Mr. Cope lays great stress on the existence of a special developmental force termed "bathmism" or growth-force, which acts by means of retardation and acceleration "without any reference to fitness at all;" that "instead of being controlled by fitness it is the controller of fitness." He argues that "all the characteristics of generalised groups from genera up (excepting, perhaps, families) have been evolved under the law of acceleration and retardation," combined with some intervention of natural selection; and that specific characters, or species, have been evolved by natural selection with some assistance from the higher law. He, therefore, makes species and genera two absolutely distinct things, the latter not developed out of the former; generic characters and specific characters are, in his opinion, fundamentally different, and have had different origins, and whole groups of species have been simultaneously modified, so as to belong to another genus; whence he thinks it "highly probable that the same specific form has existed through a succession of genera, and perhaps in different epochs of geologic time."

Useful characters, he concludes, have been produced by the special location of growth-force by use; useless ones have been produced by location of growth-force without the influence of use. Another element which determines the direction of growth-force, and which precedes use, is effort; and "it is thought that effort becomes incorporated into the metaphysical acquisitions of the parent, and is inherited with other metaphysical qualities by the young, which, during the period of growth, is much more susceptible to modifying influences, and is likely to exhibit structural change in consequence."[204]

From these few examples of their teachings, it is clear that these American evolutionists have departed very widely from the views of Mr. Darwin, and in place of the well-established causes and admitted laws to which he appeals have introduced theoretical conceptions which have not yet been tested by experiments or facts, as well as metaphysical conceptions which are incapable of proof. And when they come to illustrate these views by an appeal to palaeontology or morphology, we find that a far simpler and more complete explanation of the facts is afforded by the established principles of variation and natural selection. The confidence with which these new ideas are enunciated, and the repeated assertion that without them Darwinism is powerless to explain the origin of organic forms, renders it necessary to bestow a little more time on the explanations they give us of well-known phenomena with which, they assert, other theories are incompetent to grapple.

As examples of use producing structural change, Mr. Cope adduces the hooked and toothed beaks of the falcons and the butcher-birds, and he argues that the fact of these birds belonging to widely different groups proves that similarity of use has produced a similar structural result. But no attempt is made to show any direct causal connection between the use of a bill to cut or tear flesh and the development of a tooth on the mandible. Such use might conceivably strengthen the bill or increase its size, but not cause a special tooth-like outgrowth which was not present in the ancestral thrush-like forms of the butcher-bird. On the other hand, it is clear that any variations of the bill tending towards a hook or tooth would give the possessor some advantage in seizing and tearing its prey, and would thus be preserved and increased by natural selection. Again, Mr. Cope urges the effects of a supposed "law of polar or centrifugal growth" to counteract a tendency to unsymmetrical growth, where one side of the body is used more than the other. But the undoubted hurtfulness of want of symmetry in many important actions or functions would rapidly eliminate any such tendency. When, however, it has become useful, as in the case of the single enlarged claw of many Crustacea, it has been preserved by natural selection.

Origin of the Feet of the Ungulates.

Perhaps the most original and suggestive of Mr. Cope's applications of the theory of use and effort in modifying structure are, his chapters "On the Origin of the Foot-Structure of the Ungulates;" and that "On the Effect of Impacts and Strains on the Feet of Mammalia;" and they will serve also to show the comparative merits of this theory and that of natural selection in explaining a difficult case of modification, especially as it is an explanation claimed as new and original when first enunciated in 1881. Let us, then, see how he deals with the problem.

The remarkable progressive change of a four or five-toed ancestor into the one-toed horse, and the equally remarkable division of the whole group of ungulate animals into the odd-toed and even-toed divisions, Mr. Cope attempts to explain by the effects of impact and use among animals which frequented hard or swampy ground respectively. On hard ground, it is urged, the long middle toe would be most used and subjected to the greatest strains, and would therefore acquire both strength and development. It would then be still more exclusively used, and the extra nourishment required by it would be drawn from the adjacent less-used toes, which would accordingly diminish in size, till, after a long series of changes, the records of which are so well preserved in the American tertiary rocks, the true one-toed horse was developed. In soft or swampy ground, on the other hand, the tendency would be to spread out the foot so that there were two toes on each side. The two middle toes would thus be most used and most subject to strains, and would, therefore, increase at the expense of the lateral toes. There would be, no doubt, an advantage in these two functional toes being of equal size, so as to prevent twisting of the foot while walking; and variations tending to bring this about would be advantageous, and would therefore be preserved. Thus, by a parallel series of changes in another direction, adapted to a distinct set of conditions, we should arrive at the symmetrical divided hoofs of our deer and cattle. The fact that sheep and goats are specially mountain and rock-loving animals may be explained by their being a later modification, since the divided hoof once formed is evidently well adapted to secure a firm footing on rugged and precipitous ground, although it could hardly have been first developed in such localities. Mr. Cope thus concludes: "Certain it is that the length of the bones in the feet of the ungulate orders has a direct relation to the dryness of the ground they inhabit, and the possibility of speed which their habit permits them or necessarily imposes on them."[205]

If there is any truth in the explanation here briefly summarised, it must entirely depend on the fact of individual modifications thus produced being hereditary, and we yet await the proof of this. In the meantime it is clear that the very same results could have been brought about by variation and natural selection. For the toes, like all other organs, vary in size and proportions, and in their degree of union or separation; and if in one group of animals it was beneficial to have the middle toe larger and longer, and in another set to have the two middle toes of the same size, nothing can be more certain than that these particular modifications would be continuously preserved, and the very results we see ultimately produced.

The oft-repeated objections that the cause of variations is unknown, that there must be something to determine variations in the right direction; that "natural selection includes no actively progressive principle, but must wait for the development of variation, and then, after securing the survival of the best, wait again for the best to project its own variations for selection," we have already sufficiently answered by showing that variation—in abundant or typical species—is always present in ample amount; that it exists in all parts and organs; that these vary, for the most part, independently, so that any required combination of variations can be secured; and finally, that all variation is necessarily either in excess or defect of the mean condition, and that, consequently, the right or favourable variations are so frequently present that the unerring power of natural selection never wants materials to work upon.

Supposed Action of Animal Intelligence.

The following passage briefly summarises Mr. Cope's position: "Intelligence is a conservative principle, and will always direct effort and use into lines which will be beneficial to its possessor. Here we have the source of the fittest, i.e. addition of parts by increase and location of growth-force, directed by the influence of various kinds of compulsion in the lower, and intelligent option among higher animals. Thus intelligent choice, taking advantage of the successive evolution of physical conditions, may be regarded as the originator of the fittest, while natural selection is the tribunal to which all results of accelerated growth are submitted. This preserves or destroys them, and determines the new points of departure on which accelerated growth shall build."[206]

This notion of "intelligence"—the intelligence of the animal itself—determining its own variation, is so evidently a very partial theory, inapplicable to the whole vegetable kingdom, and almost so to all the lower forms of animals, amongst which, nevertheless, there is the very same adaptation and co-ordination of parts and functions as among the highest, that it is strange to see it put forward with such confidence as necessary for the completion of Darwin's theory. If "the various kinds of compulsion"—by which are apparently meant the laws of variation, growth, and reproduction, the struggle for existence, and the actions necessary to preserve life under the conditions of the animal's environment—are sufficient to have developed the varied forms of the lower animals and of plants, we can see no reason why the same "compulsion" should not have carried on the development of the higher animals also. The action of this "intelligent option" is altogether unproved; while the acknowledgment that natural selection is the tribunal which either preserves or destroys the variations submitted to it, seems quite inconsistent with the statement that intelligent choice is the "orginator of the fittest," since whatever is really "the fittest" can never be destroyed by natural selection, which is but another name for the survival of the fittest. If "the fittest" is always definitely produced by some other power, then natural selection is not wanted. If, on the other hand, both fit and unfit are produced, and natural selection decides between them, that is pure Darwinism, and Mr. Cope's theories have added nothing to it.



Semper on the Direct Influence of the Environment.

