Being Born Alike but Different

JUNE, 1922

BY VERNON KELLOGG

I

A LITTLE girl whom I know well and have known well for eleven years — she is not so little now, at eleven — is a constant stimulant of inquiry, passive, silent inquiry, for me. She herself is in a constant state of active inquiry of me. But always, as I watch her and hear her, I am asking myself; What will she be when she is grown up, when she is developed, fully developed? And always, close on that: What is making her, and is to make her, be what she will be? What has made her just what she is so far? And how much can anybody, including herself, help her or make her to be what it would please her parents to have her be when she is quite grown up

She has blue eyes; so has her father. Perhaps she got these blue eyes from him. But she has a firm, straight mouth, the kind of mouth her mother has. Perhaps she got her mouth from her mother. She can read and write and do fractions, and each day now can speak a little more French. Both her mother and father can read and write and do fractions, and they know some French. But, if she got these things from her parents, she got them in another way than that in which she got her blue eyes and straight mouth from them. Having blue eyes and a straight mouth came just naturally with being born. Being able to read and write came by being taught. But the being able to be taught to read and write came with being born. Some little girls of eleven cannot learn to read and write and do fractions, nor will they ever be able to, teach them as much as you like, as long as they live. On the other hand, some little girls of eleven can do rather remarkable things in singing, or playing the piano. A few little girls and boys have done very remarkable things in music at eleven. But the little girl of eleven I know so intimately cannot play the piano especially well, nor would she have been able to, even if she had had many more music lessons than she has had. She is, in a word, not a musical genius. Being a musical genius comes with being born, although to do what a genius can do at the piano requires also much of teaching and practising.

Finally, this little girl of eleven is usually well-behaved. Sometimes she is n’t so well-behaved, and after one of these times, and when there has been a general family discussion of the matter, she will decide to behave better, and will say so, and will really do so. She seems to be able to determine for herself, in some measure, what she will or will not do.

So, altogether, there is evidently a various and mixed lot of things that take part in making a lit tle girl what she is and what she is going to be. Sometimes I think this little girl is growing more and more like her mother; and I am glad. Sometimes the disturbing fear assails me that she is taking after her father altogether too much. But what can I do? And what can any of us do to have our children grow up to be what we should like them to be? We can be good examples — if we can. Yes, but good exampleship has little to do with making firm mouths and what goes with firm mouths, or with making good looks, or good brains, or musical genius. A lot goes just naturally with being bom, and this may be good, or less good, or even bad. Can this good be made better, and how much better, and this bad be made less bad, or even not bad at all, by doing something to children after birth? We all want very much to know about this. Can the biologist, who studies birth and development and heredity and variation and the influence of environment and all the rest, of the processes and ways of Nature that help to determine the fate of individuals and species — can he tell us anything worth more than merely being interesting? Can he answer any of our questions with any such degree of assurance as to help guide us in our behavior in relation to the problem of human individuals and human society presented by the likenesses and unlikenesses of human beings? I suppose we are all willing to let him try.

II

A female codfish drops into the seawater in which it lives a few million eggs. From all of these eggs which do not get eaten or otherwise destroyed, and which do get fertilized by sperm dropped into the water by a male codfish, hatch tiny creatures, all of which, excepting those that get eaten or otherwise destroyed, — and this is the fate of most of them, — grow up to be fishes that are unmistakably codfishes.

A female robin lays in a nest four or five pretty blue eggs which have been fertilized in her body; and from these eggs, if storm or blue jay or oologist does not prevent, hatch as many naked helpless birdlings, which are fed for a while by the parents, and grow up, if no ill luck befall, into unmistakable robins.

A cow produces in her body, every now and then, several eggs, from any one of which that gets fertilized in her body, a foetus develops, which, after a number of months of gestation, is born as a calf, dependent at first for food on its mother’s milk, and later able to forage for itself, and which growls up, barring misfortune, into an unmistakable cow or bull.

And, finally, and in much the same way as with cattle, our own children are conceived and develop and are born and grow up into unmistakable human beings. Codfishes, robins, cattle, and human beings all reproduce themselves in essentially the same way; and in this process the end-product, or new individual, is always of the same animal kind or species or breed as the parents. Codfishes produce codfishes, robins, robins; cattle, cattle, and Jersey cattle, Jersey cattle; human beings, human beings, and black human beings, black human beings, and yellow ones, yellow. Like begets like.

