Proceedings of the Washington Academy of Sciences
Vol. VIII, pp. 197‑403. February 13, 1907.

ASPECTS OF KINETIC EVOLUTION
By O. F. COOK

3. EVOLUTION, SPECIATION AND ADAPTATION.

One of the most frequent causes of confusion and error in evolutionary thought is the failure to distinguish clearly between evolution, speciation and adaptation; to distinguish, in other words, between the process of evolution itself and two of the relatively incidental results of environmental interference.

As long as a group of organisms remains united so that all its members interbreed freely with each other, evolution remains a unit in the sense that the whole group, though it may be changing any or all of its characters, still keeps together and retains its specific coherence. But if such a group be split into two or more parts which do not interbreed, evolution has as many separate courses, and the isolated parts attain differential characters, or, to use the words of former days, new species originate. It is obvious, however, that the differentiation of the new groups, while accomplished by evolution, is occasioned by isolation.² The multiplication of groups, which as a process may be [277] called speciation, is brought about by isolation, and is not a necessary cause nor a necessary result of evolution.

In a similar way another group of evolutionary writers have confused evolution with adaptation. Evolution results, not uncommonly, in the production of characters which give a species a specialized fitness for some particular environment. From such facts it was argued that the increase of fitness or "survival of the fittest" represented the method of evolution, or in other words, that evolution is merely a process of adaptation actuated by the selective power of the environment. The facts of nature show, however, that evolutionary motion is not at all restricted to directions of fitness, and it is also obvious that an evolution so restricted could not produce even the characters of fitness upon which it would depend for its supposed power to transform species. Fitness must be attained by evolution before the environment can give the character selective specialization by limiting the evolutionary motion and deflecting it into more definitely adaptive directions.

Evolution is the process of change by which the members of an organic group become different from their predecessors, or from other groups of common origin.

Symbasis is the normal evolutionary condition of free and extended interbreeding among the individual members of natural species.

Symbasis implies adequate diversity of descent; it is to be distinguished on the one side from the narrow inbreeding which induces abnormal mutations, and on the other from the wide cross‑breeding which produces abnormal hybrids.

The continual interweaving of the lines of descent from diverse and unrelated ancestors appears to be necessary to sustain the vitality and evolutionary progress of the higher plants and animals. The constructive evolution of new organic types does not take place on simple or narrow lines of descent, but requires [278] that large numbers of organisms advance in company, as in specific groups. A species is an organization of diverse, interbreeding individuals, dependent for its continued existence upon its ability to maintain a broad and intricately interwoven network of descent.

Specialion is the attainment of differential characters by segregated groups of organisms, that is, by subdivisions of older species.

Isolation of an organic group implies such a separation that interbreeding with members of other groups is excluded.

Isolation is of primary importance in speciation, since isolated groups of organisms always become different, but there is no indication that isolation is an evolutionary factor in the sense of causing or contributing to organic development. Its influence is negative rather then positive, for small groups of individuals advance less rapidly then large, and often deteriorate through inbreeding and inadequate diversity of descent.

The multiplying of species is a process distinct from developmental progress, and constitutes a distinct scientific problem.

Evolution might be explained without explaining speciation, and speciation without explaining evolution. Recognition of the diversity of the problems enables the factors to be separated; evolution depends upon symbasis, speciation upon isolation.

The segregation of a new group, whether by geographic barriers or by selective discrimination, merely affords opportunity for a new evolution to go forward. The means by which the progress is accomplished are to be sought inside the group, and not in the mere fact of isolation or selection. The multiplication of the number of evolving groups is a phenomenon distinct from that of the evolution itself. The evolutionary question is not how the species become isolated, but how they become different after they have been isolated.

Adaptation is the attainment of characters which place the species in a more advantageous relation with its environment.

Selection is a form of isolation which eliminates from the species individuals lacking in the expression of certain characters.

Under unconscious or natural selection only the most deficient in these characters are rejected; under conscious or artificial [279] selection by man only the most proficient are saved. Selection, by deflecting and confining the evolutionary motion of the species to particular channels, conduces to the adaptive specialization of characters, but it is not an actuating cause of their development.

