In all our study we have taken for granted the truth of the theory of evolution. If you are not already persuaded of this by the writings of Darwin, Wallace, and many others, no words or arguments of mine would convince you. We have used as the foundation of our argument only the fundamental propositions of Mr. Darwin’s theory.

But while all evolutionists accept these propositions they differ more or less in the weight or efficiency which they assign to each. In a sum in multiplication you may gain the same product by using different factors; but if the product is to be constant, if you halve one factor, you must double another. Evolution is a product of many factors. One evolutionist lays more, another less, emphasis on natural selection, according as he assigns less or more efficiency to other forces or processes. Furthermore, evolutionists differ widely in questions of detail, and some of these subsidiary questions are of great practical importance and interest. It may be useful, therefore, to review these propositions in the light of the facts which we have gathered, and to see how they are interpreted, and what emphasis is laid on each by different thinkers.

The fundamental fact on which Mr. Darwin’s theory rests is the “struggle for existence.” Life is not something to be idly enjoyed, but a prize to be won; the world is not a play-ground, but an arena. And the severity of the struggle can scarcely be overrated. Only one or two of a host of runners reach the goal, the others die along the course. Concerning this there can be no doubt, and there is little room for difference of interpretation.

The struggle may take the form of a literal battle between two individuals, or of the individual with inclemency of climate or other destructive agents. More usually it is a competition, no more noticeable and no less real than that between merchants or manufacturers in the same line of trade.

The weeds in our gardens compete with the flowers for food, light, and place, and crowd them out unless prevented by man. And when the weeds alone remain, they crowd on each other until only a few of the hardiest and most vigorous survive. And flowers, by their nectar, color, and odor, compete for the visits of insects, which insure cross-fertilization. And fruits are frequently or usually the inducements by which plants compete for the aid of animals in the dissemination of their seeds. So there is everywhere competition and struggle; many fail and perish, few succeed and survive.

In a foot-race it is often very difficult to name the winner. Muscle alone does not win, not even good heart and lungs. Good judgment, patience, coolness, courage, many mental and moral qualities, are essential to the successful athlete. So in the struggle for life. The race is not always to the swift, nor the battle to the strong.

The total of “points” which wins this “grand prize” is the aggregate of many items, some of which appear to us very insignificant. Hence, when we ask, “Who will survive?” the answer is necessarily vague. Mr. Darwin’s answer is, Those best conformed to their environment; and Mr. Spencer’s statement of the survival of the fittest means the same thing.

The judges who pronounce and execute the verdict of death, or award the prize of life, are the forces and conditions of environment. We have already considered the meaning of this word. Many of its forces and conditions are still unknown, or but very imperfectly understood. But known or unknown, visible or invisible, the result of their united action is the extinction or degradation of these individuals which deviate from certain fairly well-marked lines of development. We must keep clearly before our minds the fact that the world of living beings makes up by far the most important part of the environment of any individual plant or animal. Two plants may be equally well suited to the soil and climate of any region; but if one have a scanty development of root or leaf, or is for any reason more liable to attacks from insects or germs, other things being equal, it will in time be crowded out by its competitor. Worms are eaten by lower vertebrates, and these by higher. An animal’s environment, like that of a merchant or manufacturer, is very largely a matter of the ability and methods of its competitors. And man, compelled to live in society, makes that part of the environment by which he is most largely moulded.

This process of extinction Mr. Darwin has called “natural selection.” Natural selection is not a force, but a process, resulting from the combined action of the forces of environment. It is not a cause in any proper sense of the word, but a result of a myriad of interacting forces. The combination of these forces in a process of natural selection leading directly to a moral and spiritual goal demands an explanation in some ultimate cause. This explanation we have already tried to find.

It is a process of extinction. It favors the fittest, but only by leaving them to enjoy the food and place formerly claimed, or still furnished, by the less fit. In any advancing group, as the less fit are crowded out, and the better fitted gain more place and food and more rapid increase, the whole species becomes on an average better conformed. More abundant nourishment and increased vigor seem also to be accompanied by increased variation. And by the extinction of the less fit the probability is increased that more fit individuals will pair with one another and give rise to even fitter offspring, possessing perhaps new and still more valuable variations.

But if, of a group of weaker forms, those alone survive which adopt a parasitic life, those which in adult life move the least will survive and reproduce; there will result the survival of the least muscular and nervous. This degeneration will continue until the species has sunken into equilibrium, so to speak, with its surroundings. Here natural selection works for degeneration. Sessile animals have had a similar history. But these parasitic and sessile forms had already been hopelessly distanced in the race for life. Their presence cannot impede the leaders; indeed their survival is necessary to directly or indirectly furnish food for the better conformed. In the animal and plant world there is abundant room and advantage at the top.

Once more, natural selection works as a rule for the survival of individuals, only indirectly for that of organs composing, or of species including, these individuals. It may work for the development of a trait or structure which, while of no immediate advantage to the individual, increases the probability of its rearing a larger number of fitter offspring. Thus defence of the young by birds may be a disadvantage to the parent, but this is more than counterbalanced in the life of the species by the number of young coming to maturity and inheriting the trait. Even here natural selection favors the survival of the trait indirectly by sparing the descendants of the individual possessing it. Natural selection may always work on and through individuals without always working for their sole and selfish advantage.