But — and this is as true and important as the first axiom — like never produces exactly like. That is, while in gross the offspring are like their parents, who are like their own parents, and so on indefinitely backward, in kind or species and in race or breed, and even are more like the members of their own particular stock or family than like the offspring of other families within the same species, in detail they are always different from their own parents and grand-and great-grandparents, and they always differ from each other. No two living individuals are ever exactly alike, even if these individuals be twins, or even so-called identical twins. Biologists believe that no two organisms have ever been exactly alike, or will ever be exactly alike. No codfish is ever exactly like any other codfish, nor any robin, or cow, or human being exactly like any other individual of its own species or breed or family. This is the biological fact, or law, of variation, as the statement that like produces like expresses the biological fact, or law, of heredity.

Biologists quibble a good deal over names and definitions. Some use the word ‘heredity,’ not to name a natural law, — which is, indeed, not a ‘law’ in the usual sense of the word, but only a concise and generalized expression of a long experience or of many observations, — but to express by a single word the combination of many causes or factors which make like beget like. These biologists think of heredity as a process or an influence or a power. Some biologists include the law of variation within the law of heredity. And so on. No matter. Let us not trouble about a precise usage of terms, for there is none. Let us understand that we want to talk together about the facts and phenomena and methods and causes and, perhaps, above all, about the significance and, particularly, the significance in human life, of being bom alike but different. We shall, I think, mean what most biologists mean when we use the word ‘heredity’ to indicate that we are talking about being born alike; and we shall mean what most biologists mean when we use the word ‘ variation ’ to indicate that we are talking about being born different. Heredity and variation: being born alike but different; two things or two phases of one thing, than which I know no other thing in biology of more importance for human beings to understand, if they want to understand as much as they can of human life and of the unescapable natural conditions under which it must be lived.

Although it is about the conception, birth, and outcome through development, of human individuals that I wish especially to write, with the significance of all this to human social organization and to the fate of human individuals, communities, and races, I have bracketed animals and men together in my remarks so far. This is for two reasons: first, I want to make clear that in these matters of conception, heredity, and variation, men and animals are in the same boat, are subject to the same fundamental natural processes; and, second, I want to be able to speak freely, as a biologist speaking of any biological problem, about these matters, without offending the sensibilities of readers unused to biological discussion, — without, in a word, seeming to be indelicate. I can do this, perhaps, best by discussing birth, heredity, and variation in animals, and saying that this discussion is equally true and applicable for men, — in so far as it is, — and thus escape giving offense to the easily offended. Although I cannot help wondering why I feel that I ought to do this, when I remember that many books and plays of wide popular approval owe much of their interest and vogue to the fact that they devote themselves chiefly to an intensive and very frank consideration of a special phase of this whole matter, the phase of loving, love-making, and love-crowning; and the franker the account, the more successful the book or play.

But my most important reason for bracketing animals and man together in this discussion is to emphasize the fact that conception, birth, development, heredity, and variation are all matters truly common to both animals — and, indeed, plants — and man, and that we can no more escape — with exceptions to be noted — the control and fateful determination in human life of these things than animals or plants can. And we are quite accustomed now, since biology and evolution have come to have a certain familiarity for us, thanks to the gradually widening form of general education, to accept the validity of the relation of these things to the determination of animaland plant-life; or, as we might say, if we thought more of plants and animals as individuals and not as species, the relation of these things to the fate of individual plants and animals. Well, just so they have their close and uneseapable relation to the fate of humans.

We shall want to examine a little more carefully this matter of heredity tending to make us — by ‘us I mean other animals as well as man — like our ancestors, and variation tending to make us unlike. I shall want to go beyond the casual observation that reveals to anyone that this is true, to refer to a few examples in some detail, and to attem pt to analyze and contrast certain factors that contribute to making us alike and vet different. We recognize readily both the likenesses and unlikenesses in the case of human beings and some familiar domesticated animals, as cattle; but we are less likely to recognize the unlikenesses, and more than likely to overrate the likenesses, among codfish and robin individuals — unless we happen to be special students of codfishes and robins.

