Darwin in the fifth edition of his work, and also in a letter to Hæckel,
author of the bolder venture as to the _History of the Creation_, and
the _Evolution of Man_. This letter to Hæckel may be given here as
having considerable value in its bearing on the formation of the theory
of evolution. After referring to his early researches as to lower forms
of life, Mr. Darwin proceeds thus--"Having reflected much on the
foregoing facts, it seemed to me probable that _allied species_ were
descended from a common ancestor. But during several years I could not
conceive how each form could have been modified so as to become
admirably adapted to its place in nature. I began therefore to study
domesticated animals and cultivated plants, and after a time perceived
that _man's power of selecting and breeding_ from certain individuals
was the most powerful of all means in the production of _new races_.
Having attended to the habits of animals and their relations to the
surrounding conditions, I was able to realize the severe _struggle for
existence_ to which all organisms are subjected; and my geological
observations had allowed me to appreciate to a certain extent the
duration of past geological periods. With my mind thus prepared, I
fortunately happened to read Malthus's _Essay on Population_; and the
idea of natural selection through the struggle for existence at once
occurred to me. Of all the subordinate points in the theory, the last
which I understood was the cause of the _tendency_ in the descendants
from a common progenitor _to diverge_ in character."[BE] This short
passage in personal history may considerably aid others in their study
of the theory.
This letter may with advantage be supplemented by one or two brief
extracts from _The Origin of Species_. In one of his most recent
editions, our author says,--"It may be metaphorically said, that natural
selection is daily; and hourly scrutinizing throughout the world the
slightest variations, rejecting those that are bad, preserving and
adding up all that are good; silently and insensibly working, whenever
and wherever opportunity offers, at the improvement of each organic
being in relation to its organic and inorganic conditions of life."
Such a metaphorical representation attributing to nature different
processes, such as scrutinizing, rejecting, preserving, and working,
considerably aids us by pointing to the _intellectual_ conditions
involved in the acceptance of the theory of evolution. To this it may
suffice if there be added the closing passage in our author's work on
species, indicating his view of the relation of all to the supernatural.
It is in these words--"Thus, from the war of nature, from famine and
death, the most exalted object which we are capable of conceiving,[BF]
namely, the production of the higher animals, directly follows. There is
grandeur in this view of life, with its several powers, having been
originally breathed by the Creator into a few forms or into one; and
that whilst this planet has gone cycling on according to the fixed law
of gravity, from so simple a beginning endless forms most beautiful and
most wonderful have been, and are being evolved."[BG] On this passage,
Schmidt has remarked--"In this concession, Darwin has certainly been
untrue to himself; and it satisfies neither those who believe in the
continuous work of creation by a personal God, nor the partisans of
natural evolution." In this criticism we have a good example of the
manner in which an impression of conflict is fostered. The rejoinder to
Schmidt is obvious. Those who value religion seek no concessions, but
desire to banish from scientific and philosophic writing all thought
tending in this direction. If, however, needless complications are to be
avoided, we must have exact statements of the relative positions. The
sentence just quoted involves a misrepresentation equally of religion
and science. Belief in the supernatural does not imply belief in _a
continuous work of creation_, and therefore does not carry any thing
inherently antagonistic to the conception of evolution under natural
law. On the other hand, belief in evolution of species under the action
of natural law does not decide the question, concerning _the origin of
life_, just as a science of nature can decide nothing concerning the
supernatural.