In human society we find the selection of families, societies, nations, and civilizations going on, but mainly as the result of the survival of the fittest individuals.

There may very probably be a struggle for existence between organs or cells in the body of each individual. The amount of nutriment in the body is a more or less fixed quantity; and if one organ seizes more than its fair share, others may or must diminish for lack. But the limit to this usurpation must apparently be set by the crowding out of those individuals in which it is carried too far. Natural selection, so to speak, leaves the individual responsible for the distribution of the nutriment among the organs, and spares or destroys the individual as this usurpation proves for its advantage or disadvantage.

It makes its verdict much as the judges at a great poultry or dog show count the series of points, giving each one of them a certain value on a certain scale, and then award the prize to the individual having the highest aggregate on the whole series. Any such illustration is very liable to mislead; I wish to emphasize that fitness to survive is determined by the aggregate of the qualities of an individual.

But an animal having one organ of great value or capacity may thus carry off the prize, even though its other organs deserve a much lower mark. This is the case with man. In almost every respect, except in brain and hand, he is surpassed by the carnivora, the cat, for example. But muscle may be marked, in making up the aggregate, on a scale of 500, and brain on a scale of 5,000, or perhaps of 50,000. A very slight difference in brain capacity outweighs a great superiority in muscle in the struggle between man and the carnivora, or between man and man.

The scale on which an organ is marked will be proportional to its usefulness under the conditions given at a given time. During the period of development of worms and lower vertebrates much muscle with a little brain was more useful than more brain with less muscle. Hence, as a rule, the more muscular survived; the brain increasing slowly, at first apparently largely because of its correlation with muscle and sense-organs. At a later date muscle, tooth, and claw were more useful on the ground; brain and hand in the trees. Hence carnivora ruled the ground, and certain arboreal apes became continually more anthropoid. At a later date brain became more useful even on the ground, and was marked on a higher scale, because it could invent traps and weapons against which muscle was of little avail. Just at present brain is of use to, and valued by, a large portion of society in proportion to its efficiency in making and selfishly spending money. But slowly and surely it is becoming of use as an organ of thought, for the sake of the truth which it can discover and incarnate.

Natural selection works thus apparently for the survival of the individuals possessing in the aggregate the most complete conformity to environment. Let us now imagine that an animal is so constructed as to be capable of variation along several disadvantageous or neutral lines, and along only one which is advantageous. The development would of course proceed along the advantageous line. Let us farther imagine that to the descendants of this individual two, and only two, advantageous lines of variations are allowed by its structure. Then natural selection would probably favor the decidedly advantageous line, if such there were. But as long as the structure of the animal allows variation along only a few lines, the two advantageous variations would, according to the law of probabilities, frequently occur in the same individual. The eggs and spermatozoa of two such individuals might not infrequently unite, and thus in time the two characteristics be inherited by a large fraction of the species.

And now let me quote from Mr. Spencer:

“But in proportion as the life grows complex in proportion as a healthy existence cannot be secured by a large endowment of some one power, but demands many powers; in the same proportion do there arise obstacles to the increase of any particular power, by ‘the preservation of favored races in the struggle for life.’ As fast as the faculties are multiplied, so fast does it become possible for the several members of a species to have various kinds of superiorities over one another. While one saves its life by higher speed, another does the like by clearer vision, another by keener scent, another by quicker hearing, another by greater strength, another by unusual power of enduring cold or hunger, another by special sagacity, another by special timidity, another by special courage; and others by other bodily and mental attributes. Now it is unquestionably true that, other things equal, each of these attributes, giving its possessor an extra chance of life, is likely to be transmitted to posterity. But there seems no reason to suppose that it will be increased in subsequent generations by natural selection. That it may be thus increased, the individuals not possessing more than average endowments of it must be more frequently killed off than individuals highly endowed with it; and this can happen only when the attribute is one of greater importance, for the time being, than most of the other attributes. If those members of the species which have but ordinary shares of it, nevertheless survive by virtue of other superiorities which they severally possess, then it is not easy to see how this particular attribute can be developed by natural selection in subsequent generations. The probability seems rather to be that, by gamogenesis, this extra endowment will, on the average, be diminished in posterity just serving in the long run to compensate the deficient endowments of other individuals whose special powers lie in other directions, and so to keep up the normal structure of the species. The working out of the process is here somewhat difficult to follow; but it appears to me that as fast as the number of bodily and mental faculties increases, and as fast as the maintenance of life comes to depend less on the amount of any one, and more on the combined action of all, so fast does the production of specialties of character by natural selection alone become difficult. Particularly does this seem to be so with a species so multitudinous in its powers as mankind, and above all does it seem to be so with such of the human powers as have but minor shares in aiding the struggle for life the aesthetic faculties for example.” Spencer, “Principles of Biology,” se.

Can thus natural selection, acting upon fortuitous variations, be the sole guiding process concerned in progress? Must there not be some combining power to produce the higher individuals which are prerequisites to the working of natural selection?

