SEX IN TERMS OF INTERNAL SECRETIONS

Continuity of germplasm; The sex chromosome; The internal secretions and the sex complex; The male and the female type of body; How removal of sex glands affects body type; Sex determination; Share of egg and sperm in heredity; Nature of sex sexual selection of little importance; The four main types of secretory systems; Sex and sex-instincts of rats modified by surgery; Dual basis for sex; Opposite-sex basis in every individual; The Free-Martin cattle; Partial reversal of sex in man.

In Chapter I, the “immortality” of the protoplasm in the germ cells of higher animals, as well as in simpler forms without distinct bodies, was mentioned. In these higher animals this protoplasm is known as germplasm, that in body cells as somatoplasm.

All that is really meant by “immortality” in a germplasm is continuity. That is, while an individual may consist of a colony of millions of cells, all of these spring from one cell and it a germ cell the fertilized ovum. This first divides to form a new group of germ cells, which are within the embryo or new body when it begins to develop, and so on through indefinite generations. Thus the germ cells in an individual living to-day are the lineal descendants, by simple division, of the germ cells in his ancestors as many generations, or thousands of generations, ago as we care to imagine. All the complicated body specializations and sex phenomena may be regarded as super-imposed upon or grouped around this succession of germ cells, continuous by simple division.

The type of body in each generation depends upon this germplasm, but the germplasm is not supposed to be in any way modified by the body (except, of course, that severe enough accidents might damage it). Thus we resemble our parents only because the germplasm which directs our development is a split-off portion of the same continuous line of germ cells which directed their development, that of their fathers, and so on back. This now universally accepted theory is called the “continuity of the germplasm.”

It will be seen at once that this seems to preclude any possibility of a child’s inheriting from its parents anything which these did not themselves inherit. The bodies of each generation are, so to speak, mere “buds” from the continuous lines of germplasm. If we develop our muscles or our musical talent, this development is of the body and dies with it, though the physical basis or capacity we ourselves inherited is still in the germplasm and is therefore passed along to our children. We may also furnish our children an environment which will stimulate their desire and lend opportunity for similar or greater advancement than our own. This is social inheritance, or the product of environment easy to confuse with that of heredity and very difficult to separate, especially in the case of mental traits.

It will likewise become clear as we proceed that there is no mechanism or relationship known to biology which could account for what is popularly termed “pre-natal influence.” A developing embryo has its own circulation, so insulated from that of the mother that only a few of the most virulent and insidious disease germs can ever pass the barrier. The general health of the mother is of utmost importance to the vitality, chances of life, constitution and immunity from disease of the unborn child. Especially must she be free from diseases which may be communicated to the child either before or at the time of birth. This applies particularly to gonorrhoea, one of the most widely prevalent as well as most ancient of maladies, and syphilis, another disastrous and very common plague which is directly communicable. As to “birthmarks” and the like being directly caused by things the mother has seen or thought about, such beliefs seem to be founded on a few remarkable pure coincidences and a great deal of folk-lore.

Reproduction in its simplest form is, then, simply the division of one cell into two parts, each of which develops into a replica of the original. Division is also the first stage in reproduction in the most complicated animal bodies. To get an idea of what takes place in such a division we must remember that a cell consists of three distinct parts: (a) the protoplasm or cytoplasm, (b) the nucleus, and (c) a small body known as the centrosome which need not be discussed here.

When a cell division takes place, the nucleus breaks up into a number of thread-like portions which are known as chromosomes. There are supposed to be 24 pairs, or 48, in the human cell. All the evidence indicates that these chromosomes carry the “factors” in inheritance which produces the characters or characteristics of the individual body.

In mitosis or ordinary cell division, these chromosomes split lengthwise, so that the new cells always have the same number as the original one. When the germ-cells of the male and female make the division which marks the first step in reproduction, however, the process is different. Half the chromatin material passes into each of the two cells formed. This is called maturation, or the maturation division, and the new cells have only half the original number of chromosomes. Each of these divides again by mitosis (the chromosomes splitting lengthwise), the half or haploid number remaining. The result is the gametes (literally “marrying cells” from the Greek game, signifying marriage). Those from the male are called sperms or spermatozoa and those from the female eggs or ova. (The divisions to form ova present certain complications which need not be taken up in detail here.) Of the 24 chromosomes in each sperm or egg we are here concerned with only one, known as the sex chromosome because, in addition to transmitting other characteristics, it determines the sex of the new individual.

Neither the ovum nor the spermatozoon (the human race is referred to) is capable alone of developing into a new individual. They must join in the process known as fertilization. The sperm penetrates the egg (within the body of the female) and the 24 chromosomes from each source, male and female, are re-grouped in a new nucleus with 48 chromosomes the full number.