Professor Schmidt is, however, so far from clearly and consistently
recognizing the exact limit of the theory, that within the compass of a
single page he first affirms the limitation, and then denies it. First
vindicating Darwin from the attack of Max Müller as to beginning and
end of living organism, he says, "The origin of life has in fact nothing
to do with actual Darwinism, or natural selection, unless the principle
of selection be extended to the inorganic world of matter,"[BH] an
entanglement which Schmidt is willing to avoid, and which Darwin
carefully shuns, distinctly stating that "Science in her present state
does not countenance the belief that living creatures are now ever
produced from inorganic matter."[BI] But Schmidt has no sooner placed
himself behind this line of defence, than he attacks Darwin for
acknowledging origin of life by creation, maintaining that "it is
directly incompatible with the doctrine of descent."[BJ] The theorist
must take either one side or the other. Either he must maintain that the
theory of descent has "nothing to do with the origin of life," and in
that case there is no conflict with religious thought; or that the
theory of descent is incompatible with creation, and in that case there
is conflict with religious thought, and at the same time inconsistency
with science, in respect of its own definition as an explanation of
nature, and in respect of its own results which do not involve
"spontaneous generation," but do include the position that not a single
particle of matter can be originated or destroyed by any power
recognized in operation. No one will "dispute the claims of the
investigation of nature to its logical inferences," but "where the
material substratum is deficient," most reasonable men will demand that
distinct acknowledgment be made of the fact, and that the boundaries of
science be defined accordingly. If, however, any one be inclined to
maintain that "where the material substratum is deficient," all inquiry
must terminate, and human thought must refuse to go further, or to
attempt to rise higher, this certainly is not science, but an illogical
attempt to make the science of nature commensurate with the boundaries
of thought,--an arbitrary declaration that "the causal series" within
the material universe is the sum total of causality. Such an affirmation
can not warrantably attach itself to a theory of descent, as it can not
be tested by observational methods, but altogether by reference to the
laws of thought determining the value of rationalizing processes. The
theory of "natural evolution," implies evolution from something; it
postulates a beginning from which it takes procedure, and it exhausts
itself in observations concerning such deviations as occur in the annals
of natural history. If, therefore, any of "the partisans of natural
evolution," take up a position involving denial of a rational
acknowledgment of the supernatural, they isolate themselves in so doing,
leaving the theory free from responsibility as to their attitude, and
taking upon themselves the logical necessity for vindicating their
position on grounds with which the theory of evolution itself has no
concern.
Having thus vindicated the theory of natural evolution from all share in
the denial of creation, and having entered a protest upon purely
scientific grounds against the attempt to translate a scientific theory
concerning a limited order of facts within the universe into a
metaphysical theory concerning the origin of the universe, we are in a
position to concentrate upon the theory itself as an attempt to provide
a scientific explanation of the history of living organism. And this is
here done with the view of ascertaining, in a general and necessarily
restricted manner, the value of the evidence presented for its
acceptance, thereby ascertaining its relations to the essential
characteristics of religious thought.
The first and simplest part of the task is to indicate the favorable
impression it has made on the minds of men,--the conquest it has already
won for itself,--as a theory carrying within it a large amount of truth,
whatever may be its final form, after the very intricate and difficult
questions involved have been carefully examined. The theory has carried
general approval for the position that "allied species are descended
from a common ancestor," or, stating the same view in the manner
suggested by experiment, that it is possible to obtain in the history of
a single race of animals, considerable deviations in structure, and to
give these deviations fixedness or permanence by continuance of selected
features along the line of hereditary descent. This has been amply
illustrated by the examples of the various orders of pigeons, and of
dogs; both classes of animals having been largely experimented upon, and
the distinct varieties being easily recognized and popularly known.
Comparatively little hesitation exists as to acknowledging that the
different orders of pigeons have had a common ancestry; and that the
same may be said of the different races of dogs. These examples afford
the governing conception of the evolution theory, presenting the type of
evidence which has led on to the wider generalization. Under the
discussions which the theory has originated facts previously familiar
have been contemplated in a different light, as bearing upon a general
plan or order of procedure apparent in the history of organized
existence. The consequent gain for the theory is altogether favorable to
the restricted doctrine that allied species have had a common descent,
or that a single type of organism may under the law of evolution lead to
the appearance of different orders or races of animals.
