of God which alone
is compatible with the monistic conception of the universe, and which
recognizes God’s spirit and power in all phenomena without exception.
This monistic idea of God, which belongs to the future, has already been
expressed by Giordano Bruno in the following words:—“A spirit exists in
all things, and no body is so small but contains a part of the divine
substance within itself, by which it is animated.” It is of this noble
idea of God that Goethe says:—“Certainly there does not exist a more
beautiful worship of God than that which needs no image, but which
arises in our heart from converse with Nature.” By it we arrive at the
sublime idea of the Unity of God and Nature.

CHAPTER IV.

THEORY OF DEVELOPMENT ACCORDING TO GOETHE AND OKEN.

Scientific Insufficiency of all Conceptions of a Creation
of Individual Species.—Necessity of the Counter Theories
of Development.—Historical Survey of the Most Important
Theories of Development.—Aristotle.—His Doctrine of
Spontaneous Generation.—The Meaning of Natural
Philosophy.—Goethe.—His Merits as a Naturalist.—His
Metamorphosis of Plants.—His Vertebral Theory of the
Skull.—His Discovery of the Mid Jawbone in
Man.—Goethe’s Interest in the Dispute between Cuvier and
Geoffroy St. Hilaire.—Goethe’s Discovery of the Two
Organic Formative Principles, of the Conservative
Principle of Specification (by Inheritance), and of the
Progressive Principle of Transformation (by
Adaptation).—Goethe’s Views of the Common Descent of all
Vertebrate Animals, including Man.—Theory of Development
according to Gottfried Reinhold Treviranus.—His Monistic
Conception of Nature.—Oken.—His Natural
Philosophy.—Oken’s Theory of Protoplasm.—Oken’s Theory
of Infusoria (Cell Theory).—Oken’s Theory of
Development.

All the different ideas which we may form of a separate and independent
origin of the individual organic species by creation lead us, when
logically carried out, to a so-called _anthropomorphism_, that is, to
imagining the Creator as a man-like being, as was shown in our last
chapter. The Creator becomes an organism who designs a plan, reflects
upon and varies this plan, and finally forms creatures according to this
plan, as a human architect would his building. If even such eminent
naturalists as Linnæus, Cuvier, and Agassiz, the principal
representatives of the dualistic hypothesis of creation, could not
arrive at a more satisfactory view, we may take it as evidence of the
insufficiency of all those conceptions which would derive the various
forms of organic nature from a creation of individual species.

Some naturalists, indeed, seeing the complete insufficiency of these
views, have tried to replace the idea of a personal Creator by that of
an unconsciously active and creative Force of Nature; yet this
expression is evidently merely an evasive phrase, as long as it is not
clearly shown what this force of nature is, and how it works. Hence
these attempts, also, have been absolute failures. In fact, whenever an
independent origin of the different forms of animals and plants has been
assumed, naturalists have found themselves compelled to fall back upon
so many “acts of creation,” that is, on supernatural interferences of
the Creator in the natural course of things, which in all other cases
goes on without interference.

It is true that several teleological naturalists, feeling the scientific
insufficiency of a supernatural “_creation_,” have endeavoured to save
the hypothesis by wishing it to be understood that creation “is nothing
else than a way of coming into being, unknown and inconceivable to us.”
The eminent Fritz Müller has cut off from this sophistic evasion every
chance of escape by the following striking remark:—“It is intended here
only to express in a disguised manner the shamefaced confession, that
they neither have, nor care to have, _any opinion_ about the origin of
species. According to this explanation of the word, we might as well
speak of the creation of cholera, or syphilis, of the creation of a
conflagration, or of a railway accident, as of the creation of man.”
(Jenaische Zestscrift, bd. v. p. 272.)

In the face, then, of these hypotheses of creation, which are
scientifically insufficient, we are forced to seek refuge in the
_counter-theory of development_ of organisms, if we wish to come to a
rational conception of the origin of organisms. We are forced and
obliged to do so, even if the theory of development only throws a
glimmer of probability upon a mechanical, natural origin of the animal
and vegetable species; but all the more if, as we shall see, this theory
explains all facts simply and clearly, as well as completely and
comprehensively. The theories of development are by no means, as they
often falsely are represented to be, arbitrary fancies, or wilful
products of the imagination, which only attempt approximately to explain
the origin of this or that individual organism; but they are theories
founded strictly on science, which explain in the simplest manner, from
a fixed and clear point of view, the whole of organic natural phenomena,
and more especially the origin of organic species, and demonstrate them
to be the necessary consequences of mechanical processes in nature.

As I have already shown in the second chapter, all these theories of
development coincide naturally with that general theory of the universe
which is usually designated as the uniform or _monistic_, often also as
the _mechanical_ or causal, because it only assumes mechanical causes,
or _causes working by necessity_ (causæ efficientes), for the
explanation of natural phenomena. In like manner, on the other hand, the
supernatural hypotheses of creation which we have already discussed
coincide completely with the opposite view of the universe, which in
contrast to the former is called the twofold or _dualistic_, often the
_teleological_ or vital, because it traces the organic natural phenomena
to final causes, acting and _working for a definite purpose_ (causæ
finales). It is this deep and intrinsic connection of the different
theories of creation with the most important questions of philosophy
that incites us to their closer examination.

The fundamental idea, which must necessarily lie at the bottom of all
natural theories of development, is that of a _gradual development of
all (even the most perfect) organisms_ out of a single, or out of a very
few, quite simple, and quite imperfect original beings, which came into
existence, not by supernatural creation, but by _spontaneous
generation_, or archigony, out of inorganic matter. In reality, there
are two distinct conceptions united in this fundamental idea, but which
have, nevertheless, a deep intrinsic connection—namely, first, the idea
of spontaneous generation (or archigony) of the original primary beings;
and secondly, the idea of the progressive development of the various
species of organisms from those most simple primary beings. These two
important mechanical conceptions are the inseparable fundamental ideas
of every theory of development, if scientifically carried out. As it
maintains the derivation of the different species of animals and plants
from the simplest, common primary species, we may term it also the
Doctrine of Filiation, or _Theory of Descent_; as there is also a change
of species connected with it, it may also be termed the _Transmutation
Theory_.

While the supernatural histories of creation must have originated
thousands of years ago, in that very remote primitive age when man,
first developing out of the monkey-state, began for the first time to
think more closely about himself, and about the origin of the world
around him, the natural theories of development, on the other hand, are
necessarily of much more recent origin. These views are met with only
among nations of a more matured civilization, to whom, by philosophic
culture, the necessity of a knowledge of natural causes has become
apparent; and even among these, only individual and specially gifted
natures can be expected to have recognized the origin of the world of
phenomena, as well as its course of development, as the necessary
consequences of mechanical, naturally active causes. In no nation have
these preliminary conditions, for the origin of a natural theory of
development, ever existed in so high a degree as among the Greeks of
classic antiquity. But, on the other hand, they lacked a close
acquaintance with the facts of the processes and forms of nature, and,
consequently, the foundation based upon experience, for a satisfactory
unravelling of the problem of development. Exact investigation of
nature, and the knowledge of nature founded on an experimental basis,
was of course almost unknown to antiquity, as well as to the Middle
Ages, and is only an acquisition of modern times. We have therefore here
no special occasion to examine the natural theories of development of
the various Greek philosophers, since they were wanting in the knowledge
gained by experience, both of organic and inorganic nature, and since
they almost always, as the consequence, lost themselves in airy
speculations.

One man only must be mentioned here by way of exception,—Aristotle, the
greatest and the only truly great naturalist of antiquity and the Middle
Ages, one of the grandest geniuses of all time. To what a degree he
stands there alone, during a period of more than two thousand years, in
the region of empirico-philosophical knowledge of nature, and especially
in his knowledge of organic nature, is proved to us by the precious
remains of his but partially surviving works. In them many traces are
found of a theory of natural development. Aristotle assumes, as a matter
of certainty, that spontaneous generation was the natural manner in
which the lower organic creatures came into existence. He describes
animals and plants originating from matter itself, through its own
original force; as, for example, moths from wool, fleas from putrid
dung, wood-lice from damp wood, etc. But as the distinction of organic
species, which Linnæus only arrived at two thousand years later, was
unknown to him, he could form no ideas about their genealogical
relations.

The fundamental notion of the theory of development, that the different
species of animals and plants have been developed from a common primary
species by transformation, could of course only be clearly asserted
after the kinds of species themselves had become better known, and after
the extinct species had been carefully examined and compared with the
living ones. This was not done until the end of the last and the
beginning of the present century. It was not until the year 1801 that
the great Lamarck expressed the theory of development, which he, in
1809, further elaborated in his classical “Philosophie Zoologique.”
While Lamarck and his countryman, Geoffroy St. Hilaire, in France,
opposed Cuvier’s views, and maintained a natural development of organic
species by transformation and descent, Goethe and Oken at the same time
pursued the same course in Germany, and helped to establish the theory
of development. As these naturalists are generally called
nature-philosophers (Naturphilosophen), and as this ambiguous
designation is correct in a certain sense, it appears to me appropriate
here to say a few words about the correct estimate of the
“Natur-philosophie.”

Although for many years in England the ideas of natural science and
philosophy have been looked upon as almost equivalent, and as every
truly scientific investigator of nature is most justly called there a
“natural philosopher,” yet in Germany for more than half a century
natural science has been kept strictly distinct from philosophy, and the
union of the two into a true philosophy of nature is recognized only by
the few. This misapprehension is owing to the fantastic eccentricities
of earlier German natural-philosophers, such as Oken, Schelling, etc.;
they believed that they were able to construct the laws of nature in
their own heads, without being obliged to take their stand upon the
grounds of actual experience. When the complete hollowness of their
assumptions had been demonstrated, naturalists, in “the nation of
thinkers,” fell into the very opposite extreme, believing that they
would be able to reach the high aim of science, that is, the knowledge
of truth, by the mere experience of the senses, and without any
philosophical activity of thought.

From that time, but especially since 1830, most naturalists have shown a
strong aversion to any general, philosophical view of nature. The real
aim of natural science was now supposed to consist in the knowledge of
details, and it was believed that this would be attained in the study of
biology, when the forms and the phenomena of life, in all individual
organisms, had become accurately known, by the help of the finest
instruments and means of observation. It is true that among these
strictly empirical, or so-called exact naturalists, there were always
very many who rose above this narrow point of view, and sought the final
aim in a knowledge of the general laws of organization. Yet the great
majority of zoologists and botanists, during the thirty or forty years
preceding Darwin, refused to concern themselves about such general laws;
all they admitted was, that perhaps in the far distant future, when the
end of all empiric knowledge should have been arrived at, when all
individual animals and plants should have been thoroughly examined,
naturalists might begin to think of discovering general biological laws.

If we consider and compare the most important advances which the human
mind has made in the knowledge of truth, we shall soon see that it is
always owing to philosophical mental operations that these advances have
been made, and that the experience of the senses which certainly and
necessarily precedes these operations, and the knowledge of details
gained thereby, only furnish the basis for those general laws.
Experience and philosophy, therefore, by no means stand in such
exclusive opposition to each other as most men have hitherto supposed;
they rather necessarily supplement each other. The philosopher who is
wanting in the firm foundation of sensuous experience, of empirical
knowledge, is very apt to arrive at false conclusions in his general
speculations, which even a moderately informed naturalist can refute at
once. On the other hand, the purely empiric naturalists, who do not
trouble themselves about the philosophical comprehension of their
sensuous experiences, and who do not strive after general knowledge, can
promote science only in a very slight degree, and the chief value of
their hard-won knowledge of details lies in the general results which
more comprehensive minds will one day derive from them.

From a general survey of the course of biological development since
Linnæus’ time, we can easily see, as Bär has pointed out, a continual
vacillation between these two tendencies, at one time a prevalence of
the empirical—the so-called exact—and then again of the philosophical
or speculative tendency. Thus at the end of the last century, in
opposition to Linnæus’ purely empirical school, a natural-philosophical
reaction took place, the moving spirits of which, Lamarck, Geoffroy St.
Hilaire, Goethe, and Oken, endeavoured by their mental work to introduce
light and order into the chaos of the accumulated empirical raw
material. In opposition to the many errors and speculations of these
natural philosophers, who went too far, Cuvier then came forward,
introducing a second, purely empirical period. It reached its most
one-sided development between the years 1830-1860, and there now
followed a second philosophical reaction, caused by Darwin’s work. Thus
during the last ten years, men again have begun to endeavour to obtain a
knowledge of the general laws of nature, to which, after all, all
detailed knowledge of experience serves only as a foundation, and
through which alone it acquires its true value. It is through philosophy
alone that natural knowledge becomes a true science, that is, a
philosophy of nature. (Gen. Morph. i. 63-108.)

Jean Lamarck and Wolfgang Goethe stand at the head of all the great
philosophers of nature who first established a theory of organic
development, and who are the illustrious fellow-workers of Darwin. I
turn first to our beloved Goethe, who, among all, stands in the closest
relations to us Germans. However, before I explain his special services
to the theory of development, it seems to me necessary to say a few
words about his importance as a naturalist in general, as it is commonly
very little known.

I am sure most of my readers honour Goethe only as a poet and a man;
only a few have any conception of the high value of his scientific
works, and of the gigantic stride with which he advanced before his own
age—advanced so much that most naturalists of that time were unable to
follow him. In several passages of his scientific writings he bitterly
complains of the narrow-mindedness of professed naturalists, who do not
know how to value his works (who cannot see the wood for the trees), and
who cannot rouse themselves to discover the general laws of nature among
the mass of details. He is only too just when he utters the
reproach—“The philosophers will very soon discover that observers
rarely rise to a stand-point from which they can survey so many
important objects.” It is true, at the same time, that their want of
appreciation was caused by the false road into which Goethe was led in
his theory of colours.

This theory of colours, which he himself designates as the favourite
production of his leisure, however much that is beautiful it may
contain, is a complete failure in regard to its foundations. The exact
mathematical method by means of which alone it is possible, in inorganic
sciences, but above all in physics, to raise a structure step by step on
a thoroughly firm basis, was altogether repugnant to Goethe. In
rejecting it he allowed himself not only to be very unjust towards the
most eminent physicists, but to be led into errors which have greatly
injured the fame of his other valuable works. It is quite different in
the organic sciences, in which we are but rarely able to proceed, from
the beginning, upon a firm mathematical basis; we are rather compelled,
by the infinitely difficult and intricate nature of the problem, at the
first to form inductions—that is, we are obliged to endeavour to
establish general laws by numerous individual observations, which are
not quite complete. A comparison of kindred series of phenomena, or the
method of combination, is here the most important instrument for
inquiry, and this method was applied by Goethe with as much success as
with conscious knowledge of its value, in his works relating to the
philosophy of nature.

The most celebrated among Goethe’s writings relating to organic nature
is his _Metamorphosis of Plants_, which appeared in 1790, a work which
distinctly shows a grasp of the fundamental idea of the theory of
development, inasmuch as Goethe, in it, was labouring to point out a
single organ, by the infinitely varied development and metamorphosis of
which the whole of the endless variety of forms in the world of plants
might be conceived to have arisen; this fundamental organ he found in
the _leaf_. If at that time the microscope had been generally employed,
if Goethe had examined the structure of organisms by the means of the
microscope he would have gone still further, and would have seen that
the leaf is itself a compound of individual parts of a lower order, that
is, of _cells_. He would then not have declared that the leaf, but that
the _cell_ is the real fundamental organ by the multiplication,
transformation, and combination (synthesis) of which, in the first
place, the leaf is formed; and that, in the next place, by
transformation, variation, and combination of leaves there arise all
the varied beauties in form and colour which we admire in the green
parts, as well as in the organs of propagation, or the flowers of
plants. Goethe here showed that in order to comprehend the whole of the
phenomena, we must in the first place compare them, and, secondly,
search for a simple type, a simple fundamental form, of which all other
forms are only infinite variations.

Something similar to what he had here done for the metamorphosis of
plants he then did for the Vertebrate animals, in his celebrated
_vertebral theory of the skull_. Goethe was the first to show,
independently of Oken, who almost simultaneously arrived at the same
thought, that the skull of man and of all Vertebrate animals, in
particular mammals, is nothing more than a bony case, formed of the same
bones,—that is, vertebræ,—out of which the spine also is composed. The
vertebræ of the skull are like those of the spine, bony rings lying
behind each other, but in the skull are peculiarly changed and
specialized (differentiated). Although this idea has been strongly
modified by recent discoveries, yet in Goethe’s day it was one of the
greatest advances in comparative anatomy, and was not only one of the
first advances towards the understanding of the structure of Vertebrate
animals, but at the same time explained many individual phenomena. When
two parts of a body, such as the skull and spine, which appear at first
sight so different, were proved to be parts originally the same,
developed out of one and the same foundation, one of the difficult
problems of the philosophy of nature was solved. Here again we meet the
notion of a single type—the conception of a single principle, which
becomes infinitely varied in the different species, and in the parts of
individual species.

But Goethe did not merely endeavour to search for such far-reaching
laws, he also occupied himself most actively for a long time with
numerous individual researches, especially in comparative anatomy. Among
these, none is perhaps more interesting than the discovery of the _mid
jawbone in man_. As this is, in several respects, of importance to the
theory of development, I shall briefly explain it here. There exist in
all mammals two little bones in the upper jaw, which meet in the centre
of the face, below the nose, and which lie between the two halves of the
real upper jawbone. These two bones, which hold the four upper cutting
teeth, are recognized without difficulty in most mammals; in man,
however, they were at that time unknown, and celebrated comparative
anatomists even laid great stress upon this want of a mid jawbone, as
they considered it to constitute the principal difference between men
and apes—the want of a mid jawbone was, curiously enough, looked upon
as the most human of all human characteristics. But Goethe could not
accept the notion that man, who in all other corporeal respects was
clearly only a mammal of higher development, should lack this mid
jawbone.

By the general law of induction as to the mid jawbone he arrived at the
special deductive conclusion that it must exist in man also, and Goethe
did not rest until, after comparing a great number of human skulls, he
really found the mid jawbone. In some individuals it is preserved
throughout a whole lifetime, but usually at an early age it coalesces
with the neighbouring upper jawbone, and is therefore only to be found
as an independent bone in very youthful skulls. In human embryos it can
now be pointed out at any moment. In man, therefore, the mid jawbone
actually exists, and to Goethe the honour is due of having first firmly
established this fact, so important in many respects; and this he did
while opposed by the celebrated anatomist, Peter Camper, one of the most
important professional authorities. The way by which Goethe succeeded in
establishing this fact is especially interesting; it is the way by which
we continually advance in biological science, namely, by way of
induction and deduction. _Induction_ is the inference of a general law
from the observation of numerous individual cases; _deduction_, on the
other hand, is an inference from this general law applied to a single
case which has not yet been actually observed. From the collected
empirical knowledge of those days, the inductive conclusion was arrived
at that all mammals had mid jawbones. Goethe drew from this the
deductive conclusion, that man, whose organization was in all other
respects not essentially different from mammals, must also possess this
mid jawbone; and on close examination it was actually found. The
deductive conclusion was confirmed and verified by experience.

Even these few remarks may serve to show the great value which we must
ascribe to Goethe’s biological researches. Unfortunately most of his
labours devoted to this subject are so hidden in his collected works,
and his most important observations and remarks so scattered in numerous
individual treatises—devoted to other subjects—that it is difficult to
find them out. It also sometimes happens that an excellent, truly
scientific remark is so much interwoven with a mass of useless
philosophical fancies, that the latter greatly detract from the former.

Nothing is perhaps more characteristic of the extraordinary interest
which Goethe took in the investigation of organic nature than the lively
way in which, even in his last years, he followed the dispute which
broke out in France between Cuvier and Geoffroy de St. Hilaire. Goethe,
in a special treatise which was only finished a few days before his
death, in March, 1832, has given an interesting description of this
remarkable dispute and its general importance, as well as an excellent
sketch of the two great opponents. This treatise bears the title
“Principes de Philosophic Zoologique par M. Geoffroy de Saint Hilaire”;
it is Goethe’s last work, and forms the conclusion of the collected
edition of his works. The dispute itself was, in several respects, of
the highest interest. It turned essentially upon the justification of
the theory of development. It was carried on, moreover, in the bosom of
the French Academy, by both opponents, with a personal vehemence almost
unheard of in the dignified sessions of that learned body; this proved
that both naturalists were fighting for their most sacred and deepest
convictions. The conflict began on the 22nd of February, and was
followed by several others; the fiercest took place on the 19th of July,
1830. Geoffroy, as the chief of the French nature-philosophers,
represented the theory of natural development and the monistic
conception of nature. He maintained the mutability of organic species,
the common descent of the individual species from common primary forms,
and the unity of their organization—or the unity of the plan of
structure, as it was then called.

Cuvier was the most decided opponent of these views, and according to
what we have seen, it could not be otherwise. He endeavoured to show
that the nature-philosophers had no right to rear such comprehensive
conclusions on the basis of the empirical knowledge then possessed, and
that the unity of organization—or plan of structure of organisms—as
maintained by them, did not exist. He represented the teleological
(dualistic) conception of nature, and maintained that “the immutability
of species was a necessary condition for the existence of a scientific
history of nature,” Cuvier had the great advantage over his opponent,
that he was able to bring towards the proof of his assertions things
obvious to the eye; these, however, were only individual facts taken out
of their connection with others. Geoffroy was not able to prove the
higher and general connection of individual phenomena which he
maintained, by equally tangible details. Hence Cuvier, in the eyes of
the majority, gained the victory, and decided the defeat of the
nature-philosophy and the supremacy of the strictly empiric tendency for
the next thirty years.

Goethe of course supported Geoffroy’s views. How deeply interested he
was, even in his 81st year, in this great contest is proved by the
following anecdote related by Soret:—

“Monday, Aug. 2nd, 1830.—The news of the outbreak of the revolution of
July arrived in Weimar to-day, and has caused general excitement. In the
course of the afternoon I went to Goethe. ‘Well?’ he exclaimed as I
entered, ‘what do you think of this great event? The volcano has burst
forth, all is in flames, and there are no more negotiations behind
closed doors.’ ‘A dreadful affair,’ I answered; ‘but what else could be
expected under the circumstances, and with such a ministry, except that
it would end in the expulsion of the present royal family?’ ‘We do not
seem to understand each other, my dear friend,’ replied Goethe. ‘I am
not speaking of those people at all; I am interested in something very
different, I mean the dispute between Cuvier and Geoffroy de Saint
Hilaire, which has broken out in the Academy, and which is of such great
importance to science.’ This remark of Goethe’s came upon me so
unexpectedly, that I did not know what to say, and my thoughts for some
minutes seemed to have come to a complete standstill. ‘The affair is of
the utmost importance,’ he continued, ‘and you cannot form any idea of
what I felt on receiving the news of the meeting on the 19th. In
Geoffroy de Saint Hilaire we have now a mighty ally for a long time to
come. But I see also how great the sympathy of the French scientific
world must be in this affair, for, in spite of the terrible political
excitement, the meeting on the 19th was attended by a full house. The
best of it is, however, that the synthetic treatment of nature,
introduced into France by Geoffroy, can now no longer be stopped. This
matter has now become public through the discussions in the Academy,
carried on in the presence of a large audience; it can no longer be
referred to secret committees, or be settled or suppressed behind closed
doors.’”

In my book on “The General Morphology of Organisms” I have placed as
headings to the different books and chapters a selection of the numerous
interesting and important sentences in which Goethe clearly expresses
his view of organic nature and its constant development. I will here
quote a passage from the poem entitled, “The Metamorphosis of Animals”
(1819).

“All members develop themselves according to eternal laws,
And the rarest form mysteriously preserves the primitive type,
Form therefore determines the animal’s way of life,
And in turn the way of life powerfully reacts upon all form.
Thus the orderly growth of form is seen to hold
Whilst yielding to change from externally acting causes.”[3]

Here, clearly enough, the contrast between two different organic
constructive forms is intimated, which are opposed to one another, and
which by their interaction determine the form of the organism; on the
one hand, a common inner original type, firmly maintaining itself,
constitutes the foundation of the most different forms; on the other
hand, the externally active influence of surroundings and mode of life,
which influence the original type and transform it. This contrast is
still more definitely pointed out in the following passage:—

“An inner original community forms the foundation of all organization;
the variety of forms, on the other hand, arises from the necessary
relations to the outer world, and we may therefore justly assume an
original difference of conditions, together with an uninterruptedly
progressive transformation, in order to be able to comprehend the
constancy as well as the variations of the phenomena of form.”

The “original type” which constitutes the foundation of
every organic form “as the inner original community” is the _inner
constructive force_, which receives the original direction of
form-production—that is, the tendency to give rise to a particular
form—and is propagated by _Inheritance_. The “uninterruptedly
progressive transformation,” on the other hand, which “springs from the
necessary relations to the outer world,” acting as an _external
formative force_, produces, by _Adaptation_ to the surrounding
conditions of life, the “infinite variety of forms” (Gen. Morph. i. 154;
ii. 224). The internal formative tendency of _Inheritance_, which
retains the unity of the original type, is called by Goethe in another
passage the _centripetal force_ of the organism, or its tendency to
specification; in contrast with this he calls the external formative
tendency of _Adaptation_, which produces the variety of organic forms,
the _centrifugal force_ of organisms, or their tendency to variation.
The passage in which he clearly indicates the “equilibrium” of these two
extremely important organic formative tendencies, runs as follows: “The
idea of _metamorphosis_ resembles the vis centrifuga, and would lose
itself in the infinite, if a counterpoise were not added to it: I mean
the tendency to _specification_, the strong power to preserve what once
has come into being, a vis centripeta, which in its deepest foundation
cannot be affected by anything external.”

Metamorphosis, according to Goethe, consists not merely, as the word is
now generally understood, in the changes of form which the organic
individual experiences during its individual development, but, in a
wider sense, in the transformation of organic forms in general. His idea
of metamorphosis is almost synonymous with the theory of development.
This is clear, among other things, from the following passage:—“The
triumph of physiological metamorphosis manifests itself where the whole
separates and transforms itself into families, the families into genera,
the genera into species, and then again into other varieties down to the
individual. This operation of nature goes on ad infinitum; she cannot
rest inactive, but neither can she keep and preserve all that she has
produced. From seeds there are always developed varying plants,
exhibiting the relations of their parts to one another in an altered
manner.”

Goethe had, in truth, discovered two great mechanical forces of nature,
which are the active causes of organic formations, his two organic
formative tendencies—on the one hand the conservative, centripetal, and
internal formative tendency of Inheritance or specification; and on the
other hand the progressive, centrifugal, and external formative tendency
of Adaptation, or metamorphosis. This profound biological intuition
could not but lead him naturally to the fundamental idea of the Doctrine
of Filiation, that is, to the conception that the organic species
resembling one another in form are actually related by blood, and that
they are descended from a common original type. In regard to the most
important of all animal groups, namely that of Vertebrate animals,
Goethe expresses this doctrine in the following passage (1796):—“Thus
much then we have gained, that we may assert without hesitation that all
the more perfect organic natures, such as fishes, amphibious animals,
birds, mammals, and man at the head of the last, were all formed upon
one original type, which only varies more or less in parts which are
none the less permanent, and still daily changes and modifies its form
by propagation.”

This sentence is of interest in more than one way. The theory that all
“the more perfect organic natures,” that is all Vertebrate animals, are
descended from one common prototype, that they have arisen from it by
propagation (Inheritance) and transformation (Adaptation), may be
distinctly inferred. But it is especially interesting to observe that
Goethe admits no exceptional position for man, but rather expressly
includes him in the tribe of the other Vertebrate animals. The most
important special inference of the Doctrine of Filiation, that man is
descended from other Vertebrate animals, may here be recognized in the
germ.(3)

This exceedingly important fundamental idea is expressed by Goethe still
more clearly in another passage (1807), in the following words:—“If we
consider plants and animals in their most imperfect condition, they can
scarcely be distinguished. But this much we can say, that the creatures
which by degrees emerge as plants and animals out of a common phase,
where they are barely distinguishable, arrive at perfection in two
opposite directions; so that the plant in the end reaches its highest
glory in the tree, which is immovable and stiff, the animal in man, who
possesses the greatest elasticity and freedom.” This remarkable passage
not only indicates most explicitly the genealogical relationship between
the vegetable and animal kingdoms, but contains the germ of the
monophyletic hypothesis of descent, the importance of which I shall have
to explain hereafter. (Compare Chapter XVI. and the Pedigree, p. 398.)

At the time when Goethe in this way sketched the fundamental features of
the Theory of Descent, another German philosopher, Gottfried Reinhold
Treviranus, of Bremen (born 1776, died 1837), was zealously engaged at
the same work. As Wilhelm Focke has recently shown, Treviranus, even in
the earliest of his greater works, “The Biology or Philosophy of Animate
Nature,” which appeared at the beginning of the present century, had
already developed monistic views of the unity of nature, and of the
genealogical connection of the species of organisms, which entirely
correspond with our present view of the matter. In the first three
volumes of the Biology, which appeared successively in 1802, 1803, and
1805 (therefore several years before Oken’s and Lamarck’s principal
works), we find numerous passages which are of interest in this respect.
I shall here quote only a few of the most important.

In speaking of the principal question of our theory, the question of the
origin of organic species, Treviranus makes the following
remarks:—“Every form of life can be produced by physical forces in one
of two ways: either by coming into being out of formless matter, or by
modification of an already existing form by a continued process of
shaping. In the latter case the cause of this modification may lie
either in the influence of a dissimilar male generative matter upon the
female germ, or in the influence of other powers which operate only
after procreation. In every living being there exists the capability of
an endless variety of form-assumption; each possesses the power to adapt
its organization to the changes of the outer world, and it is this power
put into action by the change of the universe that has raised the simple
zoophytes of the primitive world to continually higher stages of
organization, and has introduced a countless variety of species into
animate nature.”

By _zoophytes_, Treviranus here means organisms of the lowest order and
of the simplest character, namely, those neutral primitive beings which
stand midway between animals and plants, and on the whole correspond
with our _protista_. “These zoophytes,” he remarks in another passage,
“are the original forms out of which all the organisms of the higher
classes have arisen by gradual development. We are further of opinion
that every species, as well as every individual, has certain periods of
growth, of bloom, and of decay, but that the decay of a species is
_degeneration_, not dissolution, as in the case of the individual. From
this it appears to us to follow that it was not the great catastrophes
of the earth (as is generally supposed) which destroyed the animals of
the primitive world, but that many survived them, and it is more
probable that they have disappeared from existing nature, because the
species to which they belonged have completed the circle of their
existence, and have become changed into other kinds.”

When Treviranus, in this and other passages, points to _degeneration_ as
the most important cause of the transformation of the animal and
vegetable species, he does not understand by it what is now commonly
called degeneration. With him “degeneration” is exactly what we now call
_Adaptation_ or _modification_, by the action of external formative
forces. That Treviranus explained this trans-transformation of organic
species by Adaptation, and its preservation by Inheritance, and thus the
whole variety of organic forms by the interaction of Adaptation and
Inheritance, is clear also from several other passages. How profoundly
he grasped the mutual dependence of all living creatures on one another,
and in general the _universal connection between cause and effect_—that
is, the monistic causal connection between all members and parts of the
universe—is further shown, among others, by the following remarks in
his Biology:—“The living individual is dependent upon the species, the
species upon the fauna, the fauna upon the whole of animate nature, and
the latter upon the organism of the earth. The individual possesses
indeed a peculiar life, and so far forms its own world. But just because
its life is limited it constitutes at the same time an organ in the
general organism. Every living body exists in consequence of the
universe, but the universe, on the other hand, exists in consequence of
it.”

It is self-evident that so profound and clear a thinker as Treviranus,
in accordance with this grand mechanical conception of the universe,
could not admit for man a privileged and exceptional position in nature,
but assumed his gradual development from lower animal forms. And it is
equally self-evident, on the other hand, that he did not admit a chasm
between organic and inorganic nature, but maintained the absolute unity
of the organization of the whole universe. This is specially attested by
the following sentence:—“Every inquiry into the influence of the whole
of nature on the living world must start from the principle, that all
living forms are products of physical influences, which are acting even
now, and are changed only in degree, or in their direction.” Hereby, as
Treviranus himself says, “The fundamental problem of biology is solved,”
and we add, solved in a purely mechanical or monistic sense.

Neither Treviranus nor Goethe is commonly considered the most eminent of
the German nature-philosophers, but Lorenz Oken, who, in establishing
the vertebral theory of the skull, came forward as a rival to Goethe,
and did not entertain a very kindly feeling towards him. Although they
lived for some time in the same neighbourhood, yet the natures of these
two men were so very different, that they could not well be drawn
towards each other. Oken’s “Manual of the Philosophy of Nature,” which
may be designated as the most important production of the
nature-philosophy school then existing in Germany, appeared in 1809, the
same year in which Lamarck’s fundamental work, the “Philosophie
Zoologique,” was published. As early as 1802, Oken had published an
“Outline of the Philosophy of Nature.” As we have already intimated, in
Oken’s as in Goethe’s works, a number of valuable and profound thoughts
are hidden among a mass of erroneous, very eccentric, and fantastic
conceptions. Some of these ideas have only quite recently and gradually
become recognized in science, many years after they were first
expressed. I shall here quote only two thoughts, which are almost
prophetic, and which at the same time stand in the closest relation to
the theory of development.

One of the most important of Oken’s theories, which was formerly very
much decried, and was most strongly combatted, especially by the
so-called “exact experimentalists,” is the idea that the phenomena of
life in all organisms proceed from a common chemical substance, so to
say, from a general simple _vital-substance_, which he designated by the
name _Urschleim_, or _original slime_. By it he meant, as the name
indicates, a mucilaginous substance, an albuminous combination, which
exists in a semi-fluid condition of aggregation, and possesses the
power, by adaptation to different conditions of existence in the outer
world and by interaction with its material, of producing the most
various forms. Now, we need only change the expression “original slime”
(Urschleim) into _Protoplasm_, or _cell-substance_, in order to arrive
at one of the grandest results which we owe to microscopic
investigations during the last ten years, more especially to those of
Max Schultze. By these investigations it has been shown that in all
living bodies, without exception, there exists a certain quantity of
mucilaginous albuminous matter, in a semi-fluid condition; and that this
nitrogen-holding carbon-compound is exclusively the original seat and
agent of all the phenomena of life, and of all production of organic
forms. All other substances which appear in the organism, besides these,
are either formed by this active matter of life, or have been introduced
from without. The organic egg, the original cell out of which every
animal and plant is first developed, consists essentially only of one
round little lump of such albuminous matter. Even the yolk of an egg is
nothing but albumen, mixed with granules of fat. Oken was therefore
right when, more divining than knowing, he made the assertion—“Every
organic thing has arisen out of slime, and is nothing but slime in
different forms. This primitive slime originated in the sea, from
inorganic matter in the course of planetary-evolution.”

Another equally grand idea of the same philosopher is closely connected
with his theory of primitive slime, which coincides with the extremely
important _Protoplasm theory_. For Oken, as early as 1809, asserted that
the primitive slime produced in the sea by spontaneous generation, at
once assumed the form of microscopically small bladders, which he called
“_Mile_,” or “_Infusoria_.” “Organic nature has for its basis an
infinity of such vesicles.” These little bladders arise from original
semi-fluid globules of the primitive slime, by the fact of their
periphery becoming condensed. The simplest organism, as well as every
animal and every plant of higher kind, is nothing else than “an
accumulation (synthesis) of such infusorial bladders, which by various
combinations assume various forms, and thus develop into higher
organisms.” Here again we need only translate the expression _little
bladder_, or _infusorium_, by the word _cell_, and we arrive at the Cell
theory, one of the grandest biological theories of our century.
Schleiden and Schwann, about thirty years ago, were the first to furnish
experiential proof that all organisms are either simple cells, or
accumulations (syntheses) of such cells, and the more recent protoplasm
theory has shown that protoplasm (the original slime) is the most
essential (and sometimes the only) constituent part of the genuine cell.
The properties which Oken ascribes to his Infusoria are exactly the
properties of cells, the properties of elementary beings, by whose
accumulation, combination, and varying development, the higher organisms
are formed.

These two extremely fruitful thoughts of Oken, on account of the absurd
form in which he expressed them, were at first little heeded, or
entirely misunderstood, and it was reserved for a much later era to
establish them by actual observation. The supposition that the
individual species of plants and animals originated from common
prototypes by a slow and gradual development of the higher organisms out
of lower ones, was of course most closely connected with these ideas.
Man’s descent from lower organisms was likewise asserted by Oken—“Man
has been developed, not created.” Although many arbitrary perversities
and extravagant fancies may be found in Oken’s philosophy of nature,
they must not prevent us paying our just admiration to these grand
ideas, which were so far in advance of their age. This much is clearly
evident from the statements of Goethe and Oken which we have quoted, and
from the views of Lamarck and Geoffroy which have to be discussed next,
that during the first decade of our century no doctrine approached so
nearly to the natural Theory of Descent, newly established by Darwin, as
the much decried “Natur-philosophie.”

CHAPTER V.

THEORY OF DEVELOPMENT ACCORDING TO KANT AND LAMARCK.

Kant’s Dualistic Biology.—His Conception of the Origin
of Inorganic Nature by Mechanical Causes, of Organic
Nature by Causes acting for a Definite
Purpose.—Contradiction of this Conception with his
leaning towards the Theory of Descent.—Kant’s
Genealogical Theory of Development.—Its Limitation by
his Teleology.—Comparison of Genealogical Biology with
Comparative Philology.—Views in favour of the Theory of
Descent entertained by Leopold Buch, Bär, Schleiden,
Unger, Schaafhausen, Victor Carus, Büchner.—French
Nature-philosophy.—Lamarck’s Philosophie
Zoologique.—Lamarck’s Monistic (mechanical) System of
Nature.—His Views of the Interaction of the Two Organic
Formative Tendencies of Inheritance and
Adaptation.—Lamarck’s Conception of Man’s Development
from Ape-like Mammals.—Geoffroy St. Hilaire’s, Naudin’s,
and Lecoq’s Defence of the Theory of Descent.—English
Nature-philosophy.—Views in favour of the Theory of
Descent, entertained by Erasmus Darwin, W. Herbert,
Grant, Freke, Herbert Spencer, Hooker, Huxley.—The
Double Merit of Charles Darwin.

The teleological view of nature, which explains the phenomena of the
organic world by the action of a personal Creator acting for a definite
purpose, necessarily leads, when carried to its extreme consequences,
either to utterly untenable contradictions, or to a twofold (dualistic)
conception of nature, which most directly contradicts the unity and
simplicity of the supreme laws which are everywhere perceptible. The
philosophers who embrace teleology must necessarily assume two
fundamentally different natures: an _inorganic_ nature, which must be
explained by causes acting _mechanically_ (causæ efficientes), and an
_organic_ nature, which must be explained by _causes acting for a
definite purpose_ (causæ finales). (Compare p. 34.)

This dualism meets us in a striking manner when considering the
conceptions of nature formed by Kant, one of the greatest German
philosophers, and his ideas of the coming into being of organisms. A
closer examination of these ideas is forced upon us here, because in
Kant we honour one of the few philosophers who combine a solid
scientific culture with an extraordinary clearness and profundity of
speculation. The Königsberg philosopher gained the highest celebrity,
not only among speculative philosophers as the founder of critical
philosophy, but acquired a brilliant name also among naturalists by his
mechanical cosmogeny. Even in the year 1755, in his “General History of
Nature, and Theory of the Heavens,”(22) he made the bold attempt “to
discuss the constitution and the mechanical origin of the whole
universe, according to Newton’s principles,” and to explain them
mechanically by the natural course of development, to the exclusion of
all miracles. This cosmogeny of Kant, or “cosmological gas theory,”
which we shall briefly discuss in a future chapter, was at a later day
fully established by the French mathematician Laplace and the English
astronomer Herschel, and enjoys at the present day almost universal
recognition. On account of this important work alone, in which exact
knowledge is coupled with most profound speculation, Kant deserves the
honourable name of a natural philosopher in the best and purest sense of
the word.

If we read Kant’s Criticism of the Teleological Faculty of Judgment, his
most important biological work, we perceive that in contemplating
organic nature he always maintains what is essentially the teleological
or dualistic point of view; whilst for inorganic nature he,
unconditionally and without reserve, assumes the mechanical or monistic
method of explanation. He affirms that in the domain of inorganic nature
all the phenomena can be explained by mechanical causes, by the moving
forces of matter itself, but not so in the domain of organic nature. In
the whole of Anorganology (in Geology and Mineralogy, in Meteorology and
Astronomy, in the physics and chemistry of inorganic natural bodies),
all phenomena are said to be explicable merely by _mechanism_ (causa
efficiens), without the intervention of a final purpose. In the whole
domain of Biology, on the other hand—in Botany, Zoology, and
Anthropology—mechanism is not considered sufficient to explain to us
all their phenomena; but we are supposed to be able to comprehend them
only by an assumption of a _final cause_ acting for a definite purpose
(causa finalis). In several passages Kant emphatically remarks that,
from a strictly scientific point of view, _all_ phenomena, without
exception, require a mechanical interpretation, and that _mechanism
alone can offer a true explanation_. But at the same time he thinks,
that in regard to living natural bodies, animals and plants, our human
power of comprehension is limited, and not sufficient for arriving at
the real cause of organic processes, especially at the origin of organic
forms. The _right_ of human reason to explain all phenomena mechanically
is unlimited, he says, but its _power_ is limited by the fact that
organic nature can be conceived only from a teleological point of view.

Some passages are, however, very remarkable, in which Kant in a
surprising manner deviates from this mode of viewing things, and
expresses, more or less distinctly, the fundamental idea of the Theory
of Descent. He even asserts the necessity of a genealogical conception
of the series of organisms, if we at all wish to understand it
scientifically. The most important and remarkable of these passages
occurs in his “Methodical System of the Teleological Faculty of
Judgment” (§ 79), which appeared in 1790 in the “Criticism of the
Faculty of Judgment.” Considering the extraordinary interest which this
passage possesses, both for forming a correct estimate of Kant’s
philosophy, as well as for the Theory of Descent, I shall here insert it
_verbatim_.

“It is desirable to examine the great domain of organized nature by
means of a methodical comparative anatomy, in order to discover whether
we may not find in it something resembling a system, and that too in
connection with the mode of generation, so that we may no longer be
compelled to stop short with a mere consideration of forms as they
are—which gives us no insight into their generation—and need no longer
give up in despair all hope of gaining a full insight into this
department of nature. The agreement of so many kinds of animals in a
certain common plan of structure, which seems to be visible not only in
their skeletons, but also in the arrangement of the remaining parts—so
that a wonderfully simple typical form, by the shortening and
lengthening of some parts, and by the suppression and development of
others, might be able to produce an immense variety of species—gives us
a ray of hope, though feeble, that here perhaps some result may be
obtained, by the application of the principle of the _mechanism of
nature_, without which, in fact, no science can exist. This analogy of
forms (in so far as they seem to have been produced in accordance with a
common prototype, notwithstanding their great variety) strengthens the
supposition that they have an actual blood-relationship, due to
origination from a common parent; a supposition which is arrived at by
observation of the graduated approximation of one class of animals to
another, beginning with the one in which the principle of purposiveness
seems to be most conspicuous, that is man, and extending down to the
polyps, and from these even down to mosses and lichens, and arriving
finally at raw matter, the lowest stage of nature observable by us. From
this matter and its forces the whole apparatus of Nature seems to have
descended according to mechanical laws (such as those which she follows
in the production of crystals); yet this apparatus, as seen in organic
beings, is so incomprehensible to us, that we feel ourselves compelled
to conceive for it a different principle. But it would seem that the
archæologist of Nature is at liberty to regard the great _Family_ of
creatures (for as a Family we must conceive it, if the above-mentioned
continuous and connected relationship has a real foundation) as having
sprung from the immediate results of her earliest revolutions, judging
from all the laws of their mechanism known to or conjectured by him.”

If we take this remarkable passage out of Kant’s “Criticism of the
Teleological Faculty of Judgment,” and consider it by itself, we cannot
but be astonished to find how profoundly and clearly the great thinker,
even in 1790, had recognized the inevitable necessity of the Doctrine of
Descent, and designated it as the only possible way of explaining
organic nature by mechanical laws—that is, by true scientific
reasoning. On account of this one passage taken by itself, we might
place Kant beside Goethe and Lamarck, as one of the first founders of
the Doctrine of Descent; and considering the high authority which Kant’s
Critical Philosophy most justly enjoys, this circumstance might perhaps
induce many a philosopher to decide in favour of the theory. But as soon
as we consider this passage in connection with the other train of
thoughts in the “Criticism of the Faculty of Judgment,” and balance it
against other directly contradictory passages, we see clearly that Kant,
in these and some similar (but weaker) sentences, went beyond himself,
and abandoned the teleological point of view which he usually adopts in
Biology.

Directly after the admirable passage which I have just quoted, there
follows a remark which completely takes off its edge. After having quite
correctly maintained the origin of organic forms out of raw matter by
mechanical laws (in the manner of crystallization), as well as a gradual
development of the different species by descent from one common original
parent, Kant adds, “But he (the archæologist of nature, that is the
palæontologist) must for this end ascribe to the common mother an
organization ordained purposely with a view to the needs of all her
offspring, otherwise the possibility of suitability of form in the
products of the animal and vegetable kingdoms (_i.e._ teleological
adaptation) cannot be conceived at all.” This addition clearly
contradicts the most important fundamental thought of the preceding
passage, viz., that a purely mechanical explanation of organic nature
becomes possible through the Theory of Descent. And that the
teleological conception of organic nature predominated with Kant, is
shown by the heading of the remarkable § 79, which contains the two
contradictory passages cited: “_Of the Necessary Subordination of the
Mechanical to the Teleological Principle, in the explanation of a thing
as a purpose or object of Nature._”

He expresses himself most decidedly against the mechanical explanation
of organic nature in the following passage (§ 74): “It is quite certain
that we cannot become sufficiently acquainted with organized creatures
and their hidden potentialities by aid of purely mechanical natural
principles, much less can we explain them; and this is so certain, that
we may boldly assert that it is absurd for man even to conceive such an
idea, or to hope that a Newton may one day arise able to make the
production of a blade of grass comprehensible, according to natural laws
ordained by no intention; such an insight we must absolutely deny to
man.” Now, however, this impossible Newton has really appeared seventy
years later in Darwin, whose Theory of Selection has actually solved the
problem, the solution of which Kant had considered absolutely
inconceivable!

In connection with Kant and the German philosophers whose theories of
development have already occupied us in the preceding chapter, it seems
justifiable to consider briefly some other German naturalists and
philosophers, who, in the course of our century, have more or less
distinctly resisted the prevailing teleological views of creation, and
vindicated the mechanical conception of things which is the basis of the
Doctrine of Filiation. Sometimes general philosophical considerations,
sometimes special empirical observations, were the motives which led
these thinking men to form the idea that the various individual species
of organisms must have originated from common primary forms. Among them
I must first mention the great German geologist, Leopold Buch. Important
observations as to the geographical distribution of plants led him to
the following remarkable assertion in his excellent “Physical
Description of the Canary Islands”:—

“The individuals of genera, on continents, spread and widely diffuse
themselves, and by the difference of localities, nourishment, and soil,
form varieties; and being in consequence of their isolation never
crossed by other varieties, and so brought back to the main type, they
in the end become a permanent and a distinct species. Then, perhaps, in
other ways, they once more become associated with other descendants of
the original form—which have likewise become new varieties—and both
now appear as very distinct species, no longer mingling with one
another. Not so on islands. Being commonly confined in narrow valleys or
within the limit of small zones, individuals can reach one another and
destroy every commencing production of a permanent variety. Much in the
same way the peculiarities or faults in language, originating with the
head of some family, become, through the extension of the family,
indigenous throughout a whole district. If the district is separated and
isolated, and if the language is not brought back to its former purity
by constant connection with that spoken in neighbouring districts, a
dialect will be the result. If natural obstacles, forests, constitution,
form of government, unite the inhabitants of the separate district still
more closely, and separate them still more completely from their
neighbours, the dialect is fixed, and becomes a completely distinct
language.” (Uebersicht der Flora auf den Canarien, S. 133.)

We perceive that Buch is here led to the fundamental idea of the Theory
of Descent by the phenomena of the geography of plants, a department of
biological knowledge which in fact furnishes a mass of proofs in favour
of it. Darwin has minutely discussed these proofs in two separate
chapters of his book (the 11th and 12th). Buch’s remark is further of
interest, because it leads us to the exceedingly instructive comparison
of the different branches of language with the species of organisms, a
comparison which is of the greatest use to Comparative Philology, as
well as to Comparative Botany and Zoology. Just as, for example, the
different dialects, provincialisms, branches, and off-shoots of the
German, Slavonic, Greco-Latin, and Irano-Indian parent language, are
derived from a single common Indo-Germanic parent tongue, and just as
their _differences_ are explained by _Adaptation_, and their common
_fundamental characters_ explained by _Inheritance_, so in like manner
the different species, genera, families, orders, and classes of
Vertebrate animals are derived from a single common vertebrate form of
animal. Here also Adaptation is the cause of differences, Inheritance
the cause of community of character. This interesting parallelism in the
divergent development of the forms of speech and the forms of organisms
has been discussed in the clearest manner by one of our first
comparative philologists, the talented Augustus Schleicher, whose
premature death, four years ago, remains an irreparable loss, not only
to our University of Jena, but to the whole of monistic science.(6)

Among other eminent German naturalists who have expressed their belief
in the Theory of Descent more or less distinctly, arriving at their
conclusion in very various ways, I must next mention Carl Ernst Bär,
the great reformer of animal embryology. In a lecture delivered in 1834,
entitled “The Most General Laws of Nature in All Development,” he shows,
in the clearest way, that only in a very childish view of nature could
organic species be regarded as permanent and unchangeable types, and
that really they can be only passing series of generations, which have
developed by transformation from a common original form. The same
conception again received firm support from Baer, in 1859, through a
consideration of the laws of the geographical distribution of organisms.