The chances are half and half that the new individual thus begun will be of a given sex, for the following reason: There is a structural difference, supposed to be fundamentally chemical, between the cells of a female body and those of a male. The result is that the gametes (sperm and eggs) they respectively produce in maturation are not exactly alike as to chromosome composition. All the eggs contain what is known as the “X” type of sex chromosome. But only half the male sperm have this type in the other half is found one of somewhat different type, known as “Y.” (This, again, is for the human species in some animals the mechanism and arrangement is somewhat different.) If a sperm and egg both carrying the X-type of chromosome unite in fertilization, the resulting embryo is a female. If an X unites with a Y, the result is a male. Since each combination happens in about half the cases, the race is about half male and half female.

Thus sex is inherited, like other characters, by the action of the chromatin material of the cell nucleus. As Goldschmidt remarks, this theory of the visible mechanism of sex distribution “is to-day so far proven that the demonstration stands on the level of an experimental proof in physics or chemistry.” But why and how does this nuclear material determine sex? In other words, what is the nature of the process of differentiation into male and female which it sets in motion?

To begin with, we must give some account of the difference between the cells of male and female origin, an unlikeness capable of producing the two distinct types of gametes, not only in external appearance, but in chromosome makeup as well. It is due to the presence in the bodies of higher animals of a considerable number of glands, such as the thyroid in the throat and the suprarenals just over the kidneys. These pour secretions into the blood stream, determining its chemical quality and hence how it will influence the growth or, when grown, the stable structure of other organs and cells. They are called endocrine glands or organs, and their chemical contributions to the blood are known as hormones.

Sometimes those which do nothing but furnish these secretions are spoken of as “ductless glands,” from their structure. The hormones (endocrine or internal secretions) do not come from the ductless glands alone but the liver and other glands contribute hormones to the blood stream, in addition to their other functions. Some authorities think that “every cell in the body is an organ of internal secretion", and that thus each influences all the others. The sex glands are especially important as endocrine organs; in fact the somatic cells are organized around the germ cells, as pointed out above. Hence the sex glands may be considered as the keys or central factors in the two chemical systems, the male and the female type.

These various hormones or chemical controllers in the blood interact in a nicely balanced chemical system. Taken as a whole this is often called the “secretory balance” or “internal secretory balance.” This balance is literally the key to the sex differences we see, because it lies back of them; i.e., there are two general types of secretory balance, one for males and one for females. Not only are the secretions from the male and the female sex glands themselves quite unlike, but the whole chemical system, balance or “complex” involved is different. Because of this dual basis for metabolism or body chemistry, centering in the sex glands, no organ or cell in a male body can be exactly like the corresponding one in a female body.

In highly organized forms like the mammals (including man), sex is linked up with all the internal secretions, and hence is of the whole body. As Bell [2, ] states it: “We must focus at one and the same time the two essential processes of life the individual metabolism and the reproductive metabolism. They are interdependent. Indeed, the individual metabolism is the reproductive metabolism.”

Here, then, is the reason men have larger, differently formed bodies than women why they have heavier bones, tend to grow beards, and so on. The sex glands are only part of what we may call a well-organized chemical laboratory, delivering various products to the blood, but always in the same general proportions for a given sex. The ingredients which come from the sex glands are also qualitatively different, as has been repeatedly proved by injections and otherwise.

Each of these sex types, male and female, varies somewhat within itself, as is true of everything living. The two are not so far apart but that they may overlap occasionally in some details. For instance, some women are larger than are some men have lower pitched voices, etc. The whole bodily metabolism, resting as it does upon a chemical complex, is obviously more like the male average in some women than it is in others, and vice versa. But the average physical make-up which we find associated with the male and female sex glands, respectively, is distinctive in each case, and a vast majority of individuals of each sex conform nearly enough to the average so that classification presents no difficulty.

The extreme as well as the average body types existing in the presence of the respective types of sex-glands are different. For example, we find an occasional hen with male spurs, comb or wattles, though she is a normal female in every other respect, and lays eggs. But we never find a functional female (which lays eggs) with all the typical characteristics of the male body. Body variation can go only so far in the presence of each type of primary sexuality (i.e., sex-glands).

The bodily peculiarities of each sex, as distinguished from the sex-glands or gonads themselves, are known as secondary sex characters. To put our statement in the paragraph above in another form, the primary and secondary sex do not always correspond in all details. We shall find as we proceed that our original tentative definition of sex as the ability to produce in the one case sperm, in the other eggs, is sometimes difficult to apply. What shall we say of a sterile individual, which produces neither? The problem is especially embarrassing when the primary and secondary sex do not correspond, as is sometimes the case.

