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EVOLUTION
ITS NATURE, ITS EVIDENCES, AND ITS
RELATION TO RELIGIOUS THOUGHT
BY
JOSEPH LE CONTE
AUTHOR OF “RELIGION AND SCIENCE,” ETC.
AND PROFESSOR OF GEOLOGY AND NATURAL HISTORY IN THE
UNIVERSITY OF CALIFORNIA
_SECOND EDITION, REVISED_
NEW YORK:
D. APPLETON AND COMPANY,
72 FIFTH AVENUE.
1897.
COPYRIGHT, 1888, 1891,
BY D. APPLETON AND COMPANY.
PREFACE TO THE SECOND EDITION.
The three years which have elapsed since the publication of the first
edition of this work have been years of great activity of thought on
many of the subjects treated therein. Some changes and additions seemed
therefore imperatively called for.
For example: There has sprung up recently among the foremost writers on
evolution a warm discussion on the _factors_ of evolution, their number
and relative importance. I have therefore added a chapter (Chap. III,
Part II) on this subject--not, indeed, to discuss it fully (for this
would be impossible in the limits of a chapter), but to put the mind of
the reader in position to understand it and to judge for himself.
Again: Every reader of the first edition must have remarked that there
are many fundamental religious questions which I have not touched at
all in Part III. I had avoided these because my own mind was not yet
fully clear. I regarded what I then wrote as only a little leaven
in a very large lump. I was willing to wait and let it work. In the
mean time it has worked in my own mind, and I hope in the minds of
others. I have therefore added two chapters to this part. In one I
simply carry out to their logical consequences the doctrine of the
Divine Immanency. This brings up the questions of _First and Second
Causes_; of _General and Special Providence_; of the _Natural and the
Supernatural_; of _Mind vs. Mechanics in Nature_, etc., and shows the
necessary changes of view which are enforced by the theory of evolution.
In the other I take up very briefly “_The Relation of Evolution to the
Doctrine of the Christ_.” In the discussion of this I restrain myself
strictly within the limits of the subject as stated above.
The only other important changes are in Chapter IV, Part III, “_On the
Relation of Man to Nature_.” As I regard this as the most important
chapter in the whole book, I have endeavored still further to enforce
my view of the origin of man’s spirit, and especially to make it
clearer by means of several additional illustrations.
JOSEPH LE CONTE.
BERKELEY, CAL., _July 1, 1891_.
PREFACE TO THE FIRST EDITION.
The subject of the following work may be expressed in three questions:
What is evolution? Is it true? What then? Surely, there are no
questions of the day more burning than these. Much has been written
on each of them, addressed to different classes of minds: some to
the scientific, some to the popular, and some to the religious and
theological; but nothing has yet appeared which covers the whole ground
and connects the different parts together. Much, very much has been
written, especially on the nature and the evidences of evolution, but
the literature is so voluminous, much of it so fragmentary, and most
of it so technical, that even very intelligent persons have still very
vague ideas on the subject. I have attempted to give (1) a very concise
account of what we mean by evolution, (2) an outline of the evidences
of its truth drawn from many different sources, and (3) its relation to
fundamental religious beliefs. I have determined, above all, to make
a book so small that it may be read through without much expense of
time and patience. But the subject is so large that in order to do so
it was necessary to sacrifice all but what was most essential, and to
forego all redundancy (the bane of so-called popular science) even at
the risk of baldness and obscurity. Nevertheless, I hope that the first
and second parts will be found not only interesting to the intelligent
general reader, but even profitable to the special biologist. I have
tried to make these parts as untechnical as possible, but I hope not
on that account the less scientific. For I am among these who think
that it is not necessary to be superficial in order to be popular--that
science may be adapted to the intelligent popular mind without ceasing
to be science.
The third part seems to me still more important just now. There is
a deep and widespread belief in the popular mind, and even to some
extent in the scientific mind, that there is something exceptional in
the doctrine of evolution as regards its relation to religious thought
and moral conduct. Other scientific theories have required only some
modifications of religious conceptions, but this utterly destroys
the possibility of all religious belief by demonstrating a pure
materialism. Now this, I believe, is a complete misconception. Thinking
men are fast coming to see this; some, indeed, have mistaken the
change for a reaction against evolution. It is a reaction not against
evolution, but only against its materialistic implication. Evolution is
more and more firmly established every year. The tide of conviction is
one which knows no ebb. Some clear statement, in brief space, of its
true relation to religious thought seems, therefore, very important at
this time.
BERKELEY, CAL., _May, 1887_.
CONTENTS.
PART I.
_WHAT IS EVOLUTION?_
CHAPTER I.
ITS SCOPE AND DEFINITION.
PAGE
_A type of evolution_--Development of an egg 3
_Universality of evolution_--Pervades all nature and concerns
all departments of thought--One half of all science--
Illustrated (1) by human body, (2) by solar system, (3) by
society, (4) by earth, (5) by organic kingdom--The term
evolution usually, but not rightly, confined to this last 3
_Definition of evolution_--_I. Progressive change_--Shown in
the animal body, or the _Ontogenic_ series--In the animal
scale, or the _Taxonomic_ series--In the geological, or
_Phylogenic_ series--The three series similar, though not
identical 8
_II. Change according to certain laws_--Three laws of succession
of organic forms 11
(_a_) _Law of differentiation_--Early forms are generalized;
afterwards separated into specialized forms--Illustrated
by fishes, by birds--Whole process of differentiation
illustrated by growth and branching of a tree 11
(_b_) _Law of progress of the whole_--Mistake of confounding
evolution with upward progress--How far true, and how far
false--Illustrated by branching tree--Examples of this
mistake in the popular mind--In the scientific mind 13
(_c_) _Law of cyclical movement_--Shown in geological history--
Age of mollusks, fishes, reptiles, mammals, man--Illustrated
again by a branching tree--Increasing complexity as well as
height--Illustrated by diagram 16
_The above three laws are laws of evolution_--_Differentiation_
--Shown in the development of an egg, the type of evolution 19
_Progress of the whole_--Not progress of all parts--Shown in
the development of an egg 22
_Cyclical movement_--Less fundamental than other two--Shown in
Ontogeny of body, of mind--Increasing complexity--Necessity
of continued advance--Otherwise deterioration--All these
laws shown in progress of society---Differentiation shown--
Progress of the whole but not of all parts shown--Cyclical
movement shown--In social evolution, however, there is
another element, viz., conscious voluntary progress---This
kind of evolution contrasted with the other 22
_III. Change by means of resident forces_--This is the point of
dispute--Sense in which we use term resident forces--Does
not touch question of origin of natural forces 27
_The two views of the origin of organic forms briefly contrasted_
--As to whether natural or supernatural--As to variability,
definite or indefinite--As to change from one species to
another by transmutation or substitution--As to universality
of law of continuity 29
CHAPTER II.
THE RELATION OF LOUIS AGASSIZ TO THE THEORY OF EVOLUTION.
General misunderstanding on this subject--Necessary to give
sketch of history of the idea--Greeks, Lucretius, Swedenborg,
and Kant--First scientific presentation by Lamarck--General
character of Lamarck’s views--Failed, and rightly so--Next,
Chambers’s “Vestiges of Creation”--Its general character--
Failed, and rightly so--Some think this unfortunate--Why
not so--An obstacle must be removed and a basis laid 32
_The obstacle removed_--Old views in regard to forces--
Correlation of forces established--But vital force considered
exception--Therefore living forms also supposed exception
to mode of origin of other forms--Then vital forces also
correlated--Therefore, _a priori_ probable that living forms
also correlated with other forms as to mode of origin--Thus
obstacle removed 35
_The basis laid_--Agassiz laid inductive _basis_ of evolution,
although he refused to build--He established the laws of
evolution and perfected the method of comparison--Importance
of method discussed--The method of _notation_--The method
of experiment--The difficulty of applying these to life
phenomena--Method of comparison shown--(1) In Taxonomic
series--(2) In Ontogenic series--(3) In Phylogenic series
--Cuvier the great worker by comparison in the Taxonomic
series--Agassiz in the Ontogenic and Phylogenic--Agassiz
also established the three laws of evolution given in previous
chapter--Thus he laid foundation--Why he did not build--
Supposed identity of evolution and materialism--The obstacle
being removed and the basis laid, when evolution again brought
forward it was universally accepted, because the world was
prepared--Place of Agassiz and Darwin compared--Formal
science _vs._ physical science--Illustrated by relation of
Kepler to Newton--Relation of Agassiz to time cosmos similar
to that of Kepler to space cosmos--So Darwin to Newton--
Some reflections on the above--Gravitation is the law of
space cosmos--Evolution of time cosmos--Of the divine
spheral music gravitation is the chordal harmony and evolution
the melody 37
PART II.
_EVIDENCES OF THE TRUTH OF EVOLUTION._
CHAPTER I.
GENERAL EVIDENCES OF EVOLUTION AS A UNIVERSAL LAW.
_Evolution is continuity, causal relation, gradual becoming_
--Increasing acceptance of this idea--First accepted
for inorganic forms, mountains, continents and seas, rocks
and soils, earth as a whole, heavenly bodies--Therefore
acknowledged for all inorganics--Influence of geology in
bringing about this change--Organic forms: acknowledged
for individuals, true for classes, orders, families, genera
--Races and varieties also formed gradually--Artificial
species formed gradually--Examples of gradual changes in wild
species--Hyatt’s researches--Other examples--Summing up
of general evidence--Sufficient ground for induction--
But evolution is not only inductively probable but certain,
axiomatic--It is the law of causation applied to forms, and
therefore a necessary truth 53
CHAPTER II.
SPECIAL PROOFS OF EVOLUTION.
_Introductory._
_Special proofs necessary_--Evolution, though certain, is not
yet accepted by the popular mind--Different departments from
which proofs are drawn 67
_Origin of new organic forms; the old view briefly stated_--
Necessary to give a brief statement of theories--Old view--
Permanency of specific types--Supernatural origin of species
--Centers of creation--Explanation of facts of geographical
distribution--Of geological distribution--Modification of
extreme view--Variability, but within limits--Illustrated 68
_The new view briefly stated_--Indefinite variability of organic
forms--Effect of environment on rigid forms--On plastic
forms--Taxonomic groups represent degrees of kinship 72
_Factors of evolution_--(1) Physical environment--(2) Use
and disuse of organs--(3) Natural selection--(4) Sexual
selection--(5) Physiological selection--Its necessity shown
--Its operation explained--Compared with natural selection
--Cause of variation unknown--Explanation of this is the
next great step in the theory of evolution 73
CHAPTER III.
THE GRADES OF THE FACTORS OF EVOLUTION AND THE ORDER OF THEIR
APPEARANCE.
_Factors of evolution restated; their grades and the order of
their introduction shown_--Lamarckian factors, first
in order because they precede sexual reproduction--(1)
Environment--(2) Use and disuse--With sexual reproduction
selective factors introduced--(3) Natural selection--(4)
Physiological selection--(5) Sexual selection--With man
was introduced (6) the rational factor--In this process
two striking stages--viz., the introduction of sex and the
introduction of reason--Effect of each to hasten the steps of
evolution--The last by far the greater change 81
_Contrast between organic and human evolution_--(1) The
meaning of term _fittest_ in each--(2) Destiny of the
weak and helpless in each--(3) The nature of evolutionary
transformation in each--(4) The law of strait and narrow way
applied in each--(5) Human evolution is a different kind and
on a higher plane 88
_Application to some questions of the day._
I. Neo-Darwinists, their position explained--Reasons for
dissenting--(_a_) Lamarckian factors preceded all others--
(_b_) Though now subordinate, they still underlie and condition
all other factors--(_c_) Shown by comparison of phylogeny
with ontogeny 92
II. Human progress not identical with organic evolution--Mistake
of the materialists--But neither is it wholly different, as
some suppose 96
III. Neo-Darwinism is fatal to hopes of human progress--Reason
may use freely Lamarckian factors, but can not use natural
selection in the same way as Nature does 97
CHAPTER IV.
SPECIAL PROOFS FROM THE GENERAL LAWS OF ANIMAL STRUCTURE, OR
COMPARISON IN THE TAXONOMIC SERIES.
_General Principles._
_Analogy and homology_--Defined and illustrated by examples--
Wings and limbs--Lungs, gradual formation of, traced in the
Taxonomic series--Traced in the Ontogenic series--Examples
of homology in plants: tuber, cactus-leaf, acacia-leaf--
Definitions repeated and further explained--Common origin is
the only explanation of homology 99
_Primary divisions of the animal kingdom_--True ground of such
divisions is ability to trace homology--We take examples
only from vertebrata and articulata--Compare to styles of
architecture--To machines--To branching stem 107
CHAPTER V.
PROOFS FROM HOMOLOGIES OF THE VERTEBRATE SKELETON.