We are considering the efficiency of natural selection in enhancing useful variations through a series of generations. Let us return to the distinction between productiveness and prospectiveness of social capital. Applied to variations productiveness means immediate advantage, prospectiveness the greater future and permanent returns. Now all persisting variations must, in animals below man, apparently be somewhat productive, else they would not continue, much less increase. Now the immediate return from prospective variations is often smaller than from productive. It looks at first as if productive variations would always be preserved by natural selection, and that prospective variations would not long advance. Yet in the muscular system variations valuable largely for their future value are neither few nor unimportant. How can the brain in its infancy develop until it gains supremacy over muscle, or muscle have done the same with digestion? Now a partial explanation of this is to be found in the correlation of organs. This is therefore a factor of vast importance in progress through evolution.

Progress in any one line demands correlated changes in many organs. Thus in the advance of annelids to insects the muscular system increases in relative bulk, and absolutely in complexity. But a change or increase in the muscle must be accompanied by corresponding changes in the motor-nerve fibrils; and these again would be useless unless accompanied by increased complexity and more or less readjustment of the cells and fibrils of the nerve-centres. And all these additions to, and readjustments of, the nerve-centres must take place without any disturbance of the other necessary adjustments already attained. This is no simple problem.

We will here neglect the fact that many other changes are going on simultaneously. Legs are being formed or moulded into jaws, the anterior segments are fusing into a head, and their ganglia into a brain; an external skeleton is developing. Furthermore the increase of the muscular and nervous systems must be accompanied by increased powers of digestion, respiration, and excretion. Practically the whole body is being recast. We insist only on the necessity of simultaneous and parallel changes in muscles, nerves, and nerve-centres; though what is true of these is true, in greater or less degree, of all the other organs.

You may answer that this is to be explained by the law of correlation of organs; that when changes in one organ demand corresponding changes in another, these two change similarly and more or less at the same time and rate. But this is evidently not an explanation but a restatement of the fact. The question remains, What makes the organs vary simultaneously so as to always correspond to each other? The whole series of changes must to some extent be effected at once and in the same individual, if it is to be preserved by natural selection. Fortuitous variations here and there along the line of the series are of little or no avail. That the whole series of variations should happen to occur in one animal is altogether against the law of probabilities; if the favorable variation occurs in only a part of the series it remains useless until the corresponding variation has taken place in the other terms. And while the variation is thus awaiting its completion, so to speak, it is useless, and cannot be fostered by natural selection.

Evolution by means of fortuitous variations, combined and controlled only through natural selection, seems to me at least impossible; and this view is, I think, steadily gaining ground.

Natural selection, while a real and very important factor in evolution, cannot be its sole and exclusive explanation. It presupposes other factors, which we as yet but dimly perceive. And this does not impeach the validity of Mr. Darwin’s theory any more than Newton’s theory of gravitation is impeached by the fact that it offers no explanation as to why the apple falls or how bodies attract one another.

For natural selection explains the survival, but not the origin, of the fittest. Given a species or other group composed of more and less fit individuals and the fittest will survive. How does it come about that there are any more and less fit individuals? This brings us to the consideration of the subject of variation.

Let us begin with a simple case of change in the adult body. The workman grasps his tools day after day, and his hands become horny. The skin has evidently thickened, somewhat as on the soles of the feet. This is no mere mechanical result of pressure alone. Continuous pressure would produce the opposite result. But under the stimulus of intermittent pressure the capillaries, or smallest blood vessels, furnish more nutriment to the cells composing the lowest layer of the outer skin or epidermis. These cells, being better nourished, reproduce by division more rapidly, and the epidermis, becoming composed of a greater number of layers of cells, thickens. The outer-most layers, being farthest from the blood supply, dry up and are packed together into a horny mass.

If I go out into the sunshine I become tanned. This again is not a direct and purely chemical or physical result of the sun’s rays, but these have stimulated the cells of the skin to undergo certain modifications. Any change in the living body under changed conditions is not passive, but an active reaction to a stimulus furnished by the surroundings. The same stimulus may excite very different reactions in different individuals or species.

Early in this century a farmer, Seth Wright, found among his lambs a young ram with short legs and long body. The farmer kept the ram, reasoning that his short legs would prevent him from leading the flock over the farm-walls and fences. From this ram was descended the breed of ancon, or otter, sheep. Now the stimulus which had excited this variation must have been applied early in embryonic life, or perhaps during the formation or maturing of the germ-cells themselves. Such a variation we call a congenital variation.

These cases are merely illustrations of the general truth that in every variation there are two factors concerned: the living being with its constitution and inherent tendencies and the external stimulus.

The courses of the different balls in a charge of grape-shot, hurled from a cannon, are evidently due to two sets of forces 1, their initial energy and the direction of their aim; 2, the deflecting power of resisting objects or forces or the different balls might roll with great velocity down a precipitous mountain-side. In the first case velocity and direction of course would be determined largely by initial impulse; in the second, by the attraction of the earth and by the inequalities of its surface.

