ooking around our planet today, it’s hard not to be struck by humanity’s uniqueness. We are the only species around that writes books, runs experiments, and builds skyscrapers. Our intelligence must have also been useful when we were evolving—presumably it helped us to be better hunters and avoid being hunted ourselves, for instance. Perhaps even more importantly, our growing intelligence enabled early humans to compete with each other: We evolved to be intelligent to keep up with everybody else evolving to be intelligent. Smarter people are more attractive to others, and are better at jockeying for status within complex social groups. It is well-known that humans underwent an intelligence arms race that resulted in a rapid growth in cognitive ability. What is less well-known is how the need for women to be able to walk and run helped this boom in smarts.
A lot of our growth in intelligence is due to an increase in brain size. Even when looking at the differences between one person and another, brain size accounts for 16% of the variance in intelligence. A bigger brain might have been the simplest way to make us smarter. As brain sizes grew, so did the pelvises of the women who had to give birth to all of these big-headed babies.