_Common general plan_--In several respects--Strongly suggestive of
common origin--Details of structure demonstrative of the same 111
_Special homology of vertebrate limbs_ 113
_Fore-limbs_--Comparison of fore-limbs of mammals, birds,
reptiles, and fishes, part for part--Gradual changes in
collar-bone and coracoid--In position of elbow--In bones
of forearm--In position of wrist--In the tread--The term
manus--Number of toes--Modifications for flight in various
animals--For swimming in whales and fishes 113
_Hind-limbs_--Comparison of hind-limbs of several mammals--
Position of knee--Of heel--Plantigrade and digitigrade
--Degrees of the latter--Number of toes--General law in
regard to number of similar parts--Order of toe-dropping in
artiodactyles--In perissodactyles 121
_Genesis of the horse_--Changes in foot-structure--Same true
of other parts of skeleton--Only natural explanation is
derivation--Nature compared with man in mode of working--
Angels--Griffins--Centaurs--Muscular and nervous systems
--Visceral organs 126
CHAPTER VI.
HOMOLOGIES OF THE ARTICULATE SKELETON.
_Illustrations from this type_--Plan of structure entirely
different--General plan of structure explained and
modifications shown--Shrimp--Modification of segments and
of appendages for various purposes: swimming, walking, eating,
sense--Illustrated by other crustaceans--By myriapods--
By marine worms--Crabs--Embryonic development of crabs--
insects--Modification of segments and appendages--Mouth
parts of insects 132
_Illustration of the law of differentiation_--Cells--Segments
--Individuals--Homologies in other departments of animals,
but these are less familiar--Between primary groups, homology
untraceable in adult forms--But these also probably connected
by common origin--Different views as to origin of vertebrates 144
CHAPTER VII.
PROOFS FROM EMBRYOLOGY, OR COMPARISON IN THE ONTOGENIC SERIES.
_Resemblance of the three series_--Frog, in Ontogeny passes
through main stages of Taxonomy and Phylogeny--Resemblance
only general--Many steps dropped out in Ontogeny 148
(1) _Ontogeny of tailless amphibians_--The frog: fish stage,
perennibranch stage, caducibranch stage, aneural stage--Same
stages in Phylogeny 150
(2) _Aortic arches_--Those of lizard described--Origin from
gill-arches of fish--Change from one to the other in Ontogeny
of a frog--Same changes in Phylogeny of lizard--Embryonic
condition of mammalian heart and vessels--Gradual change and
final condition in birds--In mammals--Gradual decrease in
number of aortic arches as we go up the vertebrate scale--
Cogency of the argument from aortic arches 151
(3) _Vertebrate brain_--Fish brain--Brain of reptiles, birds,
mammals, man compared--Human brain passes through similar
stages--Changes in complexity of structure in Taxonomy--
Same changes in Ontogeny of mammals--Same in Phylogeny of
reptiles, birds, mammals 162
_Cephalization_--Explanation of, in body, in mind 171
(4) _Fish-tails_--Homocercal and heterocercal--Vertebrated
and non-vertebrated--Order of change in Ontogeny--Same
in Phylogeny--Similar changes in birds’ tails in Ontogeny
and Phylogeny--In other tailless animals--Examples from
articulates, insects, crustaceans, etc. 172
_Illustration of the differentiation of the whole animal kingdom_
--Development of eggs of all kinds of animals--This a type
of changes in Phylogeny--Why Ontogeny repeats Phylogeny--
Law of acceleration 176
_Proofs from rudimentary and useless organs_--Examples from
whale: Teeth--Limbs--Hair--Olfactive organs--Examples
from man: muscles, cæcal appendage--Significance of useless
organs 179
CHAPTER VIII.
PROOFS FROM GEOGRAPHICAL DISTRIBUTION OF ORGANISMS.
_Geographical faunas and floras_--Conditions which limit 183
_Temperature-regions_--Illustrated by plants--In latitude and
in elevation--Same in animal species 184
_More perfect definition of regions_--Range of different
Taxonomic groups--Gradual shadings on borders of range--
Shadings out of individuals in number and vigor, but not in
specific character--As if centers of origin--Effect of east
and west barriers--Temperature regions repeated south of the
equator, but not species--As if centers of origin 186
_Continental faunas and floras_--Temperature zones continuous,
but not species--Reason: ocean barriers--As if centers
of origin--Polar regions: one. Why--Temperate zone--
Different species in different continents--Species of United
States and of Europe almost wholly different--As if origin
local--Exceptions--(1) Introduced species--(2) Hardy or
else wide-migrating species--(3) Alpine species--Tropical
zone of two continents still more different--Same true of
south temperate zone 188
_Subdivisions of continental faunas and floras_--Illustrated by
fauna and flora of United States 191
_Special Cases_--Australia--Madagascar--Galapagos--River
mussels 192
_Marine species_--Same principles applicable--Therefore organic
forms grouped in regions, sub-regions, provinces, etc.--
Primary regions according to Wallace--According to Allen 192
_Theory of the origin of geographical diversity_--Specific
centers of creation--Objections to. The element of time left
out--Progressive change in unlimited time, or evolution the
only rational explanation--This connects with geographical
changes in geological times, especially the Glacial epoch--
Geographical diversity in other times 193
_Most probable view of the general process_--Last great period
of change was the Glacial epoch--This, therefore, is the key
to geographical distribution--Condition of things during the
Glacial epoch---In America--Changes in temperature--In
physical geography and in species--In Europe--Application
of principles 196
(1) _Australia_--Characteristics of its fauna--Explanation
of--Isolation very early--Position of marsupials and
monotremes in the Taxonomic scale--Australia isolated before
the Tertiary--Effect of competition on evolution 200
(2) _Africa_--African region defined--Two groups of its
mammals, indigenes, and invaders--Effect of the invasion 204
(3) _Madagascar_--Characteristics of its fauna--Relation
to African indigenes--Separated before the invasion--
Significance of its lemurs 205
(4) _Island life_--Two kinds of islands--Defined and
illustrated by examples--(_a_) _Continental islands_--
General character of fauna--Illustrated by Madagascar,
New Zealand, British Islands, coast-islands of California
--Characteristics of the faunas of these explained--(b)
_Oceanic Islands_--Defined--Characteristics of faunas and
their origin 207
(5) _Alpine species_--Characteristics of and their origin
explained--Migrations of Arctic species during Glacial times,
and their isolation on mountains 215
_Objection_--Mode of change of species on borders of ranges--
Examples--Sweet-gum--Sequoia 217
_Answer_--Distribution of these forms in time, and their
migrations--They are remnants--Intermediate forms are extinct 219
CHAPTER IX.
PROOFS FROM VARIATION OF ORGANIC FORMS, ARTIFICIAL AND NATURAL.
_Limitation of the use of experiment in morphology_--Unconscious
experiments in breeding, and their results--Principles
involved--Inheritance, immediate and ancestral--Effect of
true breeding long continued--Method of selection illustrated
by diagram--Formation of a race--Process the same in nature
--Show selective effect of physical environment--Of organic
environment--Of migrations--Of unlimited time--Other
factors of change, and their effects shown in nature and in
domestication--Differences between artificial and natural
species 222
_First difference, reversion_--The tendency to reversion
described--The reason explained--Illustrated by the case of
the pointer 229
_Second difference, intermediate forms_--Reason is, these are
eliminated in nature 232
_Third difference, cross-fertility_--Natural species are usually
cross-sterile--Degrees of cross-sterility--Two bases of
species, morphological and physiological--Two kinds of
isolation, sexual repugnance and cross-sterility--Latter most
essential--Illustrated by plants and hermaphrodite animals--
Former only higher animals--Natural laws interfered with by
domestication--Illustrated by plants and animals 232
_Law of cross-breeding_--Effect of close breeding--Of crossing
varieties to a limit--The law investigated--Reproduction in
lowest organisms--Fission--Gemmation--Internal gemmation
--Sex introduced--Effect of, is funding of differences in
offspring and tendency to variation--Sexual and non-sexual
reproduction compared--Separation of sex elements--
Of sex-individuals--Introduction of sex-attraction--
Funding of greater differences in offspring--Crossing of
varieties--Diagram illustrating effect in vigor--Effect
also in plasticity--Application of these principles--
Necessity of sexual isolation to produce species--Origin of
cross-sterility and thus of species by Dr. Romanes’s idea--
Why artificial varieties are cross-fertile--Geographical
species sometimes cross-fertile--Application of principles--
Absence of intermediate links in natural species explained--
Under what conditions such are found--Further explanation of
this point--Illustrated by a growing tree 236
_Objection answered_--Intermediate links ought to be found fossil
--Answer (1) Imperfection of record. (2) The term species
indefinite. (3) Transitions between all other taxonomic groups
abundant. (4) Between species, also, both living and fossil
--Of fossil, Planorbis of Steinheim--Other examples--(5)
Why transition-forms are rare--Answer--Changes in every
department of nature are paroxysmal--Illustrated--So the
steps of evolution paroxysmal--Critical periods in evolution
--Causes of rapid advance--Apparent discontinuity between
species--(1) changes paroxysmal--(2) Brooks’s idea--Male
sex is the progressive element--Illustrated by society--
Effect of prosperous times--Mrs. Treat’s experiments--Hard
times produce excess of males, and therefore tend to diversity
--Summary 248
_Objection_--Egyptian drawings and mummy plants, show no change
--Answer (1) Time too short. (2) We are now in time of slow
change. (3) All species don’t change, most become extinct. (4)
Evolution is probably slower now than formerly--Reasons for
so thinking--Organic evolution approaching completion--
Other supposed objections 265
_Origin of beauty_--Explanation of, in higher animals--In
flowering plants--But in many cases we can’t explain 269
_Incipient organs_--Difficulty of explaining--But these are
not objections to the _fact_ of evolution, but only to the
sufficiency of the present _theories_ of evolution. Therefore,
all discussion concerns special theories. The fact of evolution
is certain 270
PART III.
_THE RELATION OF EVOLUTION TO RELIGIOUS THOUGHT._
CHAPTER I.
INTRODUCTORY.
_Evolution if true affects every department of thought_--What
will be its effect on religious beliefs?--Objection that
truth-seeker has nothing to do with effects--Answered 275
_Relation of the true and the good_ 277
_Relation of philosophy to life_--The three necessary elements
of a rational philosophy--Application to the case in hand--
And the subject of Part III justified--Exaggerated fears--
Different forms of the conflict of science and religion--(1)
Heliocentric theory--First effect and final result--(2) Law
of gravitation--Effect and result--(3) Antiquity of the
earth and cosmos--Effect and result--(4) Antiquity of man
--(5) Evolution 277
CHAPTER II.
THE RELATION OF EVOLUTION TO MATERIALISM.
_Supposed identity_--Tendency of the age--Evolution does not
differ in this regard from other laws of Nature--Absurdity
of identification illustrated in many ways--(1) Effect of
discovery of process of making--(2) Effect of new form of old
truth--(3) Manner in which vexed questions are settled and
rational philosophy found--Illustrated--A true philosophy
is a reconciliation of partial views--Three possible views
of origin of individuals and of species; two one-sided and
partial, and the third combining, reconciling, and therefore
rational--The only bar to speedy reconciliation is dogmatism
--Theological and scientific--The appropriate rebuke for
each--Therefore evolution does not differ from other laws in
regard to its relation to materialism--Nevertheless, great
changes in our traditional beliefs impending--Main changes
are notions concerning God, Nature, and man, in their relations
to one another 284
CHAPTER III.
THE RELATION OF GOD TO NATURE.
The issue in regard to this relation stated--The growth of the
issue described--The old view of direct relation--The
effect of science and the resulting view--The compromise--
Destroyed by evolution--The issue forced--The alternative
view--Immanence of Deity--This view explained--Objection
of idealism--Answered--It is not subjective idealism--
Objection of pantheism--Answer deferred--Objection that the
view is incompatible with practical life--Answered 297
CHAPTER IV.
THE RELATION OF MAN TO NATURE.
_The two extreme views in this regard_--They are views from
different points, psychical and material--The latter very
productive in modern times--But many fear the final effect--
Reconciliation is possible--Scientific materialism has two
branches--_Physiological branch_ explained--Conclusion--
Answer--Relation of psychic to brain changes is inscrutable
--The mystery illustrated--Outside and inside view--
Different from other phenomena in this regard 304
_Evolution branch_--Close relation of man to animals--Therefore
must extend immortal spirit to animals--to plants--to all
existence, and thus identify immortality with conservation
of force--Embryonic series--Where did spirit enter?--
Evolution series--Where did spirit enter?--Answer--
Derived from Nature--The true view of origin stated--Show
that it is not in discord with other phenomena of evolution
--The five planes of matter and of force--The change from
one to another not gradual now nor in the evolution of natural
forces--Consecutive births into higher forms--Every step
of these changes taking place now--Relation of these facts
to immortality--The process briefly stated--Omnipresent
divine energy individuated to separate entity in man--Anima
of animals is spirit in embryo--Came to birth in man--
Illustrated in other ways--(1) By more or less completed
water-drop--(2) By submergence and emergence--(3) By
planet birth--(4) By physical birth--(5) By grades of
organic individuality--(6) By the body as an instrument of
communication between two worlds--Self-consciousness the sign
of spirit-individuality--Any animal conscious of self would
be immortal--Similar changes in passing from animals to man
in all other departments of psychic activity--Objection that
other changes of energy not permanent; answered--Our view
of origin compared with alternative views--Plato’s view--
Orthodox view 311
_Some general conclusions_--(1) Two series of changes,
brain-changes and mind-changes--The initiative in animals
--In man--(2) Justification of term “_vital principle_”
--Becomes entity in man--(3) This view is a complete
reconciliation of realism and nominalism--(4) No meaning in
Nature without spirit--And no meaning in geological history
without derivative origin of spirit--Material evolution finds
its goal in man, psychic evolution in the divine man 327
CHAPTER V.
