Dr. Lloyd Jones has determined that between 17 and 45 years of age the specific gravity of the blood of women is lower than that of men. In old women the specific gravity rises above that of old men, and he suggests that their greater longevity is due to this.[92] No doubt the greater longevity of women is to be associated with the rise in specific gravity of their blood, but this rise in the specific gravity of women after 45 years is consequent upon their anabolic constitution. High specific gravity in general is associated with abundant and rich nutrition; it falls in women during pregnancy, lactation, and menstruation, and when these functions cease it is natural that the constructive metabolic tendency on which they are dependent should show itself in a heightened specific gravity of the blood (i.e., greater richness), and in consequence greater longevity.
Some facts in the brain development of women point to the same conclusion. The growth of the brain is relatively more rapid in women than in men before the twentieth year. Between 15 and 20 it has reached its maximum, and from that time there is a gradual decline in weight until about the fiftieth year, when there is an acceleration of growth, followed by a renewed diminution after the sixtieth year. The maximum of brain weight is almost reached by men at 20 years, but there is a slow increase until 30 or 35 years. There is then a diminution until the fiftieth year, followed by an acceleration, and at 60 years again a rapid diminution in weight; but the acceleration is more marked and the final diminution less marked in woman than in man.[93] A table prepared by Topinard shows that woman from 20 to 60 years of age has from 126 to 164 grams less brain weight than man, while her deficit from 60 to 90 years is from 123 to 158 grams.[94]
The only explanation at hand of this relative superiority of brain weight in old women is that with the close of the period of reproduction (the anabolic surplus being no longer consumed in the processes associated with reproduction) the constructive tendency still asserts itself, and a slight access of growth and vitality results to the organism.
It must be confessed that the testimony of anthropologists on the difference in variability of men and women is to be accepted with great caution. As a class they have gone on the assumption that woman is an inferior creation, and have almost totally neglected to distinguish between the congenital characters of woman and those acquired as the result of a totally different relation to society on the part of women and men. They have also failed to appreciate the fact that differences from man are not necessarily points of inferiority, but adaptations to different and specialized modes of functioning. But, whatever may be the final interpretation of details, I think the evidence is sufficient to establish the following main propositions: Man consumes energy more rapidly; woman is more conservative of it. The structural variability of man is mainly toward motion; woman's variational tendency is not toward motion, but toward reproduction. Man is fitted for feats of strength and bursts of energy; woman has more stability and endurance. While woman remains nearer to the infantile type, man approaches more to the senile. The extreme variational tendency of man expresses itself in a larger percentage of genius, insanity, and idiocy; woman remains more nearly normal.
The fact that society is composed of two sexes, numerically almost equal, but differing in organic and social habits, is too significant to remain without influence on the structural and occupational sides of human life, and in the following chapters we shall note some of the influences of sex, and of the differences in bodily habit of men and women, on social forms and activities.
SEX AND PRIMITIVE SOCIAL CONTROL
The greater strength and restlessness of man and the more stationary condition of woman have a striking social expression in the fact that the earliest groupings of population were about the females rather than the males.
While at a disadvantage in point of force when compared with the male, the female has enjoyed a negative superiority in the fact that her sexual appetite was not so sharp as that of the male. Primitive man, when he desired a mate, sought her. The female was more passive and stationary. She exercised the right of choice, and had the power to transfer her choice more arbitrarily than has usually been recognized; but the need of protection and assistance in providing for offspring inclined her to a permanent union, and doubtless natural selection favored the groups in which parents co-operated in caring for the offspring. But assuming a relation permanent enough to be called marriage, the man was still, as compared with the woman, unsettled and unsocial. He secured food by violence or cunning, and hunting and fighting were fit expressions of his somatic habit.