Cuvier, Haller and Leibnitz adopted substantially these views. The latter found them to support his opinion that everything was the result of growth from monads, and that there was no such thing in all nature as generation.

Such a theory was very simple, but it explained nothing except the bare production of offspring. It gave no clue to their endless variations, nor to the fact that they often resembled the father more than the mother. According to this theory the offspring should resemble the mother, as the complete individual is formed by her and should be in her image.

Leeuwenhock, one of the early microscopists, by the aid of his lenses, opened a new world to mankind, and discovered the sperm cells to be active, living, moving elements, and he gave a death-blow to the belief that the perfect organism exists in the ovum; but he went to the opposite extreme, and maintained that it exists in the male cell and that it is only fed and developed by the female. Even today we find in a vague way both these theories held by educated persons.

We are indebted to Harvey in the early part of the eighteenth century for advocating the view held by Aristotle, now known as _Epigenesis_, and combatting the view of growth from a miniature, but already perfectly formed animal, to a visible one. Epigenesis consists in the successive differentiation from the relatively h.o.m.ogeneous elements as found in the egg, to the complicated parts and structure as seen in the offspring.

According to Huxley, this work of Harvey alone would have ent.i.tled him to recognition as one of the founders of biological science, had he not immortalized himself as the discoverer of the circulation of the blood.

Not long after Harvey's publication, Casper Frederick Wolf established the theory of epigenesis upon a firm foundation, where it still remains.

The doctrine of _epigenesis_ has very much complicated the whole question of heredity. No wonder even so great a mind as that of Darwin exclaimed, "The whole subject is wonderful." How can an egg, which in structure is comparatively simple, an aggregation of cells, not one of which bears the slightest resemblance to any organ in the body, develop into the perfect individual? How can this egg, formed in special organs, develop other organs than those like the ones in which it was formed?

How can s.e.xual cells develop brain cells, with their wonderful modes of action?

We cannot explain the philosophy of heredity without being able to answer these questions; but difficult as is the problem, our biologists have made various attempts at an explanation. I cannot go over all the various speculations, but only those most intimately connected with the subject will be mentioned.

The first is Darwin's own attempt at an explanation by the theory of _pangenesis_, or genesis from every part. He saw the necessity of having in the s.e.xual cells some power or force to represent the other organs and functions of the body, else how could these organs be formed in the embryo? Pangenesis was supposed to be accomplished as follows: Every organ through its cells gives off _gemmules_. These are inconceivably small, too small for any microscopical vision; also inconceivably great in numbers, and with great power of growth and multiplication. They pa.s.s from the various organs in which they are formed to the special s.e.x organs for generating the s.e.xual cells; some of them are stored up as representatives of the various organs from which they have been given off. The consequence is that every egg has in it something from every organ in the body of both parents which is able, during gestation, to develop into that organ.

According to this theory, for instance, if no gemmules are given off from the brain, then no brain can be developed from the egg, and so of other organs. As in a representative government, all parts of the country send representatives to the capitol to do the bidding of the people, so every organ of the body sends representatives to the s.e.xual cells to form their respective organs; without them these organs would not be formed.

There are many objections to pangenesis, but they need not be named here. It occurred to Galton, whose studies in heredity have been more prolific of good than those of any other man, to test it by practical experiment. If these gemmules are circulating in the blood of animals before being stored up in the s.e.xual cells, by transfusing blood from one variety of any species to another it ought to affect the offspring of this other. For his test cases he chose eighteen silvergrey rabbits which breed true, and into their bodies he transfused the blood of other different varieties, in several cases replacing one-half of this fluid.