Another eminent naturalist, Professor Karl Semper of Wuerzburg, also adopts the view of the direct transforming power of the environment, and has brought together an immense body of interesting facts showing the influence of food, of light, of temperature, of still water and moving water, of the atmosphere and its currents, of gravitation, and of other organisms, in modifying the forms and other characteristics of animals.[207] He believes that these various influences produce a direct and important effect, and that this effect is accumulated by inheritance; yet he acknowledges that we have no direct evidence of this, and there is hardly a single case adduced in the book which is not equally well explained by adaptation, brought about by the survival of beneficial variations. Perhaps the most remarkable case he has brought forward is that of the transformation of species of crustaceans by a change in the saltness of the water (see Fig. 35). Artemia salina lives in brackish water, while A. Milhausenii inhabits water which is much salter. They differ greatly in the form of the tail-lobes, and in the presence or absence of spines upon the tail, and had always been considered perfectly distinct species. Yet either was transformed into the other in a few generations, during which the saltness of the water was gradually altered. Yet more, A. salina was gradually accustomed to fresher water, and in the course of a few generations, when the water had become perfectly fresh, the species was changed into Branchipus stagnalis, which had always been considered to belong to a different genus on account of differences in the form of the antennae and of the posterior segments of the body (see Fig. 36). This certainly appears to be a proof of change of conditions producing a change of form independently of selection, and of that change of form, while remaining under the same conditions, being inherited. Yet there is this peculiarity in the case, that there is a chemical change in the water, and that this water permeates the whole body, and must be absorbed by the tissues, and thus affect the ova and even the reproductive elements, and in this way may profoundly modify the whole organisation. Why and how the external effects are limited to special details of the structure we do not know; but it does not seem as if any far-reaching conclusions as to the cumulative effect of external conditions on the higher terrestrial animals and plants, can be drawn from such an exceptional phenomenon. It seems rather analogous to those effects of external influences on the very lowest organisms in which the vegetative and reproductive organs are hardly differentiated, in which case such effects are doubtless inherited.[208]



Professor Geddes's Theory of Variation in Plants.

In a paper read before the Edinburgh Botanical Society in 1886 Mr. Patrick Geddes laid down the outlines of a fundamental theory of plant variation, which he has further extended in the article "Variation and Selection" in the Encydopaedia Britannica, and in a paper read before the Linnaean Society but not yet published.

A theory of variation should deal alike with the origin of specific distinctions and with those vaster differences which characterise the larger groups, and he thinks it should answer such questions as—How an axis comes to be arrested to form a flower? how the various forms of inflorescence were evolved? how did perigynous or epigynous flowers arise from hypogynous flowers? and many others equally fundamental. Natural selection acting upon numerous accidental variations will not, he urges, account for such general facts as these, which must depend on some constant law of variation. This law he believes to be the well-known antagonism of vegetative and reproductive growth acting throughout the whole course of plant development; and he uses it to explain many of the most characteristic features of the structure of flowers and fruits.

Commencing with the origin of the flower, which all botanists agree in regarding as a shortened branch, he explains this shortening as an inevitable physiological fact, since the cost of the development of the reproductive elements is so great as necessarily to check vegetative growth. In the same manner the shortening of the inflorescence from raceme to spike or umbel, and thence to the capitulum or dense flower-head of the composite plants is brought about. This shortening, carried still further, produces the flattened leaf-like receptacle of Dorstenia, and further still the deeply hollowed fruity receptacle of the fig.

The flower itself undergoes a parallel modification due to a similar cause. It is formed by a series of modified leaves arranged round a shortened axis. In its earlier stages the number of these modified leaves is indefinite, as in many Ranunculaceae; and the axis itself is not greatly shortened, as in Myosurus. The first advance is to a definite number of parts and a permanently shortened axis, in the arrangement termed hypogynous, in which all the whorls are quite distinct from each other. In the next stage there is a further shortening of the central axis, leaving the outer portion as a ring on which the petals are inserted, producing the arrangement termed perigynous. A still further advance is made by the contraction of the axis, so as to leave the central part forming the ovary quite below the flower, which is then termed epigynous.

These several modifications are said to be parallel and definite, and to be determined by the continuous checking of vegetation by reproduction along what is an absolute groove of progressive change. This being the case, the importance of natural selection is greatly diminished. Instead of selecting and accumulating spontaneous indefinite variations, its function is to retard them after the stage of maximum utility has been independently reached. The same simple conception is said to unlock innumerable problems of vegetable morphology, large and small alike. It explains the inevitable development of gymnosperm into angiosperm by the checked vegetative growth of the ovule-bearing leaf or carpel; while such minor adaptations as the splitting fruit of the geranium or the cupped stigma of the pansy, can be no longer looked upon as achievements of natural selection, but must be regarded as naturally traceable to the vegetative checking of their respective types of leaf organ. Again, a detailed examination of spiny plants practically excludes the hypothesis of mammalian selection altogether, and shows spines to arise as an expression of the diminishing vegetativeness—in fact, the ebbing vitality of a species.[209]

Objections to the Theory.

The theory here sketched out is enticing, and at first sight seems calculated to throw much light on the history of plant development; but on further consideration, it seems wanting in definiteness, while it is beset with difficulties at every step. Take first the shortening of the raceme into the umbel and the capitulum, said to be caused by arrest of vegetative growth, due to the antagonism of reproduction. If this were the whole explanation of the phenomenon, we should expect the quantity of seed to increase as this vegetative growth diminished, since the seed is the product of the reproductive energy of the plant, and its quantity the best measure of that energy. But is this the case? The ranunculus has comparatively few seeds, and the flowers are not numerous; while in the same order the larkspur and the columbine have far more seeds as well as more flowers, but there is no shortening of the raceme or diminution of the foliage, although the flowers are large and complex. So, the extremely shortened and compressed flower-heads of the compositae produce comparatively few seeds—one only to each flower; while the foxglove, with its long spike of showy flowers, produces an enormous number.

Again, if the shortening of the central axis in the successive stages of hypogynous, perigynous, and epigynous flowers were an indication of preponderant reproduction and diminished vegetation, we should find everywhere some clear indications of this fact. The plants with hypogynous flowers should, as a rule, have less seed and more vigorous and abundant foliage than those at the other extreme with epigynous flowers. But the hypogynous poppies, pinks, and St. John's worts have abundance of seed and rather scanty foliage; while the epigynous dogwoods and honeysuckles have few seeds and abundant foliage. If, instead of the number of the seeds, we take the size of the fruit as an indication of reproductive energy, we find this at a maximum in the gourd family, yet their rapid and luxuriant growth shows no diminution of vegetative power. So that the statement that plant modifications proceed "along an absolute groove of progressive change" is contradicted by innumerable facts indicating advance and regression, improvement or degradation, according as the ever-changing environment renders one form more advantageous than the other. As one instance I may mention the Anonaceae or custard-apple tribe, which are certainly an advance from the Ranunculaceae; yet in the genus Polyalthea the fruit consists of a number of separate carpels, each borne on a long stalk, as if reverting to the primitive stalked carpellary leaves.

On the Origin of Spines.

But perhaps the most extraordinary application of the theory is that which considers spines to be an indication of the "ebbing vitality of a species," and which excludes "mammalian selection altogether." If this were true, spines should occur mainly in feeble, rare, and dying-out species, instead of which we have the hawthorn, one of our most vigorous shrubs or trees, with abundant vitality and an extensive range over the whole Palaearctic region, showing that it is really a dominant species. In North America the numerous thorny species of Crataegus are equally vigorous, as are the false acacia (Robinia) and the honey-locust (Gleditschia). Neither have the numerous species of very spiny Acacias been noticed to be rarer or less vigorous than the unarmed kinds.

On the other point—that spines are not due to mammalian selection—we are able to adduce what must be considered direct and conclusive evidence. For if spines, admittedly produced by aborted branches, petioles, or peduncles, are due solely or mainly to diminished vegetativeness or ebbing vitality, they ought to occur in all countries alike, or at all events in all whose similar conditions tend to check vegetation; whereas, if they are, solely or mainly, developed as a protection against the attacks of herbivorous mammals, they ought to be most abundant where these are plentiful, and rare or absent where indigenous mammalia are wanting. Oceanic islands, as compared with continents, would thus furnish a crucial test of the two theories; and Mr. Hemsley of Kew, who has specially studied insular floras, has given me some valuable information on this point. He says: "There are no spiny or prickly plants in the indigenous element of the St. Helena flora. The relatively rich flora of the Sandwich Isles is not absolutely without a prickly plant, but almost so. All the endemic genera are unarmed, and the endemic species of almost every other genus. Even such genera as Zanthoxylon, Acacia, Xylosoma, Lycium, and Solanum, of which there are many armed species in other countries, are only represented by unarmed species. The two endemic Rubi have the prickles reduced to the setaceous condition, and the two palms are unarmed.

"The flora of the Galapagos includes a number of prickly plants, among them several cacti (these have not been investigated and may be American species), but I do not think one of the known endemic species of any family is prickly or spiny.

"Spiny and prickly plants are also rare in New Zealand, but there are the formidably armed species of wild Spaniard (Aciphylla), one species of Rubus, the pungent-leaved Epacrideae and a few others."