THE RELATION OF GOD TO MAN.
_Question of revelation_--Difficulty of the subject--Operation
of divine spirit on spirit of man more direct than on Nature
--This is revelation--This is no violation of law, but
operation by higher law--Term supernatural is relative--
Illustrated--There is but one kind of revelation, and this to
all men in different degrees--Always imperfect, and therefore
must be tried by reason 331
CHAPTER VI.
THE OBJECTION, THAT THE ABOVE VIEW IMPLIES PANTHEISM, ANSWERED.
_The objection stated and the general answer_--In deepest
questions single lines of thought lead to extreme views--Must
follow other lines--These lead to personality 335
(1) Exact character of relation of God and of necessary law to
man’s freedom is inscrutable 338
(2) On the inside of brain-changes we find personality--So on
the inside of natural phenomena must also be person--In
either case science studies the outside only--In Nature
all is mechanics on the outside, but all is mind on the
inside--Thought behind brain-changes compels belief in same
behind natural phenomena--Law of infinite expansion--
Illustrated by ideas of Space and Time--So also with idea
of self--Infinite person inconceivable, but contrary is more
inconceivable--Illustrated by ideas of Space and Time 338
(3) Idea of _Causation_ and of _Force_--Derived from _within_
--Steps of the evolution of this idea--Final result is one
infinite personal will--Expansion of idea of causal nexus
between phenomena to the idea of one infinite cause 342
(4) Idea of _design_ also originates _within_--Ineradicable, but
changes form--Expands to infinity--Same change produced by
science in all our notions concerning God--Same in our sense
of _mystery_--Same in our notions concerning _creation_--
Same in our conceptions of _design_--Thus, self-consciousness
behind brain-changes compels belief in God behind Nature--The
closeness of connection in the one case necessitates closeness
of connection in the other--Every material change in Nature
caused by a mental change behind Nature 345
CHAPTER VII.
SOME LOGICAL CONSEQUENCES OF THE DOCTRINE OF THE DIVINE IMMANENCY.
Religious thought subject to the law of evolution; three main
stages 351
I. _Conception of God_--The three stages shown--(1)
Anthropomorphism--(2) Absentee landlordism--(3) Immanence 351
II. _Question of First and Second Causes_--The three stages shown
here--(1) All is First Cause but man-like--(2) Distinction
of first and second causes introduced--(3) Identification of
these 354
III. _General and Special Providence_--The same three stages
shown and the same outcome--viz., identification 355
IV. _Natural and the supernatural_--The same stages and the same
final identification--Question of miracles 355
V. _Question of design or mind in Nature_--The same three stages
and the same solution shown here--Confusion in the minds of
modern writers 357
VI. _Question of mode of creation_--Old and new views contrasted 358
CHAPTER VIII.
RELATION OF EVOLUTION TO THE IDEA OF THE CHRIST.
Comparison of organic with human evolution--The idea of the first
is _man_, of the second is the _Christ_--Definition of the
Christ as _ideal man_--The Christ ought to differ from us
in a superhuman way--Shown by several illustrations--The
Christ, as ideal man, a true object of rational worship--The
ideal of organic evolution comes _at the end_--Ideal of human
evolution must come _in the course_--Objection that there are
many partial ideals answered--Relative vs. absolute moral
ideal. 360
CHAPTER IX.
THE RELATION OF EVOLUTION TO THE PROBLEM OF EVIL.
The difficulty of the problem--The light on it by evolution--
Evil must be based on the constitution of Nature and therefore
universal--Some of its forms 365
(1) _Physical evil in animal kingdom_--Condition of organic
evolution is struggle with an apparently inimical environment
--In its course it seems evil--Looking back from the end it
is good. 365
(2) _Physical evil in relation to man_--Necessary condition
of social evolution is also struggle with a seeming evil
environment--But looking back from the end this evil is also
seen to be good--Without it man would never have emerged from
animality. 366
(3) _Organic evil--Disease_--This also is the necessary
condition of acquisition of knowledge of organic Nature--In
the course of evolution it seems evil, but from the end it is
seen to be good--In the physical world, laws of Nature are
beneficent in their general operation, and only evil in their
specific operation through our ignorance. 367
(4) _Moral evil--Moral disease_--Difference between this
and other forms of evil--Can this also be transmuted into
good?--This is only the highest form of evil, and therefore
subject to the same laws of evolution--Here also elevation
comes only through knowledge and power, and these only through
struggle with apparent evil--In course it seems evil,
looking back from end it is seen to be good to the race--
In all, therefore, the individual is sacrificed to the race,
but impossible here--A way of escape found in the nature of
a moral being--In this case not only final victory for the
race, but also within the power of the individual--In this
case success is in proportion to honest effort in right spirit
--Roots, of evil in the necessary law of evolution--It is
the necessary condition of all progress--Without it a moral
being is impossible--From philosophic point of view things
are not good and evil, but only higher and lower--All things
good in their places--Evil is discord--Good is due relation
--Action and reaction of higher and lower is the necessary
condition of true virtue 369
PART I.
_WHAT IS EVOLUTION?_
CHAPTER I.
ITS SCOPE AND DEFINITION.
=A Type of Evolution.=--Every one is familiar with the main facts
connected with the development of an egg. We all know that it begins as
a microscopic germ-cell, then grows into an egg, then organizes into
a chick, and finally grows into a cock; and that the whole process
follows some general, well-recognized law. Now, this process is
evolution. It is more--it is _the_ type of all evolution. It is that
from which we get our idea of evolution, and without which there would
be no such word. Whenever and wherever we find a process of change
more or less resembling this, and following laws similar to those
determining the development of an egg, we call it evolution.
_Universality of Evolution._--Evolution as a _process_ is not
confined to one thing, the egg, nor as a doctrine is it confined
to one department of science--biology. The process pervades the
whole universe, and the doctrine concerns alike every department of
science--yea, every department of human thought. It is literally one
half of all science. Therefore, its truth or falseness, its acceptance
or rejection, is no trifling matter, affecting only one small corner
of the thought-realm. On the contrary, it affects profoundly the
foundations of philosophy, and therefore the whole domain of thought.
It determines the whole attitude of the mind toward Nature and God.
I have said evolution constitutes one half of all science. This may
seem to some a startling proposition. I stop to make it good.
Every system of correlated parts may be studied from two points of
view, which give rise to two departments of science, one of which--and
the greater and more complex--is evolution. The one concerns changes
within the system by action and reaction between the parts, producing
equilibrium and stability; the other concerns the progressive movement
of the system, as a whole, to higher and higher conditions--the
movement of the point of equilibrium itself, by constant slight
disturbance and readjustment of parts on a higher plane, with more
complex inter-relations. The one concerns the laws of sustentation of
the system, the other the laws of evolution. The one concerns things as
they are, the other the process by which they become so. Now, Nature
as a whole is such a system of correlated parts. Every department and
sub-department of Nature, whether it be the solar system or the earth,
or the organic kingdom, or human society, or the human body, is such a
system of correlated parts, and is therefore subject to evolution. We
can best make this thought clear by examples:
1. Take, then, the _human body_. This complex and beautiful system
of correlated and nicely-adjusted parts may be studied in a state of
maturity and equilibrium, in which all the organs and functions by
action and reaction co-operate to produce perfect stability, health,
and physical happiness. This study is physiology. Or else the same may
be studied in a state of progressive change. Now, we perceive that the
stability is never perfect--the point of equilibrium is ever moving. By
the ever-changing number and relative power of the co-operating parts
the equilibrium is ever being disturbed, only to be readjusted on a
higher plane, with still more beautiful and complex inter-relations.
This is growth, development, evolution. Its study is called embryology.
2. Take another example--_the solar system_. We may study sun, planets,
and satellites in their mutual actions and reactions, co-operating to
produce perfect equilibrium, stability, beautiful order, and musical
harmony. This is the ideal of physical astronomy as embodied in
Laplace’s “Mécanique Céleste.” Or we may study the same in its origin
and progressive change. Now, we perceive that equilibrium and stability
are never absolutely perfect, but, on the contrary, there is continual
disturbance with readjustment on a higher plane--continual introduction
of infinitesimal discord, only to enhance the grandeur and complexity
of the harmonic relations. This is the nebular hypothesis--the theory
of the development of the solar system. It is cosmogony; it is
evolution. 3. Again: _society_ may be studied in the mutual play of
all its social functions so adjusted as to produce social equilibrium,
happiness, prosperity, and good government. This is social statics.
But equilibrium and stability are never perfect. Permanent social
equilibrium would be social stagnation and decay. Therefore, we must
study society also in its onward movement--the equilibrium ever
disturbed, only to be readjusted on a higher plane with more and more
complexly inter-related parts. This is dynamics--social progress. It
is evolution. 4. Again: the _earth_, as a whole, may be studied in
its present forms, and the mutual action of all its parts--lands and
seas, mountains and valleys, rivers, gulfs, and bays, currents of air
and ocean--and the manner in which all these, by action and reaction,
co-operate to produce climates and physical conditions such as we now
find them. This is physical geography. Or, we may study the earth
in its gradual progress toward its present condition--the changes
which have taken place in all these parts, and consequent changes in
climate; in a word, the gradual process of becoming what it now is.
This is physical geology--it is evolution. 5. Lastly, we may study
the whole _organic kingdom_ in its entirety as we now find it--the
mutual relation of different classes, orders, genera, and species to
each other and to external conditions, and the action and reaction
of these in the struggle for life--the geographical distribution of
species and their relation to climate and other physical conditions,
the whole constituting a complexly adjusted and permanent equilibrium.
This is a science of great importance, but one not yet distinctly
conceived, much less named.[1] Or, we may study the same in its gradual
progressive approach, throughout all geological times, toward the
present condition of things, by continual changes in the parts, and
therefore disturbance of equilibrium and readjustment on a higher plane
with more complex inter-relations. This is development of the organic
kingdom. In the popular mind it is, _par excellence_, evolution.
We might multiply examples without limit. There are the same two
points of view on all subjects. As already said, in the one we are
concerned with things as they are; in the other, with the process
by which they became so. This “law of becoming” in all things--this
universal law of progressive inter-connected change--may be called the
law of continuity. We all recognize the universal relation of things,
gravitative or other, in space. This asserts the universal causal
relation of things in _time_. This is the universal law of evolution.
But it has so happened that in the popular mind the term evolution
is mostly confined to the development of the organic kingdom, or
the law of continuity as applied to this department of Nature. The
reason of this is that this department was the last to acknowledge
the supremacy of this law; this is the domain in which the advocates
of supernaturalism in the realm of Nature had made their last stand.
But it is wholly unphilosophical thus to limit the term. If there be
any evolution, _par excellence_, it is evolution of the individual or
embryonic development. This is the clearest, the most familiar, and
most easily understood, and therefore the type of evolution. We first
take our idea of evolution from this form, and then extend it to other
forms of continuous change following a similar law. But, since the
popular mind limits the term to development of the organic kingdom, and
since, moreover, this is now the battleground between the advocates
of continuity and discontinuity--of naturalism and supernaturalism in
the _realm of Nature_--what we shall say will have reference chiefly
to this department, though we shall illustrate freely by reference to
other forms of evolution.
DEFINITION OF EVOLUTION.
Evolution is (1) continuous _progressive change_, (2) _according to
certain laws_, (3) and by means of _resident forces_. It may doubtless
be defined in other and perhaps better terms, but this suits our
purposes best. Embryonic development is the type of evolution. It
will be admitted that this definition is completely realized in this
process. The change here is certainly continuously progressive; it is
according to certain well-ascertained laws; it is by forces (vital
forces) resident in the egg itself. Is, then, the process of change
in the organic kingdom throughout geologic times like this? Does it
correspond to the definition given above? Does IT also deserve the
name of evolution? We shall see.
