The present evolution of man

Title page, Contents, etc.

THE PRESENT EVOLUTION OF MAN

THE PRESENT

EVOLUTION OF MAN

Part 1.1. Organic evolution: Physical evolution

PART I

ORGANIC EVOLUTION

PHYSICAL EVOLUTION

CHAPTER I

"During the quarter of a century which has elapsed since Biology began to occupy itself again with general problems, at least one main fact has been made clear by the united labours of numerous men of science, viz. the fact that the theory of descent, the idea of development in the organic world, is the only conception as to the origin of the latter which is scientifically tenable. It is not only that, in the light of this theory, numerous facts receive for the first time a meaning and a significance; it is not that, under its influence, all the ascertained facts can be harmoniously grouped together; but in some departments it has already yielded the highest results which can be expected from any theory, it has rendered possible the prediction of facts, not indeed with the absolute certainty of calculation, but with a high degree of probability. It has been predicted that man, who in the adult state only possesses twelve pairs of ribs, would be found to have thirteen or fourteen in his embryonic state; it has been predicted that, in this early period in his existence, he would possess the insignificant remnant of a very small bone in his wrist, the so-called os centrale, which must have existed in the adult condition of his extremely remote ancestors. Both predictions have been fulfilled, just as the planet Neptune was discovered after its existence had been predicted from the disturbance induced in the orbit of Uranus.

"That existing species have not arisen independently, but have been derived from other and mostly extinct species, and that on the whole this development has taken place in the direction of greater complexity, may be maintained with the same degree of certainty as that with which astronomy asserts that the earth moves round the sun; for a conclusion may be arrived at as safely by other methods as by mathematical calculation.

"If I make this assertion so unhesitatingly I do not make it in the belief that I am bringing forward anything new, nor because I think that any opposition will be encountered, but simply because I wish to begin by pointing out the firm ground on which we stand, before considering the numerous problems which still remain unsolved.

"Such problems appear as soon as we pass from the facts of the case to their explanation; as soon as we pass from the statement, The organic world has arisen by development, to the question, But how has this been effected, by the action of what forces, by what means, and under what circumstances?

"In attempting to answer these questions we are very far from dealing with certainties; and opinions are still conflicting. But the answer lies in the domain of future investigation, that unknown country which we have to explore.

"It is true that this country is not entirely unknown, and if I am not mistaken, Charles Darwin, who in our time has been the first to revive the long dormant theory of descent, has already given a sketch, which may well serve as a basis for the complete map of the domain; although perhaps many details will be added, and many others taken away. In the principle of natural selection, Darwin has indicated the route by which we must enter this unknown land."—Weismann.

"The continuity of the germ plasm, like Darwin's selection, is a fact not a theory."—Haycraft.

"'Struggle for existence,' as perhaps it was in Mr. Darwin's world of advancing beasts and developing vegetables. But now the plan is so turned about by the arrival of man on the scene, and by his civilization, that you cannot watch even Darwin and Huxley themselves without seeing that the struggle that they and other good men wage is no struggle for existence but a struggle against mere existence. The struggle for existence is brutal life; a struggle to do something more than exist is human life—the mission of the human soul. What is the use of alcohol in such a struggle? The question is a wide one. It might lead us to inquire what that is which men want to obtain beyond mere existence. Watching some eminent teachers, you might suppose it to be a very detailed knowledge of the common frog. But men are human because they look upwards and to the future, not downwards to the past. And Darwin and Huxley, and even Haeckel, will in time learn that over-scrutinizing insufficient evidence does not make it more complete."—Moxon.

Above I give three extracts—one from the writings of a very eminent naturalist, the second from those of an eminent physiologist, and the third from those of a physician, also eminent. They disclose a difference of opinion which is remarkable. Professor Weismann scarcely deigns to discuss the theory of evolution, since, in his opinion, it must be considered as proved with as much certainty as is the fact that the world moves round the sun, or as if it had been demonstrated mathematically; and he adds, that we have now only to discuss the details, merely to fill in the minutiæ of the map, the outlines of which Darwin has already sketched. Dr. Haycraft also thinks that the theory of evolution has passed from the category of mere hypothesis into the category of that which must be accepted as proven fact. But Dr. Moxon appears to think that, if a struggle for existence leading to evolution ever did occur, it has now ceased so far at least as man is concerned, and the struggle has become one against mere existence, whatever that may mean, and he adds—"Darwin, Huxley, and even Haeckel will in time learn that over-scrutinizing insufficient evidence does not make it more complete."