There were eighty-six offspring bred at once from these silvergrey rabbits, and all true silvergreys. The theory did not work. But if it did not work in practice, it certainly worked on the intellects of biologists everywhere, exactly what Darwin wished; it set them to thinking. It acted as a ferment, so to say, and brought forth a rich harvest in speculation if not in actual knowledge.[106:A]

CONTINUITY OF THE GERM-PLASM.--The only other theory which I shall mention is that of Weismann, which has been before the public for more than a decade, and it is safe to say it has produced a more profound impression upon biologists than all others. It has its basis in what he calls _continuity of the germ-plasm_. By the germ-plasm is meant that part of the germ cell containing all the chemical and physical properties, including the molecular structure, which enables it to become, under appropriate conditions, a new individual of the same species as the parents. In it lies hidden all the characteristics both of the species and of the future individual. In it lies all the phenomena of heredity. It is the product of the coalescence of the male and female elements requisite for reproduction. Only, however, in the nuclear substance is to be found the hereditary tendencies. Now, this germ-plasm is _continuous_, that is to say, it contains not only material from both parents, but from grandparents and greatgrandparents, and so on indefinitely. This germ-plasm is exceedingly minute in quant.i.ty, but has great power of growth. Not all is used up in the production of any individual, but some is left over and stored up for the next generation. The germ-plasm might be represented as a long creeping root, from which arise at intervals all the individuals of successive generations. The amount of ancestral germ-plasm in each fertilized ovum is calculated in the same way that stock breeders calculate the amount of blood of any ancestor running in any individual.

For instance: The germ-plasm contributed by the father and mother is each one-half; each grandparent one fourth, and so on. Ten generations back each ancestor contributes only one part in one thousand and twenty-four parts. This continuity has by some been called the immortality of the germ-plasm. Theoretically, the original Adam and Eve have contributed an infinitesimal part. This probably explains why there is so much of the original Adam in most of us. By it we are able to explain that wonderful fact of _atavism_, or the appearance of characters from a remote ancestor in offspring. Some of the germ-plasm from this ancestor by some means has had an opportunity to grow rapidly and contribute more than its share in the production of the individual in which it appears.

It also enables us to explain the fact that no two individuals are quite alike, but that there is constant variation. Each person is the product of a mult.i.tude of ancestors, and the germ-plasm which produced them is never mixed, in quite the same proportion, nor do the different parts grow with quite the same vigor.

It was on this theory of the continuity of the germ-plasm that Weismann built his doctrine of the non-transmission of acquired characters. On this subject he says: "Hence it follows that the transmission of acquired characters is an impossibility, for if the germ-plasm is not formed anew in each individual, but is derived from that which preceded it, its structure, and above all, its molecular const.i.tution, cannot depend upon the individual in which it happens to occur, but such an individual only forms, as it were, the nutritive soil at the expense of which it grows, while the latter possessed its character from the beginning, that is, before the commencement of growth." Of this, however, I will speak later.

A RATIONAL VIEW OF HEREDITY.--I might continue giving other theories of heredity--Haeckel's, for instance--or the metaphysical theory, but it is hardly necessary. I do not accept in full any of them. Their authors, it seems to me, have not worked along the lines of evolution, but have gone further than was necessary into the fields of speculation. Darwin, in his theory of Pangenesis, admitted this frankly, and yet he clung to the idea with great tenacity. If we take the unicellular organisms which multiply by division, we may see that heredity is simple. One unicellular individual growing larger than is convenient, divides into two. Each is like the other. It could hardly be different. Reproduction by spores or buds is practically the same thing. The spores or buds are minute particles of the parent organism. When it comes to the coalescence of the germ and sperm elements from two organisms, the phenomena become more complicated, and it is still more so as the animal rises in the scale of creation; but I believe the processes of organic evolution have gone on so slowly that the s.e.xual cells have acquired the power to transmit the whole organism without the necessity of the germ-plasm being continued from parent to offspring indefinitely, and also without the aid of pangenesis.

The egg has acquired a tendency to develop in a certain direction. Just how we cannot tell, further than to say that it was probably the result of variation first and natural selection selecting out those variations most suitable. It is this tendency to vary that gives rise to many of the phenomena of heredity. The subject is, for the present, beyond our power to settle satisfactorily, and so hypotheses must be resorted to.

The s.e.xual cells, comparatively simple in anatomical structure, must be highly complex in their molecular structure; and the more highly evolved the organism, the more complex becomes this molecular structure. If it were possible to study this molecular structure we should be able to understand the whole subject far better than is possible now. But this is not possible, and there is little hope that we shall ever be able to accomplish it.