In evolution, environment, roughly speaking, corresponds to these deflecting or attracting external objects or forces; inherent tendencies to initial impulse. If we lay great weight on initial tendencies, inherent in protoplasm from the very beginning, we shall probably lay less stress on natural selection as a guiding, directing process.

The great botanist, Naegeli, has propounded a most ingenious and elaborate theory of evolution, as dependent mainly on inherent initial tendency. We can notice only one or two of its salient points. All development is, according to his view, due to a tendency in the primitive living substance toward more complete division of labor and greater complexity. This tendency, which he calls progression, or the tendency toward perfection, is the result of the chemical and molecular structure of the formative controlling protoplasm (idioplasm) of the body, and is transmitted with other parental traits from generation to generation. And structural complexity thus increases like money at compound interest. Development is a process of unfolding or of realization of the possibilities of this tendency under the stimulus of surrounding influences. Environment plays an essential part in his system. But only such changes are transmissible to future generations as have resulted from modifications arising in the idioplasm. Descendants of plants which have varied under changed conditions revert, as a rule, to the old type, when returned to the old surroundings. And in the animal world effects of use and disuse are, according to his view, not transmissible.

Natural selection plays a very subordinate part. It is purely destructive. Given an infinity of place and nourishment do away, that is, with all struggle and selection and the living world would have advanced, purely by the force of the progressive tendency, just as far as it now has; only there would have survived an indefinite number of intermediate forms. It would have differed from our present living world as the milky way does from the starry firmament.

He compares the plant kingdom to a great, luxurious tree, branching from its very base, whose twigs would represent the present stage of our different species. Left to itself it would put out a chaos of innumerable branches. Natural selection, like a gardener, prunes the tree into shape. Children might imagine that the gardener caused the growth; but the tree would have been broader and have branched more luxuriantly if left to itself.

Every species must vary perpetually. Now this proposition is apparently not in accord with fact; for some have remained unchanged during immense periods. And natural selection, by removing the less fit, certainly appears to contribute to progress by raising the average of the species. The theory seems extreme and one-sided. And yet it has done great service by calling in question the all-sufficiency of natural selection and the modifying power of environment, and by emphasizing, probably overmuch, the importance of initial inherent tendency, whose value has been entirely neglected by many evolutionists.

Lack of space compels us to leave unnoticed most of the exceedingly valuable suggestions of Naegeli’s brilliant work.

It is still less possible to do any justice in a few words to Weismann’s theory. Into its various modifications, as it has grown from year to year, we have no time to enter. And we must confine ourselves to his views of variation and heredity.

In studying protozoa we noticed that they reproduced by fission, each adult individual dividing into two young ones. There is therefore no old parent left to die. Natural death does not occur here, only death by violence or unfavorable conditions. The protozoa are immortal, not in the sense of the endless persistence of the individual, but of the absence of death. Heredity is here easily comprehensible, for one-half, or less frequently a smaller fraction, of the substance of the parent goes to form the new individual. There is direct continuity of substance from generation to generation.

But in volvox a change has taken place. The fertilized egg-cell, formed by the union of egg and spermatozoon, is a single cell, like the individual resulting from the conjugation or fusion of two protozoa. But in the many-celled individual, which develops out of the fertilized egg, there are two kinds of cell. There are other egg-cells, like the first, each one of which can, under favorable conditions, develop into a multicellular individual like the parent. And the germ-cells (eggs and spermatozoa) of volvox are immortal like the protozoa. But, 2, there are nutritive, somatic cells, which nourish and transport the germ-cells, and after their discharge die. These somatic cells, being mortal, differ altogether from the germ-cells and the protozoa. The protoplasm must differ in chemical, or molecular, or other structure in the two cases, and we distinguish the germ-plasm of the germ-cells, resembling in certain respects Naegeli’s idioplasm, from somatoplasm, which performs most of the functions of the cell. The somatoplasm arises from, and hence must be regarded as a modification of, the germ-plasm. The germ-plasm can increase indefinitely in the lapse of generations, increase of the somatoplasm is limited.

When a new individual develops, a certain portion of the germ-plasm of the egg is set aside and remains unchanged in structure. This, increasing in quantity, forms the reproductive elements for the next generation. The germ-plasm, which does not form the whole of each reproductive element, but only a part of the nucleus, is thus an exceedingly stable substance. And there is a just as real continuity of germ-plasm through successive generations of volvox, or of any higher plants or animals, as in successive generations of protozoa.

In certain plants there is an underground stem or rootstock, which grows perennially, and each year produces a plant from a bud at its end. This underground rootstock would represent the continuous germ-plasm of successive generations; the plants which yearly arise from it would represent the successive generations of adult individuals, composed mainly of somatoplasm. Or we may imagine a long chain, with a pendant attached to each tenth or one-hundredth link. The links of the chain would represent the series of generations of germ-cells; the pendants, the adults of successive generations.

But any leaf of begonia can be made to develop into a new plant, giving rise to germ-cells. Here there must be scattered through the leaves of the plant small portions of germ-plasm, which generally remain dormant, and only under special conditions increase and give rise to germ-cells.