Mr. J.G. Baker of Kew, who has specially studied the flora of Mauritius and the adjacent islands, also writes me on this point. He says: "Taking Mauritius alone, I do not call to mind a single species that is a spinose endemic tree or shrub. If you take the whole group of islands (Mauritius, Bourbon, Seychelles, and Rodriguez), there will be about a dozen species, but then nine of these are palms. Leaving out palms, the trees and shrubs of that part of the world are exceptionally non-spinose."

These are certainly remarkable facts, and quite inexplicable on the theory of spines being caused solely by checked vegetative growth, due to weakness of constitution or to an arid soil and climate. For the Galapagos and many parts of the Sandwich Islands are very arid, as is a considerable part of the North Island of New Zealand. Yet in our own moist climate and with our very limited number of trees and shrubs we have about eighteen spiny or prickly species, more, apparently, than in the whole endemic floras of the Mauritius, Sandwich Islands, and Galapagos, though these are all especially rich in shrubby and arboreal species. In New Zealand the prickly Rubus is a leafless trailing plant, and its prickles are probably a protection against the large snails of the country, several of which have shells from two to three and a half inches long.[210] The "wild Spaniards" are very spiny herbaceous Umbelliferae, and may have gained their spines to preserve them from being trodden down or eaten by the Moas, which, for countless ages, took the place of mammals in New Zealand. The exact use or meaning of the spines in palms is more doubtful, though they are, no doubt, protective against some animals; but it is certainly an extraordinary fact that in the entire flora of the Mauritius, so largely consisting of trees and shrubs, not a single endemic species should be thorny or spiny.

If now we consider that every continental flora produces a considerable proportion of spiny and thorny species, and that these rise to a maximum in South Africa, where herbivorous mammalia were (before the settlement of the country), perhaps, more abundant and varied than in any other part of the world; while another district, remarkable for well-armed vegetation, is Chile, where the camel-like vicugnas, llamas, and alpacas, and an abundance of large rodents wage perpetual war against shrubby vegetation, we shall see the full significance of the almost total absence of thorny and spiny plants in the chief oceanic islands; and so far from "excluding the hypothesis of mammalian selection altogether," we shall find in this hypothesis the only satisfactory explanation of the facts.

From the brief consideration of Professor Geddes's theory now given, we conclude that, although the antagonism between vegetative and reproductive growth is a real agency, and must be taken account of in our endeavour to explain many of the fundamental facts in the structure and form of plants, yet it is so overpowered and directed at every step by the natural selection of favourable variations, that the results of its exclusive and unmodified action are nowhere to be found in nature. It may be allowed to rank as one of those "laws of growth," of which so many have now been indicated, and which were always recognised by Darwin as underlying all variation; but unless we bear in mind that its action must always be subordinated to natural selection, and that it is continually checked, or diverted, or even reversed by the necessity of adaptation to the environment, we shall be liable to fall into such glaring errors as the imputing to "ebbing vitality" alone such a widespread phenomenon as the occurrence of spines and thorns, while ignoring altogether the influence of the organic environment in their production.[211]

The sketch now given of the chief attempts that have been made to prove that either the direct action of the environment or certain fundamental laws of variation are independent causes of modification of species, shows us that their authors have, in every case, failed to establish their contention. Any direct action of the environment, or any characters acquired by use or disuse, can have no effect whatever upon the race unless they are inherited; and that they are inherited in any case, except when they directly affect the reproductive cells, has not been proved. On the other hand, as we shall presently show, there is much reason for believing that such acquired characters are in their nature non-heritable.

Variation and Selection Overpower the Effects of Use and Disuse.

But there is another objection to this theory arising from the very nature of the effects produced. In each generation the effects of use or disuse, or of effort, will certainly be very small, while of this small effect it is not maintained that the whole will be always inherited by the next generation. How small the effect is we have no means of determining, except in the case of disuse, which Mr. Darwin investigated carefully. He found that in twelve fancy breeds of pigeons, which are often kept in aviaries, or if free fly but little, the sternum had been reduced by about one-seventh or one-eighth of its entire length, and that of the scapula about one-ninth. In domestic ducks the weight of the wing-bones in proportion to that of the whole skeleton had decreased about one-tenth. In domestic rabbits the bones of the legs were found to have increased in weight in due proportion to the increased weight of the body, but those of the hind legs were rather less in proportion to those of the fore legs than in the wild animal, a difference which may be imputed to their being less used in rapid motion. The pigeons, therefore, afford the greatest amount of reduction by disuse—one-seventh of the length of the sternum. But the pigeon has certainly been domesticated four or five thousand years; and if the reduction of the wings by disuse has only been going on for the last thousand years, the amount of reduction in each generation would be absolutely imperceptible, and quite within the limits of the reduction due to the absence of selection, as already explained. But, as we have seen in Chapter III, the fortuitous variation of every part or organ usually amounts to one-tenth, and often to one-sixth of the average dimensions—that is, the fortuitous variation in one generation among a limited number of the individuals of a species is as great as the cumulative effects of disuse in a thousand generations! If we assume that the effects of use or of effort in the individual are equal to the effects of disuse, or even ten or a hundred times greater, they will even then not equal, in each generation, the amount of the fortuitous variations of the same part. If it be urged that the effects of use would modify all the individuals of a species, while the fortuitous variations to the amount named only apply to a portion of them, it may be replied, that that portion is sufficiently large to afford ample materials for selection, since it often equals the numbers that can annually survive; while the recurrence in each successive generation of a like amount of variation would render possible such a rapid adjustment to new conditions that the effects of use or disuse would be as nothing in comparison. It follows, that even admitting the modifying effects of the environment, and that such modifications are inherited, they would yet be entirely swamped by the greater effects of fortuitous variation, and the far more rapid cumulative results of the selection of such variations.

Supposed Action of the Environment in Initiating Variations.

It is, however, urged that the reaction of the environment initiates variations, which without it would never arise; such, for instance, as the origin of horns through the pressures and irritations caused by butting, or otherwise using the head as a weapon or for defence. Admitting, for the sake of argument, that this is so, all the evidence we possess shows that, from the very first appearance of the rudiment of such an organ, it would vary to a greater extent than the amount of growth directly produced by use; and these variations would be subject to selection, and would thus modify the organ in ways which use alone would never bring about. We have seen that this has been the case with the branching antlers of the stag, which have been modified by selection, so as to become useful in other ways than as a mere weapon; and the same has almost certainly been the case with the variously curved and twisted horns of antelopes. In like manner, every conceivable rudiment would, from its first appearance, be subject to the law of variation and selection, to which, thenceforth, the direct effect of the environment would be altogether subordinate.

A very similar mode of reasoning will apply to the other branch of the subject—the initiation of structures and organs by the action of the fundamental laws of growth. Admitting that such laws have determined some of the main divisions of the animal and vegetable kingdom, have originated certain important organs, and have been the fundamental cause of certain lines of development, yet at every step of the process these laws must have acted in entire subordination to the law of natural selection. No modification thus initiated could have advanced a single step, unless it were, on the whole, a useful modification; while its entire future course would be necessarily subject to the laws of variation and selection, by which it would be sometimes checked, sometimes hastened on, sometimes diverted to one purpose, sometimes to another, according as the needs of the organism, under the special conditions of its existence, required such modification. We need not deny that such laws and influences may have acted in the manner suggested, but what we do deny is that they could possibly escape from the ever-present and all-powerful modifying effects of variation and natural selection.[212]

Weismann's Theory of Heredity.

Professor August Weismann has put forth a new theory of heredity founded upon the "continuity of the germ-plasm," one of the logical consequences of which is, that acquired characters of whatever kind are not transmitted from parent to offspring. As this is a matter of vital importance to the theory of natural selection, and as, if well founded, it strikes away the foundations of most of the theories discussed in the present chapter, a brief outline of Weismann's views must be attempted, although it is very difficult to make them intelligible to persons unfamiliar with the main facts of modern embryology.[213]

The problem is thus stated by Weismann: "How is it that in the case of all higher animals and plants a single cell is able to separate itself from amongst the millions of most various kinds of which an organism is composed, and by division and complicated differentiation to reconstruct a new individual with marvellous likeness, unchanged in many cases even throughout whole geological periods?" Darwin attempted to solve the problem by his theory of "Pangenesis," which supposed that every individual cell in the body gave off gemmules or germs capable of reproducing themselves, and that portions of these germs of each of the almost infinite number of cells permeate the whole body and become collected in the generative cells, and are thus able to reproduce the whole organism. This theory is felt to be so ponderously complex and difficult that it has met with no general acceptance among physiologists.