His attitude is very characteristic of that of the vast majority of the general public, and characteristic also of that of the majority of medical men, who, while observing the effects of disease on man the individual, have signally failed to observe its effects on man the species. Had Dr. Moxon, when he wrote his essay on alcoholism, which in its effects is a disease, occupied a wider outlook, had he considered the species as well as the individual, he might perhaps have been led to conclusions which are as true as they are surprising.

Taking into account this attitude of the general public, and in particular that of the mass of medical men, to whom, if to any, this work should prove of interest, and considering also that a wide audience must be appealed to if it is to have that amount of practical usefulness which the author hopes for it, it seems needful, before proceeding with the main body of the work, to set forth as briefly and clearly as possible certain biological data on which the argument is founded; especially as, so far as the author is aware, they have never yet been explained in sufficiently simple terms to be comprehensible by the general reader; and more especially since, in his conception of the process of evolution, the author differs somewhat from accepted views, or rather since in his opinion acknowledged authorities have not recognized or have not laid sufficient stress on certain processes of evolution which appear to him of the greatest importance. This book is therefore divisible into two parts: in the first the problem of evolution in general is very briefly dealt with, but an attempt is made to penetrate somewhat deeper in certain directions than has hitherto been done; in the second part, the conclusions arrived at in the first are applied to the problem of man's present evolution, and an endeavour is made to show that this evolution is proceeding in a direction hitherto altogether unsuspected.

To many, and, surprising as it may seem, even to some medical men, in spite of what ought to be a scientific training, the theory of evolution means nothing more than the theory of the descent of man from the monkey. In reality it means much more; it teaches that plant and animal types have not persisted unchanged from the time life first became possible on the cooling surface of the globe, but that all types known to us have arisen by a process of gradual evolution from pre-existing types, and that this process of evolution has generally been in an upward direction from the low to the high, from the small to the great, from the simple to the complex. Pushed to its logical conclusion the theory teaches yet more; it teaches, as the only hypothesis scientifically tenable, that life originally arose by a process of evolution from that which was non-living; that under conditions of which we are ignorant, of moisture, or of heat, light, electricity, or other of the protean forms of energy, non-living chemical compounds did in the beginning of life overpass the border space which divides the non-living from the living, and become living beings. The lowest living beings, or rather those highest chemical compounds which first display signs, however slight, of what is called life, if any such now exist on earth, probably exist in masses so minute and so little differentiated from mere chemical compounds, as to be beyond all devisable means of observation. Regarding them therefore there is no evidence to offer, but as regards the evolution of higher life from lower life, the evidence is so vast and so decisive that it is impossible to avoid coming to the conclusion that Darwin, Huxley, and even Haeckel did not over-scrutinize insufficient evidence, but that Dr. Moxon under-scrutinized overwhelming evidence, that, in fact, he adopted the device familiar to theologians and dear to them, of abusing evidence instead of examining it.

But quite apart from all evidence that evolution has occurred, the conditions of life are such that we may infer from them with mathematical certainty that it must have occurred. It is a matter of common knowledge and experience (1) that in both the animal and vegetable kingdoms every individual differs somewhat from every other individual, but that (2) while the offspring is never an exact copy of the parent, there is yet a tendency for the peculiarities of the parent to reappear in the offspring in a greater or lesser degree. Whence it is clear, if some individuals of a species possess a peculiarity, such as a superior keenness of sight, or of hearing, or of scent, or a power of muscle, or a capacity of resisting heat, or cold, or hunger, or thirst, or disease, &c., in a greater degree than that possessed by the other members of the species, under conditions which render this peculiarity of importance in the struggle for existence, that the individuals which possess the peculiarity in the greater degree will be at an advantage, and will, on the whole, survive in greater numbers, and, consequently, other things equal, have a more numerous offspring than those which possess the peculiarity in the lesser degree. And further, since the offspring, while inheriting their parents' peculiarities, tend, to vary somewhat from them, there will, in the next generation, probably be some who have the peculiarity in a greater degree than their parents, and others who have it in a lesser degree, when, if the conditions remain the same, there will be such a new survival of the fit, and such a fresh elimination of the unfit, as will leave the survivors in the third generation with the peculiarity developed, in however slight a degree, more than it was developed in their grandparents; and it follows that this process, repeating itself through innumerable generations, and during long epochs of time, will at length develop the peculiarity to a point beyond which any further increase is no longer useful, or to a point beyond which it is so little useful, that those individuals who possess the increase are no longer at such an advantage in the struggle for existence as to survive to an appreciable extent beyond those who have it not. Therefore since individuals vary each one from all others, since the offspring, while varying somewhat from their parents, tend to transmit the peculiarities of their parents, and since individuals that vary favourably tend of course to survive and have offspring, whereas individuals that vary unfavourably tend to be eliminated and have no offspring, it is deductively so certain that whenever there is a struggle for existence,—and throughout nature there is always such a struggle,—the survival of the fittest must lead to evolution, that it is scarcely necessary to appeal to facts for inductive confirmation. If, however, we do seek such confirmation, we find it in three great bodies of facts collected mainly in different fields of research, each of which is separately decisive, and which collectively furnish confirmation so absolute that, practically speaking, no student of biological science now believes otherwise than that the whole organic world arose by a process of evolution.