A large part of the germ-plasm of the fertilized egg is used to give rise to the somatoplasm composing the different systems of the embryo and adult. Weismann’s explanation of this change of germ-plasm into somatoplasm is very ingenious, and depends upon his theory of the structure of the germ-plasm; and this latter theory forms the basis of his theory of evolution. It would take too long to state his theory of the structure of germ-plasm, but an illustration may present fairly clear all that is of special importance to us.

The molecules of germ-plasm are grouped in units, and these in an ascending series of units of continually increasing complexity, until at last we find the highest unit represented in the nucleus of the germ-cell. This grouping of molecules in units of increasing complexity is like the grouping of the men of an army in companies, regiments, brigades, divisions, etc.

To form the somatoplasm of the different tissues of the body, this complicated organization breaks up, as the egg divides, into an ever-increasing number of cells. First, so to speak, the corps separate to preside over the formation of different body regions. Then the different divisions, brigades, and regiments, composing each next higher unit, separate, being detailed to form ever smaller portions of the body. The process of changing germ-plasm into somatoplasm is one of disintegration. The germ-plasm contains representatives of the whole army; a somatic cell only representatives of one special arm of a special training. Germ-plasm in the egg is like Humpty-Dumpty on the wall; somatoplasm, like Humpty-Dumpty after his great fall.

I use these rude illustrations to make clear one point: Germ-plasm can easily change into somatoplasm, but somatoplasm once formed can never be reconverted into germ-plasm, any more than the fallen hero of the nursery rhyme could ever be restored.

The germ-plasm is, according to Weismann, a very peculiar, complex, stable substance, continuous from generation to generation since the first appearance of life on the globe. It is in the body of the parent, but scarcely of it. Its relation to the body is like that of a plant to the soil or of a parasite to its host. It receives from the body practically only transport and nourishment. It is like a self-perpetuating, close corporation; and the somatoplasm has no means of either controlling it or of gaining representation in it.

Says Weismann: “The germ-cells are contained in the organism, and the external influences which affect them are intimately connected with the state of the organism in which they lie hid. If it be well nourished, the germ-cells will have abundant nutriment; and, conversely, if it be weak and sickly, the germ-cells will be arrested in their growth. It is even possible that the effects of these influences may be more specialized; that is to say, they may act only upon certain parts of the germ-cells. But this is indeed very different from believing that the changes of the organism which result from external stimuli can be transmitted to the germ-cells and will redevelop in the next generation at the same time as that at which they arose in the parent, and in the same part of the organism.”

But if the germ-plasm has this constitution and relation to the rest of the body, how is any variation possible? Different individuals of any species have slightly different congenital tendencies. Hence in the act of fertilization two germ-plasms of slightly different structure and tendency are mingled. The mingling of the two produces a germ-plasm and individual differing from both of the parents. Thus, according to Weismann’s earlier view, the origin of variation was to be sought in sexual reproduction through the mingling of slightly different germ-plasms.

But how did these two germ-plasms come to be different? How was the variation started? To explain this Weismann went back to the unicellular protozoa. These animals are undoubtedly influenced by environment and vary under its stimuli. Here the variations were stamped upon the germ-plasm, and the commingling of these variously stamped germ-plasms has resulted in all the variations of higher animals.

Of late Weismann has modified and greatly improved this portion of his theory. He now accepts the view that external influences may act upon the germ-plasm not only in protozoa but also in all higher animals. Variation is thus due to the action or stimulus of external influences, supplemented by sexual reproduction.

But the very constitution of the germ-plasm and its relation to the body absolutely forbids the transmission of acquired somatic characteristics and of the special effects of use and disuse. Muscular activity promotes general health, and might thus conduce to better-nourished germ-cells and to more vigorous and therefore athletic descendants. The exercise of the muscles might possibly cause such a condition of the blood that the portion of the germ-plasm representing the muscular system of the next generation might be especially nourished or stimulated. Thus an athletic parent might produce more athletic children.

But let us imagine twin brothers of equal muscular development. One from childhood on exercises the lower half of his body; the other, the upper. Both take the same amount of exercise, and have perhaps equal muscular development, but located in different halves of the body. Now it is hard to conceive that it can make any difference in the nourishing or stimulating influence of the blood, whether the muscular activity resides in one half of the body or the other. The children might be exactly alike.

One man drives the pen, a second plays the piano, and a third wields a light hammer. All three use different muscles of the hand and arm. How can this use of special muscles stamp itself upon the germ-cells in such a way that the offspring will have these special muscles enlarged? Granting that external influences of environment and bodily condition may effect the germ-cells; granting even that some of the most general effects of use and disuse might be transmitted, what warrant have we for believing that the special acquired characteristic can be transmitted? Weismann answers, None at all. The somatoplasm can only in the most general way affect the self-perpetuating, close corporation of the germ-plasm.

There is thus, according to Weismann, nothing to direct variation to certain organs, or to guide and combine the variations of these organs along certain lines, except natural selection. To a certain extent variation may be limited by the very structure of the animal. But within these limits there are wide ranges where one variation is apparently just as likely to occur as another.