HEREDITY AND THE EDUCATION OF CHILDREN.--The next question which comes up for consideration is that of the education of children and its relation to heredity. This brings us at once to the problem as to whether acquired characters are transmitted to offspring or not. If acquired characters are transmitted, the relation of heredity to education must be very close and important. If acquired characters are not inherited, then heredity and education have a very different relation. That acquired characters are transmitted has long been believed. It was the belief of Lamarck. He tried to explain the structure of the organism by this principle. The ill.u.s.tration of the long neck of the giraffe is familiar to every one. It originated by the constant stretching of this part to obtain food from the trees. In times of scarcity, he had to exert himself in this way still more to reach the higher branches. The young of the giraffe had longer necks than their parents because of the efforts of the latter in this way. So the keen sight of birds, it was argued, was acquired in the same manner. The hawk had to exercise his eyes most vigorously to discern his prey at a distance, and his offspring inherited this keenness of sight acquired by the exercise of his ancestors.

Darwin believed that the effects of the exercise of any part were transmitted. He says: "We may feel a.s.sured that the inherited effects of the use and disuse of parts will have done much in the same direction with natural selection in modifying man's structure of body."

We may say that this belief has been held by the common people, uneducated in science. They not unfrequently get at truths in a rude way long before the scientists do. Many parents tell us their children are strongly influenced by some particular occupation of the mother during pregnancy. So strong is this belief, that many mothers are in our times trying to influence the character of their unborn children by special modes of life, by cultivating music or art, or science, in order to give the child a love for these pursuits.

It is by Herbert Spencer that this has been most ably presented. Indeed, he holds that there is no explanation of evolution without the transmission of the effects of the use and disuse of parts. His words are: "If there has been no transmission of acquired character there has been no evolution."

He also says: "If we go back to the genesis of the human type from some lower type of primates, we see that while the little toe has ceased to be of any use for climbing purposes, it has not come into any considerable use for walking or running. It is manifest that the great toes have been immensely developed since there took place the change from arboreal to terrestrial habits. A study of the mechanism of walking shows why this has happened. Stability requires that the line of direction--the vertical line, let fall from the center of gravity--shall fall within the base, and the walking shall be brought at each step within the area of support, or so near that any tendency to fall may be checked at the next step. A necessary result is that _if_ at each step the chief stress of support is thrown on the outer side of the foot, the body must be swayed so that the line of direction may fall within the outside of the foot, or close to it; and when the next step is taken it must be similarly swayed in an opposite direction, so that the outer side of the foot may bear the weight. That is to say, the body must oscillate from side to side, or waddle. The movement of the duck when walking shows what happens when the points of support are far apart.

This kind of movement conflicts with efficient locomotion. There is a waste of muscular energy in making these lateral movements, and they are at variance with the forward movement. We may infer, then, that the developing man profited by throwing the stress as much as possible on the inner side of the feet, and was especially led to do this when going fast, which enabled him to abridge the oscillations, as indeed we see it now in the drunken man. Then there was thrown a continually increasing stress upon the inner digits as they progressively developed from the efforts of use, until now the inner digits, so large compared with the outer, bear the greater part of the weight, and being relatively near one another render needless any swaying of the body from side to side in walking. But what has meanwhile happened to the outer digits? Evidently as fast as the great toes have come more and more into play and the small ones have gone more and more out of play, dwindling for--how long shall we say?--perhaps 100,000 years." In other and simpler words, the great toe of man has wonderfully developed since he began to walk upright. This has been from greater use, and the transmission of the effects of this use to offspring. The small toe has decreased in size proportionately. This we can reasonably infer has been the result of disuse, the effects of which were also transmitted to offspring.

A still more remarkable ill.u.s.tration of the effects of use and disuse is seen in the sense of touch in different parts of the body. Prof. Weber, in his laboratory for experimental psychology, has worked out this difference most minutely. He finds that by taking a pair of compa.s.ses, the points of which are less than one-twelfth of an inch apart, the end of the forefinger is not able to distinguish more than one point. Going to the middle of the back we have the least discriminating power in the skin, for the points must be separated two and one half inches before the nerves can decide that there are two. Any one may test this on himself. Between these extremes we have many differences. The end of the nose has four times as great power of discrimination as the forehead. When we come to the tip of the tongue, we find it far excels any part of the body in its power of tactual discrimination, it being twice that of the forefinger. In every case we find there is greatest delicacy of touch in those parts where this sense has been most exercised. The tongue is being constantly exercised on our food, on the roof of the mouth, the teeth, etc. It is rarely idle. There is in man no advantage for his survival, Mr. Spencer a.s.serts, by having such a sensitive tongue. He could get on just as well without it. He regards it as a case where the exercise of a function has exalted it remarkably, and this exaltation has been transmitted to offspring. Natural selection, he thinks, is not sufficient to account for it. Natural selection only preserves those characters which will give their possessor some advantage in the struggle for existence.