The fact that the germ-cells do reproduce with wonderful accuracy not only the general characters of the species, but many of the individual characteristics of the parents or more remote ancestors, and that this process is continued from generation to generation, can be accounted for, Weismann thinks, only on two suppositions which are physiologically possible. Either the substance of the parent germ-cell, after passing through a cycle of changes required for the construction of a new individual, possesses the capability of producing anew germ-cells identical with those from which that individual was developed, or the new germ-cells arise, as far as their essential and characteristic substance is concerned, not at all out of the body of the individual, but direct from the parent germ-cell. This latter view Weismann holds to be the correct one, and, on this theory, heredity depends on the fact that a substance of special molecular composition passes over from one generation to another. This is the "germ-plasm," the power of which to develop itself into a perfect organism depends on the extraordinary complication of its minutest structure. At every new birth a portion of the specific germ-plasm, which the parent egg-cell contains, is not used up in producing the offspring, but is reserved unchanged to produce the germ-cells of the following generation. Thus the germ-cells—so far as regards their essential part the germ-plasm—are not a product of the body itself, but are related to one another in the same way as are a series of generations of unicellular organisms derived from one another by a continuous course of simple division. Thus the question of heredity is reduced to one of growth. A minute portion of the very same germ-plasm from which, first the germ-cell, and then the whole organism of the parent, were developed, becomes the starting-point of the growth of the child.

The Cause of Variation.

But if this were all, the offspring would reproduce the parent exactly, in every detail of form and structure; and here we see the importance of sex, for each new germ grows out of the united germ-plasms of two parents, whence arises a mingling of their characters in the offspring. This occurs in each generation; hence every individual is a complex result reproducing in ever-varying degrees the diverse characteristics of his two parents, four grandparents, eight great-grandparents, and other more remote ancestors; and that ever-present individual variation arises which furnishes the material for natural selection to act upon. Diversity of sex becomes, therefore, of primary importance as the cause of variation. Where asexual generation prevails, the characteristics of the individual alone are reproduced, and there are thus no means of effecting the change of form or structure required by changed conditions of existence. Under such changed conditions a complex organism, if only asexually propagated, would become extinct. But when a complex organism is sexually propagated, there is an ever-present cause of change which, though slight in any one generation, is cumulative, and under the influence of selection is sufficient to keep up the harmony between the organism and its slowly changing environment.[214]

The Non-Heredity of Acquired Characters.

Certain observations on the embryology of the lower animals are held to afford direct proof of this theory of heredity, but they are too technical to be made clear to ordinary readers. A logical result of the theory is the impossibility of the transmission of acquired characters, since the molecular structure of the germ-plasm is already determined within the embryo; and Weismann holds that there are no facts which really prove that acquired characters can be inherited, although their inheritance has, by most writers, been considered so probable as hardly to stand in need of direct proof.

We have already shown, in the earlier part of this chapter, that many instances of change, imputed to the inheritance of acquired variations, are really cases of selection; while the very fact that use implies usefulness renders it almost impossible to eliminate the action of selection in a state of nature. As regards mutilations, it is generally admitted that they are not hereditary, and there is ample evidence on this point. When it was the fashion to dock horses' tails, it was not found that horses were born with short tails; nor are Chinese women born with distorted feet; nor are any of the numerous forms of racial mutilation in man, which have in some cases been carried on for hundreds of generations, inherited. Nevertheless, a few cases of apparent inheritance of mutilations have been recorded,[215] and these, if trustworthy, are difficulties in the way of the theory. The undoubted inheritance of disease is hardly a difficulty, because the predisposition to disease is a congenital, not an acquired character, and as such would be the subject of inheritance. The often-quoted case of a disease induced by mutilation being inherited (Brown-Sequard's epileptic guinea-pigs) has been discussed by Professor Weismann, and shown to be not conclusive. The mutilation itself—a section of certain nerves—was never inherited, but the resulting epilepsy, or a general state of weakness, deformity, or sores, was sometimes inherited. It is, however, possible that the mere injury introduced and encouraged the growth of certain microbes, which, spreading through the organism, sometimes reached the germ-cells, and thus transmitted a diseased condition to the offspring. Such a transference of microbes is believed to occur in syphilis and tuberculosis, and has been ascertained to occur in the case of the muscardine silkworm disease.[216]

The Theory of Instinct.

The theory now briefly outlined cannot be said to be proved, but it commends itself to many physiologists as being inherently probable, and as furnishing a good working hypothesis till displaced by a better. We cannot, therefore, accept any arguments against the agency of natural selection which are based upon the opposite and equally unproved theory that acquired characters are inherited; and as this applies to the whole school of what may be termed Neo-Lamarckians, their speculations cease to have any weight.

The same remark applies to the popular theory of instincts as being inherited habits; though Darwin gave very little weight to this, but derived almost all instincts from spontaneous useful variations which, like other spontaneous variations, are of course inherited. At first sight it appears as if the acquired habits of our trained dogs—pointers, retrievers, etc.—are certainly inherited; but this need not be the case, because there must be some structural or psychical peculiarities, such as modifications in the attachments of muscles, increased delicacy of smell or sight, or peculiar likes and dislikes, which are inherited; and from these, peculiar habits follow as a natural consequence, or are easily acquired. Now, as selection has been constantly at work in improving all our domestic animals, we have unconsciously modified the structure, while preserving only those animals which best served our purpose in their peculiar faculties, instincts, or habits.

Much of the mystery of instinct arises from the persistent refusal to recognise the agency of imitation, memory, observation, and reason as often forming part of it. Yet there is ample evidence that such agency must be taken into account. Both Wilson and Leroy state that young birds build inferior nests to old ones, and the latter author observes that the best nests are made by birds whose young remain longest in the nest. So, migration is now well ascertained to be effected by means of vision, long flights being made on bright moonlight nights when the birds fly very high, while on cloudy nights they fly low, and then often lose their way. Thousands annually fly out to sea and perish, showing that the instinct to migrate is imperfect, and is not a good substitute for reason and observation.

Again, much of the perfection of instinct is due to the extreme severity of the selection during its development, any failure involving destruction. The chick which cannot break the eggshell, the caterpillar that fails to suspend itself properly or to spin a safe cocoon, the bees that lose their way or that fail to store honey, inevitably perish. So the birds that fail to feed and protect their young, or the butterflies that lay their eggs on the wrong food-plant, leave no offspring, and the race with imperfect instincts perishes. Now, during the long and very slow course of development of each organism, this rigid selection at every step of progress has led to the preservation of every detail of structure, faculty, or habit that has been necessary for the preservation of the race, and has thus gradually built up the various instincts which seem so marvellous to us, but which can yet be shown to be in many cases still imperfect. Here, as everywhere else in nature, we find comparative, not absolute perfection, with every gradation from what is clearly due to imitation or reason up to what seems to us perfect instinct—that in which a complex action is performed without any previous experience or instruction.[217]

Concluding Remarks.

Having now passed in review the more important of the recent objections to, or criticisms of, the theory of natural selection, we have arrived at the conclusion that in no one case have the writers in question been able materially to diminish its importance, or to show that any of the laws or forces to which they appeal can act otherwise than in strict subordination to it. The direct action of the environment as set forth by Mr. Herbert Spencer, Dr. Cope, and Dr. Karl Semper, even if we admit that its effects on the individual are transmitted by inheritance, are so small in comparison with the amount of spontaneous variation of every part of the organism that they must be quite overshadowed by the latter. And if such direct action may, in some cases, have initiated certain organs or outgrowths, these must from their very first beginnings have been subject to variation and natural selection, and their further development have been almost wholly due to these ever-present and powerful causes. The same remark applies to the views of Professor Geddes on the laws of growth which have determined certain essential features in the morphology of plants and animals. The attempt to substitute these laws for those of variation and natural selection has failed in cases where we can apply a definite test, as in that of the origin of spines on trees and shrubs; while the extreme diversity of vegetable structure and form among the plants of the same country and of the same natural order, of itself affords a proof of the preponderating influence of variation and natural selection in keeping the many diverse forms in harmony with the highly complex and ever-changing environment.

Lastly, we have seen that Professor Weismann's theory of the continuity of the germ-plasm and the consequent non-heredity of acquired characters, while in perfect harmony with all the well-ascertained facts of heredity and development, adds greatly to the importance of natural selection as the one invariable and ever-present factor in all organic change, and that which can alone have produced the temporary fixity combined with the secular modification of species. While admitting, as Darwin always admitted, the co-operation of the fundamental laws of growth and variation, of correlation and heredity, in determining the direction of lines of variation or in the initiation of peculiar organs, we find that variation and natural selection are ever-present agencies, which take possession, as it were, of every minute change originated by these fundamental causes, check or favour their further development, or modify them in countless varied ways according to the varying needs of the organism. Whatever other causes have been at work, Natural Selection is supreme, to an extent which even Darwin himself hesitated to claim for it. The more we study it the more we are convinced of its overpowering importance, and the more confidently we claim, in Darwin's own words, that it "has been the most important, but not the exclusive, means of modification."