Symbasis is a primary factor in evolution, an obstacle or negative factor in speciation. Selection often accounts for the accentuation of differences between related species, but is not on this account to be reckoned as an actuating cause or principle of evolution. It may explain the direction which evolution has taken with reference to a particular character, but does not show how the evolution has been accomplished.

Adaptation represents the bionomic aspect of evolution, speciation the taxonomic. Selection strengthens adaptations; isolation multiplies species; symbasis conducts evolution. Adaptation and speciation have appeared to many writers as causes of evolution, but in the kinetic or physiological interpretation they appear only as results, quite incidental to the true evolutionary process of progressive change in species.

RELATION BETWEEN HETERISM AND SPECIATION.

Recognition of the phenomena of heterism, the normal diversity of the interbreeding members of specific groups, is necessary, perhaps, to a full appreciation of the preceding distinctions between evolutionary change or vital motion and the subdivision or multiplication of species. Although commonly treated together, or even indiscriminately confused, these two processes are quite distinct. They may even run counter to each other, for evolutionary progress is not assisted by the subdivision of a subdivision of a species, but more likely to be hindered. The larger the number of interbreeding individuals the larger are the possibilities that desirable variations will appear, and the wider are the opportunities of a progressive utilization of a new feature. The group, as a whole, will advance more rapidly than if the range of transmission be narrowed by subdivision.

Segregation permits the subordinate groups to become differentiated, but it does not conduce to the advance of the whole series. The newly segregated groups become capable of taxonomic [280] recognition as species, but this is a mere incident of evolution, not an actuating cause nor a necessary effect.

The recognition of heterism or diverse, alternative descent, and the frequent development of sexual and other specializations of heterism inside specific lines, shows that the subdivision of species is to a very small extent, if any, the direct result of evolutionary advance. Not only can diverse characteristics exist inside specific lines, but it is an advantage to maintain just such heterogeneity. The only condition in which heterism would directly conduce to the formation of a new species would be that of alternative characters which hindered interbreeding. It is conceivable, for example, that a species might contain at the same time variations both toward earlier and later flowering, and that, instead of counteracting each other, both tendencies might become gradually more accentuated. The incidental result would be that interbreeding would cease and two separate groups would become established.¹ In such a case it might well be claimed that evolution had directly resulted in the multiplication of species, but it would still be true that it had done so only by means of segregation, and would show only that evolution might result in segregation, not that segregation is a factor in evolution, as often supposed. Isolation is an important consideration in phylogeny or historical biology, which undertakes to tell why the species are in the places we find them. But isolation and species‑subdivision have only a remote and incidental connection with evolution; they do not cause the progressive change.

The confusion of evolution with speciation has greatly impeded the progress of evolutionary science by withdrawing attention from the real issues to relatively unimportant considerations. It has misled many students of evolution into the belief that isolation or segregation is an important factor of evolutionary progress, whereas its influence is negative rather than positive. The selection doctrine of Darwin and the mutation doctrine of De Vries are both theories of speciation rather than of evolution. [281] They hold that new groups have to be isolated, that new species have to be made, in order to originate and preserve new characters.

"Each new variety or species, when formed, will generally take the place of, and thus exterminate its less well‑fitted parent. This, I believe to be the origin of the classification and affinities of organic beings at all times; for organic beings always seem to branch and sub‑branch like the limbs of a tree from a common trunk, the flourishing and diverging twigs destroying the less vigorous, the dead and lost branches rudely representing extinct genera and families."

Evolution, on this basis, would not be a process of transformation so much as of elimination and substitution. The parental type remains relatively stationary and unmodified until the new form can expand and replace it. The same is true of the mutation theory of De Vries, except that the new variations are supposed to be larger. The new character can persist only as it is able to crowd out its parent or neighbor and to conquer for itself a place in nature. Every new character which has been preserved, must, under these theories, be environmentally useful, which a very large proportion of the characters and differences of plants and animals are not, as even the most pronounced Darwinians like Professor Lankester now admit.

