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

By O. F. C

THE kinetic theory of evolution finds in the facts of organic development indications that the characters of species change spontaneously, or without environmental causation. Evolutionary progress is further conceived as accomplished through the union of the normally diverse individual members of species into a coherent network of interbreeding lines of descent, rather than by the isolation of variant individuals or by the selective restriction of descent to individuals possessing particular characters.

Former theories have undertaken to explain the method of evolution by reference to the dendritic figure of descent as shown in the ever-branching relationships of species, genera and families. The kinetic interpretation of the evolutionary process is based on what may be called the intraspecific figure of descent, the relationship of organisms inside the species, which is reticular or net-like, and not tree-like.

Theories based on the dendritic conception of descent may also be described as differential; that is, they have given attention chiefly to the problems of distinction and separation of organic groups. The kinetic theory is integral or synthetic, and conceives the evolutionary process as conducted by the accumulation and combination of the variations which appear among the members of the species.

These simple distinctions are fundamental, and will necessitate an extensive readjustment of methods of thought and investigation in the field of evolution.

[198] Various aspects of the kinetic theory have been presented in earlier essays, of which the present chapters are a continuation. Indeed, it is likely to become apparent to the reader that they have been written at different times and that they often lack unity and consistency. The same ground has in some cases been traversed repeatedly and in different directions, but the frequent restatement of the same distinctions appears to be necessary in the development of so large and complicated a subject. My thanks are due Mr. Walter T. Swingle for much helpful interest and criticism.


The theory that evolution is caused by natural selection and the survival of the fittest is now commonly admitted to be inadequate, but our studies tend, as usual, to follow the beaten paths of thought, and adjust themselves only with reluctance to new interpretations. The point at which the selection theory becomes obviously deficient is that it does not account for the fitness to which the evolutionary progress is ascribed. This has given rise to the attempt in recent years to penetrate farther into what has been called "the problem of fitness," on the natural assumption that more light could certainly be reached in the quarter whence came the first suggestions of evolutionary illumination. Nevertheless, those who have followed closely on the route of natural selection have not yet come through into regions of clear vision.

Fitness is the primary idea of the doctrine of evolution by selection. Fitness affords the cogs, as it were, by which evolution is supposed to be worked by the environment. Even if we were to admit, for the argument, that evolutionary motion could be caused by selection towards greater fitness, the evolutionary factory would still lack the very important facility for providing these cogs of fitness by which the environment could gain a hold upon the species and roll them along. Some selective evolutionists have assumed that environment could form the cogs by impressing itself upon the species, and others that the species could, as it were, wrinkle itself in response to external stimuli, and thus give the environment a selective impingement.

[199] These suggestions have not been able to retain the full confidence of biologists for the selective theory, as witness the recent remarkable diversions towards Mendelism and mutationism. The prompt acceptance of these doctrines by so many students of evolution is not justified by any indication of general pertinence for the facts on which they are based. They met with immediate welcome because they afforded a suggestion, at least, of methods by which new characters or character-combinations could be produced. They promised, in other words, the long-needed supplement of the selective theory, the cogs which selection might turn.

The kinetic theory recognizes that evolution does not depend upon selection nor upon the environment, and still less upon mutation and Mendelism. The evolutionary causes are in the species, not in the environments. They are resident, moreover, in species as constituted in nature, and are exemplified only abnormally in the phenomena which become prominent in the close-bred domesticated plants to which the studies of Mendel and De Vries were mostly directed.


The current belief in the environmental causation of evolution is largely due to the confusion of two different kinds of organic fitness. (1) The general fitness of the species for the environments in which they exist; and (2) the special fitness or power of adjustment of the individual organisms to particular conditions which they may encounter. An interesting example of the extent to which these two distinct phenomena have been confused may be found in so well known a work of reference as the Standard Dictionary. Adaptation is defined as "an advantageous conformation of an organism to changes in its environments," but the quotation given to illustrate the use of the word in this sense alludes to the "special adaptations" of deepsea organisms. The definition applies to the second type, fitness by individual adjustment, while the example refers only to the first type, the general fitness of the species, genus or family as a whole.

No method has been suggested whereby either type of fitness [200] can be caused by the environment, but the fact that individual adjustments do have definite relations to the environment, has served to sustain a belief in the environmental causation of evolution. All species have, of course, fitness for their environments; otherwise they would not continue to exist. They must be more fit than other species which have had access to the same environments, or they would be driven out. Nevertheless, inside of the general environment, or place of the species in the economy of nature, there is still a very great diversity of individual experience to which each organism must adjust itself. The environment at all times determines the relation of fitness, but the characters which afford the fitness are as truly results of evolution as any other characters. It has not been shown that they are caused by the environment or that they can be inherited from it.

The doctrine of environmental causation of evolution supports one assumption by another equally baseless. It takes for granted that adjustment differences between individuals of the same species are caused by the environmental differences which are met by these same adjustments. It also takes for granted that the general fitness or adaptation of the species is merely a product of the fitness of individual adjustment, whereas there are two phenomena of fitness which are quite distinct in their relations to the problem of evolutionary causes, though neither of them affords any special indication regarding the nature of such causes. The adjustment of individuals to differences of environment is a form of organic elasticity which permits lateral vibrations or displacements of characters, while the fitness of a species or genus as a whole is, obviously, an accomplished result of evolution instead of being a formative principle or cause.


To say, as has been the custom of writers on evolution, that organisms are plastic or susceptible of environmental influences, is only half of the truth. Organisms are not merely plastic, but versatile. Under different conditions they are able to grow in different ways, and often in ways which qualify them better for existence in these particular conditions, though not necessarily [201] so. A Guatemalan variety of the cotton plant takes on in Texas a robust, upright habit of growth very distinct from that of its Central American ancestor. It might be held that this deviation from the previous type serves a purpose in the internal economy of the plants, in enabling them to carry on more efficiently the process of vegetative development. Nevertheless, it cannot be reckoned as a truly adaptive change, since it does not improve the chances of the survival of the variety in the new environment. These very large and vigorous plants are relatively infertile, and ripen their fruits much later than those which retain the normal low-growing parental form. This behavior of the cotton plant is not the exception, but accords with a general tendency of tropical plants toward excessive vegetative development when first planted in northern latitudes. The longer days and higher temperatures of our summer seasons are not utilized for earlier and larger production of fruit, but are wasted in riotous vegetative expansion often cut short by frost before a single seed has been formed.