FOOTNOTES:

[Footnote 198: See the Duke of Argyll's letter in Nature, vol. xxxiv. p. 336.]

[Footnote 199: Journal of the Anthropological Institute, vol. xv. pp. 246-260.]

[Footnote 200: The idea of the non-heredity of acquired variations was suggested by the summary of Professor Weismann's views, in Nature, referred to later on. But since this chapter was written I have, through the kindness of Mr. E.B. Poulton, seen some of the proofs of the forthcoming translation of Weismann's Essays on Heredity, in which he sets forth an explanation very similar to that here given. On the difficult question of the almost entire disappearance of organs, as in the limbs of snakes and of some lizards, he adduces "a certain form of correlation, which Roux calls 'the struggle of the parts in the organism,'" as playing an important part. Atrophy following disuse is nearly always attended by the corresponding increase of other organs: blind animals possess more developed organs of touch, hearing, and smell; the loss of power in the wings is accompanied by increased strength of the legs, etc. Now as these latter characters, being useful, will be selected, it is easy to understand that a congenital increase of these will be accompanied by a corresponding congenital diminution of the unused organ; and in cases where the means of nutrition are deficient, every diminution of these useless parts will be a gain to the whole organism, and thus their complete disappearance will, in some cases, be brought about directly by natural selection. This corresponds with what we know of these rudimentary organs.

It must, however, be pointed out that the non-heredity of acquired characters was maintained by Mr. Francis Galton more than twelve years ago, on theoretical considerations almost identical with those urged by Professor Weismann; while the insufficiency of the evidence for their hereditary transmission was shown, by similar arguments to those used above and in the work of Professor Weismann already referred to (see "A Theory of Heredity," in Journ. Anthrop. Instit., vol. v. pp. 343-345).]

[Footnote 201: This explanation is derived from Weismann's Theory of the Continuity of the Germ-Plasm as summarised in Nature.]

[Footnote 202: See a collection of his essays under the title, The Origin of the Fittest: Essays on Evolution, D. Appleton and Co. New York. 1887.]

[Footnote 203: Origin of the Fittest, p. 174.]

[Footnote 204: Ibid. p. 29. It may be here noted that Darwin found these theories unintelligible. In a letter to Professor E.T. Morse in 1877, he writes: "There is one point which I regret you did not make clear in your Address, namely, what is the meaning and importance of Professors Cope and Hyatt's views on acceleration and retardation? I have endeavoured, and given up in despair, the attempt to grasp their meaning" (Life and Letters, vol. iii. p. 233).]

[Footnote 205: Origin of the Fittest, p. 374.]

[Footnote 206: Origin of the Fittest, p. 40.]

[Footnote 207: The Natural Conditions of Existence as they Affect Animal Life. London, 1883.]

[Footnote 208: In Dr. Weismann's essay on "Heredity," already referred to, he considers it not improbable that changes in organisms produced by climatic influences may be inherited, because, as these changes do not affect the external parts of an organism only, but often, as in the case of warmth or moisture permeate the whole structure, they may possibly modify the germ-plasm itself, and thus induce variations in the next generation. In this way, he thinks, may possibly be explained the climatic varieties of certain butterflies, and some other changes which seem to be effected by change of climate in a few generations.]

[Footnote 209: This brief indication of Professor Geddes's views is taken from the article "Variation and Selection" in the Encyclopedia Britannica, and a paper "On the Nature and Causes of Variation in Plants" in Trans. and Proc. of the Edinburgh Botanical Society, 1886; and is, for the most part, expressed in his own words.]

[Footnote 210: Placostylis bovinus, 31/2 inches long; Paryphanta Busbyi, 3 in. diam.; P. Hochstetteri, 23/4 in. diam.]

[Footnote 211: The general arguments and objections here set forth will apply with equal force to Professor G. Henslow's theory of the origin of the various forms and structures of flowers as due to "the responsive actions of the protoplasm in consequence of the irritations set up by the weights, pressures, thrusts, tensions, etc., of the insect visitors" (The Origin of Floral Structures through Insect and other Agencies, p. 340). On the assumption that acquired characters are inherited, such irritations may have had something to do with the initiation of variations and with the production of certain details of structure, but they are clearly incompetent to have brought about the more important structural and functional modifications of flowers. Such are, the various adjustments of length and position of the stamens to bring the pollen to the insect and from the insect to the stigma; the various motions of stamens and styles at the right time and the right direction; the physiological adjustments bringing about fertility or sterility in heterostyled plants; the traps, springs, and complex movements of various parts of orchids; and innumerable other remarkable phenomena.

For the explanation of these we have no resource but variation and selection, to the effects of which, acting alternately with regression or degradation as above explained (p. 328) must be imputed the development of the countless floral structures we now behold. Even the primitive flowers, whose initiation may, perhaps, have been caused, or rendered possible, by the irritation set up by insects' visits, must, from their very origin, have been modified, in accordance with the supreme law of utility, by means of variation and survival of the fittest.]

[Footnote 212: In an essay on "The Duration of Life," forming part of the translation of Dr. Weismann's papers already referred to, the author still further extends the sphere of natural selection by showing that the average duration of life in each species has been determined by it. A certain length of life is essential in order that the species may produce offspring sufficient to ensure its continuance under the most unfavourable conditions; and it is shown that the remarkable inequalities of longevity in different species and groups may be thus accounted for. Yet more, the occurrence of death in the higher organisms, in place of the continued survival of the unicellular organisms however much they may increase by subdivision, may be traced to the same great law of utility for the race and survival of the fittest. The whole essay is of exceeding interest, and will repay a careful perusal. A similar idea occurred to the present writer about twenty years back, and was briefly noted down at the time, but subsequently forgotten.]

[Footnote 213: The outline here given is derived from two articles in Nature, vol. xxxiii. p. 154, and vol. xxxiv. p. 629, in which Weismann's papers are summarised and partly translated.]

[Footnote 214: There are many indications that this explanation of the cause of variation is the true one. Mr. E.B. Poulton suggests one, in the fact that parthenogenetic reproduction only occurs in isolated species, not in groups of related species; as this shows that parthenogenesis cannot lead to the evolution of new forms. Again, in parthenogenetic females the complete apparatus for fertilisation remains unreduced; but if these varied as do sexually produced animals, the organs referred to, being unused, would become rudimentary.

Even more important is the significance of the "polar bodies," as explained by Weismann in one of his Essays; since, if his interpretation of them be correct, variability is a necessary consequence of sexual generation.]

[Footnote 215: Darwin's Animals and Plants, vol. ii. pp. 23, 24.]

[Footnote 216: In his essay on "Heredity," Dr. Weismann discusses many other cases of supposed inheritance of acquired characters, and shows that they can all be explained in other ways. Shortsightedness among civilised nations, for example, is due partly to the absence of selection and consequent regression towards a mean, and partly to its individual production by constant reading.]

[Footnote 217: Weismann explains instinct on similar lines, and gives many interesting illustrations (see Essays on Heredity). He holds "that all instinct is entirely due to the operation of natural selection, and has its foundation, not upon inherited experiences, but upon variations of the germ." Many interesting and difficult cases of instinct are discussed by Darwin in Chapter VIII of the Origin of Species, which should be read in connection with the above remarks.

Since this chapter was written my attention has been directed to Mr. Francis Galton's Theory of Heredity (already referred to at p. 417) which was published thirteen years ago as an alternative for Darwin's theory of pangenesis.

Mr. Galton's theory, although it attracted little attention, appears to me to be substantially the same as that of Professor Weismann. Galton's "stirp" is Weismann's "germ-plasm." Galton supposes the sexual elements in the offspring to be directly formed from the residue of the stirp not used up in the development of the body of the parent—Weismann's "continuity of the germ-plasm." Galton also draws many of the same conclusions from his theory. He maintains that characters acquired by the individual as the result of external influences cannot be inherited, unless such influences act directly on the reproductive elements—instancing the possible heredity of alcoholism, because the alcohol permeates the tissues and may reach the sexual elements. He discusses the supposed heredity of effects produced by use or disuse, and explains them much in the same manner as does Weismann. Galton is an anthropologist, and applies the theory, mainly, to explain the peculiarities of hereditary transmission in man, many of which peculiarities he discusses and elucidates. Weismann is a biologist, and is mostly concerned with the application of the theory to explain variation and instinct, and to the further development of the theory of evolution. He has worked it out more thoroughly, and has adduced embryological evidence in its support; but the views of both writers are substantially the same, and their theories were arrived at quite independently. The names of Galton and Weismann should therefore be associated as discoverers of what may be considered (if finally established) the most important contribution to the evolution theory since the appearance of the Origin of Species.]