Even in a fully grown animal, to remove or exchange the sex glands (by surgery) modifies the bodily type. One of the most familiar cases of removal is the gelding or desexed horse. His appearance and disposition are different from the stallion, especially if the operation takes place while he is very young. The reason he resembles a normal male in many respects is simply that sexuality in such highly-organized mammals is of the whole body, not of the sex-glands or organs alone.

Suppose this horse was desexed at two years old. Nearly three years had elapsed since he was a fertilized egg. During the eleven months or so he spent within his mother, he developed a very complicated body. Beginning as a male, with a male-type metabolism (that is, as the result of a union between an X and a Y chromosome, not two X’s), all his glands, as well as the body structures they control, developed in its presence. Not only the sex glands, but the liver, suprarenals, thyroid the whole body in fact became adjusted to the male type. He had long before birth what we call a male sex complex. Complex it is, but it is, nevertheless, easy enough to imagine its nature for illustrative purposes. It is simply all the endocrine or hormone-producing organs organized into a balanced chemical system adjusted to each other.

When the horse had had this body and this gland system for nearly three years (eleven months within his mother’s body and twenty-four outside), it had become pretty well organised and fixed. When a single chemical element (the hormones from the sex-glands) was withdrawn, the system (thus stereotyped in a developed body and glands) was modified but not entirely upset. The sex complex remained male in many respects. It had come to depend upon the other chemical plants, so to speak, quite as much as upon the sex glands. The later the castration is performed the more fixed the body and gland type has become the closer the horse will resemble a normal male. Much laboratory experimentation now goes to show that some accident while this horse was still a fertilized egg or a very small embryo might have upset this male type of body chemistry perhaps even caused him to develop into a female instead, if it took place early enough. This is well illustrated by the so-called “Free-Martin” cattle, to be described later.

For a long time a controversy raged as to whether sex is determined at the time of fertilization, before or after. Biologists now generally prefer to say that a fertilized egg is “predisposed” to maleness or femaleness, instead of “determined.” The word “determined” suggests finality, whereas the embryo appears to have in the beginning only a strong tendency or predisposition toward one sex type or the other. It is now quite commonly believed that this predisposition arises from the quantity rather than the quality or kind of factors in the chemical impetus in the nuclei of the conjugating gametes. A later chapter will be devoted to explaining the quantitative theory of sex.

Hence the modern theory of “sex determination” has become:

1. That the chemical factors which give rise to one sex or the other are present in the sperm and ovum before fertilization;

2. That a tendency or predisposition toward maleness or femaleness arises at the time of fertilization, depending upon which type of sperm unites with the uniform type of egg (in some species the sperm is uniform while the egg varies);

3. That this predisposition is:

a. Weaker at first, before it builds up much of a body and gland system
to fix it;

b. Increasingly stronger as the new body becomes organized and
developed;

c. Liable to partial or complete upset in the very early stages;

d. Probably quantitative stronger in some cases than in others.

The new definition is, then, really a combination and amplification of the three older points of view.

The term “sex determination” does not mean to the biologist the changing or determining of the sex at will on the part of the experimenter. This might be done by what is known as “selective fertilization” artificially with only the kind of sperm (X or Y as to chromosomes) which would produce the desired result. There is as yet no way to thus select the sperm of higher animals. It has been authoritatively claimed that feeding with certain chemicals, and other methods to be discussed later, has affected the sex of offspring. These experiments (and controversies) need not detain us, since they are not applicable to the human species.

Let us consider this fertilized egg the contributions of the father and the mother. The total length of the spermatozoon is only about 1/300 of an inch, and 4/5 of this is the tail. This tail does not enter the egg, and has no other known function than that of a propeller. Its movement has been studied and found to be about 1/8 of an inch per minute. Only the head and neck enter the egg. This head consists almost entirely of the nuclear material which is supposed to determine the characters of the future individual.

The ovum or egg contributed by the mother is much larger nearly round in shape and about 1/120 of an inch in diameter. Besides its nucleus, it contains a considerable amount of what used to be considered as “stored nutritive material” for the early development of the individual.

In ancient times the female was quite commonly supposed to be a mere medium of development for the male seed. Thus the Laws of Manu stated that woman was the soil in which the male seed was planted. In the Greek Eumenides, Orestes’ mother did not generate him, but only received and nursed the germ. These quaint ideas of course originated merely from observation of the fact that the woman carries the young until birth, and must not lead us to imagine that the ancients actually separated the germ and somatic cells in their thinking.