New environments may also throw plants into a condition of morphological instability which can scarcely have any relation to adaptation, since the result is an endless diversity of abrupt variations or mutations along many different lines, including the most opposite. The hereditary coherence of the species or variety is lost, and the individuals scatter, as it were, in all directions. This explosive type of variation is occasioned, obviously, by changes of environment, but it is equally obvious that one and the same change of environment cannot be directly described as having caused many diverse variations; it need only be thought of as having occasioned an abnormal intensification of normal individual diversity.

In some manner, quite unknown as yet, changes of conditions do induce changes of methods of development, but to infer that these changes are always advantageous, or that the external causes actuate the modified development of the organisms, is bad logic and worse biology.

Curiously enough, it is only at one particular point that such reckless conclusions are indulged. When we find a dozen different species of plants growing on the same square yard of soil, [202] it does not occur to us to suppose that their diversities are due to the different conditions under which they have grown, for the conditions are the same. We accept without debate the fact that the plants are developing each according to the methods of its own species. It is only when we find plants of the same species following different methods of growth when under different conditions that we can be betrayed into supposing that the conditions are producing the characters of the organisms. In reality this reasoning has no more propriety when we compare a plant or an animal with another member of its own species than when we compare it with a member of a different species.

As long as the adjustments are physiological only, we do not find it necessary to marvel, but when they become appreciable from the morphological standpoint our interest is aroused. And when accommodations cause taxonomic difficulties by affecting the characters by which we have described species, some are ready to believe that environment must be responsible for evolution because it can be alleged to change the characters of species. To reach this conclusion the amassing of detailed knowledge of plants and animals was superfluous. It could have been based quite as logically on the fact that rain "causes" us to carry umbrellas, and to wear waterproof coats. The African variety of mankind adopts the reverse policy, but no less appropriate to the occasion. He discards all of his scanty wardrobe and gives his naked skin a coat of palm oil. The birds can not change or take off their feathers, but their own organization provides a convenient supply of oil, and an instinct to use it when needed. Plants can neither go in when it rains nor oil themselves, but many plants grow a water-shedding coat of wax or of fine hairs on the upper surfaces of their leaves.

All species of plants and animals have, as already remarked, not only their general specific methods of development, but they have in addition certain ranges of adjustment to the different conditions under which they are able to exist. The environmental qualifications of a species are not to be represented by a single point, but by maximal and minimal boundaries, like the geographical latitudes and longitudes which may be used to indicate its position on the earth's surface. [203]

It is usually possible to discover somewhere between the prohibitive extremes an optimum condition, or a locality where the fullest development of the species takes place. Unfavorable conditions multiply as the boundaries are approached, and development is variously impeded and restricted, but surely the ability of the organisms to accept or to avoid a measure of such restrictions and to achieve an existence in spite of them, is small warrant for concluding that the conditions afford an adequate biological explanation of the characters. Still less are we justified in supposing that the unfavorable peripheral conditions are any more truly causative than the central optima. Adverse circumstances, by restricting development, would seem rather to require the organism to put forth more active energies, not of development merely, but of accommodation as well. And yet it is in abnormal features arising under abnormal conditions that the evidences of environmental causation have been chiefly found.

If each species were restricted to an absolute uniformity of conditions and materials, the doctrine of environmental causation would have had at least a partial justification, whereas the versatility of organisms, instead of demonstrating environmental causation, renders it highly improbable. The individual members of species in nature are different, even under the same conditions; why should we expect them to be alike under different conditions?

For some species the range of environmental conditions is very broad, in others very narrow. The fitness of the latter type of species may appear to be greater than the former, in the sense of being more highly specialized. It is not, however, the extent of narrowly specialized fitness, but the extent of widely varied adjustment which generally determines the range of distribution and the numerical prosperity of the species.

1Metcalf, M. M., 1906. The Influence of Plasticity of Organisms upon Evolution, Science, N. S. 23: 789.

In a general way the power of a species to accommodate itself to different environments might be held to favor evolution, because it would improve the chances of sustained numerical prosperity, which is an evolutionary advantage. It does not appear, however, that "plasticity" would be especially helpful in the evolution of the particular characters which might be [204] modified in adjustments to the different conditions. The "plasticity" might hinder, even, as Professor Metcalf has recently pointed out, for the ability of the species to accommodate itself promptly would render unnecessary any permanent progress in the direction of these particular changes.1

Of permanent effects arising from the influence of environment upon adjustment changes, there would remain only the possibility that a species which had once possessed a wide range of accommodation, might lose this by long disuse, and might thus become more narrowly specialized as a result of environmental influence. Thus an amphibious species, if confined long enough to a strictly terrestrial habitat, might forget, as it were, how to grow in water.

2An additional reason for caution in denying the possibility of a loss of the power of accommodation from disuse is found in the phenomenon of "fixing the type" of a variety by selection. The normal diversity tends to disappear when only one carefully selected type of the variety is bred for several generations.

That experiments have not yet demonstrated such an effect does not justify a general denial of the possibility. The phenomenon would be no less real if it took a hundred or a thousand years to produce it than if it required only five or ten.2 But in any case the result would be negative rather than positive, involving a diminution of the powers of the species rather than an enlargement of them. There would be a loss of characters instead of an addition, and no occasion to infer that environment had aided evolution. The case would be quite analogous with the influence of environment through natural selection, which is likewise not constructive, but wholly restrictive.

