Sexual differentiation

“ From the very beginning of sexuality, when the idea of a bisexual differentiation dawns for the first time in the brain of the little girl, down to the sexual death of the withered matron, who laments the loss of her sexual potency, physical and mental activity, work and thought, function and sensation, arise for the most part, wittingly or unwittingly, from that germinal energy which is the manifestation of the unalterable law that the existing organism endeavors to reproduce its kind. ”

“ Whatever view we hold regarding this matter, the sexually differentiated love-games of young animals must be regarded as a manifestation of the sexual life. None the less, in sexually immature animals, just as in the case of children, sexual differentiation is not always so marked as it is in adults; and it may happen that the sexes may exchange their rôles. Cases observed by Seitz have been published by Groos and also by myself. ”

“ The lower forms of animal and plant life often reproduce themselves without the aid of sex, and it has even been argued that reproduction and sex are directly antagonistic, that active propagation is always checked when sexual differentiation is established. "The impression one gains of sexuality," remarks Professor Coulter, foremost of American botanists, "is that it represents reproduction under peculiar difficulties." ”

“ And when such differences appear in childhood, we find that they are quantitatively less extensive than the sexual differences of adults. For the sexual life is in the child less developed than it is in the adult. We shall learn that in the matter of the sexual impulse, the child exhibits an imperfect differentiation. A similarly imperfect differentiation is found in childhood in respect of a number of other qualities. Thus, there are many diseases which later in life manifest a sexual differentiation, but in childhood are undifferentiated. ”

“ In the previous chapter, I have described the differences between the reproductive organs of men and women, and between those of adults and children, respectively. Man and woman are, however, distinguished one from the other, not only by differences in their reproductive organs, but by other qualities as well, some of these being bodily, others mental. Such distinctive characters are spoken of as secondary sexual characters, in contradistinction to the primary sexual characters, the reproductive organs. ”

“ The sexually differentiated qualities in any individual may be regarded as inborn, and yet we may admit that the differentiation was originally the result of education, if we suppose that in earlier generations in either sex certain qualities were developed, and that gradually, by monosexual inheritance, the differences became confirmed, until finally they became inborn. ”

“ 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? ”

“ 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. ”

“ 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. ”

“ The best equipped males will thus crowd out the less well-equipped in the matter of reproduction, and thus the relevant characters will be increased and perfected through sexual selection. It is, of course, a necessary assumption that these secondary sexual characters may be transmitted to the female, although perhaps in rudimentary form. ”

“ As I pointed out in my Sexual Dimorphism (1900) , the common characteristic of somatic sexual characters is their adaptive relation to some function in the sexual habits of the species in which they occur. There is no universal characteristic of sex except the difference between the gametes and the reproductive organs (gonads) in which they are produced. All other differences, therefore, including genital ducts and copulatory or intromittent organs, are somatic. ”

“ This indicates that there is no cause-and-effect relation between the feminine secondary sexual characters and the love for the male sex, but that they are twin effects of a common cause, namely, the presence in the male body of the particular kind of governing corpuscles or germs ordinarily found only in the protoplasm of females. ”

“ The degree to which the female organism as a whole is influenced by the processes of the sexual life that occur in the genital organ depends upon many of the characteristics that combine to make up the individuality. Inherited characteristics, temperament, and race, play a great part in this connection; and not less important than these are the social conditions, the environment, in which the women under consideration pass their life. ”

“ In higher orders of animals, fecundation takes place within the generative organs of the female by contact between the male and the female organs. To effect this, there are necessitated certain accessory organs, the penis in the male and the vagina in the female.
Nothing in all the range of nature is more remarkable than the adaptation of the two varieties of sexual organs in each species. This necessary provision is both a powerful means of securing the perpetuation of the species, and an almost impassable barrier against amalgamation. ”

“ It is clear then that, granting the biological premises of our author that the lowest sexual organisms are virtually female and that in the hermaphrodites the female element predominates; that in the earliest forms of bi-sexuality the fertilising or male element was merely an offshoot of the female trunk and that this offshoot develops, mainly by means of sexual selection on the part of the female, into an organism similar to the latter; that not until we reach the higher vertebrates, the birds and the mammals, do we find any traces of male superiority ”

“ 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. ”