Still another argument is drawn from the whale. This monster once lived, it is believed, partly on land, probably on low land near water, and must have been smaller than now. It had hind legs; but since it has lived continuously in the water its tail has so developed as to make a far better organ of locomotion, and the legs have dwindled from disuse, so that now there is only a remnant left, and this is hidden beneath the skin. The tail has become more efficient from use, and this has been transmitted so that all whales are born with well developed tails. The legs have dwindled for want of use until they have almost disappeared; and this effect of disuse has also been transmitted to offspring.

Another ill.u.s.tration is furnished by Havelock Charles, an English surgeon, who has spent much time among the Punjab tribes in India, and studied them anthropologically. His account is given in "The Journal of Anatomy," in a paper on the structure of the skeletons of these people.

It appears they have facets on the bones, fitting them for the sitting posture. These do not develop after birth, but are seen in the fetus. It seems hardly possible that these facets could have any other origin except by transmission after being acquired by ages of use of sitting posture.

Another argument is drawn from the coadaptation of parts. We know that the male sheep, likewise the goat, the stag, and the males of many other animals, have large horns. They are supposed to be useful in fighting with rivals in order to secure as large a number of females as possible.

Now these large horns require at the same time a greater development of the bones of the head to hold them, also larger and stronger vertebrae of the neck and back, and larger muscles of these parts to maintain and use them effectively. In other words, there must be coadaptation of all the parts, otherwise these larger horns would be an inc.u.mbrance and useless. Now, if we accept the theory of the inheritance of acquired characters, this is all simple. The use of the head in b.u.t.ting against other males exercises all these parts simultaneously, and they develop equally and at the same time. If, however, inheritance has no part in the matter, then we must fall back on variation in the germ-plasm and natural selection for an explanation; but it is difficult or, as Spencer says, impossible to conceive of variation producing large and heavy horns on these animals and at the same time coadaptation of all the other parts to hold and use them. Sometimes coadaptation does not take place, as in the common brook crab, familiar to every country boy. Its foreclaws or fingers are out of all proportion to the rest of the leg, and its awkwardness is well known. The lobster is another case. Even in human beings we have instances of non-coadaptation, as where the head and brain are out of proportion to the size of the body, or the reverse.

I need not multiply instances.

Now, if acquired characters are transmitted, any system of training which exists for a considerable time must necessarily appear in the structure of the body and in the character. If the training is not in accord with the laws of evolution, it causes the race to deviate from the true line of progress, and by just so much hinder advancement. If, on the other hand, our systems of education conform to correct principles, progress is advanced by them.

Quite recently an entirely new theory has grown up, opposed to Lamarckianism, and the theory of the transmission of acquired characters. It has been before the world little more than a decade and has made remarkable progress, though it is too soon to say it has been established beyond dispute. Prof. Weismann, its author, is well equipped as a biologist to maintain and defend it. I have already stated briefly his theory of heredity, namely, that the germ-plasm is continuous from parent to offspring. This necessitates a remodeling of commonly accepted views, an entire giving up of the Lamarckian belief that use and disuse have their effect on progeny. If the germ-plasm continues from one generation to another, then it must already have been formed, or at least provided for, even before the birth of the parents. They may modify it, through growth and nutrition, but not through exercise of any function. Prof. Weismann went at the demonstration of his views in a thoroughly scientific way by the making of experiments on living animals and the collection of facts. From his experiments it is now pretty well established that wounds and injuries, which he considers to be acquired characters, are not transmitted. No matter for how many generations you cut off the tails of dogs, cats, horses or sheep, the effects of this removal do not appear in the progeny. Most parents have some mark on the body, received in early life, some cut or bruise, some scratch, but their children do not inherit them. The famous experiment of cutting off the tails of mice, for generation after generation, and then breeding from them was one of Weismann's methods of substantiating the theory that acquired character is not inherited. The offspring of these mutilated mice had as long tails as if those of their parents had not been removed. The explanation is, the germ-plasm was not in any way affected by the bodily mutilation. The practice of the Flathead Indian is another case. The children of parents whose heads have been artificially flattened are not affected by it. The small feet of Chinese women, made so by binding them and preventing their growth, may also be mentioned.