A modern version of this old belief was the idea advanced by Harvey that the ovum consisted of fluid in which the embryo appeared by spontaneous generation. Loeuwenhoek’s development of the microscope in the 17th century led immediately to the discovery of the spermatozoon by one of his students. At the time, the “preformation theory” was probably the most widely accepted i.e., that the adult form exists in miniature in the egg or germ, development being merely an unfolding of these preformed parts. With the discovery of the spermatozoon the preformationists were divided into two schools, one (the ovists) holding that the ovum was the container of the miniature individual, the other (animalculists) according this function to the spermatozoon. According to the ovists, the ovum needed merely the stimulation of the spermatozoon to cause its contained individual to undergo development, while the animalculists looked upon the spermatozoon as the essential embryo container, the ovum serving merely as a suitable food supply or growing place.

This nine-lived notion of male supremacy in inheritance was rather reinforced than removed by the breeding of domestic animals in the still more recent past. Attention has been focused on a few great males. For example, the breed of American trotting horses all goes back to one sire Hambletonian 10. The great Orloff Stud Book, registering over a million individuals, is in the beginning founded on a single horse a male. It is not strange that we still find among some breeders vestiges of the ancient belief that the male predominates in inheritance. A superior male can impress his characters in a single year upon 100 times as many colts as a female of equal quality could produce in her lifetime. So slight an incident in his life is this reproductive process for each individual that he could if he devoted his life solely to reproduction stamp his characters upon a thousand times as many colts as could a female. Thus under artificial breeding conditions, the good males do have a tremendously disproportionate share in improving the whole breed of horses, though each single horse gets his qualities equally from his male and female parents.

Though Mendel knew an astonishing amount about inheritance a half-century ago, it is worth noting that the foundation upon which rests our present knowledge of sex has been discovered less than twenty years before the reference is, of course, to the chromosomes as the carriers of inheritance. While from the standpoint of biology the opinions of two decades ago about sex literally belong to a different age, some of them have been so persistent in sociological thought and writings that they must be briefly reviewed in order that the reader may be on his guard against them. Books which still have a wide circulation deal with the sex problem in terms of a biology now no more tenable than the flatness of the earth.

On the one hand were the ancient traditions of male predominance in inheritance, reinforced by the peculiar emphasis which animal breeding places upon males. On the other hand, biologists like Andrew Wilson had argued as early as the seventies of the past century for female predominance, from the general evidence of spiders, birds, etc. Lester F. Ward crystallized the arguments for this view in an article entitled “Our Better Halves” in The Forum in 1888. This philosophy of sex, which he christened the “Gynaecocentric Theory,” is best known as expanded into the fourteenth chapter of his “Pure Sociology,” published fifteen years later. Its publication at this late date gave it an unfortunate vitality long after its main tenets had been disproved in the biological laboratory. Germ-cell and body-cell functions were not separated. Arguments from social structures, from cosmic, natural and human history, much of it deduced by analogy, were jumbled together in a fashion which seems amazing to us now, though common enough thirty years ago. It was not a wild hypothesis in 1888, its real date, but its repeated republication (in the original and in the works of other writers who accepted it as authoritative) since 1903 has done much to discredit sociology with biologists and, what is more serious, to muddle ideas about sex and society.

In 1903, Weismann’s theory of the continuity of the germplasm was ten years old. De Vries’ experiments in variation and Mendel’s rediscovered work on plant hybridization had hopelessly undermined the older notion that the evolution or progress of species has taken place through the inheritance of acquired characters that is, that the individuals developed or adapted themselves to suit their surroundings and that these body-modifications were inherited by their offspring. As pointed out in Chapter I, biologists have accepted Weismann’s theory of a continuous germplasm, and that this germplasm, not the body, is the carrier of inheritance. Nobody has so far produced evidence of any trace of any biological mechanism whereby development of part of the body say the biceps of the brain of the individual could possibly produce such a specific modification of the germplasm he carries as to result in the inheritance of a similar development by his offspring.

Mendel’s experiments had shown that the characters we inherit are units or combinations of units, very difficult to permanently change or modify. They combine with each other in all sorts of complicated ways. Sometimes one will “dominate” another, causing it to disappear for a generation or more; but it is not broken up. These characters have a remarkable way of becoming “segregated” once more that is, of appearing intact later on.