But before doing this, and in order to do this intelligently, we need to scrape rapid acquaintance with some of the details of the phenomena of conception, and embryonic and postembryonic development, common to the production of all new individuals, and out of which appear the final likenesses and unlikenesses among them.

The biologist likes to work back to beginnings. So do the geologist and physicist and chemist. To the evolutionist, getting at the beginnings is the absolute prerequisite to getting at the evolutionary course and probable evolutionary fate of chemical elements — rocks, plants, animals, human beings, the cart h and other planets, the sun and other stars, the universe. The evolutionist is the most aspiring of scientific men, for he studies the past and present primarily to become able to prophesy the future. And to prophesy is the ultimate aim of science. Let us then hitch our wagon to the stars: let us call ourselves evolutionists.

III

Biologists have a convenient single word to express the life history, from the beginning egg, through all the development and maturity and senescence and, finally, the death, of a single individual. The word is ontogeny. As a running mate for this word, they have another, to express the evolutionary history of a single species or race, its beginning by sudden mutation or gradual transformation from another species, its evolutionary course and final fate, and its genealogic relation to other species or races. This other word is phylogeny.

There is a sort of fundamental parallelism between the ontogeny, or the life history of an individual, and the phylogeny, or evolutionary history of the species to which the individual belongs. The parallelism has been expressed by the generalization that ‘ontogeny recapitulates phylogeny, which is the basis of the ‘ recapitulation theory’ of von Baer, Haeckel, and other generalizing biologists, of some years ago, who saw in this generalized fact an easy way of learning about the evolution and genetic relationship of any plant or animal species, by making an intensive study of the development of a single individual of the species. It was this generalization that gave such an impetus several years ago to the study of embryology, and upon which, some years later, certain pedagogue devotees of child study based their interesting, but rather undiscriminating, recognition of the monkey stages in child life.

The difficulty about the recapitulation theory is that it is n’t true — in detail. In a large way, it is true. In the embryonic life of a child, that is in its earlier and, to most of us, hidden stages, from fertilized egg through foetal development to time of birth, it does pass through stages which pretty clearly reveal our fundamental evolutionary relationship to the loner animals. It passes through stages, common, with characteristic variations, to the development of all mammals. You have seen the familiar pictures of the early embryos of various animals and man, showing them all so much alike that only a trained student of embryology can confidently distinguish the genera! group of animals to which a given embryo belongs. But, by the time the human babe is born, it has got on so far in its development that it is well by all fish and monkey stages and is unmistakably and fascinatingly human. It is more than that: it, is a human being of a given race, Negro or Mongolian or Indian or Caucasian. And it already shows various specific physical, and, very soon, various mental characteristics, which not only indicate its particular stock, but which are to have a large part in determining its fate as a human individual. It is born, in a word, with all of the general characters of humanness, and with an hereditary endowment of particular physical and mental traits already apparent, and potentialities of other traits which are to appear in due course in its development to maturity, or, as the biologist puts it, in its post-embryonic development.

For any individual to recapitulate in its short ontogeny, — from a few hours to a few years, depending on the kind of animal, — in any detail and with anything like completeness, the phylogeny of its species, is simply impossible; and it, equally simply, does not achieve this impossibility. Whole phyletic stages are suppressed; others are compressed and modified. And, in addition, new non-phyletic adaptive stages, necessary to the successful life of the individual as embryo under conditions not at all identical with the external conditions surrounding any stages in the phyletic history of the species, are interpolated into this ontogeny, tending to confuse, and mislead, the student trying to unravel from a study of individual ontogeny the phyletic history of the species.

Take, for instance, a single example: the ontogeny of a butterfly. Born as a caterpillar (larva), representing in gross some wormlike ancestor in its phyletic history, but in detail very different from any worm that ever existed, it leads an active life for a few weeks or months, equipped by adaptive physical structures to crawl and eat leaves. Then it changes to a non-eating, immobile chrysalis (pupa), in which stage a breakdown of its caterpillar organs occurs, with the simultaneous development of very different organs; and, finally, after some days, weeks, or months, depending on the kind of butterfly it is, it issues as a flying, nectarsucking, very unwormlike creature, for poets to sing about and entomologists to chase and kill and pin up in their cabinet cemeteries.

