Sexual dimorphism

“ Different kinds of animals and plants may be distinguished by the extent to which the characters of one sex are rudimentary in the other. The most extreme case of sexual differentiation, the sharpest gonochorism, occurs in sexual dimorphism, that is to say, in that condition of affairs in which (as for instance in some water-fleas) the males and females of the same species differ as much or even more from each other as the members of different species, or genera. ”

“ Thus these moths furnish an excellent illustration of what is called sexual dimorphism, a term used for those animals in which the sexes are very different in appearance, a subject to which Charles Darwin gave considerable attention, in his "Descent of Man." ”

“ The prospects of the movement for intellectual advance on the part of women are not very promising; but still less promising is another view, sometimes discussed in the same connection, the view that the human race is moving towards a complete sexual differentiation, a definite sexual dimorphism. ”

“ Dimorphism of men and women varies according to race or rather according to species. Very feeble in most blacks and reds it is accentuated among Semites, Aryans, and Finns. But in man as in all animals of separate sexes one must differentiate between the primary dimorphism, which is necessary and produced by the specialization of sexual organs, and the secondary dimorphism with which the relation of sex is less evident or wholly uncertain. Limited to the non-sexual elements, human dimorphism is very feeble. ”

“ It varies individually, even during the years of greatest reproductivity, in males feebly sexed and in women heavily sexed: that is to say there are men and women whose type closely approaches the type-ideal formed by the fusion of sexes; neither one nor the other escapes the radical dimorphism imposed by the difference of sexual organs. ”

“ We had then concluded from our examination of the sexual habits of insects, mammals, and birds that a marked differentiation between the female and the male existed already in the early stages of the development of species, and that such divergence, or sex-dimorphism, to use the biological term, becomes more and more frequent and conspicuous as we ascend to the higher types. The essential functions of females and males become more separate, their habits of life tend to diverge, and to the primary differences there are added all manner of secondary peculiarities. ”

“ The chief remaining differences, the growth of the beard and the pubic hair, and the development of the characteristically masculine larynx, usually manifest themselves after the close of the second period of childhood--that is to say, during the period of youth.
As children become physically differentiated in respect of sex, so also does a mental differentiation ensue. Authorities are not agreed as to whether mental sexual differentiation exists in the very earliest years of life. ”

“ There exists vast diversity in the anatomy and psyche of androgynes—just as, from the standpoint of size and shape of the genitalia and sexual tastes, any two full-fledged males or any two full-fledged females differ more or less. ”

“ It is true that the tendency of the dream and the unconscious fancy to utilize the sexual symbol bisexually betrays an archaic trend, for in childhood a difference in the genitals is unknown, and the same genitals are attributed to both sexes. ”

“ Your view seems to be that variations occurring in one sex are transmitted either to that sex exclusively or to both sexes equally, or more rarely partially transferred. But we have every gradation of sexual colours, from total dissimilarity to perfect identity. ”

“ But when the colours are diversified and strongly pronounced, when they are not developed until near maturity, and when they are lost after emasculation, we can hardly avoid the conclusion that they have been acquired through sexual selection for the sake of ornament, and have been transmitted exclusively, or almost exclusively, to the same sex. ”

“ These characteristics of one sex that are wanting in the other, and that are not directly connected with the sexual organs—such as the man's beard, the woman's breasts, the lion's mane, or the goat's horns—have also an æsthetic interest; they have, as Darwin showed, been acquired by sexual selection, as weapons of the male in the struggle for the female, and vice versa. ”

“ The absence of hair on the body is to a certain extent a secondary sexual character; for in all parts of the world women are less hairy than men. Therefore we may reasonably suspect that this is a character which has been gained through sexual selection. ”

“ Thus we find, among most of the peoples of Europe, Asia, and Africa, the chief continents of the world, that the large hips and buttocks of women are commonly regarded as an important feature of beauty. This secondary sexual character represents the most decided structural deviation of the feminine type from the masculine, a deviation demanded by the reproductive function of women, and in the admiration it arouses sexual selection is thus working in a line with natural selection. ”

“ The one physical feminine stigma that is indispensable to the possession of a decidedly feminine psyche and the quasi-female method of sexual expression is the female variety of brain protoplasm. For there have probably lived naturally beardless men, males possessing milk glands or sissie voices, etc., who have nevertheless not been at all homosexual. ”

“ The physical bisexual characters—those of the opposite sex being present in rudimentary form—are readily observable. In the male, there are the vestigial breasts and nipples, and other rudimentary features less prominent; and sometimes a general feminine contour of body is noticeable in the male. ”

“ Similarly, the smooth-bodied negroes, transported to America, and subjected at once to a change of conditions and to circumstances which would render sexual selection impossible as regards the hairlessness of the body, rapidly redevelop hair upon the chest. For we must remember that sexual selection can only act in this direction while a race remains wholly or mainly naked. Clothing, by concealing the greater part of the skin, necessarily confines the selective process to features, complexion, and figure. ”

“ If, as seems probable, they habitually drive away rival females, and by the display of their bright colours or other charms endeavour to attract the males, we can understand how it is that they have gradually been rendered, by means of sexual selection and sexually-limited transmission, more beautiful than the males—the latter being left unmodified or only slightly modified. ”