While it follows from Weismann’s theory that an adaptation acquired by an individual during his lifetime cannot be transmitted to his offspring, it remained for De Vries to show authoritatively that evolution can, and does, take place without this. Once this was established, biologists cheerfully abandoned the earlier notion. Lester Ward and the biologists of his day in general not only believed in the transmission of acquired characters, but they filled the obvious gaps which occurred in trying to apply this theory to the observed facts by placing a fantastic emphasis upon sexual selection. That is, much progress was accounted for through the selection by the females of the superior males. This, as a prime factor in evolution, has since been almost “wholly discredited” (Kellogg’s phrase) by the careful experiments of Mayer, Soule, Douglass, Duerigen, Morgan and others. The belief in sexual selection involved a long string of corollaries, of which biology has about purged itself, but they hang on tenaciously in sociological and popular literature. For instance, Ward believed in the tendency of opposites to mate (tall men with short women, blonds with brunettes, etc.), although Karl Pearson had published a statistical refutation in his Grammar of Science, which had run through two editions when the Pure Sociology appeared. The greater variability of males than females, another gynaecocentric dogma had also been attacked by Pearson on statistical evidence in 1897 (in the well-known essay on Variation in Man and Woman, in Chances of Death) and has become increasingly unacceptable through the researches of Mrs. Hollingworth[6,7,8]. The idea of a vanished age of mother-rule in human society, so essential to the complete theory, has long since been modified by anthropologists.

De Vries’ experiments showed that a moderately simple fact practically makes all these complicated theories unnecessary. No two living things are exactly alike that is, all living matter is more or less variable. Some variations are more fortunate than others, and these variants are the ones which survive the ones best adapted to their environment. Given this fact of the constant variation of living matter, natural selection (i.e., survival of the fittest and elimination of the unfit) is the mechanism of evolution or progress which best accounts for the observed facts. Such variation is called “chance variation,” not because it takes place by “chance” in the properly accepted sense of the term, but because it is so tremendously varied is evidently due to such complicated and little-understood circumstances that it can best be studied mathematically, using statistical applications of the “theory of probabilities.”

The fine-spun, elaborate theories about sex, so current twenty years ago, have fallen into almost complete desuetude among scientists. With the discovery of the place of the chromosomes in inheritance, biologists began to give their almost undivided attention to a rigid laboratory examination of the cell. This has included sex phenomena since McClung and Sutton pointed out the function of the sex chromosome in 1902 and 1903. Present-day “theories” are little more than working hypotheses, developed, not in a library or study, but with one eye glued to a high-power microscope.

Besides its faulty foundation as to facts, the old gynaecocentric theory involved a method of treatment by historical analogy which biologists have almost entirely discarded. Anyone interested in the relative value of different kinds of biological data for social problems would do well to read the opening chapter of Prof. Morgan’s “Critique of the Theory of Evolution", for even a summary of which space is lacking here. College reference shelves are still stocked with books on sex sociology which are totally oblivious of present-day biology. For example, Mrs Gilman (Man-Made World), Mrs Hartley (Truth About Woman) and the Nearings (Woman and Social Progress) adhere to Ward’s theory in substantially its primitive form, and not even sociologists like Professor Thomas (Sex and Society) have been able to entirely break away from it.

The old question of male and female predominance in inheritance has been to a considerable extent cleared up, to the discomfiture of both sides to the controversy. Most exhaustive experiments failed to trace any characters to any other part of either sperm or egg than the nucleus. Transmission of characteristics seemed to be absolutely equal by the two parents. The male nucleus enters the egg practically naked. Hence if the characters are transmitted equally, there is certainly ground for supposing that only the nucleus of the egg has such functions, and that the remainder merely provides material for early development. Yet this does not seem to be strictly true.

Parthenogenesis (development of eggs without agency of male sperm) proves that in many simple forms the female nucleus alone possesses all the essential determiners for a new individual. Boveri’s classic experiment proved the same thing for the male nucleus. He removed the nuclei from sea-urchin eggs and replaced them with male nuclei. Normal individuals developed. To make things still more certain, he replaced the female nucleus with a male one from a different variety of sea-urchin. The resulting individual exhibited the characteristics of the male nucleus only none of those of the species represented by the egg. Here, then, was inheritance definitely traced to the nucleus. If this nucleus is a male the characters are those of the male line; if a female those of the female line, and in sexual reproduction where the two are fused, half and half.

Yet the fact remained that all efforts to develop the spermatozoon alone (without the agency of any egg material at all) into an individual had signally failed. Conklin had found out in 1904 and 1905 that the egg cytoplasm in Ascidians is not only composed of different materials, but that these give rise to definite structures in the embryo later on. So a good many biologists believed, and still believe[12,13,14] that the egg is, before fertilization, a sort of “rough preformation of the future embryo” and that the Mendelian factors in the nuclei “only impress the individual (and variety) characters upon this rough block.”