J. M. Schleiden, who founded, thirty years ago, in Jena, a new epoch in
Botany by his strictly empirico-philosophical and truly scientific
method, illustrated the philosophical significance of the conception of
organic species in his incisive “Outlines of Scientific Botany,”(7) and
showed that it had only a subjective origin in the general _law of
specification_. The different species of plants are only the specified
productions of the formative tendencies of plants, which arise from the
various combinations of the fundamental forces of organic matter.

The eminent botanist, F. Unger, of Vienna, was led by his profound and
comprehensive investigations on extinct vegetable species, to a
palæontological history of the development of the vegetable kingdom,
which distinctly asserts the principle of the Theory of Descent. In his
“Attempt at a History of the World of Plants” (1852), he maintains the
derivation of all different species of plants from a few primary forms,
and perhaps from a single original plant, a simple vegetable cell. He
shows that this view is founded on the genetic connection of all
vegetable forms, and is necessary, not merely upon philosophical
grounds, but upon those of experience and observation.(8)

Victor Carus, of Leipzig, in the Introduction to his excellent “System
of Animal Morphology,”(9) published in 1853, in which he endeavours to
establish in a philosophical manner the universal constructive laws of
the animal body through comparative anatomy and the history of
development, makes the following remark:—“The organisms buried in the
most ancient geological strata must be looked upon as the ancestors from
whom the rich diversity of forms of the present creation have originated
by continued generation, and by accommodation to progressive and very
different conditions of life.”

In the same year (1853) Schaaffhausen, the anthropologist of Bonn, in an
Essay “On the Permanence and Transformation of Species,” declared
himself decidedly in favour of the Theory of Descent. According to him,
the living species of animals and plants are the transformed descendants
of extinct species, from which they have arisen by gradual modification.
The divergence or separation of the most nearly allied species takes
place by the destruction of the connecting intermediate stages.
Schaaffhausen also maintained, with distinctness, the origin of the
human race from animals, and its gradual development from ape-like
animals, the most important deduction from the Doctrine of Filiation.

Lastly, we have still to mention among the German Nature-philosophers
the name of Louis Büchner, who, in his celebrated work, “Force and
Matter” (1855), also independently developed the principles of the
Theory of Descent, taking his stand mainly on the ground of the
undeniable evidences of fact which are furnished by the palæontological
and individual development of organisms, as well as by their
comparative anatomy and by the parallelism of these series of
development. Büchner showed very clearly that, even from such data
alone, the derivation of the different organic species from common
primary forms followed as a necessary conclusion, and that the origin of
these original primary forms could only be conceived of as the result of
a spontaneous generation.

We now turn from the German to the French Nature-philosophers, who have
likewise held the Theory of Descent, since the beginning of the present
century. At their head stands Jean Lamarck, who occupies the first place
next to Darwin and Goethe in the history of the Doctrine of Filiation.
To him will always belong the immortal glory of having for the first
time worked out the Theory of Descent, as an independent scientific
theory of the first order, and as the philosophical foundation of the
whole science of Biology. Although Lamarck was born as early as 1744, he
did not begin the publication of his theory until the commencement of
the present century, in 1801, and established it more fully only in
1809, in his classic “Philosophie Zoologique.”(2) This admirable work is
the first connected exposition of the Theory of Descent carried out
strictly into all its consequences. By its purely mechanical method of
viewing organic nature, and the strictly philosophical proofs brought
forward in it, Lamarck’s work is raised far above the prevailing
dualistic views of his time; and with the exception of Darwin’s work,
which appeared just half a century later, we know of none which we could
in this respect place by the side of the “Philosophie Zoologique.” How
far it was in advance of its time is perhaps best seen from the
circumstance that it was not understood by most men, and for fifty
years was not spoken of at all. Cuvier, Lamarck’s greatest opponent, in
his “Report on the Progress of Natural Sciences,” in which the most
unimportant anatomical investigations are enumerated, does not devote a
single word to this work, which forms an epoch in science. Goethe, also,
who took such a lively interest in the French nature-philosophy and in
“the thoughts of kindred minds beyond the Rhine,” nowhere mentions
Lamarck, and does not seem to have known the “Philosophie Zoologique” at
all. The great reputation which Lamarck gained as a naturalist he does
not owe to his highly important general work, but to numerous special
treatises on the lower animals, particularly on Molluscs, as well as to
an excellent “Natural History of Invertebrate Animals,” which appeared,
in seven volumes, between the years 1815-1822. The first volume of this
celebrated work contains in the general introduction a detailed
exposition of his theory of filiation. I can, perhaps, give no better
idea of the extraordinary importance of the “Philosophie Zoologique”
than by quoting _verbatim_ some of the most important passages
therefrom:—

“The systematic divisions of classes, orders, families, genera, and
species, as well as their designations, are the arbitrary and artificial
productions of man. The kinds or species of organisms are of unequal
age, developed one after the other, and show only a relative and
temporary persistence; species arise out of varieties. The differences
in the conditions of life have a modifying influence on the
organization, the general form, and the parts of animals, and so has the
use or disuse of organs. In the first beginning only the very simplest
and lowest animals and plants came into existence; those of a more
complex organization only at a later period. The course of the earth’s
development, and that of its organic inhabitants, was continuous, not
interrupted by violent revolutions. Life is purely a physical
phenomenon. All the phenomena of life depend on mechanical, physical,
and chemical causes, which are inherent in the nature of matter itself.
The simplest animals and the simplest plants, which stand at the lowest
point in the scale of organization, have originated and still originate
by spontaneous generation. All animate natural bodies or organisms are
subject to the same laws as inanimate natural bodies or anorgana. The
ideas and actions of the understanding are the motional phenomena of the
central nervous system. The will is in truth never free. Reason is only
a higher degree of development and combination of judgments.”

These are indeed astonishingly bold, grand, and far-reaching views, and
were expressed by Lamarck sixty years ago; in fact, at a time when their
establishment, by a mass of facts, was not nearly as possible as it is
in our day. Indeed Lamarck’s work is really a complete and strictly
monistic (mechanical) system of nature, and all the important general
principles of monistic Biology are already enunciated by him: the unity
of the active causes in organic and inorganic nature; the ultimate
explanation of these causes in the chemical and physical properties of
matter itself; the absence of a special vital power, or of an organic
final cause; the derivation of all organisms from some few, most simple
original forms, which have come into existence by spontaneous generation
out of inorganic matter; the coherent course of the whole earth’s
history; the absence of violent cataclysmic revolutions; and in general
the inconceivableness of any miracle, of any supernatural interference,
in the natural course of the development of matter.

The fact that Lamarck’s wonderful intellectual feat met with scarcely
any recognition, arises partly from the immense length of the gigantic
stride with which he had advanced beyond the next fifty years, partly
from its defective empirical foundation, and from the somewhat one-sided
character of some of his arguments. Lamarck quite correctly recognizes
_Adaptation_ as the first mechanical cause which effects the continual
transformation of organic forms, while he traces with equal justice the
similarity in form of different species, genera, families, etc., to
their blood-relationship, and thus explains it by _Inheritance_.
Adaptation, according to him, consists in this, that the perpetual, slow
change of the outer world causes a corresponding change in the actions
of organisms, and thereby also causes a further change in their forms.
He lays the greatest stress upon the effect of _habit_ upon the use and
disuse of organs. This is certainly of great importance in the
transformation of organic forms, as we shall see later. However, the way
in which Lamarck wished to explain exclusively, or at any rate mainly,
the change of forms, is after all in most cases not possible. He says,
for example, that the long neck of the giraffe has arisen from its
constantly stretching out its neck at high trees, and from the endeavour
to pick the leaves off their branches; as giraffes generally inhabit dry
districts, where only the foliage of trees afford them nourishment, they
were forced to this action. In like manner the long tongues of
wood-peckers, humming-birds, and ant-eaters, are said by him to have
arisen from the habit of fetching their food out of narrow, small, and
deep crevices or channels. The webs between the toes of the webbed feet
in frogs and other aquatic animals have arisen solely from the constant
endeavour to swim, from striking their feet against the water, and from
the very movements of swimming. Inheritance fixed these habits on the
descendants, and finally, by further elaboration, the organs were
entirely transformed. However correct, as a whole, this fundamental
thought may be, yet Lamarck lays the stress too exclusively on _habit_
(use and non-use of organs), certainly one of the most important, but
not the only cause of the change of forms. Still this cannot prevent our
acknowledging that Lamarck quite correctly appreciated the mutual
co-operation of the two organic formative tendencies of Adaptation and
Inheritance. What he failed to grasp is the exceedingly important
principle of “Natural Selection in the Struggle for Existence,” with
which Darwin, fifty years later, made us acquainted.

It still remains to be mentioned as a special merit of Lamarck, that he
endeavoured to prove the _development of the human race_ from other
primitive, ape-like mammals. Here again it was, above all, to habit that
he ascribed the transforming, the ennobling influence. He assumed that
the lowest, original men had originated out of men-like apes, by the
latter accustoming themselves to walk upright. The raising of the body,
the constant effort to keep upright, in the first place led to a
transformation of the limbs, to a stronger differentiation or separation
of the fore and hinder extremities, which is justly considered one of
the most essential distinctions between man and the ape. Behind, the
calf of the leg and the flat soles of the feet were developed; in
front, the arms and hands, for the purpose of seizing objects. The
upright walk was then followed by a freer view over the surrounding
objects, and led consequently to an important progress in mental
development. Human apes thereby soon gained a great advantage over the
other apes, and further, over surrounding organisms in general. In order
to maintain the supremacy over them, they formed themselves into
companies, and there arose, as in the case of all animals living in
company, the desire of communicating to one another their desires and
thoughts. Thus arose the necessity of language, which, consisting at
first of rough and disjointed sounds, soon became more connected,
developed, and articulate. The development of articulate speech now in
turn became the strongest lever for a further progressive development of
the organism, and above all, of the brain, and so ape-like men became
gradually and slowly transformed into real men. In this way the actual
descent of the lowest and rudest primitive men from the most highly
developed apes was distinctly maintained by Lamarck, and supported by a
series of the most important proofs.

The honour of being the chief French nature-philosopher is not usually
assigned to Lamarck, but to Etienne Geoffroy St. Hilaire (the elder),
born in 1771, the same in whom Goethe was especially interested, and
with whom we have already become acquainted as Cuvier’s most prominent
opponent. He developed his ideas about the transformation of organic
species as far back as the end of the last century, but published them
only in the year 1828, and then in the following years, especially in
1830, defended them bravely against Cuvier. Geoffroy St. Hilaire in all
essentials adopted Lamarck’s Theory of Descent, yet he believed that
the transformation of animal and vegetable species was less effected by
the action of the organism itself (by habit, practice, use, or disuse of
organs) than by the “monde ambiant,” that is, by the continual change of
the outer world, especially of the atmosphere. He conceives the organism
as passive, in regard to the vital conditions of the outer world, while
Lamarck, on the contrary, regards it as active. Geoffroy thinks, for
example, that birds originated from lizard-like reptiles, simply by a
diminution of the carbonic acid in the atmosphere, in consequence of
which the breathing process became more animated and energetic through
the increased proportion of oxygen in the atmosphere. Thus there arose a
higher temperature of the blood, an increased activity of the nerves and
muscles, and the scales of the reptiles became the feathers of the
birds, etc. This conception is based upon a correct thought, but
although the change of the atmosphere, as well as the change of every
other external condition of existence, certainly effects directly or
indirectly the transformation of the organism, yet this single cause is
by itself too unimportant for such effects to be ascribed to it. It is
even less important than practice and habit, upon which Lamarck lays too
much stress. Geoffroy’s chief merit consists in his having vindicated
the monistic conception of nature, the unity of organic forms, and the
deep genealogical connection of the different organic types in the face
of Cuvier’s powerful influence. I have already mentioned in the
preceding chapter (pp. 87, 88) the celebrated disputes between the two
great opponents in the Academy of Paris, especially the fierce conflicts
on the 22nd of February, and on the 19th of July, in which Goethe took
so lively an interest. On that occasion Cuvier remained the
acknowledged victor, and since that time very little, or rather nothing,
more has been done in France to further the development of the Doctrine
of Filiation, and complete the monistic theory of development. This is
evidently to be ascribed principally to the repressive influence
exercised by Cuvier’s great authority. Even at the present day the
majority of the French naturalists are the disciples and blind followers
of Cuvier. In no civilized country of Europe has Darwin’s doctrine had
so little effect and been so little understood as in France, so that in
the further course of our examination we need not take the French
naturalists into consideration. At most, there are two distinguished
botanists, among the recent French naturalists, whom we may mention as
having ventured to express themselves in favour of the mutability and
transformation of species. These two men are Naudin (1852) and Lecoq
(1854).

Having discussed the early services of German and French
nature-philosophy in establishing the doctrine of descent, we turn to
the third great country of Europe, to free England, which during the
last ten years has become the chief seat and starting-point for the
further working out and definite establishment of the theory of
development. Englishmen, who now take such an active part in every great
scientific progress of humanity, and are the first to promote the
eternal truths of natural science, at the beginning of the century took
but little part in the continental nature-philosophy and its most
important progress, the Theory of Descent. Almost the only earlier
English naturalist whom we have here to mention is Erasmus Darwin, the
grandfather of the reformer of the Theory of Descent. In 1795 he
published, under the title of “Zoonomia,” a scientific work in which he
expresses views very similar to those of Goethe and Lamarck, without,
however, then knowing anything about these two men. It is evident that
the Theory of Descent at that time pervaded the intellectual atmosphere.
Erasmus Darwin lays great stress upon the transformation of animal and
vegetable species by their own vital action and by their becoming
accustomed to changed conditions of existence, etc. Next, W. Herbert, in
1822, expressed the opinion that species of animals and plants are
nothing but varieties which have become permanent. In like manner Grant,
in Edinburgh, in 1826, declared that new species proceed from existing
species by continued transformation. In 1841 Freke maintained that all
organic beings must be descended from a single primitive type. In 1852
Herbert Spencer demonstrated minutely, and in a very clear and
philosophic manner, the necessity of the Doctrine of Filiation, and
established it more firmly in his excellent “Essays,” which appeared in
1858, and in his “Principles of Biology,” which was published at a later
date. He has, at the same time, the great merit of having applied the
theory of development to psychology, and of having shown that the
emotional and intellectual faculties could only have been acquired by
degrees and developed gradually. Lastly, we have to mention that in 1859
Huxley, the first of English zoologists, spoke of the Theory of Descent
as the only hypothesis of creation reconcilable with scientific
physiology. The same year produced the “Introduction to the Flora of
Tasmania,” in which Hooker, the celebrated English botanist, adopts the
Theory of Descent, supporting it with important observations of his
own.

All the naturalists and philosophers with whom we have become acquainted
in this brief historical survey, as men adopting the Theory of
Development, merely arrived at the conception that all the different
species of animals and plants which at any time have lived, and still
live, upon the earth, are the gradually changed and transformed
descendants of one or some few original and very simple prototypes,
which latter arose out of inorganic matter by spontaneous generation.
But none of them succeeded in placing this fundamental element of the
doctrine of descent in relation with some cause, nor in satisfactorily
explaining the transformation of organic species by the true
demonstration of its mechanical antecedents. Charles Darwin was the
first who solved this most difficult problem, and this forms the broad
gulf which separates him from his predecessors.

The special merit of Charles Darwin is, in my opinion, twofold: in the
first place, the doctrine of descent, the fundamental idea of which was
already clearly expressed by Goethe and Lamarck, has been developed by
him much more comprehensively, has been traced much more minutely in all
directions, and carried out much more strictly and connectedly than by
any of his predecessors; and secondly, he has established a new theory,
which reveals to us the natural causes of organic development, the
acting causes (causæ efficientes) of organic form-production, and of the
changes and transformations of animal and vegetable species. This is the
theory which we call the Theory of Selection, or more accurately, the
Theory of Natural Selection (selectio naturalis).

When we reflect that (with the few exceptions above mentioned) the
whole science of Biology, before Darwin’s time, was elaborated in
accordance with the opposite views, and that almost all zoologists and
botanists regarded the absolute independence of organic species as a
self-evident inference from the results of all study of forms, we shall
certainly not lightly value the twofold merit of Darwin. The false
doctrine of the constancy and independent creation of individual species
had gained such high authority, was so generally recognized, and was,
moreover, so much favoured by delusive appearances, accepted by
superficial observation, that, indeed, no small degree of courage,
strength, and intelligence was required to rise as a reformer against
its omnipotence, and to dash to pieces the structure artificially
erected upon it. But, in addition to this, Darwin added to Lamarck’s and
Goethe’s doctrine of descent the new and highly important principle of
“natural selection.”

We must sharply distinguish the two points—though this is usually not
done—first, Lamarck’s Theory of Descent, which only asserts _that_ all
animal and vegetable species are descended from common, most simple, and
spontaneously generated prototypes; and secondly, Darwin’s Theory of
Selection, which shows us _why_ this progressive transformation of
organic forms took place, and what causes, acting mechanically, effected
the uninterrupted production of new forms, and the ever increasing
variety of animals and plants.

Darwin’s immortal merit cannot be justly estimated until a later period,
when the Theory of Development, after overthrowing all other theories of
creation, will be recognized as the supreme principle of explanation in
Anthropology, and, consequently, in all other sciences. At present,
while in the hot contest for truth the name of Darwin is the watchword
to the advocates of the natural theory of development, his merits are
inaccurately appreciated on both sides, for some persons overestimate
them as much as others underestimate them.

His merit is overestimated when he is regarded as the founder of the
Theory of Descent, or of the whole of the Theory of Development. We have
seen from the historical sketch in this and the preceding chapters, that
the Theory of Development, as such, is not new; all philosophers who
have refused to be led captive by the blind dogma of a supernatural
creation, have been compelled to assume a natural development. But the
Theory of Descent constituting the specially biological part of the
universal Theory of Development, had already been so clearly expressed
by Lamarck, and carried out so fully by him to its most important
consequences, that we must honour him as the real founder of it. Hence
it is only the Theory of Selection, and not that of Descent, which may
be called _Darwinism_; but this is in itself of so much importance, that
its value can scarcely be overestimated.

Darwin’s merit is naturally underestimated by all his opponents. But it
is scarcely possible in this matter to point to scientific opponents,
who are entitled by profound biological culture to pronounce an opinion.
For among all the works opposed to Darwin and the Theory of Descent yet
published, with the exception of that of Agassiz, not one deserves
consideration, much less refutation; all have so evidently been written
either without thorough knowledge of biological facts, or without a
clear philosophical understanding of the question in hand. We need not
trouble ourselves at all about the attacks of theologians and other
unscientific men, who really know nothing whatever of nature.

The only eminent scientific adversary who still remains opposed to
Darwin and the whole theory of development is Louis Agassiz; but the
principle of his opposition in reality deserves notice only as a
philosophical curiosity. In a French translation of his “Essay on
Classification,”(5) which we have spoken of before, published in Paris
in 1869, Agassiz has most formally announced his opposition to
Darwinism, which he had previously expressed in many ways. To this
translation he has appended a treatise of sixteen pages, bearing the
title, “Le Darwinisme. Classification de Haeckel.” This curious chapter
contains the most wonderful things; as, for example, “Darwin’s idea is a
conception _à priori_. Darwinism is a burlesque of facts. Science would
renounce the claim which it has hitherto possessed to the confidence of
earnest minds if such sketches were to be accepted as indications of a
true progress.” The following passage, however, is the climax of this
strange polemic: “Darwinism shuts out almost the whole mass of acquired
knowledge in order to retain and assimilate to itself that only which
may serve its doctrine.”

Surely this is what we may call turning the whole affair topsy-turvy!
The biologist who knows the facts must be astounded at Agassiz’s courage
in uttering such sentences—sentences without a word of truth in them,
and which he cannot himself believe! The impregnable strength of the
Theory of Descent lies just in the fact that all biological facts are
explicable only through it, and that without it they remain
unintelligible miracles. All our “laborious knowledge” in comparative
anatomy and physiology—in embryology and palæontology—in the doctrine
of the geographical and topographical distribution of organisms, etc.,
constitutes an irrefutable testimony to the truth of the Theory of
Descent.

In my General Morphology, especially in the sixth book (in the General
Phylogeny), I have minutely refuted Agassiz’s “Essay on Classification”
in all essential points. The twenty-fourth chapter I have devoted to a
very detailed and strictly scientific discussion of that section which
Agassiz himself considers the most important (the groups or categories
of systematic zoology and botany), and have shown that this part of his
work is purely chimerical, without any trace of real foundation. Agassiz
takes good care not to venture anywhere to touch upon my refutation,
because, forsooth, he is not in a position to produce anything
substantial against it. He fights not with arguments, but with phrases.
However, such opposition will not delay the complete victory of the
Theory of Development, but only accelerate it.

CHAPTER VI.

THEORY OF DEVELOPMENT ACCORDING TO LYELL AND DARWIN.

Charles Lyell’s Principles of Geology.—His Natural
History of the Earth’s Development.—Origin of the
Greatest Effects through the Multiplication of the
Smallest Causes.—Unlimited Extent of Geological
Periods.—Lyell’s Refutation of Cuvier’s History of
Creation.—The Establishment of the Uninterrupted
Connection of Historical Development by Lyell and
Darwin.—Biographical Notice of Charles Darwin.—His
Scientific Works.—His Theory of Coral Reefs.—Development
of the Theory of Selection.—A Letter of Darwin’s.—The
Contemporaneous Appearance of Darwin’s and Alfred
Wallace’s Theory of Selection.—Darwin’s Study of Domestic
Animals and Cultivated Plants.—Andreas Wagner’s notions
as to the Special Creation of Cultivated Organisms for the
good of Man.—The Tree of Knowledge in
Paradise.—Comparison between Wild and Cultivated
Organisms.—Darwin’s Study of Domestic
Pigeons.—Importance of Pigeon Breeding.—Common Descent
of all Races of Pigeons.

During the thirty years, from 1830 until 1859, when Darwin’s work
appeared, the ideas of creation introduced by Cuvier remained
predominant in the sciences of organic nature. People rested satisfied
with the unscientific assumption, that in the course of the earth’s
history, a series of inexplicable revolutions had periodically
annihilated the whole world of animals and plants, and that at the end
of each revolution, and the beginning of a new period, a new enlarged,
and improved edition of the organic population had appeared. Although
the number of these editions of creation was altogether problematical,
and in truth could not be fixed at all, and although the numerous
advances which, during this time, were made in all the departments of
zoology and botany demonstrated more and more that Cuvier’s hypothesis
was unfounded and untenable, and that Lamarck’s natural theory of
development was nearer the truth, yet the former maintained its
authority almost universally among biologists. This must, above all, be
ascribed to the veneration which Cuvier had acquired, and strikingly
illustrates how injurious to the progress of humanity a faith in any
definite authority may become. Authority, as Goethe once admirably said,
perpetuates the individual, which as an individual should pass away,
rejects and allows to pass that which should be held fast, and is the
main obstacle to the advance of humanity.

It is only by having regard to the great weight of Cuvier’s authority,
and to the mighty potency of human indolence, which is with difficulty
induced to depart from the broad and comfortable way of everyday
conceptions, and to enter upon new paths not yet made easy, that we can
comprehend how it is that Lamarck’s Theory of Descent did not gain its
due recognition until 1859, after Darwin had given it a new foundation.
The soil had long been prepared for it by the works of Charles Lyell,
another English naturalist, whose views are of great importance for the
natural history of creation, and must accordingly here be briefly
explained.

In 1830 Charles Lyell published, under the title of “Principles of
Geology,” a work in which he thoroughly reformed the science of Geology
and the history of the earth’s development, and effected this reform in
a manner similar to that in which, thirty years later, Darwin in his
work reformed the science of Biology. Lyell’s great treatise, which
radically destroyed Cuvier’s hypothesis of creation, appeared in the
same year in which Cuvier celebrated his triumph over the
nature-philosophy, and established his supremacy in the domain of
morphology for the following thirty years. Whilst Cuvier, by his
artificial hypothesis of creation and his theory of catastrophes
connected with it, directly obstructed the path of the theory of natural
development, and cut off all chance of a natural explanation, Lyell once
more opened a free road, and brought forward convincing geological
evidence to show that Cuvier’s dualistic conceptions were as unfounded
as they were superfluous. He demonstrated that those changes of the
earth’s surface, which are still taking place before our eyes, are
perfectly sufficient to explain everything we know of the development of
the earth’s crust in general, and that it is superfluous and useless to
seek for mysterious causes in inexplicable revolutions. He showed that
we need only have recourse to the hypothesis of exceedingly long periods
of time in order to explain the formation of the crust of the earth in
the simplest and most natural manner by means of the very same causes
which are still active. Many geologists had previously imagined that the
highest chains of mountains which rise on the surface of the earth could
owe their origin only to enormous revolutions transforming a great part
of the earth’s surface, especially to colossal volcanic eruptions. Such
chains of mountains as those of the Alps or the Cordilleras were
believed to have arisen direct from the fiery fluid of the interior of
the earth, through an enormous chasm in the broken crust. Lyell, on the
other hand, showed that we can explain the formation of such enormous
chains of mountains quite naturally by the same slow and imperceptible
risings and depressions of the earth’s surface which are still
continually taking place, and the causes of which are by no means
miraculous. Although these depressions and risings may perhaps amount
only to a few inches, or at most a few feet, in the course of a century;
still, in the course of some millions of years they are perfectly
sufficient to raise up the highest chains of mountains, without the aid
of mysterious and incomprehensible revolutions. In like manner, the
meteorological action of the atmosphere, the influence of rain and snow,
and, lastly, the breakers on the coasts, which by themselves seem to
produce an insignificant effect, must cause the greatest changes if we
only allow sufficiently long periods for their action. The
multiplication of the smallest causes produces the greatest effects.
Drops of water produce a cavity in a rock.

I shall afterwards be obliged again to recur to the immeasurable length
of geological periods which are necessary for this purpose, for, as we
shall see, Darwin’s theory, as well as that of Lyell, renders the
assumption of immense periods absolutely necessary. If the earth and its
organisms have actually developed in a natural way, this slow and
gradual development must certainly have taken a length of time which
surpasses our powers of comprehension. But as many men see in this very
circumstance one of the principal difficulties in the way of those
theories of development, I beg leave here to remark that we have not a
single rational ground for conceiving the time requisite to be limited
in any way. Not only many ordinary persons, but even eminent
naturalists, make it their chief objection to these theories, that they
arbitrarily claim too great a length of time: yet the ground of
objection is scarcely intelligible. For it is absolutely impossible to
see what can, in any way, limit us in assuming long periods of time. We
have long known, even from the structure of the stratified crust of the
earth alone, that its origin and the formation of neptunic rocks from
water must have taken, at least, several millions of years. From a
strictly philosophical point of view, it makes no difference whether we
hypothetically assume for this process ten millions or ten thousand
billions of years. Before us and behind us lies eternity. If the
assumption of such enormous periods is opposed to the feelings of many,
I regard this simply as the consequence of false notions which are
impressed upon us from our earliest youth concerning the short history
of the earth, which is said to embrace only a few thousands of years.
Albert Lange, in his “History of Materialism,”(12) has convincingly
shown that from a strictly philosophical point of view it is far less
objectionable in a scientific hypothesis to assume periods which are too
long than periods which are too short. Every process of development is
the more intelligible the longer it is assumed to last. A short and
limited period is the most improbable.

I have no space here to enter minutely into Lyell’s great work, and will
therefore mention only its most important result, which is, that he
completely refuted Cuvier’s history of creation with its mythical
revolutions, and established in its place the constant and slow
transformation of the earth’s crust by the continued action of forces,
which are still working on the earth’s surface, viz., the movement of
water and the volcanic fluid of the interior of earth. Lyell thus
demonstrated a continuous and uninterrupted connection of the whole
history of the earth, and he proved it so irrefutably, and established
so convincingly the supremacy of the “existing causes,” that is, of the
causes which are still active in the transformation of the earth’s
crust, that Geology in a short time completely renounced Cuvier’s
hypothesis.

Now, it is remarkable that Palæontology, the science of petrifactions,
so far as it was pursued by botanists and zoologists, remained
apparently unaffected by this great progress in geology. Biology still
continued to assume repeated new creations of the whole animal and
vegetable kingdoms, at the beginning of every new period of the earth’s
history, although this hypothesis of individual creations, shoved into
the world one after the other, without the assumption of Cuvier’s
cataclysms, became pure nonsense, and lost its foundation. It is
evidently perfectly absurd to assume a distinct new creation of the
whole world of animals and plants at definite epochs, without the crust
of the earth itself experiencing any considerable general revolution.
And although this conception is most closely connected with Cuvier’s
theory of catastrophes, still it prevailed when the latter had been
completely destroyed and abandoned.

It was reserved for the great English naturalist, Charles Darwin, to
remove this contradiction, and to show that the organic beings of the
earth have a history as continuous and connected as the inorganic crust
of the earth; that animals and plants have arisen from one another by as
gradual a transmutation as that by which the varying forms of the
earth’s crust, the forms of the continents, and of the seas surrounding
and separating them, have arisen out of earlier and quite different
forms. In this respect we may truly say that in the domain of Zoology
and Botany Darwin made the same progress as Lyell, his great countryman,
in the domain of Geology. Both proved the _uninterrupted connection of
the historical development_, and demonstrated a gradual transmutation of
the different conditions succeeding one another.

The special merit of Darwin, as I have already remarked in a preceding
chapter, is twofold. In the first place, he has treated the Theory of
Descent, put forth by Lamarck and Goethe, in a much more comprehensive
manner, as a whole, and carried it out in a much more connected manner,
than had been done by any one of his predecessors. Secondly, he has
established the causal foundation of this Theory of Descent by the
Theory of Selection, which is peculiarly his own; that is, he has
demonstrated the acting _causes of the changes_ which the Theory of
Descent simply stated, as _facts_. The Theory of Descent, introduced
into Biology in 1809, by Lamarck, asserts that all the different species
of animals and plants are descended from a single or some few most
simple prototypes, produced by spontaneous generation. The Theory of
Selection, established in 1859 by Darwin, shows us _why_ this must be
so; it points out the acting causes in a manner with which Kant would
have been delighted, and indeed, in the domain of organic nature, Darwin
has become the Newton whose advent Kant thought himself entitled
prophetically to deny.

Now, before we approach Darwin’s theory, it will perhaps be of interest
to notice a few details as to the personal character of this great
naturalist, as to his life, and the way in which he was led to form his
doctrine. Charles Robert Darwin was born at Shrewsbury, on the Severn,
on the 12th of February, 1809; therefore, at present he is sixty-three
years old. In his seventeenth year (1825) he entered the University of
Edinburgh, and two years later Christ’s College, Cambridge. When
scarcely twenty-two years old, in 1831, he was invited to take part in a
scientific expedition which was sent out by England, in order to survey
accurately the southernmost point of South America, and to examine
several parts of the South Seas. This expedition, like many other
voyages of inquiry fitted out in a praiseworthy manner by England, had
scientific objects, and at the same time was intended to solve practical
problems relating to navigation. The vessel, commanded by Captain
Fitzroy, appropriately bore the symbolic name of the _Beagle_. The
voyage of the _Beagle_, which lasted five years, was of the highest
importance to the full development of Darwin’s genius; for in the very
first year, when he set his foot on the soil of South America, the
outline of the doctrine of descent dawned upon him. Darwin himself has
described this voyage in a work which is written in a very attractive
style, and the perusal of which I strongly recommend to the reader. This
book of travel, which lies far above the usual average in interest, not
only shows in a very charming manner Darwin’s amiable character, but we
can in many ways recognize the various steps by which he arrived at his
conceptions. The result of the voyage was, first, a large scientific
work, the zoological and geological portion of which belong in a great
measure to Darwin; and secondly, a celebrated work by him alone on Coral
Reefs, which in itself would have sufficed to secure to him a lasting
reputation. It is well known that the islands in the South Seas consist
for the most part of coral reefs, and are surrounded by them. Formerly
no satisfactory explanation could be given of their different and
remarkable forms, and of their relation to those islands which are not
formed of corals. It was reserved for Darwin to solve this difficult
problem, for together with the constructive action of the coral
zoophytes, he assumed geological risings and depressions of the bottom
of the sea to account for the origin of the different forms of reefs.
Darwin’s Theory of the Origin of Coral Reefs, like his later one as to
the Origin of Organic Species, is a theory which fully explains the
phenomenon, and for this purpose assumes only the simplest natural
causes, without hypothetically supporting it with any unknown processes.
Among the remaining works of Darwin, I must not pass over his excellent
monograph on Cirrhipedia, a curious class of marine animals, which in
their outward appearance resemble mussels, and were actually considered
by Cuvier as Molluscs possessing two shells, while in truth they
belonged to the Crustacea (crabs).

The extraordinary hardships to which Darwin had been exposed during his
voyage in the _Beagle_ had injured his health to such a degree, that
after his return home he was obliged to withdraw from the restless
turmoil of London life, and since then has lived in quiet retirement on
his estate at Down, near Bromley, in Kent. This seclusion from the
restless activity of the great city certainly exercised a beneficial
influence upon Darwin, and it is probable that we owe to it, at least
partially, the formation of the Theory of Selection. Undisturbed by the
various engagements which in London would have wasted his strength, he
was enabled to concentrate his attention upon the great problem to
which his mind had been turned during his voyage in the _Beagle_. In
order to show what kind of observations during the voyage principally
gave rise to the fundamental idea of the Theory of Selection, and in
what manner he afterwards worked it out, I shall insert here a passage
from a letter which he addressed to me on the 8th of October, 1864.

_Letter from Charles Darwin to Haeckel, 8th October, 1864._

“In South America three classes of facts were brought strongly before my
mind. _Firstly_, the manner in which closely allied species replace
species in going southward. _Secondly_, the close affinity of the
species inhabiting the islands near South America to those proper to the
continent. This struck me profoundly, especially the difference of the
species in the adjoining islets in the Galopagos Archipelago. _Thirdly_,
the relation of the living Edentata and Rodentia to the extinct species.
I shall never forget my astonishment when I dug out a gigantic piece of
armour like that of the living armadillo.

“Reflecting on these facts, and collecting analogous ones, it seemed to
me probable that allied species were descended from a common parent. But
for some years I could not conceive how each form became so excellently
adapted to its habits of life. I then began systematically to study
domestic productions, and after a time saw clearly that man’s selective
power was the most important agent. I was prepared, from having studied
the habits of animals, to appreciate the struggle for existence, and my
work in geology gave me some idea of the lapse of past time. Therefore,
when I happened to read “Malthus on Population,” the idea of natural
selection flashed on me. Of all the minor points, the last which I
appreciated was the importance and cause of the principle of
divergence.”

During the leisure and retirement in which Darwin lived after his
return, he occupied himself, as we see from this letter, first and
specially with the study of organisms in their cultivated state; that
is, domestic animals and garden plants. This was undoubtedly the most
likely way to arrive at the Theory of Selection. In this, as in all his
labours, Darwin proceeded with extreme care and accuracy. With wonderful
caution and self-denial, he published nothing on this subject during a
period of twenty-one years, from 1837 to 1858, not even a preliminary
sketch of his theory, which he had written as early as 1844. He was
always anxious to collect still more certain experimental proofs, in
order to be able to establish his theory in a complete form, and on the
broadest possible foundation of experience. While he was thus aiming at
the greatest possible perfection, which might perhaps have led him never
to publish his theory at all, he was fortunately disturbed by a
countryman of his, who, independently of Darwin, had discovered the
Theory of Selection, and in 1858 sent its outlines to Darwin himself,
with the request to hand them to Lyell for publication in some English
journal. This was Alfred Wallace, one of the boldest and most
distinguished scientific travellers of modern times. For many years
Wallace had wandered alone in the wilds of the Sunda Islands, in the
dense primitive forests of the Indian Archipelago; and during this close
and comprehensive study of one of the richest and most interesting parts
of the earth, with its great variety of animals and plants, he had
arrived at exactly the same general views regarding the origin of
organic species as Darwin. Lyell and Hooker, both of whom had long known
Darwin’s work, now induced him to publish a short extract from his
manuscripts simultaneously with the manuscript sent him by Wallace. They
appeared in the _Journal of the Linnean Society_, August, 1858.

Darwin’s great work “On the Origin of Species,” in which the Theory of
Selection is carried out in detail, appeared in November, 1859. Darwin
himself, however, characterizes this book (of which a fifth edition
appeared in 1869, and the German translation by Bronn as early as
1860)(1) as only a preliminary extract from a larger and more detailed
work, which is to contain a mass of facts in favour of his theory, and
comprehensive and experimental proofs. The first part of the larger work
promised by Darwin appeared in 1868, under the title, “The Variations of
Animals and Plants in the State of Domestication,” and has been
translated into German by Victor Carus.(14) It contains a rich abundance
of the most valuable evidence as to the extraordinary changes of organic
forms which man can produce by cultivation and artificial selection.
However much we are indebted to Darwin for this abundance of convincing
facts, still we do not by any means share the opinion of those
naturalists who hold that the Theory of Selection requires for its
actual proof these further details. It is our opinion that Darwin’s
first work, which appeared in 1859, already contains sufficient proof.
The unassailable strength of his theory does not lie in the immense
amount of individual facts that may be adduced as proofs, but in the
harmonious connection of all the great and general phenomena of organic
nature, which agree in bearing testimony to the truth of the Theory of
Selection.

Darwin, at first, intentionally did not notice the important conclusion
from his Theory of Descent, namely, the descent of the human race from
other mammals. It was not till this highly important conclusion had been
definitely established by other naturalists as the necessary sequel of
the doctrine of descent, that Darwin himself expressly endorsed it, and
thereby completed his system. This was done in the highly interesting
work, “The Descent of Man, and Sexual Selection,” which appeared as late
as 1871, and has likewise been translated into German by Victor
Carus.(48)

The careful study which Darwin devoted to _domestic animals and
cultivated plants_ was of the greatest importance in establishing the
Theory of Selection. The infinitely varied changes of form which man has
produced in these domesticated organisms by artificial selection are of
the very highest importance for a right understanding of animal and
vegetable forms; and yet this study has, down to the most recent times,
been most grossly neglected by zoologists and botanists. Without
entering upon the discussion of the significance to be attached to the
idea of species itself, they have filled not only bulky volumes, but
whole libraries, with descriptions of individual species, and with most
childish controversies as to whether these species are good, or
tolerably good, and bad, or tolerably bad. If naturalists instead of
spending their time on these useless fancies had duly studied cultivated
organisms, and had examined the transmutation of the living forms,
instead of the individual dead ones, they would not have been led
captive so long by the fetters of Cuvier’s dogma. But as cultivated
organisms are so extremely inconvenient to the dogmatic conception of
the permanence of species, naturalists to a great extent intentionally
did not concern themselves about them, and even celebrated naturalists
have often expressed the opinion that cultivated organisms, domesticated
animals and garden plants, are artificial productions of man, and that
their formation and transformation could not decide anything about the
nature of species and about the origin of the forms of species that live
in a natural state.

This perverse view went so far that, for example, Andreas Wagner, a
zoologist of Munich, quite seriously made the following ridiculous
assertion:—“Animals and plants in their wild state have been called
into being by the Creator as distinctly different and unchangeable
species; but in the case of domestic animals and cultivated plants this
was not necessary, because he formed them from the beginning for the use
of man. The Creator formed man out of a clod of earth, breathed the
living breath into his nostrils, and then created for him the different
useful domestic animals and garden plants, among which he thought well
to save himself the trouble of distinguishing species.” Unfortunately,
Andreas Wagner does not tell us whether the _Tree of Knowledge_ in
Paradise was a “good” wild species, or, as a cultivated plant, “no
species” at all. As the Tree of Knowledge was placed by the Creator in
the centre of Paradise, we might be inclined to believe that it was a
highly favoured cultivated plant, and therefore no species at all. But
since, on the other hand, the fruit of the Tree of Knowledge was
forbidden to man, and since many men, as Wagner himself clearly shows,
have never eaten of the fruit, it was evidently not created for the use
of man, and therefore in all probability was a _real species!_ What a
pity Wagner has not given us any information about this important and
difficult problem!

Now, however ridiculous this view may appear to us, it is only the
logical sequence of a false view (which is widely spread) of the special
nature of cultivated organisms, and one may occasionally hear similar
objections from naturalists of great reputation. I must most decidedly,
and at once, condemn this utterly false conception. It is the same
perverseness which is committed by physicians who maintain that diseases
are artificial productions, and not natural phenomena. It has been a
work of hard labour to combat this prejudice, and it is only in recent
times that men have generally adopted the view that diseases are nothing
but natural changes of the organisms, or really natural phenomena of
life, which are produced by changed and abnormal conditions of
existence. Disease, therefore, is not a life beyond Nature’s realm (vita
præter naturam), as the early physicians used to say, but a natural life
under conditions which produce illness and threaten the body with
danger. Just in the same manner, cultivated organic forms are not
artificial works of man, but natural productions which have arisen under
the influence of peculiar conditions of life. Man by his culture can
never directly produce a new organic form, but he can breed organisms
under new conditions of life, which are such as to influence and
transform them. All domestic animals and all garden plants are
originally descended from wild species, which have been transformed by
the peculiar conditions of culture.

A thorough comparison of cultivated forms (races and varieties) with
organisms not altered by cultivation (species and varieties), is of the
utmost importance to the theory of selection. What is most surprising in
such a comparison is the remarkably short time in which man can produce
a new form, and the high degree in which this form, produced by man, can
deviate from the original form. While wild animals and plants, one year
after another, appear to the zoologist and botanist approximately in the
same form, so as to have given rise to the false doctrine of the
constancy of species, domestic animals and garden plants, on the other
hand, display the greatest changes within a few years. The perfection
which gardeners and farmers have attained in the art of selection now
enables them, in the space of a few years, arbitrarily to create
entirely new animal and vegetable forms. For this purpose it is only
necessary to keep and propagate the organism under the influence of
special conditions—which are capable of producing new formations—and
even at the end of a few generations new species may be obtained, which
differ from the original form in a much higher degree than so-called
good species in a wild state differ from one another. This fact is
extremely important, and we cannot lay sufficient stress upon it. The
assertion is not true that cultivated forms descended from one and the
same primary form do not differ from one another as much as wild animal
and vegetable species differ among themselves. If we only make
comparisons, without prejudice, we can very easily perceive that a
number of races or varieties which have been derived from a single
cultivated form, within a short series of years, differ from one another
in a higher degree than so-called good species (bonæ species), or even
different genera of one family, in the wild state.

In order to establish this extremely important fact as firmly as
possible by experiments, Darwin decided to make a special study of the
whole extent of variation in form in a single group of domesticated
animals, and for this purpose he chose the _domestic pigeons_, which are
in many respects especially suited for such a study. For a long time he
kept on his estate all possible races and varieties of pigeons which he
was able to procure, and he was helped in this by rich contributions
from all parts of the world. He also joined two London pigeon clubs, the
members of which passionately, and with truly artistic skill, carry on
the breeding of the different forms of pigeons. Lastly, he formed
connections with some of the most celebrated pigeon-fanciers; so that he
could command the richest experimental material.

The art of, and fancy for, pigeon breeding is very ancient. Even more
than 3,000 years before Christ, it was carried on by the Egyptians. The
Romans, under the emperors, laid out enormous sums upon the breeding of
pigeons, and kept accurate pedigrees of their descent, just as the Arabs
keep genealogical pedigrees of their horses, and the Mecklenburg
aristocracy of their own ancestors. In Asia, too, among the wealthy
princes, pigeon breeding was a very ancient fancy; in 1600, the court of
Akber Khan possessed more than 20,000 pigeons. Thus in the course of
several centuries, and in consequence of the various methods of breeding
practised in the different parts of the world, there has arisen out of
one single originally tamed form, an immense number of different races
and varieties, which in their most divergent forms are extremely
different from one another, and are often curiously characterized.

One of the most striking races of pigeons is the well-known fan-tailed
pigeon, which spreads its tail like the peacock, and carries a number of
(from thirty to forty) feathers placed in the form of radii, while other
pigeons possess much fewer tail feathers—generally twelve. We may here
mention that the number of feathers on the tails of birds is considered
by naturalists of great value as a systematic distinction, so that whole
orders can thereby be distinguished. For example, singing birds, almost
without exception, possess twelve tail feathers; chirping birds
(Strisores) ten, etc. Several races of pigeons, moreover, are
characterized by a tuft of neck feathers, which form a kind of periwig;
others by grotesque transformation of their beaks and feet, by peculiar
and often very remarkable decorations, as, for example, skinny lappets,
which develop on the head; by a large crop, which is formed by the
gullet being strongly inclined forward, etc. Remarkable, also, are the
strange habits which many pigeons have acquired; for example, the turtle
pigeons and the trumpeters with their musical accomplishments, the
carriers with their topographical instinct. The tumblers have the
strange habit of ascending into the air in great numbers, then turning
over and falling down through the air as if dead. The ways and habits of
these endless races of pigeons—the form, size, and colour of the
individual parts of their bodies, and their proportions, differ in a
most astonishing degree from one another; in a much higher degree than
is the case with the so-called good species, or even with the perfectly
distinct genera, of wild pigeons. And what is of the greatest
importance, is the fact that these differences are not confined to the
external form, but extend even to the most important internal parts;
there even occur great modifications of the skeleton and of the
muscular tissues. For example, we find great differences in the number
of vertebræ and ribs, in the size and shape of the gaps in the
breast-bones, in the size and shape of the merry-thought, in the lower
jaw, in the facial bones, etc. In short, the bony skeleton, which
morphologists consider a very permanent part of the body, and which
never varies to such an extent as the external parts—shows such great
changes, that many races of pigeons might be described as special
genera, and this would doubtless be done if all these different forms
had been found in a wild and natural state.

How far the differences of the races of pigeons have been carried is
best shown by the fact that all pigeon breeders are unanimously of
opinion that each peculiar or specially marked race of pigeons must be
derived from a corresponding wild original species. It is true every one
assumes a different number of original species. Yet Darwin has most
convincingly and acutely proved that all these pigeons, without
exception, must be derived from a single wild primary species—from the
blue rock-pigeon (_Columba livia_). In like manner, it can be proved of
most of the domestic animals and cultivated plants, that all the
different races are descendants of a single original wild species which
has been brought by man into a cultivated condition.

An example similar to that of the domestic pigeons is furnished among
mammals by our tame _rabbit_. All zoologists, without exception, have
long considered it proved that all its races and varieties are descended
from the common wild rabbit, that is, from a single primary species. And
yet the extreme forms of these races differ to such a degree from one
another, that every zoologist, if he met with them in a wild state,
would unhesitatingly designate them not only as an entirely distinct
“good species,” but even as species of entirely different genera of the
Leporid family. Not only does the colour, length of hair, and other
qualities of the fur of the different tame races of rabbits vary
exceedingly, and form extremely broad contrasts, but, what is still more
important, the typical form of the skeleton and its individual parts do
so also, especially the form of the skull and the jaw (which is of such
importance in systematic arrangement); further, the relative proportion
of the length of the ears, legs, etc. In all these respects the races of
tame rabbits avowedly differ from one another far more than all the
different forms of wild rabbits and hares which are scattered over all
the earth, and are the recognized “good species” of the genus _Lepus_.
And yet, in the face of these clear facts, the opponents of the theory
of development maintain that the wild species are not descended from a
common prototype, although they at once admit it in the case of the tame
races. With opponents who so intentionally close their eyes against the
clear light of truth, no further dispute can be carried on.

While in this manner it appears certain that the domestic races of
pigeons, of tame rabbits, of horses, etc., notwithstanding the
remarkable difference of their varieties, are descended in each case
from but one wild, so-called “species”; yet, on the other hand, it is
certainly probable that the great variety of races of some of the
domestic animals, especially dogs, pigs, and oxen, must be ascribed to
the existence of several wild prototypes, which have become mixed. It
is, however, to be observed that the number of these originally wild
primary species is always much smaller than that of the cultivated forms
proceeding from their mingling and selection, and naturally they were
originally derived from a single primary ancestor, common to the whole
genus. In no case is each separate cultivated race descended from a
distinct wild species.

In opposition to this, almost all farmers and gardeners maintain, with
the greatest confidence, that each separate race bred by them must be
descended from a separate wild primary species, because they clearly
perceive the differences of the races, and attach very high importance
to the inheritance of their qualities; but they do not take into
consideration the fact that these qualities have arisen only by the slow
accumulation of small and scarcely observable changes. In this respect
it is extremely instructive to compare cultivated races with wild
species.

Many naturalists, and especially the opponents of the Theory of
Development, have taken the greatest trouble to discover some
morphological or physiological mark, some characteristic property,
whereby the artificially bred and cultivated races may be clearly and
thoroughly distinguished from wild species which have arisen naturally.
All these attempts have completely failed, and have led only with
increasing certainty to the result, that such a distinction is
altogether impossible. I have minutely discussed this fact, and
illustrated it by examples in my criticism of the idea of species. (Gen.
Morph. ii. 323-364.)

I may here briefly touch on yet another side of this question, because
not only the opponents, but even a few of the most distinguished
followers of Darwin—for example, Huxley—have regarded the phenomena of
_bastard-breeding_, or _hybridism_, as one of the weakest points of
Darwinism. Between cultivated races and wild species, they say, there
exists this difference, that the former are capable of producing
fruitful bastards, but that the latter are not. Two different cultivated
races, or wild _varieties of one species_, are said in all cases to
possess the power of producing bastards which can fruitfully mix with
one another, or with one of their parent forms, and thus propagate
themselves; on the other hand, _two really different species_, two
cultivated or wild _species_ of one genus, are said _never_ to be able
to produce from one another bastards which can be fruitfully crossed
with one another, or with one of their parent species.