Much of the existing terminology of evolutionary discussion is calculated to commit us in advance to the doctrine that the adjustment is caused by the environment, whereas the fact is that the organisms are active instead of passive, and are able to put forth their own efforts toward adjustment to the varied external circumstances. It is only in a loose and figurative sense that the environment can be said to cause the adaptive adjustments. The arctic climate "causes" the Esquimaux to clothe themselves in furs, but it does not skin the fur-bearing [205] animals and sew their pelts together. We say, similarly, that a desert climate "causes" a plant to become more hairy, but this is as yet a mere figment of speech. We have no notion of the chain of biological events coming between the dryness and the hairs. We can appreciate the advantage of the reduced transpiration, but we do not know how the plant puts on the additional protection against the dry atmosphere.


We shall hardly come to understand aright the relation of fitness to evolution until we accustom ourselves to thinking of these variations of accommodation or so-called "environmental reactions" as expressions of the power of the plant or animal to choose, as it were, between alternative methods of growing and of conducting the functions of existence.

Organic versatility, plasticity, or whatever it may be called, does not conduce to the rapid development of specialized characters (adaptation), or to the multiplication of new groups (speciation), but it is undoubtedly of vast practical importance in the economy of species. Some species have little of this readiness of adjustment, while others are able to adopt a great variety of forms and can thus take advantage of opportunities of existence under a great diversity of natural conditions. By keeping open a larger number of alternative lines of progress, the power of accommodation very greatly increases the ability of species to solve their environmental problems. The environment is unable to prevent such groups from accumulating many kinds of variations or from making trial of them, as it were, in a great variety of combinations. This affords the best of opportunities for the construction of new types with enlarged environmental resources, instead of providing merely for the differentiation of narrowly localized and specialized species.

1See Fink, B., 1906. Plant World, 9 :183.

The different characters assumed by a species in accommodating itself to different environments are not less characters of the species because they are shown simultaneously than if they were developed in successive epochs of evolution. The only sense in which they are not characters of the species is the narrowly taxonomic one in which species are treated as having [206] "identity of form and structure." Characters changed when conditions change are to be reckoned as alternative characters, no less than sexual differences. Indeed, the sex determination itself sometimes appears as an incident of environmental adjustment.1

Alternation of generations and dimorphism afford further analogies. There is no warrant for the supposition that the evolutionary status of any of these kinds of characters is different from that of characters which appear in all individuals of the species. Professor Metcalf says:

"A high degree of plasticity hinders evolution by selection, of characters similar to those acquired by plastic response to the environmental influences."

This seems to imply that alternative characters which appear responsively have to be acquired over again by selection in order to become genuine results of evolution. If this were true selection might indeed be impeded. Such a distinction is not illogical, but it applies only in the metaphysical systems of evolution which assume that selection causes evolution and that environment causes characters.

A character which can be varied readily and which thus increases the power of the species to accommodate itself to varied environments is much more valuable than one which is not capable of such adjustment, and there is no reason to suppose that selection would favor the development of a non-adjustable form of the same character. Moreover, both the character itself and its adjustability or "plasticity" are already genuine evolutionary results reached by the same processes as any other characters.

It is only when we have allowed our meanings to slip from harmless abstractions to fictitious concretions that we explain evolution by selection and characters by plastic response to environmental influences. However unobjectionable such expressions may be if used in sufficiently general, literary senses, they are dangerously misleading as the basis of physiological inferences, because they take for granted unproved and improbable assumptions, such as the causing of characters by environ­ment [207] and the causing of evolution by selection, assumptions which rest in turn on the still more general and obviously erroneous assumption that species are normally uniform and stationary, whereas they are neither. It will some day be reckoned as one of the paradoxical incidents of biological history that this static theory, which is simply a relic of pre-Darwinian doctrine of special creation, should have been cherished most jealously by the ultra-materialistic school of biology.


The power of locomotion is a very important adaptive character of organisms because it gives great freedom of choice of environment. The hippopotamus, for example, is an aquatic animal, but the brief nocturnal excursions to the grassy riverbank or to the neighboring rice farm keep the huge bulk alive. Being animals ourselves and accustomed to use our powers of locomotion to change our environments, we fail to appreciate this form of adaptation and view with much wonder the fact that organic types have other means of dealing with environmental problems.

Unable to change their environments, they have the alternative power of changing their characters and of behaving in different ways in different environments. Some of the most striking instances of this kind are afforded by a series of plants (belonging to diverse and unrelated natural families) which can live either in water or on land, and which have two sets of characters appropriate to the alternative habitats. On land they have the characters of other land plants, in water the characters of other aquatics. The mystery is that they can change from the one to the other. Some have imagined that if we could find out how this change is accomplished we would have penetrated to the causes of evolutionary changes in general. The analogy between locomotion and environmental adjustment has been overlooked, along with the probability that both these methods of adjustment have been attained by the same evolutionary processes. They are finished products and not merely characters in the making.

The elasticity of muscular tissues is only one of the many [208] methods by which organisms are able to place themselves in more advantageous relations to their environment, and to manifest a power of choice with reference to external circumstances. Even among the simplest types of organic structure this faculty is definitely in evidence. The slime-moulds (myxomycetes) pass the vegetative period of their existence in rotten wood or other decaying vegetable matter. By simple amoeboid movements the naked, softly slimy protoplasm, of which these primitive organisms consist, is able to creep out at maturity to an exposed surface before giving up its water and separating itself into dry, wind-blown spores.

To better accomplish the work of dissemination many of the myxomycetes have the hereditary talent or instinct to subdivide their colony into small masses, each of which builds itself a stalk to climb upon. There is then built out from this stalk a network of threads to hold the spores so that they can be sifted out and scattered gradually by the wind, instead of falling at once to the ground. The stalk-building myxomycetes do not work, however, by any arbitrary or merely mechanical standards. When the surface of the decaying log over which they have spread themselves at maturity is uneven, so that a part of them must stand in wet depressions or chinks of the bark, these have longer stems than the others. In some species only those in the wet situations will have stems, while those in exposed places will remain seated directly on the substratum.

