From our helpless infants to the need to learn and be socialised, the years of effort required to raise human children has shaped our biological and social evolution.
The most important single biological fact in understanding human social dynamics is that we have the biosphere’s most expensive children.
A Homo sapien child does not complete the process of biological maturity until their early 20s. To get them to the stage where they can become parents is at least a 15-year investment, though longer is better.
It is not merely the length of Homo sapien childhood and adolescence that makes our children such orders of magnitude higher level of investment than the children of any other species. It is that our infants are incredibly helpless; that our toddlers need to be fed by their parents; that to be effective at being a Homo sapien, our offspring need years of learning and training. For we are the cultural species, who rely on learning to replace the instincts we mostly don’t have.
Expensive offspring to support expensive brains
All the above is both enabled and driven by us being a big-brained species. The scale of brain needed to be an effective Homo sapien means our brains have to do a lot of growing outside our mother’s womb. As it is, the size of a baby’s brain (and thus head) significantly raises the risks of childbirth for Homo sapien mothers.
Our infants are so helpless because their head is so large compared to their bodies. They need to feed voraciously to grow a body able to move our outsize brain around effectively while also continuing to develop our energy-hog brains.
Our babies have evolved for attention-grabbing cuteness to maximise the chance we will invest in them. We have the strikingly unusual pattern of maternal infanticide, as human mothers have to judge whether they have the social support to raise this child.
We are the longest-lived ape, because female Homo sapiens live for decades after menopause, so that they can switch from investing in their own children to helping invest in the children of their children. (This is known as the grandmother effect.) It allowed us to have longer childhoods.
While we are, along with chimpanzees (Pan troglodytes) the most proactively aggressive ape, we are the least reactively aggressive ape. This created sufficiently peaceful and cooperative social spaces within which to raise our expensive children.
We generally rely on prestige (bottom-up status) far more than dominance (top-down status) because our forager ancestors spent hundreds of millennia suppressing dominance behaviour. This enabled sufficiently peaceful and cooperative social spaces to raise our expensive children.
It is likely that our female forager ancestors experienced far fewer periods than modern women do, due to spending much more of their lives either pregnant or lactating. That the onset of puberty was probably later (than the more recent tendency for earlier-onset puberty) increased the effect.
As menstruation was a mark of fertility, yet was likely relatively rare, it is not surprising that it tended to be highly ritualised. For women and girls, menstruation and its ritualisation took the role that manhood initiation did for men and boys.
We are the only species whose females have breasts that are enlarged when not lactating. This is likely a signal of having the spare resources required for successfully bearing and raising our (expensive) children. Human males having relatively small testes but relatively large (but plain) penises are likely also connected to pair bonding due to having high investment offspring.
We have a history of presumptive sex roles that predates our emergence as a species because human children require constant attendance, so that human females did low-risk gathering and hunting (e.g. of lizards) that could be done while minding children. Meanwhile human males did the high-risk hunting and gathering (e.g. for honey) that needed to be done away from the kids.
We are a group-living, pair-bonding species — a very unusual combination. We pair bond so that each child presumptively had a mother and father to personally invest in their raising. (In the few societies that did not have marriage, that became mother and uncle(s).)
We are group-living species to better able to handle the risks of expensive children via expanded cooperation. Though it is probably more the case that we remained a group-living species, despite developing pair-bonding, to raise our expensive children, given that all our near-relative species are group-living species, hence our common ancestor probably was too.
None of our near relatives pair bond in the way we do, however. Gorillas are a harem species while among chimpanzees and bonobos, groups of males share groups of females.
So much of these evolutionary outcomes were likely interactive processes, for what enables also permits. Patterns that may have, at least in part, evolved for other reasons persisted because of how expensive human children became.
All these features of being a cooperative cultural species that relied on learning enabled us to become the technological species. We were tool users before our genus evolved, and tool makers before our species evolved.
All these things enabled us to become the cultural species, which required expensive brains which meant expensive offspring. For not only does what enables also permit, what permits can also enable.
As a consequence of the evolution of our technology, we now live in the first societies in human history without presumptive sex roles. This is an amazing evolutionary novelty for our species.
We also have people claiming that people who have never had, and will never have, a uterus and ovaries are nevertheless women. This is, of course, completely nuts.
This is in no way to deny trans identity. Many human societies have had trans identities. Such identities have thousands of years of history to them. Trans is clearly a human thing. But none of those societies thought a (male-to-female) trans person was a woman, because trans folk did not menstruate and could not get pregnant. Such identities were and are, very much, trans identities. They were crossing identities.
In societies where all or most people lived subsistence lives, who could and could not get pregnant was a desperately important issue. It had to be, given how expensive Homo sapien children were and how profoundly that affected the social dynamics of every human society.
How identity as a woman has come to be notionally separated from having ovaries, a uterus and functioning mammaries is a matter for separate examination. For now, let us simply take note of how important our amazingly expensive offspring are for human social dynamics and how important that has been for our evolution as the cultural species.