As regards the first of these assertions, it is simply refuted by the
fact that there are organisms which do not mix at all with their own
ancestors, and therefore can produce no fruitful descendants. Thus, for
example, our cultivated guinea-pig does not bear with its wild Brazilian
ancestor; and again, the domestic cat of Paraguay, which is descended
from our European domestic cat, no longer bears with the latter. Between
different races of our domestic dogs, for example, between the large
Newfoundland dogs and the dwarfed lap-dogs, breeding is impossible, even
for simple mechanical reasons. A particularly interesting instance is
afforded by the Porto-Santo rabbit (Lepus Huxleyi). In the year 1419, a
few rabbits, born on board ship of a tame Spanish rabbit, were put on
the island of Porto Santo, near Madeira. These little animals, there
being no beasts of prey, in a short time increased so enormously that
they became a pest to the country, and even compelled a colony to remove
from the island. They still inhabit the island in great numbers; but in
the course of four hundred and fifty years they have developed into a
quite peculiar variety—or if you will have it, into a “good
species”—which is distinguished by a peculiar colour, a rat-like shape,
small size, nocturnal life, and extraordinary wildness. The most
important fact, however, is that this new species, which I call _Lepus
Huxleyi_, no longer pairs with its European parent rabbit, and no longer
produces bastards with it.

On the other hand, we now know of numerous examples of fruitful genuine
bastards; that is, of mixings that have proceeded from the crossing of
two entirely different species, and yet propagate themselves with one
another as well as with one of their parent species. A number of such
bastard species (species Hybridæ) have long been known to botanists; for
example, among the genera of the thistle (Cirsium), the laburnum
(Cytisus), the bramble (Rubus), etc. Among animals also they are by no
means rare, perhaps even very frequent. We know of fruitful bastards
which have arisen from the crossing of two different species of a genus,
as among several genera of butterflies (Zygæna, Saturnia), the family of
carps, finches, poultry, dogs, cats, etc. One of the most interesting is
the hare-rabbit (Lepus Darwinii), the bastard of our indigenous hare and
rabbit, many generations of which have been bred in France, since 1850,
for gastronomic purposes. I myself possess such hybrids, the products of
pure in-breeding, that is, both parents of which are themselves hybrids
by a hare-father and a rabbit-mother. I possess them through the
kindness of Professor Conrad, who has repeatedly made these experiments
in breeding on his estate. The half-blood hybrid thus bred, which I name
in honour of Darwin, appears to propagate itself through many
generations by pure in-breeding, just as well as any genuine species.
Although on the whole it is more like its mother (rabbit), still in the
formation of the ears and of the hind-legs, it possesses distinct
qualities of its father (hare). Its flesh has an excellent taste, rather
resembling that of a hare, though the colour is more like that of a
rabbit. But the hare (Lepus timidus) and the rabbit (Lepus cuniculus)
are two species of the genus Lepus, so different that no systematic
zoologist will recognize them as varieties of one species. Both species,
moreover, live in such different ways, and in their wild state entertain
so great an aversion towards one another, that they do not pair so long
as they are left free. If, however, the newly-born young ones of both
species are brought up together, this aversion is not developed; they
pair with one another and produce the _Lepus Darwinii_.

Another remarkable instance of the crossing of different species (where
the two species belong even to different genera!) is furnished by the
fruitful hybrids of sheep and goats which have for a long time been bred
in Chili for industrial purposes. On what unessential circumstances in
the sexual mingling the fertility of the different species depend, is
shown by the fact that he-goats and sheep in their mingling produce
fruitful hybrids, while the ram and she-goat pair very rarely, and then
without result. The phenomena of hybridism to which undue importance has
been erroneously attributed are thus utterly unmeaning, so far as the
idea of species is concerned. The breeding of hybrids does not enable
us, any more than other phenomena, thoroughly to distinguish cultivated
races from wild species; and this circumstance is of the greatest
importance in the Theory of Selection.

CHAPTER VII.

THE THEORY OF SELECTION (DARWINISM).

Darwinism (Theory of Selection) and Lamarckism (Theory of
Descent).—The Process of Artificial Breeding.—Selection
of the Different Individuals for After-breeding.—The
Active Causes of Transmutation.—Change connected with
Food, and Transmission by Inheritance connected with
Propagation.—Mechanical Nature of these Two
Physiological Functions.—The Process of Natural
Breeding: Selection in the Struggle for
Existence.—Malthus’ Theory of Population.—The
Proportion between the Numbers of Potential and Actual
Individuals of every Species of Organisms.—General
Struggle for Existence, or Competition to attain the
Necessaries of Life.—Transforming Force of the Struggle
for Existence.—Comparison of Natural and Artificial
Breeding.—Selection in the Life of Man.—Military and
Medical Selection.

It is, properly speaking, not quite correctly that the Theory of
Development, with which we are occupied in these pages, is usually
called Darwinism. For, as we have seen from the historical sketch in the
previous chapters, the most important foundation of the Theory of
Development—that is, the Doctrine of Filiation, or Descent—had already
been distinctly enunciated at the beginning of our century, and had been
definitely introduced into science by Lamarck. The portion of the Theory
of Development which maintains the common descent of all species of
animals and plants from the simplest common original forms might,
therefore, in honour of its eminent founder, and with full justice, be
called _Lamarckism_, if the merit of having carried out such a principle
is to be linked to the name of a single distinguished naturalist. On the
other hand, the Theory of Selection, or breeding, might be justly called
_Darwinism_, being that portion of the Theory of Development which shows
us in what way and _why_ the different species of organisms have
developed from those simplest primary forms. (Gen. Morph. ii. 166.)

It is true we find the first trace of an idea of natural selection even
forty years before the appearance of Darwin’s work. For in the year 1818
there was published a paper “On a woman of the white race whose skin
partly resembled that of a negro,” which had been read before the Royal
Society as early as 1813. Its author, Dr. W. C. Wells, states that
negroes and mulattoes are distinguished from the white race by their
immunity from certain tropical diseases. On this occasion he remarks
that all animals have a tendency to change up to a certain degree, and
that farmers, by availing themselves of this tendency, and also by
selection, improve their domestic animals; and then he adds, that what
is done in this latter case “by art, seems to be done with equal
efficiency, though more slowly, by nature, in the formation of varieties
of mankind fitted for the country which they inhabit. Of the accidental
varieties of man which would occur among the first few and scattered
inhabitants of the middle regions of Africa, some one would be better
fitted than the others to bear the diseases of the country. This race
would consequently multiply, while the others would decrease; not only
from their inability to sustain the attacks of disease, but from their
incapacity of contending with their more vigorous neighbours. The
colour of this vigorous race I take for granted, from what has been
already said, would be dark. But the same disposition to form varieties
still existing, a darker and a darker race would in the course of time
occur; and as the darkest would be the best fitted for the climate, this
would at length become the most prevalent, if not the only race, in the
particular country in which it had originated.” He then extends these
same views to the white inhabitants of colder climates. Although Wells
clearly expresses and recognizes the principle of natural selection, yet
it is applied by him only to the very limited problem of the origin of
human races, and not at all to that of the origin of animal and
vegetable species. Darwin’s great merit in having independently
developed the Theory of Selection, and having brought it to complete and
well merited recognition, is as little affected by the earlier and long
forgotten remark of Wells, as by some other fragmentary observations
about natural selection made by Patrick Mathew, and hidden in his book
on “Timber for Shipbuilding, and the Cultivation of Trees,” which
appeared in 1831. The celebrated traveller, Alfred Wallace, who
developed the Theory of Selection independently of Darwin, and had
published it in 1858, simultaneously with Darwin’s first contribution,
likewise stands far behind his greater and elder countryman in regard to
profound conception, as well as to extended application of the theory.
In fact Darwin, by his extremely comprehensive and ingenious development
of the whole doctrine, has acquired a fair claim to see the theory
connected with his own name.

This Theory of Selection, Darwinism in its proper sense, to the
consideration of which we now turn our attention, rests essentially (as
has already been intimated in the last chapter) upon the comparison of
those means which man employs in the breeding of domestic animals and
the cultivation of garden plants, with those processes which in free
nature, outside the cultivated state, lead to the coming into existence
of new species and new genera. We must therefore, in order to understand
the latter processes, first turn to the artificial breeding by man, as
was, in fact, done by Darwin himself. We must inquire into the results
to which man attains by his artificial breeding, and what means are
applied in order to obtain those results; and we must then ask
ourselves, “Are there in nature similar forces and causes acting
similarly to those resorted to by man?”

First, in regard to artificial breeding, we start from the fact last
discussed above, viz., that its products in some cases differ from one
another much more than the productions of natural breeding. It is a fact
that races or varieties often differ from one another in a much greater
degree and in much more important qualities than many so-called species,
or “good species,”—nay, sometimes even more than so-called “good
genera” in their natural state. Compare, for example, the different
kinds of apples which the art of horticulture has derived from one and
the same original apple-form, or compare the different races of horses
which their breeders have derived from one and the same original form of
horse, and it will be easily observed that the differences of the most
different forms are extremely important, and much more important than
the so-called “specific differences,” which are referred to by
zoologists and botanists when comparing wild forms for the purpose of
distinguishing several so-called “good species.”

Now, by what means does man produce this extraordinary difference or
divergence of several forms which are proved to be descended from the
same primary form? In order to answer this question, let us follow a
gardener who desires to produce a new form of a plant, which is
distinguished by the beautiful colour of its flowers. He will first of
all make a selection from a great number of plants which are seedlings
from one and the same parent. He will pick out those plants which
exhibit most distinctly the colour of flower he desires. The colour of
flowers is a very changeable thing. Plants, for example, which as a rule
have a white flower, frequently show deviations into the blue or red.
Now, supposing the gardener wishes to obtain the red colour in a plant
usually producing white flowers, he will very carefully, from among the
many different individuals which are the descendants of one and the same
seed-plant, select those which most distinctly show a reddish tint, and
sow them exclusively, in order to produce new individuals of the same
kind. He would cast aside and no longer cultivate the other seedlings
which show a white or less distinct red colour. He will propagate
exclusively the individual plants whose blossoms show the red most
markedly, and he will sow the seeds produced by these selected plants.
From the seedlings of this second generation, he will again carefully
select those in which the red, which is now visible in the majority of
them, is most distinctly displayed. If such a selection is carried on
during a series of six or ten generations, and if the flower which shows
the deepest red is most carefully selected, the gardener in the sixth or
tenth generation will obtain the desired plants with flowers of a pure
red.

The farmer wishing to breed a special race of animals, for example, a
kind of sheep distinguished by particularly fine wool, proceeds in the
same manner. The only process applied in the improvement of wool
consists in this, that the farmer with the greatest care and
perseverance selects from a whole flock of sheep those individuals which
have the finest wool. These only are used in breeding, and among the
descendants of these selected sheep, those again are chosen which have
the finest wool, etc. If this careful selection is carried on through a
series of generations, the selected breeding-sheep are in the end
distinguished by a wool which differs very strikingly from the wool of
the original parent, and this is exactly the advantage which the breeder
desired.

The differences of the individuals that come into consideration in this
artificial selection are very slight. An ordinary unpractised man is
unable to discover the exceedingly minute differences of individuals
which a practised breeder perceives at the first glance. The business of
a breeder is not easy; it requires an exceedingly sharp eye, great
patience, and an extremely careful manner of treating the organisms to
be bred. In each individual generation, the differences of individuals
are perhaps not seen at all by the uninitiated; but by the accumulation
of these minute differences during a series of generations, the
deviation from the original form becomes in the end very great. It
becomes so great that the artificially produced form may in the end
differ far more from the original form than do two so-called “good
species” in their natural state. The art of breeding has now made such
progress, that man can often at discretion produce certain peculiarities
in cultivated species of animals and plants. To practised gardeners and
farmers, you may give distinct commissions, and say, for example, I wish
to have this species of plant with this or that colour, and with this or
that shape. Where breeding has reached the perfection which it has
attained in England, gardeners and farmers are frequently able to
furnish to order the desired result within a definite period, that is,
at the end of a number of generations. Sir John Sebright, one of the
most experienced English pigeon-breeders, could assert that in three
years he would produce any form of feather, but that he required six
years to obtain any desired form of the head and beak. In the process of
breeding the merino-sheep of Saxony, the animals are three times placed
on a table beside one another, and most carefully compared and studied.
Each time only the best sheep with the finest wool are selected, so that
in the end, out of a great multitude, there remain only some few
animals, but their wool is exquisitely fine, and only these last are
used in breeding. We see, therefore, that the causes through which, in
artificial breeding, great effects are produced, are unusually simple,
and these great effects are obtained simply by accumulating the
differences which in themselves are very insignificant, and become
surprisingly increased by a continually repeated selection.

Before we pass on to a comparison of this artificial with natural
breeding, let us see what natural qualities of the organisms are made
use of by the artificial breeder or cultivator. We can trace all the
different qualities which here come into play to physiological
fundamental qualities of the organism, which are common to all animals
and plants, and are most closely connected with the functions of
_propagation_ and _nutrition_. These two fundamental qualities are
_transmissivity_, or the capability of _transmitting by inheritance_,
and _mutability_, or the capability of _adaptation_. The breeder starts
from the fact that all the individuals of one and the same species are
different, though in a very slight degree, a fact which is as true of
organisms in a wild as in a cultivated state. If you look about you in a
forest consisting of only a single species of tree, for example of
beech, you will certainly not find in the whole forest two trees of this
kind which are absolutely identical or perfectly equal in the form of
their branches, the number of their branches and leaves, blossoms and
fruits. Special differences occur everywhere, just as in the case of
men. There are no two men who are absolutely identical, perfectly equal
in size, in the formation of their faces, the number of their hairs,
their temperament, character, etc. The very same is true of individuals
of all the different species of animals and plants. It is true that in
most organisms the differences are very trifling to the eye of the
uninitiated. Everything here essentially depends on the exercise of the
faculty of discovering these often very minute differences of form. The
shepherd, for example, knows every individual of his flock, solely by
accurately observing their features, while the uninitiated are incapable
of distinguishing at all the different individuals of one and the same
flock. This fact of the individual difference is the extremely important
foundation on which the whole of man’s power of breeding rests. If
individual differences did not exist everywhere, man would not be able
to produce a number of different varieties or races from one and the
same original stock. We must, at the outset, hold fast the principle
that the phenomenon is quite universal; we must necessarily assume it
even where, with the imperfect capabilities of our senses, we are unable
to discover differences. Among the higher plants (the phanerogams, or
flower-plants), where the individual stocks show such numerous
differences in the number of branches or leaves, and in the formation of
the stem and branches, we can almost always easily perceive these
differences. But this is not the case in the lower plants, such as
mosses, algæ, fungi, and in most animals, especially the lower ones. The
distinction of all the individuals of one species is here, for the most
part, extremely difficult or altogether impossible. But there is no
reason for ascribing individual differences only to those organisms in
which we can perceive them at once. We may, on the contrary, with full
certainty assume such individuality as a universal quality of all
organisms, and we can do this all the more surely since we are able to
trace the mutability of individuals to the mechanical conditions of
nutrition. We can show that by influencing nutrition we are able to
produce striking individual differences where they would not exist if
the conditions of nutrition had not been altered. The many complicated
conditions of nutrition are never absolutely identical in two
individuals of a species.

Now, just as we see that the mutability or capability of adaptation has
a causal connection with the general relations of nutrition in animals
and plants, so too we find the second fundamental phenomenon of life,
with which we are here concerned, namely, the capability of
_transmitting by inheritance_, to have a direct connection with the
phenomenon of _propagation_. The second thing that a farmer or gardener
does in artificial breeding, after he has selected, and has consequently
availed himself of the mutability, is to endeavour to hold fast and
develop the modified forms by Inheritance. He starts from the universal
fact that children resemble their parents, that “the apple does not fall
far from the tree.” This phenomenon of Inheritance has hitherto been
scientifically examined only to a very small extent, which may partly
arise from the fact that the phenomenon is of such everyday occurrence.
Every one considers it quite natural that every species should produce
its like; that a horse should not suddenly produce a goose, or a goose a
frog. We are accustomed to look upon these everyday occurrences of
Inheritance as self-evident. But this phenomenon is not so simply
self-evident as it appears at first sight, and in the examination of
Inheritance the fact is very frequently overlooked that the different
descendants, derived from one and the same parents, are in reality
_never_ quite identical, and also never absolutely like the parents, but
are always slightly different. We cannot formulate the principle of
Inheritance, as “Like produces like,” but we must limit the expression
to “Similar things produce similar things.” The gardener, as well as the
farmer, avails himself of the fact of Inheritance in its widest form,
and indeed with special regard to the fact that not only those qualities
of organisms are transmitted by inheritance which they have inherited
from _their_ parents but those also which they themselves have
_acquired_. This is an important point upon which very much depends. An
organism can transmit to its descendants not only those qualities of
form, colour, and size which it has inherited from its parents, but it
can also transmit changes of these qualities, which it has acquired
during its own life through the influence of outward circumstances, such
as climate, nourishment, training, etc.

These are the two fundamental qualities of animals and plants of which
the breeder must avail himself in order to produce new forms. The
theoretical principle of breeding is, indeed, extremely simple, but in
detail the practical application of this simple principle is difficult
and immensely complicated. A thoughtful breeder, acting according to a
definite plan, must understand the art of correctly estimating, in every
case, the general interaction between the two fundamental qualities of
heirship and mutability.

Now, if we examine the real nature of those two important properties of
life, we find that we can trace them, like all physiological functions,
to physical and chemical causes, to the properties and the phenomena of
motion of those substances of which the bodies of animals and plants
consist. As we shall hereafter have to show in the more accurate
consideration of these two functions, the transmission by _Inheritance_,
if we express ourselves quite generally, is essentially dependent upon
the material continuity and partial identity of the matter in the
producing and produced organism, the parents and the child. In every act
of breeding a certain quantity of protoplasm or albuminous matter is
transferred from the parents to the child, and along with it there is
transferred the individually _peculiar molecular motion_. These
molecular phenomena of motion in the protoplasm, which call forth the
phenomena of life, and are their active and true cause, differ more or
less in all living individuals; they are of infinite variety.

_Adaptation_, or transmutation is, on the other hand, essentially the
consequence of material influences, which the substance of the organism
experiences from the material surrounding it,—in the widest sense of
the word from the _conditions_ of life. The external influences of the
latter are communicated to the individual parts of the body by the
molecular processes of nutrition. In every act of Adaptation the
individual molecular motion of the protoplasm, peculiar to each part,
disturbs and modifies the whole individual, or part of it, by
mechanical, physical, or chemical influences. The innate, inherited
vital actions of the protoplasm—that is, the molecular phenomena of
motion of the smallest albuminous particles—are therefore more or less
modified by it. The phenomenon of Adaptation, or transmutation, depends
therefore upon the material influence which the organism experiences
from its surroundings, or its conditions of existence; while the
transmission by Inheritance is due to the partial identity of the
producing and produced organism. These are the real, simple, mechanical
foundations of the artificial process of breeding.

Now Darwin asked himself, Does there exist a similar process of
selection in nature, and are there forces in nature which take the place
of man’s activity in artificial selection? Is there a natural tendency
among wild animals and plants which acts selectingly, in a similar
manner to the artificial selection practised by the designing will of
man? All here depended upon the discovery of such a relation, and Darwin
succeeded in this so satisfactorily, that we consider his theory of
selection completely sufficient to explain, mechanically, the origin of
the wild species of animals and plants. That relation which in free
nature influences the forms of animals and plants, by selecting and
transforming them, is called by Darwin the “_Struggle for Existence_.”

The “Struggle for Existence” has rapidly become a watchword of the day.
Yet this designation is, perhaps, in many respects not very happily
chosen, and the phenomena might probably have been more accurately
described as “_Competition for the Means of Subsistence_.” For under the
name of “Struggle for Life,” many relations are comprehended which
properly and strictly speaking do not belong to it. As we have seen from
the letter inserted in the last chapter, Darwin arrived at the idea of
the “Struggle for Existence” from the study of Malthus’ book “On the
Conditions and the Consequences of the Increase of Population.” It was
proved in that important work, that the number of human beings, on the
average, increases in a geometrical progression, while the amount of
articles of food increase only in an arithmetical progression. This
disproportion gives rise to a number of inconveniences in the human
community, which cause among men a continual competition to obtain the
necessary means of life, which do not suffice for all.

Darwin’s theory of the struggle for life is, to a certain extent, a
general application of Malthus’ theory of population to the whole of
organic nature. It starts from the consideration that the number of
_possible_ organic individuals which might arise from the germs
produced, is far greater than the number of _actual_ individuals which,
in fact, do simultaneously live on the earth’s surface. The number of
possible or _potential individuals_ is given us by the number of the
eggs and organic germs produced by organisms. The number of these germs,
from each of which, under favourable circumstances, an individual might
arise, is very much larger than the number of real or actual
_individuals_—that is, of those that really arise from these germs,
come into life, and propagate themselves. By far the greater number of
germs perish in the earliest stage of life, and it is only some favoured
organisms which manage to develop, and actually survive the first period
of early youth, and finally succeed in propagating themselves. This
important fact is easily proved by a comparison of the number of eggs in
a given species with the number of individuals which exist of this
species. These numerical relations show the most striking contrast.
There are, for example, species of fowls which lay great numbers of
eggs, and yet are among the rarest of birds; and the bird which is said
to be the commonest (the most widely spread) of all, the stormy petrel
(_Procellaria glacialis_), lays only a single egg. The relation is the
same in other animals. There are many very rare invertebrate animals,
which lay immense quantities of eggs; and others again which produce
only very few eggs, and yet are among the commonest of animals. Take,
for example, the proportion which is observed among the human
tape-worms. Each tape-worm produces within a short period millions of
eggs, while man, in whom these tape-worms are lodged, forms a far
smaller number of eggs, and yet fortunately there are fewer tape-worms
than human beings. In like manner, among plants there are many splendid
orchids, which produce thousands of seeds and yet are very rare, and
some kinds of asters (Compositæ), which have but few seeds, are
exceedingly common.

This important fact might be illustrated by an immense number of
examples. It is evidently, therefore, not the number of actually
existing germs which indicates the number of individuals which
afterwards come into life and maintain themselves in life; but rather
the case is this, that the number of adult individuals is limited by
other circumstances, especially by the relations in which the organism
stands to its organic and inorganic surroundings. Every organism, from
the commencement of its existence, struggles with a number of hostile
influences: it struggles against animals which feed on it, and to which
it is the natural food, against animals of prey and parasites; it
struggles against inorganic influences of the most varied kinds, against
temperature, weather, and other circumstances; but it also struggles
(and this is much the most important!), above all, against organisms
most like and akin to itself. Every individual, of every animal and
vegetable species, is engaged in the fiercest competition with every
other individual of the same species which lives in the same place with
it. In the economy of nature the means of subsistence are nowhere
scattered in abundance, but are very limited, and far from sufficient
for the number of organisms which might develop from the germs produced.
Therefore the young individuals of most species of animals and
vegetables must have hard work in obtaining the means of subsistence;
this necessarily causes a competition among them in order to obtain the
indispensable supplies of life.

This great competition for the necessaries of life goes on everywhere
and at all times, among human beings and animals as well as among
plants; in the case of the latter this circumstance, at first sight, is
not so clearly apparent. If we examine a field which is richly sown with
wheat, we can see that of the numerous young plants (perhaps some
thousands) which shoot up on a limited space, only a very small
proportion preserve themselves in life. A competition takes place for
the space of ground which each plant requires for fixing its root, a
competition for sunlight and moisture. And in the same manner we find
that, among all animal species, all the individuals of one and the same
species compete with one another to obtain these indispensable means of
life, or the conditions of existence in the wide sense of the word. They
are equally indispensable to all, but really fall to the lot of only a
few—“Many are called, but few are chosen.” The fact of the great
competition is quite universal. You need only to cast a glance at human
society, where this competition exists everywhere, and in all the
different branches of human activity. Here, too, a struggle is brought
about by the free competition of the different labourers of one and the
same class. Here too, as everywhere, this competition benefits the
thing, or the work, which is the object of competition. The greater and
more general the competition, the more quickly improvements and
inventions are made in the branch of labour, and the higher is the grade
of perfection of the labourers themselves.

The position of the different individuals in this struggle for life is
evidently very unequal. Starting from the inequality of individuals,
which is a recognized fact, we must in all cases necessarily suppose
that all the individuals of one and the same species do not have equally
favourable prospects. Even at the beginning they are differently placed
in this competition by their different strengths and abilities,
independently of the fact that the conditions of existence are
different, and act differently at every point of the earth’s surface. We
evidently have an infinite combination of influences, which, together
with the original inequality of the individuals during the competition
for the conditions of existence, favour some individuals and prejudice
others. The favoured individuals will gain the victory over the others,
and while the latter perish more or less early, without leaving any
descendants, the former alone will be able to survive and finally to
propagate the species. As, therefore, it is clear that in the struggle
for life the favoured individuals succeed in propagating themselves, we
shall (even as the result of this relation) perceive in the next
generation differences from the preceding one. Some individuals of this
second generation, though perhaps not all of them, will, by inheritance,
receive the individual advantage by which their parents gained the
victory over their rivals.

But now—and this is a very important law of inheritance—if such a
transmission of a favourable character is continued through a series of
generations, it is not simply transmitted in the original manner, but it
is constantly increased and strengthened, and in a last generation it
attains a strength which distinguishes this generation very essentially
from the original parent. Let us, for example, examine a number of
plants of one and the same species which grow together in a very dry
soil. As the hairs on the leaves of plants are very useful for receiving
moisture from the air, and as the hairs on the leaves are very
changeable, the individuals possessing the thickest hair on their leaves
will have an advantage in this unfavourable locality where the plants
have directly to struggle with the want of water, and in addition to
this have to compete with one another for the possession of what little
water there may be. These alone hold out, while the others possessing
less hairy leaves perish; the more hairy ones will be propagated, and
their descendants will, on the average, be more distinguished by their
thick and strong hairs than the individuals of the first generation. If
this process is continued for several generations in one and the same
locality, there will arise at last such an increase of this
characteristic, such an increase of the hairs on the surface of the
leaf, that an entirely new species seems to present itself. It must here
be observed, that in consequence of the interactions of all the parts of
every organism, generally one individual part cannot be changed without
at the same time producing changes in other parts. If, for instance, in
our imaginary example, the number of the hairs on the leaves is greatly
increased, a certain amount of nourishment is thereby withdrawn from
other parts; the material which might be employed to form flowers or
seeds is diminished, and a smaller size of the flower or seed will then
be the direct or indirect consequence of the struggle for life, which in
the first place only produced a change in the leaves. Thus the struggle
for life, in this instance, acts as a means of selecting and
transforming. The struggle of the different individuals to obtain the
necessary conditions of existence, or, taking it in its widest sense,
the inter-relations of organisms to the whole of their surroundings,
produce mutations of form such as are produced in the cultivated state
by the action of man’s selection.

This agency will perhaps appear at first sight small and insignificant,
and the reader will not be inclined to concede to the action of such
relations the weight which it in reality possesses. I must therefore
find space in a subsequent chapter to put forward further examples of
the immense and far-reaching power of transformation exhibited in
natural selection. For the present I will confine myself to simply
placing side by side the two processes of artificial and natural
selection, and clearly explaining the agreement and the differences of
the two.

Both natural and artificial selection are quite simple natural,
mechanical relations of life, which depend upon the _interaction_ of two
physiological functions, namely, on _Adaptation_ and _Inheritance_,
functions which, as such, must again be traced to physical and chemical
properties of organic matter. The difference between the two forms of
selection consists in this: in artificial selection the will of man
makes the selection according to a _plan_, whereas in natural selection,
the struggle for life (that universal inter-relation of organisms) acts
_without a plan_, but otherwise produces quite the same result, namely,
a selection of a particular kind of individuals for propagation. The
alterations produced by artificial selection are turned to the advantage
of _those who make the selection_; in natural selection, on the other
hand, to the advantage of the _selected organism_.

These are the most essential differences and agreements of the two modes
of selection; it must, however, be further observed that there is
another difference, viz., in the duration of time required for the two
processes of selection. Man in his artificial selection can produce very
important changes in a very short time, while in natural selection
similar results are obtained only after a much longer time. This arises
from the fact that man can make his selection with much greater care.
Man is able with the greatest nicety to pick out individuals from a
large number, drop the others, and to employ only the privileged beings
for propagation, which is not the case in natural selection. In natural
conditions, besides the privileged individuals which first succeed in
propagating themselves, some few or many of the less distinguished
individuals will propagate themselves by the side of the former.
Moreover, man can prevent the crossing of the original and the new form,
which in natural selection is often unavoidable. If such a crossing,
that is, a sexual connection, of the new variety with the original forms
takes place, the offspring thereby produced generally returns to the
original character. In natural selection, such a crossing can be avoided
only when the new variety by migration separates from the original and
isolates itself.

Natural selection therefore acts much more slowly; it requires much
longer periods than the artificial process of selection. But it is an
essential consequence of this difference, that the product of artificial
selection disappears much more easily, and that the new form returns
rapidly to the earlier one, which is not the case in natural selection.
The new species arising from natural selection maintain themselves much
more permanently, and return much less easily to the original form, than
is the case with products of artificial selection, and accordingly
maintain themselves during a much longer time than the artificial races
produced by man. But these are only subordinate differences, which are
explained by the different conditions of natural and artificial
selection, and in reality are connected only with differences in the
duration of time. The nature of the transformation and the means by
which it is produced are entirely the same in both artificial and
natural selection. (Gen. Morph. ii. 248.)

The thoughtless and narrow-minded opponents of Darwin are never tired of
asserting that his theory of selection is a groundless conjecture, or at
least an hypothesis which has yet to be proved. That this assertion is
completely unfounded, may be perceived even from the outlines of the
doctrine of selection which have just been discussed. Darwin assumes no
kind of unknown forces of nature, nor hypothetical conditions, as the
acting causes for the transformation of organic forms, but solely and
simply the universally recognized vital activities of all organisms,
which we term _Inheritance_ and _Adaptation_. Every naturalist
acquainted with physiology knows that these two phenomena are directly
connected with the functions of propagation and nutrition, and, like all
other phenomena of life, are purely mechanical processes of nature, that
is, they depend upon the molecular phenomena of motion in organic
matter. That the interaction of these two functions effect a continual,
slow transmutation of organic forms, is a necessary result of the
struggle for existence. But this, again, is no more a hypothetical
relation, nor one requiring a proof, than is the interaction of
Inheritance and Adaptation. The struggle for life is a mathematical
necessity, arising from the disproportion between the limited number of
places in nature’s household, and the excessive number of organic germs.
The origin of new species is moreover greatly favoured by the active or
passive _migrations_ of animals and plants, which takes place everywhere
and at all times, without being, however, entitled to rank as
_necessary_ agents in the process of natural selection.

The origin of new species by natural selection, or, what is the same
thing, by the interaction of Inheritance and Adaptation in the struggle
for life, is therefore a _mathematical necessity_ of nature which needs
no further proof. Whoever, in spite of the present state of our
knowledge, still seeks for _proofs_ for the Theory of Selection, only
shows that he either does not thoroughly understand the theory, or is
not sufficiently acquainted with the biological facts—has not the
requisite amount of experimental knowledge in Anthropology, Zoology, and
Botany.

If, as we maintain, natural selection is the great active cause which
has produced the whole wonderful variety of organic life on the earth,
all the interesting phenomena of _human life_ must also be explicable
from the same cause. For man is after all only a most highly-developed
vertebrate animal, and all aspects of human life have their parallels,
or, more correctly, their lower stages of development in the animal
kingdom. The whole history of nations, or what is called “Universal
History,” must therefore be explicable by means of “natural
selection,”—must be a physico-chemical process, depending upon the
interaction of Adaptation and Inheritance in the struggle for life. And
this is actually the case. We shall give further proofs of this later
on.

It appears of interest here to remark that not only _natural_ selection,
but also _artificial_ selection exercises its influence in many ways in
universal history. A remarkable instance of _artificial selection in
man_, on a great scale, is furnished by the ancient Spartans, among
whom, in obedience to a special law, all newly-born children were
subject to a careful examination and selection. All those that were
weak, sickly, or affected with any bodily infirmity, were killed. Only
the perfectly healthy and strong children were allowed to live, and they
alone afterwards propagated the race. By this means, the Spartan race
was not only continually preserved in excellent strength and vigour, but
the perfection of their bodies increased with every generation. No doubt
the Spartans owed their rare degree of masculine strength and rough
heroic valour (for which they are eminent in ancient history) in a
great measure to this artificial selection.

Many tribes also among the Red Indians of North America (who at present
are succumbing in the struggle for life to the superior numbers of the
white intruders, in spite of a most heroic and courageous resistance)
owe their rare degree of bodily strength and warlike bravery to a
similar careful selection of the newly-born children. Among them, also,
all children that are weak or affected with any infirmity are
immediately killed, and only the perfectly strong individuals remain in
life, and propagate the race. That the race becomes greatly
strengthened, in the course of very many generations, by this artificial
selection cannot in itself be doubted, and is sufficiently proved by
many well known facts.

The opposite of this artificial selection of the wild Redskins and the
ancient Spartans is seen in the individual selection which is
universally practised in our modern military states, for the purpose of
maintaining standing armies, and which, under the name of _military
selection_, we may conveniently consider as a special form of selection.
Unfortunately, in our day, militarism is more than ever prominent in our
so-called “civilization”; all the strength and all the wealth of
flourishing civilized states are squandered on its development; whereas
the education of the young, and public instruction, which are the
foundations of the true welfare of nations and the ennobling of
humanity, are neglected and mismanaged in a most pitiable manner. And
this is done in states which believe themselves to be the privileged
leaders of the highest human intelligence, and to stand at the head of
civilization. As is well known, in order to increase the standing army
as much as possible, all healthy and strong young men are annually
selected by a strict system of recruiting. The stronger, healthier, and
more spirited a youth is, the greater is his prospect of being killed by
needle-guns, cannons, and other similar instruments of civilization. All
youths that are unhealthy, weak, or affected with infirmities, on the
other hand, are spared by the “military selection,” and remain at home
during the war, marry, and propagate themselves. The more useless, the
weaker, or infirmer the youth is, the greater is his prospect of
escaping the recruiting officer, and of founding a family. While the
healthy flower of youth dies on the battle-field, the feeble remainder
enjoy the satisfaction of reproduction and of transmitting all their
weaknesses and infirmities to their descendants. According to the laws
of transmission by inheritance, there must necessarily follow in each
succeeding generation, not only a further extension, but also a more
deeply-seated development of weakness of body, and what is inseparable
from it, a condition of mental weakness also. This and other forms of
artificial selection practised in our civilized states sufficiently
explain the sad fact that, in reality, weakness of the body and weakness
of character are on the perpetual increase among civilized nations, and
that, together with strong, healthy bodies, free and independent spirits
are becoming more and more scarce.

To the increasing enervation of modern civilized nations, which is the
necessary consequence of military selection, there is further added
another evil. The progress of modern medical science, although still
little able really to cure diseases, yet possesses and practises more
than it used to do the art of prolonging life during lingering, chronic
diseases for many years. Such ravaging evils as consumption, scrofula,
syphilis, and also many forms of mental disorders, are transmitted by
inheritance to a great extent, and transferred by sickly parents to some
of their children, or even to the whole of their descendants. Now, the
longer the diseased parents, with medical assistance, can drag on their
sickly existence, the more numerous are the descendants who will inherit
incurable evils, and the greater will be the number of individuals,
again, in the succeeding generation, thanks to that artificial “_medical
selection_,” who will be infected by their parents with lingering,
hereditary disease.

If any one were to venture the proposal, after the examples of the
Spartans and Redskins, to kill, immediately upon their birth, all
miserable, crippled children to whom with certainty a sickly life could
be prophesied, instead of keeping them in life injurious to them and to
the race, our so-called “humane civilization” would utter a cry of
indignation. But the same “humane civilization” thinks it quite as it
should be, and accepts without a murmur, that at the outbreak of every
war (and in the present state of civilized life, and in the continual
development of standing armies, wars must naturally become more
frequent) hundreds and thousands of the finest men, full of youthful
vigour, are sacrificed in the hazardous game of battles. The same
“humane civilization” at present praises the abolition of capital
punishment as a “liberal measure!” And yet capital punishment for
incorrigible and degraded criminals is not only just, but also a benefit
to the better portion of mankind; the same benefit is done by destroying
luxuriant weeds, for the prosperity of a well cultivated garden. As by
a careful rooting out of weeds, light, air, and ground is gained for
good and useful plants, in like manner, by the indiscriminate
destruction of all incorrigible criminals, not only would the struggle
for life among the better portion of mankind be made easier, but also an
advantageous artificial process of selection would be set in practice,
since the possibility of transmitting their injurious qualities by
inheritance would be taken from those degenerate outcasts.

Against the injurious influence of artificial military and medical
selection, we fortunately have a salutary counterpoise, in the
invincible and much more powerful influence of _natural selection_,
which prevails everywhere. For in the life of man, as well as in that of
animals and plants, this influence is the most important transforming
principle, and the strongest lever for progress and amelioration. The
result of the struggle for life is that, in the long run, that which is
better, because more perfect, conquers that which is weaker and
imperfect. In human life, however, this struggle for life will ever
become more and more of an intellectual struggle, not a struggle with
weapons of murder. The organ which, above all others, in man becomes
more perfect by the ennobling influence of natural selection, is the
_brain_. The man with the most perfect understanding, not the man with
the best revolver, will in the long run be victorious; he will transmit
to his descendants the qualities of the brain which assisted him in the
victory. Thus then we may justly hope, in spite of all the efforts of
retrograde forces, that the progress of mankind towards freedom, and
thus to the utmost perfection, will, by the happy influence of natural
selection, become more and more certain.

CHAPTER VIII.

TRANSMISSION BY INHERITANCE AND PROPAGATION.

Universality of Inheritance and Transmission by
Inheritance.—Special Evidences of the same.—Human
Beings with four, six, or seven Fingers and
Toes.—Porcupine Men.—Transmission of Diseases,
especially Diseases of the Mind.—Original
Sin.—Hereditary Monarchies.—Hereditary
Aristocracy.—Hereditary Talents and Mental
Qualities.—Material Causes of Transmission by
Inheritance.—Connection between Transmission by
Inheritance and Propagation.—Spontaneous Generation and
Propagation.—Non-sexual or Monogonous
Propagation.—Propagation by Self-Division.—Monera and
Amœbæ.—Propagation by the formation of Buds, by the
formation of Germ-Buds, by the formation of
Germ-Cells.—Sexual or Amphigonous
Propagation.—Formation of Hermaphrodites.—Distinction
of Sexes, or Gonochorism.—Virginal Breeding, or
Parthenogenesis.—Material Transmission of Peculiarities
of both Parents to the Child by Sexual
Propagation.—Difference between Transmission by
Inheritance in Sexual and in Asexual Propagation.

The reader has, in the last chapter, become acquainted with natural
selection according to Darwin’s theory, as the constructive force of
nature which produces the different forms of animal and vegetable
species. By natural selection we understand the interaction which takes
place in the struggle for life between the _transmission by inheritance_
and the _mutability_ of organisms, between two physiological functions
which are innate in all animals and plants, and which may be traced to
other processes of life—the functions of propagation and nutrition. All
the different forms of organisms, which people are usually inclined to
look upon as the products of a creative power, acting for a definite
purpose, we, according to the Theory of Selection, can conceive as the
necessary productions of natural selection, working without a
purpose,—as the unconscious interaction between the two properties of
Mutability and Hereditivity. Considering the importance which
accordingly belongs to these vital properties of organisms, we must
examine them a little more closely, and employ a chapter with the
consideration of Transmission by Inheritance. (Gen. Morph. ii. 170-191.)

Strictly speaking, we must distinguish between Hereditivity
(Transmissivity) and Inheritance (Transmission). Hereditivity is the
power of transmission, the capability of organisms to transfer their
peculiarities to their descendants by propagation. Transmission by
Inheritance, or Inheritance simply, on the other hand, denotes the
exercise of the capability, the actual transmission.

Hereditivity and Transmission by Inheritance are such universal,
everyday phenomena, that most people do not heed them, and but few are
inclined to reflect upon the operation and import of these phenomena of
life. It is generally thought quite natural and self-evident that every
organism should produce its like, and that children should more or less
resemble their parents. Heredity is usually only taken notice of and
discussed in cases relating to some special peculiarity, which appears
for the first time in a human individual without having been inherited,
and then is transmitted to his descendants. It shows itself in a
specially striking manner in the case of certain diseases, and in
unusual and irregular (monstrous) deviations from the usual formation of
the body.

Among these cases of the inheritance of monstrous deviations, those are
specially interesting which consist in an abnormal increase or decrease
of the number five in the fingers or toes of man. It is not unfrequently
observed in families through several generations, that individuals have
six fingers on each hand, or six toes on each foot. Less frequent is the
number of four or seven fingers or toes. The unusual formation arises at
first from a single individual who, from unknown causes, is born with an
excess of the usual number of fingers and toes, and transmits these, by
inheritance, to a portion of his descendants. In one and the same family
it has happened that, throughout three, four, or more generations,
individuals have possessed six fingers and toes. In a Spanish family
there were no less than forty individuals distinguished by this excess.
The transmission of the sixth finger or toe is not permanent or enduring
in all cases, because six-fingered people always intermarry again with
those possessing five fingers. If a six-fingered family were to
propagate by pure in-breeding, if six-fingered men were always to marry
six-fingered women, this characteristic would become permanent, and a
special six-fingered human race would arise. But as six-fingered men
usually marry five-fingered women, and _vice versâ_, their descendants
for the most part show a very mixed numerical relation, and finally,
after the course of some generations, revert again to the normal number
of five. Thus, for example, among eight children of a six-fingered
father and a five-fingered mother, two children may have on both hands
and feet six fingers and toes, four children may have a mixed number,
and two children may have the usual number of five on both hands and
feet. In a Spanish family, each child except the youngest had the number
six on both hands and feet; the youngest, only, had the usual number on
both hands and feet, and the six-fingered father of the child refused to
recognize the last one as his own.

The power of inheritance, moreover, shows itself very strikingly in the
formation and colour of the human skin and hair. It is well known how
exactly the nature of the complexion in many families—for instance, a
peculiar soft or rough skin, a peculiar luxuriance of the hair, a
peculiar colour and largeness of the eyes—is transmitted through many
generations. In like manner, peculiar local growths or spots on the
skin, the so-called moles, freckles, and other accumulations of pigment
which appear in certain places, are frequently transmitted through
several generations so exactly, that in the descendants they appear on
the same spots on which they existed in the parents. The porcupine men
of the Lambert family, who lived in London last century, are especially
celebrated. Edward Lambert, born in 1717, was remarkable for a most
unusual and monstrous formation of the skin. His whole body was covered
with a horny substance, about an inch thick, which rose in the form of
numerous thorn-shaped and scale-like processes, more than an inch long.
This monstrous formation of the outer skin, or epidermis, was
transmitted by Lambert to his sons and grandsons, but not to his
granddaughters. The transmission in this instance remained in the male
line, as is often the case. In like manner, an excessive development of
fat in certain parts of the body is often transmitted only in the
female line. I scarcely need call to mind how exactly the characteristic
formation of the face is transmitted by inheritance; sometimes it
remains within the male, sometimes within the female line; sometimes it
is blended in both.

The phenomena of transmission by inheritance of pathological conditions,
especially of the different forms of human diseases, are very
instructive and generally known. Diseases of the respiratory organs, the
glands, and of the nervous system, are specially liable to be
transmitted by inheritance. Very frequently there suddenly appears in an
otherwise healthy family a disease until then unknown among them; it is
produced by external causes, by conditions of life causing disease. This
disease, brought about in an individual by external cause, is propagated
and transmitted to his descendants, and some or all of them then suffer
from the same disease. In case of diseases of the lungs, for instance in
consumption, this sad transmission by inheritance is well known, and it
is the same with diseases of the liver, with syphilis, and diseases of
the mind. The latter are specially interesting. Just as peculiar
characteristic features of man—pride, ambition, frivolity, etc.—are
transmitted to the descendants strictly by inheritance, so too are the
peculiar abnormal manifestations of mental activity, which are usually
called fixed ideas, despondency, imbecility, and generally “diseases of
the mind.” This distinctly and irrefragably shows that the soul of man,
just as the soul of animals, is a purely mechanical activity, the sum of
the molecular phenomena of motion in the particles of the brain, and
that it is transmitted by inheritance, together with its substratum,
just as every other quality of the body is materially transmitted by
propagation.

When this exceedingly important and undeniable fact is mentioned, it
generally causes great offence, and yet in reality it is silently and
universally acknowledged. For upon what else do the ideas of “hereditary
sin,” “hereditary wisdom,” and “hereditary aristocracy,” etc., rest than
upon the conviction that the _quality of the human mind_ is transmitted
by propagation—that is, by a purely _material_ process—through the
body, from the parents to the descendants? The recognition of this great
importance of transmission by inheritance is shown in a number of human
institutions, as for example, among many nations in the division into
castes, such as the castes of warriors, castes of priests, and castes of
labourers, etc. It is evident that the institution of such castes
originally arose from the notion of the great importance of hereditary
distinctions possessed by certain families, which it was presumed would
always be transmitted by the parents to the children. The institution of
an hereditary aristocracy and an hereditary monarchy is to be traced to
the notion of such a transmission of special excellencies. However, it
is unfortunately not only virtues, but also vices that are transmitted
and accumulated by inheritance; and if, in the history of the world, we
compare the different individuals of the different dynasties, we shall
everywhere find a great number of proofs of the transmission of
qualities by inheritance, but fewer of transmissions of virtues than of
vices. Look only, for example, at the Roman emperors, at the Julii and
the Claudii, or at the Bourbons in France, Spain, and Italy!

In fact, scarcely anywhere could we find such a number of striking
examples of the remarkable transmission of bodily and mental features by
inheritance, as in the history of the reigning houses in hereditary
monarchies. This is specially true in regard to the diseases of the mind
previously mentioned. It is in reigning families that mental disorders
are hereditary in an unusual degree. Thus Esquirol, distinguished for
his knowledge of mental diseases, proved that the number of insane
individuals in the reigning houses was, in proportion to the number
among the ordinary population, as 60 to 1; that is, that disorders of
the brain occur 60 times more frequently in the privileged families of
the ruling houses than among ordinary people. If equally accurate
statistics were made of the hereditary nobility, the result would
probably be that here also we should find an incomparably larger
contingent of mental diseases than among the common, ignoble portion of
mankind. This phenomenon can scarcely astonish us if we consider what
injury these privileged castes inflict upon themselves by their
unnatural, one-sided education, and by their artificial separation from
the rest of mankind. By this means many dark sides of human nature are
specially developed and, as it were, artificially bred, and, according
to the laws of transmission by inheritance, are propagated through
series of generations with ever-increasing force and dominance.

It is sufficiently obvious from the history of nations how in successive
generations of many dynasties, for example, of the princes of Saxon
Thuringia and of the Medici, the noble solicitude for the most perfect
human accomplishments in science and art were retained and transmitted
from father to son; and how, on the other hand, in many other dynasties,
for centuries a special partiality for the profession of war, for the
oppression of human freedom, and for other rude acts of violence, have
been hereditary. In like manner talents for special mental activities
are transmitted in many families for generations, as, for instance,
talent for mathematics, poetry, music, sculpture, the investigation of
nature, philosophy, etc. In the family of Bach there have been no less
than twenty-two eminent musicians. Of course the transmission of such
peculiarities of mind depends upon the material process of reproduction,
as does the transmission of mental qualities in general. In this case
again, the vital phenomenon, the manifestation of force (as everywhere
in nature), is directly connected with definite relations in the
admixture of the material components of the organism. It is this
definite proportion and molecular motion of matter which is transmitted
by generation.

Now, before we examine the numerous, and in some cases most interesting
and important, laws of transmission by inheritance, let us make
ourselves acquainted with the actual nature of the process. The
phenomena of transmission by inheritance are generally looked upon as
something quite mysterious, as peculiar processes which cannot be
fathomed by natural science, and the causes and actual nature of which
cannot be understood. It is precisely in such a case that people very
generally assume supernatural influences. But even in the present state
of our physiology it can be proved with complete certainty that all the
phenomena of inheritance are entirely natural processes, that they are
produced by mechanical causes, and that they depend on the material
phenomena of motion in the bodies of organisms, which we may consider as
a part of the phenomena of propagation. All the phenomena of Heredity
and the laws of Transmission by Inheritance can be traced to the
material process of _Propagation_.

Every organism, every living individual, owes its existence _either_ to
an act of unparental or _Spontaneous Generation_ (Generatio Spontanea,
Archigonia), or to an act of Parental Generation or _Propagation_
(Generatio Parentalis, Tocogonia). In a future chapter we shall have to
consider Spontaneous Generation, or Archigony. At present we must occupy
ourselves with Propagation, or Tocogony, a closer examination of which
is of the utmost importance for understanding transmission by
inheritance. Most of my readers probably only know those phenomena of
Propagation which are seen universally in the higher plants and animals,
the processes of Sexual Propagation, or Amphigony. The processes of
Non-sexual Propagation, or Monogony, are much less generally known. The
latter, however, are far more suited to throw light upon the nature of
transmission by inheritance in connection with propagation.

For this reason, we shall first consider only the phenomena of
_non-sexual_ or _monogonic propagation_ (Monogonia). This appears in a
variety of different forms, as for example, self-division, formation of
buds, the formation of germ-cells or spores (Gen. Morph. ii. 36-58). It
will be most instructive, first, to examine the propagation of the
simplest organisms known to us, which we shall have to return to later,
when considering the question of spontaneous generation. These very
simplest of all organisms yet known, and which, at the same time, are
the simplest imaginable organisms, are the _Monera_ living in water;
they are very small living corpuscles, which, strictly speaking, do not
at all deserve the name of organism. For the designation “organism,”
applied to living creatures, rests upon the idea that every living
natural body is composed of organs, of various parts, which fit into
one another and work together (as do the different parts of an
artificial machine), in order to produce the action of the whole. During
late years we have become acquainted with _Monera_, organisms which are,
in fact, not composed of any organs at all, but consist entirely of
shapeless, simple, homogeneous matter. The entire body of one of these
Monera, during life, is nothing more than a shapeless, mobile, little
lump of mucus or slime, consisting of an albuminous combination of
carbon. Simpler or more imperfect organisms we cannot possibly conceive.