The building of the stem and the climbing up are not two different adaptations, but are merely the two aspects of the same act of adjustment to environmental conditions. In some connections it may do no harm to say that the wet situation causes the long stem and causes the slime mould to climb up, but for biological purposes all such statements must mean very little until we know something of the chain of events between the wetness and the building and climbing. Still less defensible is the policy of saying that the stem is "caused" by the environment while the motion is "spontaneous" in the organism. Mechanical biologists would be consistent, at least, in ascribing both acts to "stimuli."

The myxomycetes have long been objects of special interest in the [209] scientific world because they have been thought to combine the characters of animals and of plants and thus to afford a connecting link between the two organic kingdoms. Beginning with such a primitive and undifferentiated form of life, it is easy to think of the animals as gradually specializing the power of locomotion, the plants the alternative powers of morphological and physiological adjustment. The animals excel in seeking their own environments, the plants in the ability to take what comes.

The purpose of this rehearsal of elementary facts is merely to convey, if possible, the suggestion of an idea of organic elasticity, so to speak, of which muscular contractility and locomotion are the extreme specializations, but which extends into all departments of organic activity, morphological as well as physiological. Some may still prefer to say that the environment "causes" the adjustments to be made, but it will remain none the less true that the organisms themselves make the adjustments.

Zošlogists speculate on such questions as whether the eggs of Vancouver wood-peckers, if transferred to Arizona, would hatch Arizona wood-peckers, or whether the transferred individuals would gain Arizona characters in a few generations. What the wood-peckers might or might not do depends on the amount of organic elasticity which they may happen to possess, but the experiment is unnecessary for answering the general question, since plants show a high development of these powers of prompt adjustment to diverse conditions. It is not even necessary that the eggs be hatched in Arizona. Many plants, as already noted, can adjust themselves to such changes at any stage of their existence, and are regularly accustomed to do so. They are both fish and flesh. In water they have the form, structure and functions of other strictly aquatic species; on land they are equally ready to behave as terrestrial species.

Needless to say, hundreds of plants have been described as new species which proved afterward to be only land, water, shade, sun, or other environmental forms of previously known species, and such unnecessary "species" continue to be described. There is no way to ascertain from a few herbarium specimens whether their differences represent the results [210] of evolution as isolated groups or are merely adjustments to different conditions, any more than it could be ascertained without local study whether an individual bird-skin represented a regular resident, a migrant, or a still more accidental visitor.

In this merely taxonomic or nomenclatorial sense the environment can be said to cause species, but such a statement has no warrant in the field of evolution. If we have undertaken to diagnose species by characters which represent merely environmental adjustments our only course for the future is to recognize and rectify our mistakes, and not attempt to utilize them as the basis of doctrines of environmental causes of evolution.

For physiological and evolutionary purposes the species is not to be thought of in the mere systematic sense, as represented by the original specimen or even by the form in which the plant appears in what are supposed to be its normal conditions. The physiological and evolutionary species covers all the forms under which the organism can maintain itself and complete its life-history, to say nothing of the definitely abnormal results shown when conditions are too adverse.

Adjustment characters, as such, are not inherited, according to the usual definition of inheritance, that is, they are not necessarily repeated in each generation, but are readily recoverable when needed, even after long periods of time. The plant or animal if kept for many generations under the same environment may continue to show the same adjustment, but this may be completely changed by transfer to other conditions of growth. Thus at 4000 feet coffee has a more strict and upright habit of growth, darker, firmer foliage and larger seeds than at 2000 feet, but if seedlings from the two altitudes be exchanged they always grow into trees showing the characters appropriate to their new situations.

It appears, therefore, that both kinds of fitness, the general features which adapt the species as a whole to its place in nature, and the special powers of adjustment which assure to the individual a certain latitude of environmental opportunities, are normal characters of species, quite as much as those which have no such acute relations to the environment. Unless we can resume and carry to completion the Darwinian task of [211] proving that all characters have arisen as useful adaptations, other methods and causes of evolution must be sought. To question the adequacy of selective and environmental causes is to admit at least the possibility that such theories are completely erroneous, for any causes which are adequate to produce and develop useless characters can produce, a fortiori, useful ones.

There are enough adaptations to occupy many naturalists for many life-times. They can, if they prefer, live and die without hesitating to entertain doubts of the efficiency of environmental causation. And yet the fact will remain that the great majority of the differences between related species and between the individuals of the same species have no environmental utility at all, and are quite unlikely to have had any. This is not to be ascertained by denying or affirming the theoretical utility or uselessness of a few selected characters, but by observing whole orders and classes of organisms to learn the general proportions between differences of characters and differences of environmental relations, and by perceiving that the former vastly outnumber the latter.

1Knowlton, F. H. 1902. The Journeyings of Birds, Pop. Sci. Mon. 60: 323.

The fitness which the individuals of a species of plants can attain by adjusting themselves to the special conditions is, as we have seen, a kind of stepping aside, a morphological motion, put forth by the organism itself as truly as are the coordinated muscular acts which enable the higher animals to move from place to place and thus to choose their own environments. A perennial plant must arrange to tolerate whatever extremes of temperature, moisture, and exposure to sunlight its habitat may provide. Its powers of making such adjustments may be reckoned as functions of its tissues and organs in quite the same sense as locomotion and sustained high temperature are functions of the animal organism. The plant withstands a temperature range of a hundred degrees and more, but mammals and birds establish their own temperatures and keep them adjusted to tenths of degrees. It is a regular custom for many of them to travel annually for thousands of miles to find congenial conditions. The arctic plover is said to fly every year the whole length of the continent from Greenland to Patagonia and back again.1 [212]

The power to make or maintain such adjustments, whether by changes of muscular or other tissues, may well be reckoned as a character of a species, but there is nothing to show that morphological powers of adjustment are different in any evolutionary respect from the others, or that they afford any warrant for the inference that evolutionary changes are due to environmental differences, or that they arise first as adjustments to external conditions. Any change which increases fitness has the advantage of selective encouragement, and is thus able to exert a larger influence in determining the evolutionary course of the species, so that evolution tends ever toward greater fitness, though other lines of progress are not excluded. If changes could take place only in adaptive characters, the difficulty of maintaining fitness would be greatly increased, because characters would need to be useful from their very inception, whereas they have now the possibility of becoming useful at any stage of their expression. Selection begins to discriminate against a character only when it has become harmful.


