“Compared to other animals,” writes Yuval Noah Harari in his book Sapiens, “humans are born prematurely, when many of their vital systems are still under-developed.” Harari explains that humans are born so early because humans walk upright. As humans evolved, we began to stand and walk on two legs, rather than walk on four legs or primarily walk on two legs while greatly supporting ourselves with our arms. A consequence is that female hips narrowed to support an upright gait, which in turn restricted the birth canal, meaning that infants born sooner were more likely to survive because they were smaller and less of a risk to a female human with a relatively more narrow birth canal than other species.
In evolutionary terms, earlier births had additional consequences for the direction in which humans evolved. Harari continues, “since humans are born underdeveloped, they can be educated and socialized to a far greater extent than any other animal.” Raising a child is difficult work, and raising infants who are born under-developed and then develop slowly takes the work of many. Harari’s suggestion is that raising human infants was not possible for our female ancestors to do on their own – at least it was incredibly difficult compared to females raising their infants within a tribe. It would have been hard for a lone female to forage for sufficient food and to provide defense for herself and the infant. As a result, “evolution thus favored those capable of forming strong social ties,” writes Harari.
I find this explanation of the evolution of human social skills pretty convincing, even if I can imagine particular instances where it may not necessarily fit. I think it is reasonable to assume that there was a dual feedback mechanism, where evolving brains shaped our physiology, and where our evolved physiology in turn shaped our brains. As we got smarter and as evolution favored larger brains and increased cognitive capabilities, our bodies changed to adapt to our brain, and certain physiological traits were more advantageous to a species with increased cognitive abilities. Those physiological traits and characteristics, like narrow hips and birth canals, changed the size of the brain at birth, changing the cognitive capabilities of human infants. This allowed infants to be socialized at a younger age and favored individuals who were better at being part of a community, changing the dynamics for what type of cognitive abilities were favored by natural selection.
There was no clear evolutionary path and no way to predict where the future would go based on the past. Social factors, physiological factors, environmental factors, and other factors we have not identified all likely shaped the evolution of humans. We adapted to fit the circumstances and evolution favored different ways of being human at different times. I think this is a lesson we can still learn lessons from today. We can learn that we will evolve and that different ways of being human will be favored at different times based on many factors unique to our time, space, cultures, and environments.