If we look at these views from one angle, the apparent conflict disappears, as Professor Conklin points out. We can still presume that all the factors of inheritance are carried in the nucleus. But instead of commencing the life history of the individual at fertilization, we must date it back to the beginning of the development of the egg in the ovary. Whatever rude characters the egg possesses at the time of fertilization were developed under the influence of the nucleus, which in turn got them half and half from its male and female parents. These characters carried by the female across one generation are so rudimentary that they are completely covered up, in the developing embryo, by those of the new nucleus formed by the union of the sperm with the egg in fertilization.

In case fertilization does not take place, this rude beginning in the egg is lost. Since no characteristic sex is assumed until after fertilization, we may say that life begins as neuter in the individual, as it is presumed to have done in the world. It will occur to those inclined to speculation or philosophic analysis that by the word “neuter” we may mean any one or all of three things: (a) neither male nor female; (b) both male and female, as yet undifferentiated, or (c) potentially either male or female. Clearly, the above explanation assumes a certain germinal specialization of the female to reproduction, in addition to the body specialization for the intra-parental environment (in mammals).

A tremendous amount of laboratory experimentation upon animals has been done in late years to determine the nature of sex. For example, Goodale castrated a brown leghorn cockerel twenty-three days old and dropped pieces of the ovary of a female bird of the same brood and strain into the abdominal cavity. These adhered and built up circulatory systems, as an autopsy later showed. This cockerel, whose male sex glands had been exchanged for female ones, developed the female body, and colouration so completely that expert breeders of the strain pronounced it a female. He found that simply removing the female sex glands invariably led to the development of spurs and male plumage. But simple removal of the male sex glands did not alter plumage. To make sure, he replaced the male sex glands with female, and found that the former male developed female plumage.

This obviously signifies that in birds the female is an inhibited male.[4, .] Either sex when castrated has male feathers the male has them either with or without testes, unless they are inhibited by the presence of (transplanted) ovaries. It will be remembered that the sociological theory of sex held by Ward, Mrs. Hartley and a host of others was founded on the supposition that evolution or development of a species is chiefly due to selection by the females of the better males, a conclusion based almost entirely on bird evidence. Ward states that “the change or progress, as it may be called, has been wholly in the male, the female remaining unchanged”; also that “the male side of nature shot up and blossomed out in an unnatural, fantastic way....” Speaking of the highly-coloured males, especially among birds, the same writer states that “the normal colour (italics ours) is that of the young and the female, and the colour of the male is the result of his excessive variability.” Goodale’s results completely refute this idea, and should bury for ever the well-known sociological notion of “male afflorescence.”

The general doctrine of a stable, “race-type” female and a highly variable male has been widely circulated. In tracing it back through voluminous literature, it appears to have been founded on an article published by W.I. Brooks in the Popular Science Monthly for June, 1879, fourteen years before Weissmann’s enunciation of the theory of continuity of the germ-plasm. Like Wallace, Brooks continued to study and experiment till the last, and finally withdrew from his earlier position on sexual selection. However, this has not prevented others from continuing to quote his discarded views innocently, of course.

Havelock Ellis and G. Stanley Hall have applied the idea of a “race-type” female with peculiar insistence to the human race. Goodale has finally killed the bird evidence upon which earlier workers so largely founded this doctrine, by showing that the “race type” toward which birds tend unless inhibited by the female ovarian secretion is the male type, not the female. There is a great difference in the way the internal secretions act in birds and in man, as will be pointed out later. It is so important that such a major point as general variability must be supported and corroborated by mammalian evidence to prove anything positively for man. As already noted, the statistical studies of Pearson and Mrs. Hollingworth et al. have yielded uniformly negative results.

In the utilization of data gathered from non-human species, certain differences in the systems of internal secretion must be taken into account. Birds differ from the human species as to internal secretory action in two vital particulars: (a) In the higher mammals, sex depends upon a “complex” of all the glands interacting, instead of upon the sex glands alone as in birds; (b) The male bird instead of the female is homogametic for sex i.e., the sperm instead of the eggs is uniform as to the sex chromosome.

Insects are (in some cases at least) like birds as to the odd chromosome the opposite of man. But as to secondary sex-characters they differ from both. These characters do not depend upon any condition of the sex organs, but are determined directly by the chemical factors which determine sex itself.

In crustacea, the male is an inhibited female (the exact opposite of birds), as shown by the experiments of Giard and Geoffrey Smith on crabs. A parasite, Sacculina neglecta, sometimes drives root-like growths into the spider crab, causing slow castration. The females thus desexed do not assume the male type of body, but castrated males vary so far toward the female type that some lay eggs[3, ; 20]. It is the discovery of such distinctions which makes it necessary to re-examine all the older biological evidence on the sex problem, and to discard most of it as insufficiently exact.