The first complete observations on the natural history of a Moneron
(Protogenes primordialis) were made by me at Nice, in 1864. Other very
remarkable Monera I examined later (1866) in Lanzarote, one of the
Canary Islands, and in 1867 in the Straits of Gibraltar. The complete
history of one of these Monera, the orange-red _Protomyxa aurantiaca_,
is represented in Plate I, and its explanation is given in the Appendix.
I have found some curious Monera also in the North Sea, off the
Norwegian coast, near Bergen. Cienkowski has described (1865) an
interesting Moneron from fresh waters, under the name of _Vampyrella_.
But perhaps the most remarkable of all Monera was discovered by Huxley,
the celebrated English zoologist, and called _Bathybius Hæckelii_.
“Bathybius” means, living in the deep. This wonderful organism lives in
immense depths of the ocean, which are over 12,000—indeed, in some
parts 24,000 feet below the surface, and which have become known to us
within the last ten years, through the laborious investigations made by
the English. There, among the numerous Polythalamia and Radiolaria
which inhabit the fine calcareous mud of these abysses, the Bathybius is
found in great quantities, sometimes in the shape of roundish, formless
lumps of mucus, sometimes in the form of a network of mucus, covering
fragments of stone and other objects. Small particles of chalk are
frequently embedded in these mucous gelatinous masses, and are, perhaps,
products of their secretion. The entire body of this remarkable
Bathybius consists solely of shapeless plasma, or protoplasm, as in the
case of the other Monera—that is, it consists of the same albuminous
combination of carbon, which in infinite modifications is found in all
organisms, as the essential and never-failing seat of the phenomena of
life. I have given a detailed description and drawing of the Bathybius
and other Monera in my “Monographie der Moneren,” 1870,(15) from which
the drawing in Fig. 9 is taken.

[Illustration: Life history of a simplest organism. Pl. I.

E. Haeckel del. _Prototmyxa aurantiaca._ Lagesse sc.]

In a state of rest most Monera appear as small globules of mucus or
slime, invisible, or nearly so, to the naked eye; they are at most as
large as a pin’s head. When the Moneron moves itself, there are formed
on the upper surface of the little mucous globule, shapeless, fingerlike
processes, or very fine radiated threads; these are the so-called false
feet, or pseudopodia. The false feet are simple, direct continuations of
the shapeless albuminous mass, of which the whole body consists. We are
unable to perceive different parts in it, and we can give a direct proof
of the absolute simplicity of the semi-fluid mass of albumen, for with
the aid of the microscope we can follow the Moneron as it takes in
nourishment. When small particles suited for its nourishment—for
instance, small particles of decayed organic bodies or microscopic
plants and infusoria—accidentally come into contact with the Moneron,
they remain hanging to the sticky semi-fluid globule of mucus, and here
create an irritation, which is followed by a strong afflux of the mucous
substance, and, in consequence, they become finally completely inclosed
by it, or are drawn into the body of the Moneron by displacement of the
several albuminous particles, and are there digested, being absorbed by
simple diffusion (endosmosis).

[Illustration: FIG. 1.—Propagation of the simplest organism, a Moneron,
by self-division. _A._ The entire Moneron, a Protamœba. _B._ It falls
into two halves by a contraction in the middle. _C._ Each of the two
halves has separated from the other, and now represents an independent
individual.]

Just as simple as the process of nutrition is the _propagation_ of these
primitive creatures, which in reality we can neither call animals nor
plants. All Monera propagate themselves only in an asexual manner by
monogony; and in the simplest case, by that kind of monogony which we
place at the head of the different forms of propagation, that is, by
self-division. When such a little globule, for example a Protamœba or
a Protogenes, has attained a certain size by the assimilation of foreign
albuminous matter, it falls into two pieces; a pinching in takes place,
contracting the middle of the globule on all sides, and finally leads to
the separation of the two halves (compare Fig. 1). Each half then
becomes rounded off, and now appears as an independent individual, which
commences anew the simple course of the vital phenomena of nutrition and
propagation. In other Monera (Vampyrella), the body in the process of
propagation does not fall into two, but into four equal pieces, and in
others, again (Protomonas, Protomyxa, Myxastrum), at once into a number
of small globules of mucus, each of which again, by simple growth,
becomes like the parent body. Here it is evident that the process of
_propagation is nothing but a growth of the organism beyond its own
individual limit of size_.

The simple method of propagation of the Moneron by self-division is, in
reality, the most universal and most widely spread of all the different
modes of propagation; for by the same simple process of division,
_cells_ also propagate themselves. Cells are those simple organic
individuals, a large number of which constitute the bodies of most
organisms, the human body not excepted. With the exception of the
organisms of the lowest order, which have not even the perfect form of a
cell (Monera), or during life only represent a single cell (many
Protista and single-celled plants), the body of every organic individual
is composed of a great number of cells. Every organic cell is to a
certain degree an independent organism, a so-called “elementary
organism,” or an “individual of the first order.” Every higher organism
is, in a measure, a society or a state of such variously shaped
elementary individuals, variously developed by division of labour.(39)
Originally every organic cell is only a single globule of mucus, like a
Moneron, but differing from it in the fact that the homogeneous
albuminous substance has separated itself into two different parts, a
firmer albuminous body, the _cell-kernel_ (nucleus), and an external,
softer albuminous body, the _cell-substance_ or _body_ (protoplasma).
Besides this, many cells later on form a third (frequently absent)
distinct part, inasmuch as they cover themselves with a capsule, by
exuding an outer pellicle or _cell-membrane_ (membrana). All other forms
of cells, besides these, are of subordinate importance, and are of no
further interest to us here.

Every organism composed of many cells was originally a single cell, and
it becomes many-celled owing to the fact that the original cell
propagates itself by self-division, and that the new individual cells
originating in this manner remain together, and by division of labour
form a community or a state. The forms and vital phenomena of all
many-celled organisms are merely the effect or the expression of all the
forms and vital phenomena of all the individual cells of which they are
composed. The egg, from which most animals and plants are developed, is
a simple cell.

[Illustration: FIG. 2.—Propagation of a single-celled organism,
Amœba sphærococcus, by self-division. _A._ The enclosed Amœba, a
simple globular cell consisting of a lump of protoplasm (_c_), which
contains a kernel (_b_) and a kernel speck (_a_), and is surrounded by a
cell-membrane or capsule. _B._ The free Amœba, which has burst and
left the cyst or cell-membrane. _C._ It begins to divide by its kernel
forming two kernels, and by the cell-substance between the two becoming
contracted. _D._ The division is completed by the cell-substance
likewise falling into two halves (_Da_ and _Db_).]

The single-celled organisms, that is, those which during life retain the
form of a single cell, for example the Amœbæ, as a rule propagate
themselves in the simplest way by self-division. This process differs
from the previously described self-division of the Moneron only in the
fact that at the commencement the firmer cell-kernel (nucleus) falls
into two halves, by a pinching in at its middle. The two young kernels
separate from each other and act now as two distinct centres of
attraction upon the surrounding softer albuminous matter, that is, the
cell-substance (protoplasma). By this process finally the latter also
divides into two halves, and there now exist two new cells, which are
like the mother cell. If the cell was surrounded by a membrane, this
either does not divide at all, as in the case of egg-cleavage (Fig. 3,
4), or it passively follows the active pinching in of the protoplasm;
or, lastly, every new cell exudes a new membrane for itself.

[Illustration: FIG. 3.—Egg of a mammal (a simple cell). _a._ The small
kernel speck or nucleolus (the so-called germ-spot of the egg). _b._
Kernel or nucleus (the so-called germ-bladder of the egg). _c._
Cell-substance or protoplasm (the so-called yolk of the egg). _d._
Cell-capsule or membrane (membrane of the yolk) of the egg; called in
mammals, on account of its transparency, Membrana pellucida.]

The non-independent cells which remain united in communities or states,
and thus constitute the body of higher organisms, are propagated in the
same manner as are independent single-celled organisms, for example,
Amœba (Fig. 2). Just as in that case, the cell with which most
animals and plants commence their individual existence, namely, the egg,
multiplies itself by simple division. When an animal, for instance a
mammal (Fig. 3, 4), develops out of an egg, this process of development
always begins by the simple egg-cell (Fig. 3) forming an accumulation of
cells (Fig. 4) by continued self-division. The outer covering, or cell
membrane, of the globular egg remains undivided. First, the cell-kernel
of the egg (the so-called germinal vesicle) divides itself into two
kernels, then follows the cell-substance (the yolk of the egg) (Fig. 4
_A_). In like manner, the two cells, by continued self-division,
separate into four (Fig. 4 _B_), these into eight (Fig. 4 _C_), into
sixteen, thirty-two, etc., and finally there is produced a globular mass
of very numerous little cells (Fig. 4 _D_). These now, by further
increase and heterogeneous development (division of labour), gradually
build up the compound many-celled organism. Every one of us, at the
commencement of our individual development, has undergone the very same
process as that represented in Fig. 4. The egg of a mammal—represented
in Fig. 3, and its development in Fig. 4—might as well be that of a
man, as of an ape, dog, horse, or any other placental mammal.

[Illustration: FIG. 4.—First commencement of the development of a
mammal’s egg, the so-called “cleavage of the egg” (propagation of the
egg-cell by repeated self-division). _A._ The egg, by the formation of
the first furrow, falls into two cells. _B._ These separate by division
into four cells. _C._ The latter have divided into eight cells. _D._ By
repeated division a globular accumulation of numerous cells has
arisen.]

Now, when one examines this simplest form of propagation, this
self-division, it surely cannot be considered wonderful that the
products of the division of the original organism should possess the
same qualities as the parental individual. For they are parts or halves
of the parental organism, and the matter or substance in both halves is
the same, and as both the young individuals have received an equal
amount and the same quality of matter from the parent individual, one
can but consider it natural that the vital phenomena, the physiological
qualities should be the same in both children. In fact, in regard to
their form and substance, as well as to their vital phenomena, the two
produced cells can in no respect be distinguished from one another, or
from the mother cell. They have _inherited_ from her the same nature.

But this same simple propagation by self-division is not only confined
to simple cells—it is the same also in the higher many-celled
organisms; for example, in the coral zoophytes. Many of them which
exhibit a high complexity of composition and organization, nevertheless,
propagate themselves by simple division. In this case the whole
organism, with all its organs, falls into two equal halves as soon as by
growth it has attained a certain size. Each half again develops itself,
by growth, into a complete individual. Here, again, it is surely
self-evident that the two products of division will share the qualities
of the parental organism, as they themselves are in fact halves of that
parent.

Next to propagation by division we come to propagation by the _formation
of buds_. This kind of monogony is exceedingly widely spread. It occurs
both in the case of simple cells (though not frequently) and in the
higher organisms composed of many cells. The formation of buds is
universal in the vegetable kingdom, less frequent in the animal kingdom.
However, here also it occurs in the tribe of Plant-like Animals,
especially among the Coral Zoophytes, and among the greater portion of
the Hydroid Polyps very frequently, further also among some worms
(Planarian Worms, Ring-Worms, Moss Animals, Tunicates). Most branching
animal-trees or colonies, which are exceedingly like branching plants,
arise like those plants, by the formation of buds.

Propagation by the _formation of buds_ (Gemmatio) is essentially
distinguished from propagation by division, in the fact that the two
organisms thus produced by budding are not of equal age, and therefore
at first are not of equal value, as they are in the case of division. In
division we cannot clearly distinguish either of the two newly produced
individuals as the parental, that is as the producer, because, in fact,
both have an equal share in the composition of the original parental
individual. If, on the other hand, an organism sends out a bud, then the
latter is the child of the former. The two individuals are of unequal
size and of unequal form. If, for instance, a cell propagates itself by
the formation of buds, we do not see the cell fall into two equal
halves, but there appears at one point of it a protuberance, which
becomes larger and larger, more or less separates itself from the
parental cell, and then grows independently. In like manner we observe
in the budding of a plant or animal, that a small local growth arises on
a part of the mature individual, which growth becomes larger and larger,
and likewise more or less separates itself from the parental organism by
an independence in its growth. The bud, after it has attained a certain
size, may either completely separate itself from the parental
individual, or it may remain connected with it and form a stock or
colony, whilst at the same time its life may be quite independent of
that of its parent. While the growth which starts the propagation, in
the case of self-division, is a total one affecting the whole body, it
is in the formation of buds only partial, affecting merely a portion of
the parental organism. But here, also, the bud—the newly-produced
individual which remains so long most directly connected with the
parental organism, and which proceeds from it—retains the essential
qualities and the original tendency of development of its parent.

A third mode of non-sexual propagation, that of the _formation of
germ-buds_ (Polysporogonia), is intimately connected with the formation
of buds. In the case of the lower, imperfect organisms, among animals,
especially in the case of the Plant-like animals and Worms, we very
frequently find that in the interior of an individual composed of many
cells, a small group of cells separates itself from those surrounding
it, and that this small isolated group gradually develops itself into
an individual, which, becomes like the parent, and sooner or later comes
out of it. Thus, for example, in the body of the Fluke-worms
(Trematodes) there often arise numerous little bodies consisting of many
cells, that is _germ-buds_, or _polyspores_, which, at an early stage
separate themselves completely from the parent body, and leave it when
they have attained a certain stage of development.

The formation of germ-buds is evidently but little different from real
budding. But, on the other hand, it is connected with a fourth kind of
non-sexual propagation, which almost forms a transition to sexual
reproduction, namely, the _formation of germ-cells_ (Monosporogonia),
which is often briefly called formation of spores (sporogonia). In this
case it is no longer a group of cells, but a single cell, which
separates itself from the surrounding cells in the interior of the
producing organism, and which only becomes further developed after it
has come out of its parent. After this _germ-cell_, or monospore (or,
briefly, spore), has left the parental individual, it multiplies by
division, and thus forms a many-celled organism, which by growth and
gradual development attains the hereditary qualities of the parental
organism. This occurs very generally among lower plants (Cryptogama).

Although the formation of germ-cells very much resembles the formation
of germ buds, it evidently and very essentially differs from the latter,
and also from the other forms of non-sexual propagation which have
previously been mentioned, by the fact that only a very small portion of
the producing organism takes part in the propagation and, accordingly,
in the transmission by inheritance. In the case of self-division, where
the whole organism falls into two halves, in the formation of buds,
where a considerable portion of the whole body, already more or less
developed, separates from the producing individual, we easily understand
that the forms and vital phenomena should be the same in the producing
and produced organism. It is much more difficult to understand in the
formation of germ-buds, and more difficult still in the formation of
germ-cells, how this very small, quite undeveloped portion of the body,
this group of cells, or this single cell, not only directly takes with
it certain parental qualities into its independent existence, but also
after its separation from the parental individual develops into a
many-celled body, and in this repeats the forms and vital phenomena of
the original producing organism. This last form of monogonic
propagation—that of the germ cells, or spore-formation—leads us
directly to a form of propagation which is the most difficult of all to
explain, namely, sexual propagation.

_Sexual or amphigonic propagation_ (Amphigonia) is the usual method of
propagation among all higher animals and plants. It is evident that it
has only developed, at a very late period of the earth’s history, from
non-sexual propagation, and apparently in the first instance from the
method of propagation by germ-cells. In the earliest periods of the
organic history of the earth, all organisms propagated themselves in a
non-sexual manner, as numerous lower organisms still do, especially all
those which are at the lowest stage of organization, and which, strictly
speaking, can be considered neither as animals nor as plants, and which
therefore, as primary creatures, or Protista, are best excluded from
both the animal and vegetable kingdoms. In the case of the higher
animals and plants, the increase of individuals, as a rule, is at
present brought about in the majority of cases by sexual propagation.

In all the chief forms of non-sexual propagation mentioned above—in
fission, in the formation of buds, germ buds, and germ cells—the
separated cell or group of cells was able by itself to develop into a
new individual, but in the case of sexual propagation the cell must
first be fructified by another generative substance. The fructifying
male sperm must first mix with the female germ-cell (the egg) before the
latter can develop into a new individual. These two different
generative substances, the male sperm and the female egg, are either
produced by one and the same individual hermaphrodite
(Hermaphroditismus), or by two different individuals (sexual separation,
Gonochorismus) (Gen. Morph. ii. 58, 59).

The simpler and more ancient form of sexual propagation is through
double-sexed individuals (Hermaphroditismus). It occurs in the great
majority of plants, but only in a minority of animals, for example, in
the garden snails, leeches, earth-worms, and many other worms. Every
single individual among hermaphrodites produces within itself materials
of both sexes—eggs and sperm. In most of the higher plants every
blossom contains both the male organ (stamens and anther) and the female
organs (style and germ). Every garden snail produces in one part of its
sexual gland eggs, and in another part sperm. Many hermaphrodites can
fructify themselves; in others, however, copulation and reciprocal
fructification of both hermaphrodites is necessary for causing the
development of the eggs. This latter case is evidently a transition to
sexual separation.

_Sexual separation_ (Gonochorismus,) which characterizes the more
complicated of the two kinds of sexual reproduction, has evidently been
developed from the condition of hermaphroditism at a late period of the
organic history of the world. It is at present the universal method of
propagation of the higher animals, and occurs, on the other hand, only
in the minority of plants (for example, in many aquatic plants, _e.g._
Hydrocharis, Vallisneria; and in trees, _e.g._ Willows, Poplars). Every
organic individual, as a non-hermaphrodite (Gonochoristus), produces
within itself only one of two generative substances, either the male or
the female. The female individuals, both in animals and plants, produce
eggs or egg-cells. The eggs of plants in the case of flowering plants
(Phanerogama), are commonly called “embryo sacs”; in the case of
flowerless plants (Cryptogama), “fruit spores.” In animals, the male
individual secretes the fructifying sperm (sperma); in plants, the
corpuscles, which correspond to the sperm. In the Phanerogama, these are
the pollen grains, or flower-dust; in the Cryptogama, a sperm, which,
like that of most animals, consists of floating vibratile cells actively
moving in a fluid—the zoosperms, spermatozoa, or sperm-cells.

The so-called _virginal reproduction_ (Parthenogenesis) offers an
interesting form of transition from sexual reproduction to the
non-sexual formation of germ-cells (which most resembles it); it has
been demonstrated to occur in many cases among Insects, especially by
Siebold’s excellent investigations. In this case germ-cells, which
otherwise appear and are formed exactly like egg-cells, become capable
of developing themselves into new individuals without requiring the
fructifying seed. The most remarkable and most instructive of the
different partheno-genetic phenomena are furnished by those cases in
which the same germ-cells, according as they are fructified or not,
produce different kinds of individuals. Among our common honey bees, a
male individual (a drone) arises out of the eggs of the queen, if the
egg has not been fructified; a female (a queen, or working bee), if the
egg has been fructified. It is evident from this, that in reality there
exists no wide chasm between sexual and non-sexual reproduction, but
that both modes of reproduction are directly connected. The
parthenogenesis of Insects must probably be regarded as a _relapse_ from
the sexual mode of propagation (possessed by the original parents of the
insects) to the earlier condition of non-sexual propagation. (Gen.
Morph. ii. 86.) In any case, however, sexual reproduction, both in
plants and animals, which seems such a wonderful process, has only
arisen at a later date out of the more ancient process of non-sexual
reproduction. In both cases heredity is a necessary part of the
phenomenon.

In all the different modes of propagation the essential point of the
process is invariably a detachment of a portion of the parental organism
possessing the capability of leading an individual, independent
existence. We may, therefore, in all cases expect, _à priori_, that the
produced individuals—which are, in fact, as is commonly said, “the
flesh and blood” of the parents—will receive the vital characteristics
and qualities of form which the parental individuals possess. It is
simply a larger or smaller quantity of the parental material, in fact of
its albuminous protoplasm, or cell-substance, which passes to the
produced individual. But together with the material, its vital
properties—that is, the molecular motions of the plasma—are
transmitted, which then manifest themselves in its form. Inheritance by
sexual breeding loses very much of the mysterious and wonderful
character which it at first sight possesses for the uninitiated, if we
consider the above-mentioned series of the different modes of
propagation, and their connection one with another. It at first appears
exceedingly wonderful that in the sexual propagation of man, and of all
higher animals, the small egg, the minute cell, often invisible to the
naked eye, is able to transfer to the produced organism all the
qualities of the maternal organism, and, no less mysterious, that at
the same time the essential qualities of the paternal organism are
transferred to the offspring by means of the male sperm, which
fructifies the egg-cell by means of a viscid substance in which minute
thread-like cells or zoosperms move about. But as soon as we compare the
connected stages of the different kinds of propagation, in which the
produced organism separates itself more and more as a distinct growth
from the parental individual, and more or less early enters upon its
independent career; as soon as we consider, at the same time, that the
growth and development of every higher organism only depends upon the
increase of the cells composing it—that is, upon their simple
propagation by division—it becomes quite evident that all these
remarkable processes belong to one series.

The life of every organic individual is nothing but a connected chain of
very complicated material phenomena of motion. These motions must be
considered as changes in the position and combination of the molecules,
that is, of the smallest particles of animated matter (of atoms placed
together in the most varied manner). The specific, definite tendency of
these orderly, continuous, and inherent motions of life depends, in
every organism, upon the chemical mingling of the albuminous generative
matter to which it owes its origin. In man, as in the case of the higher
animals which propagate themselves in a sexual manner, the individual
vital motion commences at the moment in which the egg-cell is fructified
by the spermatic filaments of the seed, in which process both generative
substances actually mix; and here the tendency of the vital motion is
determined by the specific, or more accurately, by the individual
nature of the sperm as well as of the egg. There can be no doubt as to
the purely mechanical material nature of this process. But here we stand
full of wonder and astonishment before the infinite and inconceivable
delicacy of this albuminous matter. We are amazed at the undeniable fact
that the simple egg-cell of the maternal organism, and a single paternal
sperm-thread, transfer the molecular individual vital motion of these
two individuals to the child so accurately, that afterwards the minutest
bodily and mental peculiarities of both parents reappear in it.

Here we stand before a mechanical phenomenon of nature of which Virchow,
whose genius founded the “cellular pathology,” says with full justice:
“If the naturalist cared to follow the custom of historians and
preachers, and to clothe phenomena, which are in their way unique, with
the hollow pomp of ponderous and sounding words, this would be the
opportunity for him; for we have now approached one of those great
mysteries of animal nature, which encircle the region of animal life as
opposed to all the rest of the world of phenomena. The question of the
formation of cells, the question of the excitation of a continuous and
equable motion, and, finally, the questions of the independence of the
nervous system and of the soul—these are the great problems on which
the human mind can measure its strength.” To comprehend the relation of
the male and female to the egg-cell is almost as much as to solve all
those mysteries. The origin and development of the egg-cell in the
mother’s body, the transmission of the bodily and mental peculiarities
of the father to it by his seed, touch upon all the questions which the
human mind has ever raised about man’s existence. And, we add, these
most important questions are solved, by means of the Theory of Descent,
in a purely mechanical and purely monistic sense!

There can then be no further doubt that, in the sexual propagation of
man and all higher organisms, inheritance, which is a purely mechanical
process, is directly dependent upon the material continuity of the
producing and produced organism, just as is the case in the simplest
non-sexual propagation of the lower organisms. However, I must at once
take this opportunity of drawing attention to an important difference
which inheritance presents in sexual and non-sexual propagation. It is a
fact long since acknowledged, that the individual peculiarities of the
producing organism are much more accurately transmitted to the produced
organism by non-sexual than by sexual propagation. Gardeners have for a
long time made use of this fact in many ways. When, for instance, a
single individual of a species of tree with stiff, upright branches
accidentally produces down-hanging branches, a gardener, as a rule,
cannot transmit this peculiarity by sexual, but only by non-sexual
propagation. The twigs cut off such a weeping tree and planted as
cuttings or slips, afterwards produce trees having likewise hanging
branches, as, for example, the weeping willows and beeches. Seedlings,
on the other hand, which have been reared out of the seed of such a
weeping tree, generally have the original stiff and upright form of
branches possessed by their ancestors. The same may be observed in a
very striking manner in the so-called “copper-coloured trees,” that is,
varieties of trees which are characterized by a red or reddish brown
colour of the leaves. Off-shoots from such copper-coloured trees (for
example, the copper beech), which have been propagated by cuttings in a
non-sexual manner, show the peculiar colour and nature of the leaves
which distinguished the parental individual, while others reared from
seeds of such a copper-coloured tree return to the green-coloured
condition of leaf.

This difference in inheritance will seem very natural when we consider
that the material connection between the producing and produced
individuals is much closer and lasts much longer in non-sexual than in
sexual propagation. The special tendency of the molecular motion of life
can therefore fix itself much longer and more thoroughly in the filial
organism, and be more strictly transmitted by non-sexual than by sexual
propagation. All these phenomena, considered in connection, clearly
prove that the transmission of bodily and mental peculiarities is a
purely material and mechanical process. By propagation a greater or
lesser quantity of albuminous particles, and together with them the
individual form of motion inherent in these molecules of protoplasm, are
transmitted from the parental organism to the offspring. As this form of
motion remains continuous, the more delicate peculiarities inherent in
the parental organism must sooner or later reappear in the filial
organism.

CHAPTER IX.

LAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND NUTRITION.

Distinction between Conservative and Progressive
Transmission by Inheritance.—Laws of Conservative
Transmission: Transmission of Inherited
Characters.—Uninterrupted or Continuous
Transmission.—Interrupted or Latent
Transmission.—Alternation of
Generations.—Relapse.—Degeneracy.—Sexual
Transmission.—Secondary Sexual Characters.—Mixed or
Amphigonous Transmission.—Hybrids.—Abridged or
Simplified Transmission.—Laws of Progressive
Inheritance: Transmission of Acquired
Characters.—Adapted or Acquired Transmission.—Fixed or
Established Transmission.—Homochronous Transmission
(Identity in Epoch).—Homotopic Transmission (Identity in
Part).—Adaptation and Mutability.—Connection between
Adaptation and Nutrition.—Distinction between Indirect
and Direct Adaptation.

In the last chapter we considered Transmission by Inheritance, one of
the two universal vital activities of organisms, Adaptation and
Inheritance, which by their interaction produce the different species of
organisms, and we have endeavoured to trace this very mysterious vital
activity to a more general physiological function of organisms, namely,
to Propagation. This latter in its turn, like other vital phenomena of
animals and plants, depends on physical and chemical relations. It is
true they appear at times exceedingly complicated, but can nevertheless
in reality be traced to simple mechanical causes—that is, to the
relations of attraction and repulsion in the particles or molecules—in
fact, to the motional phenomena of matter.

Now, before we turn our attention to the second function, the phenomenon
of Adaptation or Mutability, which counteracts the Transmission by
Inheritance, it seems appropriate first to cast one more glance at the
various manifestations of Heredity, which we may perhaps even now
denominate the “_laws of transmission by inheritance._” Unfortunately,
up to the present time very little has been done for this most important
subject, either in zoology or in botany, and almost all we know of the
different laws of inheritance is confined to the experiences of
gardeners and farmers. It is not therefore to be wondered at, that on
the whole these exceedingly interesting and important phenomena have not
been investigated with desirable scientific accuracy, or reduced to the
form of scientific laws. Accordingly, what I shall relate of the
different laws of transmission are only some preliminary fragments taken
out of the infinitely rich store which lies open to our inquiry.

We may first divide all the different phenomena of inheritance into two
groups, which we may distinguish as the transmission of _inherited_
characters, and the transmission of _acquired_ characters; and we may
call the former the _conservative_ transmission, and the latter the
_progressive_ transmission by inheritance. This distinction depends upon
the exceedingly important fact that the individuals of every species of
animals and plants can transmit to their descendants, not only those
qualities which they themselves have inherited from their ancestors, but
also the peculiar, individual qualities which they have acquired during
their own life. The latter are transmitted by progressive, the former
by conservative inheritance. We have now first to examine the phenomena
of _conservative inheritance_, that is, the transmission of such
qualities as the organism has already received from its parents or
ancestors. (Gen. Morph. ii. 180.)

Among the phenomena of conservative inheritance we are first struck by
that which is its most general law, and which we may term the _law of
uninterrupted or continuous transmission_. It is so universal among the
higher animals and plants, that the uninitiated might overestimate its
action and consider it as the only normal law of transmission by
inheritance. This law simply consists in the fact that among most
species of animals and plants, every generation is, on the whole, like
the preceding—that the parents are as like the grandparents as they are
like the children. “Like produces like,” as is commonly said, but more
accurately “similar things produce similar things.” For, in reality, the
descendants of every organism are never absolutely equal in all points,
but only similar in a greater or less degree. This law is so generally
known, that I need not give any examples of it.

The _law of interrupted or latent transmission_ by inheritance, which
might also be termed alternating transmission, is in a measure opposed
to the preceding law. This important law appears principally active
among many lower animals and plants, and manifests itself in contrast to
the former in the fact that the offspring are not like their parents,
but very dissimilar, and that only the third or a later generation
becomes similar to the first. The grandchildren are like the
grandparents, but quite unlike the parents. This is a remarkable
phenomenon, and, as is well known, occurs also very frequently, though
in a less degree, in human families. Every one of my readers doubtless
knows some members of a family who, in this or that peculiarity, much
more resemble the grandfather or grandmother than the father or mother.
Sometimes it lies in bodily peculiarities, for example, features of
face, colour of hair, size of body—sometimes in mental qualities, for
example, temperament, energy, understanding—which are transmitted in
this manner. This fact may be observed in domestic animals as well as in
the case of man. Among the domestic animals most liable to vary—as the
dog, horse, and ox—breeders very frequently find that the product by
breeding resembles the grandparents far more than it does its own
parental organism. If we express this general law and the succession of
generations by the letters of the alphabet, then A = C = E, whilst
B = D = F, and so on.

This very remarkable fact appears in a more striking way in the lower
animals and plants than in the higher, and especially in the well-known
phenomenon of _alternation of generations_ (metagenesis). Here we very
frequently find—for example, among the Planarian worms, sea-squirts or
Tunicates, Zoophytes, and also among ferns and mosses—that the organic
individual in the first place produces, by propagation, a form
completely different from the parental form, and that only the
descendants of this generation, again, become like the first. This
regular change of generation was discovered by the poet Chamisso, on his
voyage round the world in 1819, among the _Salpæ_, cylindrical
tunicates, transparent like glass, which float on the surface of the
sea. Here the larger generation, the individuals of which live isolated
and possess an eye of the form of a horse-shoe, produce in a non-sexual
manner (by the formation of buds) a completely different and smaller
generation. The individuals of this second smaller generation live
united in chains and possess a cone-shaped eye. Every individual of such
a chain produces, in a sexual manner (hermaphrodite) again, a non-sexual
solitary form of the first and larger generation. Among the Salpæ,
therefore, it is always the first, third, and fifth generation, and in
like manner the second, fourth, and sixth generations, that are entirely
like one another. However, it is not always only one, but in other cases
a number of generations, which are thus leapt over; so that the first
generation resembles the fourth and seventh, the second resembles the
fifth and eighth, the third resembles the sixth and ninth, and so on.
Three different generations alternate with one another; for example,
among the neat _little sea-buoys_ (Doliolum), small tunicates closely
related to the Salpæ. In this case it is A = D = G, further, B = E = H,
and C = F = I. Among the plant-lice (Aphides), each sexual generation is
followed by a succession of from eight to ten or twelve non-sexual
generations, which are like one another, but differ from the sexual
generations. Then, again, a sexual generation reappears like the one
long before vanished.

If we further follow this remarkable law of latent or interrupted
inheritance, and take into consideration all the phenomena appertaining
to it, we may comprise under it also the well-known phenomena of
_reversion_. By the term “reversion” or “atavism” we understand the
remarkable fact known to all breeders of animals, that occasionally
single and individual animals assume a form which has not existed for
many generations, but belongs to a generation which has long since
disappeared. One of the most remarkable instances of this kind is the
fact that in some horses there sometimes appear singular dark stripes,
similar to those of the zebra, quagga, and other wild species of African
horses. Domestic horses of the most different races and of all colours
sometimes show such dark stripes; for example, a stripe along the back,
a stripe across the shoulders, and the like. The sudden appearance of
these stripes can only be explained by the supposition that it is the
effect of a latent transmission, a relapse into the ancient original
form, which has long since vanished, and was once common to all species
of horses; the original form, undoubtedly, was originally striped like
the zebras, quaggas, etc. In like manner, certain qualities in other
domestic animals sometimes appear quite suddenly, which once marked
their wild ancestors, now long since extinct. In plants, also, such a
relapse can be observed very frequently. All my readers probably know
the wild yellow toad-flax (Linaria vulgaris), a plant very common in our
fields and hedges. Its dragon-mouthed yellow flower contains two long
and two short stamens. But sometimes there appears a single blossom
(Peloria) which is funnel-shaped, and quite regularly composed of five
individual and equal sections, with five corresponding stamens. This
Peloria can only be explained as a relapse into the long since extinct
and very ancient common form of all those plants which, like the
toad-flax, possess dragon-mouthed, two-lipped flowers, with two long and
two short stamens. The original form, like the Peloria, possessed a
regular five-spurred blossom, with five equal stamens, which only later
and by degrees have become unequal (compare p. 17). All such relapses
are to be brought under the law of interrupted or latent transmission,
although the number of intervening generations may be enormous.

When cultivated plants or domestic animals become wild, when they are
withdrawn from the conditions of cultivated life, they experience
changes which appear not only as adaptations to their new mode of life,
but partially also as relapses into the ancient original form out of
which the cultivated forms have been developed. Thus the different kinds
of cabbage, which are exceedingly different in form, may be led back to
the original form, by allowing them to grow wild. In like manner, dogs,
horses, heifers, etc., when growing wild, often revert more or less to a
long extinct generation. An immensely long succession of generations may
pass away before this power of latent transmission becomes extinguished.

A third law of conservative transmission may be called the _law of
sexual transmission_, according to which each sex transmits to the
descendants of the same sex peculiarities which are not inherited by the
descendants of the other sex. The so-called secondary sexual characters,
which in many respects are of extraordinary interest, everywhere furnish
numerous examples of this law. Subordinate or secondary sexual
characters are those peculiarities of one of the two sexes which are not
directly connected with the sexual organs themselves; such characters,
which exclusively belong to the male sex, are, for example, the antlers
of the stag, the mane of the lion, and the spur of the cock. The human
beard, an ornament commonly denied to the female sex, belongs to the
same class. Similar characteristics by which the female sex is alone
distinguished are, for example, the developed breasts, with the
lactatory glands of female mammals and the pouch of the female opossum.
The bodily size, also, and complexion, differs in female animals of many
species from that of the male. All these secondary sexual qualities,
like the sexual organs themselves, are transmitted by the male organism
only to the male, not to the female, and _vice versâ_. Contrary facts
are rare exceptions to the rule.

A fourth law of transmission, which has here to be mentioned, in a
certain sense contradicts the last, and limits it, viz., the _law of
mixed or mutual_ (amphigonous) _transmission_. This law tells us that
every organic individual produced in a sexual way receives qualities
from both parents, from the father as well as from the mother. This
fact, that personal qualities of each of the two sexes are transmitted
to both male and female descendants, is very important, Goethe mentions
it of himself, in the beautiful lines—

“Von Vater hab ich die Statur, des Lebens ernstes Führen
Von Mütterchen die Frohnatur und Lust zu fabuliren.”

“From my father I have my stature and the serious tenour of my life,
From my mother a joyous nature and a turn for poetizing.”

This phenomenon, I suppose, is so well-known to all, that I need not
here enter upon it. It is according to the different portions of their
character which father and mother transmit to their children, that the
individual differences among brothers and sisters are chiefly
determined.

The very important and interesting phenomenon of _hybridism_ also
belongs to this law of mixed or amphigonous transmission. It alone,
when rightly estimated, is quite sufficient to refute the prevailing
dogma of the constancy of species. Plants, as well as animals, belonging
to quite different species, may sexually mingle with one another and
produce descendants which in many cases can again propagate themselves,
and that indeed either (more frequently) by mingling with one of the two
parental species, or (more rarely) by pure in-breeding, hybrid mixing
with hybrid. The latter is well established, for example, in the hybrids
of hares and rabbits (Lepus Darwinii, p. 147). The hybrids of a horse
and a donkey, two different species of the same genus (Equus), are well
known. These hybrids differ according as the father or the mother
belongs to the one or the other species—the horse or the donkey. The
mule produced by a mare and a he-donkey has qualities quite different
from those of the jinny (Hinnus), the hybrid of a horse and she-donkey.
In both cases the hybrid produced by the crossing of two different
species is a mixed form, which receives qualities from both parents; but
the qualities of the hybrid are different, according to the form of the
crossing. In like manner, mulattoes produced by a European and a negress
show a different mixture of characters from the hybrids produced by a
negro with a European female. In these phenomena of hybrid-breeding, as
well as in the other laws of transmission previously mentioned, we are
as yet unable to show the acting causes in detail; but no naturalist
doubts the fact that the causes are in all cases purely mechanical and
dependent upon the nature of organic matter itself. If we possessed more
delicate means of investigation than our rude organs of sense and
auxilliary instruments, we should be able to discover those causes, and
to trace them to the chemical and physical properties of matter.

Among the phenomena of conservative transmission, we must now mention,
as the fifth law, the _law of abridged or simplified transmission_. This
law is very important in regard to embryology or ontogeny, that is in
regard to the history of the development of organic individuals.
_Ontogeny_, or the history of the development of individuals, as I have
already mentioned in the first chapter (p. 10), and as I subsequently
shall explain more minutely, is nothing but a short and quick repetition
of _Phylogeny_ dependent on the laws of transmission and
adaptation—that is, a repetition of the palæontological history of
development of the whole organic tribe, or phylum, to which the organism
belongs. If, for example, we follow the individual development of a man,
an ape, or any other higher mammal within the maternal body from the
egg, we find that the fœtus or embryo arising out of the egg passes
through a series of very different forms, which on the whole agrees
with, or at least runs parallel to, a series of forms which is presented
to us by the historical chain of ancestors of the higher mammals. Among
these ancestors we may mention certain fishes, amphibians, marsupials,
etc. But the parallelism or agreement of these two series of development
is never quite complete; on the contrary, in ontogeny there are always
gaps and leaps which indicate the omission of certain stages belonging
to the phylogeny. Fritz Müller, in his excellent work, “Für Darwin,”(16)
has clearly shown in the case of the Crustacea, or crabs, that “the
historical record preserved in the individual history of development is
gradually obscured, in proportion as development takes a more and more
direct route from the egg to the complete animal.” This process of
obscuring and shortening is determined by the law of abridged
transmission, and I mention it here specially because it is of great
importance for the understanding of embryology, and because it explains
the fact, at first so strange, that the whole series of forms which our
ancestors have passed through in their gradual development are no longer
visible in the series of forms of our own individual development from
the egg.

Opposed to the laws of the conservative transmission, hitherto
discussed, are the phenomena of the transmission of the second series,
that is, the _laws of progressive transmission by inheritance_. As
already mentioned, they depend upon the fact that the organism transmits
to its descendants not only those qualities which it has inherited from
its own ancestors, but also a number of those individual qualities which
it has acquired during its own lifetime. Adaptation is here seen to be
connected with transmission by inheritance (Gen. Morph. ii. 186).

At the head of these important phenomena of progressive transmission, we
may mention the _law of adapted or acquired transmission_. In reality it
asserts nothing more than what I have said above, that in certain
circumstances the organism is capable of transmitting to its descendants
all the qualities which it has acquired during its own life by
adaptation. This phenomenon, of course, shows itself most distinctly
when the newly acquired peculiarity produces any considerable change in
the inherited form. This is the case in the examples I mentioned in the
preceding chapter as to transmission in general, in the case of the men
with six fingers and toes, the porcupine men, copper beeches, weeping
willows, etc. The transmission of acquired diseases, such as
consumption, madness, and albinism, likewise form very striking
examples. Albinoes are those individuals who are distinguished by the
absence of colouring matter, or pigments, in the skin. They are of
frequent occurrence among men, animals, and plants. In the case of
animals of a definite dark colour, individuals are not unfrequently born
which are entirely without colour, and in animals possessing eyes, this
absence of pigment extends even to the eyes, so that the iris of the
eye, which is commonly of a bright or intense colour, is colourless, but
appears red, on account of the blood-vessels being seen through it.
Among many animals, such as rabbits and mice, albinoes with white fur
and red eyes are so much liked that they are propagated in great numbers
as a special race. This would be impossible were it not for the law of
the transmission of adaptations.

Which of the changes acquired by an organism are transmitted to its
descendants, and which are not, cannot be determined _à priori_, and we
are unfortunately not acquainted with the definite conditions under
which the transmission takes place. We only know in a general way that
certain acquired qualities are much more easily transmitted than others,
for example, more easily than the mutilations caused by accidents. These
latter are generally not transmitted by inheritance, otherwise the
descendants of men who have lost their arms or legs would be born
without the corresponding arm or leg; but here, also, exceptions occur,
and a race of dogs without tails has been produced by consistently
cutting off the tails of both sexes of the dog during several
generations. A few years ago a case occurred on an estate near Jena, in
which by a careless slamming of a stable door the tail of a bull was
wrenched off, and the calves begotten by this bull were all born without
a tail. This is certainly an exception; but it is very important to note
the fact, that under certain unknown conditions such violent changes are
transmitted in the same manner as many diseases.

In very many cases the change which is transmitted and preserved by
adapted transmission is constitutional or inborn, as in the case of
albinism mentioned before. The change then depends upon that form of
adaptation which we call the indirect or potential. A very striking
instance is furnished by the hornless cattle of Paraguay, in South
America. A special race of oxen is there bred which is entirely without
horns. It is descended from a single bull, which was born in 1770 of an
ordinary pair of parents, and the absence of horns was the result of
some unknown cause. All the descendants of this bull produced with a
horned cow were entirely without horns. This quality was found
advantageous, and by propagating the hornless cattle among one another,
a hornless race was obtained, which at present has almost entirely
supplanted the horned cattle in Paraguay. The case of the otter-sheep of
North America forms a similar example. In the year 1791 a farmer, by
name Seth Wright, lived in Massachusetts, in North America; in his
normally formed flock of sheep a lamb was suddenly born with a
surprisingly long body and very short and crooked legs. It was therefore
unable to take any great leaps, and especially unable to leap across a
hedge into a neighbour’s garden—a quality which seemed advantageous to
the owner, as the territories were divided by hedges. It therefore
occurred to him to transmit this quality to other sheep, and by
crossing this ram with normally shaped ewes, he produced a whole race
of sheep, all of which had the qualities of the father, short and
crooked legs and a long body. None of them could leap across the hedges,
and they therefore were much liked and propagated in Massachusetts.

A second law, which likewise belongs to the series of progressive
transmissions, may be called the _law of established or habitual
transmission_. It manifests itself in this, that qualities acquired by
an organism during its individual life are the more certainly
transmitted to its descendants the longer the causes of that change have
been in action, and that this change becomes the more certainly the
property of all subsequent generations the longer the cause of change
acts upon these latter also. The quality newly acquired by adaptation or
mutation must be established or constituted to a certain degree before
we can calculate with any probability that it will be transmitted at all
to the descendants. In this respect transmission resembles adaptation.
The longer a newly acquired quality has been transmitted by inheritance,
the more certainly will it be preserved in future generations. If,
therefore, for example, a gardener by methodical treatment has produced
a new kind of apple, he may calculate with the greater certainty upon
preserving the desired peculiarity of this sort the longer he has
transmitted the same by inheritance. The same is clearly shown in the
transmission of diseases. The longer consumption or madness has been
hereditary in a family the deeper is the root of the evil, and the more
probable it is that all succeeding generations will suffer from it.

We may conclude the consideration of the phenomena of inheritance with
the two very important laws of _homotopic_ and _contemporaneous
transmission by inheritance_. We understand by them the fact that
changes acquired by an organism during its life, and transmitted to its
descendants, appear in the same part of the body in which the parental
organism was first affected by them, and that they also appear in the
offspring at the same age as that at which they did so in the parent.

_The law of contemporaneous or homochronous transmission_, which Darwin
calls the law of “transmission in corresponding periods of life,” can
be shown very clearly in the transmission of diseases, especially of
such as are recognized as very destructive, on account of their
hereditary character. They generally appear in the organism of the child
at the time corresponding with that in which the parental organism
contracted the disease. Hereditary diseases of the lungs, liver, teeth,
brain, skin, etc., usually appear in the descendants at the same period,
or a little earlier than they showed themselves in the parental
organism, or were contracted by it. The calf gets its horns at the same
period of life as its parents did. In like manner the young stag
receives its antlers at the same period of life in which they appeared
in its father or grandfather. In every one of the different sorts of
vine the grapes ripen at the same time as they did in the case of their
progenitors. It is well known that the time of ripening varies greatly
in the different sorts; but as all are descended from a single species,
this variation has been acquired by the progenitors of the several
sorts, and has then been transmitted by inheritance.

The _law of homotopic transmission_, which is most closely connected
with the last mentioned law, and which might be called the law of
transmission in corresponding parts of the body, may also be very
distinctly recognized in pathological cases of inheritance. Large moles,
for example, or accumulations of pigment in several parts of the skin,
tumours also, often appear during many generations, not only at the same
period of life, but also in the same part of the skin. Excessive
development of fat in certain parts of the body is likewise transmitted
by inheritance. Above all, it is to be noted that numerous examples of
this, as well as of the preceding law, may be found everywhere in the
study of embryology. Both the _law of homochronous and homotopic
transmission are fundamental laws of embryology, or ontogeny_. For these
laws explain the remarkable fact that the different successive forms of
individual development in all generations of one and the same species
always appear in the same order of succession, and that the variations
of the body always take place in the same parts. This apparently simple
and self-evident phenomenon is nevertheless exceedingly wonderful and
curious; we cannot explain its real causes, but may confidently assert
that they are due to the direct transmission of the organic matter from
the parental organism to that of the offspring, as we have seen above in
the case of the process of transmission in general, by a consideration
of the details of the various modes of reproduction.

Having thus, then, considered the most important laws of Inheritance, we
now turn to the second series of phenomena bearing on natural selection,
viz., to those of Adaptation or Variation. These phenomena, taken as a
whole, stand in a certain opposition to the phenomena of Inheritance,
and the difficulty which arises in examining them consists mainly in
the two sets of phenomena being so completely intercrossed and
interwoven. We are but seldom able to say with certainty—of the
variations of form which occur before our eyes—how much is owing to
Inheritance, and how much to Adaptation. All characters of form, by
which organisms are distinguished, are caused _either_ by Inheritance or
by Adaptation; but as both functions are continually interacting with
each other, it is extremely difficult for the systematic inquirer to
recognize the share belonging to each of the two functions in the
special structure of individual forms. This is, at present, all the more
difficult, because we are as yet scarcely aware of the immense
importance of this fact, and because most naturalists have neglected the
theory of Adaptation, as well as that of Inheritance. The laws of
Inheritance, which we have just discussed, as well as the laws of
Adaptation, which we shall consider directly, in reality form only a
small portion of the phenomena existing in this domain, but which have
not as yet been investigated; and since every one of these laws can
interact with every other, it is clear that there is an infinite
complication of physiological actions, which are at work in the
construction of organisms.

But now, as to the phenomenon of variation or adaptation in general, we
must, as in the case of inheritance, view it as a quite universal,
physiological fundamental quality of all organisms, without
exception—as a manifestation of life which cannot be separated from the
idea of organism. Strictly speaking, we must here also, as in the case
of inheritance, distinguish between Adaptation itself and Adaptability.
By Adaptation (Adaptio), or Variation (Variatio), we understand the fact
that the organism, in consequence of influences of the surrounding
outer world, assumes certain new peculiarities in its vital activity,
composition, and form which it has not inherited from its parents; these
acquired individual qualities are opposed to those which have been
inherited, or, in other words, those which have been transmitted to it
from its parents or ancestors. On the other hand, we call Adaptability
(Adaptabilitas), or Variability (Variabilitas), the capability inherent
in all organisms to acquire such new qualities under the influence of
the outer world. (Gen. Morph. ii. 191.)

The undeniable fact of organic adaptation or variation is universally
known, and can be observed at every moment in thousands of phenomena
surrounding us. But just because the phenomena of variation by external
influences appear so self-evident, they have hitherto undergone scarcely
any accurate scientific investigation. To them belong all the phenomena
which we look upon as the results of contracting and giving up habits,
of practice and giving up practices, or as the results of training, of
education, of acclimatization, of gymnastics, etc. Many permanent
variations brought about by causes producing disease, that is to say,
many diseases, are nothing but dangerous adaptations of the organism to
injurious conditions of life. In the case of cultivated plants and
domestic animals, variation is so striking and powerful that the breeder
of animals and the gardener found their whole mode of proceeding upon
it, or rather upon the interaction between these phenomena and those of
Inheritance. It is also well known to every one that animals and plants,
in their wild state, are subject to variation. Every systematic treatise
on a group of animals or plants, if it were to be quite complete and
exhaustive, ought to mention in every individual species the number of
variations which differ more or less from the prevailing or typical form
of the species. Indeed, in every careful systematic special treatise one
finds, in the case of most species, mention of a number of such
variations, which are described sometimes as individual deviations, and
sometimes as so-called races, varieties, degenerate species, or
subordinate species, and which often differ exceedingly from the
original species, solely in consequence of the adaptation of the
organism to the external conditions of life.

