As we look round us, in street or country or where you please, we see objects which may be divided into two great classes. To the first belong houses, rocks, and stones, whose is, as Wordsworth has it,

The silence and the calm

Of mute insensate things.

To the second belong such objects as men and sparrows, which have an apparent spontaneity and power of self-movement that sharply distinguish them from their inanimate surroundings. On much further consideration we find that it is necessary to include in the same class as men and birds a number of objects, mute and to all appearance insensate, which have no obvious power of self-movement, but are almost as stationary as the houses or the stones. These are trees, grass, shrubs, every form of vegetable life. They are not to be regarded as half-alive, or less endowed with vitality than the mobile bird or beast—which, indeed, ewe their life entirely and directly to that of the green plant.

We have, then, an inanimate or inorganic and a living or organic world around us. Now, if we take a crystal or a brick, we can trace its history with ease. It is simply an aggregation of smaller particles arranged in a more or less symmetrical way. No question of parentage arises. But if we consider an oak or a horse, we are assured that it has had very small beginnings; that no human hands have formed it; that the beginnings were invariably and necessarily derived from some former oak or horse — no oak, no acorn. Nor do we doubt that every human being on the earth has had parents — was not formed directly from mother-earth. Now, this belief of ours may not have been consciously extended by us to lower forms of life; we may never have considered whether every mushroom implies a preceding mushroom, every bacillus a preceding bacillus. We may even be inclined to think that if a cheese be left in a damp cupboard, mould will appear upon it by a spontaneous generation from the substance of the cheese; that though every man must have had parents, the same is hardly true of a mere mould.

Now, as a matter of fact, men of science have entered exhaustively into this question; and they most positively assert, without any qualification of the smallest, that what is true of the man is true of the mould. It also has had its parents like unto itself, and did not spontaneously develop from the cheese. We have framed various Latin dogmas on this matter—dogmas of great historical and immediate interest. The illustrious Harvey, greatest physiologist of any age, made a great contribution to this question — a contribution which would keep green his name had he not been the discoverer of the circulation of the blood. Harvey spent many an hour in preparation for his great treatise “Concerning Generation”, and concluded that omne vivum ex ovo: he found what corresponded to an egg-stage in the history of all the living things he examined. With the microscope, and especially its employment in the nineteenth century, the dogma of Harvey has been modified—it being the custom to modify scientific dogmas in accordance with new truth, a custom which is found more convenient than that of retaining the old form and giving it a new meaning.

Rudolf Virchow, the founder of the cellular pathology—that is, of modern pathology—modified Harvey’s phrase in accordance with his own researches, and propounded it in this form—minis cellula e cellula. It was thought that every living thing consists of cells; but it is at least probable that the very lowest and simplest form of living matter is not even so far evolved as to possess cellular form, so it is best to read our dogma in this form -omne vivum ex vivo. Under no conditions can all the (dead) cheese in the world produce one single unit of living matter. Such is the assertion to which very few dissentients are known among men of science at the present day. Of course I must assign the reasons which have led to the formulation and acceptance of this dogma; but before doing so I must just enumerate, as if no dogma had yet been framed, the possibilities as to the origin of life on this planet. The possible theories are three, with a semi-jocular one thrown in. In the first place, it is possible that the minutest and simplest forms of living matter are being constantly produced, wherever the conditions are suitable, today as yesterday, and ever since the temperature of the earth’s surface was cool enough to permit of the presence of water in its liquid form. This doctrine is in harmony with the laws of continuity and of evolution, which are the most universal and invaluable of all. modern conceptions. It is supported by the fact that the earth is everywhere flooded with the lowest forms of life. But, as we have seen, the prevailing scientific belief is a denial of this possibility.

On the contrary, this belief asserts that, at the present day, every living thing must have living progenitors—omne vivum ex vivo. This assertion is, of course, immediately faced with the necessity of stating how the first living thing—the veritable mother of all living—came to inhabit this planet. The overwhelming majority of biologists believe that omne vivum ex vivo was not always true. They find themselves compelled to aver that, though living cannot now be produced from inanimate matter, yet in the distant past the conditions must have been so different that life was naturally evolved upon the earth by the continued play of continuous, unexceptionable, unintermitted, un aided law. “Supposing a planet carved from the sun, and revolving round the sun at a distance equal to that of our earth, would one of the consequences of its refrigeration be the development of organic forms? I lean to the affirmative”. So said Tyndall, and so say we all—or nearly all— today. What were the past conditions of the evolution of life cannot be guessed. It cannot have been that a high temperature was needed, for the temperature must have been below that of the boiling-point of water. The (supposed) difference between that distant period—say a hundred million years ago— and the present cannot have been due to any present deficiency of suitable complex chemical stuffs today. On the contrary, the earth is filled with complex cumpounds, proteids, carbohydrates, and so forth, apparently ready to develop into living matter; yet (it is said) they do not; while living matter, containing all these bodies, was evolved in the past, when none of them was already there to aid in the process! It is a hard belief.