Do you think that in the evolutionary phylogeny or genealogy of butterflies, there was ever an ancestor like a present-day butterfly chrysalid? You do not think so; and neither does any biologist. The ontogenetic chrysalidstage of a butterfly is an interpolated adaptive stage, to meet certain needs for radical changes to be made swiftly. The butterfly issues from its protecting egg so early in its life, — so prematurely, one may say, — that it is thrust out in the world to fend for itself in an ontogenetic stage roughly corresponding to a worm-stage in its phylogeny. But it has to adapt itself to a present environment, which may be very different from the past environment in which this worm ancestor lived. And so the young (larval) butterfly is very different from any worm that, ever existed, and its necessary adaptation to a crawling, leaf-eating life carries it even away from the final butterfly-stage, which it must, after all, attain. It therefore devotes the worm-stage of its life to overeating, so that much food, in the form chiefly of fat, is stored in its body. Then it changes into a noneating, motionless stage, in which it lives on its stored fat and in which it goes through the great bodily changes necessary to become a butterfly.

Now, if human beings were thus thrust out into the world, at a much more immature stage in their development than they are actually able to reach in the protecting and food-supplying mother-body, human post-embryonic life might be very different from what it is. The young of some mammals, as the kangaroo, are at birth more immature than a human babe, and they demand a somewhat different care from the care we give a babe. The just-born young of some others, as cattle, sheep, and the ruminants generally, are distinctly more mature. The calf and lamb can use their legs for proper gamboling very soon after birth. They demand much less care than a human babe.

But our discussion has gamboled, too, instead of sticking to the sedate and ordered way of our original intention. There is so imperatively much that comes crowding forward to be got into this short story of being born, that I cannot see my way clearly. However, we were, when we began gamboling, just at the point of taking up in a little detail those processes that go with being born, which especially have to do with determining likenesses and differences among us as individuals. So let us go back to these processes.

IV

Almost every animal individual begins as an egg. An egg is a single cell, made up of a little protoplasm, differentiated into a small central nuclear portion and a larger, distinguishably differing surrounding portion, together with a smaller or larger supply of food (albuminous yolk), usually surrounding the protoplasm, though sometimes scattered through it. In the eggs of some animals, especially birds and reptiles, this food-mass may be very much larger than the protoplasmic mass, and thus make the egg very large. Usually it is very small.

If we put aside those simplest animals, called Protozoa, whose body, through their whole lifetime, is never composed of more than one cell, and among which new individuals are often produced by a simple dividing in two of the parent individual, then there are very few animal kinds among which new individuals do not always begin as eggs. Among the higher animals, and with man, beginning as an egg is the absolute rule. And this egg has to be a fertilized egg: that is, the egg, which before fertilization is a sex cell produced by a mature female individual, has to have its protoplasmic part found by and fused with a sex cell from a mature male individual of the same, or a very nearly related, species or kind of animal.

There are exceptions. These could be passed over as of little significance if they did not furnish us with a clue to the interesting fact that fertilization is a double function, and not, as perhaps commonly thought by most laymen, a single function. One part is essentially chemical or physico-chemical in its nature, and the other more truly vital or biological in its nature. Those exceptional cases in Nature in which new individuals develop from unfertilized eggs — the cases are exceptional rather as to kinds of animals which exhibit them than as to individuals, for among some kinds of insects, as aphids, the social bees and wasps, and others, more new individuals are produced from unfertilized eggs than from fertilized — have led to a lot of fascinating experimentation, associated in this country especially with the name of Jacques Loeb. The newspapers and magazines have made his ‘fatherless frogs ’ familiar to many — and probably rather irritating to him. This experimentation has shown that, with many kinds of animals which regularly, or at least usually, produce new individuals only from fertilized eggs, the application of various chemical or physical stimuli to unfertilized eggs will compel them to begin developing. This development usually does not go far; but in some cases it can, and does, go clear through to the achievement of fully developed new individuals. These cases of artificial parthenogenesis, as also the cases of natural parthenogenesis, are restricted, so far as is yet known, to the lower animals, mostly, indeed, to invertebrate animals. The fatherless frogs are at the top of the scale. No mammals are included in the list.