I. =Progressive Change.=--Every individual animal body--say man’s--has
become what it now is by a gradual process. Commencing as a microscopic
spherule of living but apparently unorganized protoplasm, it gradually
added cell to cell, tissue to tissue, organ to organ, and function to
function; thus becoming more and more complex in the mutual action of
its correlated parts, as it passed successively through the stages of
germ, egg, embryo, and infant, to maturity. This ascending series of
genetically connected stages is called the embryonic or _Ontogenic_
series.[2]
There is another series the terms of which are coexistent, and which,
therefore, is not in any sense a genetic or development series, but
which it is important to mention, because to some degree similar to
and illustrative of the last. Commencing with the lowest unicelled
microscopic organisms, and passing up to the animal scale, _as it now
exists_, we find a series of forms similar, though not identical, with
the last. Here, again, we find cell added to cell, tissue to tissue,
organ to organ, and function to function, the animal body becoming more
and more complex in structure, in the mutual action of its correlated
parts, and the mutual action with the environment, until we reach the
highest complexity of structure and of internal and external relations
only in the highest animals. This ascending series may be called
the natural history series; or, the classification or _Taxonomic
series_.[3] The terms of this series are, of course, not genetically
connected; at least, not directly so connected. In what way they are
connected, and how the series comes to be similar to the last, we shall
see by-and-by.
Finally, there is still a third series, the grandest and most
fundamental of all, but only recently recognized, and therefore
still imperfectly known. Commencing with the earliest organisms,
the very dawn of life, in the very lowest rocks, and passing onward
and upward through Eozoic, Palæozoic, Mesozoic, Cenozoic, to the
Psychozoic or present time, we again find first the lowest forms,
and then successively forms more and more complex in structure, in
the interaction of correlated parts and in interaction with the
environment, until we reach the most complex internal and external
relations, and therefore the highest structure only in the present
time.[4] This series we will call the geological or _phylogenic_
series.[5] According to the evolution theory, the terms of _this_
series also are genetically connected. It is, therefore, an evolution
series. Furthermore, it is the most fundamental of the three series,
because it is the _cause_ of the other two. The Ontogenic series is
like it because it is a brief recapitulation, through heredity, as it
were from memory, of its main points. The Taxonomic series is like
it because the _rate_ of advance along different lines was different
in every degree, and therefore every stage of the advance is still
represented in a general way among existing forms. Some of these points
will be explained more fully in future chapters, in connection with the
evidences of the truth of evolution.
It will be admitted, then, that we find _progressive change_ in organic
forms throughout geological times. This is the first point in the
definition of evolution.
II. =Change according to Certain Laws.=--We have shown continuously
progressive change in organic forms during the whole geologic history
of the earth, similar in a general way to that observed in embryonic
development. We wish now to show that the _laws of change_ are similar
in the two cases. What, then, are the laws of succession of organic
forms in geologic times? I have been accustomed to formulate them thus:
_a._ The law of differentiation; _b._ The law of progress of the whole;
_c._ The law of cyclical movement.[6] We will take up these and explain
them successively, and then, afterward, show that they are also the
laws of embryonic development, and therefore the laws of evolution.
_a._ =Law of Differentiation.=--It is a most significant fact, to
which attention was first strongly directed by Louis Agassiz, that
the earliest representatives of any group, whether class, order, or
family, were not what we would now call typical representatives of
that group; but, on the contrary, they were, in a wonderful degree,
connecting links; that is, that along with their distinctive classic,
ordinal, or family characters they possessed also other characters
which connected them closely with other classes, orders, or families,
now widely distinct, without connecting links or intermediate forms.
For example: The earliest vertebrates were fishes, but not typical
fishes. On the contrary, they were fishes so closely connected by many
characters with amphibian reptiles, that we hardly know whether to
call some of them reptilian fishes, or fish-like reptiles. From these,
as from a common vertebrate stem, were afterward separated, by slow
changes from generation to generation, in two directions, the typical
fishes and the true reptiles. So, also, to take another example, the
first birds were far different from typical birds as we now know them.
They were, on contrary, birds so reptilian in character, that there
is still some doubt whether bird-characters or reptilian characters
predominate in the mixture, and therefore whether they ought to be
called reptilian birds or bird-like reptiles. From this common stem,
the more specialized modern reptiles branched off in one direction and
typical birds in another, and intermediate forms became extinct; until
_now_, the two classes stand widely apart, without apparent genetic
connection. This subject will be more fully treated hereafter, and
other examples given. These two will be sufficient now to make the idea
clear.
Such early forms combining the characters of two or more groups,
now widely separated, were called by Agassiz _connecting_ types,
_combining_ types, _synthetic_ types, and sometimes _prophetic_ types;
by Dana, _comprehensive_ types; and by Huxley, _generalized_ types.
They are most usually known now as _generalized_ types, and their
widely-separated outcomes _specialized_ types. Thus, in general, we may
say that the widely-separated groups of the present day, when traced
back in geological times, approach one another more and more until they
finally unite to form common stems, and these in their turn unite to
form a common trunk. From such a common trunk, by successive branching
and rebranching, each branch taking a different direction, and all
growing wider and wider apart (differentiation), have been gradually
generated all the diversified forms which we see at the present day.
The last leafy ramifications--flower-bearing and fruit-bearing--of this
tree of life, are the fauna and flora of the present epoch. The law
might be called a law of ramification, of specialization of the parts,
and diversification of the whole.
_b._ =Law of Progress of the Whole.=--Many imagine that progress is
the one law of evolution; in fact, that evolution and progress are
coextensive and convertible terms. They imagine that in evolution the
movement must be upward and onward in all parts; that degeneration
is the opposite of evolution. This is far from the truth. There
is, doubtless, in evolution, progress to higher and higher planes;
but not along every line, nor in every part; for this would be
contrary to the law of differentiation. It is only progress of the
whole organic kingdom in its entirety. We can best make this clear
by an illustration. A growing tree branches and again branches _in
all directions_, some branches going upward some sidewise, and some
downward--anywhere, everywhere, for light and air; but the whole tree
grows ever taller in its higher branches, larger in the circumference
of its outstretching arms, and more diversified in structure. Even
so the tree of life, by the law of differentiation, branches and
rebranches continually in all directions--some branches going upward
to higher planes (progress), some pushing horizontally; neither rising
nor sinking, but only going farther from the generalized origin
(specialization); some going downward (degeneration), anywhere,
everywhere, for an unoccupied place in the economy of Nature, but the
whole tree grows ever higher in its highest parts, grander in its
proportions, and more complexly diversified in its structure.
It may be well to pause here a moment to show how this mistaken
identification of evolution with progress alone, without modification
by the more fundamental laws of differentiation, has given rise to
misconceptions in the popular and even in the scientific mind. The
biologist is continually met with the question, “Do you mean to say
that any one of the invertebrates, such, for instance, as a spider,
may eventually, in the course of successive generations, become a
vertebrate, or that a dog or a monkey is on the highway to become a
man?” By no means. There is but one straight and narrow way to the
highest in evolution as in all else, and few there be that have found
it--in fact, probably two or three only at every step. The animals
mentioned above have diverged from that way. In their ancestral
history, they have missed the golden opportunity, if they ever had it.
It is easy to go on in the way they have chosen, but impossible to get
back on the ascending trunk-line. To compare again with the growing
tree, only one straight trunk-line leads upward to the terminal bud. A
branch once separated must grow its own way, if it grow at all.
Of the same nature is the mistake of some extreme evolutionists,
such as Dr. Bastian and Professor Haeckel, and of nearly all
anti-evolutionists, viz., that of imagining that the truth of
evolution and that of spontaneous generation must stand or fall
together. On the contrary, _if_ life did _once_ arise spontaneously
from any lower forces, physical or chemical, by natural process,
_the conditions necessary for so extraordinary a change could hardly
be expected to occur but once in the history of the earth_. They
are, therefore, _now_, not only unreproducible, but unimaginable.
Such golden opportunities do not recur. Evolution goes only onward.
Therefore, the impossibility of the derivation of life from non-life
_now_, is no more an argument against such a derivation _once_, than
is the hopelessness of a worm ever becoming a vertebrate _now_, an
argument against the derivative origin of vertebrates. Doubtless if
life were now extinguished from the face of the earth, it could not
again be rekindled by any natural process known to us; but the same is
probably true of every step of evolution. If any class--for example,
mammals--were now destroyed, it could not be re-formed from any other
class now living. It would be necessary to go back to the time and
conditions of the separation of this class from the reptilian stem.
Therefore, the falseness of the doctrine of abiogenesis,[7] so far from
being any argument against evolution, is exactly what a true conception
of evolution and knowledge of its laws would lead us to expect.
_c._ =Law of Cyclical Movement.=--The movement of evolution has ever
been onward and upward, it is true, but not at uniform rate in the
whole, and especially in the parts. On the contrary, it has plainly
moved in successive cycles. The tide of evolution rose ever higher and
higher, without ebb, but it nevertheless came in successive waves,
each higher than the preceding and overborne by the succeeding. These
successive cycles are the dynasties or reigns of Agassiz, and ages
of Dana; the reign of mollusks, the reign of fishes, of reptiles,
of mammals, and finally of _man_. During the early Palæozoic times
(Cambrian and Silurian) there were no vertebrates.[8] But never in
the history of the earth were mollusks of greater size, number, and
variety of form than then. They were truly the rulers of these early
seas. In the absence of competition of still higher animals, they had
things all their own way, and therefore grew into a great monopoly of
power. In the later Palæozoic (Devonian) fishes were introduced. They
increased rapidly in size, number, and variety; and being of higher
organization they quickly usurped the empire of the seas, while the
mollusca dwindled in size and importance, and sought safety in a less
conspicuous position. In the Mesozoic times, reptiles, introduced a
little earlier,[9] finding congenial conditions and an unoccupied
place above, rapidly increased in number, variety, and size, until
sea and land seem to have swarmed with them. Never before or since
have reptiles existed in such numbers, in such variety of form, or
assumed such huge proportions; nor have they ever since been so
highly organized as then. They quickly became rulers in every realm
of Nature--rulers of the sea, swimming reptiles; rulers of the land,
walking reptiles; and rulers of the air, flying reptiles. In the
unequal contest, fishes therefore sought safety in subordination.
Meanwhile mammals were introduced in the Mesozoic, but small in size,
low in type (marsupials), and by no means able to contest the empire
with the great reptiles. But in the Cenozoic (Tertiary) the conditions
apparently becoming favorable for their development, they rapidly
increased in number, size, variety, and grade of organization, and
quickly overpowered the great reptiles, which almost immediately sank
into the subordinate position in which we now find them, and thus
found comparative safety. Finally, in the Quaternary, appeared man,
contending doubtfully for a while, with the great mammals, but soon (in
Psychozoic) acquiring mastery through superior intelligence. The huge
and dangerous mammals were destroyed and are still being destroyed; the
useful animals and plants were preserved and made subservient to his
wants; and all things on the face of the earth are being readjusted to
the requirements of his rule. In all cases it will be observed that
the rulers were such because, by reason of strength, organization, and
intelligence, they were fittest to rule. There is always room at the
top. To illustrate again by a growing tree: This successive culmination
of higher and higher classes may be compared to the flowering and
fruiting of successively higher and higher branches. Each uppermost
branch, under the genial heat and light of direct sunshine, received in
abundance by reason of position, grew rapidly, flowered, and fruited;
but quickly dwindled when overshadowed by still higher branches, which,
in their turn, monopolized for a time the precious sunshine.
But observe, furthermore: when each ruling class declined in
importance, it did not perish, but continued in a subordinate position.
Thus, the whole organic kingdom became not only higher and higher in
its highest forms, but also more and more complex in its structure and
in the interaction of its correlated parts. The whole process and its
result is roughly represented in the accompanying diagram, Fig. 1, in
which A B represents the course of geological time and the curve, the
rise, culmination, and decline of successive dominant classes.
[Illustration:
MOLLUSCS--Silurian.
FISHES--Devon. and Carb.
REEPTILES--Mesozoic.
MAMMALS--Tert’y and Quat.
MAN--Present.
FIG. 1.]
THE ABOVE THREE LAWS ARE LAWS OF EVOLUTION.
These three laws we have shown are distinctly recognizable in the
succession of organic forms in the geological history of the earth.
They are, therefore, undoubtedly the _general laws of succession_. Are
they also laws of evolution? Are they also discoverable in embryonic
development, the type of evolution? They are, as we now proceed to show:
=Differentiation.=--In reproduction the new individual appears: 1.