Thirdly, there is the belief of Lord Kelvin, who is not a biologist, but is assuredly the greatest living man of science, that no explanation of the origin of life is conccivable save that which refers it to the special act of a personal God. To use the great physicist‘s own words, “Science absolutely demands Creative Power”. Lord Kelvin’s recent expression of opinion on this thought raised a storm of protest from the biologists, not one of whom came to his support.

The semi-jocular theory to which I have referred we owe to Lord Kelvin himself, who suggested, many years ago, that the first germs of life might have been brought to the earth, long aeons ago, “on some moss-grown fragments from the ruins of another world”. It is a brilliant effort of the scientific imagination; but I do not fancy that Lord Kelvin could now be regarded as taking it seriously. Even were we assured that meteorites are derived from the ruins of other worlds, and not from the ruins of comets, as the astronomers have excellent reason to believe; and even if we knew that, during their passage through our atmosphere, such meteorites were not necessarily raised to such temperatures as would effectually sterilize them— yet the problem of the origin of life would face us from some planet of the past if not from our own “lukewarm bullet” of today.

No; the present controversy is between the first two hypotheses: either life is arising ubiquitously now, by what Stevenson called a “vital putrefaction of the dust”, or it arose, by a natural evolution, in the distant past, once and for all.

The controversy, I say; but it is almost universally believed that there is no controversy. Omne vivum ex vivo is taken as finally proved, as a result of the great controversy of thirty years ago, in which Tyndall, Huxley, Pasteur, and Dr. Bastian engaged. It is thought that the “myth of spontaneous generation” has been forever refuted, and onme vivum ex vivo forever established. This is what I was taught, not so many years ago, in class-rooms both of zoology and botany; and it is so taught everywhere. But lately the matter has come up again: Sir Oliver Lodge and Professor Ray Lankester have fought a drawn battle in the Times; and Dr. Bastian has published a remarkable book and made most important contributions to Nature; and we may appropriately ask ourselves what was really proved thirty years ago. It was shown, beyond dispute, that when infusions of hay, or other substances which customarily came to swarm with life in a few days, were efficiently boiled, and then protected from contamination, no life ever developed in them. The boiling had killed every gem of life in the infusion; and forevermore it must remain dead, unless living germs were brought to it from outside—vivum could only be ex vivo; spontaneous generation was a myth.

Now let us see how this view, the scientific orthodoxy of today, agrees with the opinions of the past. We shall find that, however difficult it may be to hold when we ask the origin of the first living things, yet it is perfectly compatible with the wisdom of past biology.

We have already considered the nebular theory, which asserts that the solar system has been evolved from a nebula — a cloud of gas such, though much smaller, as you may see any winter evening in the sword of Orion. When, in its turn, the embryo earth was cast off from this nebula and began to cool, there came a time when the water, till then filling the atmosphere in the form of vapor, was precipitated and formed the oceans. The famous Comte de Buffon thought that life probably began in the ocean, probably in the polar oceans, which would be the first to cool; and, only the other day, an ingenious Frenchman traced a resemblance between our body-fluids—as to saline composition, etc. — and seawater, thus lending some color to his great countryman’s hypothesis. Indeed, it appears from this Frenchman’s paper that we may look upon the human form divine as none other than a peripatetic aquarium. True to their ancestor’s original environment — assuming Buffon’s guess to be correct — the polar sea-water of many millions of years ago our body-cells are now bathed in fluids which have little varied in that long period. When, at some intervening date, certain enterprising creatures ventured to make a bid for life upon terra firma, the cells of which they were composed naturally continued to prefer the old medium, and the preference has been maintained and is gratified in us today. So that, dry though you feel, you are none other than a walking aquarium. You must try to think of your white blood-corpuscles, scurrying along in your saline blood, as minute marine creatures whose ancestors were formed from “the deep's untrampledn floor”.

