theadvancedapes, do you know if there is anything to the assertion that primates' brains evolved primarily to function socially?

It’s nice to be smart, of course, but big brains demand an enormous amount of energy and require years to grow to full size, and the larger skulls that protect them make childbirth much more dangerous. Plenty of species have thrived on this planet without much of a brain at all.

Dunbar’s argument, laid out in the Journal of Human Evolution, was that big brains evolved to solve the problem of social life. Living in large groups confers significant advantages, chief among them better protection against predators. But living together is also difficult. Members compete for food and access to mates. They have to guard against bullies and cheats—and pick their own spots to bully or cheat. “For very social species, and this applies particularly to primates, the group is an adaptation to solve particular ecological problems,” Dunbar explains. “But the group itself triggers a whole series of problems at the individual level. It’s essentially the social contract problem: People tread on your toes; they steal your food just as you’ve unearthed it.”

It seems almost too trivial of a reason to me. And it's not exactly something only primates do, though we do it in a more complex fashion than others.