It is not intended to imply that there are never any direct reactions to environmental influences or that such reactions are never of advantage to the organism. The Washingtonia palm of the deserts of Southern California has a complete covering of dead leaves over the whole length of its trunk, and secures, no doubt, a very desirable protection against the extreme heat and dryness. The retention of the leaves is made possible because the climate is dry. Palms native in humid regions usually drop their dead leaves promptly, but if not they are soon weakened by decay and fall away. Such coincidences could scarcely be avoided in any relations so complex as those of biology, but it does not appear that they are of a nature or frequency to give them more than a very subsidiary importance in evolution.

A plant or animal that encounters adverse conditions and is not able to obtain sufficient food will remain stunted. This small size is an advantage, however, in a region where food is scarce or uncertain. Nevertheless it is those individuals of the [213] species which are naturally small, that is smaller than most of their kind, even under favorable conditions, which would be able to make this reaction most successful, since they would be less stunted, or less abnormal, than the others. Thus even the simplest cases of environmental reaction are not to be separated, for evolutionary purposes, from the phenomena of normal diversity among the members of the species. Selection, as far as it influences the movement of the species toward adaptation, works through this intraspecific diversity rather than through the environmental reactions. The reactions are not selected, but the individuals which happen to excel in making the reactions.

Another case illustrating the same principles is that of the inconspicuous colors of the desert animals. Selection is supposed to have produced these inconspicuous colors because they conceal the animals, and thus give them protection against the enemies to which they would otherwise be very much exposed. The insecurity of this assumption becomes apparent as soon as we consider the equally striking fact of nature that desert plants also have the same series of dull shades of pale grayish and brownish colors. It would seem, therefore, that evolutionary inferences regarding the colors of the desert organisms will have to provide for the plants as well as for the animals, and that they must not depend wholly upon the idea of protection against predaceous foes.

From the plants it is very easy to gain another clue to causes of the obscure coloration. The vegetative tissues of desert plants are usually as green as those of species native in humid regions, but in arid climates the soft, thin-walled, green cells have to be covered by thick integuments to protect them from the dry air, and from too great intensity of light and heat. The modified colors seem to be purely incidental to the modified integuments which mask the green tissues within. The thickened, specialized outer skins simply protect the plants against the too rapid loss of water, and enable them to withstand more severe conditions of drouth. Many other species living under exactly the same conditions of exposure are nevertheless able to retain the fresh green colors of plants of humid regions, because they have solved their transpiration problems in other ways, just [214] as there are a few bright colored desert animals. The pigments which determine the color lie in the deeper layers of the skin, and are readily concealed by a thickening of the superficial layers, or by the development of darker pigments above to protect the lower cells from sunlight, as in the human species. When the color is resident in an outer covering of hairs, feathers, or scales, a very direct environmental reaction takes place, for these are no longer actively living, and the strong sunlight can bleach out the colors as well while the animals are alive as after they are dead. This is true of many insects and also of the horned toad, young or recently moulted individuals showing a bright yellow which is lacking in the old.

Finally, the protective coloration doctrine loses another installment in the fact that in the brilliant lights of deserts no colors are very conspicuous. There is no occasion, so to speak, for the development in desert animals of the brilliant tints which may enable the members of the same species to more quickly recognize each other in the sombre depths of tropical forests.

There have been, no doubt, many cases where the protective colors have been of immense advantage in the severe struggle for existence to which animals are often exposed. Selection must have had an immense influence in perfecting the marvellous adjustments which many species have with their environmental conditions. The nicety of some of these adjustments cannot be exaggeratedŃit is already past credence. A little fish, common in Liberia, is so exactly the color of the water-covered sandy stream-beds over which it swims that its presence is often betrayed only by the darting shadows. A little frog living in the sandy pools of the California desert canyons has the same elaborately speckled browns and grays, and likewise becomes invisible, except for the shadows. A slender pale gray lizard of the Colorado desert of southern California even excels the fish and the frog, for it seems to have the instinct of always facing the sun when it stands upon a stone to gain a lookout. In this position both its color and its shadow coincide with those of the stone, and the concealment is perfect.

The subject is one of tempting interest of detail, but enough has been said, perhaps, to make it evident that the dull coloration [215] of desert animals is a very complex phenomenon, not to be explained merely by coincidence, nor by environmental reaction, nor even by the selection of reactions.

The possibility of developing such elaborate contrivances is not adequately conceived until we are able to think of the species as having an active instead of a merely passive evolution, until we recognize that species have internal as well as external reasons for continuing to put forth variations of all the characters they possess, as long as the environment does not forbid. The endless possibilities of adjustment can then be realized, for the narrower the environmental road the more definitely adaptive must be the evolutionary motion of the species.


The utility of new characters is not to be narrowly restricted to the environmental sense. New characters can be thought of as having what may well be termed an organic utility, quite apart from their effects upon environmental relations. They may afford a desirable stimulation like that commonly shown in the greater vigor of crosses between organisms not too unlike, and they may also contribute to the structural perfection and general efficiency of the organism. Both these effects of new characters would give the new type environmental and selectional advantages, but indirectly, and not to the exclusion of other more definitely adaptive contributions to constructive evolution.