If we now endeavour to fathom the general causes of these phenomena of
Adaptation, we arrive at the conclusion that in reality they are as
simple as the causes of the phenomena of Inheritance. We have shown that
the nature of the process of propagation furnishes the real explanation
of the facts of Transmission by Inheritance, that is, the transmission
of parental matter to the body of the offspring; and in like manner we
can show that the physiological function of _nutrition_, or _change of
substance_, affords a general explanation of Adaptation or Variation.
When I here point to “nutrition” as the fundamental cause of variation
and adaptation, I take this word in its widest sense, and I understand
by it the whole of the material changes which the organism undergoes in
all its parts through the influences of the surrounding outer world.
Nutrition thus comprises not only the reception of actual nutritive
substances and the influence of different kinds of food, but also, for
example, the action upon the organism of water and of the atmosphere,
the influence of sunlight, of temperature, and of all those
meteorological phenomena which are implied in the term “climate.” The
indirect and direct influence of the nature of the soil and of the
dwelling-place also belong to it; and further, the extremely important
and varied influence which is exercised upon every animal and every
plant by the surrounding organisms, friends and neighbours, enemies and
robbers, parasites, etc. All these and many other very important
influences, all of which more or less modify the organism in its
material composition, must be taken into consideration in studying the
change of substance which goes on in living things. Adaptation,
accordingly, is the consequence of all those material variations which
are produced in the change of substance of the organism by the external
conditions of existence, or by the influences of the surrounding
external world.

How very much every organism is dependent upon the whole of its external
surroundings, and changed by their alteration, is, in a general way,
well known to every one. Only think how much the human power of action
is dependent upon the temperature of the air, or how much the
disposition of our minds depends upon the colour of the sky. Accordingly
as the sky is cloudless and sunny, or covered with large heavy clouds,
our state of mind is cheerful or dull. How differently do we feel and
think in a forest during a stormy winter night and during a bright
summer day! All the different moods of our soul depend upon purely
material changes of our brain, upon movements of molecular plasma, which
are started through the medium of the senses by the different influences
of light, warmth, moisture, etc. “We are a plaything to every pressure
of the air.” No less important and deeply influential are the effects
produced upon our mind and body by the different quality and quantity
of food. Our mental activity, the activity of our understanding and of
our imagination, is quite different accordingly as we have taken tea or
coffee, wine or beer, before or during our work. Our moods, wishes, and
feelings are quite different when we are hungry and when we are
satisfied. The national character of Englishmen and Gauchos, in South
America, who live principally on meat and food rich in nitrogen, is
wholly different from that of the Irish, feeding on potatoes, and that
of the Chinese, living on rice, both of whom take food deficient in
nitrogen. The latter also form much more fat than the former. Here, as
everywhere, the variations of the mind go hand in hand with the
corresponding transformations of the body; both are produced by purely
material causes. But all other organisms, in the same way as man, are
varied and changed by the different influences of nutrition. It is well
known that we can change in an arbitrary way the form, size, colour,
etc., of our cultivated plants and domestic animals, by change of food;
that, for example, we can take from or give to a plant definite
qualities, accordingly as we expose it to a greater or less degree of
sunlight and moisture. As these phenomena are generally widely known,
and as we shall proceed presently to the consideration of the different
laws of adaptation, we will not dwell here any longer on the general
facts of variation.

As the different laws of transmission may be naturally divided into the
two series of conservative and progressive transmission, so we may also
distinguish between two series of the laws of adaptation, first, the
series of laws of _indirect_, and secondly, the series of laws of
_direct_ adaptation. The latter may also be called the laws of actual,
and the former the laws of potential, adaptation.

The first series, comprising the phenomena of _indirect_ (potential)
adaptation, has, on the whole, hitherto been little attended to, and
Darwin has the merit of having directed special attention to this series
of changes. It is somewhat difficult to place this subject clearly
before the reader; I will endeavour to make it clear hereafter by
examples. Speaking quite generally, indirect or potential adaptation
consists in the fact that certain changes in the organism, effected by
the influence of nutrition (in its widest sense) and of the external
conditions of existence in general, show themselves not in the
individual form of the respective organism, but in that of its
descendants. Thus, especially in organisms propagating themselves in a
sexual way, the reproductive system, or sexual apparatus, is often
influenced by external causes (which little affect the rest of the
organism), to such a degree that its descendants show a complete
alteration of form. This can be seen very strikingly in artificially
produced monstrosities. Monstrosities can be produced by subjecting the
parental organism to certain extraordinary conditions of life, and,
curiously enough, such an extraordinary condition of life does not
produce a change of the organism itself, but a change in its
descendants. This cannot be called transmission by inheritance, because
it is not a quality existing in the parental organism that is
transmitted by inheritance. It is, on the contrary, a change affecting
the parental organism, but not perceptible in it, that appears in the
peculiar formation of its descendants. It is only the impulse to this
new formation which is transmitted in propagation through the egg of the
mother or the sperm of the father. The new formation exists in the
parental organism only as a possibility (potential); in the descendants
it becomes a reality (actual).

As this very important and very general phenomenon had hitherto been
entirely neglected, people were inclined to consider all the visible
variations and transformations of organic forms as phenomena of
adaptation of the second series, that is, as phenomena of _direct_ or
actual adaptation. The essence of this latter kind of adaptation
consists in the fact that the change affecting the organism (through
nutrition, etc.) shows itself immediately by some transformation, and
does not only make itself apparent in the descendants. To this class
belong all the well-known phenomena in which we can directly trace the
transforming influence of climate, food, education, training, etc., in
their effects upon the individual itself.

We have seen how the two series of phenomena of progressive and
conservative transmission, in spite of their difference in principle, in
many ways interfere with and modify each other, and in many ways
co-operate with and cross each other. The same is the case, in a still
higher degree, in the two series of phenomena of indirect and direct
adaptation, which are opposed to each other and yet closely connected.
Some naturalists, especially Darwin and Carl Vogt, ascribe to the
indirect or potential adaptation by far the more important and almost
exclusive influence. But the majority of naturalists have hitherto been
inclined to take the opposite view, and to attribute the principal
influence to direct or actual adaptation. I consider this controversy,
in the mean while, as almost useless. It is but seldom that we are in a
condition, in any individual case of variation, to judge how much of it
belongs to direct and how much to indirect adaptation. We are, on the
whole, still too little acquainted with these exceedingly important and
intricate relations, and can only assert, in a general way, that the
transformation of organic forms is to be ascribed _either_ to direct
adaptation alone, _or_ to indirect adaptation alone, or lastly, to the
co-operation of both direct _and_ indirect adaptation.

CHAPTER X.

LAWS OF ADAPTATION.

In the last chapter we reduced into two groups the phenomena of
Adaptation or Variation, which, in connection and interaction with the
phenomena of Heredity, produce all the endless variety of forms in
animals and plants—first, the group of indirect or potential, and
secondly, the group of direct or actual Adaptation. We shall occupy
ourselves with a closer examination of the different laws which we can
discover in these two groups of the phenomena of variation. Let us first
take into consideration the remarkable and very important, although
hitherto much neglected, phenomena of indirect variation.

_Indirect or potential adaptation_ manifests itself, it will be
remembered, in the striking and exceedingly important fact that organic
individuals experience transformations and assume forms in consequence
of changes of nutrition which have not operated on them themselves, but
upon their parental organism. The transforming influence of the external
conditions of existence, of climate, of nutrition, etc., shows its
effects here not directly in the transformation of the organism itself,
but indirectly in that of its descendants. (Gen. Morph. ii. 202.)

As the principal and most universal of the laws of indirect variation
must be mentioned _the law of individual adaptation_, or the important
proposition that all organic individuals from the commencement of their
individual existence are unequal, although often very much alike. As a
proof of this proposition, I may at once point to the fact, that in the
human race in general all brothers and sisters, all children of the same
parents, are unequal from their birth. No one will venture to assert
that two children at their birth are perfectly alike; that the size of
the individual parts of their bodies, the number of hairs on their
heads, the number of cells composing their outer skins or epidermis, the
number of blood-cells are the same in both children, or that both
children have come into the world with the same abilities or talents.
But what more specially proves this law of individual difference, is the
fact that in the case of those animals which produce several young ones
at a time,—for instance, dogs and cats,—all the young of each birth
differ from one another more or less strikingly in size and colour of
the individual parts of the body, or in strength, etc. Now this law is
universal. All organic individuals from their beginning are
distinguished by certain, though often extremely minute, differences,
and the cause of these individual differences, though in detail usually
utterly unknown to us, depends partly or entirely on certain influences
which the organs of propagation in the parental organism have undergone.

A second law of indirect adaptation, which we shall call _the law of
monstrous or sudden adaptation_, is of less importance and less general
than the law of individual adaptation. Here the divergences of the
child-organism from the parental form are so striking that, as a rule,
we may designate them as monstrosities. In many cases they are produced,
as has been proved by experiments, by the parental organism having been
subject to a certain treatment, and placed under peculiar conditions of
nutrition; for example, when air and light are withdrawn from it, or
when other influences powerfully acting upon its nutrition are changed
in a certain way. The new condition of existence causes a strong and
striking modification of form, not directly of the organism itself, but
only of that of its descendants. The mode of this influence in detail we
cannot discover, and we can only in a very general way detect a causal
connection between the abnormal formation of the child and a certain
change in the conditions of existence of its parents exerting a special
influence upon the organs of propagation in the latter. The previously
mentioned phenomenon of albinism probably belongs to this group of
abnormal or sudden variations, also the individual cases of human beings
with six fingers and toes, the case of the hornless cattle, as well as
those of sheep and goats with four or six horns. The abnormal deviation
in all these cases probably owes its origin to a cause which at first
only affected the reproductive system of the parental organism, the egg
of the mother or the sperm of the father.

A third curious manifestation of indirect adaptation may be termed _the
law of sexual adaptation_. Under this name we indicate the remarkable
fact that certain influences, which act upon the male organs of
propagation only, affect the structure of the male descendants, and in
like manner other influences, which act upon the female organs of
propagation only, manifest their effect only in the change of structure
of the female descendants. This remarkable phenomenon is still very
obscure, and has not as yet been investigated, but is probably of great
importance in regard to the origin of “secondary sexual
characteristics,” to which we have already made allusion.

All the phenomena of sexual, monstrous, and individual adaptation, which
we may comprise under the name of the laws of _indirect or potential
adaptation_, are as yet very little known to us in their real nature and
in their deeper causal connection. Only this much we can at present
maintain with certainty, that numerous and important transformations in
organic forms owe their existence to this process. Many and striking
variations of form solely depend on causes which at first only affect
the nutrition of the parental organism, and specially its organs of
propagation. Evidently the relations in which the sexual organs stand to
other parts of the body are of the greatest importance. We shall have
more to say of these presently, when we speak of the law of correlative
adaptation. How powerfully the variations in the conditions of life and
nutrition affect the propagation of organisms is rendered obvious by the
remarkable fact that numerous wild animals which we keep in our
zoological gardens, and exotic plants which are grown in our botanical
gardens, are no longer able to reproduce themselves. This is the case,
for example, with most birds of prey, parrots, and monkeys. The
elephant, also, and the animals of prey of the bear genus, in captivity
hardly ever produce young ones. In like manner many plants in a
cultivated state become sterile. The two sexes may indeed unite, but no
fructification, or no development of the fructified germ, takes place.
From this it follows with certainty that the changed mode of nutrition
in the cultivated state is able completely to destroy the capability of
reproduction, and therefore to exercise the greatest influence upon the
sexual organs. In like manner other adaptations or variations of
nutrition in the parental organism may cause, not indeed a complete want
of descendants, but still important changes in their form.

Much better known than the phenomena of indirect or potential adaptation
are those of _direct or actual adaptation_, to the consideration of
which we now turn our attention. To them belong all those changes of
organisms which are generally considered to be the results of practice,
habit, training, education, etc.; also those changes of organic forms
which are effected directly by the influence of nutrition, of climate,
and other external conditions of existence. As has already been remarked
in direct or actual adaptation, the transforming influence of the
external cause affects the form of the organism itself, and does not
only manifest itself in that of the descendants. (Gen. Morph. ii. 207.)

We may place _the law of universal adaptation_ at the head of the
different laws of direct or actual adaptation, because it is the chief
and most comprehensive among them. It may be briefly explained in the
following proposition: “All organic individuals become unequal to one
another in the course of their life by adaptation to different
conditions of life, although the individuals of one and the same species
remain mostly very much alike.” A certain inequality of organic
individuals, as we have seen, was already to be assumed in virtue of the
law of individual (indirect) adaptation. But, beyond this, the original
inequality of individuals is afterwards increased by the fact that every
individual, during its own independent life, subjects and adapts itself
to its own peculiar conditions of existence. All different individuals
of every species, however like they may be in their first stages of
life, become in the further course of their existence less like to one
another. They deviate from one another in more or less important
peculiarities, and this is a natural consequence of the different
conditions under which the individuals live. There are no two single
individuals of any species which can complete their life under exactly
the same external circumstances. The vital conditions of nutrition, of
moisture, air, light; further, the vital conditions of society, the
inter-relations with surrounding individuals of the same or other
species, are different in every individual being; and this difference
first affects the functions, and later changes the form of every
individual organism. If the children of a human family show, even at the
beginning, certain individual inequalities which we may consider as the
consequence of individual (indirect) adaptation, they will appear still
more different at a later period of life, when each child has passed
through different experiences, and has adapted itself to different
conditions of life. The original difference of the individual processes
of development, evidently becomes greater the longer the life lasts and
the more various the external conditions which influence the separate
individuals. This may be demonstrated in the simplest manner in man, as
well as in domestic animals and cultivated plants, in which the vital
conditions may be arbitrarily modified. Two brothers, of whom one is
brought up as a workman and the other as a priest, develop quite
differently in body as well as in mind; in like manner, two dogs of one
and the same birth, of which one is trained as a sporting dog and the
other chained up as a watch dog. The same observation may also readily
be made as to organic individuals in a natural state. If, for instance,
one carefully compares all the trees in a fir or beech forest, which
consists of trees of a single species, one finds that among all the
hundreds or thousands of trees, there are not two individual trees
completely agreeing in size of trunk and other parts, in the number of
branches, leaves, etc. Everywhere we find individual inequalities which,
in part at least, are merely the consequences of the different
conditions of life under which the trees have developed. It is true we
can never say with certainty how much of this dissimilarity in all the
individuals of every species may have originally been caused by indirect
individual adaptation, and how much of it acquired under the influence
of direct or universal adaptation.

A second series of phenomena of direct adaptation, which we may comprise
under _the law of cumulative adaptation_, is no less important and
general than universal adaptation. Under this name I include a great
number of very important phenomena, which are usually divided into two
quite distinct groups. Naturalists, as a rule, have distinguished,
first, those variations of organisms which are produced directly by the
permanent influence of external conditions (by the constant action of
nutrition, of climate, of surroundings, etc.), and secondly, those
variations which arise from habit and practice, from accustoming
themselves to definite conditions of life, and from the use and non-use
of organs. The latter influences have been set forth especially by
Lamarck as important causes of the change of organic forms, while the
former have for a very long time been recognized as such more generally.

The sharp distinction usually made between these two groups of
cumulative adaptation, and which even Darwin still maintains, disappears
as soon as we reflect more accurately and deeply upon the real nature
and causal foundation of these two, apparently very different, series of
adaptations. We then arrive at the conviction that in both cases there
are always two different active causes to be dealt with: on the one hand
the _external influence_ or _action_ of adaptative conditions of life,
and on the other hand the _internal reaction of the organism_ which
subjects and adapts itself to that condition of life. If cumulative
adaptation is considered from the first point of view alone, and the
transforming actions of the permanent external conditions of life are
traced to those conditions solely, then the principal stress is laid
unduly upon the external factor, and the necessary internal reaction of
the organism is not taken into proper consideration. If, on the other
hand, cumulative adaptation is unjustly regarded solely in relation to
its second factor, and the transforming action of the organism itself,
its reaction against the external influences, its change by practice,
habit, use, or non-use of organs, is put into the foreground, then we
forget that this reaction is first called into play by the action of
external conditions of existence. Hence it seems that the distinction
made between these two groups lies only in the different manner of
viewing them, and I believe that they can, with full justice, be
considered as one. The most essential fact in these phenomena of
cumulative adaptation is that the change of the organism which manifests
itself first in the functions, and at a later period in the form, is the
result either of long enduring, or of often repeated, influences of an
external cause. The smallest cause, by cumulation of its action, can
attain the greatest results.

There are innumerable examples of this kind of direct adaptation. In
whatever direction we may examine the life of animals and plants, we
discover on all hands evident and undeniable changes of this kind. Let
me first mention some of those phenomena of adaptation occasioned
directly by nutrition itself. Every one knows that the domestic animals
which are bred for certain purposes can be variously modified, according
to the different quantity and quality of the food given to them. If a
farmer in breeding sheep wishes to produce fine wool, he gives them
different food from what he would give if he wished to obtain good flesh
or an abundance of fat. Choice race and carriage horses receive better
food than dray and cart horses. Even the bodily form of man—for
example, the amount of fat—is quite different according to his
nutrition. Food containing much nitrogen produces little fat, that
containing little nitrogen produces a great deal of fat. People who, by
means of Banting’s system, at present so popular, wish to become thin
eat only meat and eggs—no bread, no potatoes. The important variations
that can be produced among cultivated plants, solely by changing the
quantity and quality of nourishment, are well known. The same plant
acquires an altogether different appearance, according as it is placed
in a dry and warm place, exposed to the sunlight or placed in a cool
damp spot in the shade. Many plants, if transferred to the sea shore,
get in a short space of time thick, fleshy leaves, and the same plants
placed in a particularly dry and hot locality get thin hairy leaves. All
these variations arise directly from the cumulative influence of changed
nutrition.

But it is not only the quantity and quality of the articles of nutrition
which affect and powerfully change and transform the organism, but it is
affected also by all the other external conditions of existence, above
all by its nearest organic surroundings, the society of friendly or
hostile organisms. One and the same kind of tree develops itself quite
differently in an open locality, where it is free on all sides, and in a
forest where it must adapt itself to its surroundings, where it is
pressed on all sides by its nearest neighbours, and is forced to shoot
upwards. In the former case, the branches of the tree spread widely out;
in the latter, the trunk extends upwards, and the top of the tree
remains small and contracted. How powerfully all these circumstances,
and how powerfully the hostile or friendly influence of surrounding
organisms, of parasites, etc., affect every animal and every plant, is
so well known, that it appears superfluous to quote further examples.
The change of form, or transformation which is thereby effected, is
never solely the direct result of the external influence, but must
always be traced to the corresponding reaction, and to the activity of
the organism itself, which consists in contracting a habit, or practice,
and in the use or non-use of organs. The fact that these latter
phenomena, as a rule, have been considered distinct from the former, is
owing first to the one-sided manner of viewing them already mentioned,
and secondly to the wrong notion which has been formed as to the nature
and the influence of the activity of the will in animals.

The activity of the will, which is the organ of habit, of practice, of
the use or non-use of organs among animals, is, like every other
activity of the animal soul, dependent upon material processes in the
central nervous system, upon peculiar motions which emanate from the
albuminous matter of the ganglion cells, and the nervous fibres
connected with them. The will, as well as the other mental activities,
in higher animals, in this respect is different from that of men only in
quantity, not in quality. The will of the animal, as well as that of
man, is never free. The widely spread dogma of the freedom of the will
is, from a scientific point of view, altogether untenable. Every
physiologist who scientifically investigates the activity of the will in
man and animals, must of necessity arrive at the conviction that _in
reality the will is never free_, but is always determined by external or
internal influences. These influences are for the most part ideas which
have been either formed by Adaptation or by Inheritance, and are
traceable to one or other of these two physiological functions. As soon
as we strictly examine the action of our own will, without the
traditional prejudice about its freedom, we perceive that every
apparently free action of the will is the result of previous ideas,
which are based on notions inherited or otherwise acquired, and are
therefore, in the end, dependent on the laws of Adaptation and
Inheritance. The same also applies to the action of the will in all
animals. As soon as their will is considered in connection with their
mode of life, in its relation to the changes which the mode of life is
subject to from external conditions, we are at once convinced that no
other view is possible. Hence the changes of the will which follow the
changes of nutrition, and which, in the form of practice, habit, etc.,
produce variations in structure, must be reckoned among the other
material processes of cumulative adaptation.

Whilst an animal’s will is adapting itself to changed conditions of
existence by the acquisition of new habits, practices, etc., it not
unfrequently effects the most remarkable transformations of the organic
form. Numerous instances of this may be found everywhere in animal life.
Thus, for example, many organs in domestic animals are suppressed, when
in consequence of a changed mode of life they cease to act. Ducks and
fowls in a wild state fly exceedingly well, but lose this facility more
or less in a cultivated state. They accustom themselves to use their
legs more than their wings, and in consequence the muscles and skeleton
used in flying are essentially changed in their development and form.
Darwin has proved this by a very careful comparative measurement and
weighing of the respective parts of the skeleton in the different races
of domestic ducks, which are all descended from the wild duck (_Anas
boschas_). The bones of the wings in tame ducks are weaker, the bones of
the legs, on the other hand, are more strongly developed than in wild
ducks. In ostriches and other running birds which have become completely
unaccustomed to fly, the consequence is that their wings are entirely
crippled and degenerate into mere “rudimentary organs” (p. 12). In many
domestic animals, especially in many races of dogs and rabbits, we find
that in the cultivated state they have acquired pendulous ears. This is
simply a consequence of a diminished use of the auricular muscles. In a
wild state these animals have to exert their ears very much in order to
discover an approaching foe, and this is accompanied by a strong
development of the muscular apparatus, which keeps the outer ears in an
upright position, and by which they can turn them in all directions. In
a domestic state the same animals no longer require to listen so
attentively, they prick up or turn their ears only a little; the
auricular muscles cease to be used, gradually become weakened, and the
ears hang down flabbily, or become rudimentary.

As in these cases the function, and consequently the form also, of the
organ becomes degenerated through disuse, so, on the other hand, it
becomes more developed by greater use. This is particularly striking if
we compare the brain, and the mental activity belonging to it, in wild
animals and those domestic animals which are descended from them. The
dog and horse, which are so vastly improved by cultivation, show an
extraordinary degree of mental development, in comparison with their
wild original ancestors, and evidently the change in the bulk of the
brain, which is connected with it, is mainly determined by persistent
exercise. It is also well known how quickly and powerfully muscles grow
and change their form by continual practice. Compare, for example, the
arms and legs of a trained gymnast with those of an immovable book-worm.

How powerfully external influences affect the habits of animals and
their mode of life, and in this way still further change their forms, is
very strikingly shown in many cases among amphibious animals and
reptiles. Our commonest indigenous snake, the ringed snake, lays eggs
which require three weeks’ time to develop. But when it is kept in
captivity, and no sand is strewn in the cage, it does not lay its eggs,
but retains them until the young ones are developed. The difference
between animals producing living offspring and those laying eggs is here
effaced simply by the change of the ground upon which the animal lives.

The water-salamanders, or tritons, which have been artificially made to
retain their original gills, are extremely interesting in this respect.
The tritons are amphibious animals, nearly akin to frogs, and possess,
like the latter, in their youth external organs of
respiration—gills—with which they, while living in water, breathe the
air dissolved in the water. At a later date a metamorphosis takes place
in tritons, as in frogs. They leave the water, lose their gills, and
accustom themselves to breathe with their lungs. But if they are
prevented from doing this by being kept shut up in a tank, they do not
lose their gills. The gills remain, and the water salamander continues
through life in that low stage of development, beyond which its lower
relations, the gilled salamanders, or Sozobranchiata, never pass. The
gilled salamander attains its full size, its sexual development, and
reproduces itself without losing its gills.

Great interest was caused a short time ago, among zoologists, by the
axolotel (Siredon pisciformis), a gilled salamander from Mexico, nearly
related to the triton; it had already been known for a long time, and
been bred on a large scale in the zoological garden in Paris. This
animal possesses external gills, like the young salamander, but retains
them all its life, like all other Sozobranchiata. This gilled salamander
generally remains in the water, with its aquatic organs of respiration,
and also propagates itself there. But in the Paris garden, unexpectedly
from among hundreds of these animals, a small number crept out of the
water on to the dry land, lost their gills, and changed themselves into
gill-less salamanders, which are not to be distinguished from a
North-American genus of tritons (Amblystoma), and breathe only through
lungs. In this exceedingly curious case we can directly follow the great
stride from water-breathing to air-breathing animals, a stride which can
indeed be observed every spring in the individual history of development
of frogs and salamanders. Just as every separate frog and every separate
salamander transforms itself from an amphibious animal breathing through
gills, at a later period into one breathing through lungs, so the whole
group of frogs and salamanders have arisen from animals breathing
through gills, and akin to the Siredon. The Sozobranchiata have remained
up to the present day in that low stage of development. Ontogeny here
explains phylogeny; the history of the development of individuals
explains that of the whole group (p. 10).

To the law of accumulative adaptation there closely follows a third law
of direct or actual adaptation, _the law of correlative adaptation_.
According to this important law, actual adaptation not only changes
those parts of the organism which are directly affected by its
influence, but other parts also not directly affected by it. This is the
consequence of organic solidarity, and especially of the unity of the
nutrition existing among all the parts of every organism. If, for
example, the hairiness of the leaves increases in a plant by its being
transferred to a dry locality, then this change reacts upon the
nutrition of other parts, and it may result in a shortening of the parts
of the stalk, and produce a more contracted form of the whole plant. In
some races of pigs and dogs—for example, in the Turkish dog—which by
adaptation to a warmer climate have more or less lost their hair, the
teeth also have degenerated. Whales and Endentata (armadillos), which by
their curious skin-covering are removed from the other mammals, also
show the greatest deviations in the formation of their teeth. Further,
those races of domestic animals (oxen and pigs) which have acquired
short legs have, as a rule, also a short and compact head. Among other
examples, the races of pigeons which have the longest legs are also
characterized by the longest beaks. The same correlation between the
length of the legs and beaks is universal in the order of stilted-birds
(Grallatores), in storks, cranes, snipe, etc. The correlations which
thus exist between different parts of the organism are most remarkable,
but their real cause is unknown to us. In general, we can of course say,
the changes of nutrition affecting an individual part must necessarily
react on the other parts, because the nutrition of every organism is a
connected, centralized activity. But why just this or that part should
exhibit this or that particular correlation is in most cases quite
unknown to us. We know a great number of such correlations in nutrition;
they are especially seen in those changes of animals and plants which
give rise to an absence of pigment (noticed previously)—in albinoes.
The want of the usual colouring matter goes hand in hand with certain
changes in the formation of other parts; for example, of the muscular
and osseous system, consequently of organic systems which are not at all
ultimately connected with the system of the outer skin. Very frequently
albinoes are more feebly developed, and consequently the whole structure
of the body is more delicate and weak than in coloured animals of the
same species. The organs of the senses and nervous system are in like
manner curiously affected when there is this want of pigment. White cats
with blue eyes are nearly always deaf. White horses are distinguished
from coloured horses by their special liability to form sarkomatous
tumours. In man, also, the degree of the development of pigment in the
outer skin greatly influences the susceptibility of the organism for
certain diseases; so that, for instance, Europeans with a dark
complexion, black hair, and brown eyes become more easily acclimatized
to tropical countries, and are less subject to the diseases there
prevalent (inflammation of the liver, yellow fever, etc.) than Europeans
of white complexion, fair hair, and blue eyes. (Compare above, p. 150.)

Among these correlations in the formation of different organs, those are
specially remarkable which exist between the sexual organs and other
parts of the body. No change of any part reacts so powerfully upon the
other parts of the body as a certain treatment of the sexual organs.
Farmers who wish to obtain an abundant formation of fat in pigs, sheep,
etc., remove the sexual organs by cutting them out (castration), and
this is indeed done to animals of both sexes. The result is an
excessive development of fat. The same is done to the singers in certain
religious corporations. These unfortunates are castrated in early youth,
in order that they may retain their high boyish voices. In consequence
of this mutilation of the genitals, the larynx remains in its youthful
stage of development. The muscular tissues of the body remain at the
same time weakly developed, while below the skin an abundance of fat
accumulates. But this mutilation also powerfully reacts upon the
development of the nervous system, the energy of the will, etc., and it
is well known that human castrates, or eunuchs, as well as castrated
animals, are utterly deficient in the special psychical character which
distinguishes the male sex. Man is a man, both in body and soul, solely
through his male generative glands.

These most important and influential correlations between the sexual
organs and the other parts of the body, especially the brain, are found
equally in both sexes. This might be expected even _à priori_, because
in most animals the two kinds of organs develop themselves from the same
foundation, and at the beginning are not different. In man, as in the
rest of the vertebrate animals, the male and female organs in the
original state of the germ are entirely the same, and the differences of
the two sexes only gradually arise in the course of embryonic
development (in man, in the ninth week of embryonic life), by one and
the same gland developing in the female as the ovary, and in the male as
the testicle. Every change of the female ovary, therefore, has a no less
important reaction upon the whole female organism than every change of
the testicle has upon the male organism. Virchow has expressed the
importance of this correlation in his admirable essay on “Das Weib und
die Zelle” (“Woman and the Cell”), in the following words:—“Woman is
woman only by her sexual glands; all the peculiarities of her body and
mind, of her nutrition and her nervous activity, the sweet delicacy and
roundness of her limbs, the peculiar formation of the pelvis, the
development of the breasts, the continuance of the high voice, that
beautiful ornament of hair on her head, with the scarcely perceptible
soft down on the rest of the skin—then again, the depth of feeling, the
truth of her direct perceptions, her gentleness, devotion, and
fidelity—in short, all the feminine qualities which we admire and
honour in a true woman are but a dependence of the ovary. Take this
ovary away, and the man-woman stands before us—a loathly abortion.”

The same close correlation between the sexual organs and the other parts
of the body occurs among plants as generally as among animals. If one
wishes to obtain an abundance of fruit from a garden plant, the growth
of the leaves is curtailed by cutting off some of them. If, on the other
hand, an ornamental plant with a luxuriance of large and beautiful
leaves is desired, then the development of the blossoms and fruit is
prevented by cutting off the flower buds. In both cases one system of
organs develops at the cost of the others. Thus, also, most variations
in the formation of leaves in wild plants result in corresponding
transformations of the generative parts or blossoms. The great
importance of this “compensation of development,” of this “correlation
of parts,” has been already set forth by Goethe, by Geoffroy St.
Hilaire, and other nature-philosophers. It rests mainly upon the fact
that direct or actual adaptation cannot produce an important change in a
single part of the body, without at the same time affecting the whole
organism.

The correlative adaptation between the reproductive organs and the other
parts of the body deserves a very special consideration, because it is,
above all others, likely to throw light upon the obscure and mysterious
phenomena of indirect or potential adaptation, which have already been
considered. For just as every change of the sexual organs powerfully
reacts upon the rest of the body, so on the other hand every important
change in another part of the body must necessarily more or less react
on the sexual organs. This reaction, however, will only become
perceptible in the formation of the offspring which arise out of the
changed generative parts. It is, in fact, precisely those remarkable and
imperceptible changes of the genital system (in themselves utterly
insignificant changes)—changes of the eggs and the sperm—brought about
by such correlations, which have the greatest influence upon the
formation of the offspring, and all the phenomena of indirect or
potential adaptation previously mentioned may in the end be traced to
correlative adaptation.

A further series of remarkable examples of correlative adaptation is
furnished by the different animals and plants which become degenerated
through parasitic life or parasitism. No other change in the mode of
life so much affects the shapes of organisms as the adoption of a
parasitical life. Plants thereby lose their green leaves; as, for
instance, our native parasitical plants, Orobanche, Lathræa, Monotropa.
Animals which originally have lived freely and independently, but
afterwards adopt a parasitical mode of life on other animals or plants,
in the first place cease to use their organs of motion and their organs
of sense. The loss of this activity is succeeded by the loss of the
organs themselves, and thus we find, for example, many crabs, or
crustacea, which in their youth possess a tolerably high degree of
organization, viz., legs, antennæ, and eyes, in old age completely
degenerate, living as parasites, without eyes, without apparatus of
motion, and without antennæ. The lively, active form of youth, has
become a shapeless, motionless lump. Only the most necessary organs of
nutrition and propagation retain their activity; all the rest of the
body has degenerated. Evidently these complete transformations are, to a
large extent, the direct consequences of cumulative adaption, of the
non-use and defective exercise of the organs, but a great portion of
them must certainly be attributed also to correlative adaptation.
(Compare Plate X. and XI.)

A seventh law of adaptation, the fourth in the group of direct
adaptation, is _the law of divergent adaptation_. By this law we
indicate the fact that parts originally formed alike have developed in
different ways under the influence of external conditions. This law of
adaptation is extremely important for the explanation of the phenomenon
of division of labour, or polymorphism. We can see this very easily in
our own selves; for instance, in the activity of our two hands. We
usually accustom our right hand to quite different work from that which
we give our left, and in consequence of the different occupation there
arises a different formation of the two hands. The right hand, which we
use much more than the left, shows a stronger development of the nerves,
muscles, and bones. The same applies to the whole arm. In most human
beings the bones and flesh of the right arm are, in consequence of their
being more employed, stronger and heavier than those of the left arm.
Now, as the special use of the right arm has been adopted and
transmitted by inheritance for thousands of years among Europeans, the
stronger shape and size of the right arm have already become hereditary.
P. Harting, an excellent Dutch naturalist, has shown by measuring and
weighing newly-born children, that even in them the right arm is more
developed than the left.

According to the same law of divergent adaptation, both eyes also
frequently develop differently. If, for example, a naturalist accustoms
himself always to use one eye for the microscope (it is better to use
the left), then that eye will acquire a power different from that of the
other, and this division of labour is of great advantage. The one eye
will become more short-sighted, and better suited for seeing things near
at hand; the other eye becomes, on the contrary, more long-sighted, more
acute for looking at an object in the distance. If, on the other hand,
the naturalist alternately uses both eyes for the microscope, he will
not acquire the short-sightedness of the one eye and the compensatory
degree of long-sight in the other, which is attained by a wise
distribution of these different functions of sight between the two eyes.
Here then again the function, that is the activity, of originally
equally-formed organs can become divergent by habit; the function reacts
again upon the form of the organ, and thus we find, after a long
duration of such an influence, a change in the more delicate parts and
the relative growth of the divergent organs, which in the end becomes
apparent even in their coarser outlines.

Divergent adaptation can very easily be perceived among plants,
especially in creepers. Branches of one and the same creeping plant,
which originally were formed alike, acquire a completely different form
and extent, a completely different degree of curvature and diameter of
spiral winding, according as they twine themselves round a thinner or a
thicker bar. The divergent change of form of parts originally identical
in form, which tending in different directions develop themselves under
different external conditions, can be distinctly demonstrated in many
other examples. As this divergent adaptation interacts with progressive
inheritance, it becomes the cause of a division of labour among the
different organs.

An eighth and last law of adaptation we may call _the law of unlimited
or infinite adaptation_. By it we simply mean to express that we know of
no limit to the variation of organic forms occasioned by the external
conditions of existence. We can assert of no single part of an organism,
that it is no longer variable, or that if it were subjected to new
external conditions it would not be changed by them. It has never yet
been proved by experience that there is a limit to variation. If, for
example, an organ degenerates from non-use, this degeneration ends
finally in a complete disappearance of the organ, as is the case with
the eyes of many animals. On the other hand, we are able, by continual
practice, habit, and the ever-increasing use of an organ, to bring it to
a degree of perfection which we should at the beginning have considered
to be impossible. If we compare the uncivilized savages with civilized
nations, we find among the former a development of the organs of
sense—sight, smell, and hearing—such as civilized nations can hardly
conceive of. On the other hand, the brain, that is mental activity,
among more civilized nations is developed to a degree of which the wild
savages have no idea.

There appears indeed to be a limit given to the adaptability of every
organism, by the “type” of its tribe or phylum; that is, by the
essential fundamental qualities of this tribe, which have been inherited
from a common ancestor, and transmitted by conservative inheritance to
all its descendants. Thus, for example, no vertebrate animal can acquire
the ventral nerve-chord of articulate animals, instead of the
characteristic spinal marrow of the vertebrate animals. However, within
this hereditary primary form, within this inalienable type, the degree
of adaptability is unlimited. The elasticity and fluidity of the organic
form manifests itself, within the type, freely in all directions, and to
an unlimited extent. But there are some animals, as, for example, the
parasitically degenerate crabs and worms, which seem to pass even the
limit of type, and have forfeited all the essential characteristics of
their tribe by an astonishing degree of degeneration. As to the
adaptability of man, it is, as in all other animals, also unlimited, and
since it is manifested in him above all other animals, in the
modifications of the brain, there can be absolutely no limit to the
knowledge which man in a further progress of mental cultivation may not
be able to exceed. The human mind, according to the law of unlimited
adaptation, enjoys an infinite perspective of becoming ever more and
more perfect.

These remarks are sufficient to show the extent of the phenomena of
Adaptation, and the great importance to be attached to them. The laws of
Adaptation, or the facts of Variation caused by the influence of
external conditions, are just as important as the laws of Inheritance.
All phenomena of Adaptation, in the end, can be traced to conditions of
nutrition of the organism, in the same way as the phenomena of
Inheritance are referable to conditions of reproduction; but the latter,
as well as the former, may further be traced to chemical and physical,
that is to mechanical, causes. According to Darwin’s Theory of Selection
the new forms of organisms, the transformations which artificial
selection produces in the state of cultivation, and which natural
selection produces in the state of nature, arise solely by the
interaction of such causes.

CHAPTER XI.

NATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION OF LABOUR AND
PROGRESS.

Interaction of the Two Organic Formative Causes,
Inheritance and Adaptation.—Natural and Artificial
Selection.—Struggle for Existence, or Competition for
the Necessaries of Life.—Disproportion between the
Number of Possible or Potential, and the Number of Real
or Actual Individuals.—Complicated Correlations of all
Neighbouring Organisms.—Mode of Action in Natural
Selection.—Homochromic Selection as the Cause of
Sympathetic Colourings.—Sexual Selection as the Cause of
the Secondary Sexual Characters.—Law of Separation or
Division of Labour (Polymorphism, Differentiation,
Divergence of Characters).—Transition of Varieties into
Species.—Idea of Species.—Hybridism.—Law of Progress
or Perfectioning (Progressus, Teleosis).

In order to arrive at a right understanding of Darwinism, it is, above
all, necessary that the two organic functions of _Inheritance and
Adaptation_, which we spoke of in our last chapter, should be more
closely examined. If we do not, on the one hand, examine the purely
mechanical nature of these two physiological activities, and the various
action of their different laws, and if, on the other hand, we do not
consider how complicated the interaction of these different laws of
Inheritance and Adaptation must be, we shall not be able to understand
how these two functions, by themselves, have been able to produce all
the variety of animal and vegetable forms, which, in fact, they have.
We have, at least, hitherto been unable to discover any other formative
causes besides these two, and if we rightly understand the necessary and
infinitely complicated interaction of Inheritance and Adaptation, we do
not require to look for other unknown causes for the change of organic
forms. These two fundamental causes are, as far as we can see,
completely sufficient.

Even long before Darwin had published his Theory of Selection, some
naturalists, and especially Goethe, had assumed the interaction of two
distinct formative tendencies—a conservative or preserving, and a
progressive or changing formative tendency—as the causes of the variety
of organic forms. The former was called by Goethe the centripetal or
specifying tendency, the latter the centrifugal tendency, or the
tendency to metamorphosis (p. 89). These two tendencies completely
correspond with the two processes of Inheritance and Adaptation.
_Inheritance_ is the _centripetal_ or _internal formative tendency_
which strives to keep the organic form in its species, to form the
descendants like the parents, and always to produce identical things
from generation to generation. _Adaptation_, on the other hand, which
counteracts inheritance, is the _centrifugal_ or _external formative
tendency_, which constantly strives to change the organic forms through
the influence of the varying agencies of the outer world, to create new
forms out of those existing, and entirely to destroy the constancy or
permanency of species. Accordingly as Inheritance or Adaptation
predominates in the struggle, the specific form either remains constant
or changes into a new species. The degree of constancy of form in the
different species of animals and plants, which obtains at any moment,
is simply the necessary result of the momentary predominance which
either of these two formative powers (or physiological activities) has
acquired over the other.

If we now return to the consideration of the process of selection or
choice, the outlines of which we have already examined, we shall be in a
position to see clearly and distinctly that both artificial and natural
selection rest solely upon the interaction of these two formative
tendencies. If we carefully watch the proceedings of an artificial
selector—a farmer or a gardener—we find that only these two
constructive forces are used by him for the production of new forms. The
whole art of artificial selection rests solely upon a thoughtful and
wise application of the laws of Inheritance and Adaptation, and upon
their being applied and regulated in an artistic and systematic manner.
Here the will of man constitutes the selecting force.

The case of natural selection is quite similar, for it also employs
merely these two organic constructive forces, these ingrained
physiological properties of Adaptation and Heredity, in order to produce
the different species. But the selecting principle or force, which in
_artificial_ selection is represented by the conscious _will of man_
acting for a definite purpose, consists in _natural_ selection of the
unconscious _struggle for existence_ acting without a definite plan.
What we mean by “struggle for existence” has already been explained in
the seventh chapter. It is the recognition of this exceedingly important
identity which constitutes one of the greatest of Darwin’s merits. But
as this relation is very frequently imperfectly or falsely understood,
it is necessary to examine it now more closely, and to illustrate by a
few examples the operation of the struggle for life, and the operation
of natural selection _by means of_ the struggle for life (Gen. Morph.
ii. 231).

When considering the struggle for life, we started from the fact that
the number of germs which all animals and plants produce is infinitely
greater than the number of individuals which actually come to life and
remain alive for a longer or shorter time. Most organisms produce during
life thousands or millions of germs, from each of which, under
favourable circumstances, a new individual might arise. In most animals
and plants these germs are eggs, that is cells, which for their
development require sexual fructification. But among the Protista, the
lowest organisms, which are neither animals nor plants, and which
propagate themselves only in a non-sexual manner, the germ-cells, or
spores, require no fructification. Now, in all cases the number of
unsexual, as well as of sexual germs, is out of all proportion to the
number of actually living individuals of every species.

Taken as a whole, the number of living animals and plants on our earth
remains always about the same. The number of places in the economy of
nature is limited, and in most parts of the earth’s surface these places
are always approximately occupied. Certainly there occur everywhere and
in every year fluctuations in the absolute and in the relative number of
individuals of all species. However, taken as a whole, these
fluctuations are of little importance, and it is broadly the fact that
the total number of all individuals remains, on an average, almost
constant. There is a constant fluctuation, which depends on the fact
that in one year or another one or other series of animals and plants
predominates, and that every year the struggle for life somewhat alters
their relations.

Every single species of animals and plants would have densely peopled
the whole earth’s surface in a short time, if it had not had to struggle
against a number of enemies and hostile influences. Even Linnæus
calculated that if an annual plant only produced two seeds (and there is
not one which produces so few), it would have yielded in twenty years a
million of individuals. Darwin has calculated of elephants, which of all
animals seem the slowest to increase, that in seven hundred and fifty
years the descendants of a single pair would amount to nineteen millions
of individuals; this is supposing that every elephant, during its period
of fertility (from the 30th to the 90th year), produced only three pairs
of young ones, and survived itself to its hundredth year. In like manner
the increase of the number of human beings—if calculated on the average
proportion of births to population, and no hindrances to the natural
increase stood in the way—would be such as to double the total in
twenty-five years. In every century the total number of men would have
increased sixteen-fold; whereas we know that the total number of human
beings increases but slowly, and that the increase of population is very
different in different countries. While European tribes spread over the
whole globe, other tribes or species of men every year draw nearer to
their complete extinction. This is the case especially with the redskins
of America, and with the copper-coloured natives of Australia. Even if
these races were to propagate more abundantly than the white Europeans,
yet they would sooner or later succumb to the latter in the struggle for
life. But of all human individuals, as of all other organisms, by far
the majority perish at the earliest period of their lives. Of the
immense quantity of germs which every species produce, only very few
actually succeed in developing, and of these few it is again only a very
small portion which attain to the age in which they can reproduce
themselves (compare p. 161).

From the disproportion between the immense excess of organic germs and
the small number of chosen individuals which are actually able to
continue in existence beside one another, there follows of necessity
that universal struggle for life, that constant fight for existence,
that perpetual competition for the necessaries of life, of which I gave
a sketch in my seventh chapter. It is this struggle for life which
brings natural selection into play, which in its turn is made use of by
the interaction of the phenomena of Inheritance and Adaptation as a
sifting agency, and which thus causes a continual change in all organic
forms. In this struggle for acquiring the necessary conditions of
existence, those individuals will always overpower their rivals who
possess any individual privilege, any advantageous quality, of which
their fellow competitors are destitute. It is true we are able only in
the fewest cases (in those animals and plants best known to us) to form
an approximate conception of the infinitely complicated interaction of
the numerous circumstances, all of which here come into combination.
Only think how infinitely varied and complicated are the relations of
every single human being to the rest of mankind, and in general, to the
whole of the surrounding outer world. But similar relations prevail also
among all animals and plants which live together in one place. All
influence one another actively or passively. Every animal and every
plant struggles directly with a number of enemies, beasts of prey,
parasitic animals, etc. Plants standing together struggle with one
another for the space of ground requisite for their roots, for the
necessary amount of light, air, moisture, etc. In like-manner, animals
living together struggle with one another for their food,
dwelling-place, etc. In this most active and complicated struggle, any
personal superiority, however small, any individual advantage, may
possibly decide the issue in favour of the one possessing it. This
privileged individual remains the victor in the struggle, and propagates
itself, while its fellow-competitors perish before they succeed in
propagating themselves. The personal advantage which gave it the victory
is transmitted by inheritance to its descendants, and by a further
development may become so strongly marked as to cause us to consider the
later generations as a new species.

The infinitely complicated correlations which exist between the
organisms of every district, and which must be looked upon as the real
conditions of the struggle for life, are mostly unknown to us, and are
very difficult to discover. We have hitherto been able to trace them
only to a certain point in individual cases, as in the example given by
Darwin of the relations between cats and red clover in England. The red
clover (_Trifolium pratense_), which in England is among the best fodder
for cattle, requires the visit of humming-bees in order to attain the
formation of seeds. These insects, while sucking the honey from the
bottom of the flower, bring the pollen in contact with the stigma, and
thus cause the fructification of the flower, which never takes place
without it. Darwin has shown by experiments, that red clover which is
not visited by humming-bees does not yield a single seed. The number of
bees is determined by the number of their enemies, the most destructive
of which are the field-mice. The more the field-mice predominate, the
less the clover is fructified. The number of field-mice, again, is
dependent upon the number of their enemies, principally cats. Hence in
the neighbourhood of villages and towns, where many cats are kept, there
are plenty of bees. A great number of cats, therefore, is evidently of
great advantage for the fructification of clover. This example may be
followed still further, as has been done by Carl Vogt, if we consider
that cattle which feed on red clover are one of the most important
foundations of the wealth of England. Englishmen preserve their bodily
and mental powers chiefly by making excellent meat—roast beef and
beefsteak—their principal food. The English owe the superiority of
their brains and minds over those of other nations in a great measure to
their excellent meat. But this is clearly indirectly dependent upon the
cats, which pursue the mice. We may, with Huxley, even trace the chain
of causes to those old maids who cherish and keep cats, and,
consequently, are of the greatest importance to the fructification of
the clover and to the prosperity of England. From this example we can
see that the further it is traced the wider is the circle of action and
of correlation. We can with certainty maintain that there exist a great
number of such correlations in every plant and in every animal, only we
are not always able to point out and survey their concatenation as in
the last instance.

Another remarkable example of important correlations is the following,
given by Darwin. In Paraguay, there are no wild oxen and horses, as in
the neighbouring parts of South America, both north and south of
Paraguay. This surprising circumstance is explained simply by the fact
that in that country a kind of small fly is very frequent, and is in the
habit of laying its eggs in the navel of newly-born calves and foals.
The newly-born animals die in consequence of this attack, and the small
deadly fly is therefore the cause of oxen and horses never becoming wild
in that district. Supposing that this fly were destroyed by some
insect-eating bird, then these large mammals would grow wild in
Paraguay, as well as in the neighbouring parts of South America; and as
they would eat a quantity of certain species of plants, the whole flora,
and, consequently again, the whole fauna of the country would become
changed. It is hardly necessary to state, that at the same time the
whole economy, and consequently the character, of the human population
would alter.

Thus the prosperity, nay, even the existence of whole populations can be
indirectly determined by a single small animal or vegetable form in
itself extremely insignificant. There are small coral islands whose
human inhabitants live almost entirely upon the fruit of a species of
palm. The fructification of this palm is principally effected by
insects, which carry the pollen from the male to the female palm trees.
The existence of these useful insects is endangered by insect-eating
birds, which in their turn are pursued by birds of prey. The birds of
prey, however, often succumb to the attack of a small parasitical mite,
which develops itself in millions in their feathers. This small,
dangerous parasite, again, may be killed by parasitical moulds. Moulds,
birds of prey, and insects would in this case favour the prosperity of
the palm, and consequently of man; birds, mites, and insect-eating birds
would, on the other hand, endanger it.

Interesting examples in relation to the change of correlations in the
struggle for life are furnished also by those isolated oceanic islands,
uninhabited by man, on which at different times goats and pigs have been
placed by navigators. These animals become wild, and having no enemies,
they increase in number so excessively, that the rest of the animal and
vegetable population suffer in consequence, and the island finally may
become almost a waste, because there is insufficient food for the large
mammals which increase too numerously. In some cases on an island thus
overrun with goats and pigs, other navigators have let loose a couple of
dogs, who enjoyed this superabundance of food, and they again increased
so numerously, and made such havoc among the herds, that after several
years the dogs themselves lacked food, and they also almost died out.
The equilibrium of species continually changes in this manner in
nature’s economy, accordingly as one or another species increases at the
expense of the rest. In most cases the relations of different species of
animals and plants to one another are much too complicated for us to be
able to follow them, and I leave it to the reader to picture to himself
what an infinitely complicated machinery is at work in every part of the
world in consequence of this struggle. The impulses which started the
struggle, and which altered and modified it in different places, are in
the end seen to be the impulses of self-preservation—in fact, the
instinct leading individuals to preserve themselves (the instinct of
obtaining food), and the instinct leading them to preserve the species
(instinct of propagation). It is these two fundamental instincts of
organic self-preservation of which Schiller, the idealist (not Goethe,
the realist!) says:

“Meanwhile, until philosophy
Sustains the structure of the world,
Her workings will be carried on
By hunger and by love.”[4]

It is these two powerful fundamental instincts which, by their varying
activity, produce such extraordinary differences in species through the
struggle for life. They are the foundations of the phenomena of
Inheritance and Adaptation. We have, in fact, traced all phenomena of
Inheritance to propagation, all phenomena of Adaptation to nutrition, as
the two wider classes of material phenomena to which they belong.