INTELLECTUAL ACQUIREMENTS.--Not to depend on such evidence, however, he adduces that of a very different character, namely, the non-transmission of intellectual acquirements. Language is an example. Although human beings have been communicating their thoughts to each other from very ancient times by speech, yet every child has to learn how to do this for itself. No matter how many languages the parents master, their children have to go over all the ground the parents did, make all the toil and effort to learn to speak. The children of the most gifted linguists, if brought up without coming in contact with those who can teach them to talk, will never learn a single word. There are, it is claimed, a few cases on record of children who never acquired their natural tongue because they had lived among animals and not among human beings. They learned to make the same vocal sounds the animals did, no more. The environment in this case was everything, the parental acquirements nothing.

Music, like language, is also an acquired character, and it is probably not transmitted. Our musical geniuses are not the children of great musicians, but in most cases the reverse. They seem to spring into existence from lowly sources, or at least from parents whose advantages for a musical education have been very limited, though generally they have had good health, and a climatic environment of a favorable kind.

Great musical talent usually dies out in any family in a few generations, no matter how much it is cultivated, or, if it does not die out entirely, it becomes mediocre; and yet the opportunities of the children of great musicians, and the ambition of their parents for its culture, are usually very favorable.

INSTINCT.--In accepting the theory of the non-transmission of acquired characters, it becomes necessary to give up prevailing views of the origin of instinct. According to the old belief it was a gift of G.o.d, and not acquired by any effort on the part of its possessor. In speaking of the instinct of bees, Sidney Smith says: "_Providence has done it._ There are the bees, there is the comb, and the honey, get rid of it or find some other explanation if you can."

The early evolutionists changed all this, and made instinct the inheritance of an oft-repeated act. The young kitten, as soon as old enough, hunts for a mouse and catches it without any training. The sight of the mouse acts on its nervous system in such a way as to compel it to creep up softly, jump on it, toy and play with it, and finally kill and eat it. It would have required long practice on the part of its ancestors before so wonderful a character could have become fixed. The same is true of the setter dog.

The new view is, that instincts arise from variations in the germ-plasm.

The union of the germ elements of two individuals causes it to vary more or less from either parent. These variations will be favorable and unfavorable. The unfavorable ones will produce offspring handicapped in the struggle for life and they will disappear. The favorable variations will produce descendants possessing advantages for survival and leave numerous offspring.

It is not easy to accept this view, but I think there are some facts that support it. I will advance a few. The hive of the honey-bee contains three kinds of insects: the queen, the drones or males, and the workers. The queen makes her nuptial flight but once in a life-time, and does it from instinct. How can an instinct like this have been acquired by being performed but once? The drones are derived from unfertilized eggs; yet their instincts are those of the male, not of the female. As they have no male ancestors, it seems probable there was in the germ-plasm of some queen bee, at a time far back, some change which allowed unfertilized eggs to produce males.

The workers are all females, not fully developed s.e.xually on account of a diet with too small a proportion of nitrogenous food and containing so large a proportion of the hydrocarbons. They inherit from the mother, or rather from the germ-plasm, the instinct to gather honey, yet neither their male nor female ancestors ever gathered any honey in their lives, nor have they for ages. Far back in antiquity the queen, no doubt, did gather honey, but the disuse of this instinct has not caused it to disappear in the working bee, as it should have done according to the Lamarckian theory of disuse causing decay of function. Is there any way to account for this, except on the theory that the germ-plasm produces working bees as well as the other kinds, irrespective of the habits of the queen? Her character in this respect is fixed and does not change.

Is it unreasonable to think that some time in the past, in some queen bee, was formed a germ-plasm capable of producing three varieties, and that there was such an advantage in it for survival, that it has been continued ever since by natural selection? Queens not able to do this have not been selected, left no offspring, and thus the perfection of the stock has been a.s.sured.