In the recognition of physiological values for new characters the kinetic theory of evolution diverges widely from the older doctrine that species are normally constant and stationary until changes are brought about by environmental influences. Although often misnamed dynamic, this conception was in reality static, for the organisms were supposed to have no power of change except as worked upon by the external causes. Nevertheless, variations, even when ascribed to the environment, were often held to be merely fortuitous in their relations to evolution, for it was not believed that they would be preserved and accentuated except by natural selection. The development of useless characters could not be admitted under this theory, although it [216] has become increasingly obvious that many of the characters which differentiate related species and genera are quite lacking in environmental utility, and probably always have been. Many characters which are now useful could have had little or no utility at the time of their inception unless they appeared suddenly in a highly developed state, as suggested by the now popular doctrine of mutation.

The kinetic theory enables us to understand that during the earlier period, while a character has only an organic utility, it nevertheless tends to be preserved and to become more and more accentuated, in accordance with the principle of kinesis or prepotency of new variations and recently acquired characters, just as though the species were actively concerned to test the environmental possibilities of each of the new characters it may be able to develop. In this view there is no period in which the new character is entirely useless. Its continued development is normal and advantageous on the ground of organic utility, unless it happens to encounter some environmental obstacle which forbids further advance, or unless an excessive development is attained which weakens or unbalances the organism.

In comparatively rare cases an acute natural selection may intervene and establish a standard for the species by eliminating all individuals which do not have a certain character developed to a required degree. If only one course of evolution remains open, progress in this direction may be greatly accelerated, for as the normal diversity of descent is eliminated the prepotency of the remaining variations appears to increase. This is not because the environment is hastening the perfection of a new form of fitness, but because it is of the nature of species to change, and to continue in the direction of further development of the characters already possessed.

As far as environmental causes are concerned, there appears to be complete fortuity in the appearance and development of characters, except as selective specialization intervenes. This may occur, of course, at any time in the development of the character, and may lend it an environmental significance not possessed before, and perhaps not continued except for a limited [217] period or stage of development. Thus the monkeys and anthropoid apes seem to have secured from their larger brains no special advantage over other animals. No species of anthropoids seems to have become very abundant or widely distributed. Only one member of the group continued brain-development to the point of utility in the struggle for existence, and gradually gained supremacy over the mundane creation. But mental development has by no means remained restricted to simple environmental requirements. Cerebral convolutions have continued to multiply among the more specialized or highly civilized varieties of mankind until they have become, if recent statistics are to be trusted, a positive hindrance to the well-being of the species, like the overgrown plumage of the pheasants and birds-of-paradise, or the burdensome antlers of the extinct Irish elk. Civilized man is now facing a crisis in his own evolution. He must soon decide whether he will make use of his over-developed intellect for solving the problems which now beset his existence, or allow it to carry him entirely out of contact with his environment and compass his destruction. As the supply of barbarous peoples of high mentality has almost run out, the present experiment of our race with civilization presents an element of historical finality which adds, if possible, to the natural interest of such phenomena. All former civilizations of the European or Mediterranean peoples have proved suicidal. It remains to be seen whether the modern faith in science will be justified by the finding of means to avoid another repetition of history.

Capable individuals tend always to assume parasitic habits and to become infertile, until the race is represented only by the relatively incapable immunes, upon whom civilization gets no hold. Science must make plain to capable people the folly of becoming parasites, or of permitting parasitism. Scientific discoveries have placed civilized man in many new relations with his environment, but these relations must have complete biological adjustment if they are to contribute to the evolutionary progress of the race. Scientific discoveries have transformed the arts of production and transportation, but they have had no corresponding influences upon social organization. Luxury, idleness and over-education are dangers to society, not merely [218] nor principally because they are connected with an unjust division of material wealth, but also because they rob the race of its most capable elements. However cruel and pitiful the fate of the incapable who are being eliminated in slums and factories, deterioration is no less real at the other end of the social series, and the loss to the race is far greater.

Instead of dwelling, as has been customary, upon the fortuity of variations and of evolution, we might often gain a clearer insight by reversing the points of view and appreciating the fact that it is the environment which is fortuitous rather than the development of species. Whether a character be useful or useless depends entirely upon the circumstances in which the organism is obliged to exist. Nowhere is this better shown than in man himself. The qualities necessary to a safe and prosperous existence in barbarism may be thoroughly disadvantageous in a member of a civilized community. The only way in which the development of desirable qualities may be substantially encouraged is by furnishing conditions in which they are advantageous, not, perhaps, in the way in which advantage is commonly reckoned, but in ways which shall conduce to the biological end of increasing, relatively at least, the better elements of the race, instead of tending to eliminate them.

The causes and remedies of these conditions are not to be considered here, the object being merely to illustrate from the history of man what is no doubt a general experience of species in nature, the change of the status of a character from useless to useful and then to harmful, depending upon this fortuitous relation between the character and the conditions. That only one species out of the millions which share with us the surface of our Earth should have developed intelligence, reason, consciousness, and personality, has appeared very strange, but it seems still more remarkable, when the vicissitudes of the journey are considered, that even this one should have reached so unique a distinction, and more mysterious yet that it should continue to climb the same summit far beyond any environmental or selective requirements, and even in despite of such requirements. Nevertheless, we are but doing what other species of organisms and other races of men have done before, with the single exception, [219] perhaps, of a better appreciation of the fate that is already befalling us.

Another highly specialized animal, the fig insect, affords an equally instructive illustration of the possibility that a character may develop past the point of fitness, and become dangerous to the species. The fig insects are much too highly specialized to be able to lead a free existence. They live only in the fruits of fig trees, which may very properly be said to have domesticated them as their only means of securing cross-fertilization. The two species, the insect and its fig tree, have thus a mutual interdependence of a very complete kind. In addition to their physical peculiarities, the female insects have the highly specialized instinct to find the young fig fruits and to force their way into them, often with much difficulty and the loss of their wings, so that further flight is impossible. The utility of the insect depends finally upon the fact that it is stupid enough not to distinguish between the male and female fig trees. The difference is a fatal one for the individual insect, for those which enter the female figs are lost. Their eggs never develop, and they leave no progeny, the perpetuation of the species devolving upon the relatively few insects which happen to reach male instead of female trees. Young male flowers are extremely scarce at the time when the principal generation of insects emerges, as though to definitely force them to carry pollen to the female trees.

