This was great - except for the harems thing? What's your supporting info for that? If we’d had harems hundreds of thousands of years ago, we would have died out as a species. Humans evolved as cooperative breeders, meaning that everyone in the tribe of 20-50 looked out for each other's children and people mated with who they wanted to mate with. Harems are a hierarchical power structure that didn't exist until the advent of patriarchy 6-9 K years ago. Before that, social cooperation on all fronts was a primary survival strategy - as was egalitarianism. No harems - we would never have evolved as a species if we'd had them all along.
There's still a lot of alloparenting in the world today, but there are almost no harems. Yes to all the rest of it though. I underlined a lot!
The great anthropologist and comparativist Sarah Hrdy tells us that, across species, including among humans, the best mother for many eons was the one who was, under particular and far-from-rare ecological circumstances, promiscuous. By being so, she could hedge against male infertility, up her odds of a healthy pregnancy and robust offspring, and create a wider network of support by lining up two or three males who figured the offspring might be theirs. (5)
Partible paternity, where a woman mates with several men, who are then all considered partial fathers of the offspring, still takes place in lowland South America. “Among the Bari of Venezuela, many women, but not all, take lovers during their pregnancy. They later identify these men as secondary fathers of their children. In this case, “possession of a secondary father was associated with a heightened probability that a pregnancy would eventually produce an adult Bari individual,”(6)
Marriage, Monogamy and the Nuclear Family Are Not Human Universals
In many cultures, there is no expectation of fidelity or only two parents
Communities that are more cooperative and interdependent in other ways are more likely to enhance group bonding through shared sex, co-marriage, and alloparenting than cultures that are more individualistic.