There’s two notable side-effects of this big-brained-ness. The first is well-known: women used to regularly die in childbirth. Until the first years of the 20th century, about one in one hundred pregnancies ended with the death of the mother. That’s an extraordinarily high rate, particularly given that a women might give birth to seven or eight children over their lifetime. Now that we have survivable Caesarian sections and all sorts of other medical interventions, death in childbirth is much rarer – perhaps 1 in 10,000 births. Nowhere else among the mammals can you find this kind of danger surrounding the delivery of offspring. This is the real high price we pay for being big-brained: we very nearly kill our mothers.
The second side-effect is less well-known, but so pervasive we simply accept it as a part of reality: humans need other humans to assist in childbirth. This isn’t true for any other mammal species – or any other species, period. But there are very few (one or two) examples of cultures where women give childbirth by themselves. Until the 20th century medicalization of pregnancy and childbirth, this was ‘women’s work’, and a thriving culture of midwives managed the hard work of delivery. (The image of the nervous father, waiting outside the maternity ward for news of his newborn infant, is far older than the 20th century.)
For at least a few hundred thousand years – and probably a great deal longer than that – the act of childbirth has been intensely social. Women come together to help their sisters, cousins and daughters pass through the dangers and into motherhood. If you can’t rally your sisters together when you need them, childbirth will be a lonely and possibly lethal experience. We entered the world because of the social capabilities of our mothers: this is what it means to be human. Women who had strong social capabilities, who could bring her sisters to her aid, would have an easier time in childbirth, and would be more likely to live through childbirth, as would their children.
After the child has been born, mothers need even more help from their female peers; in the first few hours, when the mother is weak, other women must provide food and shelter. As that child grows, the mother will periodically need help with childcare, particularly if she’s just given birth to another child. Mothers who can use their social capabilities to deliver these resources will thrive. Their children will thrive. This means that these capabilities tended to be passed down, through the generations. Just as men had their social skills honed by generations upon generations of warfare, women had their social skills sharpened by generations upon generations of childbirth and child rearing.