Just as the older theory was framed on the assumption that life is not formed de novo today, so we find, again, that when Spencer came to consider this question he accepted the current biological teaching—not then as firmly held as at present—that life is not now evolved from inanimate matter. But his contributions to the problem of the gradual development of inorganic into organic molecules are of equal importance whether we believe that the process occurred once for all in the past, or that it is occurring everywhere on the surface of the globe today.

Charles Darwin, when he proved the possibility of the origin of species of plants and animals by natural selection, began by assuming the existence of a “few simple forms” of living matter; and never discussed the question of their origin, which was outside his province. Professor Haeckel, of Jena, has a carbon-theory of the origin of life which, as far as I know, is supported by no one. He also is content to accept the doctrine that life cannot now originate from inanimate matter. The supposed occurrence, in the far past, of this evolution was termed by Dr. Charlton Bastian archebiosis (The nature and origin of living matter); but Huxley’s less-satisfactory term abiagenesis has been preferred, doubtless owing to the great and greatly deserved fame of its inventor

Now it is true that boiled fluids, uncontaminated, will remain sterile indefinitely. It is also true that, under the conditions which they set themselves, our experimenters have completely failed to manufacture life in the laboratory. At best, the most successful followers of M. Berthelot, the great founder of synthetic chemistry, can only manufacture the very simplest forms of proteid or albuminous matter, and this by use of temperatures and effort of which no need is manifested by living nature.

Furthermore, it is true that if a hay infusion,for instance, be passed through a Pasteur-Chamberland or Berkefeld filter, which excludes even the minutest of known living organisms, the filtered fluid will remain sterile as long as it is uncontaminated. In so far, this experiment goes to confirm the results obtained by boiling, and the whole question seems closed.

Thirty years ago Dr. Charlton Bastian, F.R.S., was among what appeared and still appears to be the defeated party. He believed in spontaneous generation. But other duties claimed him and his ultimate silence was taken for conviction. He had published important books, with many drawings made by himself, illustrating what he asserted no that the microscope had revealed to him. People shrugged their shoulders, and hinted at the value of imagination in guiding the pencil. Dr. Bastian bided his time. Finally he resigned his professorship at University College Hospital, London, five years before he need, learned the difficult art of photographing under the microscope, and has since taken more than five thousand photo-micrographs with his own hands, which bear, directly or indirectly, upon the origin of life. The most striking of all his observations—one which he has again and again repeated—was embodied by him in a paper which he sent to the Royal Society, of which he is a distinguished fellow. Not only was the paper refused, but a well-known member of the committee, responsible for its refusal, actually refused point-blank to move three yards in the library of the Royal Society to see Dr. Bastian’s specimens.

Now let us consider first Dr. Bastian’s criticism of the experiments in which fluids are boiled or filtered. He reasonably regards it as necessary for the production of life that certain chemical compounds be present. If it can be shown that boiling destroys these compounds, then the boiling experiment cannot be held to prove that life cannot originate in non-living fluids. It is known that boiling does alter or “degrade” the chemical compounds in the boiled fluid. It might be thought that, if boiling be not performed, but merely filtering through a germ-proof filter, the result (the non-development of life) would be conclusive; but it has been shown that such filtration alone suffices to alter the chemical nature of the filtered fluid. “Spontaneous generation” is not, therefore, proved to be a myth even by this experiment. So much for destructive criticism.

But Dr. Bastian has also positive results to offer. He has seen, he tells me, the development, in a previously clear fluid, of minute, black spots, which gradually enlarge, and at last become motile bacteria. This change cannot successfully be recorded; but it seems to me to be not inconceivable that a cinematographic apparatus might be adjusted to the microscope, and thus demonstrate, beyond all cavil, the evolution which Dr. Bastian declares that he has seen.

The most remarkable photograph that Dr. Bastian has taken shows the spines, magnified seven hundred times, of a minute water-animal known as the Cyclops. In these spines, which are absolutely impervious to the smallest known organisms, there develop a number of spots, which finally are recognizable as bacteria. This his photographs clearly show. Either these bacteria have arisen de novo in the tissue of the spine, or they are the enlarged forms of some bacteria, hitherto unknown, which are too small for the microscope to detect— are ultramicroscopic—and which have somehow made their way through the tough covering of the spine. But this is pure hypothesis, without a shadow of proof; and to assert it, simply because you decline to believe that the bacteria can have arisen de novo in the spine, is not science, but prejudice. It remains for those who deny that the bacteria can have arisen de novo—since this would clash with their dogma—to prove that such ultramicroscopic bacteria do exist, and can force their way into the spine of the Cyclops—or else to admit that their dogma is improved.