One more case. Some years ago, when interested in agricultural entomology, I made a study of the so-called seventeen-year locust.

Noting the wonderful precision with which the female cuts into a soft twig of a tree and lays its eggs in two rows, the thought was suggested to me, how can an instinct, used only a few hours, once in seventeen years, be acquired by exercise and persist in the offspring seventeen years later? Weismann's theory of the origin of instinct from favorable variations in the germ-plasm offers, it seems to me, a rational explanation.

I do not need to extend ill.u.s.trations which abound in the insect world, especially among the ants, which furnish cases of coadaptation that cannot be transmitted, as they do not propagate, so I will not mention them here.

Now, if acquired characters _are not_ transmitted to offspring, how should these facts affect our methods of educating children?

One advantage will be evident, I think, to all. Erroneous systems of training, which do not injure the health, will not appear through heredity in the offspring of parents thus wrongly trained, except as a result of environment. That is to say, the injury does not become congenital--will not be in the blood--and, consequently, it will be less difficult to eradicate it and to introduce better systems. This may be considered an advantage. But it is not all. If heredity takes place only through the germ-plasm, then it seems to me that whatever promotes a knowledge of how to maintain it in a high degree of health, and how to favor more perfectly natural selection, are subjects with which our educators may busy themselves far more than they do. That is to say, the study of biology, of life--of the laws of human growth and development, and of evolution, will become, more and more, important factors in our school curriculum. We can hardly imagine how much our common every-day life has been aided by even the slight knowledge of mathematics gained by an acquaintance with addition, subtraction, multiplication and division. By it we are able to keep our little accounts correctly, and neither cheat our creditors nor be cheated by them. Could we not by a knowledge of the laws of evolution, and also the laws of growth and development, keep our larger account with nature in a far better condition? Could we not keep ourselves from being cheated out of our health and happiness, and also do something to put an end to physical, intellectual and moral deterioration which threatens so many families and even races? It seems to me that the time is not far distant when these studies will be quite as much attended to as the not unimportant ones of arithmetic and grammar.

KNOWLEDGE OF HEREDITY.--Whatever doctrine of heredity prevails, however, one thing is certain, some knowledge of the subject will be very useful to those who have in care the training of children. To them, often more than to the parent, is entrusted the task of developing the character and the individuality of the child. Can he do this well if he knows nothing of what the bent of the child's genius from ancestral influence is? I doubt very much if any of us realize how important it is that this individuality should have its proper share of attention. As the evolution of society goes on, more and more must there be differentiation of our various activities. If every boy and every girl can be educated so that to a considerable extent they can follow the bent of their genius, _whenever that bent is a normal one_, will not the available intellectual and moral energy of society be considerably augmented? If you educate a boy which nature intended for a blacksmith for a preacher, has not the world lost something? Educate another for a blacksmith who should have been a preacher, is there not also a great loss? There are a few children who will come out all right, no matter how much they are schooled, or whether they have any schooling, so well have they been born, but with the majority this is not the case. Now it seems to me that the teacher who knows the natures of his pupils, and something of their ancestors', can direct their energies more satisfactorily than the one who does not. If there are hereditary defects of intellect or morals, he can more easily correct them. If there are ancestral tendencies to disease through imperfections of certain organs, for instance, the lungs or the brain, he can often put the child on such a course of physical culture or mental training as to lift it above danger, so that it may go through life a useful person instead of a feeble one or a lunatic. Even the tendency to crime might be averted.

INDIVIDUALITY.--If we could educate the young so as to bring out more fully their normal individualities we should be able to cultivate in them more independence of character. On this subject Prof. Mills says: "With all its imperfections, I am bound to say that the individuality of the pupils in the old log school-house was often more developed than in the city public schools of today, where for a boy to be himself frequently brings with it the ridicule of his fellows--a condition of things that has its effect afterward on the lad at college. I find that this fear of being considered odd,--out of harmony with what others may think,--one of the greatest drawbacks to the development of independent investigating students at college. The case is still worse for girls.

When women begin to be really independent in thought, in feeling, in action, I shall be more hopeful of the progress of mankind. Happily, the dawn of this day is already begun."