It is evident that the continued success of this method of pollination depends upon a very acute adjustment of the intelligence of the insects. They must know enough to seek, enter and fertilize the fig flowers, but not enough to distinguish between those of the male and of the female trees. All of the insects which are really useful to the fig species in enabling it to ripen its seed are lost to the insect species, for their eggs have no chance of development. From the standpoint of the insect species there is an acute natural selection in favor of those which go to the flowers of male trees, but if there should anywhere be developed an instinctive preference for the male trees so that the fruits of the female trees remained unvisited, the fig would cease, in that region, to produce seed, and would become extinct, along with its insect tenant. [220]

1A wild species of fig native in the Comitan district of the Mexican state of Chiapas has its fruits so completely closed that even the fig insects can no longer emerge by the natural aperture, but are obliged to bore through the wall of the fruit to let themselves out. Mr. W. T. Swingle informs me that this is true also of the sycamore-figs of the Old World.

The selection which would eliminate the over-wise insects would not be applied to them directly, but to the trees which have become completely dependent upon their insect servants. Their highly specialized flower-receptacles are so tightly closed that no other insects will enter.1 When once such a delicate adjustment of structures and instincts breaks down, the parts are as useless as a watch that will not keep time. The utility depends only on the adjustment, and when the adjustment has become highly complex changes are far more likely to disturb than to improve it. Highly specialized types, those upon which selection has exerted the most successful influence, are ever the most liable to sudden and complete extinction, as geological history has already shown.

Close adjustments induced by selective influence are not, in the long run, truly advantageous. The chances of survival are not increased by close adjustment, but by the continuation of development of characters which allow a wide range of possibilities of existence under different environmental conditions. From the standpoint of the species, changes of the environment are fortuitous, and the utility of adjustments is also fortuitous and temporary. Indeed, the study of adaptations alone might have suggested caution in the acceptance of the doctrine of environmental causation, for a vast number of adaptations, and perhaps the majority of them, do not have reference to the environment, but are devices for keeping the species together, that is, for facilitating symbasic interbreeding. To this class of symbasic adaptations belong the whole series of specializations of flowers to secure the visits of insects, the group of phenomena which has probably figured more largely than any other as an evidence that adaptation is a genuine phenomenon of nature and not merely an elaborate collection of coincidences. These cross-fertilizing adaptations are real and wonderful, but the plants instead of having been acted upon by external influences have taken advantage of the environment to enable them to [221] maintain and extend the normal organization of the species. The individual plant gains no advantage from cross-fertilization; the advantage appears only when the results are viewed from the standpoint of the species.


No one has appreciated more keenly than Darwin himself the limitation of his doctrine of selection in the way of providing new characters of fitness on which selection could work. He continued with persistence the search for adaptive significances of characters, and supplemented his discoveries in that direction by the hypothesis of the correlation of variations. This assumes that the characters which are being developed by selection carry with them the development of other characters, some of which may remain useless while others attain utility and thus become in turn the objects of selective education. It is as though characters were fastened together in groups like chairs and tables so that they could be hitched along first by one leg and then by another.

Instances of correlation between characters have been found, and the suggestion gains somewhat from the fact that mutations of independent origin often show close similarity although differing from the parent type in numerous characters instead of in one only. Such a mutation might receive a selective advantage for one character, though the others would be preserved at the same time. Nevertheless, this suggestion would be subject to the same objection as the mutation theory as a whole, that the phenomena are abnormal and do not afford a true indication of the method of evolution in nature, for there the diversity appears not to be of the mutation type, but shows unlimited intergradations of all the characters, as though to give absolute freedom in the making of truly constructive combinations.

Correlations between different parts and tissues undoubtedly exist, but we may believe that they are brought about by normal evolutionary processes instead of supposing that characters have been tied up in arbitrary groups or bundles, which only explains one difficulty by imagining others still more mysterious. Such a character-complex would be, in effect, a suborganic organization, [222] if such an expression may be permitted. The hereditary instinct or spirit of the species would be subdivided, like the spirits of the gods of the Japanese mythology. We would then need to speculate on the nature and relations of these subordinate entities whose only purpose, after all, was to stop a gap in a theory. While selection appeared as the only method of actuating evolutionary motion it was justifiable, perhaps, to use a charitable imagination on this suggestion of fitness by correlation, but in the kinetic interpretation, where it is perceived that selection is not the cause of evolution, the correlation assumption does not need to be invoked. It is excluded, as the logicians would say, by the law of paucity, a beneficent selection which eliminates unnecessarily complicated hypotheses.


Weismann's recognition of the noninheritance of "acquired characters" or "direct adaptations" destroyed the foundation of the older selective doctrine of evolution by environmental causation, and left the means by which adaptation had been attained a complete mystery, especially for those who continued to hold the other half of the doctrine of selection, that species are normally stationary. To logical minds it has appeared obvious that a new foundation must be found or that the whole doctrine of evolution must be given up, whence the special attention given in later years to the "Origin of Fitness," in the hope of finding some way in which the external conditions can produce heritable internal changes in organisms. If the present interpretation of the facts be correct, this is a completely insoluble problem, or rather it is a gratuitous and artificial one, for there is no such relation as that which the selective school of "Genuine Darwinians" has hoped to ascertain.

1The word environment is itself the occasion of great ambiguity in evolutionary literature, some writers using it with reference to its supposed power to cause favorable variations, and others merely as a summary of selective influences. Between these two extremes there are many gradations of emphasis, so that two writers may use the same words in expressing contradictory opinions.