Other remarkable photographs show a similar evolution of bacteria—parentless bacteria—in the cells of a potato. Of course, in both of these cases, the bacteria arise in tissue that is already organic; but, if they can so arise, we must cease to hold the accepted belief that the bacteria of today have all descended from bacterial ancestors which were present on the earth scores of millions of years ago.

The easiest and most natural belief, according with the law of continuity and with all known analogies, is that life still arises on the earth by natural processes. Harmonizing with this belief of Dr. Bastian’s — or at any rate conflicting with Lord Kelvin’s—is a recent paper by Professor Pickering, who finds excellent reason to believe that there are upon the moon traces of the action of vegetation. Now, the moon was certainly born from the earth when she was far too hot to sustain life; so that, if Professor Pickering be right, living matter has spontaneously developed on the moon. Surely no one will suggest any exercise of a deliberate creative act so apparently purposeless as the formation of living vegetation on the surface of the moon.

Of course all this conflicts with the popular notion of the Eternal power. But, on the other hand, it perfectly consorts with the philosophic conception of the Eternal who sustains and informs all things, the “All-Upholder”, as Goethe calls Him. Suppose that all the phenomena of stars and suns, of life and of mind, be reduced beyond dispute, to the law of continuity. Suppose that we know in detail the steps by which the Book of Job or the prelude to “Parsifal” evolved from the nebula which developed into the solar system; suppose that we can explain not only life itself, but even the genesis of such as these, its noblest products—“can we escape from the overwhelming consciousness of the Eternal and eternally creative power from which oil things proceed?”. Assuredly not; he who has some conception of the Eternal as nearly adequate as the poor human mind can form, will be no whit disturbed to learn that Dr. Bastian is right, or— someday—that life can be manufactured at will in the laboratory; for pray how would such manufacture exclude or deny or derogate from the ineffableness of the power that “rolls through all things?”

While these pages were passing through the press, Mr. Butler Burke, of the Cavendish Laboratory, Cambridge, made a first announcement of some experiments which he has been conducting for some years back. He has demonstrated the development, in sterilized bouillon subjected to the action of sterilized radium chloride or bromide, of minute bodies which exhibit growth and subdivision. The American reader will find an account of this work in an article contributed by me to Harper's Weekly for July 22, 1905. I make no detailed reference to it here, though I have had the opportunity of studying Mr. Burke’s results for myself, since he is about to publish a volume on the subject, and since the nature, origin, destiny, and distribution of life must engage me for a subsequent volume.




Heredity and variation are the two facts without which organic evolution would be impossible. Since Darwin’s work, which somewhat obscured the initial questions that they raise, but demonstrated their stupendous consequences, biologists have spent much labor in discussing the causes and conditions of the two facts, that like tends to beget like, but that like does not beget exactly like. The subject is worthy of study, for it is evident that without variation there could be no differentiation of species; while without inheritance of variations no differentiation could survive for more than one generation. Natural selection presupposes variation, and now we have ceased to doubt that natural selection is a fact, biologists are going back to the beginning and studying that factor from which attention was long diverted by the influence of Darwin’s masterpiece.

Some forty years ago the Abbé Mendel took to experimenting with peas. For some thirty-five years his work was left unnoticed, but within the last lustrum it has come into its own, his essential discovery being now regarded by many, in Professor Bateson’s words, as “one of the lasting triumphs of the human mind”.

Until the rediscoveries which have brought Mendel’s work into recognition, the popular view was simply this: like produces not exactly like; this fortuitous difference between parent and child we call variation; by the operation of natural selection favorable variations are perpetuated, and unfavorable ones die out; hence, the origin of species — subsidiary factors being ignored as nom existent by the school of Weismann, and as relatively unimportant by the majority of biologists.

But natural selection selects; it does not originate or create. And all these decades past, while fully discussing the consequences of variation, we have ignored the fundamental question, simply accepting it as a mysterious fact hardly likely to repay investigation. Now, let me attempt to show what Mendel and his successors of this generation have accomplished, premising that the facts — if not, indeed, the interpretation of them—are no longer in dispute, and that they will be familiar to every amateur student in a decade. How satisfactory to the students of Herbert Spencer are these latest advances in biology, along lines which he discerned long ago, I can hardly say.

