It is, however, desirable here, in order to give completeness to our view of the present situation, to remark that among scientific men there are some who have no expectation of a scientific explanation of the origin of life; while others are exceedingly hopeful that such explanation may be reached, in the latter cla.s.s appearing naturally all those who openly proclaim against what they name an "incomprehensible act of creation," and voluntarily place themselves in antagonism to religious thought. It is, therefore, of some consequence to indicate the grounds on which such opposite views rest. On the one side, Professor Tait, while suggesting the possibility of yet discovering the physical principles which determine life, nevertheless adds, "Let no one imagine that, should we ever penetrate this mystery, we shall thereby be enabled to produce, except from life, even the lowest form of life."[AQ] On the other hand Professor Schmidt of Strasburg maintains the opposite view, affirming that "the investigation of nature does not shrink from enrolling _life_, and the processes of life in the world of the comprehensible."[AR] This latter a.s.sertion is not to be accounted for on the ground that Schmidt is the ardent admirer and defender of the theory of origin of species by natural selection, for it is clear, as he maintains in replying to Max Muller, that "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."[AS] Mr. Darwin himself does not suggest any such extension, and his theory of species is not chargeable with it. It should, indeed, be clearly recognized on all hands that the naturalist confines himself to a narrower range of inquiry, taking existing phases of life as the subject of his study. Accordingly, whoever claims that the origin of life comes within the compa.s.s of science, does so on the ground that there is no demarcation between the organic and the inorganic,--that the former may arise directly from the latter,--and so he commits himself to a doctrine of descent world-wide in its application, involving development in the world of all its varied phases of existence from a ma.s.s of unorganized matter.
This explains the difference of opinion among scientific men as to the possibility of accounting for the origin of life. A certain number deny the possibility, as they do the possibility of explaining scientifically the origin of matter on the explicit ground indicated by Laplace,--"Present events are connected with the events of the past by a link resting on the obvious principle, that a thing can not begin to exist without a cause which produces it."[AT] They do not find in inorganic matter sufficient cause to account for life, and their expectations are restricted accordingly. Those who cherish a contrary expectation, do not vindicate it by contradiction of the obvious principle enunciated by Laplace, or even by maintaining that inorganic matter is adequate to produce living organism. They cling to the more general and doubtful position that no limits are to be a.s.signed to science, or as it is often stated, all nature belongs to the comprehensible. The failure of past experiments is no proof that inevitable failure awaits other experiments which may yet be made. To abandon expectation seems to them to be unfaithful to science. In this fashion, Professor Schmidt declares that "to any one who holds open the possibility that, even now, animate may be evolved from inanimate, without the mediation of progenitors, _the first origin of life in this natural method is at once self-evident_."[AU] To this view the other side may legitimately reply, that if the origin of life be as easily accounted for, as provision is here made for the "self-evident," science will soon be at a discount. To those regarding the matter from without, and waiting for testimony as to what is scientifically established, it is clear that there is no explanation of the origin of life; and I think it will be most commonly held that the weight of reason as to expectations for the future lies with those who abandon the antic.i.p.ation of any scientific explanation. There is, however, in actual conclusions on scientific evidence nothing involving conflict with religious conviction; and allowance will be made for continued and extended experiments, provided only that the "holding open the possibility," does not make the probability "self-evident."
Pa.s.sing thus from the unsolved problem of the origin of life,--with the attendant acknowledgment that there is no scientific theory of the world"s descent from primordial atoms, we advance to the testimony of science concerning different orders of life, and their relations to each other. Here there is no restriction as to the use of scientific methods; there is wide range for free action by the hosts of observers required for the work. A sense of the relief which this implies, in contrast with the hampering restraints surrounding the earlier question, imparts to the words of Schmidt a more jubilant tone, as he says, "Between beginning and end, we naturalists may do as we please."[AV]
In this region it will be universally admitted that the development of species by selection is the conception which has gained greatest hold upon the scientific mind within recent times. Accordingly it seems better to begin with an outline of this theory, and of its history as developed by Mr. Darwin, keeping, however, steadily in view the range of problem with which the theory has to deal.
As already remarked the origin of life is a problem quite distinct, and the theory of selection does not entangle itself by maintaining origin of life by development from unorganized matter. Mr. Darwin clearly guarded himself against responsibility for such a conception of its origin.[AW] Restricting thus far, we have to keep in view the vast range of the problem demanding scientific explanation.