CHAPTER XV

DARWINISM APPLIED TO MAN

General identity of human and animal structure—Rudiments and variations showing relation of man to other mammals—The embryonic development of man and other mammalia—Diseases common to man and the lower animals—The animals most nearly allied to man—The brains of man and apes—External differences of man and apes—Summary of the animal characteristics of man—The geological antiquity of man—The probable birthplace of man—The origin of the moral and intellectual nature of man—The argument from continuity—The origin of the mathematical faculty—The origin of the musical and artistic faculties—Independent proof that these faculties have not been developed by natural selection—The interpretation of the facts—Concluding remarks.



Our review of modern Darwinism might fitly have terminated with the preceding chapter; but the immense interest that attaches to the origin of the human race, and the amount of misconception which prevails regarding the essential teachings of Darwin's theory on this question, as well as regarding my own special views upon it, induce me to devote a final chapter to its discussion.

To any one who considers the structure of man's body, even in the most superficial manner, it must be evident that it is the body of an animal, differing greatly, it is true, from the bodies of all other animals, but agreeing with them in all essential features. The bony structure of man classes him as a vertebrate; the mode of suckling his young classes him as a mammal; his blood, his muscles, and his nerves, the structure of his heart with its veins and arteries, his lungs and his whole respiratory and circulatory systems, all closely correspond to those of other mammals, and are often almost identical with them. He possesses the same number of limbs terminating in the same number of digits as belong fundamentally to the mammalian class. His senses are identical with theirs, and his organs of sense are the same in number and occupy the same relative position. Every detail of structure which is common to the mammalia as a class is found also in man, while he only differs from them in such ways and degrees as the various species or groups of mammals differ from each other. If, then, we have good reason to believe that every existing group of mammalia has descended from some common ancestral form—as we saw to be so completely demonstrated in the case of the horse tribe,—and that each family, each order, and even the whole class must similarly have descended from some much more ancient and more generalised type, it would be in the highest degree improbable—so improbable as to be almost inconceivable—that man, agreeing with them so closely in every detail of his structure, should have had some quite distinct mode of origin. Let us, then, see what other evidence bears upon the question, and whether it is sufficient to convert the probability of his animal origin into a practical certainty.

Rudiments and Variations as Indicating the Relation of Man to other Mammals.

All the higher animals present rudiments of organs which, though useless to them, are useful in some allied group, and are believed to have descended from a common ancestor in which they were useful. Thus there are in ruminants rudiments of incisor teeth which, in some species, never cut through the gums; many lizards have external rudimentary legs; while many birds, as the Apteryx, have quite rudimentary wings. Now man possesses similar rudiments, sometimes constantly, sometimes only occasionally present, which serve intimately to connect his bodily structure with that of the lower animals. Many animals, for example, have a special muscle for moving or twitching the skin. In man there are remnants of this in certain parts of the body, especially in the forehead, enabling us to raise our eyebrows; but some persons have it in other parts. A few persons are able to move the whole scalp so as to throw off any object placed on the head, and this property has been proved, in one case, to be inherited. In the outer fold of the ear there is sometimes a projecting point, corresponding in position to the pointed ear of many animals, and believed to be a rudiment of it. In the alimentary canal there is a rudiment—the vermiform appendage of the caecum—which is not only useless, but is sometimes a cause of disease and death in man; yet in many vegetable feeding animals it is very long, and even in the orang-utan it is of considerable length and convoluted. So, man possesses rudimentary bones of a tail concealed beneath the skin, and, in some rare cases, this forms a minute external tail.

The variability of every part of man's structure is very great, and many of these variations tend to approximate towards the structure of other animals. The courses of the arteries are eminently variable, so that for surgical purposes it has been necessary to determine the probable proportion of each variation. The muscles are so variable that in fifty cases the muscles of the foot were found to be not strictly alike in any two, and in some the deviations were considerable; while in thirty-six subjects Mr. J. Wood observed no fewer than 558 muscular variations. The same author states that in a single male subject there were no fewer than seven muscular variations, all of which plainly represented muscles proper to various kinds of apes. The muscles of the hands and arms—parts which are so eminently characteristic of man—are extremely liable to vary, so as to resemble the corresponding muscles of the lower animals. That such variations are due to reversion to a former state of existence Mr. Darwin thinks highly probable, and he adds: "It is quite incredible that a man should, through mere accident, abnormally resemble certain apes in no less than seven of his muscles, if there had been no genetic connection between them. On the other hand, if man is descended from some ape-like creature, no valid reason can be assigned why certain muscles should not suddenly reappear after an interval of many thousand generations, in the same manner as, with horses, asses, and mules, dark coloured stripes suddenly reappear on the legs and shoulders, after an interval of hundreds, or more probably of thousands of generations."[218]

The Embryonic Development of Man and other Mammalia.

The progressive development of any vertebrate from the ovum or minute embryonic egg affords one of the most marvellous chapters in Natural History. We see the contents of the ovum undergoing numerous definite changes, its interior dividing and subdividing till it consists of a mass of cells, then a groove appears marking out the median line or vertebral column of the future animal, and thereafter are slowly developed the various essential organs of the body. After describing in some detail what takes place in the case of the ovum of the dog, Professor Huxley continues: "The history of the development of any other vertebrate animal, lizard, snake, frog, or fish tells the same story. There is always to begin with, an egg having the same essential structure as that of the dog; the yelk of that egg undergoes division or segmentation, as it is called, the ultimate products of that segmentation constitute the building materials for the body of the young animal; and this is built up round a primitive groove, in the floor of which a notochord is developed. Furthermore, there is a period in which the young of all these animals resemble one another, not merely in outward form, but in all essentials of structure, so closely, that the differences between them are inconsiderable, while in their subsequent course they diverge more and more widely from one another. And it is a general law that the more closely any animals resemble one another in adult structure, the larger and the more intimately do their embryos resemble one another; so that, for example, the embryos of a snake and of a lizard remain like one another longer than do those of a snake and a bird; and the embryos of a dog and of a cat remain like one another for a far longer period than do those of a dog and a bird, or of a dog and an opossum, or even than those of a dog and a monkey."[219]

We thus see that the study of development affords a test of affinity in animals that are externally very much unlike each other; and we naturally ask how this applies to man. Is he developed in a different way from other mammals, as we should certainly expect if he has had a distinct and altogether different origin? "The reply," says Professor Huxley, "is not doubtful for a moment. Without question, the mode of origin and the early stages of the development of man are identical with those of the animals immediately below him in the scale." And again he tells us: "It is very long before the body of the young human being can be readily discriminated from that of the young puppy; but at a tolerably early period the two become distinguishable by the different forms of their adjuncts, the yelk-sac and the allantois;" and after describing these differences he continues: "But exactly in those respects in which the developing man differs from the dog, he resembles the ape.... So that it is only quite in the latter stages of development that the young human being presents marked differences from the young ape, while the latter departs as much from the dog in its development as the man does. Startling as this last assertion may appear to be, it is demonstrably true, and it alone appears to me sufficient to place beyond all doubt the structural unity of man with the rest of the animal world, and more particularly and closely with the apes."[220]

A few of the curious details in which man passes through stages common to the lower animals may be mentioned. At one stage the os coccyx projects like a true tail, extending considerably beyond the rudimentary legs. In the seventh month the convolutions of the brain resemble those of an adult baboon. The great toe, so characteristic of man, forming the fulcrum which most assists him in standing erect, in an early stage of the embryo is much shorter than the other toes, and instead of being parallel with them, projects at an angle from the side of the foot, thus corresponding with its permanent condition in the quadrumana. Numerous other examples might be quoted, all illustrating the same general law.

Diseases Common to Man and the Lower Animals.

