It was Robin Dunbar who did this, and what he found shook the field. This correlation has been confirmed across many primates: the bigger the neocortex of a primate, the bigger its social group. But monkeys and apes are far from the only mammals, let alone animals, that live in groups. And interestingly, this correlation does not hold for most other animals. The brain of a buffalo living in a thousand-member herd is not meaningfully bigger than the brain of a solitary moose. It isn’t group size in general but the specific type of group that early primates created that seemed to have required
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