Within these wide limits variation appears to be fortuitous. Natural selection must wait until the individuals appear in which these variations occur already correlated, and then seize upon these individuals. It is apparently the only guiding, directing force. Linear variation, that is, a variation advancing continuously along one or very few straight lines, would appear to be impossible.

In Naegeli’s theory initial tendency is overwhelmingly dominant; in Weismann’s, natural selection is almighty.

Weismann’s followers have received the name of Neo-Darwinians. The so-called Neo-Lamarckian school believes in the transmissibility of acquired characteristics, and of at least particular effects of use and disuse. The one theory is neither more nor less Darwinian than the other. For while Darwin emphasized natural selection, he accepted to a certain extent the transmission of special effects of use and disuse.

A special theory of heredity, pangenesis, has been accepted by many of the Neo-Lamarckian school. The theory of pangenesis, as propounded by Mr. Darwin, may be very briefly stated as follows: The cells in all parts of the body are continually throwing off germinal particles, or “gemmules.” These become scattered through the body, grow, and multiply by division. On account of mutual attraction they unite in the reproductive glands to form eggs or spermatozoa. The germ-cells are thus the bearers of heredity because they contain samples, so to speak, of all the organs of the body.

In heredity, according to Weismann’s theory, the egg is the centre of control, the continuous germ-plasm the source of all transmitted changes; according to Darwin’s theory, the body is the source, and the egg is derived in great part at least from it. If you put to the two the time-honored question, Which is first, the owl or the egg? Weismann would announce, with emphasis, The egg; Darwin would say, The owl. One proposition is the converse of the other, and most facts accord almost equally well with both theories.

In any family, devoted for generations to literary or artistic pursuits, the children show, as a rule, an aptitude for such pursuits not manifested by those of other families. According to the Neo-Lamarckian view, this inherited aptitude is to a certain extent the result of the constant exercise of these faculties through a series of generations. The active efforts and voluntary disposition of the parents have given an increased predisposition to the child. “Quite the reverse,” says Weismann, “the increase of an organ in the course of generations does not depend upon the summation of exercise taken during single lives, but upon the summation of more favorable predispositions in the germ.” “An organism cannot acquire anything unless it already possesses the predisposition to acquire it."

We may accept or deny this last statement, but it is evident that facts like these, and indeed the origin of most or all characteristics involving use or disuse, may be explained almost equally well by either theory.

But as far as the transmission of effects of somatic changes is concerned, if protozoa undergo special modifications under the influence of external conditions, will not the germ-cells undergo special modification under the influence of changes in the somatoplasm which forms their immediate environment? We must never forget the close relationship between all the cells of the body, and how slight a change in the body or its surroundings may conduce to sterility or fertility. Such isolation and independence in the body, on the part of the germ-cells, is opposed to all that we know of the organic unity of the body, whose cells have arisen by the differentiation of, and division of labor between, cells primitively alike. The facts of bud-variation, of changes in the parent stock due to grafting, and others, of which Mr. Darwin has given a summary in the eleventh chapter of the first volume of his “Plants and Animals under Domestication,” have never been adequately explained by Weismann in accordance with his theory. He has perhaps succeeded in parrying their force by showing that some such explanation is conceivable; they still point strongly against him.

Wilson has good reason for his “steadily growing conviction that the cell is not a self-regulating mechanism in itself, that no cell is isolated, and that Weismann’s fundamental proposition is false.”

But, granting the force of these criticisms, the question still remains, Is the special effect of use or disuse transmissible? Would the blacksmith’s son have a stronger right arm?

1. The isolation and independence of the germ-cells, which Weismann postulates as opposing this, can hardly be as great as he think. It is in his view impossible to conceive how these acquired characteristics can in any way reach and affect the germ-cells in such a manner as to reappear in the next generatio. All variations can be explained by his own theory without such transmission. Why then believe that acquired characteristics can in some inconceivable way affect the germ-cells so as to reappear in the next generation, as long as all the facts can be explained in a more simple and easily conceivable manner?

As to his second argument, I would readily acknowledge that it is at present difficult or impossible for me to conceive how any cell can act upon another, except through the nutrient or other fluids which it can produce. But though I cannot conceive how one cell can affect another, I may be compelled to believe that it does so. And this Weismann readily acknowledges.

Driesch changed by pressure the relative position of the cells of a very young embryo, so that those which in a normal embryo would have produced one organ were now compelled, if used at all, to form quite a different one. And yet these displaced cells formed the organ required of cells normally occupying this new position, not the one for which they were normally intended. And the organ which they would have builded in a normal embryo was now formed by other cells transferred to their rightful place.

What made them thus change? Not change of substance or structure, for the slight pressure could hardly have modified this. Not change of nutriment. The only visible or easily conceivable change was in position relative to other cells of the embryo.

Let us in imagination simplify Driesch’s experiment, for the sake of gaining a clearer view of its meaning. In a certain embryo at an early stage are certain cells whose descendants should form the lining of the intestine and be used in the adult for digestion. A second set of cells should form muscle endowed mainly with contractility. When these two sets of cells, or some of them, exchange positions in the embryo, they exchange lines of development. The first set now form muscle, the second digestive tissue. The only change has been in their relative positions. Driesch maintains, therefore, that the goal of development in any embryonic cell is determined not by structure or nutriment but by position. And this would seem to be true of the cells of the earliest embryonic stages.