As a _germ_-cell--a single microscopic living cell. 2. Then, by
growth and multiplication of cells, it becomes an _egg_. This may be
characterized as an aggregate of _similar_ cells, and therefore is
not yet differentiated into tissues and organs. In other words, it
is not yet visibly organized; for organization may be defined as the
possession of different parts, performing different functions, and
all co-operating for one given end, viz., the life and well-being of
the organism. 3. Then commences the really characteristic process of
development, viz., _differentiation_ or diversification. The cells
are at first all alike in form and function, for all are globular in
form, and each performs all the functions necessary for life. From
this common point now commences development in _different directions_,
which may be compared to a branching and rebranching, with more and
more complex results, according as the animal is higher in the scale
of organization and advances toward a state of maturity. First, the
cell-aggregate (egg) separates into three distinct layers of cells,
called ecto-blast, endo-blast, and meso-blast. These by further
differentiation form the three fundamental groups of organs and
functions, viz., the _nervous system_, the _nutritive system_, and the
_blood system_: the first presiding over the exchange of _force_ or
influence, by action and reaction with the environment, and between the
different parts of the organism; the second presiding over the exchange
of _matter_ with the environment, by absorption and elimination; the
third presiding over exchanges of matter between different parts of
the organism. The first system of functions and organs may be compared
to a system of telegraphy, foreign and domestic; the second to foreign
commerce; the third to an internal carrying-trade. Following out any
one of these groups in higher animals, say the nervous system, it
quickly differentiates again into two sub-systems, viz., cerebro-spinal
and ganglionic, each having its own distinctive functions, which we
can not stop to explain. Then the cerebro-spinal again differentiates
into voluntary and reflex systems. All of these have meanwhile
separated into sensory and motor centers and fibers. Then, taking
only the sensory fibers, these again are differentiated into five
special senses, each having a wholly different function. Then, finally,
taking any one of these, say the _sense of touch_ or feeling, this
again is differentiated into many kinds of fibers, each responding to
a different impression, some to heat, others to cold, still others
to pressure, etc. We have taken the nervous system; but the same
differentiation and redifferentiation takes place in all other systems,
and is carried to higher and higher points according to the position in
the scale of the animal which is to be formed.
Or, to vary the mode of presentation a little, the cells of the
original aggregate, commencing all alike, immediately begin to take on
different forms, in order to perform different functions. Some cells
take on a certain form and aggregate themselves to form a peculiar
tissue which we call muscle, and which does nothing else, can do
nothing else, than contract under stimulus. Another group of cells
take on another peculiar form and aggregate themselves to form another
and very different tissue, viz., nervous tissue, which does nothing
and can do nothing but carry influence back and forth between the
great external world and the little world of consciousness within.
Still another group of cells take still another form and aggregate
to form still another tissue, viz., the _epithelial_, whose only
function is to absorb nutritive and eliminate waste matters. Thus, by
differentiation of form and limitation of function, or division of
labor, the different parts of the organism are bound more and more
closely together by mutual dependence, and the whole becomes more and
more distinctly individuated, and separation of parts becomes more and
more a mutilation, and finally becomes impossible without death. This
process, as already said, reaches its highest point only in the later
stages of development of the highest animals.
=Progress.=--The _law of progress_ is, of course, admitted to be a
law of ontogeny; but observe here, also, it is true only of the whole
and not necessarily of all the parts, _except from the point of view
of the whole_. Thus, for example, starting all from a common form or
generalized type, some cells _advance_ to the dignity of brain-cells,
whose function is somehow connected with the generation or at least
the manifestation of thought, will, and emotion; other cells _descend_
to the position of kidney-cells, whose sole function is the excretion
of urine. But here, also, the highest cells are successively higher,
and the whole aggregate is successively nobler and more complex. It
is again a branching and rebranching, in every direction, some going
upward, some downward, some horizontally, anywhere, everywhere, to
increase the complexity of relations internal and external, and
therefore to elevate the plane of the whole.
=Cyclical Movement.=--Lastly, the law of cyclical movement is also a
law of ontogeny and therefore of evolution. This law, however, is less
fundamental than the other two, and is, therefore, less conspicuous in
the ontogenic than in the phylogenic series. It is conspicuous only in
the later stages of ontogeny, and in other higher kinds of evolution,
such as social evolution. For example, in the ontogenic development of
the body and mind from childhood to manhood we have plainly successive
culminations and declines of higher and higher functions. In bodily
development we have culminating first the _nutritive_ functions, then
the _reproductive_ and _muscular_, and last the _cerebral_. In mental
development we have culmination first of the receptive and retentive
faculties in childhood, then of imaginative and æsthetic faculties
in youth and young manhood; then of the reflective and elaborative
faculties--the faculties of productive work in mature manhood; and,
finally, the moral and religious sentiments in old age. The first
gathers and stores materials; the second vivifies and makes them
plastic building materials; the third uses them in actual constructive
work--in building the temple of science and philosophy; and the fourth
dedicates that temple only to noblest purposes.
Observe here, also, that when each group of faculties culminates and
declines, it does not perish, but only becomes subordinate to the next
higher dominant group, and the whole psychical organism becomes not
only higher and higher in its highest parts, but also more and more
complex in its structure and in the interaction of its correlated parts.
Observe, again, the necessity laid upon us by this law--the necessity
of continued evolution to the end. Childhood, beautiful childhood,
can not remain--it must quickly pass. If, with the decline of its
characteristic faculties, the next higher group characteristic of youth
do not increase and become dominant, then the glory of life is already
past and deterioration begins. Have we not all seen sad examples of
this? Youth, glorious youth, must also pass. If the next higher group
of reflective and elaborative faculties do not arise and dominate, then
progressive deterioration of character commences here--thenceforward
the whole nature becomes coarse, as we so often see in young men,
or else shrivels and withers, as we so often see in young women.
Finally, manhood, strong and self-relying manhood, must also pass. If
the moral and religious sentiments have not been slowly growing and
gathering strength all along, and do not now assert their dominance
over the whole man, then commences the final and saddest decline of
all, and old age becomes the pitiable thing we so often see it. But,
if the evolution have been normal throughout; if the highest moral and
religious nature have been gathering strength through all, and now
dominates all, then the psychic evolution rises to the end--then the
course of life is like a wave rising and cresting only at the moment
of its dissolution, or, like the course of the sun, if not brightest
at least most glorious in its setting. And thus--may we not hope?--the
glories of the close of a well-spent life become the pledge and
harbinger of an eternal to-morrow?
We have thus far illustrated the three laws of succession of organic
forms by ontogeny, because this is the type of evolution; but they
may be illustrated also by other forms of evolution. Next to the
development of the individual, undoubtedly the _progress of society_
furnishes the best illustration of these laws.
Commencing with a condition in which each individual performs all
necessary social functions, but very imperfectly; in which each
individual is his own shoemaker and tailor, and house-builder and
farmer, and therefore all persons are socially alike; as society
advances, the constituent members begin to diverge, some taking on
one social function and some another, until in the highest stages of
social organization this diversification or division and subdivision
of labor reaches its highest point, and each member of the aggregate
can do perfectly but one thing. Thus, the social organism becomes
more and more strongly bound together by mutual dependence, and
separation becomes mutilation. I do not mean to say that this extreme
is desirable, but only that an approach to this is _a_ natural law of
social development. _Is not this the law of differentiation?_
So also _progress_ is here, as in other forms of evolution--a _progress
of the whole_, but not necessarily of every part. Some members of
the social aggregate advance _upward_ to the dignity of statesmen,
philosophers, and poets; some advance _downward_ to the position
of scavengers and sewer-cleansers.[10] But the highest members are
progressively higher, and the whole aggregate is progressively grander
and more complex in structure and functions.
So, again, the _law of cyclical movement_ is equally conspicuous here.
Society everywhere advances, not uniformly, but by successive waves,
each higher than the last; each urged by a new and higher social
force, and embodying a new and higher phase of civilization. Again:
as each phase declines, its characteristic social force is not lost,
but becomes incorporated into the next higher phase as a subordinate
principle, and thus the social organism as a whole becomes not only
higher and higher, but also more and more complex in the mutual
relations of its interacting social forces.
Let us not be misunderstood, however. There is undoubtedly in social
evolution something more and higher than we have described, but which
does not concern us here, except to guard against misconstruction.
There is in society a _voluntary progress_ wholly different from the
evolution we have been describing. In _true_ or material evolution
natural law works for the betterment of the whole utterly regardless
of the elevation of the individual, and the individual contributes to
the advance of the whole quite unconsciously while striving only for
his own betterment. This unconscious evolution by natural law inherited
from the animal kingdom is conspicuous enough in society, especially in
its early stages, but we would make a great mistake if we imagined, as
some do, that this is all. Besides the unconscious evolution by natural
laws, _inherited from below_, there is a higher evolution, _inherited
from above_, indissolubly connected with man’s spiritual nature--a
conscious, voluntary striving of the best members of the social
aggregate for the betterment of the whole--a conscious, voluntary
striving both of the individual and of society toward a recognized
_ideal_. In the one kind of evolution the fittest are those most in
harmony with the environment, and which therefore always survive; in
the other, the fittest are those most in harmony with the ideal, and
which often do not survive. The laws of this free voluntary progress
are little understood. They are of supreme importance, but do not
specially concern us here. We will speak of it again in another chapter.
The three laws above mentioned might be illustrated equally well by all
other forms of evolution. We have selected only those which are most
familiar. They may, therefore, be truly called the laws of evolution.
We have shown that they are the laws of succession of organic forms.
=III. Change by Means of Resident Forces.=--Thus far in our argument
I suppose that most well-informed men will raise no objection. It
will be admitted, I think, even by those most bitterly opposed to
the theory of evolution, that there has been throughout the whole
geological history of the earth an onward movement of the organic
kingdom to higher and higher levels. It will be admitted, also, that
there is a grand and most significant resemblance between the course
of development of the organic kingdom and the course of embryonic
development--between the laws of succession of organic forms and the
laws of ontogenic evolution. But there is another essential element in
ontogenic evolution. It is that the _forces_ or causes of evolution
are _natural_; that they reside in the thing developing and in the
reacting environment. This we know is true of embryonic development; is
it true also of the geologic succession of organic forms? It is true of
ontogeny; is it true also of phylogeny? If not, then only by a metaphor
can we call the process of change in the organic kingdom throughout
geological history an evolution. This is the point of discussion, and
not only of discussion, but, alas! of heated and even angry dispute.
The field of discussion is thus narrowed to this third point only.
Before stating the two opposite views of the cause of evolution, it
is necessary to remind the reader that when the evolutionist speaks
of the forces that determine progressive changes in organic forms
as _resident_ or _inherent_, all that he means, or ought to mean,
is that they are resident in the same sense as all natural forces
are resident; in the same sense that the vital forces of the embryo
are resident in the embryo, or that the forces of the development of
the solar system according to the nebular or any other cosmogonic
hypotheses are resident in that system. In other words, they mean only
that they are _natural_, not supernatural. This does not, of course,
touch that deeper, that deepest of all questions, viz., the essential
_nature and origin of natural forces_; how far they are independent
and self-existent, and how far they are only modes of divine energy.
This is a question of philosophy, not of science. This question is
briefly discussed in another place (Part III, Chap. III); it does not
immediately concern us here.
=The Two Views briefly Contrasted.=--As already stated, all will admit
a grand resemblance between the stages of embryonic development and
those of the development of the organic kingdom. This was first brought
out clearly by Louis Agassiz, and is, in fact, the greatest result
of his life-work. All admit, also, that the embryonic development is
a natural process. Is the development of the organic kingdom also a
natural process? All biologists of the present day contend that it
is; all the old-school naturalists, with Agassiz at their head, and
all anti-evolutionists of every school, contend that it is not. We
take Agassiz as the type of this school, because he has most fully
elaborated and most distinctly formulated this view. As formulated by
him, it has stood in the minds of many as an alternative and substitute
for evolution.
According to the evolutionists, all organic forms, whether species,
genera, families, orders, classes, etc., are variable, and, if external
conditions favor, these variations accumulate in one direction and
gradually produce new forms, the intermediate links being usually
destroyed or dying out. According to Agassiz, the higher groups,
such as genera, families, orders, etc., are indeed variable by the
introduction of new species, but species are the ultimate elements of
classification, and, like the ultimate elements of chemistry, are
unchangeable; and, therefore, the speculations of the evolutionist
concerning the transmutation of species are as vain as were the
speculations of the alchemists concerning the transmutation of
metals--that the origin of man, for example, from any lower species
is as impossible as the origin of gold from any baser metal. Both
sides admit frequent change of species during geological history, but
one regards the change as a change by gradual _transmutation_ of one
species _into_ another through successive generations and by _natural_
process, the other as change by _substitution_ of one species _for_
another by direct supernatural _creative act_. Both admit the gradual
development of the organic kingdom as a whole through stages similar
to those of embryonic development; but the one regards the whole
process as natural, and therefore strictly comparable to embryonic
development, the other as requiring frequent special interference of
creative energy, and therefore comparable rather to the development
of a building under the hand and according to the preconceived plan
of an architect--a plan, in this case, conceived in eternity and
carried out consistently through infinite time. It is seen that the
essential point of difference is this: The one asserts the variability
of species (if conditions favor, and time enough is given) without
limit; the other asserts the permanency of specific forms, or their
variability only within narrow limits. The one asserts the origin
of species by “_descent with modifications_”; the other, the origin
of species by “_special act of creation_.” The one asserts the law
of continuity (i. e., that each stage is the natural outcome of the
immediately preceding stage) in this, as in every other department of
Nature; the other asserts that the law of continuity (i. e., of cause
and effect) does not hold in this department; that the links of the
chain of changes are discontinuous, the connection between them being
intellectual, not physical.
