Examining difference in fertility, it is clear that fertility is primarily controlled by female status relative to their husbands. The more women are subordinated, the higher the fertility. Japan is a good test case. Not only did fertility dramatically drop when General McArthur emancipated women, but in feudal Japan, fertility among high status families was below replacement when women were high status, indicated by upward mobility and room at the top. Later in the feudal era, when women were low status, fertility well above replacement, leading to a massive oversupply of elite children relative to available elite positions. It is difficult to assess Japanese feudal fertility exactly, but it seems to have been similar in patriarchal feudal Japan as it was in the immediate postwar period in patriarchal industrial Japan, the same laws leading to similar fertility in industrial and feudal Japan.
Modern contraceptive technology changes little, for we have always had infanticide, always had non reproductive sex, long had abortion. Early feudal era upper class Japanese women, late Spartan women, women of the upper classes of the Roman empire, and late Bronze age Egyptian women also had well below replacement fertility.
Societies with emancipated women do not reproduce very successfully.
Men want to have sex with as many women as possible, and give them no support.
Women want to have sex with the highest status men available (as women perceive male status, which is similar to the way a small evil child raised by cannibal head hunters perceives status) and be supported by men.
A prisoner’s dilemma problem, the war of the sexes, ensues.
If both freely pursue their interests, we get a defect/defect equilibrium, where a small minority of men have casual no strings attached sex with the large majority of women. Women get the sex they want until they approach the end of their fertile years, but children don’t get fathers. Since producing fatherless children places a large burden on women, women do not have children until used up on the cock carousel and approaching the end of their fertile years.
Both sides of the war are better off if a cooperate/cooperate equilibrium is coercively imposed. One could in principle have legal enforcement of the marriage contract, with women being severely unequal inside marriage, but equal (eg, no child support, no special privileges, freedom of association permited) outside marriage. But a society in which women are equal is going to find it hard to uphold and protect marriage. Further, because women are not in reality equal, women cannot be equal in a society with freedom of association, because people will not want to associate with bastards, because most of the high status associations will choose to be male only, and so on and so forth.
To enforce a cooperate cooperate equilibrium, mating choice has to restricted, denying men access to women, and women access to men. Women have to be compelled to mate with their husbands, and forbidden to mate with anyone else.
Fertility is determined by the extent that we have a cooperate cooperate equilibrium starting early in a woman’s fertile years.
A ship can have only one captain, and household only one head. If men and women equal, requires separation. If separation, one side or the other is denied the opportunity to invest in their children.
So, patriarchy. If men own women, except that they may not resell them, cruelly mistreat them, rent them out, abandon them, nor even allow them to rent themselves out, then both men and women know who their children are and live with their children. The converse system, women owning men, would not work, because men would not know who their children were, would be denied the opportunity to invest in their children, and would therefore revolt.
It might be argued we have the converse system now, and yet men are not exactly revolting, but they are dropping out and refusing to participate. They will not support or protect women on current terms.
We have always had fertility control in the form of infanticide, and have fully adapted to it. We have had fertility control in the form of abortion for around three and half thousand years, and have substantially adapted to it. We have had condoms for long enough that men have evolved to dislike them and women are beginning to evolve to dislike them.
Children by previous lovers get in the way, hated by their mother’s new lover, inconvenient to their mother. Such inconveniences are, as in fairy tales, apt to be eradicated. This is the most ancient fertility control solution. Tomcats notoriously apply it. Humans and cats are behaviorally adapted to optimal application of this solution.
With cryptic estrus and lengthy infancy, if males and females each freely pursue their biologically optimal strategy without regard to the interests of the people they mate with, very few will successfully reproduce, because almost all infants get infanticided. Prisoner’s dilemma, defect defect equilibrium. Successful reproduction requires enforcement of the cooperate cooperate equilibrium.
In a species with cryptic estrus and lengthy infancy, women have to be subjugated for the species to successfully reproduce. Matriarchal societies did not vanish from history because conquered. They vanished from history for failure to reproduce.
In modern times, we are more civilized, and contracept children or abort them to avoid the embarrassment of mummy’s latest boyfriend grabbing the child by its feet and smashing its head against the bedpost, but modern mummies have a strange tendency to acquiesce in such “accidents”, when they discover just how much their former husband’s children cramp their style. There is a very high rate of “accidents” among fatherless children.
If children go with the mother, Gnon demands future male lovers commit infanticide. Civilization avoids this bloody embarrassment with the delicately civilized abortion.
Cooperate cooperate equilibrium is that the man and the women are stuck with each other. He owns her, but does not own her in the sense that he can resell her to the highest bidder, nor punish her without cause or in ways likely to cause injury. There is an approximately equal distribution of women between the men, socialist rationing of women, and each man respects all other men’s property rights in their women, with severe punishment for violators the male who sleeps with another man’s wife punished by law, the wife punished by her husband at her husband’s discretion.
Under this circumstance, men can invest in their wives and children with confidence in paternity and without fear of losing them, without fear that any attempt to support them will result in them supporting their wife’s bad boy lover instead.
In defect/defect, investment in children is inadvisable, for the woman will probably wind up a single mother, and a man a cuckold. Any children with her are likely by previous lovers, so should be mistreated or eradicated, and any children he might have with her are likely to be similarly mistreated by future lovers.