Now, from the observations of these cases of inducing development by a chemical or physical stimulation of unfertilized eggs, those biologists belonging to the mechanist school, who see in so-called vital phenomena only more complex — and not always more complex — phenomena of physics and chemistry than the physicists and chemists usually have to deal with, claim, very plausibly, that fertilization is, at least partly, nothing more than physicochemical stimulation.

And they can similarly explain the mysterious, or apparently conscious, seeking and finding of the immobile female egg by the smaller, free-swimming, male sperm, as no more than a phenomenon simply induced by the presence of some chemical substance in the egg irresistibly attractive to the sperm. For example, I remember an experiment that the famous plant physiologist, Pfeffer, of the University of Leipzig, used to make in the course of his lectures. He would put a tiny glass tube, open at both ends, filled with diluted malic acid, in a vessel of water in which were millions of the swimming sperm-cells of a fern. In a short time, as the malic acid began to diffuse into the water from the ends of the tube, the fern sperm would gather about the tubeends and then go into the tube, until finally it was crowded with them.

‘And so you see, meine Herren,’ declared the professor triumphantly, ‘all that the fern egg-cells need in order to get fertilized is to have a small quantity of malic acid in them, which, as a matter of fact, they have. There is no mystery of vitalism about it.’

But there is, of course, another and very important matter about fertilization. That is the matter of endowing the young with the double line of heredity represented by, and coming through, both mother and father, and passed on to the new individual by the fused sexcells of which the fertilized egg is composed. The fatherless frogs and the parthenogenetically produced aphids have only one line of heredity represented in them — the maternal line. But the new individuals that come from fertilized eggs have two lines of heredity physically inherent in their bodies. And we shall see that the great, and biologically very important, fact of variation depends in no little degree on the fusing of two different lines of heredity. This fusion of body-part (sex cells) and of heredities, perhaps for the sake of producing variation, perhaps for some other reason, is the other function of fertilization.

V

Now, what the fertilized egg, which is a single cell produced by the fusion of two cells, first does in the way of development into a new complete individual, composed of thousands or millions or billions of cells, is to divide in two. And then each of these two daughter cells, — which, of course, do not separate and move apart, as they do in the case of the formation of new individuals by the fission of a one-celled (Protozoan) animal, — after growing a little larger (sometimes as large as the parent egg-cell), divides into two; and then these four cells similarly divide, and so on, until the developing egg is a small, usually spherical, mass of cells, usually similar in appearance though, with some animals, varying in size.

An interesting series of performances on the part, first, of the one-celled egg, and then of the daughter cells, goes on in connection with all of this dividing. These performances are too many and too elaborate to be described here, but they are very significant and important. The result of them is to achieve a very precise division of the cell material, which affects nucleus as well as general cell protoplasm, and special elements in the nucleus, called chromosomes, as well as the undifferentiated rest of the nucleus. These chromosomes are broken-up bits of a special part, usually in threadlike shape, of the nuclear material, called chromatin (because it is especially easily and strongly colored by the stains used by cell students in their efforts to make visible the differentiation that exists in the cell structure).

Now, these chromosomes are believed by most students of the mechanism of heredity to be the actual carriers of the hereditary potentialities of the new individual which is to develop from the egg. That is, they are supposed to be composed of actual physical unit representatives in the egg of the many traits of structure, physiology, mentality, and even of soul, — if we go to the logical extreme — which the developed individual will possess by virtue of inheritance. Of course, as they exist in the egg, they are not such traits, nor in the slightest degree suggestive of them — nobody inherits any traits as traits; but because of these physical particles in, or composing, the chromosomes. Such-and-such specific traits will develop and be possessed by the new individual.

These traits, I say, have to develop. The human egg is not, nor does it contain, as some of the earlier naturalists, before the days of better microscopes, believed, an homunculus, a tiny human being with all its organs in miniature, needing simply to grow, or enlarge, to be the new baby and then the new man. But neither is it, as many naturalists came to believe, when the improvements in the microscope enabled them to prove the falsity of the earlier ‘preformation theory,’ a simple bit of undifferentiated protoplasm, capable, by virtue of response to external stimulus and environment, of developing into a new, highly organized creature. We know now that, while there is no preformed tiny human being in the human egg, the egg is, nevertheless, more or less, perhaps very highly, differentiated, with parts that have direct correspondence to future parts of the new individual. But we know also that the conditions under which the development of the egg goes on can greatly modify the fate of any part of the egg mosaic; can modify profoundly the developmental plan, as it were; and that, without proper stimulus and environment this plan, with all the physical representation of it in the egg, can come to nothing. Inherited traits appear because they are represent,ed some way in the egg. And other traits can appear because some special environmental influence forces them on to the developing individual. These latter new traits, or modifications of already represented traits, are said to be ‘acquired.’ They differ importantly from the so-called inherited traits, in that they will not appear in the children of the new individual acquiring them, unless the similar special environmental conditions that surrounded the parent and determined the development of these special acquirements are repeated during the development of the children. On the contrary, the inherited traits of the parent, will tend to appear again in the children — although in never the same condition — under the usual normal environment of the species.