Make the Abbé Mendel’s discovery simple I cannot, the facts being complex; but I must do my best. Each of the higher animals and plants is formed by the union of two cells of different sex, which are called gametes; and in these the problem of heredity obviously centres. The child “has his father's smile”, we say; and we know that this character must have been transmitted in the paternal gamete. Now the first question we must ask is plainly this: How are the gametes formed? And we know that each gamete— of either sex  is formed by a series of cell-divisions, beginning in what we may call a germ mother-cell. Now the essence of Mendel’s discovery is this: The germ mother-cell which is about to divide and form the gametes that are to reproduce any individual in his or her descendants, itself contains characters derived from both the parents of that individual. These characters exist in the germ mother-cell in opposed pairs —e.g., a character corresponding to the white pigmentation of the individual's father, and another corresponding to the black pigmentation of the mother—and when the germ mother-cells divides so as to form gametes, these pairs are split up or segregated, the black character going to one gamete and the white to another. Thus the gametes or sex-cells of a gray individual will not be potentially gray, but either black or white. Observe the result. The individuals of the new generation may be of three kinds in respect of any given character. Some of them will be white, since they were formed by the union of a white-bearing gamete from each parent, some black since formed by the union of two black-bearing gametes, and some gray like their gray parents, since formed by the union of a black with a white gamete. But the gametes of this new gray individual will not be gray, but black or white, as before. If this is unintelligible, I can only express my regret.

This discovery that variation—e.g., the production of a black individual from gray parents— is really a form of heredity, proceeding according to definite laws, instead of being a sort of “bad shot” at heredity, clearly marks a new epoch in our conceptions of the subject. The above assertion of the working of the process constitutes Mendel’s “law of segregation”.

Let us observe some of the consequences. We now know that new species can and do arise by the operation of the laws of heredity quite apart from any slow accumulation of variations under the influence of natural selection. As Professor Bateson says: “The dread test of natural selection must be passed by every aspirant to existence, however brief”; but that expresses the totality of its power. Observe further that the scholastic dictum, natura non facit saltum, which has so long been believed, cannot hold. Nature does sometimes make leaps; and the modern belief in discontinuous variation is a denial of the old dogma.

There are many facts which the mutation theory explains. What, for instance, could be more puzzling than the unquestioned fact that hemophilia, or the “bleeding-disease”, is constantly transmitted by men to their sons, not to their daughters, but through their daughters to their grandsons; but not their granddaughters? In other words, the males inherit, suffer and trans­mit; the females inherit and transmit, but do not suffer! And now it seems that the abbé with his peas gave us the key to this forty years ago. It becomes intelligible if we conceive that certain characters are linked in the gametes. For instance, the bleeding character may be linked with the “maleness” character; the two are segregated together; when one appears both appear; when one is latent, as in the case of the female, so is the other.

Mendelism is in its infancy; but it is already potent for good. We could “exterminate the simpler vices” if we pleased; and Mr. Galton’s Eugenics is not a dream. Someday the race will undoubtedly realize that education in all its forms is but the “giving or withholding of opportunity”, and then will face the root problem in earnest. Meanwhile, to quote Professor Bateson, “So long as, in our actual laws of breeding, superstition remains the guide of nations, rising ever fresh and unhurt from the assaults of knowledge, there is nothing to hope or to fear from these sciences.”


the factors of organic evolution


The word Darwinismus is widely used on the Continent, especially in Germany, and its English equivalent is familiar to us, but there are serious objections to its use. It cannot be taken as a synonym for organic evolution, since the origin of species by natural processes had frequently been suggested before Darwin’s birth. The only other meaning the word can bear is the doctrine of the origin of species by natural selection, which Darwin brought into so much and so necessary prominence. This use of the term is not only illegitimate but quite unfair to Darwin, who was one of the broadest minded of men and had not a trace of the dogmatist in his composition. Darwin expressly asserted that he attributed to the inheritance of acquired characters an important share in the origin of man. He dealt with this at no length, for the excellent reasons that the principle had already been enunciated by Lamarck, and that he himself had his hands full in elucidating his own contribution to the discussion.