Certain other experiments point in the same direction. Cut a hydra into equal halves and each half will form a complete animal. The lower half forms a new top, with mouth and tentacles; the upper half, a new base. Cut the other hydra a hair’s-breadth farther up. The same layer of cells which in the first animal formed the lower exposed surface of the upper half now forms the upper exposed surface of the lower half. And with this change of position it has changed its line of development; it will now give rise to a new upper half, not a base as before. The same experiment can be tried on certain worms with similar results, only head and tail differ far more than top and base of hydra. Difference in the position of cells has made vast difference in their line of development. Now in both embryo and adult there must be some directing influence guiding these cells. What is it?

An army is more than a mob of individuals; it is individuals plus organization, discipline, authority. A republic is not square miles of territory and thousands or millions of inhabitants. It is these plus organization, central government. Webster claimed that the central government was, and had to be, before the states. The organism cannot exist without its parts; it has a very real existence in and through them. It can coerce them. The state may be an abstraction, but it is one against which it is usually fatal to rebel, and which can say to a citizen, Go and be hanged, and he straightway mounts the scaffold. Now these are analogies and prove nothing. But in so far as they throw light on the essential idea of an organism, they may aid us in gaining a right view of our “cell republic.”

Says Whitman in a very interesting article on the “Inadequacy of the Cell-Theory”: “That organization precedes cell-formation and regulates it, rather than the reverse, is a conclusion that forces itself upon us from many sides.” “The structure which we see in a cell-mosaic is something superadded to organization, not itself the foundation of organization. Comparative embryology reminds us at every turn that the organism dominates cell-formation, using for the same purpose one, several, or many cells, massing its material and directing its movements, and shaping its organs as if cells did not exist, or as if they existed only in complete subordination to its will, if I may so speak. The organization of the egg is carried forward to the adult as an unbroken physiological unity, or individuality, through all modifications and transformations.” And Wilson, Whitman, Hertwig, and others urge “that the organism as a whole controls the formative processes going on in each part” of the embryo. And many years ago Huxley wrote, “They (the cells) are no more the producers of the vital phenomena than the shells scattered along the sea-beach are the instruments by which the gravitative force of the moon acts upon the ocean. Like these, the cells mark only where the vital tides have been, and how they have acted."

“Interaction of cells” can help us but little. For how can neighboring cells direct others placed in a new position? The expression, if not positively misleading and untrue, is at the best only a restatement of fact. It certainly offers no explanation. Flood-tide is not due to the interaction of particles of water, though this may influence the form of the waves.

The centre of control is therefore not to be sought in individual cells, whether germ-cells or somatic, but in the organism. And it is the whole organism, one and indivisible, which controls in germ, embryo, and adult, in egg and owl. This individuality, or whatever you will call it, impresses itself upon developing somatic cells, moulding them into appropriate organs, and upon germ-cells in process of formation, moulding them so that they may continue its sway. The muscle, modified by use or disuse, is a better expression of the individuality of its possessor, and the same individuality moulds similarly and simultaneously the germ-cells. Both are different expressions or manifestations of the same individuality. Only slowly does the individuality mould the muscles and nerves of the adult body to its use. Still more slow may be the moulding of the still more refractory germ-plasm, if such there be. But the moulding process goes on parallel in the two cases.

But Weismann’s argument rests not merely upon any difficulty or impossibility of the transmissibility of acquired characteristics. His argument is rather that all facts can be better explained by his theory without postulating or accepting such transmission, cases of which have never been absolutely proven. But the question is not whether his theory offers a possible explanation of the facts, but whether it is the most probable explanation of all the facts. No one would deny, I think, that the continuity of the germ-plasm offers the best and most natural explanation of heredity; and that variations could be produced by the influence on the germ-plasm of external conditions seems entirely probable.

But when we consider the aggregation of these variations in a process of evolution, his theory seems unsatisfactory. We have already seen that what we commonly call a variation involves not one change, but a series of changes, each term of which is necessary. Muscle, nerve, and ganglion must all vary simultaneously and correspondingly. Correlation and combination are just as essential as variation. And evolution often demands the disappearance of less fit structures just as much as the advance of the fittest. Says Osborne, “It is misleading to base our theory of evolution and heredity solely upon entire organs; in the hand and foot we have numerous cases of muscles in close contiguity, one steadily developing, the other degenerating.” Weismann offers the explanation that “if the average amount of food which an animal can assimilate every day remains constant for a considerable time, it follows that a strong influx toward one organ must be accompanied by a drain upon others, and this tendency will increase, from generation to generation, in proportion to the development of the growing organ, which is favored by natural selection in its increased blood-supply, etc.; while the operation of natural selection has also determined the organ which can bear a corresponding loss without detriment to the organism as a whole."