So much for sharp contrasting characterization of the two views,
necessary for clear understanding of much that follows. We will have
to give them more fully hereafter when we take up the evidences of
evolution in Part II.
CHAPTER II.
THE RELATION OF LOUIS AGASSIZ TO THE THEORY OF EVOLUTION.
In order to clear up the conception of evolution, it is necessary
to give a brief history of the idea, and especially to explain the
relation of Louis Agassiz to that theory. This is the more necessary,
because there is a deep and wide-spread misunderstanding on this
subject, and thus scant justice has been done our great naturalist,
especially by the English and Germans; and also because this relation
is an admirable illustration of an important principle in scientific
philosophy.
Like all great ideas, we find the first germs of this in Greek
philosophy, in the cosmic speculations of Thales and Pythagoras.
Next (about 100 B. C.) we find it more clearly expressed by the Roman
thinker, Lucretius, in his great philosophic poem entitled “De Rerum
Natura.” After a dormancy of nearly eighteen centuries it next emerges
with still more clearness in the theological speculations of Swedenborg
and the philosophical speculations of Kant. All these we pass over with
bare mention, because these thinkers approached the subject from the
philosophic rather than the scientific side--in the metaphysical rather
than the scientific spirit.
The first serious attempt at scientific presentation of the subject was
by the celebrated naturalist, Lamarck, in a work entitled “Philosophie
Zoölogique,” published in 1809. It is not necessary, in this rapid
sketch, to give a full account of Lamarck’s views. Suffice it to say
that the essential idea of evolution, viz., the indefinite variability
and the derivative origin of species, was insisted on with great
learning and skill, and illustrated by many examples. With Lamarck,
the factors of evolution or causes of change of organic forms were--1.
Modification of organs in function and therefore in structure, by a
changing environment--external factor; and, 2. Modification of organs
by _use_ and _disuse_--internal factor. In both cases the modifications
are inherited and increased from generation to generation, without
limit. This second factor seems to have taken, in the mind of Lamarck,
the somewhat vague and transcendental form of aspiration or upward
striving of the animal toward higher conditions. These are acknowledged
to-day as true factors of evolution, but the distinctively Darwinian
factor, viz., “divergent variation and natural selection,” was not then
thought of. The publication of Lamarck’s views produced a powerful
impression, but only for a little while. Pierced by the shafts of
ridicule shot by nimble wits of Paris, and crushed beneath the heavy
weight of the authority of Cuvier, the greatest naturalist and
comparative anatomist of that or perhaps of any time, it fell almost
still-born. I believe it was best that it should thus perish. Its birth
was premature; it was not fit to live. The world was not yet prepared
for a true scientific theory. Nevertheless, the work was not without
its effect upon some of the most advanced thinkers of that time; upon
Saint-Hilaire and Comte in France, and upon Goethe and Oken in Germany.
It was good seed sown and destined to spring up and bear fruit in
suitable environment; but not yet.
The next attempt worthy of attention in this rapid sketch is that
of Robert Chambers, in a little volume entitled “Vestiges of a
Natural History of Creation,” published in 1844. It was essentially a
reproduction of Lamarck’s views in a more popular form. It was not a
truly scientific work nor written by a scientific man. It was rather an
appeal from the too technical court of science to the supposed wider
and more unprejudiced court of popular intelligence. It was therefore
far more eloquent than accurate; far more specious than profound.
It was, indeed, full of false facts and inconsequent reasonings.
Nevertheless, it produced a very strong impression on the thinking,
popular mind. But _it_ also quickly fell, pierced by keen shafts of
ridicule, and crushed beneath the heavy weight of the authority of all
the most prominent naturalists of that time, with Agassiz at their
head. The question for the time seemed closed. I believe, again, it was
best so, for the time was not yet fully ripe.
I know full well that many think with Haeckel that biology was kept
back half a century by the baneful authority of Cuvier and Agassiz;
but I can not think so. The hypothesis was contrary to the facts
of science _as then known and understood_. It was conceived in the
spirit of baseless speculation, rather than of cautious induction; of
skillful elaboration rather than of earnest truth-seeking. Its general
acceptance would have debauched the true spirit of science. I repeat
it: the time was not yet ripe for a scientific theory. The ground
must first be cleared and a solid foundation built; an insuperable
_obstacle_ to hearty rational acceptance must first be removed, and an
inductive _basis_ must be laid.
=The Obstacle removed.=--The obstacle in the way of the acceptance
of the derivative origin of species was the then prevalent _notion
concerning the nature of life_. We must briefly sketch the change which
has taken place in the last forty years in our ideas on this subject.
Until about forty years ago, the different forces of Nature, such
as gravity, electricity, magnetism, light, heat, chemical affinity,
etc., were supposed to be entirely distinct. The realm of Nature was
divided up into a number of distinct and independent principalities,
each subject to its own sovereign force and ruled by its own petty
laws. About that time it began to be evident, and is now universally
acknowledged, that all these forces are but different _forms_ of one,
universal, omnipresent energy, and are transmutable unto one another
back and forth without loss. This is the doctrine of correlation of
forces and conservation of energy, one of the grandest ideas of modern
times. But _one_ force seemed still to be an exception. Life-force
was still believed to be a peculiar, mysterious principle or entity,
standing above other forces and subordinating them; not correlated
with, not transmutable unto, nor derivable from, other and lower
forces, and therefore in some sense supernatural. Now, if this be true
of living _forces_, it is perfectly natural, yea, almost necessary,
to believe that living _forms_ are wholly different from other forms
in their origin. New forms of dead matter may be derived, but new
living forms are _underived_. Other new forms come by natural process,
new organic forms by supernatural process. The conclusion was almost
unavoidable. But soon vital force also yielded to the general law of
correlation of natural forces. Vital forces are also transmutable into
and derivable from physical and chemical forces. Sun-force, falling on
the green leaves of plants, is absorbed and converted into vital force,
disappears as _light_ to reappear as _life_. The amount of life-force
generated is measured by the amount of light extinguished. The same
is true of animal life. As in the steam-engine the locomotive energy
is derived from the fuel consumed and measured by its amount, so in
the animal body, the animal heat and animal force are derived from and
measured by the food and tissue consumed by combustion. Thus, vital
force may be regarded as so much force withdrawn from the general fund
of chemical and physical forces, to be again refunded without loss at
death. This obstacle is, therefore, now removed. If vital force falls
in the same category as other natural forces, there is no reason why
living forms should not fall into the same category in this regard
as other natural forms. If new forms of dead matter are derived from
old forms by modification, according to _physical_ laws, there is no
reason why new living forms should not also be derived from old forms
by modification according to _physiological_ laws. Thus, at last, the
obstacle was removed--the ground was cleared.
=The Basis laid.=--But Science is not content with removal of _a
priori_ objections. She must also have positive proofs. The ground
must not only be cleared, but a true inductive basis of facts, and
especially of laws and methods, must be laid. _This was the life-work
of Agassiz._ Yes, as strange as it may seem to some, it is nevertheless
true that the whole inductive basis, upon which was afterward built
the modern theory of evolution, was laid by Agassiz, although he
himself persistently refused to build upon it any really scientific
superstructure. It is plain, then, that all attempts at building
previous to Agassiz’s work must, of necessity, have resulted in an
unsubstantial structure--an edifice built on sand, which could not
and ought not to stand. I must stop here in order to explain somewhat
fully this important point, and thus to give due credit to the work of
Agassiz.
The title of any scientist to greatness must be determined, not so much
by the multitude of new facts he has discovered as by the new laws he
has established, and especially by the new methods he has inaugurated
or perfected. Now, I think it can be shown that to Agassiz, more
than to any other man, is due the credit of having _established the
laws of succession of living forms_ in the geological history of the
earth--laws upon which must rest any true theory of evolution. Also,
that to him, more than to any other man, is due the credit of having
_perfected the method_ (method of comparison) by the use of which alone
biological science has advanced so rapidly in modern times. This is
high praise. I wish to justify it. I begin with the method.
Scientific methods bear the same relation to _intellectual progress_
that tools, instruments, machines, mechanical contrivances of
all sorts, bear to _material progress_. They are intellectual
_contrivances_--indirect ways of accomplishing results far too hard
for bare-handed, unaided intellectual strength. As the civilized man
has little or no advantage over the savage in bare-handed strength of
muscle, and the enormous superiority of the latter in accomplishing
material results is due wholly to the use of mechanical contrivances
or machines; even so, in the higher sphere of intellect, the scientist
makes no pretension to the possession of greater unaided intellectual
strength than belongs to the uncultured man, or even perhaps to the
savage. The amazing intellectual results achieved by science are due
wholly to the use of intellectual contrivances or scientific methods.
As in the lower sphere of material progress the greatest benefactors of
the race are the inventors or perfecters of new mechanical contrivances
or _machines_, so also in the higher sphere of intellectual progress
the greatest benefactors of the race are the inventors or perfecters of
new intellectual contrivances or _methods of research_.
To illustrate the power of methods, and the necessity of their use,
take the case of the _method of notation_, so characteristic of
mathematics, and take it even in its simplest and most familiar form:
Nine numeral figures, having each a value of its own, and another
dependent upon its position; a few letters, _a_ and _b_, and _x_ and
_y_, connected by symbols, + and-and =: that is all. And yet, by the
use of this simple contrivance, the dullest school-boy accomplishes
intellectual results which would defy the utmost efforts of the
unaided strength of the greatest genius. And this is only the simplest
tool-form of this method. Think of the results accomplished by the use
of the more complex machinery of the higher mathematics!
Take next the method of experiment so characteristic of physics and
chemistry. The phenomena of the external world are far too complex and
far too much affected by disturbing forces and modifying conditions to
be understood at once by bare, unaided intellectual insight. They must
first be simplified. The physicist, therefore, contrives artificial
phenomena under ideal conditions. He removes one complicating condition
after another, one disturbing cause and then another, watching
meanwhile the result, until finally the necessary condition and the
true cause are discovered. On this method rests the whole fabric of the
physical and chemical sciences.
But when we rise still higher, viz., into the plane of life, the
phenomena of Nature become still more complex and difficult to
understand directly; and yet just here, where we are the most powerless
without some method, our method of experiment almost wholly _fails
us_. The phenomena of life are not only far more complex than those
of dead matter, but the conditions of life are so nicely adjusted,
the equilibrium of forces so delicately balanced, that, when we
attempt to introduce our clumsy hands in the way of experiment, we
are in danger of overthrowing the equilibrium, of destroying the
conditions of the experiment, viz., life; and then the whole problem
falls immediately into the domain of chemistry. What shall we do?
In this dilemma we find that Nature herself has already prepared
for us, ready to hand, an elaborate series of simplified conditions
equivalent to experiments. The phenomena of life are, indeed, far too
complex to be at once understood--the problem of life too hard to be
solved--in the higher animals; but, as we go down the animal scale,
complicating conditions are removed one by one, the phenomena of life
become simpler and simpler, until in the lowest microscopic cell or
spherule of living protoplasm we finally reach the simplest possible
expression of life. The equation of life is reduced to its simplest
terms, and now, if ever, we begin to understand the true value of the
unknown quantity. This is the natural history series, or _Taxonomic_
series, already spoken of on page 10. Again, Nature has prepared, and
is now preparing daily before our eyes, another series of gradually
simplified conditions. Commencing with the mature condition of one of
the higher animals--for example, man--and going backward along the
line of individual history through the stages of infant embryo, egg
and germ, we find again the phenomena of life becoming simpler and
simpler, until we again reach the simplest conceivable condition in
the single microscopic cell or spherule of living protoplasm. This, as
already explained, is the embryonic or _Ontogenic_ series. Again, that
there be no excuse for man’s ignorance of the laws of life, Nature has
prepared still another series; and this the grandest of all, for it is
the cause of both the others. Commencing with the plants and animals of
the present epoch, and going back along the track of geological times,
through Cenozoic, Mesozoic, Palæozoic, Eozoic, to the very dawn of
life--the first syllable of recorded time--and we find again a series
of organic forms growing simpler and simpler, until, if we could find
the very first, we would undoubtedly again reach the simplest condition
in the lowest conceivable forms of life. This, as we have already seen,
is the geologic or evolution, or _Phylogenic_ series. We have already
explained these three series, only in this connection it suits our
purpose to take the terms backward.
Now, it is by _comparison_ of the terms of each of these series going
up and down, and watching the first appearance, the growth, and the
perfecting of tissues, organs, functions, and by the comparison of
the three series with one another term by term--I say it is wholly
by comparison of this kind that biology has in recent times become a
true inductive science. This is the “_method of comparison_.” It is
the great method of research in all those departments which can not be
readily managed by the method of experiment. It has already regenerated
biology, and is now applied with like success in sociology under the
name of _historic method_. Yes; anatomy became scientific only through
comparative anatomy, physiology through comparative physiology, and
embryology through comparative embryology. May we not add, sociology
will become truly scientific only through comparative sociology, and
psychology through comparative psychology?