The struggle for life in natural selection acts with as much selective
power as does the will of man in artificial selection. The latter,
however, acts according to a plan and consciously, the former without a
plan and unconsciously. This important difference between artificial and
natural selection deserves especial consideration. For we learn by it to
understand how _arrangements serving a purpose can be produced by
mechanical causes acting without an object, as well as by causes acting
for an object_. The products of natural selection are arranged even more
for a purpose than the artificial products of man, and yet they owe
their existence not to a creative power acting for a definite purpose,
but to a mechanical relation acting unconsciously and without a plan.
If we had not thoroughly considered the interaction of Inheritance and
Adaptation under the influence of the struggle for life, we should not
at first be inclined to expect such results from this natural process of
selection as are, in fact, furnished by it. It may therefore be
appropriate here to mention a few especially striking examples of the
activity of natural selection.

Let us first take _Darwin’s homochromic selection_ of animals, or the
so-called “sympathetic selection of colours,” into consideration.
Earlier naturalists have remarked that numerous animals are of nearly
the same colour as their dwelling-place, or the surroundings in which
they permanently live. Thus, for example, plant-lice and many other
insects living on leaves are of a green colour. The inhabitants of the
deserts, the jerboa, or leaping mice, foxes of the desert, gazelles,
lions, etc., are mostly of a yellow or yellowish-brown colour, like the
sand of the desert. The polar animals, which live on the ice and snow,
are white or grey, like ice and snow. Many of these animals change their
colour in summer and winter. In summer, when the snow partly vanishes,
the fur of these polar creatures becomes brownish-grey or blackish, like
the naked earth, while in winter it again becomes white. Butterflies and
insects which hover round the gay and bright flowers are like them in
colour. Now, Darwin explains this surprising circumstance quite simply
by the fact that such colours as agree with the colour of the habitation
are of the greatest use to the animals concerned. If these animals are
animals of prey, they will be able to approach the object of their
pursuit more safely and with less likelihood of observation, and, in
like manner, those animals which are pursued will be able to escape
more easily, if their colour is as little different as possible from
that of their surroundings. If therefore originally an animal species
varied so as to present cases of all colours, those individuals whose
colour most resembled the surroundings must have been most favoured in
the struggle for life. They remained more unobserved, maintained and
propagated themselves, while those individuals or varieties differently
coloured died out.

I have tried to explain, by the same sympathetic selection of colour,
the wonderful fact that the majority of pelagic animals—that is, of
those which live on the surface of the open sea—are bluish, or
completely colourless and transparent, like glass and water itself. Such
colourless, glassy animals are met with in the most different classes.
To them belong, among fish, the Helmicthyidæ, through whose crystalline
bodies the words of a book can be read; among the molluscs, the finned
snails (Heteropods) and sea-butterflies, or whales-food (Pteropods);
among worms, the Salpæ, Alciope, and Sagitta; further, a great number of
pelagic crabs (Crustacea), and the greater part of the Medusæ
Umbrella-jellies, (Discomedusæ); Comb-jellies, (Ctenophora). All of
these pelagic animals, which float on the surface of the ocean, are
transparent and colourless, like glass and like the water itself, while
their nearest kin live at the bottom of the ocean, and are coloured and
opaque like the inhabitants of the land. This remarkable fact, like the
sympathetic colouring of the inhabitants of the earth, can be explained
by natural selection. Among the ancestors of the pelagic glass-like
animals which showed a different degree of colourlessness and
transparency, those that were the most colourless and transparent must
have been most favoured in the active struggle for life which takes
place on the surface of the ocean. They were enabled to approach their
prey the most easily unobserved, and were themselves least observed by
their enemies. Hence they could preserve and propagate themselves more
easily than their more coloured and opaque relatives; and finally, by
accumulative adaptation and transmission by inheritance, through natural
selection, in the course of many generations their bodies would attain
that degree of crystal-like transparency and colourlessness which we at
present admire in them. (Gen. Morph. ii. 242.)

No less interesting and instructive than homochromic selection is that
species of natural selection which Darwin calls “_sexual selection_,”
which explains the origin of the so-called “secondary sexual
characters.” We have already mentioned these subordinate sexual
characteristics, so instructive in many respects. They comprise those
peculiarities of animals and plants which belong only to one of the two
sexes, and which do not stand in any direct relation to the act of
propagation itself (compare above, p. 244). Such secondary sexual
characters occur in great variety among animals. We all know how
striking is the difference of the two sexes in size and colour in many
birds and butterflies. The male sex is generally the larger and more
beautiful. It often possesses special decorations or weapons; as for
example, the spur and comb of the cock, the antlers of the stag and
deer, etc. All these peculiarities of the two sexes have nothing
directly to do with propagation itself, which is effected by the
“primary sexual characters,” or actual sexual organs.

Now, the origin of these remarkable “secondary sexual characters” is
explained by Darwin simply by a choice or selection which takes place
in the propagation of animals. In most animals the number of individuals
of both sexes is unequal; either the number of the female or the number
of the male individuals is greater, and, as a rule, when the season of
propagation approaches, a struggle takes place between the rivals for
the possession of the animals of the other sex. It is well known with
what vigour and vehemence this struggle is fought out among the higher
animals—among mammals and birds—especially among those of polygamous
habits. Among gallinaceous birds, where for one cock there are several
hens, a severe struggle takes place between the competing cocks for as
large a harem as possible. The same is the case with many ruminating
animals. Among stags and deer, for instance, at the period of rut,
deadly struggles take place between the males for the possession of the
females. The secondary sexual character which here distinguishes the
males—the antlers of stags and deer—not possessed by the female, is,
according to Darwin, the consequence of that struggle. Here the motive
and cause determining the struggle is not, as in the case of the
struggle for individual existence, self-preservation, but the
preservation of the species—propagation. There are numerous passive
weapons of defence, as well as active weapons for attack. The lion’s
mane, not possessed by the female, is evidently such a weapon of
defence; it is an excellent means of protection against the bites which
the male lions try to inflict on each other’s necks when fighting for
the females; consequently those males with the strongest manes have the
greatest advantage in the sexual struggle. The dewlap of the ox and the
comb of the cock are similar defensive weapons. Active weapons of
attack, on the other hand, are the antlers of the stag, the tusks of
the boar, the spur of the cock, and the hugely developed pair of jaws in
the male stag-beetle; all are instruments employed by the males in the
struggle for the females, for annihilating or chasing away their rivals.

In the cases just mentioned, it is the bodily “struggle to the death”
which determines the origin of the secondary sexual characters. But,
besides these mortal struggles, there are other important competitions
in sexual selection, which no less influence the structure of the
rivals. These consist principally in the fact that the courting sex
tries to please the other by external finery, by beauty of form, or by a
melodious voice. Darwin thinks that the beautiful voices of singing
birds have principally originated in this way. Many male birds carry on
a regular musical contest when they contend for the possession of the
females. It is known of several singing birds, that in the breeding
season the males assemble in numbers round the females, and let their
songs resound before them, and that then the females choose the singers
who best please them for their mates. Among other songsters, individual
males pour out their songs in the loneliness of the forest in order to
attract the females, and the latter follow the most attractive calls. A
similar musical contest, though certainly less melodious, takes place
among crickets and grasshoppers. The male cricket has on its belly two
instruments like drums, and produces with these the sharp chirping notes
which the ancient Greeks curiously enough thought beautiful music. Male
grasshoppers, partly by using their hind-legs like the bow of a violin
against their wing coverings, and partly by rubbing their wing coverings
together, bring out tones which are, indeed, not melodious to us, but
which please the female grasshoppers so much that they choose the male
who fiddles the best.

Among other insects and birds it is not song or, in fact, any musical
accomplishment, but finery or beauty of the one sex which attracts the
other. Thus we find that, among most gallinaceous birds, the cocks are
distinguished by combs on their heads, or by a beautiful tail, which
they can spread out like a fan; as for example, in the case of the
peacock and turkey-cock. The magnificent tail of the bird of paradise is
also an exclusive ornament of the male sex. In like manner, among very
many other birds and very many insects, principally among butterflies,
the males are distinguished from the females by special colours or other
decorations. These are evidently the results of sexual selection. As the
females do not possess these attractions and decorations, we must come
to the conclusion that they have been acquired by degrees by the males
in the competition for the females, which takes its origin in the
selective discrimination of the females.

We may easily picture to ourselves, in detail, the application of this
interesting conclusion to the human community. Here, also, the same
causes have evidently influenced the development of the secondary sexual
characters. The characteristics distinguishing the man, as well as those
distinguishing the woman, owe their origin, certainly for the most part,
to the sexual selection of the other sex. In antiquity and in the Middle
Ages, especially in the romantic age of chivalry, it was the bodily
struggles to the death—the tournaments and duels—which determined the
choice of the bride; the strongest carried home the bride. In more
recent times, however, in our so-called “polished” or “highly
civilized” society, competing rivals prefer to contend indirectly by
means of musical accomplishments, instrumental performances and song, by
bodily charms, natural beauty, or artificial decoration. But by far the
most important of these different forms of sexual selection in man is
that form which is the most exalted, namely, _psychical selection_, in
which the mental excellencies of the one sex influence and determine the
choice of the other. The most highly intellectually developed types of
men have, throughout generations, when choosing a partner in life, been
guided by her excellencies of soul, and have thus transmitted these
qualities to their posterity, and they have in this way, more than by
any other thing, helped to create the deep chasm which at present
separates civilized men from the rudest savages, and from our common
animal ancestors. In fact, both the part played by the prevalence of a
higher standard of sexual selection, and the part played by the due
division of labour between the two sexes, is exceedingly important, and
I believe that here we must seek for the most powerful causes which have
determined the origin and the historical development of the races of
man. (Gen. Morph. ii. 247.) As Darwin, in his exceedingly interesting
work, published in 1871, on “The Origin of Man and Sexual
Selection,”(48) has discussed this subject in the most masterly manner,
and has illustrated it by most remarkable examples, I refer for further
detail to that work.

But now let us look again at two extremely important organic laws which
can be explained by the theory of selection, as necessary consequences
of natural selection in the struggle for existence. I mean the law of
_division of labour_, or _differentiation_, and the law of _progress_,
or _perfecting_. When the phenomena due to these two laws first became
known, through observation of the historical development, the individual
development, and the comparative anatomy of animals and plants,
naturalists were inclined to trace them to a direct creative influence.
It was supposed to be part of the plan of the Creator, acting for a
definite purpose, in the course of time to develop the forms of animals
and plants more and more variously, and to bring them more and more to a
state of perfection. We shall evidently make a great advance in the
knowledge of nature if we reject this teleological and anthropomorphic
conception, and if we can prove the two laws of Division of Labour and
Perfecting to be the necessary consequences of natural selection in the
struggle for life.

The first great law which follows directly and of necessity from natural
selection, is that of _separation_, or _differentiation_, which is
frequently called _division of labour_, or _polymorphism_, and which
Darwin speaks of as _divergence of character_. (Gen. Morph. ii. 249.) We
understand by it the general tendency of all organic individuals to
develop themselves more and more diversely, and to deviate from the
common primary type. The cause of this general inclination towards
differentiation and the formation of heterogeneous forms from
homogeneous beginnings is, according to Darwin, simply to be traced to
the circumstance that the struggle for life between every two organisms
rages all the more fiercely the nearer the relation in which they stand
to one another, or the more nearly alike they are. This is an
exceedingly important, and in reality an exceedingly simple relation,
but it is usually not duly considered.

It must be obvious to every one, that in a field of a certain size,
beside the corn-plants which have been sown, a great number of weeds
can exist, and, moreover, in places which could not have been occupied
by corn-plants. The more dry and sterile places of the ground, in which
no corn-plant would thrive, may still furnish sustenance to weeds of
different kinds; and such species and individuals of weeds will more
readily be able to exist in such conditions, in proportion as they are
suited to adapt themselves to the different parts of the ground. It is
the same with animals. It is evident that a much greater number of
animal individuals can live together in one and the same limited
district, if they are of various and different natures, than if they are
all alike. There are trees (for example, the oak) on which a couple of
hundred of different species of insects live together. Some feed on the
fruits of the tree, others on the leaves, others again on the bark, the
root, etc. It would be quite impossible for an equal number of
individuals to live on this tree if all were of one species; if, for
example, all fed on the bark, or only upon the leaves. Exactly the same
is the case in human society. In one and the same small town, only a
certain number of workmen can exist, even when they follow different
occupations. The division of labour, which is of the greatest use to the
whole community, as well as to the individual workman, is a direct
consequence of the struggle for life, of natural selection; for this
struggle can be sustained more easily the more the activities, and
hence, also, the forms of the different individuals deviate from one
another. The different function naturally produces its reaction in
changing the form, and the physiological division of labour necessarily
determines the morphological differentiation, that is, the “divergence
of character.”(37)

Now, I beg the reader again to remember that all species of animals and
plants are variable, and possess the capability of adapting themselves
to different places or to local relations. The varieties or races of
each species, according to the laws of adaptation, deviate all the more
from the original primary species, the greater the difference of the new
conditions to which they adapt themselves. If we imagine these
varieties—which have proceeded from a common primary form—to be
disposed in the shape of a branching, radiating bunch, then those
varieties will be best able to exist side by side and propagate which
are most distant from one another, which stand at the ends of the
series, or at the opposite sides of the bunch. Those forms, on the other
hand, occupying a middle position—presenting a state of
transition—have the most difficult position in the struggle for life.
The necessaries of life differ most in the two extremes, in the
varieties most distant from one another, and consequently these will get
into the least serious conflict with one another in the general struggle
for life. But the intermediate forms, which have deviated less from the
original primary form, require nearly the same necessaries of life as
the original form, and therefore, in competing for them, they will have
to struggle most with, and be most seriously threatened by, its members.
Consequently, when numerous varieties of a species live side by side on
the same spot of the earth, the extremes, or those forms deviating most
from one another, can much more easily continue to exist beside one
another than the intermediate forms which have to struggle with each of
the different extremes. The intermediate forms will not be able to
resist, for any length of time, the hostile influences which the extreme
forms victoriously overcome. These alone maintain and propagate
themselves, and at length cease to be any longer connected with the
original primary species through intermediate forms of transition. Thus
arise “good species” out of varieties. Thus, then, the struggle for life
necessarily favours the general divergence of organic forms, that is,
the constant tendency of organisms to form new species. This fact does
not rest upon any mystic quality, or upon an unknown formative tendency,
but upon the interaction of Inheritance and Adaptation in the struggle
for life. As the intermediate forms, that is, the individuals in a state
of transition, of the varieties of every species die out and become
extinct, the process of divergence constantly goes further, and from the
extremes forms develop which we distinguish as new species.

Although all naturalists have been obliged to acknowledge the
variability and mutability of all species of animals and plants, yet
most of them have hitherto denied that the modification or
transformation of the organic form surpasses the original limit of the
characters of the species. Our opponents cling to the
proposition—“However far a species may exhibit deviations from its
usual form in a collection of varieties, yet the varieties of it are
never so distinct from one another as two really good species.” This
assertion, which Darwin’s opponents usually place at the head of their
arguments, is utterly untenable and unfounded. This will become quite
clear as soon as we critically compare the various attempts to define
the idea of species. No naturalist can answer the question as to what is
in reality a “genuine or good species” (“bona species”); yet every
systematic naturalist uses this expression every day, and whole
libraries have been written on the question as to whether this or that
observed form is a species or a variety, whether it is a really good or
a bad species. The most general answer to this question used to be the
following: “To one species belong all those individuals which agree in
all essential characteristics. Essential characteristics of species are
those which remain permanent or constant, and never become modified or
vary.” But as soon as a case occurred in which the characteristic—which
had hitherto been considered essential—did become modified, then it was
said, “This characteristic is not essential to the species, for
essential characteristics never vary.” Those who argued thus evidently
moved in a circle, and the naïveté with which this circular method of
defining species is laid down in thousands of books as an unassailable
truth, and is still constantly repeated, is truly astonishing.

All other attempts which have been made to arrive at a definite and
logical determination of the idea of organic “species” have, like the
last, been utterly futile, and led to no results. Considering the nature
of the case, it cannot be otherwise. The idea of species is just as
truly a relative one and not absolute, as is the idea of variety, genus,
family, order, class, etc. I have proved this in detail in the criticism
of the idea of species in my “General Morphology” (Gen. Morph. ii.
323-364). I will waste no more time on this unsatisfactory discussion,
and now only add a few words about the _relation of species to
hybridism_. Formerly it was regarded as a dogma, that two good species
could never produce hybrids which could reproduce themselves as such.
Those who thus dogmatized almost always appealed to the hybrids of a
horse and donkey, the mule and the hinny, which, truly enough, are
seldom able to reproduce themselves. But the truth is that such
unfruitful hybrids are rare examples, and in the majority of cases
hybrids of two totally different species are fruitful and able to
reproduce themselves. They can almost always fruitfully mix with one or
other of the parent species, and sometimes also among themselves; and in
this way completely new forms can originate according to the laws of
“mixed transmission by inheritance.”

Thus, in fact, _hybridism is a source of the origin of new species_,
distinct from the source we have hitherto considered—natural selection.
I have already spoken occasionally of these _hybrid species_ (species
hybridæ), especially of the hare-rabbit (Lepus Darwinii), which has
arisen from the crossing of a male hare and a female rabbit; the
goat-sheep (Capra ovina), which has arisen from the pairing of a he-goat
and ewe; also the different species of thistles (Cirsium), brambles
(Rubus), etc. It is possible that many wild species have originated in
this way, as even Linnæus assumed. At all events, these hybrid species,
which can maintain and propagate themselves as well as pure species,
prove that hybridism cannot serve in any way to give an absolute
definition to the idea of species.

I have already mentioned (p. 47) that the many vain attempts to define
the idea of species theoretically have nothing whatever to do with the
practical distinction of species. The extensive practical application of
the idea of species, as it is carried out in systematic zoology and
botany, is very instructive as furnishing an example of human folly.
Hitherto, by far the majority of zoologists and botanists, in
distinguishing and describing the different forms of animals and plants,
have endeavoured, above all things, to distinguish accurately kindred
forms as so many “good species.” However, it has been found scarcely
possible, in any group, to make an accurate and consistent distinction
of such “genuine or good species.” There are no two zoologists, no two
botanists, who agree in all cases as to which of the nearly related
forms of a genus are good species, and which are not. All authors have
different views about them. In the genus _Hieracium_, for example, one
of the commonest genera of European plants, no less than 300 species
have been distinguished in Germany alone. The botanist Fries, however,
only admits 106, Koch only 52, as “good species,” and others accept
scarcely 20. The differences in the species of brambles (Rubus) are
equally great. Where one botanist makes more than a hundred species, a
second admits only about one half of that number, a third only five or
six, or even fewer species. The birds of Germany have long been very
accurately known. Bechstein, in his careful “Natural History of German
Birds,” has distinguished 367 species, L. Reichenbach 379, Meyer and
Wolff 406, and Brehm, a clergyman learned in ornithology, distinguishes
even more than 900 different species.

Thus we see that here, and, in fact, in every other domain of systematic
zoology and botany, the most arbitrary proceedings prevail, and, from
the nature of the case, must prevail. For it is quite impossible
accurately to distinguish varieties and races from so-called “good
species.” _Varieties are commencing species._ The variability or
adaptability of species, under the influence of the struggle for life,
necessitates the continual and progressive separation or differentiation
of varieties, and the perpetual delimitation of new forms. Whenever
these are maintained throughout a number of generations by inheritance,
whilst the intermediate forms die out, they form independent “new
species.” The origin of new species by division of labour, or
separation, divergence, or differentiation of varieties, is therefore a
_necessary consequence of natural selection_.(37)

The same kind of interest attaches to a second great law which we deduce
from natural selection, and which is, indeed, closely connected with the
law of Divergence, but in no way identical with it; namely, the law of
_Progress_ (progressus), or _Perfecting_ (teleosis). (Gen. Morph. ii.
257.) This great and important law, like the law of differentiation, had
long been empirically established by palæontological experience, before
Darwin’s Theory of Selection gave us the key to the explanation of its
cause. The most distinguished palæontologists have pointed out the law
of progress as the most general result of their investigations of fossil
organisms. This has been specially done by Bronn, whose investigations
on the laws of construction(18) and the laws of the development(19) of
organisms, although little heeded, are excellent, and deserve most
careful consideration. The general results of the law of differentiation
and the law of progress, at which Bronn arrived by a purely mechanical
hypothesis, and by exceedingly accurate, laborious, and careful
investigations, are brilliant confirmations of the truth of these two
great laws which we deduce as necessary inferences from the theory of
selection.

The law of progress or of perfecting establishes the exceedingly
important fact, on the ground of palæontological experience, that in
successive periods of this earth’s history, a continual increase in the
perfection of organic formations has taken place. Since that
inconceivably remote period in which life on our planet began with the
spontaneous generation of Monera, organisms of all groups, both
collectively as well as individually, have continually become more
perfectly and highly developed. The steadily increasing variety of
living forms has always been accompanied by progress in organization.
The lower the strata of the earth in which the remains of extinct
animals and plants lie buried, that is, the older the strata are, the
more simple and imperfect are the forms which they contain. This applies
to organisms collectively, as well as to every single large or small
group of them, setting aside, of course, those exceptions which are due
to the process of degeneration, which we shall discuss hereafter.

As a confirmation of this law I shall mention only the most important of
all animal groups, the tribe of vertebrate animals. The oldest fossil
remains of vertebrate animals known to us belong to the lowest class,
that of Fishes. Upon these there followed later more perfect Amphibious
animals, then Reptiles, and lastly, at a much later period, the most
highly organized classes of vertebrate animals, Birds and Mammals. Of
the latter only the lowest and most imperfect forms, without placenta,
appeared at first, such as are the pouched animals (Marsupials), and
afterwards, at a much later period, the more perfect mammals, with
placenta. Of these, also, at first only the lower kinds appeared, the
higher forms later; and not until the late tertiary period did man
gradually develop out of these last.

If we follow the historical development of the vegetable kingdom we
shall find the same law operative there. Of plants there existed at
first only the lowest and most imperfect classes, the Algæ or tangles.
Later there followed the group of Ferns or Filicinæ (ferns, pole-reeds,
scale-plants, etc.). But as yet there existed no flowering plants, or
Phanerogama. These originated later with the Gymnosperms (firs and
cycads), whose whole structure stands far below that of the other
flowering plants (Angiosperms), and forms the transition from the group
of fern-like plants to the Angiosperms. These latter developed at a
still later date, and among them there were at first only flowering
plants without corolla (Monocotyledons and Monochlamyds); only later
were there flowering plants with a corolla (Dichlamyds). Finally, again,
among these the lower polypetalous plants preceded the higher
gamopetalous plants. The whole series thus constitutes an irrefutable
proof of the great law of progressive development.

Now, if we ask what is the cause of this fact, we again, just as in the
case of differentiation, come back to natural selection in the struggle
for life. If once more we consider the whole process of natural
selection, how it operates through the complicated interaction of the
different laws of Inheritance and Adaptation, we shall recognize not
only divergence of character, but also the perfecting of structure to be
the direct and necessary result of it. We can trace the same thing in
the history of the human race. Here, too, it is natural and necessary
that the progressive division of labour constantly furthers mankind, and
urges every individual branch of human activity into new discoveries and
improvements. This progress itself universally depends on
differentiation, and is consequently, like it, a direct result of
natural selection in the struggle for life.

CHAPTER XII.

LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS. PHYLOGENY AND
ONTOGENY.

Laws of the Development of Mankind: Differentiation and
Perfecting.—Mechanical Cause of these two Fundamental
Laws.—Progress without Differentiation, and
Differentiation without Progress.—Origin of Rudimentary
Organs by Non-use and Discontinuance of
Habit.—Ontogenesis, or Individual Development of
Organisms.—Its General Importance.—Ontogeny, or the
Individual History of Development of Vertebrate Animals,
including Man.—The Fructification of the Egg.—Formation
of the three Germ Layers.—History of the Development of
the Central Nervous System, of the Extremities, of the
Branchial Arches, and of the Tail of Vertebrate
Animals.—Causal Connection and Parallelism of
Ontogenesis and Phylogenesis, that is of the Development
of Individuals and Tribes.—Causal Connection of the
Parallelism of Phylogenesis and of Systematic
Development.—Parallelism of the three Organic Series of
Development.

If man wishes to understand his position in nature, and to comprehend as
natural facts his relations to the phenomena of the world cognisable by
him, it is absolutely necessary that he should compare human with
extra-human phenomena, and, above all, with animal phenomena. We have
already seen that the exceedingly important physiological laws of
Inheritance and Adaptation apply to the human organism in the same
manner as to the animal and vegetable kingdoms, and in both cases
interact with one another. Consequently, natural selection in the
struggle for life acts so as to transform human society, just as it
modifies animals and plants, and in both cases constantly produces new
forms. The comparison of the phenomena of human and animal
transformation is especially interesting in connection with the laws of
divergence and progress, the two fundamental laws which, at the end of
the last chapter, we proved to be direct and necessary consequences of
natural selection in the struggle for life.

A comparative survey of the history of nations, or what is called
“universal history,” will readily yield to us, as the first and most
general result, evidence of a continually _increasing variety_ of human
activities, both in the life of individuals and in that of families and
states. This differentiation or separation, this constantly increasing
divergence of human character and the form of human life, is caused by
the ever advancing and more complete division of labour among
individuals. While the most ancient and lowest stages of human
civilization show us throughout the same rude and simple conditions, we
see in every succeeding period of history, among different nations, a
greater variety of customs, practices, and institutions. The increasing
division of labour necessitates an increasing variety of forms
corresponding to it. This is expressed even in the formation of the
human face. Among the lowest tribes of nations, most of the individuals
resemble one another so much that European travellers often cannot
distinguish them at all. With increasing civilization the physiognomy of
individuals becomes differentiated, and finally, among the most highly
civilized nations, the English and Germans, the divergence in the
characters of the face is so great that we very rarely mistake one face
for another.

The second great fundamental law which is obvious in the history of
nations is the great law of progress or perfecting. Taken as a whole,
the history of man is the history of his _progressive development_. It
is true that everywhere and at all times we may notice individual
retrogressions, or observe that crooked roads towards progress have been
taken, which lead only towards one-sided and external perfecting, and
thus deviate more and more from the higher goal of internal and enduring
perfecting. However, on the whole, the movement of development of all
mankind is and remains a progressive one, inasmuch as man continually
removes himself further from his ape-like ancestors, and continually
approaches nearer to his own ideal.

Now, if we wish to know what causes actually determine these two great
laws of development in man, namely, the law of divergence and the law of
progress, we must compare them with the corresponding laws of
development in animals, and on a close examination we shall inevitably
come to the conclusion that the phenomena, as well as their causes, are
exactly the same in the two cases. The course of development in man,
just as in that of animals, being directed by the two fundamental laws
of differentiation and perfecting, is determined solely by purely
mechanical causes, and is solely the necessary consequence of natural
selection in the struggle for life.

Perhaps in the preceding discussion the question has presented itself to
some—“Are not these two laws identical? Is not progress in all cases
necessarily connected with divergence?” This question has often been
answered in the affirmative, and Carl Ernst Bär, for example, one of the
greatest investigators in the domain of the history of development, has
set forth the following proposition as one of the principal laws in the
ontogenesis of the animal body:—“The degree of development (or
perfecting) depends on the stage of separation (or differentiation) of
the parts.”(20) Correct as this proposition may be on the whole, yet it
is not universally true. In many individual cases it can be proved that
divergence and progress by no means always coincide. _Every progress is
not a differentiation, and every differentiation is not a progress._

Naturalists, guided by purely anatomical considerations, had already set
forth the law relating to progress in organization, that the perfecting
of an organism certainly depends, for the most part, upon the division
of labour among the individual organs and parts of the body, but that
there are also other organic transformations which determine a progress
in organization. One, in particular, which has been generally
recognized, is the _numerical diminution of identical parts_. If, for
example, we compare the lower articulated animals of the crustacean
group, which possess numerous pairs of legs, with spiders which never
have more than four pairs of legs, and with insects which always possess
only three pairs of legs, we find this law, for which a great number of
examples could be adduced, confirmed. The numerical diminution of pairs
of legs is a progress in the organization of articulated animals. In
like manner the numerical diminution of corresponding vertebral joints
in the trunk of vertebrate animals is a progress in their organization.
Fishes and amphibious animals with a very large number of identical
vertebral joints are, for this very reason, less perfect and lower than
birds and mammals, in which the vertebral joints, as a whole, are not
only very much more differentiated, but in which the number of
corresponding vertebræ is also much smaller. Further, according to the
same law of numerical diminution, flowers with numerous stamens are more
imperfect than the flowers of kindred plants with a smaller number of
stamens, etc. If therefore originally a great number of homogeneous
parts exist in an organic body, and if, in the course of very many
generations, this number be gradually decreased, this transformation
will be an example of perfecting.

Another law of progress, which is quite independent of differentiation,
nay, even appears to a certain extent opposed to it, is the law of
_centralization_. In general the whole organism is the more perfect the
more it is organized as a unit, the more the parts are subordinate to
the whole, and the more the functions and their organs are centralized.
Thus, for example, the system of blood-vessels is most perfect where a
centralized heart exists. In like manner, the dense mass of marrow which
forms the spinal cord of vertebrate animals, and the ventral cord of the
higher articulated animals, is more perfect than the decentralized chain
of ganglia of the lower articulated animals, and the scattered system of
ganglia in the molluscs. Considering the difficulty of explaining these
complicated laws of progress in detail, I cannot here enter upon a
closer discussion of them, and must refer to Bronn’s excellent
“Morphologischen Studien,” and to my “General Morphology” (Gen. Morph.
i. 370, 550; ii. 257-266).

Just as we have become acquainted with phenomena of progress, quite
independent of divergence, so we shall, on the other hand, very often
meet with divergencies which are not perfecting, but which are rather
the contrary, that is retrogressions or degenerations. It is easy to see
that the changes which every species of animal and plant experiences
cannot always be improvements. But rather many phenomena of
differentiation, which are of direct advantage to the organism itself,
are yet, in a wider sense, detrimental, inasmuch as they lessen its
general capabilities. Frequently a relapse to simpler conditions of life
takes place, and by adaptation to them a divergence in a retrograde
direction. If, for instance, organisms which have hitherto lived
independently accustom themselves to a parasitical life, they thereby
degenerate or retrograde. Such animals, which hitherto had possessed a
well-developed nervous system and quick organs of sense, as well as the
power of moving freely, lose these when they accustom themselves to a
parasitical mode of life; they consequently retrograde more or less.
There the differentiation viewed by itself is a degeneration, although
it is advantageous to the parasitical organism. In the struggle for life
such an animal, which has accustomed itself to live at the expense of
others, by retaining its eyes and apparatus of motion, which are of no
more use to it, would only expend so much material uselessly; and when
it loses these organs, then a great quantity of nourishment which was
employed for the maintenance of these parts, benefits other parts. In
the struggle for life between the different parasites, therefore, those
which make least pretensions will have advantage over the others, and
this favours their degeneration.

Just as this is found to be the case with the whole organism, so it is
also with the parts of the body of an individual organism. A
differentiation of parts, which leads to a partial degeneration, and
finally even to the loss of individual organs, is, when looked at by
itself, a degeneration, but yet may be advantageous to the organism in
the struggle for life. It is easier to fight when useless baggage is
thrown aside. Hence we meet everywhere, in the more highly-developed
animal and vegetable bodies, processes of divergence, the essence of
which is that they cause the degeneration, and finally the loss, of
particular parts. And at this point the most important and instructive
of all the series of phenomena bearing upon the history of organisms
presents itself to us, namely, that of _rudimentary or degenerate
organs_.

It will be remembered that even in my first chapter I considered this
exceedingly remarkable series of phenomena, from a theoretical point of
view, as one of the most important and most striking proofs of the truth
of the doctrine of descent. We designated as rudimentary organs those
parts of the body which are arranged for a definite purpose and yet are
without function. Let me remind the reader of the eyes of those animals
which live in the dark in caves and underground, and which consequently
never can use them. In these animals we find real eyes hidden under the
skin, frequently developed exactly as are the eyes of animals which
really see; and yet these eyes never perform any function, indeed
cannot, simply for the reason that they are covered by an opaque
membrane, and consequently no ray of light falls upon them (compare
above, p. 13). In the ancestors of these animals, which lived in open
daylight, the eyes were well developed, covered by a transparent horny
capsule (cornea), and actually served the purpose of seeing. But as the
animals gradually accustomed themselves to an underground mode of life,
and withdrew from the daylight and no longer used their eyes, these
became degenerated.

Very clear examples of rudimentary organs, moreover, are the wings of
animals which cannot fly; for example, the wings of the running birds,
like the ostrich, emeu, cassowary, etc., the legs of which have become
exceedingly developed. These birds having lost the habit of flying, have
consequently lost the use of their wings; however, the wings are still
there, although in a crippled form. We very frequently find such
crippled wings in the class of insects, most members of which can fly.

From reasons derived from comparative anatomy and other circumstances,
we can with certainty draw the inference that all insects now living
(all dragon-flies, grasshoppers, beetles, bees, bugs, flies,
butterflies, etc.) have originated from a single common parental form,
from a primary insect which possessed two well-developed pairs of wings,
and three pairs of legs. Yet there are very many insects in which either
one or both pairs of wings have become more or less degenerated, and
many in which they have even completely disappeared. For example, in the
whole order of flies, or Diptera, the hinder pair of wings—in the
bee-parasites, or Strepsiptera, on the other hand, the fore pair of
wings—have become degenerated or entirely disappeared. Moreover, in
every order of insects we find individual genera, or species, in which
the wings have more or less degenerated or disappeared. The latter is
the case especially in parasites. The females have frequently no wings,
whereas the males have; for instance, in the case of glow-worms
(Lampyris), Strepsiptera, etc. This partial or complete degeneration of
the wings of insects has evidently arisen from natural selection in the
struggle for life. For we find insects without wings living under
circumstances where flying would be useless, or even decidedly injurious
to them. If, for example, insects living on islands fly about much, it
may easily happen that when flying they are blown into the sea by the
wind, and if (as is always the case) the power of flying is differently
developed in different individuals, then those which fly badly have an
advantage over those which fly well; they are less easily blown into the
sea, and remain longer in life than the individuals of the same species
which fly well. In the course of many generations, by the action of
natural selection, this circumstance must necessarily lead to a complete
suppression of the wings. If this conclusion had been arrived at on
purely theoretical grounds, we might be pleased to find its truth
established by facts. For upon isolated islands the proportion of
wingless insects to those possessing wings is surprisingly large, much
larger than among the insects inhabiting continents. Thus, for example,
according to Wollaston, of the 550 species of beetles which inhabit the
island of Madeira, 220 are wingless, or possess such imperfect wings
that they can no longer fly; and of the 29 genera which belong to that
island exclusively, no less than 23 contain such species only. It is
evident that this remarkable circumstance does not need to be explained
by the special wisdom of the Creator, but is sufficiently accounted for
by natural selection, because in this case the hereditary disuse of the
wings, the discontinuance of flying in the presence of dangerous winds,
has been very advantageous in the struggle for life. In other wingless
insects the want of wings has been advantageous for other reasons.
Viewed by itself, the loss of wings is a degeneration, but in these
special conditions of life it is advantageous to the organism in the
struggle for life.

Among other rudimentary organs I may here, by way of example, further
mention the lungs of serpents and serpent-like lizards. All vertebrate
animals possessing lungs, such as amphibious animals, reptiles, birds,
and mammals, have a pair of lungs, a right and a left one. But in cases
where the body is exceedingly thin and elongated, as in serpents and
serpent-like lizards, there is no room for the one lung by the side of
the other, and it is an evident advantage to the mechanism of
respiration if only one lung is developed. A single large lung here
accomplishes more than two small ones side by side would do; and
consequently, in these animals, we invariably find only the right or
only the left lung fully developed. The other is completely aborted,
although existing as a useless rudiment. In like manner, in all birds
the right ovary is aborted and without function; only the left one is
developed, and yields all the eggs.

I mentioned in the first chapter that man also possesses such useless
and superfluous rudimentary organs, and I specified as such the muscles
which move the ears. Another of them is the rudiment of the tail which
man possesses in his 3—5 tail vertebræ, and which, in the human embryo,
stands out prominently during the first two months of its development
(compare Plates II. and III.). It afterwards becomes completely hidden.
The rudimentary little tail of man is an irrefutable proof of the fact
that he is descended from tailed ancestors. In woman the tail is
generally by one vertebra longer than in man. There still exist
rudimentary muscles in the human tail which formerly moved it.

Another case of human rudimentary organs, only belonging to the male,
and which obtains in like manner in all male mammals, is furnished by
the mammary glands on the breast, which, as a rule, are active only in
the female sex. However, cases of different mammals are known,
especially of men, sheep, and goats, in which the mammary glands were
fully developed in the male sex, and yielded milk as food for their
offspring. I have already mentioned before (p. 12) that the rudimentary
auricular muscles in man can still be employed to move their ears, by
some persons who have perseveringly practised them. In fact, rudimentary
organs are frequently very differently developed in different
individuals of the same species; in some they are tolerably large, in
others very small. This circumstance is very important for their
explanation, as is also the other circumstance that generally in
embryos, or in a very early period of life, they are much larger and
stronger in proportion to the rest of the body than they are in fully
developed and fully grown organisms. This can, in particular, be easily
pointed out in the rudimentary sexual organs of plants (stamens and
pistil), which I have already mentioned. They are proportionately much
larger in the young flower-bud than in the mature flower.

I have remarked (p. 15) that rudimentary or suppressed organs were the
strongest supports of the monistic or mechanical conception of the
universe. If its opponents, the dualists and teleologists, understood
the immense significance of rudimentary organs, it would put them into a
state of despair. Their ludicrous attempts to explain that rudimentary
organs were given to organisms by the Creator “for the sake of
symmetry,” or “as a formal provision,” or “in consideration of his
general plan of creation,” sufficiently prove the utter impotence of
their perverse conception of the universe. I must here repeat that, even
if we knew absolutely nothing of the other phenomena of development, we
should be obliged to believe in the truth of the Theory of Descent,
solely on the ground of the existence of rudimentary organs. Not one of
its opponents has been able to throw even a feeble glimmer of an
acceptable explanation upon these exceedingly remarkable and important
phenomena. There is scarcely any highly developed animal or vegetable
form which has not some rudimentary organs, and in most cases it can be
shown that they are the products of natural selection, and that they
have become suppressed by disuse. It is the reverse of the process of
formation in which new organs arise from adaptation to certain
conditions of life, and by the use of parts as yet incompletely
developed. It is true our opponents usually maintain that the origin of
altogether new parts is completely inexplicable by the Theory of
Descent. However, I distinctly assert that to those who possess a
knowledge of comparative anatomy and physiology this matter does not
present the slightest difficulty. Every one who is familiar with
comparative anatomy and the history of development will find as little
difficulty about the origin of completely new organs as about the utter
disappearance of rudimentary organs. The disappearance of the latter,
viewed by itself, is the converse of the origin of the former. Both
processes are particular phenomena of differentiation, which, like all
others, can be explained quite simply and mechanically by the action of
natural selection in the struggle for life.

The infinitely important study of rudimentary organs and their origin,
the comparison of their palæontological and embryological development,
now naturally leads us to the consideration of one of the most important
and instructive of all biological phenomena, namely, the parallelism
which the phenomena of progress and divergence present to us in three
different series. When, in the last chapter, we spoke of perfecting and
division of labour, we understood by those words progress and
separation, and those changes effected by them, which in the long and
slow course of the earth’s history have led to a continual variation of
the flora and fauna, to the origin of new and to the disappearance of
ancient species of animals and plants. Now, if we follow the origin, the
development, and the life of every single organic individual, we meet
with exactly the same phenomena of progress and differentiation. The
individual development, or the _ontogenesis_ of every single organism,
from the egg to the complete form is nothing but a growth attended by a
series of diverging and progressive changes. This applies equally to
animals, plants, and protista. If, for example, we consider the ontogeny
of any mammal, of man, of an ape, or of a pouched animal, or if we
follow the individual development of any other vertebrate animal of
another class, we everywhere find essentially the same phenomena. Every
one of these animals develops itself originally out of a single cell,
the egg. This cell increases by self-division, and forms a number of
cells, and by the growth of this accumulation of cells, by the divergent
development of originally identical cells, by the division of labour
among them, and by their perfecting, there arises the perfect organism,
the complicated composition of which excites our admiration.

It seems to me here indispensable to draw attention more closely to
those infinitely important and interesting processes which accompany
_ontogenesis, or the individual development of organisms_, and
especially to that of vertebrate animals, man included. I wish
especially to recommend these exceedingly remarkable and instructive
phenomena to the reader’s most careful consideration, first, because
they are among the strongest supports of the Theory of Descent, and
secondly, because, considering their immense general importance, they
have hitherto been properly considered only by a few privileged persons.

We cannot indeed but be astonished when we consider the deep ignorance
which still prevails, in the widest circles, about the facts of the
individual development of man and organisms in general. These facts, the
universal importance of which cannot be estimated too highly, were
established, in their most important outlines, even more than a hundred
years ago, in 1759, by the great German naturalist Caspar Friedriech
Wolff, in his classical “Theoria Generationis.” But, just as Lamarck’s
Theory of Descent, founded in 1809, lay dormant for half a century, and
was only awakened to new and imperishable life in 1859, by Darwin, in
like manner Wolff’s Theory of Epigenesis remained unknown for nearly
half a century; and it was only after Oken, in 1806 had published his
history of the development of the intestinal tube, and after Meckel, in
1812, had translated Wolff’s work (written in Latin) on the same subject
into German, that Wolff’s theory of epigenesis became more generally
known, and formed the foundation of all subsequent investigations of the
history of individual development. The study of ontogenesis now received
a great stimulus, and soon there appeared the classical investigations
of the two friends, Christian Pander (1817) and Carl Ernst Bär (1819).
Bär, in his remarkable “Entwickelungsgeschichte der Thiere,”(20) worked
out the ontogeny of vertebrate animals in all its important facts. He
carried out a series of such excellent observations, and illustrated
them by such profound philosophical reflections, that his work became
the foundation for a thorough understanding of this important group of
animals, to which, of course, man also belongs. The facts of embryology
alone would be sufficient to solve the question of man’s position in
nature, which is the highest of all problems. Look attentively at and
compare the eight figures which are represented on the adjoining Plates
II. and III., and it will be seen that the philosophical importance of
embryology cannot be too highly estimated.

We may well ask, What do our so-called “educated” circles, who think so
much of the high civilization of the 19th century, know of these most
important biological facts, of these indispensable foundations for
understanding their own organism? How much do our speculative
philosophers and theologians know about them, who fancy they can arrive
at an understanding of the human organism by mere guesswork or divine
inspiration? What indeed do the majority of naturalists, not excepting
the majority of the so-called “zoologists” (including the
entomologists!), know about them?

The answer to this question tells much to the shame of the persons above
indicated, and we must confess, willingly or unwillingly, that these
invaluable facts of human ontogeny are, even at the present day, utterly
unknown to most people, or are in no way valued as they deserve to be.
It is in the face of such a condition of things as this that we see
clearly upon what a wrong and one-sided road the much vaunted culture of
the 19th century still moves. Ignorance and superstition are the
foundations upon which most men construct their conception of their own
organism and its relation to the totality of things; and these palpable
facts of the history of development, which might throw the light of
truth upon them, are ignored. It is true these facts are not calculated
to excite approval among those who assume a thorough difference between
man and the rest of nature, and who will not acknowledge the animal
origin of the human race. That origin must be a very unpleasant truth to
members of the ruling and privileged castes in those nations among which
there exists an hereditary division of social classes, in consequence of
false ideas about the laws of inheritance. It is well known that, even
in our day, in many civilized countries the idea of hereditary grades of
rank goes so far, that, for example, the aristocracy imagine themselves
to be of a nature totally different from that of ordinary citizens, and
nobles who commit a disgraceful offence are punished by being expelled
from the caste of nobles, and thrust down among the pariahs of “vulgar
citizens.” What are these nobles to think of the noble blood which flows
in their privileged veins, when they learn that all human embryos, those
of nobles as well as commoners, during the first two months of
development, are scarcely distinguishable from the tailed embryos of
dogs and other mammals?

As the object of these pages is solely to further the general knowledge
of natural truths, and to spread, in wider circles, a natural conception
of the relations of man to the rest of nature, I shall be justified if I
do not pay any regard to the widely-spread prejudice in favour of an
exceptional and privileged position for man in creation, and simply give
here the embryological facts from which the reader will be able to draw
conclusions affirming the groundlessness of those prejudices. I wish all
the more to entreat him to reflect carefully upon these facts of
ontogeny, as it is my firm conviction that a general knowledge of them
can only promote the intellectual advance, and thereby the mental
perfecting, of the human race.

Amidst all the infinitely rich and interesting material which lies
before us in the ontogeny of vertebrate animals, that is, in the history
of their individual development, I shall here confine myself to showing
some of those facts which are of the greatest importance to the Theory
of Descent in general, as well as in its special application to man. Man
is at the beginning of his individual existence a simple egg, a single
little cell, just the same as every animal organism which originates by
sexual generation. The human egg is essentially the same as that of all
other mammals, and cannot be distinguished from the egg of the higher
mammals. The egg represented in Fig. 5 might be that of a man or an ape
as well as of a dog, a horse, or any other mammal. Not only the form and
structure, but even the size of the egg in most mammals is the same as
in man, namely, about the 120th part of an inch in diameter, so that the
egg under favorable circumstances, with the naked eye, can just be
perceived as a small speck. The differences which really exist between
the eggs of different mammals and that of man do not consist in the
form, but in the chemical mixture, in the molecular composition of the
albuminous combination of carbon, of which the egg essentially consists.
These minute individual differences of all eggs, which depend upon
indirect or potential adaptation (and especially upon the law of
individual adaptation), are indeed not directly perceptible to the
exceedingly imperfect senses of man, but are cognisable through indirect
means, as the primary causes of the difference of all individuals.

[Illustration: FIG. 5.—The human egg a hundred times enlarged. _a._ The
kernel speck, or nucleolus (the so-called germinal spot of the egg).
_b._ Kernel, or nucleus (the so-called germinal vesicle of the egg).
_c._ Cell-substance, or protoplasm (so-called yolk of the egg). _d._
Cell-membrane (the yolk-membrane of the egg; in mammals, on account of
its transparency, called zona pellucida). The eggs of other mammals are
of the same form.]

The human egg is, like that of all other mammals, a small globular
bladder, which contains all the constituent parts of a simple organic
cell (Fig. 5). The most essential parts of it are the mucous
cell-substance, or the protoplasma (_c_), which in an egg is called the
“yolk,” and the cell-kernel, or nucleus (_b_), surrounded by it, which
is here called by the special name of the “germinal vesicle.” The latter
is a delicate, clear, glassy globule of albumen, of about 1-600th part
of an inch in diameter, and surrounds, a still smaller, sharply-marked,
rounded granule (_a_), the kernel-speck, or the nucleolus of the cell
(in the egg it is called the “germinal spot”). The outside of the
globular egg-cell of a mammal is surrounded by a thick pellucid
membrane, the cell-membrane or yolk-membrane, which here bears the
special name of zona pellucida (_d_). The eggs of many lower animals
(for example of many Medusæ) differ from this in being _naked_ cells, as
the outer covering, or cell-membrane, is wanting.

As soon as the egg (ovulum) of the mammal has attained its full
maturity, it leaves the ovary of the female, in which it originates, and
passes into the oviduct, and through this narrow passage into the wider
pouch or womb (uterus). If, meanwhile, the egg is fructified by the male
seed (sperm), it develops itself in this pouch into an embryo, and does
not leave it until perfectly developed and capable of coming into the
world at birth as a young mammal.

The variations of form and transformations which the fructified egg must
go through within the uterus before it assumes the form of the mammal
are exceedingly remarkable, and proceed from the beginning in man, in
precisely the same way as in the other mammals. At first the fructified
egg of the mammal acts as a single-celled organism, which is about to
propagate independently and increase itself; for example, an Amœba
(compare Fig. 2, p. 188). In point of fact the simple egg-cell becomes
two, by the process of cell-division which I have previously described.
There arise from the single germinal spot (the small kernel-speck of the
original simple egg-cell) two new kernel-specks, and then in like
manner, out of the germinal vesicle (the nucleus), two new cell-kernels.
Then, and not until then, does the globular protoplasma first separate
itself by an equatorial furrow into two halves, in such a manner that
each half encloses one of the two kernels, together with its
kernel-speck. Thus the simple egg-cell, within the original cellular
membrane, has become two naked cells, each possessing its own kernel
(Fig. 6).

[Illustration: FIG. 6.—First commencement of the development of a
mammal’s egg, the so-called “yolk-cleavage” (propagation of the egg-cell
by repeated self-division). _A._ The egg, by the formation of the first
furrow, falls into two cells. _B._ These by division fall into four
cells. _C._ These latter have fallen into eight cells. _D._ By continued
division a globular mass of numerous cells has arisen.]

The same process of cell-division now repeats itself several times in
succession. In this way, from two cells (Fig. 6 _A_) there arise four
(Fig. 6 _B_); from four, eight (Fig. 6 _C_); from eight, sixteen; from
these, thirty-two, etc. Each time the division of the kernel-speck
precedes that of the kernel; this, again, precedes that of the
cell-substance, or protoplasma. As the division of the latter always
commences with the formation of a superficial annular _furrow_, or
cleft, the whole process is usually called the _furrowing of the egg_,
or yolk-cleavage, and the products of it, that is, the cells arising
from the continued halving, are called the _cleavage spheres_. However,
the whole process is nothing more than a simple, oft-repeated _division
of cells_, and the products of it are actual, naked _cells_. Finally,
through the continued division or “furrowing” of the mammal’s egg there
arises a mulberry-shaped ball, which is composed of a great number of
small spheres, naked cells, containing kernels (Fig. 6 _D_). These cells
are the materials out of which the body of the young mammal is
constructed. Every one of us has once been such a simple mulberry-shaped
ball, composed only of small equi-formal cells.