The clear advance thus made in our conceptions of the history of the
universe will appear by simple statement of negative results following
from the admission of the modified form of doctrine just given. These
involve the rejection of views previously held, not by religious men in
religious interests, but by men generally, as the natural consequence
of the want of scientific investigations fitted to guide the public
mind. So far as a general conclusion has gained assent, men show no
reluctance to accept the clear logical inferences following from the
investigation of nature.
Among these results is _rejection of fixedness of species_ as implying
impossibility of deviation from a single normal type of structure. The
possibility of adaptive changes being granted, the absolute fixedness of
species in the rigid sense formerly acknowledged is abandoned. How great
the modification of view must be, is much more difficult to decide, and
hardly admits of exact statement. There is certainly no denial of
distinction of species, nor can such denial ever find acceptance,
whatever be the advance of theory, for the distinctions are so broad as
to render this impossible. But the whole work of classification of the
different orders of animal life, exceedingly difficult in any case, has
been rendered much more perplexing in consequence of the accumulation of
evidence favoring the doctrine of evolution. What can properly be
regarded as the origin of a new species, and what as a mere modification
or advance in a species already recognized, are questions for which it
is difficult to find an exact answer. The theory of the "origin of
species" by natural selection seems placed in an awkward perplexity as
to what constitutes _origin_ of a new order of life. And this difficulty
must be regarded as a constant attendant on the scheme of thought, since
"adaptive changes" must be of slow progress, and historically obscure,
inasmuch as a succession of very slight differences must contribute to a
general result. In this way it may even become matter of keen discussion
what actually constitutes organic advance. Mr. Darwin admits serious
difficulty at this point. He says, "Here we enter on a very intricate
subject, for naturalists have not defined to each other's satisfaction
what is meant by an advance in organization."[BK] Thus there is dispute
among competent authorities as to which may properly be considered the
highest order of plants, and which the highest order of fishes. On the
other hand, it is comparatively easy to decide among the more highly
organized animals, when an advance is made, by reference to increased
complexity in structure, or provision of separate organs for
accomplishment of distinct functions. These considerations, however,
suffice to indicate how many and complicated are the subjects requiring
to be examined on evidence, and adjusted in their relations to each
other, before it can be possible to get beyond surmise, in order to
formulate a complete scientific theory. That "adaptive changes" by
natural law of evolution are not only possible, but that they frequently
occur under observation, admits of no question; but whether this
includes changes of structure such as imply origin of species may still
be subject of grave doubt. The alterations made by Mr. Darwin in
successive editions of his book, from the first edition in 1859, to the
sixth edition in 1872,[BL] introduced, as he explains, "according as the
evidence has become somewhat stronger or weaker," are sufficient to
suggest that a vast amount of work remains to be done before a
well-defined theory can be formulated. While there is universal
agreement as to the possibility of "adaptive changes" to which Mr.
Darwin provisionally restricted his theory on account of the
investigations of Nageli as to plants, and those of Broca as to
animals, there is much diversity of opinion concerning the wider
application of the theory of evolution. This diversity arises in part
from the varying estimate of the value of evidence as now accumulated,
and in part from the varying conception of the completeness of our
records of the ancient history of organism as presented by geology.
There is as yet no general consensus of opinion, nor is there likely to
be for a long time to come. Mr. Darwin himself is sufficiently cautious
and faithful to observational methods, to admit that there are serious
difficulties, of some of which he ventures only to say that they "are
greatly diminished," while some have disappeared. Other writers, such as
Hæckel, with greatly less caution, and with much greater alacrity in
leaping over chasms, are prepared to go much further and faster than
Darwin. Many more are exceedingly doubtful as to the scientific value of
the evidence at command, being, as Mr. Darwin has said, "much shaken in
their former belief."[BM] And of many it must be said that they are
convinced that the evidence is far from warranting the conclusion that
all organized existence can be traced to "only a few forms," or to
"one," according to the alternatives suggested by Darwin in the closing
sentence of his book.