Now, while it is true that this method, like all other methods, has
been used, from the earliest dawn of thought, in a loose and imperfect
way, yet it is only in very recent times that it has been organized,
systematized, perfected, as a true scientific method, as a great
instrument of research; and the prodigious recent advance of biology is
due wholly to this cause. Now, among the great leaders of this modern
movement, Agassiz undoubtedly stands in the very first rank. I must try
to make this point plain, for it is by no means generally understood.
Cuvier is acknowledged to be the great founder of comparative anatomy.
He it was that first perfected the method of comparison, but comparison
only in one series--the _Taxonomic_. Von Baer and Agassiz added to
this comparison in the ontogenic series also, and comparison of
these two series with each other, and therefore the application of
embryology to the classification of animals. If Von Baer was the
first announcer, Agassiz was the first great practical worker by this
method. Last and most important of all, in its relation to evolution,
Agassiz added _comparison in the geologic or phylogenic series_. The
one grand idea underlying Agassiz’s whole life-work was the essential
identity of the three series, and therefore the light which they must
shed on one another. The two guiding and animating principles of his
scientific work were--1. That the embryonic development of one of the
higher representatives of any group repeated in a general way the
terms of the Taxonomic series in the same group, and therefore that
embryology furnished the key to a true classification; and, 2. That the
succession of forms and structure in geological times in any group is
similar to the succession of forms and structure in the development of
the individual in the same group, and thus that embryology furnishes
also the key to geological succession. In other words, during his
whole life, Agassiz insisted that the laws of embryonic development
(ontogeny) are also the laws of geological succession (phylogeny).
Surely this is the foundation, the only solid foundation, of a true
theory of evolution. It is true that Agassiz, holding as he did the
doctrine of permanency of specific types, and therefore rejecting the
doctrine of the derivative origin of species, did not admit the causal
or natural relation of phylogenic succession to embryonic succession
and taxonomic order as we now believe it--it is true that for him the
relation between the three series was an intellectual not a physical
one--consisted in the preordained plans of the Creator, and not in
any genetic connection or inherited property; but evidently the first
and greatest step was the discovery of the relation itself, however
accounted for. The rest was sure to follow.
But more. Not only did Agassiz establish the essential identity of the
geologic and embryonic succession, the general similarity of the two
series, phylogenic and ontogenic, but he also announced and enforced
all the formal laws of geologic succession (i. e., of evolution), as
we now know them. These, as already stated and illustrated, are the
law of differentiation, the law of progress of the whole, and the law
of cyclical movement, although he did not formulate them in these
words. No true inductive evidence of evolution was possible without
the knowledge of these laws, and for this knowledge we are mainly
indebted to Agassiz. He well knew also that they were the laws of
embryonic development and therefore of evolution; but he avoided the
word evolution, as implying the derivative origin of species, and
used instead the word _development_, though it is hard to see in what
the words differ. Thus, it is evident that Agassiz laid the whole
foundation of evolution, solid and broad, but refused to build any
scientific structure on it; he refused to recognize the legitimate, the
scientifically necessary outcome of his own work. Nevertheless, without
his work a scientific theory of evolution would have been impossible.
Without Agassiz (or his equivalent), there would have been no Darwin.
There is something to us supremely grand in this refusal of Agassiz to
accept the theory of evolution. The opportunity to become the leader of
modern thought, the foremost man of the century, was in his hands, and
he refused, because his religious, or, perhaps better, his philosophic
intuitions, forbade. To Agassiz, and, indeed, to all men of that time,
to many, alas! even now, evolution is materialism. But materialism is
Atheism. Will some one say, the genuine Truth-seeker follows where she
seems to lead _whatever be the consequences_? Yes; whatever be the
consequences to one’s self, to one’s opinions, prejudices, theories,
philosophies, but not to _still more certain truth_. Now, to Agassiz,
as to all genuine thinkers, the existence of God, like our own
existence, is more certain than any scientific theory, than anything
can possibly be made by proof. From his standpoint, therefore, he was
right in rejecting evolution as conflicting with still more certain
truth. The mistake which he made was in imagining that there was any
such conflict at all. But this was the universal mistake of the age. A
lesser man would have seen less clearly the higher truth and accepted
the lower. A greater man would have risen above the age, and seen that
there was no conflict, and so accepted both. All thinking men are
coming to this conclusion now, but none had done so then.
Now, then, at last, the obstacle of supernaturalism in the realm of
Nature having been removed by the establishment of the doctrine of
correlation of natural forces, and the extension of this doctrine
to embrace also life-force; and now also a broad and firm basis of
carefully-observed facts and well-established laws of succession
of organic forms having been laid by Agassiz, when again, for the
third time, the doctrine of origin of species “by derivation with
modifications” was brought forward by Darwin in a far more perfect
form, with more abundant illustrative materials, and with a new
and most potent factor of modification--viz., divergent variations
and natural selection--it found the scientific world already fully
prepared, and anxiously waiting. I say _anxiously_ waiting--for the
supposed supernatural origin of species had been the one exception
to the otherwise universal law of cause and effect, or the law of
continuity. It was therefore in open contradiction to the whole drift
of scientific thought for five hundred years. Is it any wonder,
then, that the derivative origin of species was welcomed with joy by
the scientific world? For five hundred years, scientific thought,
like a rising tide which knows no ebb, had tended thitherward with
ever-increasing pressure, but kept back by the one supposed fact of
the supernatural origin of species. Darwin lifted the gate, and the
in-rushing tide flooded the whole domain of thought.
What, then, is the place of Agassiz in biological science? What is the
relation of Agassiz to Darwin--of Agassizian development to Darwinian
evolution? I answer, it is the relation of formal science to physical
or causal science. Agassiz advanced biology to the _formal_ stage;
Darwin carried it forward, to some extent at least, to the _physical_
stage. All true inductive sciences in their complete development pass
through these two stages. Science in the one stage treats of the _laws_
of phenomena; in the other, of the _causes_ or explanation of these
laws. The former must precede the latter, and form its foundation;
the latter must follow the former, and constitute its completion. The
change from the one to the other is always attended with prodigious
impulse to science.
To illustrate: Until Kepler, astronomy was little more than
an accumulation of disconnected facts concerning celestial
motions--abundant materials, but no science; piles of brick and stone,
but no building. Kepler reduced this chaos to beautiful order and
musical harmony by the discovery of the three great laws which bear his
name, and therefore he has been justly called the legislator of the
heavens--_the lawgiver of space_. But, had he been asked the _cause_
of these beautiful laws, he could only have answered, “The _first
cause_--the direct will of the Deity.” A good answer and a true, but
not scientific; because it places the question beyond the domain of
science, which deals only with second or physical causes. But Newton
comes forward and gives a _physical cause_. He shows that all these
beautiful laws are the necessary result of gravitation; and thus
astronomy becomes a physical science. So, until Agassiz, the facts
of geological succession of organic forms were in a state of lawless
confusion. Agassiz by establishing the three great laws of succession,
which ought to bear his name, reduced this chaos to order and beauty;
and, therefore, he might justly be called the legislator of geological
history--the _lawgiver of time_. But, when asked the cause of these
laws, he could only answer, and did indeed answer, “The plans of the
Creator.” A noble answer and true, but not scientific. Darwin now comes
forward and gives, partly at least, the cause of these laws. He shows
that all these beautiful laws are explained by the doctrine of “origin
of species by derivation with modifications”; that these laws are
not ultimate, but derivative from more fundamental laws of life; and
thus biology is advanced one step, at least, toward the causal stage.
Newton and Darwin substituted second causes for first cause--natural
for supernatural. They each in his own department broke the bonds of
supernaturalism in the domain of Nature.
One more important reflection: There are two, and only two, fundamental
conditions of material existence--_space_ and _time_. There are,
therefore, two, and only two, cosmoses--space-cosmos and time-cosmos.
These have been redeemed from confusion and reduced to law and order
and beauty--changed from chaos to cosmos--by science. For this result
we are chiefly indebted, in the one case, to Kepler and Newton; in the
other, to Agassiz and Darwin. The universal law, in the one cosmos, is
the _law of gravitation_; in the other, the _law of evolution_. Traced
by analysis to its deepest roots of philosophic truth, the one law
may be called the divine mode of sustentation; the other, the divine
process of creation.
Or again: we have all heard of the “music of the spheres”--a beautiful
and significant name used by the old thinkers for the divine order of
the universe--a music heard not by human ear, but only by the attentive
human spirit. Harmonic relation apprehended by _reason_ we call _Law_,
and its embodiment Science; the same apprehended by the imagination
and æsthetic sense, we call _Beauty_, and its embodiment _Art_,
_music_. Now, in music there are two kinds of harmony, simultaneous
and consecutive--chordal harmony and melody. These must be combined
to produce the grandest effect. So in cosmic order, too, there are
two kinds of harmonic relation--the _co-existent in space_ and the
_consecutive in time_. The law of gravitation expresses the universal
harmonic inter-relation of _objects_ co-existent in space, the law of
evolution, the universal harmonic relation of _forms_ successive in
time. Of the divine spheral music, the one is the chordal harmony, the
other the consecutive harmony or melody. Combined they form the divine
chorus which “the morning stars sang together.”
PART II.
_EVIDENCES OF THE TRUTH OF EVOLUTION._
CHAPTER I.
GENERAL EVIDENCES OF EVOLUTION AS A UNIVERSAL LAW.
Let us again remind the reader that evolution means, first of all,
_continuity_. The law of evolution, although it doubtless means much
more, means, first of all, a law of continuity, or _causal relation
throughout Nature_. It means that, alike in every department of Nature,
each state or condition grew _naturally_ out of the immediately
preceding. In a word, it means that, in the course of Nature, nothing
appears suddenly and without natural cause, but, on the contrary,
everything is the natural and usually the gradual outcome of a previous
condition. This is _now_ admitted by every one in regard to _nearly_
everything: evolutionists apply it to the whole course of Nature.
I said this is _now_ admitted by every one in regard to _nearly_
everything; but this has not always been so. The world has come to its
present position on this subject only by a very gradual process. Let
us then trace rapidly the history of the gradual change, for it will
prepare us for much that follows.
There was a time (and that not many decades ago) when all things, the
origin of which transcends our ordinary experience, were supposed to
have originated suddenly and without natural process--to have been made
at once, out of hand. There was a time when, for example, mountains
were supposed to have been made at once, with all their diversified
forms, of beetling cliffs and thundering waterfalls, or gentle slopes
and smiling valleys, just as we now find them. But _now_ we know that
they have become so only by a very gradual process, and are still
changing under our very eyes. In a word, they have been formed by a
_process of evolution_. We know now the date of mountain-births; we
trace their growth, maturity, decay, and death; and find even, as it
were, the fossil bones of extinct mountains in the crumpled strata
of their former places. There was a time when continents and seas,
gulfs, bays, and rivers, were supposed to have originated at once,
substantially as we now see them. _Now_, we know that they have been
changing throughout all geological time, and are still changing. Not,
however, change back and forth in any direction indifferently and
without goal, but gradual change from less perfect to more perfect
condition, with more and more complex inter-relations--i. e., by a
_process of evolution_. We are able now, though still imperfectly,
to trace some of the stages of this evolution. There was a time when
rocks and soils were supposed to have been always rocks and soils; when
soils were regarded as an original clothing made on purpose to hide the
rocky nakedness of the new-born earth. God clothed the earth so, and
there an end. _Now_ we know that rocks rot down to soils; soils are
carried down and deposited as sediments; and sediments re-consolidate
as rocks--the same materials being worked over and over again, passing
through all these stages many times in the history of the earth. In
a word, there was a time when it was thought that the earth with
substantially its present form, configuration, and climate, was made
at once out of hand, as a fit habitation for man and animals. _Now_
we know that it has been changing, preparing, becoming what it is by
a slow process, through a lapse of time so vast that the mind sinks
exhausted in the attempt to grasp it. It has become what it now is
by a _process of evolution_. The same change of view has taken place
concerning the origin of all the heavenly bodies. We may, therefore,
confidently generalize--we may assert without fear of contradiction
that _all inorganic forms_, without exception, have originated by a
process of evolution.
The proof of all this we owe to geology--a science born of the present
century. This science establishes the law of _universal continuity_ of
events, through infinite _time_, as astronomy does that of _universal
inter-relation_ of objects through infinite _space_. How great the
change these two sciences have made in the realm of human thought!
Until the birth of modern astronomy the intellectual _space-horizon_
of the human mind was bounded substantially by the dimensions of
our earth; sun, moon, and stars, being but inconsiderable bodies
circulating at a little distance about the earth, and for our behoof.