Here again natural selection of individuals, not the diminished supply of nutriment, has to determine which of many muscles shall be poorly fed and which favored. But natural selection can favor special organs only indirectly through the individuals which possess such organs. Variation is fortuitous, and there is nothing, except natural selection, to combine or direct them. And, I think, we have already seen that any theory which neglects or excludes such directing and combining agencies must be unsatisfactory and inadequate. Weismann has promised us an explanation of correlation of variation in accordance with his theory; and if such an explanation can be made, it would remove one of the strongest objections. But for the present the objection has very great weight.

Furthermore, as Osborne has insisted, linear variations, or variations proceeding along certain single and well-marked lines, would seem inexplicable by, if not fatal to, Weismann’s theory. And yet Osborne, Cope, and others have shown that the teeth of mammals have developed steadily along well-marked lines. They have apparently not resulted at all by selection from a host of fortuitous variations.

Says Osborne in his “Cartwright Lectures": “It is evident that use and disuse characterize all the centres of evolution; that changes of structure are slowly following on changes of function or habit. In eight independent regions of evolution in the human body there are upward of twenty developing organs, upward of thirty degenerating organs.” Now this parallelism, through a long series of generations, between the evolution of organs, their advance or degeneration, and the use or disuse of these same organs, that is, of the habits of the individual, is certainly of great significance. It must have an explanation; and the most natural one would seem to be the transmission of the effects of use and disuse.

On the whole Osborne’s verdict would seem just: The Neo-Lamarckian theory fails to explain heredity, Weismann’s theory does not explain evolution. But, if the effects of use and disuse are transmitted, correlation of variation is to be expected. Muscle, nerve, and ganglion all vary in correlation because they are all used together and in like degree. Evolution and degeneration of muscles in hand and foot go on side by side, because some are used and some are disused. Centres of use and disuse must be centres of evolution. And there would be as many distinct centres of evolution in different parts of the body as there were centres of use and disuse. And between these centres there might be no correlation except that of use and disuse. Brain, muscles, and jaws would develop simultaneously in the ancestors of insects. And the effects of use and disuse, transmitted through a series of generations, would be cumulative. The species advances rapidly because all its members have in general the same habits; the same parts are advancing or degenerating, although at different rates, in all its individuals. An animal having an organ highly developed is far less likely to pair with one having a lower development of the same organ. The Neo-Lamarckian theory supplies thus what is lacking in the Neo-Darwinian.

In lower forms, like hydra, of simple structure and comparatively few possibilities of variation, natural selection is dominant. In higher forms, like vertebrates, and especially in man, it is of decidedly subordinate value as a promoter of evolution. For man, as we have seen, is a marvellously complex being. The great difficulty in his case is not so much to quickly gain new and favorable variations as to keep all the organs and powers of the body steadily advancing side by side. Natural selection has in man the important but subordinate position of the judge in a criminal court, to pronounce the death verdict on the hopeless and incorrigible.

Both Neo-Darwinians and Neo-Lamarckians have erred in being too exclusively mechanical in their theories. It is the main business of the scientific man to discover and study mechanisms. But he must remember that mechanism does not produce force, it only transmits it. If he maintains that he has nothing to do with anything outside of mechanism, that the invisible and imponderable force lies outside of his domain, he has handed over to metaphysics the fairest and richest portion of his realm. In our fear of being metaphysical we have swung to another extreme, and have lost sight of valuable truth which lay at the bottom of the old vitalistic theories. Cells, tissues, and organs are but channels along which the flood of life-force flows. Boveri has well said, “There is too much intelligence (Verstand) in nature for any purely mechanical theory to be possible.”

Each theory contains important truth. Naegeli’s view of the importance of initial tendencies, inherent in the original living substance, is too often undervalued. My own conviction, at least, is steadily strengthening that, without some such original tendency or aim, evolution would never have reached its present culmination in man. His error lies in emphasizing this factor too exclusively. The fundamental proposition of Weismann’s theory, that heredity is due to continuity of germ-plasm, seems to contain important truth. But we need not therefore accept his theory of a germ-plasm so isolated and independent as to be beyond control or influence by the habits of the body. The importance of use and disuse, and the transmissibility of their effects, would seem to supply a factor essential to evolution. Weismann has done good service in emphasizing the stability of the germ-plasm. Evolution is always slow, and, for that very reason, sure.

If these conclusions are correct, they have an important practical bearing. Struggle and effort are essential to progress. Not inborn talent alone, but the use which one makes of it, counts in evolution. The effects of use and disuse are cumulative. The hard-fought battle of past generations becomes an easy victory in the present, just because of the strength acquired and handed down from the past struggle. Persistent variation toward evil is in time weeded out by natural selection. And, while evil remains in the world, we are to lay up stores of strength for ourselves and our descendants by sturdily fighting it. But the effects of right living through a hundred generations are not overcome by the criminal life of one or two. Evil surroundings weigh more in producing criminals than heredity, and their children are not irreclaimable.

The struggles and victories of each one of us encourage the rest. There is, to borrow Mr. Huxley’s language, not only a survival of the fittest, but a fitting of as many as possible to survive. And in the midst of the hardest struggle there is the peace which comes from the assurance of a glorious triumph.