Waiving, then, meanwhile, as the state of scientific evidence warrants
us to do, the question of the probable number of primordial forms in
which organized existence appeared, there is at least another definite
result to be recorded as following from even a modified recognition of a
theory of development, that is the _rejection of belief in the
simultaneous origin of all species_ or orders of animal life existing
now in the world. The scientific conception of the history of animal
life is, that there has been a historical progression in the appearance
of animals, in so far as lower orders took precedence of higher, while
the higher have shown large power of adaptation to the circumstances in
which they have been placed. In accordance with the whole principles
regulating the relations of religion and science, religious men,
scientific and non-scientific, will readily acquiesce in this
modification of general belief, as largely favored by evidence which
geology supplies, and supported by testimony drawn from the actually
existing order of things; and they will do so with clear recognition
that this view involves no conflict with scriptural statement, and is so
far from containing in it any thing antagonistic to the fundamental
conception of the supernatural origin of existence, that it harmonizes
with it, even intensifying the demand upon a transcendent cause for the
rational explanation of the admitted order of things.
Having thus indicated in definite form the favorable impression made on
the public mind by the theory of evolution under a law of natural
selection, it will suffice to indicate very briefly the more prominent
difficulties with which the theory has grappled, but from which it has
not escaped. In doing so, it should be said that the careful and
deliberate manner in which Mr. Darwin has faced the host of difficulties
which have gathered around is deserving of highest praise, as in harmony
with the scientific spirit, and in marked contrast with the
light-and-go-easy style in which others, such as Hæckel, and even
Schmidt, pass over the ground, announcing things as undoubted facts, and
even "self-evident" truths, of which no man can speak with any degree
of certainty. On the other hand, it seems a reasonable ground of
complaint against many opponents of the theory, which Mr. Darwin urges
specially against Mr. St. George Mivart, that it is no part of their
plan "to give the various facts and considerations opposed to their own
conclusions," while marshalling the difficulties against an evolution
theory. And yet it should be remembered that a great service is done to
science in a period of transition, when difficulties are powerfully
urged against a popular hypothesis, as an injury is done to science by
precipitate and ill-considered arguments in support of such a
hypothesis.
Of the most serious difficulties in the way of a theory of descent by
evolution, the _first_ concerns _the nature of the evidence_, inasmuch
as all change coming under observation does not indicate progression or
improvement in the organism. The importance of this may be best
indicated by quoting Mr. Darwin's explanatory words as to alterations in
the fifth edition of his book on species. He says, "In the earlier
editions of my _Origin of Species_, I probably attributed too much to
the action of natural selection or survival of the fittest. I have
altered the fifth edition of the _Origin_ so as to confine my remarks to
adaptive changes of structure. I had not formerly sufficiently
considered the existence of many structures, which appear to be, as far
as we can judge, neither beneficial nor injurious, and this I believe to
be one of the greatest oversights as yet detected in my work." When it
is certain that deviation from the normal structure may take place which
is a disadvantage to the individual, and that this may descend to
offspring; when it is also shown that deviation may occur which appears
to serve no end, that is, contributes to no phase of functional
activity; when besides advantages gained are lost, and the race returns
to its original type of structure; and when farther there are examples
of degeneration, as in parasitic races,--such facts interpose special
difficulties in the way of an all-embracing theory of progress by
natural selection. Besides, as deviations occur of an unfavorable kind
among domesticated animals under the care of man, it becomes obvious
that progress may be readily lost even in most favorable circumstances.
The next outstanding difficulty is that of _meeting the requirements of
logical inference_. This has been specially urged by Mr. Mivart as
bearing upon the "incipient stages" of advance, and the difficulty
certainly presses heavily at that point. Natural selection may account
for much in the history of higher organisms where powers of sensibility
and locomotion are great, but how can we find in natural selection an
adequate explanation of progress in organisms within which these powers
are at the lowest. The difficulty is to get a cause sufficient to
account for the start of a movement so vast as that which is to
culminate in man. Mr. Darwin feels the force of this difficulty, and
replies thus, "as we have no facts to guide us, speculation on the
subject is almost useless."[BN] But this perplexity which is most
glaring at the beginning of the upward course, clings to the theory at
every stage in the combination of struggle and improvement,--descent
involving a real _ascent_. Whether the organism be more or less complex,
it depends upon _external causes_ for its improvement, and the
dependence continues at every stage. Granting that there is everywhere
struggle for existence and survival of the fittest, are these sufficient
to account for results so great as are involved in unceasing advance of
organism?