The first great mass of evidence is furnished by the science of Comparative Anatomy, especially by that branch of it which deals with Comparative Embryology. In the interests of the general reader, we may with advantage defer the consideration of it.

The second great mass of evidence is furnished by the science of Paleontology, which teaches, on the evidence of fossil remains, that the earth has not always been inhabited by the same forms of life, but that during the whole vast period which intervened between the deposit of the earliest fossiliferous rocks and the present age, there occurred a constant but gradual change of form, as a result of which type shaded into type, generally in an upward direction, and which can have been due to evolution only, or, as the single other alternative, to an immense series of special creations, made not only when life began, but also during its entire continuance, in exact imitation of a process of evolution—a preposterous theory, for which there is no more warrant than for the hypothesis that our various breeds of dogs have not descended from a common ancestry, but were separately created.

The third great mass of evidence is that furnished by experiment. It is therefore the most conclusive of all, since any theory which can be proved experimentally may be said to be proved decisively. For instance, if we have a theory that the boiling-point of water varies with the atmospheric pressure, and find on experiment that it does so vary, we may conclude that we have proved our theory beyond cavil. As a disputed point is involved, which it will be advantageous to discuss thus early, we will consider this part of the evidence more at length than we did the rest. The theory of evolution may be put to the test of experiment. We may take any species of plant and animal, and by copying the process of natural selection, by destroying those individuals of the species which we regard as unfit,—i.e. those which vary unfavourably as regards any peculiarity we wish to develop,—and by allowing only those individuals who vary favourably as regards that peculiarity to continue the race, we may develop the chosen peculiarity in the chosen species to almost any extent; the one condition being, that our operations shall extend over a sufficient number of generations. The efforts of man to improve his cultivated plants and domesticated animals may be described as a lengthened series of such experiments, conducted on a gigantic scale, with the result that he has been able to vary plant and animal structures almost at will, and so greatly that, in the absence of scientific and historic testimony, no one could guess that the peach and nectarine, for instance, were cultivated varieties of the wild almond, or that the various breeds of dogs have a common and, geologically speaking, very recent ancestry.

It may be objected however, and it often is objected, that natural selection is not the same thing as artificial selection; but the objection cannot be sustained, for in effect it is the same thing, artificial selection being merely natural selection with man as the governing agent. Man, for instance, has caused the evolution of speed in the greyhound and in the race-horse by breeding, on the whole, from the swiftest animals of each species; in like manner the carnivora have caused the evolution of speed in the hare and the antelope by permitting, other things equal, only the swiftest to continue the race. Artificially caused evolution differs from naturally caused evolution only in that it is usually more rapid; for man, in his endeavours to produce a wished-for evolution, fixes his attention on but a few traits, and breeds with the intention of developing those traits only. Thus in the case of the greyhound he has bred, generally speaking, with the intention of producing a very swift animal with sight keen enough to see the prey, and jaws and teeth adapted to seize and kill it. In the case of the racehorse he has bred with the intention of producing another swift animal, strong enough and tractable enough to carry him. But natural selection in the hare and the antelope has developed not only speed, but also hearing, watchfulness, and many other traits which are as essential.