In considering the factors of organic evolution, then, let us first concentrate our attention on one point, the controversy — incorrectly and unjustly named, as I have shown —between Darwinism and Lamarckism. The only possible excuse for these terms is their focussing the attention on two great names; but, as I say, they do an injustice to the younger thinker, if not the older too. Every one knows that Professor Auguste Weismann, now happily enjoying his eighth decade, has taken up the cudgels for a “Darwinism” which is more than ultra-Darwinian; and his school is a great and flourishing one. Weismann denies in toto the possibility that any character acquired by the parent can be transmitted to the child. To Darwin’s “natural selection” he attributes far more than did Darwin himself; and the pupil’s pupils have even outrun him. Here again time has vin­dicated Spencer—so that one begins to understand Grant Allen‘s remark, “the twenty-fifth century will appreciate him”. The echoes of his controversy with Weismann have died down and the inner ring of the non-scientific public is becoming familiar with the dogma of non-transmissibility of acquired characters, but Weismann himself has made the most significant concessions, and biologists are now well aware that the dogma can be no longer maintained. Choose your own instances and you may make anything ridiculous—to those who have not discrimination enough to appraise your method. If the belief of Lamarck, amplified and upheld by Spencer for decades against an overwhelming majority, he construed into an assertion that cutting off a rat’s tail will make its progeny tailless, or the similarly indefensible assertion that the giraffe has its long neck as a result of the incessant stretching to which that structure has been subjected by its hungry ancestors, or the inane joke about man’s loss of his tail by virtue of his ancestors sitting upon theirs : then certainly Larmarckism is sheer nonsense. But Weismannism has been reduced to just such blatant absurdity by some of its adherents, who deny that germ-cells, for instance, can be affected by the presence of alcohol in the body-fluids which circulate in the individual containing them and by which they are themselves nourished—or injured. Pledged to deny that any circumstance connected with the individual can in any way affect his off­spring, these enthusiasts are compelled simultane­ously to flout fact, logic, and probability.

The first thinker to propose the theory now known as Lamarckism was Erasmus Darwin, physician, zoologist, and poet, who was Charles Darwin’s grandfather. Thus Darwinism would be perhaps the best and most accurate name for Lamarckism. Erasmus Darwin’s enunciation, however, of the principle that individuals alter by reaction with their environment, and transmit the altered or acquired character to their descendants, was extremely vague. But in his Philosophic Zoologique, which appeared in 1809, Jean Baptiste de Lamarck, already a man of sixty-five, gave detailed expression to this theory. Undoubtedly he exaggerated its importance, and it is significant that the general doctrine of organic evolution did not through it gain acceptance, but had to wait fifty years until Darwin’s assertion of another factor came to its aid. At the present time, the Lamarckian principle is in low repute, despite the acceptance of it by Darwin and Spencer’s long championship of it.

Nevertheless, it would be unwise to omit this principle—the inheritance of acquired characters—as a factor in organic evolution. It is assuredly of more than historic interest. In his latest book, the Wunderleben, Professor Haeckel declares his continued adherence to a belief in what the school of Weismann so strenuously deny; and Haeckel’s discussion of the subject is heartily to be recommended to the student, for, though the veteran evolutionist of Jena is not above resort to indecency in theological controversy, and is merely ridiculous as a philosopher, he certainly disputes with Weismann the honor of being the greatest living biologist, and he has been fighting the battle for organic evolution ever since 1866.

Professor Haeckel adduces, in the book named, an unquestionable instance of the transmission of acquired characters. Every one knows that when pathogenic or disease-producing bacteria are passed through the body of a highly susceptible animal, they become possessed of a much greater degree of virulence than formerly. More accurately stated, this resolves itself into the assertion that the progeny of such bacteria, often after tens or hundreds of generations, are possessed of a character which was acquired by their ancestors during their passage through the body of the susceptible animal. This is as clear a case of the transmission of acquired characters as any one can ask for. It does not follow from this that all acquired character, in one of the higher animals or plants, can be transmitted; but it is something to have an instance, familiar and indisputable, which cannot be reconciled with the dogma of Weismann.

Certain acquired characters cannot be conceived to affect the germ-cells of an individual of one of the higher types. These cells are certainly not, as Darwin supposed, formed by pangenesis—that is to say, by contribution of representative units from all the cells of the body. On the contrary, we are now compelled to believe, with Weismann, in the doctrine of the “continuity of the germ-plasm”, which asserts that the original cell from which any individual is formed divides into two portions, one of which becomes the individual and the other his own germ-cells. If this be true, acquired characters can be transmitted only when they can influence the, germ-cells through the blood­stream. Certain characters, such as immunity to disease, may conceivably be thus transmitted, but there is no room for belief in the transmission of such an acquired character as baldness, any more than of such characters as dust-laden finger­nails or acquired ideas.