If it be argued that they are sufficient, a serious perplexity comes
from the opposite quarter,--How does it happen that all organic
existence does not advance together to a common elevation? If the theory
accounts for advance, how shall we account for the want of it? The
difficulties are as great for the theory in view of the large body of
facts it does not attempt to include, as in the facts it strives to
embrace. Agassiz put this difficulty with much force in 1857, and it has
not received any satisfactory answer. He said, "It is a fact which seems
to be entirely overlooked by those who assume an extensive influence of
physical causes upon the very existence of organized beings, that the
most diversified types of animals and plants are everywhere found under
identical circumstances."[BO] If, as Mr. Darwin says, "looking to the
first dawn of life," we may believe that "all organic beings presented
the simplest structure"; if the struggle for existence is uniformly
encountered and leads to survival of the fittest, how is it that within
the same area, organism has not advanced to similar complexity? If under
constraint of the evidence for the theory, we surrender the doctrine of
inevitable fixedness of species, how shall we nevertheless account for
the permanence of species? It is not suggested that there is at
successive stages "new and simple forms continually being produced by
spontaneous generation." This hypothesis of Lamark is rejected by Mr.
Darwin,[BP] as it is by almost all scientific observers? How, then, can
we explain the facts? We are told that certain orders have "fallen out"
in the march of progress; but we need a scientific account of this which
shall harmonize with a theory of action of environment, and such an
account is not forthcoming. It may be said that the very success of the
theory by accumulation of most striking and important evidence, is
bringing it into difficulty, and suggesting its insufficiency. The more
powerful and imposing the action of the law of natural selection, the
more pressing becomes the need for a scientific explanation, at once
distinct and harmonious, which will account for the persistence of
species, when struggle for existence goes on under similar or even
analogous action of environment. The presence everywhere of these lower
forms alongside of the higher, adds greatly to the attractiveness of
nature, and not even the grandeur of a universal advance towards the
higher levels of organization would make up for the disappearance of the
marvels of lower orders of animals. A monotony of grandeur may compare
unfavorably with the wealth of variety and adversity; and so a law of
continuity or persistence may be found adding to the greatness of a
universe in which a law of progress or evolution also finds uniform
application.
Upon this contrast between persistence and progress, general attention
will henceforth be concentrated in judging of the place and value of a
theory of descent. There is no need for hurry or impatience in this
matter. The words of Mr. Darwin will find ready assent as he says, "No
one ought to feel surprise at much yet remaining unexplained on the
origin of species, if we make due allowance for our profound ignorance
on the mutual relations of the inhabitants of the world at the present
time, and still more during past ages."[BQ] In accordance with this
acknowledgment, a wide range of scientific research still remains to be
undertaken, and religious thought can have nothing but friendly interest
in the work, as it may well be assured of drawing thence fresh
contributions of great value for higher speculation concerning the
government of the universe.
FOOTNOTES:
[AO] Tait's _Recent Advances_, p. 23.
[AP] Lyell's _Elements of Geology_, p. 2.
[AQ] _Recent Advances_, p. 24.
[AR] _Doctrine of Descent_, p. 20.
[AS] _Ib._ p. 161.
[AT] _Introduction to the Theory of Science_.
[AU] _Doctrine of Descent_, p. 163.
[AV] _Doctrine of Descent_, p. 162.
[AW] _Origin of Species_, p. 577.
[AX] See Appendix VII.
[AY] See Appendix V.