Animal life manifests itself by spontaneous movement,--movement from within the living organism, in contrast with movement caused by energy applied from without. This holds true of every living germ, from which a mature animal form may be developed. This is the test of the presence of life under the microscope in minute germinal structures otherwise incapable of observation. In its lowest known form life appears in a minute vessel containing so much nourishment, which is within a nucleus or vital centre from which movement originates.[AX] This depends for its development on external conditions such as heat and moisture.[AY]
Advance in the scale is connected with greater complexity in the organism. As we ascend, separate organs appear, fulfilling distinct functions, and controlled by means of a nerve system whose ramifications are according to the intricacy of the organism. The appearance of such a nerve system implies sensibility and motor activity, provision for an _experience_ more or less varied, and _movement_ in some measure according with it, or adapted to it. From a nerve system consisting of a centre and a few fibres, we gradually ascend, until in the higher vertebrate orders, we find a vast system of nerves harmonized and governed from a grand centre or terminus const.i.tuting the brain.[AZ]
With the steadily advancing complexity of nerve system, there is great diversity in the orders of animals, in the variety of actions of which they are capable, in adaptation to different conditions of life, and in the modes in which they obtain subsistence. The scientific problem is--How far can we account for all this complex system of things by the action of natural causes?
As we are here specially concerned with ruling conceptions, and only indirectly with details, the relations of the animal and vegetable kingdoms may be pa.s.sed, with the acknowledgment that the two are obviously distinct, and yet that the vegetable very nearly merges into the animal at certain points, as ill.u.s.trated by sensibility, if not by locomotion. So may we waive discussion of the cla.s.sification of animals, which involves important points closely connected with the main question. Allowing that the wonderful diversity in animal organization, may admit of different modes of cla.s.sification; and yet granting that the structure of the animal economy in all its forms proceeds on common principles, which must lead to practical agreement as to modes of cla.s.sification; we deal with the single question as to the natural causes serving to explain different orders.
Mr. Darwin"s suggestion, largely supported by evidence from many quarters, and now commanding a very general support is, that all this diversity may be regarded as the product of a long process of development. This theory takes the whole orders of existence into one sweep. The lowest type of animal life presents to view the beginning of a protracted history; the highest order of animate existence indicates the stage of advance at which we observe things at the present period.
For such a theory the history of individual development belonging to whatever order, and the history of distinct orders as indicating improvement and deviation of whatever aspect, present evidence of special value. The most important causes relied upon as contributing to the formation of a scientific theory may be presented under these four heads--(1) The action of external causes as provided for by environment; (2) power of adaptability within each organism, providing for changes according to requirement from without, which may be described as "adaptive changes of structure;" (3) "the struggle for existence," in accordance with which the strongest gain the mastery and consequent advantage in obtaining the means of subsistence; and (4) "natural selection" among the s.e.xes, giving to the offspring all advantages according to the laws of hereditary descent.
The essential feature in this theory is the _power of adaptability inherent in the organism_. This is postulated as characteristic of all organized existence; and it is implied, that this power of adaptability multiplies in a degree approximating to the measure of complexity belonging to the organism. The inherent capacity for deviation is thus much less in the mollusk than in the bird; and in the bird much less than in the quadruped. Thus the development process which must, according to this view, have been exceedingly slow in the earlier stages, must have been greatly accelerated when more complex organisms had come into existence, and all the advantages accrued from greater diversity of materials. Such is a brief outline of the theory; and looked at simply as a theory, there is a manifest attraction in the boldness of the conception, and the wide sweep of the generalization which it includes. Taken merely as an intellectual representation setting forth a conceivable order of things in the universe, it has a great deal to command attention and awaken interest. It is, indeed, a novelty in the history of scientific thought, and as such at variance with previous conceptions, both scientific and non-scientific. But it is no more at variance with religious thought, than with ordinary notions of preceding times; while to the author whose name is now a.s.sociated with it all over the scientific world, it is a more striking testimony of the marvels of creative power,[BA] than notions previously current, which regarded it as historically true that every existing variety of animal was launched into being by a distinct creative act. Whatever may be the ultimate view of the history of life on the earth, based on purely scientific data,--and we are still a far way removed from what may be regarded as scientific evidence for such a view,--the fewer the primordial forms to which the multiplicity of existing species can be traced, the greater is the marvel which science presents, and the more convincing becomes the intellectual necessity by which we travel back to a Supernatural Intelligence as the source of all. On the other hand, the slow process by which scientific research tends to make out the natural history of living organisms far removed from each other in the scale of being, tracing many groups to a common parentage, and a.s.signing their appearance in the world to distinct periods in its history, will be seen to be so far antic.i.p.ated and favored by the graphic description of the introduction of animal life given in the opening page of revelation, where different orders are a.s.signed to successive epochs.