Turn we now to the factor of organic evolution which is known as natural selection or the survival of the fittest. The history of this idea has already been alluded to, in relation to atoms, societies, and living species. For a further discussion of it the reader may be referred to the historical sketch prefixed to the later editions of the Origin of Species. But though Darwin was preceded by other thinkers, in biology and other realms, in the enunciation of this idea, and though the famous paper read before the Linniean Society in 1858 was the joint product of Darwin and Mr. Alfred Russel Wallace, yet it is beyond all question the name of Charles Robert Darwin, the greatest biologist of any age, that will ever and rightly be associated with this idea. Others had enunciated it, but he alone demonstrated its truth. We learn from an early letter that he began to collect facts bearing on the question of the origin of species nearly twenty years before his masterpiece saw the light; and his great labors did not cease for more than twenty years thereafter. The idea of organic evolution had been hinted at, or definitely supported, by his grandfather, by Lamarck and Goethe and Spencer and Robert Chambers, but it was not until the factor of natural selection was demonstrated by Darwin that the doctrine of special creation received its death-blow. The average man, and even the professed biologist, had not the mental fervor of Spencer, who renounced the old doctrine in 1840, when he was still an infant in the eyes of the law, and who was destined to spend many hours in trying to convince Huxley of the truth of organic evolution. Spencer accepted it at this early date not because he was unaware of the difficulties in the way, but because he saw that there was no choice save between special creation and evolution, and because he recognized the old dogma as really a “pseud-idea”, in the last resort “unthinkable”.

But our business here is to inquire into the status of the idea of natural selection today, nearly half a century after Darwin’s enunciation of it. It is but eleven years since the late Marquis of Salisbury, in his notorious Presidential Address delivered before the British Association at its Oxford meeting in 1894, declared that “no one had seen natural selection at work”. Since then, however, we have seen natural selection at work in more than one instance. There is abundance of experimental evidence to support the retort of Herbert Spencer that the opposite of the survival of the fittest-viz., the survival of the unfittest, is inconceivable.

It is impossible in a work of this scope to treat all details in such complete fashion as one might desire; and it is necessary, therefore, to refer the reader to a volume by an expert which will suffice to convince him that, in such instances as the shore-crabs near Plymouth Sound and the English sparrow introduced into North America, the action of natural selection has been demonstrated. For this purpose the reader should consult Variation in Animals and Plants, by Dr. H. M. Vernon, of Oxford.

We may take it, then, distinguished amateurs notwithstanding, that natural selection, or the survival of the fittest, is a fact. We shall necessarily recur to it when we come to consider the ethics and the ethical forecast of the evolution theory. Meanwhile we must briefly note the conditions upon which its action depends; the primal conditions of heredity and variation being, of course, taken for granted.

Natural selection is not an inevitable and constant factor in the course of animal and vegetable life. The popular fallacy that progress is an invariable law of nature appears to depend upon the idea that natural selection is always and necessarily in operation. But its existence was suggested both to Darwin and Wallace, by consideration of a special case. This is the case discussed by Malthus in his famous essay on population, published in 1798. Malthus discussed the consequences of an increase of population in geometrical progression while the necessaries of life increased only in arithmetical progression. In other words, he discussed the case of what Wallace calls the “struggle for existence”. If the means of subsistence be superabundant, natural selection can scarcely operate. It depends for any considerable sphere of action upon the occurrence of a struggle for existence. Given such a struggle, it stands to reason that the fittest must survive. That there be no struggle may perhaps be conceived as the happiest, the ideal, state of affairs; but given a struggle, it follows that the law of natural selection is a beneficent one, as Darwin clearly showed. Unfortunately, these considerations, very imperfectly thought out and uncorrected by any others, have led such writers as Nietzsche and his followers to assume that might is right, and that science has demonstrated the uprightness and expediency of the doctrine “Each man for himself, and the devil take the hindmost”. In a subsequent chapter it will be shown how imperfectly and rudely the Nietzschean doctrine is in correspondence with the facts.

On that factor of organic evolution which Darwin discerned and named sexual selection we need not dwell here; or, at any rate, we need not recount the main theses of the Descent of Man, for that work, like its predecessor, may now he purchased for a sum so small that no one who affects an interest in the science of life can confess that he does not possess a copy of it.

My purpose, in this as in other instances, is to show that recent study has confirmed the beliefs of the evolutionists. Darwin himself, after much consideration, said, “I still strongly think . . . that sexual selection has been the main agent in forming the races of man.” The Darwinian idea is based partly on the conception of struggle, partly on the conception of taste. Males with certain advantages, such as fleetness and strength, would tend to leave more offspring than their rivals; while the taste of the females would choose certain males rather than others, and so would tend to perpetuate and accentuate certain characters. The male beard, for instance, is a “secondary sexual character” so produced.

