Monkeys With Larger Brains Live in Larger Groups

Female monkeys with bigger brains live in larger groups and can juggle a larger number of grooming partners, scientists say.

The study of the grooming patterns of 11 species of Old World monkeys could provide clues into the way humans manage social networks and intimate friendships.

The researchers at the University of Oxford and Roehampton University found a relationship between brain size — in particular the size of the neocortex, the area responsible for learning, memory and complex thought — and social group complexity.

The monkey species with a larger neocortex relative to brain size spent more time grooming a smaller group of monkeys, but also maintained relationships with other members of their group. Monkeys with smaller neocortices — and less ability for higher-level thinking — had a less complex social structure.

Species with large neocortices lived in groups of 25 to 50 monkeys, while those with smaller neocortices lived in smaller groups, of about 10 to 20 monkeys.

The researchers, led by Julia Lehman of Roehampton University, concluded that in the species with large neocortices, the monkeys are able to maintain large social groups by carefully balancing the demands of a few close relationships with maintaining a larger network of acquaintances.

"We found that in primates the key to socializing in a wider and more effective way ultimately involves being able to balance the interests of a small number of very intimate relationships while at the same time maintaining social cohesion," said Lehmann, in a statement.

The scientists, whose research was published in the Proceedings of the Royal Society, could provide clues into how humans are able to manage complex social networks of family, close friends and business acquaintances.

"Our neocortex is three times larger than that of other monkeys and apes, and this allows us to manage larger, more dispersed social groups as a result," said Robin Dunbar of Oxford's School of Anthropology.

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