VI

These references to preformation in the egg, or predetermination of the course of development, and to environmental necessities and possibilities in development, introduce us to a fascinating phase of biological study and special investigation, called by the Germans, who were the pioneers in it, Entwicklungs-Mechanik, the mechanics of development. Its importance comes especially from two principal things about it; first, it introduces into biological study, which for a long time was almost exclusively simply an observational study, the reasoned application of careful experimental work, with constant references to facts of physics and chemistry and an adoption of the methods which have led to the high development of these sciences as exact sciences; and, second, it involves the getting at, and close observation of, the earlier and presumably simpler stages of animal development, and of the factors that control this development. It is a kind of study more exact and, to its disciples, perhaps no less interesting than child study. At any rate, these disciples would maintain that their intensive study of the mechanics of development should be of some use to scientific students of child development.

We can, of course, do hardly more in this paper than just venture to suggest the significance of certain outstanding facts revealed by the study of Entwicklungs-Mechanik. Indeed, you may have become already impatient of my persistence in so long trying to hold your attention to the egg and embryo stages of existence. But knowledge of the varying things that help control the development and outcome of the egg and embryo is knowledge that throws much light on the phenomena of later development, and that can help us to understand what may be possible and what is impossible in connection with our attempt to make this later development run according to our desires.

One of the outstanding problems in this later development is that of recognizing in it, and appraising, the relative influence and importance of nature and nurture, that is, the influence of heredity and the influence of environment and education. Which has the greater importance in determining the course and outcome of this development? What part of this outcome results from the one, what from the other? Well, the same problem faces the student of developing egg and embryo. But in the case of the study of the animal egg and embryo, one has more opportunity to apply the experimental method than in the study of the post-embryonic development; although it must be admitted that a good deal of experimenting, of a kind unfortunately not too scientific in manner, is done in the case of the developing child and youth. A good deal of our education seems still to be more of the nature of experiment than of well-determined method.

But let us now take our last, look, with the aid of some light, from Entwicklungs-Mechanik, at the developing egg and embryo.

Recall, please, the more obvious phenomena in the course of the early stages of the development of the fertilized egg; and in doing this, keep in mind the two contrasting, although closely correlated, sets of influences determining these phenomena. The early stages are the division of the singlecelled egg into two cells, and then into four and eight and sixteen and so on, until there are many adherent cells. And then the gradual specializing of these cells, at first similar, into different kinds of cells, elementary nervecells and muscle cells and epithelial cells and blood cells and sex cells and so on, forming different tissues, and the simultaneous gradual arranging and grouping of these specializing cells and tissues into different organs and bodyregions. The two sets of contrasting, although mutually interacting and correlated, influences may be called influences of predetermination, or intrinsic or hereditary influences, and influences of epigenesis, or extrinsic or environmental influences.

And now, keeping this in mind, let us play with our developing egg and embryo. For this we need a good microscope, because an animal egg, or at any rate, the part of it that is not yolk (food) but is the developing germ, is very small. And we need several very finely pointed needles, and a wonderful pair of scissors with minutest of blades, and a few other simple instruments, and some chemicals. Also, we need a lot of patience, and perhaps somebody to bring our meals to us while we stick to the microscope; for we may have to sit for many hours with hardly an interruption to our close watching. I knew a German Privatdozent in the University of Leipzig, famous for his studies of cell genealogy, who kept up his continual watching of a developing egg of Ascaris, worm parasite of horses, for all of a day and a night and the next day. But he discovered many things of great interest and significance, whose telling made him the author of a monograph in biological science which is now a classic. And that is high reward for a biologist.