Other things—i.e. other essential traits—equal, preeminence in one or more essential traits is favourable to survival. But because in a state of nature many traits are essential, evolution by natural selection must proceed along many lines, and, in consequence, be corre- spondingly slow. To take an example—a buck and a doe antelope, whose sight and hearing respectively are keener than the average, but whose other qualities are equal to the mean of the species, are at an advantage as regards the sense of sight and hearing respectively. If they mate, the offspring, while attaining to the specific mean in the other qualities, will in general surpass it as regards sight and hearing, but will fall below the male parent as regards the sight, and the female parent as regards the hearing; for the comparative dullness of the male's hearing will militate in the offspring against the keenness of the female's hearing, and vice versa as regards the sight. So also with the offspring of a buck pre-eminent for endurance and a doe pre-eminent for speed. Then, if the offspring of the two pairs mate, their offspring will surpass, but in a lessening degree, the specific mean in keenness of sight and hearing, in speed and in endurance, but will fall below each of the grandparents as regards the one quality in which that grandparent excelled, though they will surpass each of them as regards all the other qualities. Therefore if the essential qualities are numerous,—and they always are so in the case of wild animals,—the descendants of numerous ancestors, each one of whom was pre-eminent in one of these qualities, will tend more and more, generation after generation, to approach the general racial mean as regards all these qualities;—which appears to lead to the absurd conclusion, that in the end there will be no evolution at all. But in coming to that conclusion we shall have forgotten that the offspring never present an exact mixture of the qualities of the parents, but that spontaneous variations, caused we know not how, continually arise, in consequence of which one or more of the offspring of the keen-sighted father and the quick-hearing mother (for instance) may surpass both parents as regards both qualities; and though there is reason, as we shall presently see, to conclude that on the whole the offspring are usually inferior to the parents, nevertheless, since they are generally numerous, and the process of selection almost always severe, the survivors in each generation, as a rule, surpass their parents in the sum of their qualities; and as a result, there is usually evolution as regards the whole race even when the essential qualities are many. Moreover, we have assumed for the sake of simplicity that each ancestor was pre-eminent in one quality only, but of course, as constantly happens in nature, a single individual may approach pre-eminence in several or many qualities, or conversely, may fall below the specific mean in several or many qualities: in the latter case he tends of course to be eliminated, and to leave no offspring, and therefore to have no influence on the future of the race; but in the former he tends, even more than if he were eminent in one quality only, to survive and to leave offspring who, inheriting his characteristics, tend as a result to survive in greater numbers than the offspring of the less happily endowed, and therefore to render concurrent evolution in several directions more rapid.

Lastly, the statement that artificial selection differs from natural selection in that but a few qualities are developed by it, is true in a very limited sense only; for instance, by causing the evolution of the greyhound man has necessarily caused the evolution of a great number of subsidiary qualities, each subserved by a number, in some cases by an immense number, of finely co-ordinated structures. Therefore though speed alone has been aimed at, yet to obtain it evolution in many directions has been necessary (e.g. in "wind," "limb," circulatory and nervous systems, &c.). On this score then there is no essential difference between artificial and natural selection, and the evolution which results from the former therefore furnishes experimental (i.e. conclusive) proof of the evolution which results from the latter.

The reduction towards the specific mean which interbreeding tends to bring about in the qualities of individuals as exhibited in their descendants, has caused some biologists to insist that isolation is a necessary antecedent to evolution. But if we bear in mind the fact (to be more fully discussed in a future page) that evolution proceeds not on lines of traits, however favourable, which occur infrequently or abnormally, but on lines of traits common to all the individuals of the whole species, that is, in which every individual rises above or falls below the specific average; and bear in mind also, that generally those individuals who on the whole vary fortunately as regards these traits, survive and have offspring, whereas generally those who on the whole vary unfortunately are eliminated and have no offspring, we shall have no difficulty in understanding that evolution is quite possible in the absence of isolation. What is not possible in the absence of isolation is evolution on diverging lines. For instance, if the whole of a species of antelope inhabited an open plain under conditions common to all there might be evolution, but it would be in a direction common to the whole species. But if, owing to any circumstance, such as a deficiency of food supply, a portion of the species separated from the rest, and migrated permanently to forest land, then the two divisions of the species, being unable to interbreed, and differently conditioned as to the environment, would develop on divergent lines of evolution.

The conclusion, deductively arrived at, that the conditions under which life has existed and still exists, are such that evolution must have occurred and still occurs, is therefore decisively confirmed by the conclusion, inductively arrived at, that evolution certainly has occurred, and therefore, though in the subsequent pages of this work many proofs will incidentally be afforded of the actuality of Organic Evolution, in future it will be assumed that the truth of it is admitted, and we shall endeavour only to fill in the details of the map as to the fidelity of the outlines of which no well-informed man any longer entertains a doubt.