“ Or, granting that differentiation has occurred, if the mating preferences are then stereotyped, all further differentiation, so far as colour and form are concerned, will be rendered impossible; for divergent modifications, not meeting the stereotyped standard of taste, will for that reason fail to be perpetuated. We must admit, then, that these mating preferences are subject to variation. And now we come to the central question with regard to sexual selection by means of preferential mating. What guides the variation along special lines leading to heightened beauty? ”

“ If to every deviation from that original form and structure, which gives character to the productions of nature, we apply the term monster, we shall find but very few, and from this whole class there will be a very small number indeed of sexual malformations. If the sexes be deprived of the generative organs, they approach each other in disposition and appearance. All those who are partly male and partly female in their organization, unite, to a certain extent, the characteristics of both sexes. When the female loses her prolific powers, many of her sexual peculiarities and attractions wane. ”

“ Now it will be admitted—or, at any rate, it seems likely—that the principal differences in the psychology of the sexes have their root in the sexual separation itself, inasmuch as certain main channels of thought and feeling seem by this to be cut off from the one sex or the other, especially from the male one. ”

“ And as no other function can be assigned to it than that of charming the female when it is erected in courtship, the peculiarity of form and mechanism which it presents—like the elaboration of patterns in cases where colour only is concerned—virtually compels us to recognise in sexual selection the only conceivable cause of its production. ”

“ This process, however, though it might lead to the modification of both sexes, would not make the one sex different from the other, unless, indeed, their tastes for the beautiful differed; but this is a supposition too improbable to be worth considering in the case of any animal excepting man. There are, however, many animals in which the sexes resemble each other, both being furnished with the same ornaments, which analogy would lead us to attribute to the agency of sexual selection. ”

“ But the evidence is rendered as complete as it can ever be, only when the more ornamented individuals, almost always the males, voluntarily display their attractions before the other sex; for we cannot believe that such display is useless, and if it be advantageous, sexual selection will almost inevitably follow. We may, however, extend this conclusion to both sexes, when coloured alike, if their colours are plainly analogous to those of one sex alone in certain other species of the same group. ”

“ The most extreme deviation of sexual type approaching the opposite sex, such as hypertrophy of the clitoris and full facial hair growth in the female, or hypospadia penis-scrotalis and gynecomasty in the male are found linked with heterosexuality more often than with homosexuality. ”

“ Most of our domestic races have been formed by the accumulation of many slight variations; and as some of the successive steps have been transmitted to one sex alone, and some to both sexes, we find in the different breeds of the same species all gradations between great sexual dissimilarity and complete similarity. ”

“ The problem of the bisexual girl-boy or androgyne has been presented for the learned professions in my Autobiography of an Androgyne and The Riddle of the Underworld. But to accomplish my three aims, it is necessary that the general reader have instilled into his mind that sexual intermediates are not to blame for their cross-sex idiosyncrasies. Such knowledge could not besmirch the soul of the general reader, but only benefit him morally. ”

“ In the first place it is matter of common knowledge that many women, who so far as their physical reproductive capacity goes are perfectly normal, show various mental traits which are more characteristic of men, and vice versa. What is more, the “masculinoid” woman (to use the current jargon) tends physically also to be less feminine, to have the feminine secondary sexual characteristics in stature, form of skeleton, distribution of fat, breasts, etc.—less strongly developed than normal, while the “feminoid” man shows the reverse tendency. ”

“ On the other hand, the differences in colour between the sexes, whether great or small, may to a large extent be explained on the principle of the successive variations, acquired by the males through sexual selection, having been from the first more or less limited in their transmission to the females. ”

“ We are assured, however, that it is not alone to the reproductive organs and their functions that we are to look for the chief differences in the constitution and character of the sexes. Neither is it entirely to Natural Selection that we are to seek for the causes which underlie the specialization peculiar to the two diverging lines of sexual demarcation ”

“ But in Europe men often develop hair about the chest and legs, though not upon the back and shoulders, while women seldom or never do so. Here we see that the hair reappears in the less differentiated male sex rather than in the more differentiated females, with whom sexual selection has produced greater effects ”

“ What is inherited, then, may well be not the secondary sexual characters themselves, but the influence of the genitalia, the tendency to the disruption of spare material and its deposition in particular regions, a process which certainly appears to become fixed after numerous generations. ”

“ There may be simply a union of the perfect body of one sex with the susceptibility to such sexual charms as ordinarily attract the other sex alone, or with the mental traits of the other sex. Or the individual may possess the male genitals, but be beardless, or else possess mammary glands, broad pelvis, and sacral dimples; or possessing the female genitals, have a rudimentary moustache, or else meagrely developed breasts, narrow pelvis, etc. Instances have been known of human beings with an ovary on one side of the body and a testicle on the other, and of males who were able to suckle infants. ”

“ We now know that the problem of sex does not rest merely in the complete development of the primary sexual organs; we know that fertile unions do not depend merely on the act of pairing, but on the functional activity of those ancillary glands already referred to. And it may well be that some change in the character of the secretions has not only altered the numerical values of the sexes, but reversed the normal rôle of coloration and behaviour. ”

“ From the ardour of the male throughout the animal kingdom, he is generally willing to accept any female; and it is the female which usually exerts a choice. Hence if sexual selection has here acted, the male, when the sexes differ, ought to be the most brilliantly coloured; and this undoubtedly is the ordinary rule. When the sexes are brilliantly coloured and resemble each other, the characters acquired by the males appear to have been transmitted to both sexes. But will this explanation of the similarity and dissimilarity in colour between the sexes suffice? ”