The work of Steinach[12, pp.225f.] on rats is another well-known example of changing sex characters by surgery. Steinach found that an ovary transplanted into a male body changed its characteristics and instincts into the female type. The growth of the male sex organs he found to be definitely inhibited by the ovaries. He went so far as to transplant the whole uterus and tube into the male body, where it developed normally. One of the most interesting of his results is the observation of how the instincts were changed along with the type of body. The feminized males behaved like normal females toward the other males and toward females. Likewise they were treated as normal females by the males.

It would be impossible to give here any just idea of the vast amount of rigid scientific experimentation which has been carried on in this field, or the certainty of many of the results. Sex is really known, about as well as anything can be known, to arise from the chemical causes discussed above. That is, the endocrine explanation is the correct one.

One of the most significant results of the transplantation experiments is the evidence that each individual carries the fundamental bases for both sexes. When Goodale changed a male bird into a female as to secondary characters and instincts by replacing one secretion with another, he was faced with the following problem: How can a single secretion be responsible for innumerable changes as to feather length, form and colouring, as to spurs, comb and almost an endless array of other details? To suppose that a secretion could be so complicated in its action as to determine each one of a thousand different items of structure, colour and behaviour would be preposterous. Besides, we know that some of these internal secretions are not excessively complicated for instance adrenalin (the suprarenal secretion) can be compounded in the laboratory. We may say that it cannot possibly be that the ovarian or testicular secretion is composed of enough different chemical substances to produce each different effect.

There remains only the supposition that the female already possesses the genetic basis for becoming a male, and vice versa. This is in accord with the observed facts. In countless experiments it is shown that the transformed female becomes like the male of her own strain and brood to state it simply, like the male she would have been if she had not been a female. If we think of this basis as single, then it must exhibit itself in one way in the presence of the male secretions, in another way under the influence of the female secretions. In this way a very simple chemical agent in the secretion might account for the whole difference merely causing a genetic basis already present to express itself in the one or the other manner.

This may be illustrated by the familiar case of the crustacea Artemia salina and Artemia Milhausenii. These are so unlike that they were long supposed to be different species; but it was later discovered that the genetic basis is exactly the same. One lives in 4 to 8% salt water, the other in 25% or over. If, however, the fresh-water variety is put in the saltier water with the salt-water variety, all develop exactly alike, into the salt-water kind. Likewise, if the salt-water variety is developed in fresh water, it assumes all the characteristics of the fresh-water kind. Thus the addition or subtraction of a single chemical agent common salt makes all the difference.

If this basis for sex is single, it is represented by the male plumage in domestic birds, the secretions from the sex-glands acting as modifiers. But a great deal of evidence has been produced to show that the genetic basis, in man and some other forms at least, is double. That is, we must think of two genetic bases existing in each individual each representing one of the two types of secondary sex characters. The primary sex (i.e., the sex glands) would then determine which is to express itself. In the domestic birds described above, the male type of body appears in the absence of the ovarian secretion, and the female type in its presence. In man and the more highly organized mammals, we must use “secretions” in the plural, since a number of them, from different glands, act together in a “complex.” Goodale, experimenting with birds, was unable to definitely decide whether the basis for sex was single or double in that material, though he favoured the latter explanation.

Dr Bell, the English gynecologist, using human surgical cases as a basis, commits himself strongly to the dual basis.[2, .] “Every fertilized ovum,” he says, “is potentially bisexual,” but has “a predominating tendency ... toward masculinity or femininity.” But “at the same time,” he remarks, “it is equally obvious that latent traits of the opposite sex are always present.” After discussing mental traits observed in each sex which normally belong to the other, he concludes as follows: “If further evidence of this bisexuality, which exists in everyone, were required, it is to be found in the embryological remains of the latent sex, which always exist in the genital ducts.”

In some lower forms, dual sexuality is apparent until the animal is fairly well developed. In frogs, for example, the sex glands of both sexes contain eggs in early life, and it is not possible to tell them apart with certainty, until they are about four months old.[12, .] Then the eggs gradually disappear in the male.

However, we need not depend upon non-mammalian evidence for either the secretory explanation or the dual basis. An ideal case would be to observe the effects of circulating the blood of one sex in a developing embryo of the other. This blood-transfusion occurs in nature in the “Free-Martin” cattle.