This idea of sexual selection has lately undergone a most interesting development at the hands of Professor Karl Pearson (The grammar of science) and his followers. Professor Pearson distinguishes two kinds of sexual selection. The first, which Darwin discussed, is based on the conception of taste and may be called preferential mating. It probably exists in human society at the present day, but great difficulties are encountered in the attempt to measure it. The second kind of sexual selection may be called assortative mating. It depends on the fact that like tends to mate with like. This principle of homogamy may indeed turn out to be that “unknown factor” in organic evolution which many have declared to be the operation of design on the part of a Creator. Homogamy may indeed have been a necessary factor in the isolation of species as we know them today.

In its widest sense, homogamy is, of course, an obvious fact. The bird does not mate with the mammal, nor the reptile with the insect. Furthermore, the dog does not mate save with the dog, nor the sparrow with any bird not of its own kind. These are obvious illustrations of that kind of sexual selection which Professor Pearson calls assortative mating. But what he has discovered is the extension of this principle to mating within the limits of the species; or, at any rate, he has shown it in the case of man.

Professor Pearson and his coworker, Professor Weldon, have made a most exhaustive research upon human marriage from this point of view, by studying, for instance, the tombstones of rural Oxfordshire, the dales of Yorkshire, and the London cemeteries; and by inquiries into pedigrees, such as those furnished by the Society of Friends. These, studies have given them material for estimating the extent to which people of strong constitutions marry their like and conversely, since longevity, as recorded on tombstones, may be taken as a criterion of general bodily vigor. In addition, thousands of married persons have been examined with regard to height, eye-color, and many other characters.

The biometricians have thus been able to show, by statistics analyzed and checked in a manner quite impossible for any but the trained mathematician and logician, that, for instance, a blue-eyed man is more likely than a brown-eyed one to marry a blue-eyed woman. People with a “strong constitution” (estimated as we have seen) tend to marry their like; short men tend to marry shorter women than do tall men and so forth, over as many characters as have hitherto been examined. Various possible fallacies have had to be excluded, such as the effect of resemblance among local races, and the effect of exposing husband and wife to the same environment; but the essence of biometry is that it seeks all possible explanations and then proceeds systematically to test them. After so doing, the conclusion in this instance is that “there is a real selection in marriage between husband and wife on the basis of general constitutional resemblance”.

Now if this be true of man, may we not reasonably expect homogamy to occur in lower forms of life? This may surely be expected, unless we agree with Darwin that sexual selection depends upon the existence of some considerable measure of aesthetic perception. There is reason to believe, however, that homogamy is not conscious and deliberate, depending upon an exercise od “taste”, but is unconscious and “instinctive”. Professor Pearson has been able to find record of only one research into this subject besides his own; but this is directed to an order of living creatures so remote from man that it perhaps justifies us in drawing an inference as to the existence of homogamy in intermediate orders of life. The research is that of Professor Raymond Pearl, of the University of Michigan, on the conjugation or mating of the Paramecium, a unicellular animal about one-hundredth of an inch in length, which no one would accuse of possessing high perceptive or asthetic powers. By making many thousands of careful measurements, Professor Pearl has been able to show that a paramecium of a given size tends to mate with another of the same size.

The general significance of these recent biometric studies is very wide indeed. It is plain that homogamy, if indeed, as is probable, it acts throughout the realm of animal life, must tend to split up races into endogamous groups, the individuals of which marry only within the group-limit, and which therefore tend to diverge more and more from each other in physical characters. Here I cannot doubt that we have a most important factor in organic evolution.

The factors of organic evolution hitherto named are adaptation with inheritance, natural selection, sexual selection, homogamy, and what De Vries calls mutation. Are any others yet to be discovered? The answer to this question depends on our estimate of the adequacy of these factors. Probably most biologists would say that they are completely adequate. There will long remain, however, critics who will attempt to show that these cannot be regarded as adequate for the production of the multitudinous species that exist today and have existed in time past, without aid from a principle of telesis, or design. One author succeeds another in the attempt to show that Darwinism is a half-truth, and that without a principle of “directivity” the facts cannot be explained. But as this belief depends upon an assumption of an anthropoid Deity, we may leave it to stand or fall therewith.