But the higher up one goes in the scale of evolution, the greater becomes the distinction between the sexes. Anatomic hermaphroditism becomes a rare anomaly. Life appears to have perfected this trick of separate sexes, sex specialization, in short, for the sake of the efficiency which goes with specialization.
When a germ cell divides, its nuclear material breaks up into segments known as chromosomes. Now it has been found, for example in the case of the common squash bug, anasa tristis, that there are 22 chromosomes in the female, and 21 in the male. In the female two of these are visibly different from the rest, while in the male there is one odd one, the remaining 20 being like the corresponding 20 of the female. Before the germ cell becomes fit to mix with a germ cell of opposite sex, in the process of fertilization, it must lose one half of these. So the number of chromosomes for the species is kept the same or constant. This is the process of maturation. In the process, when the chromosome number is halved among the females, 11 go into each mature egg. But among the males, the odd chromosome, also known as the X-chromosome, can perforce go only into half of the sperm cells, leaving the others without it. So the sperm are formed in equal numbers of 10 and 11 chromosomes respectively.
When fertilization occurs, and the sperm cell fuses with the egg, the following may take place: (1) a ten chromosome sperm may unite with the eleven chromosome egg, and produce a twenty-one chromosome individual or (2) an eleven chromosome sperm may unite with an eleven chromosome egg producing a twenty-two chromosome individual. It has been found that the twenty-two chromosome individual invariably develops into a female, and the twenty-one into a male. Therefore, femaleness is a positive quality, dependent upon the action of the X-chromosome, and maleness an absence of femaleness, due to lack of the extra, odd chromosome. In man, two X-chromosomes have been discovered, half the sperm containing 12, and the other half containing only 10 chromosomes. The number of chromosomes in human cells consequently is 22 in the male and 24 in the female.
The X-chromosome is the bearer of sex destiny. There still remains the work to be done on the actual control of sex by man, apart from its natural determination. For the time being, let the feminists glory in the fact that they have two more chromosomes to each cell than their opponents. Certainly there can be no talk here of a natural inferiority of women.
THE SECONDARY OR ENDOCRINE SEX TRAITS
Yet the matter is after all not so simple as this would make it out to be. All that can be safely laid down is that the character of the reproductive organs is determined by the extra chromosomes. And though these reproductive organs have a good deal to do with the masculine or feminine quality of the organism as a whole, through their internal secretions, they are not alone. All the other internal secretions have their say in the final outcome, determining what may be called the dominant sex quality, but leaving inherent the latent soil of the other sex. This may become active and dominant in its turn, under certain conditions of stimulation, abnormality, or disease, dependent upon a rearrangement of status and influence among the ductless glands. Bisexuality preceded monosexuality in the animal pedigree, and co-exists with it even at the highest points of the genealogical tree.
While from the standpoint of the species, the criterion of the sex classification of its members will depend upon their capacity to fertilize or to be fertilized, a quality that may, therefore, be spoken of as the primary sex character, a number of other traits have been evolved by sexual selection, the secondary sex traits. They have come to be just as important, to the individual, as far as his or her consciousness of sex attitudes and reactions to it are concerned. The terms primary and secondary sex characteristics, though inapt, must be allowed to stand.
These accessory sex-serving traits undoubtedly survived because of their usefulness in external adornment for attracting attention in courtship, in the metabolic requirements of sex combat and the sex act, and in the necessities of caring for the young, until well-grown. The rooster's comb and spurs, the male frog's claspers, the stag's antlers, and so on, are familiarly and obviously so useful. Besides there are fundamental differences in inner physiology. The human male consumes more oxygen than the female per minute, since he has more red corpuscles in his blood. In some caterpillars the blood is yellow in the males and green in the females. W.I. Thomas has devoted an essay of some fifty pages to a review of the organic differences between man and woman. The ordinary criteria, employed every day by the man in the street to distinguish man from woman may be arranged as follows:
Man Woman
Hair on face Hairless face
Skin coarse and lean Skin fine and plump
Muscles powerful Relatively weak
Bones heavy Bones light
Aggressive—bass voice Reserved—treble voice