Two embryos (twins) begin to develop in separate membranes or chorions. At an early stage in this development, however, the arteries and veins of the two become connected, so that the blood of each may circulate through the body of the other. “If both are males or both are females no harm results from this...,” since the chemical balance which determines the bodily form in each case is of the same type. But if one is a male and the other a female, the male secretory balance dominates the female in a very peculiar fashion. The female reproductive system is largely suppressed. She even develops certain male organs, and her general bodily appearance is so decidedly masculine that until Dr Lillie worked out the case she had always been supposed to be a non-functional male. She is sterile. The blood transfusion not only alters the sex-type of her body, but it actually modifies the sex glands themselves, so that the ovary resembles a testicle, though dissection proves the contrary.

Why does not the female become a true, functional male? Perhaps she does in some cases. Such a one would not be investigated, since there would be no visible peculiarity. In all the cases examined, the embryo had begun its female development and specialization under the influence of a predisposition of the female type in the fertilized egg, before the transfusion began. There is no absolutely convincing mammalian evidence of the complete upset of this predisposition, so all one can say is that it is theoretically possible. Cases of partial reversal, sometimes called “intersexes,” are common enough. In birds and insects, where the material is less expensive and experimentation simpler, males have been produced from female-predisposed fertilized eggs and vice versa, as we shall see in the next chapter.

Dr Bell[2, pp.133f.] points out that the so-called human “hermaphrodites” are simply partial reversals of the sex type from that originally fixed in the fertilized egg. As has been remarked earlier in these pages, there is rarely if ever true hermaphroditism in higher animals i.e., cases of two functional sexes in the same individual. In fact, the pathological cases in the human species called by that name are probably not capable of reproduction at all.

Like the Free-Martin cattle, some accident has resulted in a mixture of male and female characteristics. This accident occurs after a certain amount of embryonic development has taken place under the influence of the original predisposition of the fertilized egg. The delicate secretory balance, so complex in man, is upset. With partially developed organs of one type and with a blood-chemistry of the opposite one, some curious results follow, as the illustrative plates in Dr Bell’s book show.

It should be remembered that sex in higher mammals is of the whole body, and depends upon all the secretions. Hence an accident to one of the other glands may upset the balance as well as one to the sex glands themselves. For example, 15% of Neugebauer’s cases of female tubular partial hermaphroditism had abnormal growths in the suprarenals.

Thus in the human species, it is possible for one type of sex glands to exist in the opposite type of body, as we saw it to be in cattle though it apparently could not occur unless compensated for in some way by the other secretions. This is a very great departure from birds, rats and guinea pigs, whose bodies change over their sex type when the gonads are transplanted. Birds take on the male appearance when the sex glands are removed (or retain it, if they are males). This is not true of man. The chemical life processes of the two sexes after puberty in the human species are quite characteristic. The male and female types are both very different from the infantile. When it becomes necessary to desex men, the resulting condition is infantile, not female.

The desexed man is of course the eunuch of ancient literature. If desexed near maturity, he might look like a normal man in many respects; but if the operation were performed before puberty, his development is simply arrested and remains infantile incomplete. Only in 1878 was the practice of desexing boys to get the famous adult male soprano voices for the Sistine Choir discontinued.

Removal of the ovaries in women likewise produces an infantile condition, which is pronounced only in case the operation takes place very young. From his clinical experience, Dr Bell [2, ] concludes that no very definite modifications can be produced in an adult woman by withdrawal of the ovarian secretion alone. “There must be,” he says, “some gross change in those parts of the endocritic system, especially apart from the genital glands, which normally produce masculinity potentiality that appears to be concentrated in the suprarenals, the pituitary and probably in the pineal.”

What, then, do we mean by “male” and “female” in man? Take Dr Russell Andrews’ patient: photographs[2, plate opposite ] show a rounded bodily outline, hairless face, well-developed mammae the female sex characteristics in every respect which the ordinary person could detect. Yet an operation proved that the sex glands themselves were male.

Presumably extreme cases like the above are rare. Obviously operations cannot be performed on all those with female-type bodies who do not bear children, to determine the primary sex, and conversely with men. This does, however, point the obvious question: Are not some we classify as men more male or masculine than others some we classify as women more feminine than others? Bearing in mind the fact that the genetic basis for both sexes exists in each individual, are not some women more masculine than others, some men more feminine than others? However much we may object to stating it just that way, the biological fact remains thus. The Greeks called these intermediate types urnings modern biology knows them as “intersexes.”

Only within the past few years have the general phenomena of intersexuality been cleared up to any considerable extent naturally on the basis of the secretory explanation of sex. This secretory or endocrine idea has also given us an entirely new view of sex differences. These are best discussed as functional rather than as structural. To correlate this material, we must next give a rude sketch of the quantitative theory of sex.