The non-inheritance of "acquired characters" proves that the changes which the environment "causes" are not those on which evolution proceeds, and forbids us to assert any directly causal connection between evolution and environment. Progress toward greater fitness arises and goes forward in quite the same manner as other forms of evolutionary change. The environment establishes, however, requirements of fitness, at times very [223] rigorous with regard to some particular faculty or feature, but generally allowing wide liberty of chance and choice in other respects. The adaptations are seldom so close that no further beneficial or indifferent changes can be made. If we attempt, by artificial selection, to enforce too narrow restrictions and maintain a closely uniform type, the effort always fails through the deterioration of the organism. The total fitness of species to their environments is simply the summary of their past histories. It has nothing in particular to do with evolutionary causes.1 The problem of fitness appears to be truly insoluble under the idea of normally stationary species. The postulates of the older selective doctrine are in direct logical agreement with each other, but one without the other is completely inoperative as a working hypothesis. Some have even denied adaptation because they despaired of explaining it, but all these difficulties disappear when the point of view is changed. Kinetic evolution supplies more abundant materials on which selection can act, and explains how fitness can come about without environmental causation. We are not obliged to discredit the evidence of our senses that adaptations exist, nor to reject the obvious probability that they are induced, though not caused, by the environment itself. All the difficulties are surmounted when we appreciate the fact that the environment works by the restriction and deflection of a normal evolutionary motion, and not as a direct or actuating cause. The environment furnishes certain specifications regarding what may be built, but builds nothing itself. Changes of the environments imply changes of the vital specifications; they enable new evolutionary steps to be taken, but the species itself must originate and develop the appropriate variations before selection can favor them with its discriminating encouragement.

The strength of the theory called Darwinism, that evolution is caused by natural selection, lay largely in the fact that it presented a solution of the problem of fitness, and could then explain evolution through adaptation. Darwinism was rational [224] as a theory, but the facts have refused to sustain it. Subsequent efforts by Naegeli, Weismann, De Vries, and others to supplement or supplant selection as an evolutionary cause have failed to command general confidence, largely because they provided no logical or adequate solution of the fitness problem, and undertook to deny adaptation or to explain it away as a mere coincidence. The best that could be done under the static hypothesis was to suppose that if the new types happened to differ from the old in characters of greater adaptive utility they could survive, and, it might be, exterminate their parents. No means not wholly hypothetical were suggested whereby the environment could exert a definite influence upon the course of evolution.

The kinetic theory more than makes good these deficiencies. It removes all need or temptation to minimize the extent of adaptation or the obviously very important role of selection in evolution. Though providing more generously than Darwinism itself the materials for selection to work upon, it does not carry us upon the dangerous ground of supposing that selection itself is an evolutionary cause, or that evolution is limited to adaptive characters. Darwinism assumed too much and explained too little. It predicated an important causal relation where none existed, and could still explain the evolution of adaptive characters only. Kinetic evolution assumes less and explains more. In recognizing the fact that the species are normally in motion it allows for the development of useless as well as of useful characters, and explains also how selection can contribute to adaptive specialization.


The problem of fitness is a crucial defect in the doctrine of evolution by selection, because in this theory selection does not become effective until enough fitness has been obtained to give a character selective value. The fact that organisms are often able to adjust themselves to different environments has been taken to prove that the environment causes variations of selective value. Environmental selection of these adjustment characters yielded the logically complete idea of an evolution initiated and actuated by environment. [225]

The kinetic theory rejects the hypothesis of environmental causation of evolution as fatally discordant with the facts of organic nature. The individual members of species are normally diverse, even under the same conditions; the fact that they may differ under different conditions is not to be accepted as a proof of environmental causation of evolution.

There are two phenomena of organic fitness: first the adaptation to environment afforded by the general characters of the species; and second, the power often shown by individual plants and animals to adjust themselves to varied environmental conditions. The latter is a form of organic elasticity comparable, in a general evolutionary sense, to muscular contraction and locomotion, and with no special significance as a factor of evolution, nor any special pertinence as an example of the method of evolution.

Both kinds of fitness are results of evolution, instead of being causes. They are fruits of the tree, not the roots. Fitness is maintained because evolution continues, not because the environment works changes in organisms. For the static evolutionist, fitness becomes an abstract and insoluble problem. Viewed from the kinetic standpoint, it appears as a natural and necessary consequence of a spontaneous evolutionary motion controlled or deflected by selective influence.

Environments continually change, and with them the relative utility of characters. A feature useless in one environment may be of value in another, or a useful character may become useless or even detrimental, depending on external circumstances.

There is thus a real and intimate relation between fitness and environment, but not a relation which can justify recourse either to natural selection or to direct adaptation, as causes of evolution. It is not to be taken for granted that all the differences shown by plants or animals when environments are changed are in the direction of fitness. With different conditions and materials, organisms build differently, or they may wander from the pathway of normal development in unwonted surroundings. Natural selection encourages fitness by preserving the fittest, but there are also environmental differences with no adaptive relation, and upon which selection exerts no influence. [226]

To find that organisms differ in different environments is, after all, only to find that they exist, for where the conditions of existence differ the organisms must differ. The power of organisms to form adjustments is a measure of their ability to exist, for no environments are absolutely constant. Species strive, as it were, by every artifice at their command to enlarge their environments, to conquer more opportunities of existence. Now and then a successful combination is attained.

Causes which can bring characters of selective value into existence can bring other characters as well, and can carry forward their development. It is no longer necessary to suppose that natural selection is an evolutionary cause at all, in the strict sense of the word. Selection may still be recognized as a condition or an influence in evolution, but there is nothing to show that evolutionary progress is actuated by selection. Fitness, in last analysis, comes by evolution, not evolution by fitness. Selection helps to explain adaptation, but it does not explain evolution; it enables us to understand why evolution follows some courses and not others, but it does not show how the evolutionary advance is accomplished, nor how a new character can develop to the point of utility or harmfulness, so that selection can encourage or restrict it.

The Lamarckian and the Darwinian theories ascribed evolution to causes resident in the environment. The kinetic theory ascribes it to causes resident in the species. The causes of evolution are not to be ascertained by the solution of the problem of fitness, but lie rather in the constitution of species and in the methods of organic descent.