The objectively best strategy for a group is for women to seek reproduction with the most alpha male that they can, while at the same time trading sex and affection for reliable resources, status, and defense from non-alphas. And as far as I can tell, this is what they do. And they vary their strategy based upon the availability of men. Just as men vary their strategy based upon the availability of women.
This would mean we would likely only see monogamy in upper classes, and that the upper classes would improve the mean and develop into a caste, and the lower classes would regress to the mean or below it.
Unless of course it is nearly impossible to survive without the cooperation of members of a family – since a woman without a husband only places additional burden on the carrying capacity of her birth group.
The strategy for the aristocracy then should be to use their abilities to obtain positions of rule, and specialize in developing an aristocracy, and taxing the daylights out of the underclasses that do not imitate them, while accepting all those who can demonstrate membership in aristocracy through their actions.
The problem is that we live too long. If we died at 40 that would be one thing. But it is very hard to survive late in life on one’s personal productivity, in a world of increasing competitiveness given the rest of the world is no longer so intellectually, technologically, and institutionally far behind. And so larger and larger households will likely continue to evolve, and mobility will decrease since the absurdities of the 20th century are no longer possible.
The likely scenario is that the wealthy and able will insulate themselves behind automatons that do not have to be incentivized and the rest of mankind will revert to near animal barbarism.
That is the next source of speciation that I see on the horizon.