The further development of the globular lump of cells, which now
represents the young body of the mammal, consists first in its changing
into a globular bladder, as fluid accumulates within it. This bladder is
called the germ-bladder (vesicula blastodermica). Its wall is at first
composed of merely equi-formal cells. But soon, at one point on the
wall, arises a disc-shaped thickening, as the cells here increase
rapidly, and this thickening is now the foundation of the actual body of
the germ or embryo, while the other parts of the germ-bladder serve only
for its nutrition. The thickened disc, or foundation of the embryo, soon
assumes an oblong, and then a fiddle-shaped form, in consequence of its
right and left walls becoming convex (Fig. 7, p. 304). At this stage of
development in the first form of their germ or embryo, not only all
mammals, including man, but even all vertebrate animals in
general—birds, reptiles, amphibious animals, and fishes—can either not
be distinguished from one another at all, or only by very unessential
differences, such as the arrangement of the egg-coverings. In all the
whole body consists of nothing but a quite simple, oblong, oval, or
violin-shaped thin disc, which is composed of three closely connected
membranes or plates, lying one above another. Each of the three plates
or layers of the germ consists simply of cells all exactly like one
another; but each layer has a different function in the building up of
the vertebrate animal body. Out of the upper or outer germ-layer arises
solely the outer skin (epidermis), together with the central parts of
the nervous system (spinal marrow and brain); out of the lower or inner
layer arises only the inner delicate skin (epithelium) which lines the
whole intestinal tube from the mouth to the anus, together with all the
glands connected with it (lung, liver, salivary glands, etc.); out of
the middle germ-layer lying between the two others arise all the other
organs, muscles, bones, blood-vessels. Now, the processes by which the
various and exceedingly complicated parts of the fully-formed body of
vertebrate animals arise out of such simple material—out of the three
germ-layers composed only of cells—are, in the first place, the
repeated division, and consequently the increase of cells; in the second
place, the division of labour or differentiation of these cells; and
thirdly, the union of the variously developed or differentiated cells,
for the formation of the different organs. Thus arises the gradual
progress or perfecting which can be traced step by step in the
development of the embryonic body. The simple embryonic cells, which are
to constitute the body of the vertebrate animal, stand in the same
relation to each other as citizens who wish to found a state. Some take
to one occupation, others to another, and work together for the good of
the whole. By this division of labour, or differentiation, and the
perfecting (the organic progress) which is connected with it, it becomes
possible for the whole state to accomplish undertakings which would have
been impossible to the single individual. The whole body of the
vertebrate animal, like every other many-celled organism, is a
republican state of cells, and consequently it can accomplish organic
functions which the individual cell, as a solitary individual (for
example, an Amœba, or a single-celled plant), could never perform.

No sensible person supposes that carefully devised institutions, which
have been established for the good of the whole, as well as for the
individual, in every human state, are the results of the action of a
personal and supernatural Creator, acting for a definite purpose. On the
contrary, every one knows that these useful institutions of organization
in the state are the consequences of the co-operation of the individual
citizens and their common government, as well as of adaptation to the
conditions of existence of the outer world. Just in the same way we must
judge of the many-celled organism. In it also all the useful
arrangements are solely the natural and necessary result of the
co-operation, differentiation, and perfecting of the individual
citizens—the cells—and by no means the artificial arrangements of a
Creator acting for a definite purpose. If we rightly consider this
comparison, and pursue it further, we can distinctly see the perversity
of that dualistic conception of nature which discovers the action of a
creative plan of construction in the various adaptations of the
organization of living things.

Let us pursue the individual development of the vertebrate animal body a
few stages further, and see what is next done by the citizens of this
embryonic organism. In the central line of the violin-shaped disc, which
is composed of the three cellular germ-layers, there arises a straight
delicate furrow, the so-called “primitive streak,” by which the
violin-shaped body is divided into two equal lateral halves—a right and
a left part or “antimer.” On both sides of that streak or furrow, the
upper or external germ-layer rises in the form of a longitudinal fold,
and both folds then grow together over the furrow in the central line,
and thus form a cylindrical tube. This tube is called the marrow-tube,
or medullary canal, because it is the foundation of the central nervous
system, the _spinal marrow_ (medulla spinalis). At first it is pointed
both in front and behind, and it remains so for life in the lowest
vertebrate animal, the brainless, skull-less Lancelet (Amphioxus). But
in all other vertebrate animals, which we distinguish from the latter as
skulled animals, or Craniota, a difference between the fore and hinder
end of the marrow tube soon becomes visible, the fore end becoming
dilated, and changing into a roundish bladder, the foundation of the
_brain_.

In all Craniota, that is, in all vertebrate animals possessing skull and
brain, the brain, which is at first only the bladder-shaped dilatation
of the anterior end of the spinal marrow, divides into five bladders
lying one behind the other, four superficial, transverse in-nippings
being formed. These _five brain-bladders_, out of which afterwards arise
all the different parts of the intricately constructed brain, can be
seen in their original condition in the embryo represented in Fig. 7. It
is just the same whether we examine the embryo of a dog, a fowl, a
lizard, or any other higher vertebrate animal. For the embryos of the
different skulled animals (at least the three higher classes of them,
the reptiles, birds and mammals) cannot be in any way distinguished at
the stage represented in Fig. 7. The whole form of the body is as yet
exceedingly simple, being merely a thin, leaf-like disc. Face, legs,
intestines, etc., are as yet completely wanting. But the five bladders
are already quite distinct from one another.

[Illustration: FIG. 7.—Embryo of a mammal or bird, in which the five
brain-bladders have just commenced to develop. _v._ Fore brain. _z._
Twixt brain. _m._ Mid brain. _h._ Hind brain. _n._ After brain. _p._
Spinal-marrow. _a._ Eye-bladders. _w._ Primitive vertebræ. _d._
Spinal-axis or notochord.]

The _first_ bladder, the _fore brain_ (_a_), is in so far the most
important that it principally forms the hemispheres of the so-called
larger brain (cerebrum), that part which is the seat of the higher
mental activities. The more these activities are developed in the series
of vertebrate animals, the more do the two lateral halves of the fore
brain, or the hemispheres, grow at the expense of the other bladders,
and overlap them in front and from above. In man, where they are most
strongly developed, agreeing with his higher mental activity, they
eventually almost entirely cover the other parts from above (compare
Plates II. and III.) The _second_ bladder, the _twixt brain_ (_z_),
forms that portion of the brain which is called the _centre of sight_,
and stands in the closest relation to the eyes (_a_), which grow right
and left out of the fore brain in the shape of two bladders, and later
lie at the bottom of the twixt brain. The _third_ bladder, the _mid
brain_ (_m_), for the most part vanishes in the formation of the
so-called _four bulbs_, a bossy portion of the brain, which is strongly
developed in reptiles and birds (Fig. _E_, _F_, Plate II.), whereas in
mammals it recedes much more (Fig. _G_, _H_, Plate III.). The _fourth_
bladder, the _hind brain_ (_h_), forms the so-called _little
hemispheres_, together with the middle part of the _small brain_
(cerebellum), a part of the brain as to the function of which the most
contradictory conjectures are entertained, but which seems principally
to regulate the co-ordination of movements. Lastly, the _fifth_ bladder,
the _after brain_ (_n_), develops into that very important part of the
central nervous system which is called the _prolonged marrow_ (medulla
oblongata). It is the central organ of the respiratory movements, and of
other important functions, and an injury to it immediately causes death,
whereas the large hemispheres of the fore brain (or the organ of the
“soul,” in a restricted sense) can be removed bit by bit, and even
completely destroyed, without causing the death of the vertebrate
animal—only its higher mental activities disappearing in consequence.

These five brain bladders, in all vertebrate animals which possess a
brain at all, are originally arranged in the same manner and develop
gradually in the different groups so differently, that it is afterwards
very difficult to recognize the corresponding parts in the
fully-developed brains. In the early stage of development which is
represented in Fig. 7, it seems as yet quite impossible to distinguish
the embryos of the different mammals, birds, and reptiles, from one
another. But if we compare the much more developed embryos on Plates II.
and III. with one another, we can clearly see an inequality in their
development, and especially it will be perceived that the brain of the
two mammals (_G_ and _H_) already strongly differ from that of birds
(_F_) and of reptiles (_E_). In the two latter the mid brain
predominates, but in the former the fore brain. Even at this stage the
brain of the bird (_F_) is scarcely distinguishable from that of the
tortoise (_E_), and in like manner the brain of the dog (_G_) is as yet
almost the same as that of man (_H_). If, on the other hand, we compare
the brains of these four vertebrate animals in a fully developed
condition, we find them so very different in all anatomical particulars,
that we cannot doubt for a moment as to which animal each brain belongs.

I have here explained the original equality, the gradual commencement,
and the ever increasing separation or differentiation of the embryos in
the different vertebrate animals, taking the brain as a special example,
just because this organ of the soul’s activity is of special interest.
But I might as well have discussed in its stead the heart, or the liver,
or the limbs, in short, any other part of the body, since the same
wonder of creation is here ever repeated, namely, this, that all parts
are originally the same in the different vertebrate animals, and that
the variations by which the different classes, orders, families, genera,
etc., differ and deviate from one another, are only gradually developed.

There are certainly few parts of the body which are so differently
constructed as the _limbs or extremities_ of the vertebrate animals.
Now, I wish the reader to compare in Fig. _A-H_ on Plates II. and III.,
the four extremities (_bv_) of the embryos with one another, and he will
scarcely be able to perceive any important differences between the human
arm (_H bv_), the wing of a bird (_F bv_), the slim foreleg of a dog (_G
bv_), and the plump foreleg of the tortoise (_E bv_). In comparing the
hinder extremities (_bh_) in these figures he will find it equally
difficult to distinguish the leg of a man (_H bh_), of a bird (_F bh_),
the hind-leg of a dog (_G bh_), and that of a tortoise (_E bh_). The
fore as well as the hinder extremities are as yet short, broad
lumps, at the ends of which the foundations of the five toes are placed,
connected as yet by a membrane. At a still earlier stage (Fig. _A-D_)
the five toes are not marked out at all, and it is quite impossible to
distinguish even the fore and hinder extremities from one another. The
latter, as well as the former, are nothing but simple roundish
processes, which have grown out of the side of the trunk. At the very
early stage represented in Fig. 7 they are completely wanting, and the
whole embryo is a simple trunk without a trace of limbs.

[Illustration: Pl. II. Germs or Embryos of four Vertebrates.

_v._ Fore-brain. _z._ Twixt-brain. _m._ Mid-brain. _h._ Hind-brain. _n._
After-brain. _w._ Spine. _r._ Spinal-cord.]

[Illustration: Pl. III. Germs or Embryos of four Vertebrates.

_na._ Nose. _a._ Eyes. _o._ Ear. _k{1} k{2} k{3}._ Gill-arches.
_s._ Tail. _bv._ Fore-leg. _bh._ Hind-leg.]

I wish especially to draw attention in Plates II. and III., which
represents embryos in early stages of development (Fig. _A-D_)—and in
which we are not able to recognize a trace of the full-grown animal—to
an exceedingly important formation, which originally is common to all
vertebrate animals, but which at a later period is transformed into the
most different organs. Every one surely knows the _gill-arches_ of fish,
those arched bones which lie behind one another, to the number of three
or four, on each side of the neck, and which support the gills, the
respiratory organs of the fish (double rows of red leaves, which are
popularly called “fishes’ ears.”) Now, these gill-arches originally
exist exactly the same in man (_D_), in dogs (_C_), in fowls (_B_), and
in tortoises (_A_), as well as in all other vertebrate animals. (In Fig.
_A-D_ the three gill-arches of the right side of the neck are marked
_k{1} k{2} k{3}_). Now, it is only in fishes that these remain in
their original form, and develop into respiratory organs. In the other
vertebrate animals they are partly employed in the formation of the face
(especially the jaw apparatus), and partly in the formation of the organ
of hearing.

Finally, when comparing the embryos on Plates II. and III., we must not
fail to give attention again to the _human tail_ (_s_), an organ which,
in the original condition, man shares with all other vertebrate animals.
The discovery of tailed men was long anxiously expected by many monistic
philosophers, in order to establish a closer relationship between man
and the other mammals. And in like manner their dualistic opponents
often maintained with pride that the complete want of a tail formed one
of the most important bodily distinctions between men and animals,
though they did not bear in mind the many tailless animals which really
exist. Now, man in the first months of development possesses a real tail
as well as his nearest kindred, the tailless apes (orang-outang,
chimpanzee, gorilla), and vertebrate animals in general. But whereas, in
most of them—for example, the dog (_C_, _G_)—in the course of
development it always grows longer, in man (Fig. _D_, _H_) and in
tailless mammals, at a certain period of development, it degenerates and
finally completely disappears. However, even in fully developed men, the
remnant of the tail is seen in the three, four, or five tail vertebræ
(vertebræ coccygeæ) as an aborted or rudimentary organ, which forms the
hinder or lower end of the vertebral column (p. 289).

Most persons even now refuse to acknowledge the most important deduction
of the Theory of Descent, that is, the palæontological development of
man from ape-like, and through them from still lower, mammals, and
consider such a transformation of organic form as impossible. But, I
ask, are the phenomena of the individual development of man, the
fundamental features of which I have here given, in any way less
wonderful? Is it not in the highest degree remarkable that all
vertebrate animals of the most different classes—fishes, amphibious
animals, reptiles, birds, and mammals—in the first periods of their
embryonic development cannot be distinguished at all, and even much
later, at a time when reptiles and birds are already distinctly
different from mammals, that the dog and the man are almost identical?
Verily, if we compare those two series of development with one another,
and ask ourselves which of the two is the more wonderful, it must be
confessed that _ontogeny_, or the short and quick history of development
of the _individual_, is much more mysterious than _phylogeny_, or the
long and slow history of development of the _tribe_. For one and the
same grand change of form is accomplished by the latter in the course of
many thousands of years, and by the former in the course of a few
months. Evidently this most rapid and astonishing transformation of the
individual in ontogenesis, which we can actually point out at any moment
by direct observation, is in itself much more wonderful and astonishing
than the corresponding, but much slower and gradual transformation which
the long chain of ancestors of the same individual has gone through in
phylogenesis.

The two series of organic development, the ontogenesis of the individual
and the phylogenesis of the tribe to which it belongs, stand in the
closest causal connection with each other. I have endeavoured, in the
second volume of the “General Morphology,”(4) to establish this theory
in detail, as I consider it exceedingly important. As I have there
shown, _ontogenesis, or the development of the individual, is a short
and quick repetition_ (recapitulation) _of phylogenesis, or the
development of the tribe to which it belongs, determined by the laws of
inheritance and adaptation_; by tribe I mean the ancestors which form
the chain of progenitors of the individual concerned. (Gen. Morph. ii.
110-147, 371.)

In this intimate connection of ontogeny and phylogeny, I see one of the
most important and irrefutable proofs of the Theory of Descent. No one
can explain these phenomena unless he has recourse to the laws of
Inheritance and Adaptation; by these alone are they explicable. These
laws, which we have previously explained, are _the laws of abbreviated,
of homochronic, and of homotopic inheritance_, and here deserve renewed
consideration. As so high and complicated an organism as that of man, or
the organism of every other mammal, rises upwards from a simple cellular
state, and as it progresses in its differentiation and perfecting it
passes through the same series of transformations which its animal
progenitors have passed through, during immense spaces of time,
inconceivable ages ago. I have already pointed out this extremely
important parallelism of the development of individuals and tribes (p.
10). Certain very early and low stages in the development of man, and
the other vertebrate animals in general, correspond completely in many
points of structure with conditions which last for life in the lower
fishes. The next phase which follows upon this presents us with a change
of the fish-like being into a kind of amphibious animal. At a later
period the mammal, with its special characteristics, develops out of the
amphibian, and we can clearly see, in the successive stages of its later
development, a series of steps of progressive transformation which
evidently correspond with the differences of different mammalian orders
and families. Now, it is precisely in the same succession that we also
see the ancestors of man, and of the higher mammals, appear one after
the other in the earth’s history; first fishes, then amphibians, later
the lower, and at last the higher mammals. Here, therefore, the
embryonic development of the individual is completely parallel to the
palæontological development of the whole tribe to which it belongs, and
this exceedingly interesting and important phenomenon can be explained
only by the interaction of the laws of Inheritance and Adaptation.

The example last mentioned, of the parallelism of the palæontological
and of the individual developmental series, now directs our attention to
a third developmental series, which stands in the closest relations to
these two, and which likewise runs, on the whole, parallel to them. I
mean that series of development of forms which constitutes the object of
investigation in _comparative anatomy_, and which I will briefly call
the _systematic developmental series of species_. By this we understand
the chain of the different, but related and connected forms, which exist
_side by side_ at any one period of the earth’s history; as for example,
at the present moment. While comparative anatomy compares the different
forms of fully-developed organisms with one another, it endeavours to
discover the common prototypes which underlie, as it were, the manifold
forms of kindred genera, classes, etc., and which are more or less
concealed by their particular differentiation. It endeavours to make out
the series of progressive steps which are indicated in the different
degrees of perfection of the divergent branches of the tribe. To make
use again of the same particular instance, comparative anatomy shows us
how the individual organs and systems of organs in the tribe of
vertebrate animals—in the different classes, families, and species of
it—have unequally developed, differentiated, and perfected themselves.
It shows us how far the succession of classes of vertebrate animals,
from the Fishes upwards, through the Amphibia to the Mammals, and here
again, from the lower to the higher orders of Mammals, forms a
progressive series or ladder. This attempt to establish a connected
anatomical developmental series we may discover in the works of the
great comparative anatomists of all ages—in the works of Goethe,
Meckel, Cuvier, Johannes Müller, Gegenbaur, and Huxley.

The developmental series of mature forms, which comparative anatomy
points out in the different diverging and ascending steps of the organic
system, and which we call the systematic developmental series, is
parallel to the palæontological developmental series, because it deals
with the _result_ of palæontological development, and it is parallel to
the individual developmental series, because this is parallel to the
palæontological series. If two parallels are parallel to a third, they
must be parallel to one another.

The varied differentiation, and the unequal degree of perfecting which
comparative anatomy points out in the developmental series of the
System, is chiefly determined by the ever increasing variety of
conditions of existence to which the different groups adapt themselves
in the struggle for life, and by the different degrees of rapidity and
completeness with which this adaptation has been effected. Conservative
groups which have retained their inherited peculiarities most
tenaciously remain, in consequence, at the lowest and rudest stage of
development. Those groups progressing most rapidly and variously, and
which have adapted themselves to changed conditions of existence most
readily have attained the highest degree of perfection. The further the
organic world developed in the course of the earth’s history, the
greater must the gap between the lower conservative and the higher
progressive groups have become, as in fact may be seen too in the
history of nations. In this way also is explained the historical fact,
that the most perfect animal and vegetable groups have developed
themselves in a comparatively short time to a considerable height, while
the lowest or most conservative groups have remained stationary
throughout all ages in their original simple stage, or have progressed,
but very slowly and gradually. The series of man’s progenitors clearly
shows this state of things. The sharks of the present day are still very
like the primary fish, which are among the most ancient vertebrate
progenitors of man, and the lowest amphibians of the present day (the
gilled salamanders and salamanders) are very like the amphibians which
first developed themselves out of fishes. So, too, the later ancestors
of man, the Monotremata and Marsupials, the most ancient mammals, are at
the same time the most imperfect animals of the class which still exist.

The laws of inheritance and adaptation known to us are completely
sufficient to explain this exceedingly important and interesting
phenomenon, which may be briefly designated as the _parallelism of
individual, of palæontological, and of systematic development_. No
opponent of the Theory of Descent has been able to give an explanation
of this extremely wonderful fact, whereas it is perfectly explained,
according to the Theory of Descent, by the laws of Inheritance and
Adaptation.

If we examine this parallelism of the three organic series of
development more accurately, we have to add the following special
qualifications. _Ontogeny_, or the history of the individual development
of every organism (embryology and metamorphology), presents us with a
simple _unbranching_ or graduated chain of forms; and so it is with that
_portion of phylogeny_ which comprises the palæontological history of
development of the _direct ancestors only_ of an individual organism.
But _the whole of phylogeny_—which meets us in the _natural system_ of
every organic tribe or phylum, and which is concerned with the
investigation of the palæontological development _of all_ the branches
of this tribe—forms a _branching_ or tree-shaped developmental series,
a veritable pedigree. If we examine and compare the branches of this
pedigree, and place them together according to the degree of their
differentiation and perfection, we obtain the tree-shaped, branching,
_systematic developmental series of comparative anatomy_. Strictly
speaking, therefore, the latter is parallel to _the whole of phylogeny_,
and consequently is only partially parallel to ontogeny; for ontogeny
itself is parallel only to _a portion_ of phylogeny.

All the phenomena of organic development above discussed, especially the
threefold genealogical parallelism, and the laws of differentiation and
progress, which are evident in each of these three series of organic
development, and, further, the whole history of rudimentary organs, are
exceedingly important proofs of the truth of the Theory of Descent. For
by it alone can they be explained, whereas its opponents cannot even
offer a shadow of an explanation of them. Without the Doctrine of
Filiation, the fact of organic development in general cannot be
understood. We should therefore, for this reason alone, be forced to
accept Lamarck’s Theory of Descent, even if we did not possess Darwin’s
Theory of Selection.

CHAPTER XIII.

THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE EARTH. SPONTANEOUS
GENERATION. THE CARBON THEORY. THE PLASTID THEORY.

History of the Development of the Earth.—Kant’s Theory
of the Development of the Universe, or the Cosmological
Gas Theory.—Development of Suns, Planets, and
Moons.—First Origin of Water.—Comparison of Organisms
and Anorgana.—Organic and Inorganic Substances.—Degrees
of Density, or Conditions of Aggregation.—Albuminous
Combinations of Carbon.—Organic and Inorganic
Forms.—Crystals and Formless Organisms without
Organs.—Stereometrical Fundamental Forms of Crystals and
of Organisms.—Organic and Inorganic Forces.—Vital
Force.—Growth and Adaptation in Crystals and in
Organisms.—Formative Tendencies of Crystals.—Unity of
Organic and Inorganic Nature.—Spontaneous Generation, or
Archigony.—Autogony and Plasmogony.—Origin of Monera by
Spontaneous Generation.—Origin of Cells from
Monera.—The Cell Theory.—The Plastid Theory.—Plastids,
or Structural Units.—Cytods and Cells.—Four Different
Kinds of Plastids.

In our considerations hitherto we have endeavoured to answer the
question, “By what causes have new species of animals and plants arisen
out of existing species?” We have answered this question according to
Darwin’s theory, that natural selection in the struggle for
existence—that is, the interaction of the laws of Inheritance and
Adaptation—is completely sufficient for producing mechanically the
endless variety of the different animals and plants, which have the
appearance of being organized according to a plan for a definite
purpose. Meanwhile the question must have already repeatedly presented
itself to the reader, how did the first organisms, or that one original
and primæval organism arise, from which we derive all the others?

This question Lamarck(2) answered by the hypothesis of _spontaneous
generation_, or _archigony_. But Darwin passes over and avoids this
subject, as he expressly remarks that he has “nothing to do with the
origin of the soul, nor with that of life itself.” At the conclusion of
his work he expresses himself more distinctly in the following
words:—“I imagine that probably all organic beings which ever lived on
this earth descended from some primitive form, which was first called
into life by the Creator.” Moreover, Darwin, for the consolation of
those who see in the Theory of Descent the destruction of the whole
“moral order of the universe,” appeals to the celebrated author and
divine who wrote to him, that “he has gradually learnt to see that it is
just as noble a conception of the Deity to believe that he created a few
original forms capable of self-development into other and needful forms,
as to believe that he required a fresh act of creation to supply the
voids caused by the action of his laws.”

Those to whom the belief in a supernatural creation is an emotional
necessity may rest satisfied with this conception. They may reconcile
that belief with the Theory of Descent; for in the creation of a single
original organism possessing the capability to develop all others out of
itself by inheritance and adaptation, they can really find much more
cause for admiring the power and wisdom of the Creator than in the
independent creation of different species.

If, taking this point of view, we were to explain the origin of the
first terrestrial organisms, from which all the others are descended, as
due to the action of a personal Creator acting according to a definite
plan, we should of course have to renounce all scientific knowledge of
the process, and pass from the domain of true science to the completely
distinct domain of poetical faith. By assuming a supernatural act of
creation we should be taking a leap into the inconceivable. Before we
decide upon this latter step, and thereby renounce all pretension to a
scientific knowledge of the process, we are at all events in duty bound
to endeavour to examine it in the light of a mechanical hypothesis. We
must at least examine whether this process is really so wonderful, and
whether we cannot form a tenable conception of a completely
non-miraculous origin of the first primary organism. We might then be
able entirely to reject miracle in creation.

It will be necessary for this purpose, first of all, to go back further
into the past, and to examine the history of the creation of the earth.
Going back still further, we shall find it necessary to consider the
history of the creation of the whole universe in its most general
outlines. All my readers undoubtedly know that from the structure of the
earth, as it is at present known to us, the notion has been derived, and
as yet has not been refuted, that its interior is in a fiery fluid
condition, and that the firm crust, composed of different strata, on the
surface of which organisms are living, forms only a very thin pellicle
or shell round the fiery fluid centre. We have arrived at this idea by
different confirmatory experiments and reasonings. In the first place,
the observation that the temperature of the earth’s crust continually
increases towards the centre is in favour of this supposition. The
deeper we descend, the greater the warmth of the ground, and in such
proportion, that with every 100 feet the temperature increases about one
degree. At a depth of six miles, therefore, a heat of 1500° would be
attained, sufficient to keep most of the firm substances of our earth’s
crust in a molten, fiery, fluid state. This depth, however, is only the
286th part of the whole diameter of the earth (1717 miles). We further
know that springs which rise out of a considerable depth possess a very
high temperature, and sometimes even throw water up to the surface in a
boiling state. Lastly, very important proofs are furnished by volcanic
phenomena, the eruption of fiery fluid masses of stone bursting through
certain parts of the earth’s crust. All these phenomena lead us with
great certainty to the important assumption that the firm crust of the
earth forms only quite a small fraction, not nearly the one-thousandth
part of the whole diameter of the terrestrial globe, and that the rest
is still for the most part in a molten or fiery fluid state.

Now if, starting with this assumption, we reflect on the ancient history
of the development of the globe, we are logically carried back a step
further, namely, to the assumption that at an earlier date the whole
earth was a fiery fluid body, and that the formation of a thin,
stiffened crust on the surface was only a later process. Only gradually,
by radiating its intrinsic heat into the cold space of the universe, has
the surface of the glowing ball become condensed into a thin crust.
That the temperature of the earth in remote times was much higher than
it is now, is proved by many phenomena. Among other things, this is
rendered probable by the equal distribution of organisms in remote times
of the earth’s history. While at present, as is well known, the
different populations of animals and plants correspond to the different
zones of the earth and their appropriate temperature, in earlier times
this was distinctly not the case.

We see from the distribution of fossils in the remoter ages, that it was
only at a very late date, in fact, at a comparatively recent period of
the organic history of the earth (at the beginning of the so-called
cænolithic or tertiary period), that a separation of zones and of the
corresponding organic populations occurred. During the immensely long
primary and secondary periods, tropical plants, which require a very
high degree of temperature, lived not only in the present torrid zone,
under the equator, but also in the present temperate and frigid zones.
Many other phenomena also demonstrate a gradual decrease of the
temperature of the globe as a whole, and especially a late and gradual
cooling of the earth’s crust about the poles. Bronn, in his excellent
“Investigations of the Laws of Development of the Organic World,” has
collected numerous geological and palæontological proofs of this fact.

These phenomena and the mathematico-astronomical knowledge of the
structure of the universe justify the theory that, inconceivable ages
ago, long before the first existence of organisms, the whole earth was a
fiery fluid globe. Now, this theory corresponds with the grand theory of
the origin of the universe, and especially of our planetary system,
which, on the ground of mathematical and astronomical facts, was put
forward in 1755 by our critical philosopher Kant,(22) and was later more
thoroughly established by the celebrated mathematicians, Laplace and
Herschel. This cosmogeny, or theory of the development of the universe,
is now almost universally acknowledged; it has not been replaced by a
better one, and mathematicians, astronomers, and geologists have
continually, by various arguments, strengthened its position.

Kant’s cosmogeny maintains that _the whole universe, inconceivable ages
ago, consisted of a gaseous chaos_. All the substances which are found
at present separated on the earth, and other bodies of the universe, in
different conditions of density—in the solid, semi-fluid, liquid, and
elastic fluid or gaseous states of aggregation—originally constituted
together one single homogeneous mass, equally filling up the space of
the universe, which, in consequence of an extremely high degree of
temperature, was in an exceedingly thin gaseous or nebulous state. The
millions of bodies in the universe which at present form the different
solar systems did not then exist. They originated only in consequence of
a universal rotatory movement, or rotation, during which a number of
masses acquired greater density than the remaining gaseous mass, and
then acted upon the latter as central points of attraction. Thus arose a
separation of the chaotic primary nebula, or gaseous universe, into a
number of rotating nebulous spheres, which became more and more
condensed. Our solar system was such a gigantic gaseous or nebulous
ball, all the particles of which revolved round a common central point,
the solar nucleus. The nebulous ball itself, like all the rest, in
consequence of its rotatory movement, assumed a spheroidal or a
flattened globular form.

While the centripetal force attracted the rotating particles nearer and
nearer to the firm central point of the nebulous ball, and thus
condensed the latter more and more, the centrifugal force, on the other
hand, always tended to separate the peripheral particles further and
further from it, and to hurl them off. On the equatorial sides of the
ball, which was flattened at both poles, this centrifugal force was
strongest, and as soon as, by increase of density, it attained
predominance over the centripetal force, a circular nebulous ring
separated itself from the rotating ball. This nebulous ring marked the
course of future planets. The nebulous mass of the ring gradually
condensed, and became a planet, which revolved round its own axis, and
at the same time rotated round the central body. In precisely the same
manner, from the equator of the planetary mass, as soon as the
centrifugal force gained predominance over the centripetal force, new
nebulous rings were ejected, which moved round the planets as the latter
moved round the sun. These nebulous rings, too, became condensed into
rotating balls. Thus arose the moons, only one of which moves round our
earth, whilst four move round Jupiter, and six round Uranus. The ring of
Saturn still shows us a moon in its early stage of development. As by
increasing refrigeration these simple processes of condensation and
expulsion repeated themselves over and over again, there arose the
different solar systems, the planets rotating round their central suns,
and the satellites or moons moving round their planets.

The original gaseous condition of the rotating bodies of the universe
gradually changed, by increasing refrigeration and condensation, into
the fiery fluid or molten state of aggregation. By the process of
condensation, a great quantity of heat was emitted, and the rotating
suns, planets, and moons, soon changed into glowing balls of fire, like
gigantic drops of melted metal, which emitted light and heat. By loss of
heat, the melted mass on the surface of the fiery fluid ball became
further condensed, and thus arose a thin, firm crust, which enclosed a
fiery fluid nucleus. In all essential respects our mother earth probably
did not differ from the other bodies of the universe.

In view of the object of these pages, it will not be of especial
interest to follow in detail the _history of the natural creation of the
universe_, with its different solar and planetary systems, and to
establish it mathematically by the different astronomical and geological
proofs. The outlines of it, which I have just mentioned, must be
sufficient here, and for further details I refer to Kant’s[5] “General
History of Nature and Theory of the Heavens.”(22) I will only add that
this wonderful theory, which might be called _the cosmological gas
theory_, harmonizes with all the general series of phenomena at present
known to us, and stands in no irreconcilable contradiction to any one of
them. Moreover, it is purely mechanical or monistic, makes use
exclusively of the inherent forces of eternal matter, and entirely
excludes every supernatural process, every prearranged and conscious
action of a personal Creator. Kant’s Cosmological Gas Theory
consequently occupies a similar supreme position in _Anorganology_,
especially in _Geology_, and forms the crown of our knowledge in that
department, in the same way as Lamarck’s Theory of Descent does in
_Biology_, and especially in _Anthropology_. Both rest exclusively upon
mechanical or unconscious causes (causæ efficientes), in no case upon
prearranged or conscious causes (causæ finales). (Compare above, p.
100-106.) Both therefore fulfil all the demands of a scientific theory,
and consequently will remain generally acknowledged until they are
replaced by better ones.

I will, however, not deny that Kant’s grand cosmogeny has some weak
points, which prevent our placing the same unconditional confidence in
it as in Lamarck’s Theory of Descent. The notion of an original gaseous
chaos filling the whole universe presents great difficulties of various
kinds. A great and unsolved difficulty lies in the fact that the
Cosmological Gas Theory furnishes no starting-point at all in
explanation of the first impulse which caused the rotary motion in the
gas-filled universe. In seeking for such an impulse, we are
involuntarily led to the mistaken questioning about a “first beginning.”
We can as little imagine a _first beginning_ of the eternal phenomena of
the motion of the universe as of its final end.

The universe is unlimited and immeasurable in both space and time. It is
eternal, and it is infinite. Nor can we imagine a beginning or end to
the uninterrupted and eternal motion in which all particles of the
universe are always engaged. The great laws of the _conservation of
force_(38) and the _conservation of matter_, the foundations of our
whole conception of nature, admit of no other supposition. The universe,
as far as it is cognisable to human capability, appears as a connected
chain of material phenomena of motion, necessitating a continual change
of forms. Every form, as the temporary result of a multiplicity of
phenomena of motion, is as such perishable, and of limited duration.
But, in the continual change of forms, matter and the motion inseparable
from it remain eternal and indestructible.

Now, although Kant’s Cosmological Gas Theory is not able to explain the
development of motion in the whole universe in a satisfactory manner,
beyond that gaseous state of chaos, and although many other weighty
considerations may be brought forward against it, especially by
chemistry and geology, yet we must on the whole acknowledge its great
merit, inasmuch as it explains in an excellent manner, by due
consideration of development, the whole structure of all that is
accessible to our observation, that is, the anatomy of the solar
systems, and especially of our planetary system. It may be that this
development was altogether different from what Kant supposes, and our
earth may have arisen by the aggregation of numberless small meteorides,
scattered in space, or in any other manner, but hitherto no one has as
yet been able to establish any other theory of development, or to offer
one in the place of Kant’s cosmogeny.

After this general glance at the monistic cosmogeny, or the
non-miraculous history of the development of the universe, let us now
return to a minute fraction of it, to our mother earth, which we left as
a ball flattened at both poles and in a fiery fluid state, its surface
having condensed by becoming cooled into a very thin firm crust. The
crust, on first cooling, must have covered the whole surface of the
terrestrial sphere as a continuous smooth and thin shell. But soon it
must have become uneven and hummocky; for, since during the continued
cooling, the fiery fluid nucleus became more and more condensed and
contracted, and consequently the diameter of the earth diminished, the
thin cold crust, which could not closely follow the softer nuclear mass,
must have fallen in, in many places. An empty space would have arisen
between the two, had not the pressure of the outer atmosphere forced
down the fragile crust towards the interior, breaking it in so doing.
Other unevennesses probably arose from the fact that, in different
parts, the cooled crust during the process of refrigeration contracted
also itself, and thus became fissured with cracks and rents. The fiery
fluid nucleus flowed up to the external surface through these cracks,
and again became cooled and stiff. Thus, even at an early period there
arose many elevations and depressions, which were the first foundations
of mountains and valleys.

After the temperature of the cooled terrestrial ball had fallen to a
certain degree, a very important new process was effected, namely, the
_first origin of water_. Water had until then existed only in the form
of steam in the atmosphere surrounding the globe. The water could
evidently not condense into a state of fluid drops until the temperature
of the atmosphere had considerably decreased. Now, then, there began a
further transformation of the earth’s crust by the force of water. It
continually fell in the form of rain, and in that form washed down the
elevations of the earth’s crust, filling the depressions with the mud
carried along, and, by depositing it in layers, it caused the extremely
important neptunic transformations of the earth’s crust, which have
continued since then uninterruptedly, and which in our next chapter we
shall examine a little more closely.

It was not till the earth’s crust had so far cooled that the water had
condensed into a fluid form, it was not till the hitherto dry crust of
the earth had for the first time become covered with liquid water, that
the origin of the first organisms could take place. For all animals and
all plants—in fact, all organisms—consist in great measure of fluid
water, which combines in a peculiar manner with other substances, and
brings them into a semi-fluid state of aggregation. We can therefore,
from these general outlines of the inorganic history of the earth’s
crust, deduce the important fact, that at a certain definite time life
had its beginning on earth, and that terrestrial organisms did not exist
from eternity, but at a certain period came into existence for the first
time.

Now, how are we to conceive of this origin of the first organisms? This
is the point at which most naturalists, even at the present day, are
inclined to give up the attempt at natural explanation, and take refuge
in the miracle of an inconceivable creation. In doing so, as has already
been remarked, they quit the domain of scientific knowledge, and
renounce all further insight into the eternal laws which have determined
nature’s history. But before despondingly taking such a step, and before
we despair of the possibility of any knowledge of this important
process, we may at least make an attempt to understand it. Let us see if
in reality the origin of a first organism out of inorganic matter, the
origin of a living body out of lifeless matter, is so utterly
inconceivable and beyond all experience. In one word, let us examine the
question of _spontaneous generation, or archigony_. In so doing, it is
above all things necessary to form a clear idea of the principal
properties of the two chief groups of natural bodies, the so-called
inanimate or inorganic, and the animate or organic bodies, and then
establish what is common to, and what are the differences between, the
two groups. It is desirable to go somewhat carefully into the
_comparison of organisms and anorgana_, since it is commonly very much
neglected, although it is necessary for a right understanding of nature
from the monistic point of view. It will be most advantageous here to
look separately at the three fundamental properties of every natural
body; these are matter, form, and force. Let us begin with _matter_.
(Gen. Morph. iii.)

By chemistry we have succeeded in analysing all bodies known to us into
a small number of elements or simple substances, which cannot be further
divided, for example, carbon, oxygen, nitrogen, sulphur, and the
different metals: potassium, sodium, iron, gold, etc. At present we know
about seventy such elements or simple substances. The majority of them
are unimportant and rare; the minority only are widely distributed, and
compose not only most of the anorgana, but also all organisms. If we
compare those elements which constitute the body of organisms with those
which are met with in anorgana, we have first to note the highly
important fact that in animal and vegetable bodies no element occurs but
what can be found outside of them in inanimate nature. There are no
special organic elements or simple organic substances.

The chemical and physical differences existing between organisms and
anorgana, consequently, do not lie in their material foundation; they do
not arise from the different nature of the _elements_ composing them,
but from the different manner in which the latter are united by
chemical _combination_. This different manner of combination gives rise
to certain physical peculiarities, especially in density of substance,
which at first sight seems to constitute a deep chasm between the two
groups of bodies. Inorganic or inanimate natural bodies, such as
crystals and the amorphous rocks, are in a state of density which we
call the firm or solid state, and which we oppose to the liquid state of
water and to the gaseous state of air. It is familiar to every one that
these three different degrees of density, or states of aggregation of
anorgana, are by no means peculiar to the different elements, but are
the results of a certain degree of temperature. Every inorganic solid
body, by increase of temperature, can be reduced to the liquid or melted
state, and, by further heat, to the gaseous or elastic state. In the
same way most gaseous bodies, by a proper decrease of temperature can
first be converted into a liquid state, and further, into a solid state
of density.

In opposition to these three states of density of anorgana, the living
body of all organisms—animals as well as plants—is in an altogether
peculiar fourth state of aggregation. It is neither solid like stone,
nor liquid like water, but presents rather a medium between these two
states, which may therefore be designated as the firm-fluid or swollen
state of aggregation (viscid). In all living bodies, without exception,
there is a certain quantity of water combined in a peculiar way with
solid matter, and owing to this characteristic combination of water with
solid matter we have that soft state of aggregation, neither solid nor
liquid, which is of great importance in the mechanical explanation of
the phenomena of life. Its cause lies essentially in the physical and
chemical properties of a simple, indivisible, elementary substance,
namely, _carbon_ (Gen. Morph. i. 122-130).

Of all elements, carbon is to us by far the most important and
interesting, because this simple substance plays the largest part in all
animal and vegetable bodies known to us. It is that element which, by
its peculiar tendency to form complicated combinations with the other
elements, produces the greatest variety of chemical compounds, and among
them the forms and living substance of animal and vegetable bodies.
Carbon is especially distinguished by the fact that it can unite with
the other elements in infinitely manifold relations of number and
weight. By the combination of carbon with three other elements, with
oxygen, hydrogen, and nitrogen (to which generally sulphur, and
frequently, also, phosphorus is added), there arise those exceedingly
important compounds which we have become acquainted with as the first
and most indispensable substratum of all vital phenomena, the albuminous
combinations, or albuminous bodies (protean matter).

We have before this (p. 185) become acquainted with the simplest of all
species of organisms in the Monera, whose entire bodies when completely
developed consist of nothing but a semi-fluid albuminous lump; they are
organisms which are of the utmost importance for the theory of the first
origin of life. But most other organisms, also, at a certain period of
their existence—at least, in the first period of their life—in the
shape of egg-cells or germ-cells, are essentially nothing but simple
little lumps of such albuminous formative matter, known as plasma, or
protoplasma. They then differ from the Monera only by the fact that in
the interior of the albuminous corpuscle the cell-kernel, or nucleus,
has separated itself from the surrounding cell-substance (protoplasma).
As we have already pointed out, the cells, with their simple attributes,
are so many citizens, who by co-operation and differentiation build up
the body of even the most perfect organism; this being, as it were, a
cell republic (p. 301). The fully developed form and the vital phenomena
of such an organism are determined solely by the activities of these
small albuminous corpuscles.

It may be considered as one of the greatest triumphs of recent biology,
especially of the theory of tissues, that we are now able to trace the
wonder of the phenomena of life to these substances, and that we can
demonstrate the _infinitely manifold and complicated physical and
chemical properties of the albuminous bodies to be the real cause of
organic or vital phenomena_. All the different forms of organisms are
simply and directly the result of the combination of the different forms
of cells. The infinitely manifold varieties of form, size, and
combination of the cells have arisen only gradually by the division of
labour, and by the gradual adaptation of the simple homogeneous lumps of
plasma, which originally were the only constituents of the cell-mass.
From this it follows of necessity that the fundamental phenomena of
life—nutrition and generation—in their highest manifestations, as well
as in their simplest expressions, must also be traced to the material
nature of that albuminous formative substance. The other vital
activities are gradually evolved from these two. Thus, then, the general
explanation of life is now no more difficult to us than the explanation
of the physical properties of inorganic bodies. All vital phenomena and
formative processes of organisms are as directly dependent upon the
chemical composition and the physical forces of organic matter as the
vital phenomena of inorganic crystals—that is, the process of _their_
growth and _their_ specific formation—are the direct results of their
chemical composition and of their physical condition. The _ultimate
causes_, it is true, remain in _both_ cases concealed from us. When gold
and copper crystallize in a cubical, bismuth and antimony in a
hexagonal, iodine and sulphur in a rhombic form of crystal, the
occurrence is in reality neither more nor less mysterious to us than is
every elementary process of organic formation, every self-formation of
the organic cell. In this respect we can no longer draw a fundamental
distinction between organisms and anorgana, a distinction of which,
formerly, naturalists were generally convinced.

Let us secondly examine the agreements and differences which are
presented to us in the _formation_ of organic and inorganic natural
bodies (Gen. Morph. i. 130). Formerly the simple structure of the latter
and the composite structure of the former were looked upon as the
principal distinction. The body of all organisms was supposed to consist
of dissimilar or heterogeneous parts, of instruments or organs which
worked together for the purposes of life. On the other hand, the most
perfect anorgana, that is to say, crystals, were supposed to consist
entirely of continuous or homogeneous matter. This distinction appears
very essential. But it loses all importance through the fact that in
late years we have become acquainted with the exceedingly remarkable and
important Monera.(15) (Compare above, p. 185.) The whole body of these
most simple of all organisms—a semi-fluid, formless, and simple lump of
albumen—consists, in fact, of only a single chemical combination, and
is as perfectly simple in its structure as any crystal, which consists
of a single inorganic combination, for example, of a metallic salt or of
a silicate of the earths and alkalies.

As naturalists believed in differences in the inner structure or
composition, so they supposed themselves able to find complete
differences in the external forms of organisms and anorgana, especially
in the mathematically determinable crystalline forms of the latter.
Certainly crystallization is pre-eminently a quality of the so-called
anorgana. Crystals are limited by plane surfaces, which meet in straight
lines and at certain measurable angles. Animal and vegetable forms, on
the contrary, seem at first sight to admit of no such geometrical
determination. They are for the most part limited by curved surfaces and
crooked lines, which meet at variable angles. But in recent times we
have become acquainted, among Radiolaria(23) and among many other
Protista, with a large number of lower organisms, whose body, in the
same way as crystals, may be traced to a mathematically determinable
fundamental form, and whose form in its whole, as well as in its parts,
is bounded by definite geometrically determinable planes and angles. In
my general doctrine of _Fundamental Forms, or Promorphology_, I have
given detailed proofs of this, and at the same time established a
general system of forms, the ideal stereometrical type-forms, which
explain the real forms of inorganic crystals, as well as of organic
individuals (Gen. Morph. i. 375-574). Moreover, there are also perfectly
amorphous organisms, like the Monera, Amœba, etc., which change their
forms every moment, and in which we are as little able to point out a
definite fundamental form as in the case of the shapeless or amorphous
anorgana, such as non-crystallized stones, deposits, etc. We are
consequently unable to find any essential difference in the external
forms or the inner structure of anorgana and organisms.

Thirdly, let us turn to the _forces_ or the _phenomena of motion_ of
these two different groups of bodies (Gen. Morph. i. 140). Here we meet
with the greatest difficulties. The vital phenomena, known as a rule
only in the highly developed organisms, in the more perfect animals and
plants, seem there so mysterious, so wonderful, so peculiar, that most
persons are decidedly of opinion that in inorganic nature there occurs
nothing at all similar, or in the least degree comparable to them.
Organisms are for this very reason called animate, and the anorgana,
inanimate natural bodies. Hence, even so late as the commencement of the
present century, the science which investigates the phenomena of life,
namely physiology, retained the erroneous idea that the physical and
chemical properties of matter were not sufficient for explaining these
phenomena. In our own day, especially during the last ten years, this
idea may be regarded as having been completely refuted. In physiology,
at least, it has now no place. It now never occurs to a physiologist to
consider any of the vital phenomena as the result of a mysterious _vital
force_, of an active power working for a definite purpose, standing
outside of matter, and, so to speak, taking only the physico-chemical
forces into its service. Modern physiology has arrived at the strictly
monistic conviction that all of the vital phenomena, and, above all, the
two fundamental phenomena of nutrition and propagation are purely
physico-chemical processes, and directly dependent on the material
nature of the organism, just as all the physical and chemical qualities
of every crystal are determined solely by its material composition. Now,
as the elementary substance which determines the peculiar material
composition of organisms is carbon, we must ultimately reduce all vital
phenomena, and, above all, the two fundamental phenomena of nutrition
and propagation to the properties of the carbon. _The
peculiar-chemico-physical properties, and especially the semi-fluid
state of aggregation, and the easy decomposibility of the exceedingly
composite albuminous combinations of carbon, are the mechanical causes
of those peculiar phenomena of motion which distinguish organisms from
anorgana, and which in a narrow sense are usually called “life.”_

In order to understand this “_carbon theory_,” which I have established
in detail in the second book of my General Morphology, it is necessary,
above all things, closely to examine those phenomena of motion which are
common to both groups of natural bodies. First among them is the
_process of growth_. If we cause any inorganic solution of salt slowly
to evaporate, crystals are formed in it, which slowly increase in size
during the continued evaporation of the water. This process of growth
arises from the fact that new particles continually pass over from the
fluid state of aggregation into the solid, and, according to certain
laws, deposit themselves upon the firm kernel of the crystal already
formed. From such an apposition of particles arise the mathematically
definite crystalline shapes. In like manner the growth of organisms
takes place by the accession of new particles. The only difference is
that in the growth of organisms, in consequence of their semi-fluid
state of aggregation, the newly-added particles penetrate into the
interior of the organism (inter-susception), whereas anorgana receive
homogeneous matter from without only by apposition or an addition of new
particles to the surface. This important difference of growth by
inter-susception and by apposition is obviously only the necessary and
direct result of the different conditions of density or state of
aggregation in organisms and anorgana.