The upward march of life from the earliest beginnings may be compared to that of a horde of men, leaving their old habitations and entering new lands; travelling ever forwards, but ever sending out branch swarms that part from the parent horde, never to reunite with it, and ever leaving some of their members behind on the way, some of whom may journey backwards; such hordes as those which in ancient times came from the East, settled the countries they passed over, sent offshoots to the North and South, and rolled on the tide of conquest till they destroyed the old Roman Empire. The lowest, or in other words the least differentiated and specialized forms of life, may be compared to those members of the horde that stayed behind in the original habitat, the intermediate forms to those that halted and settled by the way, and the highest forms to those that journeyed till they reached the farthest limits of the wanderings. The comparison is made yet closer if we imagine, as generally true of life, that which is generally true of emigrant swarms of men, namely, that those that stayed in the original habitat, that those that halted, diverged, or retrogressed by the way, and that those that reached the farthest limits, did not remain altogether unchanged, but changed somewhat as ages passed and generations lived and died; those that remained in the original habitat having changed least, those that wandered farther having changed more, and those that wandered farthest having changed most, and this for the reason that though the environment nowhere remained absolutely unaltered, yet for those that travelled farthest it altered most; so those Aryans who dwell in or near the original habitat of the race have changed least, those who halted by the way have changed more, and those that journeyed farthest to the West, or diverged to the North or South, have changed most. So also in the march of life, the lowest organisms may be considered as having stayed behind at or near the original starting-point; the sponges as having diverged from the main road at an early period; the Cœlenterates, the Mollusks, the Annulosa to have halted by the way at a later stage; whereas the Vertebrates, with mammals at their head, and man at the head of the mammals, may be considered as having reached the farthest limits. But just as it becomes increasingly difficult the farther we penetrate into historical antiquity to trace the descent of the nations of any race of human beings,—the Teutonic for example,—not only for the reason that the peoples who have travelled farthest have changed so much, have undergone evolution, and because the peoples who halted by the way or stayed behind have changed also, but because some of the links of the chain are broken, because some of the nations which halted by the way are lost and cannot be recognized, or because they have perished utterly in the struggle for existence; so also the farther we penetrate into geological antiquity, the harder it becomes to trace the descent of species, the more numerous become the broken links, the wider the gaps; nevertheless, however numerous the broken links, however wide the gaps, just as it is in general possible to trace with more or less accuracy the descent of the nations, so it is in general possible to trace the descent of species.

CHAPTER II

It has already been pointed out, that the conditions of life are usually such as to cause the number of traits necessary for survival to be numerous, and that this again causes the process of evolution to be slow, though it is no bar to it as some biologists have supposed. But however slow the multiplicity of essential traits may render evolution, it is difficult at first sight to understand why evolution should be so extremely slow as it generally is. Every plant or animal pair usually gives origin to numerous offspring, sometimes the offspring are numbered by millions (e.g. the offspring of cod-fish); yet the number of individuals in each species does not increase as a rule, whence it is clear that nature, by destroying the majority of the offspring, exercises her power of selection with extreme stringency. Under the circumstances we might à priori expect evolution to be rapid. But what are the facts? Some types, such as the lamp-shells, have persisted almost unchanged during enormous epochs of time, and in almost all cases nature requires hundreds, nay thousands or tens of thousands of years to bring about comparatively trifling changes of structure. Why is this?

The answer is probably found if we consider certain groups of apparently unconnected facts. Children who do not especially resemble their parents often resemble their grandparents, or even more remote ancestors; at any rate they more often resemble an ancestor than they do any other given individual. For instance, if before a child is born we indicate any individual of our acquaintance, the chances are immensely greater that the child when grown will resemble a particular ancestor than that he will resemble the person indicated. That is to say, there is a greater tendency for the child to vary from its parents in the direction of its ancestry than in any other given direction. Now if the parent has varied from the grandparent in any other direction than towards the ancestry, this, the child's variation towards the ancestry, is evidently an omission of the last step made in the evolution of the race. It is what is known as atavism and is sometimes carried so far that the variations (i.e. the evolution) of hundreds of ancestors nearest it are omitted, and the child resembles some extremely remote ancestor, being ape-like in features, especially in times of famine, when want of nourishment checks the development, and sometimes being covered with long hair. So also the progeny of a pair of thoroughbred horses is sometimes an "arrant weed," or it may revert to an even more remote ancestor, by showing zebra-like stripes. So also "a blue pigeon, like the ancient Columba Livia, may be hatched in the dovecot." On the other hand, the progeny of a pair of ordinary horses never has the peculiar characteristics of the racer; nor has the progeny of a blue pigeon ever those of the pouter or fantail.