The kinetic theory does not encounter these difficulties and improbabilities. It recognizes speciation and evolution as entirely distinct problems, and does not require that a new species be made in order to preserve a new character, or even that characters must be useful. Characters may be preserved even when they are harmful, and may contribute to the extinction of the species. Evolution, in the kinetic theory, is definitely a process of transformation by the adoption and propagation of new variations in existing species. New variations are not segregated from the parental type, but interbreed freely with it, and thus bring about its evolutionary progress.

SELECTION EXPLAINED BY EVOLUTION.

As so often happens, the philosophical abstractions of logic have yielded very little assistance in the comprehension and [282] description of the facts of evolution. Numerous attempts have been made to define the relations of selection and evolution by means of Aristotle's categories of causation. Perhaps the best example of this is by Professor Cattell:

"In discussions on the theory of evolution we find Neo‑Darwinians saying that 'natural selection' is the cause of the origin of species, and Neo‑Lamarckians saying that the environment and the movements of the animal are the causes of adaptations. Now in these cases the word 'cause' is used ambiguously, ignorance of the facts of evolution being concealed by the exhibition of ignorance of logic.

"I wonder how many men of science have read Aristotle, or understand his distinctions between material, efficient, formal and final causes. We are not here concerned with a formal cause, the idea or plan of a thing, nor with a final cause, the end for which it is made; but no student of organic evolution can afford to ignore the distinction between material and efficient causes, or between the occasion and the efficient cause of an event. The material cause is that of which a thing is made, one of the occasions or necessary conditions of its existence; the efficient cause is that which produces a thing and makes it what it is. When no qualification is used cause should mean efficient cause or vera causa.

" 'Natural selection' is no cause of the origin of species, but may be the cause of the annihilation of unfit species. Whether or not the environment, or consciousness, or the movements of animals are causes of hereditary modifications are open questions. What is called the cause of an adaptation is, however, usually only its occasion." ¹

Selection is neither a formal, a final, a material nor an efficient cause of evolution. Evolution goes on without selection. This shows how poorly adapted the Aristotelian categories are for the expression of relations so complex as those of evolution. Those who depend upon systems of abstract formulation for the comprehension of biology can fit selection and evolution into these categories only by saying that evolution is the cause of [283] selection. This, at least, would not wholly misrepresent the facts of nature, for evolution accomplishes the results which it has been customary to ascribe to selection.

Unless evolution were going on the selective effects would not appear. The older writers commonly made the confusion even worse by assuming that adaptation and evolution are the same. Adaptation is not evolution, but only a special kind or result of evolution. Selection aids evolution to produce adaptation. Translating again into scholastic language, evolution is the efficient cause of adaptations, while selection is the occasional cause or condition which conduces to adaptations. Adaptive characters are brought into existence in the same way as other characters, by the evolutionary motion of species. Adaptation can be said to be caused by selection only as a pure abstraction, when it refers merely to the deflection which environmental obstacles have induced in the normal motion of the species.

The confusion of ideas has not been limited to advocates of natural selection, but is shared even by its most active opponents. Thus Mivart, in a book written to show the inadequacy of the selective theory of evolution, admits, for selection a power which it does not have:

" 'Natural Selection,' simply and by itself, is potent to explain the maintenance or the further extension and development of favorable variations, which are at once sufficiently considerable to be useful from the first to the individual possessing them. But Natural Selection utterly fails to account for the conservation and development of the minute and rudimentary beginnings, the slight and infinitesimal commencements of structures, however useful those structures may afterward become."¹

As long as we fail to perceive that selection is not a cause of evolution the issue remains uncertain. If selection is able to cause even a little evolution it might, with time, cause much. The "slight individual differences" may suffice for the work, as Darwin claimed, and the practicability of a selective evolution appears to turn on such arguments as the amount of time estimated by geologists and physicists from considerations even more obscure than those of biology itself. Selection is not [284] merely inadequate as a cause of evolution; it is not an evolutionary cause at all, but only a test and an evidence of the efficiency of other causes which reside in the species and enable it to go forward with persistence, even when obliged to follow a narrow path between environmental obstacles.