Unfortunately I cannot here follow in detail the various exceedingly
interesting parallels and analogies which occur between the formation of
the most perfect anorgana, the crystals, and the formation of the
simplest organisms, the Monera and their next kindred forms. For this I
must refer to a minute comparison of organisms and anorgana, which I
have carried out in the fifth chapter of my General Morphology (Gen.
Morph. i. 111-160). I have there shown in detail that there exist no
complete differences between organic and inorganic natural bodies,
neither in respect to form and structure, nor in respect to matter and
force; and that the actually existing differences are dependent upon the
peculiar nature of the _carbon_; and that there exists no insurmountable
chasm between organic and inorganic nature. We can perceive this most
important fact very clearly if we examine and compare the origin of the
forms in crystals and in the simplest organic individuals. In the
formation of crystal individuals, two different counteracting formative
tendencies come into operation. The _inner constructive force_, or the
inner formative tendency, which corresponds to the Heredity of
organisms, in the case of the crystal is the direct result of its
material constitution or of its chemical composition. The form of the
crystal, so far as it is determined by this inner original formative
tendency, is the result of the specific and definite way in which the
smallest particles of the crystallizing matter unite together in
different directions according to law. That independent inner formative
force, which is directly inherent in the matter itself, is directly
counteracted by a second formative force. The _external constructive
force_, or the external formative tendency, may be called Adaptation in
crystals as well as in organisms. Every crystal individual during its
formation, like every organic individual, must submit and adapt itself
to the surrounding influences and conditions of existence of the outer
world. In fact, the form and size of every crystal is dependent upon its
whole surroundings, for example, upon the vessel in which the
crystallization takes place, upon the temperature and the pressure of
the air under which the crystal is formed, upon the presence or absence
of heterogeneous bodies, etc. Consequently, the form of every single
crystal, like the form of every single organism, is the result of the
interaction of two opposing factors—the _inner_ formative tendency,
which is determined by the chemical constitution of the _matter itself_,
and of the _external_ formative tendency, which is dependent upon the
influence of _surrounding_ matter. Both these constructive forces
interact similarly also in the organism, and, just as in the crystal,
are of a purely mechanical nature and directly inherent in the substance
of the body. If we designate the growth and the formation of organisms
as a process of life, we may with equal reason apply the same term to
the developing crystal. The teleological conception of nature, which
looks upon organisms as machines of creation arranged for a definite
purpose, must logically acknowledge the same also in regard to the
forms of crystals. The differences which exist between the simplest
organic individuals and inorganic crystals are determined by the _solid_
state of aggregation of the latter, and by the _semi-fluid_ state of the
former. Beyond that the causes producing form are exactly the same in
both. This conviction forces itself upon us most clearly, if we compare
the exceedingly remarkable phenomena of growth, adaptation, and the
“correlation of parts” of developing crystals with the corresponding
phenomena of the origin of the simplest organic individuals (Monera and
cells). The analogy between the two is so great that, in reality, no
accurate boundary can be drawn. In my General Morphology I have quoted
in support of this a number of striking facts (Gen. Morph. i. 146, 156,
158.)

If we vividly picture to ourselves this “_unity of organic and inorganic
nature_” this essential agreement of organisms and anorgana in matter,
form, and force, and if we bear in mind that we are not able to
establish any one fundamental distinction between these two groups of
bodies (as was formerly generally assumed), then the question of
spontaneous generation will lose a great deal of the difficulty which at
first seems to surround it. Then the development of the first organism
out of inorganic matter will appear a much more easily conceivable and
intelligible process than has hitherto been the case, whilst an
artificial absolute barrier between organic or animate, and inorganic or
inanimate nature was maintained.

In the question of _spontaneous generation, or archigony_, which we can
now answer more definitely, it must be borne in mind that by this
conception we understand generally the _non-parental generation of an
organic individual_, the origin of an organism independent of a
parental or producing organism. It is in this sense that on a former
occasion (p. 183) I mentioned spontaneous generation (archigony) as
opposed to parental generation or propagation (tocogony). In the latter
case the organic individual arises by a greater or less portion of an
already existing organism separating itself and growing independently.
(Gen. Morph. ii. 32.)

In spontaneous generation, which is often also called original
generation (generatio spontanea, æquivoca, primaria etc.), we must first
distinguish two essentially different kinds, namely, _autogeny_ and
_plasmogeny_. By _autogeny_ we understand the origin of a most simple
organic individual in an _inorganic formative fluid_, that is, in a
fluid which contains the fundamental substances for the composition of
the organism dissolved in simple and loose combinations (for example,
carbonic acid, ammonia, binary salts, etc.). On the other hand, we call
spontaneous generation _plasmogeny_ when the organism arises in an
_organic formative fluid_, that is, in a fluid which contains those
requisite fundamental substances dissolved in the form of complicated
and fluid combinations of carbon (for example, albumen, fat, hydrate of
carbon, etc.). (Gen. Morph. i. 174, ii. 33.)

Neither the process of autogeny, nor that of plasmogeny, has yet been
directly observed with perfect certainty. In early, and also in more
recent times, numerous and interesting experiments have been made as to
the possibility or reality of spontaneous generation. Almost all these
experiments refer not to autogeny, but to plasmogeny, to the origin of
an organism out of already formed organic matter. It is evident,
however, that this latter process is only of subordinate interest for
our history of creation. It is much more important for us to solve the
question, “Is there such a thing as autogeny? Is it possible that an
organism can arise, not out of pre-existing organic, but out of purely
inorganic, matter?” Hence we can quietly lay aside all the numerous
experiments which refer only to plasmogeny, which have been carried on
very zealously during the last ten years, and which for the most part
have had a negative result. For even supposing that the reality of
plasmogeny were strictly proved, still autogeny would not be explained
by it.

The experiments on autogeny have likewise as yet furnished no certain
and positive result. Yet we must at the outset most distinctly protest
against the notion that these experiments have proved the impossibility
of spontaneous generation in general. Most naturalists who have
endeavoured to decide this question experimentally, and who, after
having employed all possible precautionary measures, under
well-ascertained conditions, have seen no organisms come into being,
have straightway made the assertion, on the ground of these negative
results: “That it is altogether impossible for organisms to come into
existence by themselves without parental generation.” This hasty and
inconsiderate assertion they have supported by the negative results of
their experiments, which, after all, could prove nothing except that,
under these or those highly artificial circumstances created by the
experimenters themselves, no organism was developed. From these
experiments, which have been for the most part made under the most
unnatural conditions, and in a highly artificial manner, we can by no
means draw the conclusion that spontaneous generation in general is
impossible. The impossibility of such a process can, in fact, never be
proved. For how can we know that in remote primæval times there did not
exist conditions quite different from those at present obtaining, and
which may have rendered spontaneous generation possible? Indeed, we can
even positively and with full assurance maintain that the general
conditions of life in primæval times must have been entirely different
from those of the present time. Think only of the fact that the enormous
masses of carbon which we now find deposited in the primary coal
mountains were first reduced to a solid form by the action of vegetable
life, and are the compressed and condensed remains of innumerable
vegetable substances, which have accumulated in the course of many
millions of years. But at the time when, after the origin of water in a
liquid state on the cooled crust of the earth, organisms were first
formed by spontaneous generation, those immeasurable quantities of
carbon existed in a totally different form, probably for the most part
dispersed in the atmosphere in the shape of carbonic acid. The whole
composition of the atmosphere was therefore extremely different from the
present. Further, as may be inferred upon chemical, physical, and
geological grounds, the density and the electrical conditions of the
atmosphere were quite different. In like manner the chemical and
physical nature of the primæval ocean, which then continuously covered
the whole surface of the earth as an uninterrupted watery sheet, was
quite peculiar. The temperature, the density, the amount of salt, etc.,
must have been very different from those of the present ocean. In any
case, therefore, even if we do not know anything more about it, there
remains to us the supposition, which can at least not be disputed, that
at that time, under conditions quite different from those of to-day, a
spontaneous generation, which now is perhaps no longer possible, may
have taken place.

But it is necessary to add here that, by the recent progress of
chemistry and physiology, the mysterious and miraculous character which
at first seems to belong to this much disputed and yet inevitable
process of spontaneous generation, has been to a great extent, or almost
entirely, destroyed. Not fifty years ago, all chemists maintained that
we were unable to produce artificially in our laboratories any
complicated combination of carbon, or so-called “organic combination.”
The mystic “vital force” alone was supposed to be able to produce these
combinations. When, therefore, in 1828, Wöhler, in Göttingen, for the
first time refuted this dogma, and exhibited pure “organic” urea,
obtained in an artificial manner from a purely inorganic body (cyanate
of ammonium), it caused the greatest surprise and astonishment. In more
recent times, by the progress of synthetic chemistry, we have succeeded
in producing in our laboratories a great variety of similar “organic”
combinations of carbon, by purely artificial means—for example alcohol,
acetic acid, formic acid. Indeed, many exceedingly complicated
combinations of carbon are now artificially produced, so that there is
every likelihood, sooner or later, of our producing artificially the
most complicated, and at the same time the most important of all,
namely, the albuminous combinations, or plasma-bodies. By the
consideration of this probability, the deep chasm which was formerly
and generally believed to exist between organic and inorganic bodies is
almost or entirely removed, and the way is paved for the conception of
spontaneous generation.

Of still greater, nay, the very greatest importance to the hypothesis of
spontaneous generation are, finally, the exceedingly remarkable
_Monera_, those creatures which we have already so frequently mentioned,
and which are not only the simplest of all observed organisms, but even
the simplest of all imaginable organisms. I have already described these
wonderful “_organisms without organs_,” when examining the simplest
phenomena of propagation and inheritance. We already know seven
different genera of these Monera, some of which live in fresh water,
others in the sea (compare above, p. 184; also Plate I. and its
explanation in the Appendix). In a perfectly developed and freely motile
state, they one and all present us with nothing but a simple little lump
of an albuminous combination of carbon. The individual genera and
species differ only a little in the manner of propagation and
development, and in the way of taking nourishment. Through the discovery
of these organisms, which are of the utmost importance, the supposition
of a spontaneous generation loses most of its difficulties. For as all
trace of organization—all distinction of heterogeneous parts—is still
wanting in them, and as all the vital phenomena are performed by one and
the same homogeneous and formless matter, we can easily imagine their
origin by spontaneous generation. If this happens through _plasmogeny_,
and if plasma capable of life already exists, it then only needs to
individualize itself in the same way as the mother liquor of crystals
individualizes itself in crystallization. If, on the other hand, the
spontaneous generation of the Monera takes place by true _autogeny_,
then it is further requisite that that plasma capable of life, that
primæval mucus, should be formed out of simpler combinations of carbon.
As we are now able artificially to produce, in our laboratories,
combinations of carbon similar to this in the complexity of their
constitution, there is absolutely no reason for supposing that there are
not conditions in free nature also, in which such combinations could
take place. Formerly, when the doctrine of spontaneous generation was
advocated, it failed at once to obtain adherents on account of the
composite structure of the simplest organisms then known. It is only
since we have discovered the exceedingly important Monera, only since we
have become acquainted in them with organisms not in any way built up of
distinct organs, but which consist solely of a single chemical
combination, and yet grow, nourish, and propagate themselves, that this
great difficulty has been removed, and the hypothesis of spontaneous
generation has gained a degree of probability which entitles it to fill
up the gap existing between Kant’s cosmogony and Lamarck’s Theory of
Descent. Even among the Monera at present known there is a species which
probably, even now, always comes into existence by spontaneous
generation. This is the wonderful _Bathybius Hæckelii_, discovered and
described by Huxley. As I have already mentioned (p. 184), this Moneron
is found in the greatest depths of the sea, at a depth of between 12,000
and 24,000 feet, where it covers the ground partly as retiform threads
and plaits of plasma, partly in the form of larger or smaller irregular
lumps of the same material.[6]

Only such homogeneous organisms as are yet not differentiated, and are
similar to inorganic crystals in being homogeneously composed of one
single substance, could arise by spontaneous generation, and could
become the primæval parents of all other organisms. In their further
development we have pointed out that the most important process is the
formation of a _kernel_ or _nucleus_ in the simple little lump of
albumen. We can conceive this to take place in a purely physical manner,
by the condensation of the innermost central part of the albumen. The
more solid central mass, which at first gradually shaded off into the
peripheral plasma, becomes sharply separated from it, and thus forms an
independent, round, albuminous corpuscle, the kernel; and by this
process the Moneron becomes a _cell_. Now, it must have become evident
from our previous chapters, that the further development of all other
organisms out of such a cell presents no difficulty, for every animal
and every plant, in the beginning of its individual life, is a simple
cell. Man, as well as every other animal, is at first nothing but a
simple egg-cell, a single lump of mucus, containing a kernel (p. 297,
Fig. 5).

In the same way as the kernel of the organic cell arose in the interior
or central mass of the originally homogeneous lump of plasma, by
separation, so, too, the first _cell-membrane_ was formed on its
surface. This simple, but most important process, as has already been
remarked, can likewise be explained in a purely physical manner, either
as a chemical deposit, or as a physical condensation in the uppermost
stratum of the mass, or as a secretion. One of the first processes of
adaptation effected by the Moneron originating by spontaneous generation
must have been the condensation of an external crust, which as a
protecting covering shut in the softer interior from the hostile
influences of the outer world. As soon as, by condensation of the
homogeneous Moneron, a cell-kernel arose in the interior and a membrane
arose on the surface, all the fundamental parts of the unit were
furnished, out of which, by infinitely manifold repetition and
combination, as attested by actual observation, the body of higher
organisms is constructed.

As has already been mentioned, our whole understanding of an organism
rests upon the cell theory established thirty years ago by Schleiden and
Schwann. According to it, every organism is either a simple cell or a
cell-community, a republic of closely connected cells. All the forms and
vital phenomena of every organism are the collective result of the forms
and vital phenomena of all the single cells of which it is composed. By
the recent progress of the cell theory it has become necessary to give
the elementary organisms, that is, the “organic” individuals of the
first order, which are usually designated as _cells_, the more general
and more suitable name of _form-units_, or _plastids_. Among these
form-units we distinguish two main groups, namely, the cytods and the
genuine cells. The _cytods_ are, like the Monera, pieces of plasma
without a kernel (p. 186, Fig. 1). _Cells_, on the other hand, are
pieces of plasma containing a kernel or nucleus (p. 188, Fig. 2). Each
of these two main groups of plastids is again divided into two
subordinate groups, according as they possess or do not possess an
external covering (skin, shell, or membrane). We may accordingly
distinguish the following four grades or species of plastids, namely: 1.
_Simple cytods_ (p. 186, Fig. 1 _A_); 2. _Encased cytods_; 3. _Simple
cells_ (p. 188, Fig. 2 _B_); 4. _Encased cells_ (p. 188, Fig. 2 _A_).
(Gen. Morph. i. 269-289.)

Concerning the relation of these four forms of plastids to spontaneous
generation, the following is the most probable:—1. The _simple cytods_
(Gymnocytoda), naked particles of plasma without kernel, like the still
living Monera, are the only plastids which directly come into existence
by spontaneous generation. 2. The _enclosed cytods_ (Lepocytoda),
particles of plasma without kernel, which are surrounded by a covering
(membrane or shell), arose out of the simple cytods either by the
condensation of the outer layers of plasma or by the secretion of a
covering. 3. The _simple cells_ (Gymnocyta), or naked cells, particles
of plasma with kernel, but without covering, arose out of the simple
cytods by the condensation of the innermost particles of plasma into a
kernel, or nucleus, by differentiation of a central kernel and
peripheral cell-substance. 4. The _enclosed cells_ (Lepocyta), or
testaceous cells, particles of plasma with kernel and an outer covering
(membrane or shell), arose either out of the enclosed cytods by the
formation of a kernel, or out of the simple cells by the formation of a
membrane. All the other forms of form-units, or plastids, met with,
besides these, have only subsequently arisen out of these four
fundamental forms by natural selection, by descent with adaptation, by
differentiation and transformation.

By this _theory of plastids_, by deducing all the different forms of
plastids, and hence, also, all organisms composed of them, from the
Monera, we obtain a simple and natural connection in the whole series of
the development of nature. The origin of the first Monera by spontaneous
generation appears to us as a simple and necessary event in the process
of the development of the earth. We admit that this process, as long as
it is not directly observed or repeated by experiment, remains a pure
hypothesis. But I must again say that this hypothesis is indispensable
for the consistent completion of the non-miraculous history of creation,
that it has absolutely nothing forced or miraculous about it, and that
certainly it can never be positively refuted. It must be taken into
consideration that the process of spontaneous generation, even if it
still took place daily and hourly, would in any case be exceedingly
difficult to observe and establish with absolute certainty as such. With
regard to the Monera, we find ourselves placed before the following
alternative: _either_ they are actually directly derived from
pre-existing, or “created,” most ancient Monera, and in this case they
would have had to propagate themselves unchanged for many millions of
years, and to have maintained their original form of simple particles of
plasma; _or_, the _present_ Monera have originated much later in the
course of the organic history of the earth, by repeated acts of
spontaneous generation, and in this case spontaneous generation may take
place now as well as then. The latter supposition has evidently much
more probability on its side than the former.

If we do not accept the hypothesis of spontaneous generation, then at
this one point of the history of development we must have recourse to
the miracle of a _supernatural creation_. The Creator must have created
the first organism, or a few first organisms, from which all others are
derived, and as such he must have created the simplest Monera, or
primæval cytods, and given them the capability of developing further in
a mechanical way. I leave it to each one of my readers to choose between
this idea and the hypothesis of spontaneous generation. To me the idea
that the Creator should have in this one point arbitrarily interfered
with the regular process of development of matter, which in all other
cases proceeds entirely without his interposition, seems to be just as
unsatisfactory to a believing mind as to a scientific intellect. If, on
the other hand, we assume the hypothesis of spontaneous generation for
the origin of the first organisms, which in consequence of reasons
mentioned above, and especially in consequence of the discovery of the
Monera, has lost its former difficulty, then we arrive at the
establishment of an uninterrupted natural connection between the
development of the earth and the organisms produced on it, and, in this
last remaining lurking-place of obscurity, we can proclaim the _unity of
all Nature, and the unity of her laws of Development_ (Gen. Morph. i.
164).

CHAPTER XIV.

MIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE ICE-PERIOD OF
THE EARTH.

Chorological Facts and Causes.—Origin of most Species in
one Single Locality: “Centres of Creation.”—Distribution
by Migration.—Active and Passive Migrations of Animals
and Plants.—Means of Transport.—Transport of Germs by
Water and by Wind.—Continual Change of the Area of
Distribution by Elevations and Depressions of the
Ground.—Chorological Importance of Geological
Processes.—Influence of the Change of Climate.—Ice or
Glacial Period.—Its Importance to Chorology.—Importance
of Migrations for the Origin of New Species.—Isolation
of Colonists.—Wagner’s Law of Migration.—Connection
between the Theory of Migration and the Theory of
Selection.—Agreement of its Results with the Theory of
Descent.

As I have repeatedly said, but cannot too much emphasize, the actual
value and invincible strength of the Theory of Descent does not lie in
its explaining this or that single phenomenon, but in the fact that it
explains _all_ biological phenomena, that it makes _all_ botanical and
zoological series of phenomena intelligible in their relations to one
another. Hence every thoughtful investigator is the more firmly and
deeply convinced of its truth the more he advances from single
biological observations to a general view of the whole domain of animal
and vegetable life. Let us now, starting from this comprehensive point
of view, survey a biological domain, the varied and complicated
phenomena of which may be explained with remarkable simplicity and
clearness by the theory of selection. I mean _Chorology_, or the theory
of the _local distribution of organisms over the surface of the earth_.
By this I do not only mean the _geographical_ distribution of animal and
vegetable species over the different parts and provinces of the earth,
over continents and islands, seas, and rivers; but also their
_topographical_ distribution in a _vertical_ direction, their ascending
to the heights of mountains, and their descending into the depths of the
ocean. (Gen. Morph. ii. 286.)

The strange chorological series of phenomena which show the horizontal
distribution of organisms over parts of the earth, and their vertical
distribution in heights and depths, have long since excited general
interest. In recent times Alexander Humboldt(39) and Frederick Schouw
have especially discussed the geography of plants, and Berghaus and
Schmarda the geography of animals, on a large scale. But although these
and several other naturalists have in many ways increased our knowledge
of the distribution of animal and vegetable forms, and laid open to us a
new domain of science, full of wonderful and interesting phenomena, yet
Chorology as a whole remained, as far as their labours were concerned,
only a desultory knowledge of a mass of individual _facts_. It could not
be called a science as long as the _causes_ for the explanation of these
facts were wanting. These causes were first disclosed by the theory of
selection and its doctrine of the _migrations_ of animal and vegetable
species, and it is only since the works of Darwin and Wallace that we
have been able to speak of an independent _science of Chorology_.

If all the phenomena of the geographical and topographical distribution
of organisms are examined by themselves, without considering the gradual
development of species, and if at the same time, following the customary
superstition, the individual species of animals and plants are
considered as forms independently created and independent of one
another, then there remains nothing for us to do but to gaze at those
phenomena as a confused collection of incomprehensible and inexplicable
miracles. But as soon as we leave this low stand-point, and rise to the
height of the theory of development, by means of the supposition of a
blood-relationship between the different species, then all at once a
clear light falls upon this strange series of miracles, and we see that
all chorological facts can be understood quite simply and clearly by the
supposition of a common descent of the species, and their passive and
active migrations.

The most important principle from which we must start in chorology, and
of the truth of which we are convinced by due examination of the theory
of selection, is that, as a rule, every animal and vegetable species has
arisen only _once_ in the course of time and only in _one_ place on the
earth—its so-called “centre of creation”—by natural selection. I share
this opinion of Darwin’s unconditionally, in respect to the great
majority of higher and perfect organisms, and in respect to most animals
and plants in which the division of labour, or differentiation of the
cells and organs of which they are composed, has attained a certain
stage. For it is quite incredible, or could at best only be an
exceedingly rare accident, that all the manifold and complicated
circumstances—all the different conditions of the struggle for life,
which influence the origin of a new species by natural selection—should
have worked together in exactly the same agreement and combination more
than once in the earth’s history, or should have been active at the same
time at several different points of the earth’s surface.

On the other hand, I consider it to be very probable that certain
exceedingly imperfect organisms of the simplest structure, forms of
species of an exceedingly indifferent nature, as, for example, many
single-celled Protista, but especially the Monera, the simplest of them
all, should have several times or simultaneously arisen in their
specific form in several parts of the earth. For the few and very simple
conditions by which their specific form was changed in the struggle for
life may surely have often been repeated, in the course of time,
independently in different parts of the earth. Further, those higher
specific forms also, which have not arisen by natural selection, but by
_hybridism_ (the previously-mentioned hybrid species, pp. 147 and 275),
may have repeatedly arisen anew in different localities. As, however,
this proportionately small number of organisms does not especially
interest us here, we may, in respect of chorology, leave them alone, and
need only take into consideration the distribution of the great majority
of animal and vegetable species in regard to which the _single origin of
every species in a single locality_, in its so-called “central point of
creation,” can be considered as tolerably certain.

Every animal and vegetable species from the beginning of its existence
has possessed the tendency to spread beyond the limited locality of its
origin, beyond the boundary of its “centre of creation,” or, in other
words, beyond its _primæval home_, or its natal place. This is a
necessary consequence of the relations of population and over-population
(pp. 161 and 256). The more an animal or vegetable species increases,
the less is its limited natal place sufficient for its sustenance, and
the fiercer the struggle for life; the more rapid the _over-population_
of the natal spot, the more it leads to _emigration_. These _migrations_
are common to all organisms, and are the real cause of the wide
distribution of the different species of organisms over the earth’s
surface. Just as men leave over-crowded states, so all animals and
plants migrate from their over-crowded primæval homes.

Many distinguished naturalists, especially Lyell(11) and Schleiden, have
before this repeatedly drawn attention to the great importance of these
very interesting migrations of organisms. The means of transport by
which they are effected are extremely varied. Darwin has discussed these
most excellently in the eleventh and twelfth chapters of his work, which
are exclusively devoted to “geographical distribution.” The means of
transport are partly active, partly passive; that is to say, the
organism effects its migration partly by free locomotion due to its own
activity, and partly by the movements of other natural bodies in which
it has no active share.

It is self-evident that _active migrations_ play the chief part in
animals able to move freely. The more freely an animal’s organization
permits it to all move in directions, the more easily the animal species
can migrate, and the more rapidly it will spread over the earth.
_Flying_ animals are of course most favoured in this respect, among
vertebrate animals especially birds, and among articulated animals,
insects. These two classes, as soon as they came into existence, can
have more easily spread over the whole earth than any other animal, and
this fact partly explains the extraordinary uniformity of structure
which characterizes these two great classes of animals. For, although
they contain an exceedingly large number of different species, and
although the insect class alone is said to possess more different
species than all other classes of animals together, yet all the
innumerable species of insects, and in like manner, also, the different
species of birds, agree most strikingly in all essential peculiarities
of their organization. Hence, in the class of insects, as well as in
that of birds, we can distinguish only a very small number of large
natural groups or orders, and these few orders differ but very little
from one another in their internal structure. The orders of birds with
their numerous species are not nearly as distinct from one another as
the orders of the mammalian class, containing much fewer species; and
the orders of insects, which are extremely rich in genera and species,
resemble one another much more closely in their internal structure than
do the much smaller orders of the crab class. The general parallelism
between birds and insects is also very interesting in relation to
systematic zoology; and the great importance of their richness in forms,
for scientific morphology, lies in the fact that they show us how,
within the narrowest anatomical sphere, and without profound changes of
the essential internal organization, the greatest variety in external
bodily forms can be attained. The reason of this is evidently their
flying mode of life and their free locomotion. In consequence of this
birds, as well as insects, have spread very rapidly over the whole
surface of the earth, have settled in all possible localities
inaccessible to other animals, and variously modified their specific
form by superficial adaptation to particular local relations.

Next to the flying animals, those animals, of course, have spread most
quickly and furthest which were next best able to migrate, that is, the
best runners among the inhabitants of the land, and the best swimmers
among the inhabitants of the water. However, the power of such active
migrations is not confined to those animals which throughout life enjoy
free locomotion. For the fixed animals also, such as corals, tubicolous
worms, sea-squirts, lily encrinites, sea-acorns, barnacles, and many
other lower animals which adhere to seaweeds, stones, etc., enjoy, at
least at an early period of life, free locomotion. They all migrate
before they adhere to anything. Their first free locomotive condition of
early life is generally that of a “ciliated” larva, a roundish, cellular
corpuscle, which, by means of a garb of movable “flimmer-hairs,” (Latin,
“cilia”) swarms about in the water and bears the name of Planula.

But the power of free locomotion, and hence, also, of active migration,
is not confined to animals alone, but many plants likewise enjoy it.
Many lower aquatic plants, especially the class of the Tangles (Algæ),
swim about freely in the water in early life, like the lower animals
just mentioned, by means of a vibratile hairy coat, a vibrating whip, or
a covering of tremulous fringes, and only at a later period adhere to
objects. Even in the case of many higher plants, which we designate as
creepers and climbing plants, we may speak of active migration. Their
elongated stalks and perennial roots creep or climb during their long
process of growth to new positions, and by means of their widespread
branches they acquire new habitations, to which they attach themselves
by buds, and bring forth new colonies of individuals of their species.

Influential as these active migrations of most animals and many plants
are, yet alone they would by no means be sufficient to explain the
chorology of organisms. _Passive migrations_ have ever been by far the
more important, and of far greater influence, in the case of most plants
and in that of many animals. Such passive changes of locality are
produced by extremely numerous causes. Air and water in their eternal
motion, wind and waves with their manifold currents, play the chief
part. The wind in all places and at all times raises light organisms,
small animals and plants, but especially their young germs, animal eggs
and plant seeds, and carries them far over land and seas. Where they
fall into the water they are seized by currents or waves and carried to
other places. It is well known, from numerous examples, how far in many
cases trunks of trees, hard shelled fruits, and other not readily
perishable portions of plants are carried away from their original home
by the course of rivers and by the currents of the sea. Trunks of palm
trees from the West Indies are brought by the Gulf Stream to the British
and Norwegian coasts. All large rivers bring down driftwood from the
mountains, and frequently alpine plants are carried from their home at
the source of the river into the plains, and even further, down to the
sea. Frequently numerous inhabitants live between the roots of the
plants thus carried down, and between the branches of the trees thus
washed away there are various inhabitants which have to take part in the
passive migration. The bark of the tree is covered with mosses, lichens,
and parasitic insects. Other insects, spiders, etc., even small
reptiles and mammals, are hidden within the hollow trunk or cling to the
branches. In the earth adhering to the fibres of the roots, in the dust
lying in the cracks of the bark, there are innumerable germs of smaller
animals and plants. Now, if the trunk thus washed away lands safely on a
foreign shore or on a distant island, the guests who had to take part in
the involuntary voyage can leave their boat and settle in the new
country. A very remarkable kind of water-transport is formed by the
floating icebergs which annually become loosened from the eternal ice of
the Polar Sea. Although these cold regions are thinly peopled, yet many
of their inhabitants, who were accidentally upon an iceberg while it was
becoming loosened, are carried away with it by the currents, and landed
on warmer shores. In this manner, by means of loosened blocks of ice
from the northern Polar Sea, often whole populations of small animals
and plants have been carried to the northern shores of Europe and
America. Nay, even polar foxes and polar bears have been carried in this
way to Iceland and to the British Isles.

Transport by air is no less important than transport by water in this
matter of passive migration. The dust covering our streets and roofs,
the earth lying on dry fields and dried-up pools, the light moist soil
of forests, in short, the whole surface of the globe contains millions
of small organisms and their germs. Many of these small animals and
plants can without injury become completely dried up, and awake again to
life as soon as they are moistened. Every gust of wind raises up with
the dust innumerable little creatures of this kind, and often carries
them away to other places miles off. But even larger organisms, and
especially their germs, may often make distant passive journeys through
the air. The seeds of many plants are provided with light feathery
processes, which act as parachutes and facilitate their flight in the
air, and prevent their falling. Spiders make journeys of many miles
through the air on their fine filaments, their so-called gossamer
threads. Young frogs are frequently raised by whirlwinds into the air by
thousands, and fall down in a distant part as a “shower of frogs.”
Storms may carry birds and insects across half the earth’s
circumference. They drop in the United States, having risen in England.
Starting from California, they only come to rest in China. But, again,
many other organisms may make the journey from one continent to another
together with the birds and insects. Of course all parasites, the number
of which is legion, fleas, lice, mites, moulds, etc., migrate with the
organisms upon which they live. In the earth which often remains
sticking to the claws of birds there are also small animals and plants
or their germs. Thus the voluntary or involuntary migration of a single
larger organism may carry a whole small flora and fauna from one part of
the earth to another.

Besides the means of transport here mentioned, there are many others
which explain the distribution of animal and vegetable species over the
large tracts of the earth’s surface, and especially the general
distribution of the so-called cosmopolitan species. But these alone
would not nearly be sufficient to explain all chorological facts. How is
it, for example, that many inhabitants of fresh water live in various
rivers or lakes far away and quite apart from one another? How is it
that many inhabitants of mountains, which cannot exist in plains, are
found upon entirely separated and far distant chains of mountains? It
is difficult to believe, and in many cases quite inconceivable, that
these inhabitants of fresh water should have in any way, actively or
passively, migrated over the land lying between the lakes, or that the
inhabitants of mountains in any way, actively or passively, crossed the
plains lying between their mountain homes. But here geology comes to our
help, as a mighty ally, and completely solves these difficult problems
for us.

The history of the earth’s development shows us that the distribution of
land and water on its surface is ever and continually changing. In
consequence of geological changes of the earth’s crust, _elevations_ and
_depressions_ of the ground take place everywhere, sometimes more
strongly marked in one place, sometimes in another. Even if they happen
so slowly that in the course of centuries the seashore rises or sinks
only a few inches, or even only a few lines, still they nevertheless
effect great results in the course of long periods of time. And
long—immeasurably long—periods of time have not been wanting in the
earth’s history. During the course of many millions of years, ever since
organic life existed on the earth, land and water have perpetually
struggled for supremacy. Continents and islands have sunk into the sea,
and new ones have arisen out of its bosom. Lakes and seas have slowly
been raised and dried up, and new water basins have arisen by the
sinking of the ground. Peninsulas have become islands by the narrow neck
of land which connected them with the mainland sinking into the water.
The islands of an archipelago have become the peaks of a continuous
chain of mountains by the whole floor of their sea being considerably
raised.

Thus the Mediterranean at one time was an inland sea, when, in the place
of the Straits of Gibraltar, an isthmus connected Africa with Spain.
England, even during the more recent history of the earth, when man
already existed, has repeatedly been connected with the European
continent and been repeatedly separated from it. Nay, even Europe and
North America have been directly connected. The South Sea at one time
formed a large Pacific Continent, and the numerous little islands which
now lie scattered in it were simply the highest peaks of the mountains
covering that continent. The Indian Ocean formed a continent which
extended from the Sunda Islands along the southern coast of Asia to the
east coast of Africa. This large continent of former times Sclater, an
Englishman, has called _Lemuria_, from the monkey-like animals which
inhabited it, and it is at the same time of great importance from being
the probable cradle of the human race, which in all likelihood here
first developed out of anthropoid apes. The important proof which Alfred
Wallace has furnished,(36) by the help of chorological facts, that the
present Malayan Archipelago consists in reality of two completely
different divisions, is particularly interesting. The western division,
the Indo-Malayan Archipelago, comprising the large islands of Borneo,
Java, and Sumatra, was formerly connected by Malacca with the Asiatic
continent, and probably also with the Lemurian continent just mentioned.
The eastern division, on the other hand, the Austro-Malayan Archipelago,
comprising Celebes, the Moluccas, New Guinea, Solomon’s Islands, etc.,
was formerly directly connected with Australia. Both divisions were
formerly two continents separated by a strait, but they have now for
the most part sunk below the level of the sea. Wallace, solely on the
ground of his accurate chorological observations, has been able in the
most acute manner to determine the position of this former strait, the
south end of which passes between Balij and Lombok.

Thus, ever since liquid water existed on the earth, the boundaries of
water and land have eternally changed, and we may assert that the
outlines of continents and islands have never remained for an hour, nay,
even for a minute, exactly the same. For the waves eternally and
perpetually break on the edge of the coast, and whatever the land in
these places loses in extent, it gains in other places by the
accumulation of mud, which condenses into solid stone and again rises
above the level of the sea as new land. Nothing can be more erroneous
than the idea of a firm and unchangeable outline of our continents, such
as is impressed upon us in early youth by defective lessons on
geography, which are devoid of a geological basis.

I need hardly draw attention to the fact that these geological changes
of the earth’s surface have ever been exceedingly important to the
migrations of organisms, and consequently to their Chorology. From them
we learn to understand how it is that the same or nearly related species
of animals and plants can occur on different islands, although they
could not have passed through the water separating them, and how other
species living in fresh water can inhabit different enclosed
water-basins, although they could not have crossed the land lying
between them. These islands were formerly mountain peaks of a connected
continent, and these lakes were once directly connected with one
another. The former were separated by geological depressions, the latter
by elevations. Now, if we further consider how often and how unequally
these alternating elevations and depressions occur on the different
parts of the earth, and how, in consequence of this, the boundaries of
the geographical tracts of distribution of species become changed, and
if we further consider in what exceedingly various ways the active and
passive migrations of organisms must have been influenced by them, then
we shall be in a position to completely understand the great variety of
the picture which is at present offered to us by the distribution of
animal and vegetable species.

There is yet another important circumstance to be mentioned here, which
is likewise of great importance for a complete explanation of this
varied geographical picture, and which throws light upon many very
obscure facts, which, without its help, we should not be able to
comprehend. I mean the gradual _change of climate_ which has taken place
during the long course of the organic history of the earth. As we saw in
our last chapter, at the beginning of organic life on the earth a much
higher and more equal temperature must have generally prevailed than at
present. The differences of zones, which in our time are so very
striking, did not exist at all in those times. It is probable that for
many millions of years but one climate prevailed over the whole earth,
which very closely resembled, or even surpassed, the hottest tropical
climate of the present day. The highest north which man has yet reached
was then covered with palms and other tropical plants, the fossil
remains of which are still found there. The temperature of this climate
at a later period gradually decreased; but still the poles remained so
warm that the whole surface of the earth could be inhabited by
organisms. It was only at a comparatively very recent period of the
earth’s history, namely, at the beginning of the tertiary period, that
there occurred, as it seems, the first perceptible cooling of the
earth’s crust at the poles, and through this the first differentiation
or separation of the different zones of temperature or climatic zones.
But the slow and gradual decrease of temperature continued to extend
more and more within the tertiary period, until at last, at both poles
of the earth, the first permanent ice caps were formed.

I need scarcely point out in detail how very much this change of climate
must have affected the geographical distribution of organisms, and the
origin of numerous new species. The animal and vegetable species, which,
down to the tertiary period, had found an agreeable tropical climate all
over the earth, even as far as the poles, were now forced either to
adapt themselves to the intruding cold, or to flee from it. Those
species which adapted and accustomed themselves to the decreasing
temperature became new species simply by this very acclimatization,
under the influence of natural selection. The other species, which fled
from the cold, had to emigrate and seek a milder climate in lower
latitudes. The tracts of distribution which had hitherto existed must by
this have been vastly changed.

However, during the last great period of the earth’s history, during the
quaternary period (or diluvial period) succeeding the tertiary one, the
decrease of the heat of the earth from the poles did not by any means
remain stationary. The temperature fell lower and lower, nay, even far
below the present degree. Northern and Central Asia, Europe, and North
America from the north pole, were covered to a great extent by a
connected sheet of ice, which in our part of the earth seems to have
reached the Alps. In a similar manner the cold also advancing from the
south pole covered a large portion of the southern hemisphere, which is
now free from it, with a rigid sheet of ice. Thus, between these vast
lifeless ice continents there remained only a narrow zone to which the
life of the organic world had to withdraw. This period, during which
man, or at least the human ape, already existed, and which forms the
first period of the so-called _diluvial epoch_, is now universally known
as the _ice_ or _glacial period_.

The ingenious Carl Schimper is the first naturalist who clearly
conceived the idea of the ice period, and proved the great extent of the
former glaciation of Central Europe by the help of the so-called
boulders, or erratic blocks of stone, as also by the “glacier tables.”
Louis Agassiz, stimulated by him, and considerably supported by the
independent investigations of the eminent geologist Charpentier,
afterwards undertook the task of carrying out the theory of the ice
period. In England, the geologist Forbes distinguished himself in this
matter, and also was the first to apply it to the theory of migrations
and the geographical distribution of species dependent upon migration.
Agassiz, however, afterwards injured the theory by his one-sided
exaggeration, inasmuch as, from his partiality to Cuvier’s theory of
cataclysms, he endeavoured to attribute the destruction of the whole
animate creation then existing, to the sudden coming on of the cold of
the ice period and the “revolution” connected with it.

It is unnecessary here to enter into detail as to the ice period itself,
and into investigations about its limits, and I may omit this all the
more reasonably since the whole of our recent geological literature is
full of it. It will be found discussed in detail in the works of
Cotta,(31) Lyell,(30) Vogt,(27) Zittel,(32) etc. Its great importance to
us here is that it helps us to explain the most difficult chorological
problems, as Darwin has correctly perceived.

For there can be no doubt that this glaciation of the present temperate
zones must have exercised an exceedingly important influence on the
geographical and topographical distribution of organisms, and that it
must have entirely changed it. While the cold slowly advanced from the
poles towards the equator, and covered land and sea with a connected
sheet of ice, it must of course have driven the whole living world
before it. Animals and plants had to migrate if they wished to escape
being frozen. But as at that time the temperate and tropical zones were
probably no less densely peopled with animals and plants than at
present, there must have arisen a fearful struggle for life between the
latter and the intruders coming from the poles. During this struggle,
which certainly lasted many thousands of years, many species must have
perished and many become modified and been transformed into new species.
The hitherto existing tracts of distribution of species must have become
completely changed, and the struggle have been continued, nay, indeed,
must have broken out anew and been carried on in new forms, when the ice
period had reached and gone beyond its furthest point, and when in the
post-glacial period the temperature again increased, and organisms began
to migrate back again towards the poles.

In any case this great change of climate, whether a greater or less
importance be ascribed to it, is one of those occurrences in the history
of the earth which have most powerfully influenced the distribution of
organic forms. But more especially one important and difficult
chorological circumstance is explained by it in the simplest manner,
namely, the specific agreement of many of our Alpine inhabitants with
some of those living in polar regions. There is a great number of
remarkable animal and vegetable forms which are common to these two far
distant parts of the earth, and which are found nowhere in the wide
plains lying between them. Their migration from the polar lands to the
Alpine heights, or _vice versa_, would be inconceivable under the
present climatic circumstances, or could be assumed at least only in a
few rare instances. But such a migration could take place, nay, was
obliged to take place, during the gradual advance and retreat of the
ice-sheet. As the glaciation encroached from Northern Europe towards our
Alpine chains, the polar inhabitants retreating before it—gentian,
saxifrage, polar foxes, and polar hares—must have peopled Germany, in
fact all Central Europe. When the temperature again increased, only a
portion of these Arctic inhabitants returned with the retreating ice to
the Arctic zones. Another portion of them climbed up the mountains of
the Alpine chain instead, and there found the cold climate suited to
them. The problem is thus solved in a most simple manner.

We have hitherto principally considered the _theory of the migrations_
of organisms in so far as it explains the radiation of every animal and
vegetable species from a single primæval home, from a “central point of
creation,” and the dispersion of these species over a greater or less
portion of the earth’s surface. But these migrations are also of great
importance to the theory of development, because we can perceive in them
a very important means for the _origin of new species_. When animals and
plants migrate they meet in their new home, in the same way as do human
emigrants, with conditions which are more or less different from those
which they have inherited throughout generations, and to which they have
been accustomed. The emigrants must either submit and adapt themselves
to these new conditions of life or they perish. By adaptation their
peculiar specific character becomes the more changed the greater the
difference between the new and the old home. The new climate, the new
food, but above all, new neighbours in the forms of other animals and
plants, influence and tend to modify the inherited character of the
immigrant species, and if it is not hardy enough to resist the
influences, then sooner or later a new species must arise out of it. In
most cases this transformation of an immigrant species takes place so
quickly under the influence of the altered struggle for life, that even
after a few generations a new species arises from it.

Migration has an especial influence in this way on all organisms with
separate sexes. For in them the origin of new species by natural
selection is always rendered difficult, or delayed, by the fact that the
modified descendants occasionally again mix sexually with the unchanged
original form, and thus by crossing return to the first form. But if
such varieties have migrated, if great distances or barriers to
migration—seas, mountains, etc.—have separated them from the old home,
then the danger of a mingling with the primary form is prevented, and
the isolation of the emigrant form, which becomes a new species by
adaptation, prevents its breeding with the old stock, and hence prevents
its return in this way to the original form.

The importance of migration for the isolation of newly-originating
species and the prevention of a speedy return to the primary form has
been especially pointed out by the philosophic traveller, Moritz Wagner,
of Munich. In a special treatise on “Darwin’s Theory and the Law of the
Migration of Organisms,”(40) Wagner gives from his own rich experience a
great number of striking examples which confirm the theory of migration
set forth by Darwin in the eleventh and twelfth chapters of his book,
where he especially discusses the effect of the complete isolation of
emigrant organisms in the origin of new species. Wagner sets forth the
simple causes which have “locally bounded the form and founded its
typical difference,” in the following three propositions:—1. The
greater the total amount of change in the hitherto existing conditions
of life which the emigrating individuals find on entering a new
territory, the more intensely must the innate variability of every
organism manifest itself. 2. The less this increased individual
variability of organisms is disturbed in the peaceful process of
reproduction by the mingling of numerous subsequent immigrants of the
same species, the more frequently will nature succeed, by
intensification and transmission of the new characteristics, in forming
a new variety or race, that is, a commencing species. 3. The more
advantageous the changes experienced by the individual organs are to the
variety, the more readily will it be able to adapt itself to the
surrounding conditions; and the longer the undisturbed breeding of a
commencing variety of colonists in a new territory continues without its
mingling with subsequent immigrants of the same species, the oftener a
new species will arise out of the variety.

Every one will agree with these three propositions of Moritz Wagner’s.
But we must consider his view, that the migration and the subsequent
isolation of the emigrant individuals is a _necessary_ condition for the
origin of new species, to be completely erroneous. Wagner says, “without
a long-enduring separation of colonists from their former species, the
formation of a new race cannot succeed—selection, in fact, cannot take
place. Unlimited crossing, unhindered sexual mingling of all individuals
of a species will always produce uniformity, and drive varieties, whose
characteristics have not been fixed throughout a series of generations,
back to the primary form.”

This sentence, in which Wagner himself comprises the main result of his
investigations, he would be able to defend only if all organisms were of
separate sexes, if every origin of new individuals were possible only by
the mingling of male and female individuals. But this is by no means the
case. Curiously enough, Wagner says nothing of the numerous
hermaphrodites which, possessing both the sexual organs, are capable of
self-fructification, and likewise nothing of the countless organisms
which are not sexually differentiated.

Now, from the earliest times of the organic history of the earth, there
have existed thousands of organic species (thousands of which still
exist) in which no difference of sex whatever exists, and, in fact, in
which no sexual propagation takes place, and which exclusively reproduce
themselves in a non-sexual manner by division, budding, formation of
spores, etc. All the great mass of Protista, the Monera, Amœbæ,
Myxomycetes, Rhizopoda, etc., in short, all the lower organisms which we
shall have to enumerate in the domain of Protista, standing midway
between the animal and vegetable kingdoms, propagate themselves
_exclusively in a non-sexual manner_. And this domain comprises a class
of organisms which is one of the richest in forms, nay, even in a
certain respect the richest of all in forms, as all possible geometrical
fundamental forms are represented in it. I allude to the wonderful class
of the Rhizopoda, or Ray-streamers, to which the lime-shelled Acyttaria
and the flint-shelled Radiolaria belong. (Compare chapter xvi.)

It is self-evident, therefore, that Wagner’s theory is quite
inapplicable to all these non-sexual organisms. Moreover, the same
applies to all those hermaphrodites in which every individual possesses
both male and female organs and is capable of self-fructification. This
is the case, for instance, in the Flat-worms, flukes, and tape-worms,
further in the important Sack-worms (Tunicates), the invertebrate
relatives of the vertebrate animals, and in very many other organisms of
different groups. Many of these species have arisen by natural
selection, without a “crossing” of the originating species with its
primary form having been possible.

As I have already shown in the eighth chapter, the origin of the two
sexes, and consequently sexual propagation in general, must be
considered as a process which began only in later periods of the organic
history of the earth, being the result of differentiation or _division
of labour_. The most ancient terrestrial organisms can have propagated
themselves only in the simplest non-sexual manner. Even now all
Protista, as well as all the countless forms of cells, which constitute
the body of higher organisms, multiply themselves only by non-sexual
generation. And yet there arise here “new species” by differentiation in
consequence of natural selection.

But even if we were to take into consideration the animal and vegetable
species with separate sexes, in this case too we should have to oppose
Wagner’s chief proposition, that “the _migration_ of organisms and their
formation of colonies is the _necessary condition of natural
selection_.” August Weismann, in his treatise on the “Influence of
Isolation upon the Formation of Species,”(24) has already sufficiently
refuted that proposition, and has shown that even in one and the same
district one bi-sexual species may divide itself into several species by
natural selection. In relation to this question, I must again call to
mind the great influence which _division of labour, or differentiation_,
possesses, being one of the necessary results of natural selection. All
the different kinds of cells constituting the body of the higher
organisms, the nerve cells, muscle cells, gland cells, etc., all these
“good species,” these “bonæ species” of elementary organisms, have
arisen solely by division of labour, in consequence of natural
selection, although they not only never were locally isolated, but ever
since their origin have always existed in the closest local relations
one with another. Now, the same reasoning that applies to these
elementary organisms, or “individuals of the first order,” applies also
to the many-celled organisms of a higher order which only at a later
date have arisen as “good species” from among their fellows.

We are therefore of the same opinion as Darwin and Wallace, that the
migration of organisms and their isolation in their new home is a very
advantageous condition for the origin of new species; but we cannot
admit, as Wagner asserts, that it is a _necessary_ condition, and that
without it no species can arise. Wagner sets up this opinion, “that
migration is a necessary condition for natural selection,” as a special
“_law of migration_”; but we consider it sufficiently refuted by the
above-mentioned facts. We have, moreover, already pointed out that in
reality the origin of new species by natural selection is a
_mathematical and logical necessity_ which, without anything else,
follows from the simple combination of three great facts. These three
fundamental facts are—the Struggle for Life, the Adaptability, and the
Hereditivity of organisms.

We cannot here enter into detail concerning the numerous interesting
phenomena furnished by the geographical and topographical distribution
of organic species, which are all wonderfully explained by the theory of
selection and migration. For these I refer to the writings of Darwin,(1)
Wallace,(36) and Moritz Wagner,(40) in which the important doctrine of
the _limits of distribution_—seas, rivers, and mountains—is
excellently discussed and illustrated by numerous examples. Only three
other phenomena must be mentioned here on account of their special
importance. First, the close relation of forms, that is, the striking
“family likeness” existing between the characteristic local forms of
every part of the globe, and their extinct fossil ancestors in the same
part of the globe; secondly, the no less striking “family likeness”
between the inhabitants of island groups and those of the neighbouring
continent from which the islands were peopled; lastly and thirdly, the
peculiar character presented in general by the flora and fauna of
islands taken as a whole.

All these chorological facts given by Darwin, Wallace, and
Wagner—especially the remarkable phenomena of the limited local fauna
and flora, the relations of insular to continental inhabitants, the wide
distribution of the so-called “cosmopolitan species,” the close
relationship of the local species of the present day with the extinct
species of the same limited territory, the demonstrable radiation of
every species from a single central point of creation—all these, and
all other phenomena furnished to us by the geographical and the
topographical distribution of organisms, are explained in a simple and
thorough manner by the theory of selection and migration, while without
it they are simply incomprehensible. Consequently, in the whole of this
series of phenomena we find a new and weighty proof of the truth of the
Theory of Descent.

[1] The world is perfect save where Man
Comes in with his strife.

[2] Archebiosis (Bastian), Abiogenesis (Huxley).

[3] Alle Glieder bilden sich aus nach ew’gen Gesetzen,
Und die seltenste Form bewahrt im Geheimniss das Urbild.
Also bestimmt die Gestalt die Lebensweise des Thieres.
Und die Weise zu leben, sie wirkt auf alle Gestalten
Mächtig zurück. So zeiget sich fest die geordnete Bildung,
Welche zum Wechsel sich neigt durch äusserlich wirkende Wesen.

[4] “Einstweilen bis den Bau der Welt
Philosophie zusammenhält,
Erhält sich ihr Getriebe
Durch Hunger und durch Liebe.”

[5] “Allgemeine Naturgeschichte und Theorie des Himmels.”

[6] We must wait for fuller information on the subject of
Bathybius, at the hands of the naturalists of the _Challenger_
expedition, before accepting it finally as a distinct
organism.—_Editor._

END OF VOL. I.

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