“ Thus we have shown the easy gradation, and therefore the probable derivation, of the highest mode of sexual reproduction—the unisexual—from the ordinary processes of growth, through the different grades of asexual and bisexual reproduction. The derivation of different modes of sexual reproduction from each other will not, I think, be questioned. Still clearer is the fact that non-sexual reproduction is but a modification of the ordinary process of growth. The only place where there is any gap is between the asexual and the sexual modes. ”

“ It is a safer conclusion that, as vocal and instrumental organs are of special service only to the males during their courtship, these organs were developed through sexual selection and their constant use in that sex alone—the successive variations and the effects of use having been from the first more or less limited in transmission to the male offspring. ”

“ Were we not to assume as the cause of these variations the presence of a sexual determinant generally different in every cell but stable from its earliest embryonic development, then it would be simple to describe the sexuality of any individual by estimating how far its sexual glands conformed to the normal type of its sex, and the facts would be much simpler than they really are. ”

“ Owing to the fact that both male and female organs develop from more primitive structures which were sexually undifferentiated, a fundamental analogy in the sexual organs of the sexes always remains; the developed organs of one sex exist as rudiments in the other sex; the testicles correspond to the ovaries; the female clitoris is the homologue of the male penis; the scrotum of one sex is the labia majora in the other sex, and so throughout, although it is not always possible at present to be quite certain in regard to these homologics. ”

“ Düsing, starting from the common belief that all animals have the faculty, when there is a lack of individuals of one sex, of procreating an excess of offspring of the sex which is deficient and thus of restoring the balance between the sexes, maintains that numerous factors, through the co-operation of which the sexual ratio is regulated, act in temporal succession. ”

“ In the case of woman, the expression is less unsuitable, since in woman special organs exist for the maintenance of the ovum after fertilization, and these organs may perhaps lead to the production of this peculiar form of mental activity.
According to Darwin, a comparatively less intensity of sexual desire is common to the females of all species of the animal kingdom. The female demands a prolonged courtship, and often endeavors for a considerable time to elude the male. ”

“ Without that internal secretion of the ovaries, a woman would look more or less like a man; she would not develop her beautiful rounded form, her pretty long hair, her breasts, her broad pelvis, her feminine voice, etc. Second, the secretion is necessary to the proper development of her other sexual organs; if the ovaries are cut [51] out, then the uterus and the vagina and even the vulva shrivel up. Third, it is that internal secretion that excites in woman sexual desire and makes her enjoy relations with the male sex. ”

“ 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. ”

“ To answer your first question is most difficult, if not impossible, because we have no sufficient evidence in individual cases of slight sexual difference, to determine whether the male alone has acquired his superior brightness by sexual selection, or the female been made duller by need of protection, or whether the two causes have acted. Many of the sexual differences of existing species may be inherited differences from parent forms who existed under different conditions and had greater or less need of protection. ”

“ In all other mammals the female will only receive the male at certain well-defined periods, which in their turn depend on cyclical changes in the ovaries. In man this restriction has been overcome, and, in spite of the survival of a certain degree of cyclical change in feeling, neither sex is restricted any longer to certain physically-determined periods for the consummation of its sexual life. This is, we may say, a triumph of mind over matter in the human organism, of the mental elements of the sexual life over the purely physical elements. ”

“ 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. ”

“ II. That sex is determined in the moment of fertilization by the reciprocal interaction of male and female, of zoösperm and ovum. One variant of this theory maintains that each reproductive element strives for the reproduction of its own sex; that a struggle takes place and that the victor in the contest stamps its own sex-likeness upon the fertilized product. ”

“ Their 17 organization, influenced by a different genital apparatus, presents a different mode of existence, action and sensation. Thus the sexual characters are slightly marked at birth, become distinct as the genital organs develope themselves, suddenly enlarge at the period of puberty, exist in the greatest degree when these parts have come to their perfect state, and lose their energy in old age. The destruction of the testicles in the male and of the ovaries in the female prevents the regular development, or even alters the special distinctions of sex. ”

“ In the female sex, also, there are notable differences in the condition of the genital organs between the adult and the child. In the first place, the relative sizes of the various organs differ greatly. But other differences are also noticeable, not dependent, however, on differences in age, but on whether there has or has not been experience of sexual intercourse, and on whether pregnancy and parturition have occurred. When we compare a female child with an adult woman, the first obvious difference is in the shape of the external genital organs. ”