Though the fact is so well known, it is certainly one of profound significance that many animal diseases can be communicated to man, since it shows similarity, if not identity, in the minute structure of the tissues, the nature of the blood, the nerves, and the brain. Such diseases as hydrophobia, variola, the glanders, cholera, herpes, etc., can be transmitted from animals to man or the reverse; while monkeys are liable to many of the same non-contagious diseases as we are. Rengger, who carefully observed the common monkey (Cebus Azarae) in Paraguay, found it liable to catarrh, with the usual symptoms, terminating sometimes in consumption. These monkeys also suffered from apoplexy, inflammation of the bowels, and cataract in the eye. Medicines produced the same effect upon them as upon us. Many kinds of monkeys have a strong taste for tea, coffee, spirits, and even tobacco. These facts show the similarity of the nerves of taste in monkeys and in ourselves, and that their whole nervous system is affected in a similar way. Even the parasites, both external and internal, that affect man are not altogether peculiar to him, but belong to the same families or genera as those which infest animals, and in one case, scabies, even the same species.[221] These curious facts seem quite inconsistent with the idea that man's bodily structure and nature are altogether distinct from those of animals, and have had a different origin; while the facts are just what we should expect if he has been produced by descent with modification from some common ancestor.

The Animals most nearly Allied to Man.

By universal consent we see in the monkey tribe a caricature of humanity. Their faces, their hands, their actions and expressions present ludicrous resemblances to our own. But there is one group of this great tribe in which this resemblance is greatest, and they have hence been called the anthropoid or man-like apes. These are few in number, and inhabit only the equatorial regions of Africa and Asia, countries where the climate is most uniform, the forests densest, and the supply of fruit abundant throughout the year. These animals are now comparatively well known, consisting of the orang-utan of Borneo and Sumatra, the chimpanzee and the gorilla of West Africa, and the group of gibbons or long-armed apes, consisting of many species and inhabiting South-Eastern Asia and the larger Malay Islands. These last are far less like man than the other three, one or other of which has at various times been claimed to be the most man-like of the apes and our nearest relations in the animal kingdom. The question of the degree of resemblance of these animals to ourselves is one of great interest, leading, as it does, to some important conclusions as to our origin and geological antiquity, and we will therefore briefly consider it.

If we compare the skeletons of the orang or chimpanzee with that of man, we find them to be a kind of distorted copy, every bone corresponding (with very few exceptions), but altered somewhat in size, proportions, and position. So great is this resemblance that it led Professor Owen to remark: "I cannot shut my eyes to the significance of that all-pervading similitude of structure—every tooth, every bone, strictly homologous—which makes the determination of the difference between Homo and Pithecus the anatomist's difficulty."

The actual differences in the skeletons of these apes and that of man—that is, differences dependent on the presence or absence of certain bones, and not on their form or position—have been enumerated by Mr. Mivart as follows:—(1) In the breast-bone consisting of but two bones, man agrees with the gibbons; the chimpanzee and gorilla having this part consisting of seven bones in a single series, while in the orang they are arranged in a double series of ten bones. (2) The normal number of the ribs in the orang and some gibbons is twelve pairs, as in man, while in the chimpanzee and gorilla there are thirteen pairs. (3) The orang and the gibbons also agree with man in having five lumbar vertebrae, while in the gorilla and the chimpanzee there are but four, and sometimes only three. (4) The gorilla and chimpanzee agree with man in having eight small bones in the wrist, while the orang and the gibbons, as well as all other monkeys, have nine.[222]

The differences in the form, size, and attachments of the various bones, muscles, and other organs of these apes and man are very numerous and exceedingly complex, sometimes one species, sometimes another agreeing most nearly with ourselves, thus presenting a tangled web of affinities which it is very difficult to unravel. Estimated by the skeleton alone, the chimpanzee and gorilla seem nearer to man than the orang, which last is also inferior as presenting certain aberrations in the muscles. In the form of the ear the gorilla is more human than any other ape, while in the tongue the orang is the more man-like. In the stomach and liver the gibbons approach nearest to man, then come the orang and chimpanzee, while the gorilla has a degraded liver more resembling that of the lower monkeys and baboons.

The Brains of Man and Apes.

We come now to that part of his organisation in which man is so much higher than all the lower animals—the brain; and here, Mr. Mivart informs us, the orang stands highest in rank. The height of the orang's cerebrum in front is greater in proportion than in either the chimpanzee or the gorilla. "On comparing the brain of man with the brains of the orang, chimpanzee, and baboon, we find a successive decrease in the frontal lobe, and a successive and very great increase in the relative size of the occipital lobe. Concomitantly with this increase and decrease, certain folds of brain substance, called 'bridging convolutions,' which in man are conspicuously interposed between the parietal and occipital lobes, seem as utterly to disappear in the chimpanzee, as they do in the baboon. In the orang, however, though much reduced, they are still to be distinguished.... The actual and absolute mass of the brain is, however, slightly greater in the chimpanzee than in the orang, as is the relative vertical extent of the middle part of the cerebrum, although, as already stated, the frontal portion is higher in the orang; while, according to M. Gratiolet, the gorilla is not only inferior to the orang in cerebral development, but even to his smaller African congener, the chimpanzee."[223]

On the whole, then, we find that no one of the great apes can be positively asserted to be nearest to man in structure. Each of them approaches him in certain characteristics, while in others it is widely removed, giving the idea, so consonant with the theory of evolution as developed by Darwin, that all are derived from a common ancestor, from which the existing anthropoid apes as well as man have diverged. When, however, we turn from the details of anatomy to peculiarities of external form and motions, we find that, in a variety of characters, all these apes resemble each other and differ from man, so that we may fairly say that, while they have diverged somewhat from each other, they have diverged much more widely from ourselves. Let us briefly enumerate some of these differences.

External Differences of Man and Apes.

All apes have large canine teeth, while in man these are no longer than the adjacent incisors or premolars, the whole forming a perfectly even series. In apes the arms are proportionately much longer than in man, while the thighs are much shorter. No ape stands really erect, a posture which is natural in man. The thumb is proportionately larger in man, and more perfectly opposable than in that of any ape. The foot of man differs largely from that of all apes, in the horizontal sole, the projecting heel, the short toes, and the powerful great toe firmly attached parallel to the other toes; all perfectly adapted for maintaining the erect posture, and for free motion without any aid from the arms or hands. In apes the foot is formed almost exactly like our hand, with a large thumb-like great toe quite free from the other toes, and so articulated as to be opposable to them; forming with the long finger-like toes a perfect grasping hand. The sole cannot be placed horizontally on the ground; but when standing on a level surface the animal rests on the outer edge of the foot with the finger and thumb-like toes partly closed, while the hands are placed on the ground resting on the knuckles. The illustration on the next page (Fig. 37) shows, fairly well, the peculiarities of the hands and feet of the chimpanzee, and their marked differences, both in form and use, from those of man.

The four limbs, with the peculiarly formed feet and hands, are those of arboreal animals which only occasionally and awkwardly move on level ground. The arms are used in progression equally with the feet, and the hands are only adapted for uses similar to those of our hands when the animal is at rest, and then but clumsily. Lastly, the apes are all hairy animals, like the majority of other mammals, man alone having a smooth and almost naked skin. These numerous and striking differences, even more than those of the skeleton and internal anatomy, point to an enormously remote epoch when the race that was ultimately to develop into man diverged from that other stock which continued the animal type and ultimately produced the existing varieties of anthropoid apes.



Summary of the Animal Characteristics of Man.

The facts now very briefly summarised amount almost to a demonstration that man, in his bodily structure, has been derived from the lower animals, of which he is the culminating development. In his possession of rudimentary structures which are functional in some of the mammalia; in the numerous variations of his muscles and other organs agreeing with characters which are constant in some apes; in his embryonic development, absolutely identical in character with that of mammalia in general, and closely resembling in its details that of the higher quadrumana; in the diseases which he has in common with other mammalia; and in the wonderful approximation of his skeleton to those of one or other of the anthropoid apes, we have an amount of evidence in this direction which it seems impossible to explain away. And this evidence will appear more forcible if we consider for a moment what the rejection of it implies. For the only alternative supposition is, that man has been specially created—that is to say, has been produced in some quite different way from other animals and altogether independently of them. But in that case the rudimentary structures, the animal-like variations, the identical course of development, and all the other animal characteristics he possesses are deceptive, and inevitably lead us, as thinking beings making use of the reason which is our noblest and most distinctive feature, into gross error.

We cannot believe, however, that a careful study of the facts of nature leads to conclusions directly opposed to the truth; and, as we seek in vain, in our physical structure and the course of its development, for any indication of an origin independent of the rest of the animal world, we are compelled to reject the idea of "special creation" for man, as being entirely unsupported by facts as well as in the highest degree improbable.

The Geological Antiquity of Man.