If everything that determines the course of development of an egg — granted that, the necessary general external conditions are provided — is inherent in the egg itself, then we might speak of this developmental course as predetermined for any given egg, and might, even speak of the egg, or embryo, which develops from it, as preformed, although, as already said, this preformation does not mean the existence in the fertilized egg of a complex embryo in miniature. It simply means that any given part of the egg, or one of the early daughter cells into which it divides, is predestined to become, by further development, a certain given part or organ or kind of tissue of the embryo and hence of the final fully developed new individual. On the other hand, if the egg gets its stimulus for development from outside, and is chiefly controlled during its development by environmental conditions, then its manner of development will vary in accordance with any variation in the external stimuli and conditions brought to bear on it. Here the experimenter comes in.

A classic early experiment on the frog’s egg seemed to prove the theory of preformation. With a finely pointed, heated needle one of the two daughter cells into which the egg first divided was killed by the experimenter, although it was left attached to the other live cell. The other cell went on and produced a half-frog embryo! Ergo, each half of the egg, or certainly each cell arising from the first division of the egg into two cells of equal size and similar appearance, had for fixed fate the development into the right or left half of a frog.

But another experimenter, instead of killing one of the first daughter cells of the frog’s egg, succeeded in separating them entirely, — thus removing any contact stimulus from a dead but still adhering daughter cell, — and found that each daughter cell, or egg-half, developed into a whole frog embryo of half, or at least unusually small, size! And still other experimenters succeeding in separating, in the case of eggs of certain other animals of lower type than the frog, not only the first two daughter cells, but the four and the eight and even the sixteen, produced by successive divisions of the developing egg, and got from each separated cell a minute but complete embryo. A bas preformation; hock the theory of epigenesis!

But the preformationists came back. By the careful watching, like that of the Leipzig Privatdozent, of eggs of various animals developing under normal circumstances, it was shown that certain specific tissues or organs of the later developed embryo have their origin from specific single cells in the fouror eightor sixteen-cell stage of the developing egg. In other words, each of these early daughter cells, which are, in effect, specific parts of the original, one-celled fertilized egg, produces a specific part of the later embryo and developed individual. Which is what would be expected from preformation.

Also, if the group of daughter cells resulting from the repeated egg celldivisions are prevented from assuming their normal relative position with regard to each other, by being compressed between thin sheets of glass, and so made to lie all in one plane instead of in a spherical mass; or if they are otherwise constrained to depart from their usual habit of arrangement, then, when the constraint is removed, they tend strongly to assume the space-relation to each other characteristic of normal development. On the other hand, if this physical constraint lasts too long, or if the usual medium in which the egg develops, — sea water, say, — is modified by changing its physical character (density), or its chemical composition, then this change in environment produces a structural change in the character of the embryo, or larva, into which the egg develops.

In a word, the experiments of the students of Entwicklungs-Mechanik show that, while there are strong intrinsic influences in the egg, which guide its development under usual or normal environmental conditions along a definite path, yet any sufficient modification of the extrinsic conditions (environment) affecting the developing egg or embryo can change this path and produce a modified individual.

Well, we shall see (in our next paper) that exactly the same struggle or correlation exists between heredity (intrinsic influences) and environment or education (extrinsic influences) all through the post-embryonic development of any animal and the childhood and adolescence of a human being. And the outcome of this development, all the physical, mental, and spiritual characters of the new individual, is the resultant of these sometimes opposing, sometimes reinforcing, intrinsic and extrinsic factors or influences.

My little girl is what she is so far, and will be what she is at any time in her life, because of the interacting influences on her of her biological inheritance (intrinsic factors) and her social inheritance (environment and education). I cannot do anything now to change her biological inheritance, but I can do much to control her social inheritance. We are back to our question of the beginning of this paper. ‘A lot goes just naturally with being born, and this may be good, or less good, or even bad. Can this good be made better, and how much better, and this bad be made less bad, or even not bad at all, by doing something to children after birth?’

In our next paper, I propose to seek for some light on this by an examination of the facts of the ‘new heredity.’ By the new heredity I mean what has been learned in the last fifty years. It is more than had been learned in all time before.

(Dr. Kellogg’s next paper will be ‘The New Heredity’)