Astronomy was then but the geometry of the curious lines traced by
these wandering fires on the concave blackboard of heaven. With the
first glance through a telescope the phases of Venus and the satellites
of Jupiter, revealed clearly to the mind the existence of other
worlds besides and like our own. In that moment the idea of _infinite
space_, full of worlds like our own, was for the first time completely
realized, and became thenceforward the heritage of man. In that moment
the _intellectual horizon of man was infinitely extended_. So also
until the birth of geology, about the beginning of the present century,
the intellectual _time-horizon_ of the human mind was bounded by six
thousand years. The discovery about that time of vertebrate remains,
all wholly different from those now inhabiting the earth, revealed
the existence of other time-faunas, besides our own and the idea of
infinite time, of which the life of humanity is but an epoch, was
born in the mind of man; and again the intellectual horizon of man
was infinitely extended. These two are the grandest ideas, and their
introduction the grandest epochs, in the intellectual history of man.
We have long ago accepted and readjusted our mental furniture to the
requirements of the one, but the necessary readjustment to the other is
not yet complete.
All inorganic forms, then, it is admitted, have come by evolution. But
how is it with organic or living forms? Let us see.
Every one knows, because it is within the limits of ordinary
experience, that every _individual_ organism _now_ originates and
gradually becomes what we see it, by a natural process--that is, by
evolution. If, then, there be any exception, it must be only the _first
of each kind_. But what kind? There are many kinds of kinds; classes,
orders, families, genera, species, varieties. Now, many of these kinds
can be shown to have become what we see them by a gradual process
similar, at least, to evolution. Take for example, classes. The class
of fishes and the class of reptiles are _now_ widely distinct and
have little in common except a vertebrate structure; but, as already
shown, page 12, this extreme difference has not always existed. On
the contrary, the earliest representatives of these two classes so
merged into one another that each seemed either. From this common stock
the two classes were gradually separated, each going its own way and
becoming more and more widely distinct even to the present day. There
can be no doubt, therefore, that _these two classes_, as we now know
them, _have become_ what they are by a gradual process. Again: In the
whole realm of Nature there is not a class more distinctly separate
from every other and without intermediate links than birds. But this
has not always been so. They have gradually become so. The earliest
birds were so reptilian in structure and appearance that if we could
see them now we would be in doubt whether we should call them birds or
reptiles. Birds have gradually separated themselves from the reptilian
stem, becoming more and more bird-like from age to age, until now, at
last, the two classes are wholly separated and the intermediate links
destroyed. So far as external characters are concerned, birds may be
said to have finally and wholly released themselves from entangling
alliance with any other class.
Classes, then, it will be admitted, have undoubtedly become what we
now know them by a very gradual process following laws identical (as
we have already seen, page 19) with the laws of evolution. Shall we
try orders? Of the class Mammalia there are two well-recognized and
widely-distinct _orders_, viz., the Carnivores and the Herbivores. We
all know how widely diverse these are in form, in structure, in habits,
and in food. Has it always been so? Have these been made so at once?
By no means. They have gradually become so. The earliest mammals were
neither the one nor the other distinctively. They were _omnivores_,
completely intermediate in food, habits, form, and structure. From this
common stock the two orders have gradually separated, the carnivores
becoming more and more adapted to one mode of life and the herbivores
to another, by a process following the laws of evolution, as already
explained. Shall we try _families_ and _genera_? Marsh and Huxley have
shown us how completely the horse family (_Equidæ_) and the horse-genus
(_Equus_) illustrate the process of gradual becoming and the law of
evolution. Under their guidance, we see that the earliest traceable
ancestor of the horse family, before it was distinctively a horse
family at all, had on the fore-foot five toes in the Lower Eocene,
four toes in the Upper Eocene, and three toes in the Miocene; then we
see the two side-toes shortening up more and more in the Pliocene and
becoming rudimentary splints, leaving only one toe in the Quaternary
and present epochs. Thus, the side-splints in the foot of the modern
horse tell the story of its three-toed ancestry. Similar gradual
changes are clearly traceable in size, shape, structure of limbs, of
teeth, and of brain. In all respects the members of the horse family
have become more and more horse-like in the course of time.
This subject will be taken up and more fully illustrated, under the
head of special evidences, in a subsequent chapter. We here touch it
only sufficiently to illustrate this universal law of gradual becoming.
We have taken only a few examples, but the same is undoubtedly true of
all Taxonomic groups _above species_. Passing over these last for the
moment, we take next _races_ and _varieties_. These smaller groups are
admitted by all to be formed by a natural process, because not only
can we make them artificially, but all the intermediate links may be
found in Nature. So we have only _species_ remaining. Yes; species are
imagined by the old-school naturalist and by the anti-evolutionist of
to-day as the _ultimate elements_ of Taxonomy. This, then, is the _last
ditch_ upon which the defense of supernaturalism in the realm of Nature
is made. “Other groups,” they say, “may have gradually become what they
now are by the successive introduction of specific forms according
to a preordained plan which is well expressed by the formal laws of
evolution. But _species_ are without transition forms. _They_ come in
suddenly, remain unchanged while they continue, and finally pass out
suddenly, so far as specific characters are concerned. New species come
in their places by direct act of creation--by _substitution_, not by
transmutation.” This, then, is the last intrenchment. Can we give any
good evidence of gradual formation of species? I believe we can.
First, then, it is admitted that we can easily make varieties and
races artificially. We will not _now_ describe the process; we are all
familiar with the results, viz., the varieties of domestic animals
and of useful and ornamental plants; the extremely different breeds
of horses, cattle, sheep, dogs, pigeons, etc.; of wheat, cabbages,
turnips; of roses, dahlias, etc., etc. No one will doubt that the
extreme varieties of any of these, say greyhound and pug, if wild,
would be called distinct species, or even distinct genera. We do not
call them so, for two reasons: first, because we see them made; and,
second, because we find all intermediate links between them; and the
usual definition of species is that they can not be made, and they have
no intermediate links. Thus, then, the question is narrowed down to
_wild species_. They say: “We take our stand on these” (surely a very
narrow ground for so broad a philosophy). “We defy you to show gradual
formation with intermediate links.”
Now, in fact, by diligent search such intermediate links between
well-recognized species have been found in some cases, especially in
birds, on account of their great power of dispersal. Certain forms
have long been known from widely-separated regions, and universally
regarded as distinct species, as distinct as any. Then, by minute
examinations of intermediate regions, a complete series of intermediate
forms has been picked up. This has occurred not only in one case but in
many cases, and not in birds only but in many other classes--examples
increase with our increasing knowledge.[11] The only answer to such
evidence is that _these are not true species_. Now, see the fallacy
lurking here! They define species as ultimate elements of taxonomy, as
distinct and without intermediate links, and then require us to find
such intermediate links; and, finally, when with infinite pains some
such links are found, they say: “Oh! I see; we were mistaken; they are
only varieties!!” It is true that naturalists, when intermediate links
are found, usually put all together as one species, but this they do
purely for the sake of clearness of definition and description. It is
freely admitted by the evolutionist that species are _now_ usually
distinct and without intermediate links, these having been destroyed in
the struggle for life. This will be fully explained in another chapter.
It is also freely admitted that although intermediate links must have
existed at one time, their remains are rarely found. The reason of
this will also be explained hereafter. Nevertheless, in some cases, as
already seen, we do find them still existing. Now, we add that in some
cases, where they no longer exist, we find them in the form of fossil
remains. The most remarkable example of this is found in the gradual
changes in the forms of Planorbis in the fresh-water deposits of
Steinheim, as shown by the admirable researches of Hyatt.[12] We shall
discuss these also more fully in another place. Now, if there be any
such links at all, however rare, then every objection to the derivative
origin of species is removed.
Perhaps it may be well to make bare mention of another kind of
evidence, viz., the actual change of species under the eyes, by
the action of change of environment. The different species of the
genus _Artemia_ (a low form of crustacean) live in brine-pools. By
concentrating the brine of such a pool, one species (_A. salina_)
has been observed to change in successive generations into another
(_A. Muhlhausenii_), and the latter back again to the former by slow
freshening.[13] Again: The siredon and the amblystoma have always,
until recently, been regarded as not only distinct species, but
distinct genera of amphibians. Siredon was supposed to be a permanent
gill-breather, while amblystoma becomes by metamorphosis a pure
air-breather. Now, however, it is known that the former may change into
the latter. But the most curious part of the life-history of these
animals, is that if water be abundant the siredon reproduces freely,
and remains indefinitely a gill-breather; but if the water dries up
it changes into the lung-breathing amblystoma. We do not give this
as examples of change of species, for the change is in the individual
life, and therefore in the nature of metamorphosis, but as evidence
of the power of physical conditions in modifying the development of
organic forms and therefore of the manner in which gill-breathers were
probably transformed into air-breathers.
To sum up: 1. All _inorganic_ forms, without exception, have become
what we find them by a natural process--i. e., by evolution. 2. All
_organic_ or living forms within the _limits of observation_, i. e.,
every living thing, has become what we now see, by a gradual, natural
process--i. e., by evolution. 3. All taxonomic groups, except species,
have undoubtedly become what we now see them by a gradual process,
following the laws of evolution, and therefore presumably by a natural
process of evolution. 4. By artificial means, breeds, races, etc., very
similar, at least in many respects, to species, are seen to arise by
a gradual natural process--i. e., by evolution. 5. In some instances,
at least, natural species are observed to pass into one another by
intermediate links in such wise that we are forced to conclude that
they have been formed by a natural process.
May we not, then, safely generalize, and make the law universal? Is
not this a sufficient ground for confident induction? Even though
some facts are still inexplicable, is that a sufficient reason for
withholding assent to a theory which explains so much? In all induction
we first establish a law provisionally from the observation of a
comparatively few facts, and then extend it over a multitude of facts
not included in the original induction. If it explains these also,
the law is verified. The law of gravitation was first based on the
observation of a few facts, and then verified by its explanation of
nearly all the facts of celestial motion. There are some outstanding
facts of celestial motion still unexplained, but we do not, therefore,
doubt the law of gravitation. The same principle applied in biology
ought to establish the law of evolution, for it also explains all
the facts of biology as no other law can. But inductive evidence
differs from other kinds of evidence in one respect, which, in fact,
constitutes its strength to the scientific, but its weakness to the
popular mind. It is a kind of circumstantial evidence, but its force
does not consist in a few strong circumstances easily appreciated,
such as strike the popular mind, and force conviction, but rather in a
multitude of small circumstances, each by itself insignificant, but all
together pointing to one conclusion and demanding one explanation. Such
evidence is, indeed, overwhelming, but only to the mind that masters
it. The evidence for the law of gravitation is literally the whole
science of astronomy. So also the evidence for the law of evolution
is the whole science of biology. Neither of these laws can be proved
in a debating society, but only by a course of study. In the one case
the law has been universally accepted--not, however, on evidence, for
there are few indeed who appreciate the evidence, but on the authority
of scientific unanimity. In the other case there has not yet been time
enough for the already established unanimity to have its full effect.
Thus much, we believe, will be generally admitted as a very moderate
claim. Evolution is certainly a legitimate induction from the facts
of biology. But we are prepared to go much further. We are confident
that evolution is _absolutely certain_. Not, indeed, evolution as a
special theory--Lamarckian, Darwinian, Spencerian--for these are all
more or less successful modes of explaining evolution; nor evolution
as a school of thought, with its following of disciples--for in this
sense it is still in the field of discussion--but evolution as a law
of derivation of forms from previous forms; evolution as a law of
continuity, as a universal law of becoming. In this sense it is not
only certain, it is axiomatic. It is only necessary to conceive it
clearly, to see that it is a necessary truth. This may seem paradoxical
to some. I stop to justify it.
Physical phenomena we all admit follow one another in unbroken
succession, each derived from a preceding, and giving origin to a
succeeding. We call this the law of causation, and say that it is
axiomatic. We might call it a law of derivation. So also organic
_forms_ follow one another in continuous chain, each derived from a
preceding and giving origin to a succeeding. We call this a law of
derivation. We might call it a _law of causation_, and say that it too
is axiomatic. The origins of new phenomena are often obscure, even
inexplicable, but we never think to doubt that they have a natural
cause; for so to doubt is to doubt the validity of reason, and the
rational constitution of Nature. So also the origins of new organic
_forms_ may be obscure or even inexplicable, but we ought not on that
account to doubt that they had a natural cause, and came by a natural
process; for so to doubt is also to doubt the validity of reason, and
the rational constitution of organic Nature. The law of evolution
is naught else than the scientific or, indeed, the rational mode of
thinking about the origin of things in every department of Nature. In
a word, it is naught else than the law of necessary causation applied
to _forms_ instead of phenomena. Evolution, therefore, is no longer
a school of thought. The words _evolutionism_ and _evolutionist_
ought not any longer to be used, any more than _gravitationism_ and
_gravitationist_; for the law of evolution is as certain as the law of
gravitation. Nay, it is far more certain. The nexus between _successive
events in time_ (causation) is far more certain than the nexus between
_coexistent objects in space_ (gravitation). The former _is a necessary
truth_, the latter is usually classed as a contingent truth. I have
used and may continue to use the term evolutionist, but if so it is
only in deference to the views of many intelligent persons, who do not
yet see the certainty of the law.