—“Men and women are dividing duties”—
Um. Women divorce men who split duties. Women demonstrate lower sexual interest in men who split duties. Women have little need for the economic returns of a man if they can obtain child support without providing nesting, care, and sex for a man.
Men are more varied than women, and while most women are desirable to SOME man, approximately a third of men are not desirable for ANY woman. This reflects ancestral rates of reproduction. Under monogamy, the best women do not need to settle and can construct a long term marriage. However, under serial marriage (or polygyny for that matter) women can mate with better genes than they can ‘afford’ due to men’s lower demands – especially when under the influence.
And so we are seeing a return to the historical difference between upper class (propertied) marriages, and underclass (unpropertied) serial monogamy. The primary difficulty being that single mothers produce vast numbers of disastrous children.
Why? over-investment in one or two children, and the tendency not to obtain a mate, whereas single fathers nearly always obtain a new mate, providing a better household.
It’s strange but women apparently evolved to care for five or six children, and do not reach cognitive load (work that balances their sensory and intuitionistic sensitivities) until they have at least three. This is understudied but hopefully we will change that shortly.