Close observation of primate societies shows that if you get these social calculations wrong, you’ll probably eat less well, be less well protected, get beaten up more often, and lower your chances of being healthy and having healthy children.6 So sociability, cooperation, and brainpower seem to have evolved together in the history of primates. Indeed, there seems to be a rough correlation between the size of primate groups and the size of their brains. Apparently, many primate lineages were willing to pay one more entropy tax, the brain tax, if it allowed them to live in larger groups.