While, however, these things are said at the outset, as affording commencement for the study of an evolution theory, and delivering us from the supposition that there is an inevitable antagonism between science and recognition of the supernatural, we revert to the ruling principle for this whole inquiry, that science must prosecute its own researches, unfettered by forecast of consequences; and that the Bible is not to be handled as if it were a book of science, for it neither lays restraints upon human inquiry, nor delivers us from the need for it.
The best method for entering upon a study of the theory of evolution by natural selection is to take Mr. Darwin"s own account of the manner in which it began to take shape before his mind. In his "historical sketch of the recent progress of opinion on the origin of species,"[BB] he traces to Lamark the first suggestions on the subject, directing public attention to the question in 1801; thereafter a succession of naturalists including St. Hilaire, Wells, and Patrick Matthew, from separate and incidental observations, dwelt upon the difficulty of distinguishing species, and on the evidence of an archetypal idea, or common plan of structure, being applicable in the history of whole orders. Mr. Darwin then gives the following biographical references at the outset,--"When on board H. M. S. "Beagle," as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to throw some light on the origin of species--that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me in 1837, that something might perhaps be made out on this question by patiently acc.u.mulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years"
work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions which then seemed to me probable: from that period to the present day I have steadily pursued the same object."[BC] Such is Mr. Darwin"s opening paragraph in the now celebrated _Origin of Species_. No one interested in such investigations will hesitate to approve and trust the "patiently acc.u.mulating and reflecting on all sorts of facts;" nor can there be any hesitation in granting the warrantableness of his beginning to speculate as to the probable results. On the other hand, even the most ardent admirers of the evolution theory can not refuse to allow that only its principles are certain, while its ultimate form is still matter of conjecture and speculation. Quite divergent lines of speculation have found a start within the compa.s.s of the phenomena brought under review, and it is already apparent that opposite tendencies of thought have effected a lodgment under the common name of evolution. In these circ.u.mstances there is no direct call, as there are no proper materials, for attempting a reconciliation between the principles of religion, and definite scientific conclusions as to the origin of species. We are still occupying that position which makes historical treatment of the subject the most appropriate, leaving to speculation the probable lines of adjustment which may render possible a wider induction bearing on a general theory of the universe.
The observations of Alfred Russell Wallace in the Malay Archipelago led towards the same conclusions as those indicated by Darwin, to whom Mr.
Wallace dedicated his book,[BD] giving the results of research extending from 1854 to 1862, and in confirmation of Darwin"s theory, though differing on important points, Wallace published in 1870 his _Contribution to the Theory of Natural Selection_. Mr. Darwin"s views when first promulgated received decided though somewhat guarded support from Sir Charles Lyell, whose geological studies marked him out as a highly qualified witness on the subject, and were strongly favored by Dr. Hooker, author of _Introduction to the Australian Flora_, while they encountered not a little criticism, and were met with announcements of formal reservations, on the part of distinguished naturalists.
A fuller statement as to the history of his own thought was given by Mr.
Darwin in the fifth edition of his work, and also in a letter to Haeckel, author of the bolder venture as to the _History of the Creation_, and the _Evolution of Man_. This letter to Haeckel 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 pa.s.sage 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 pa.s.sage 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 pa.s.sage, 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 G.o.d, 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 compa.s.s of a single page he first affirms the limitation, and then denies it. First vindicating Darwin from the attack of Max Muller 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 att.i.tude, 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 ill.u.s.trated by the examples of the various orders of pigeons, and of dogs; both cla.s.ses 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 a.s.sent, 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 cla.s.sification of the different orders of animal life, exceedingly difficult in any case, has been rendered much more perplexing in consequence of the acc.u.mulation 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 const.i.tutes _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 const.i.tutes 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 acc.u.mulated, 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 Haeckel, 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 circ.u.mstances 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 Haeckel, and even Schmidt, pa.s.s 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 circ.u.mstances.
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. Aga.s.siz 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 a.s.sume 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 circ.u.mstances."[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 acc.u.mulation 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 a.n.a.logous 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 a.s.sent 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 a.s.sured 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.
[AZ] See Appendix IV.
[BA] _Origin of Species_, p. 577.
[BB] _The Origin of Species_, xiii. 4th ed.
[BC] _The Origin of Species_, p. 1.
[BD] _Malay Archipelago_, 1869.
[BE] The pa.s.sage is quoted as given by Schmidt in his _Doctrine of Descent_, p. 132. Italics are inserted to guide the eye of the reader to the successive stages.