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Summary
Numerous studies appear to support the link between a species' group size and neocortex size, especially among primates. And recently, a number of brain-scanning studies in humans and monkeys have found correlations between the size of social networks and that of specific brain areas linked to sociality. One study of people, for example, found a positive relationship between gray matter density and the number of Facebook friends an individual has. Yet there are competing explanations for our big brains, and some researchers are concerned that the social brain hypothesis may be too simplistic to account for the complex course of human brain evolution. (Read about more "Mysteries of the Brain.")