Selection is potent to explain the further extension and development of favorable variations only by its ability to influence an evolution which is already in progress, and not in any sense which renders it a cause of evolution. The selective potency of the environment consists only in its ability to restrict evolution, not in any power to actuate or to carry forward the process of development. Selection may still be enumerated as an evolutionary factor, but it is wholly a negative factor, restrictive and not constructive.

DARWINIAN FORMULAE OF EVOLUTION.

Evolution is a name for the process of gradual change by which the diversity of organic nature has come about. Darwin's theory of natural selection was based on the indication that some of the characters of plants and animals have been attained because individuals possessing these characters had an advantage in the struggle for existence. Many Darwinians "more Darwinian than Darwin" have made this proposition universal and say in effect that all characters of plants and animals have arisen because they give or have given their possessors advantages in the struggle for existence.

Darwin's original proposition points in the direction of an important truth, that plants and animals are specially adapted to their various environments. Great emphasis came to be placed on this point because the adjustment of species to their respective places in nature had been taken to prove the special creation of species, so that a theory of gradual development had to supply a solution for the problem of adaptation before it could expect to receive general credence or even the serious consideration of the scientific public.

In the course of the discussion which raged in the decades after the publication of the Origin of Species attention was principally directed to the phenomena of adaptation and speciation, [285] and the Darwinian doctrines were crystallized into formulae which were believed to demonstrate evolution from the facts of the struggle for existence and the survival of the fittest.

The earlier Darwinists were practical men and made the best use of the facts as they knew them. Whether the facts they regarded as proved would really be able to bring about evolution in normally stationary species is a question which might still be debated on philosophical grounds, like the fourth dimension of space and other hypothetical problems. But for practical purposes there is no need to reopen the discussion, since it is now apparent that formulae like those quoted above leave out of account a very important part of the facts of nature, the very facts, as it happens, which are most potent in the development of organic types. The evolution, if any, which the formula would provide would certainly not be that found in nature.

Scientific progress, at least in biology, does not follow the lines of formal mathematics or logic, but depends on history and human nature, like political and economic movements. It could not be expected that the evidences of evolutionary processes would be carefully weighed and correctly appreciated at a time when the very idea of evolution was being assaulted as an immoral perversion of intellect.

The best that could be done at the time was to drive the piles of accepted inferences into the mud of ignorance. The structure reared on such a foundation could not be a permanent one, but it has served to shelter a generation of students of nature, and enabled them to prepare the foundations of a more secure edifice of evolutionary doctrine based directly on ascertained facts. [286]

In popular discussions it often happens that the best and most important data are left in the background because the public is not ready to appreciate them. Thus Huxley, who rendered the most valiant service in the defense of Darwinism as a theory of environmentally caused evolution, also wrote this discriminating statement:

"It is in the recognition of a tendency to variation apart from the variation of what are ordinarily understood as external conditions that Darwin's view is such an advance on Lamarck."

To have secured popular appreciation for these nonenvironmental variations at that time was manifestly impracticable. Even after fifty years their existence is still generally unrecognized.

The credit of turning the scientific world to the study of evolution will always belong to Darwin and Huxley, but the fifty-years canvass which has now been given to the Darwinian theory of environmental action upon normally stable species has yielded nothing of moment. Huxley's appreciation of the advance of Darwin beyond Lamarck has not been shared by the evolutionary public, and the result has been a general reaction toward pre‑Darwinian conceptions, and even to some which Darwin himself considered and dismissed.¹

Perhaps the time has come to renew the consideration of the problem from the kinetic standpoint and to take into account again the normal diversity of descent and the normal interbreeding of the members of species. These facts have remained veritable stones of offense for the builders of static theories of environmental causation, but they can now be utilized as foundations of a new and more commodious structure of evolutionary thought.