The evidence we now possess of the exact nature of the resemblance of man to the various species of anthropoid apes, shows us that he has little special affinity for any one rather than another species, while he differs from them all in several important characters in which they agree with each other. The conclusion to be drawn from these facts is, that his points of affinity connect him with the whole group, while his special peculiarities equally separate him from the whole group, and that he must, therefore, have diverged from the common ancestral form before the existing types of anthropoid apes had diverged from each other. Now, this divergence almost certainly took place as early as the Miocene period, because in the Upper Miocene deposits of Western Europe remains of two species of ape have been found allied to the gibbons, one of them, Dryopithecus, nearly as large as a man, and believed by M. Lartet to have approached man in its dentition more than the existing apes. We seem hardly, therefore, to have reached, in the Upper Miocene, the epoch of the common ancestor of man and the anthropoids.

The evidence of the antiquity of man himself is also scanty, and takes us but very little way back into the past. We have clear proof of his existence in Europe in the latter stages of the glacial epoch, with many indications of his presence in interglacial or even pre-glacial times; while both the actual remains and the works of man found in the auriferous gravels of California deep under lava-flows of Pliocene age, show that he existed in the New World at least as early as in the Old.[224] These earliest remains of man have been received with doubt, and even with ridicule, as if there were some extreme improbability in them. But, in point of fact, the wonder is that human remains have not been found more frequently in pre-glacial deposits. Referring to the most ancient fossil remains found in Europe—the Engis and Neanderthal crania,—Professor Huxley makes the following weighty remark: "In conclusion, I may say, that the fossil remains of Man hitherto discovered do not seem to me to take us appreciably nearer to that lower pithecoid form, by the modification of which he has, probably, become what he is." The Californian remains and works of art, above referred to, give no indication of a specially low form of man; and it remains an unsolved problem why no traces of the long line of man's ancestors, back to the remote period when he first branched off from the pithecoid type, have yet been discovered.

It has been objected by some writers—notably by Professor Boyd Dawkins—that man did not probably exist in Pliocene times, because almost all the known mammalia of that epoch are distinct species from those now living on the earth, and that the same changes of the environment which led to the modification of other mammalian species would also have led to a change in man. But this argument overlooks the fact that man differs essentially from all other mammals in this respect, that whereas any important adaptation to new conditions can be effected in them only by a change in bodily structure, man is able to adapt himself to much greater changes of conditions by a mental development leading him to the use of fire, of tools, of clothing, of improved dwellings, of nets and snares, and of agriculture. By the help of these, without any change whatever in his bodily structure, he has been able to spread over and occupy the whole earth; to dwell securely in forest, plain, or mountain; to inhabit alike the burning desert or the arctic wastes; to cope with every kind of wild beast, and to provide himself with food in districts where, as an animal trusting to nature's unaided productions, he would have starved.[225]

It follows, therefore, that from the time when the ancestral man first walked erect, with hands freed from any active part in locomotion, and when his brain-power became sufficient to cause him to use his hands in making weapons and tools, houses and clothing, to use fire for cooking, and to plant seeds or roots to supply himself with stores of food, the power of natural selection would cease to act in producing modifications of his body, but would continuously advance his mind through the development of its organ, the brain. Hence man may have become truly man—the species, Homo sapiens—even in the Miocene period; and while all other mammals were becoming modified from age to age under the influence of ever-changing physical and biological conditions, he would be advancing mainly in intelligence, but perhaps also in stature, and by that advance alone would be able to maintain himself as the master of all other animals and as the most widespread occupier of the earth. It is quite in accordance with this view that we find the most pronounced distinction between man and the anthropoid apes in the size and complexity of his brain. Thus, Professor Huxley tells us that "it may be doubted whether a healthy human adult brain ever weighed less than 31 or 32 ounces, or that the heaviest gorilla brain has exceeded 20 ounces," although "a full-grown gorilla is probably pretty nearly twice as heavy as a Bosjes man, or as many an European woman."[226] The average human brain, however, weighs 48 or 49 ounces, and if we take the average ape brain at only 2 ounces less than the very largest gorilla's brain, or 18 ounces, we shall see better the enormous increase which has taken place in the brain of man since the time when he branched off from the apes; and this increase will be still greater if we consider that the brains of apes, like those of all other mammals, have also increased from earlier to later geological times.

If these various considerations are taken into account, we must conclude that the essential features of man's structure as compared with that of apes—his erect posture and free hands—were acquired at a comparatively early period, and were, in fact, the characteristics which gave him his superiority over other mammals, and started him on the line of development which has led to his conquest of the world. But during this long and steady development of brain and intellect, mankind must have continuously increased in numbers and in the area which they occupied—they must have formed what Darwin terms a "dominant race." For had they been few in numbers and confined to a limited area, they could hardly have successfully struggled against the numerous fierce carnivora of that period, and against those adverse influences which led to the extinction of so many more powerful animals. A large population spread over an extensive area is also needed to supply an adequate number of brain variations for man's progressive improvement. But this large population and long-continued development in a single line of advance renders it the more difficult to account for the complete absence of human or pre-human remains in all those deposits which have furnished, in such rich abundance, the remains of other land animals. It is true that the remains of apes are also very rare, and we may well suppose that the superior intelligence of man led him to avoid that extensive destruction by flood or in morass which seems to have often overwhelmed other animals. Yet, when we consider that, even in our own day, men are not unfrequently overwhelmed by volcanic eruptions, as in Java and Japan, or carried away in vast numbers by floods, as in Bengal and China, it seems impossible but that ample remains of Miocene and Pliocene man do exist buried in the most recent layers of the earth's crust, and that more extended research or some fortunate discovery will some day bring them to light.

The Probable Birthplace of Man.

It has usually been considered that the ancestral form of man originated in the tropics, where vegetation is most abundant and the climate most equable. But there are some important objections to this view. The anthropoid apes, as well as most of the monkey tribe, are essentially arboreal in their structure, whereas the great distinctive character of man is his special adaptation to terrestrial locomotion. We can hardly suppose, therefore, that he originated in a forest region, where fruits to be obtained by climbing are the chief vegetable food. It is more probable that he began his existence on the open plains or high plateaux of the temperate or sub-tropical zone, where the seeds of indigenous cereals and numerous herbivora, rodents, and game-birds, with fishes and molluscs in the lakes, rivers, and seas supplied him with an abundance of varied food. In such a region he would develop skill as a hunter, trapper, or fisherman, and later as a herdsman and cultivator,—a succession of which we find indications in the palaeolithic and neolithic races of Europe.

In seeking to determine the particular areas in which his earliest traces are likely to be found, we are restricted to some portion of the Eastern hemisphere, where alone the anthropoid apes exist, or have apparently ever existed.

There is good reason to believe, also, that Africa must be excluded, because it is known to have been separated from the northern continent in early tertiary times, and to have acquired its existing fauna of the higher mammalia by a later union with that continent after the separation from it of Madagascar, an island which has preserved for us a sample, as it were, of the early African mammalian fauna, from which not only the anthropoid apes, but all the higher quadrumana are absent.[227] There remains only the great Euro-Asiatic continent; and its enormous plateaux, extending from Persia right across Tibet and Siberia to Manchuria, afford an area, some part or other of which probably offered suitable conditions, in late Miocene or early Pliocene times, for the development of ancestral man.

It is in this area that we still find that type of mankind—the Mongolian—which retains a colour of the skin midway between the black or brown-black of the negro, and the ruddy or olive-white of the Caucasian types, a colour which still prevails over all Northern Asia, over the American continents, and over much of Polynesia. From this primary tint arose, under the influence of varied conditions, and probably in correlation with constitutional changes adapted to peculiar climates, the varied tints which still exist among mankind. If the reasoning by which this conclusion is reached be sound, and all the earlier stages of man's development from an animal form occurred in the area now indicated, we can better understand how it is that we have as yet met with no traces of the missing links, or even of man's existence during late tertiary times, because no part of the world is so entirely unexplored by the geologist as this very region. The area in question is sufficiently extensive and varied to admit of primeval man having attained to a considerable population, and having developed his full human characteristics, both physical and mental, before there was any need for him to migrate beyond its limits. One of his earliest important migrations was probably into Africa, where, spreading westward, he became modified in colour and hair in correlation with physiological changes adapting him to the climate of the equatorial lowlands. Spreading north-westward into Europe the moist and cool climate led to a modification of an opposite character, and thus may have arisen the three great human types which still exist. Somewhat later, probably, he spread eastward into North-West America and soon scattered himself over the whole continent; and all this may well have occurred in early or middle Pliocene times. Thereafter, at very long intervals, successive waves of migration carried him into every part of the habitable world, and by conquest and intermixture led ultimately to that puzzling gradation of types which the ethnologist in vain seeks to unravel.