Monkeys' grooming habits provide new clues to how we network and socialise

30 September 2009

A study of female monkeys' grooming habits is providing new clues about the way we humans network and socialise. New research, published today in Proceedings of the Royal Society, reveals that there is a link between the size of the brain, in particular the neocortex which is responsible for higher-level thinking, and the size and number of grooming clusters that monkeys belong to.

The researchers, from the University of Oxford and Roehampton University, have shown that bigger brained female monkeys invest more time grooming a smaller group of monkeys but still manage to maintain contact with other members of their group, even though they have much weaker social bonds with them. In contrast, monkeys of species with smaller neocortices, and therefore less cognitive ability, live in groups with a less complicated social structure.

An analysis of data on the grooming patterns of 11 species of Old World monkeys suggests the relative size of the neocortex is the key factor, rather than overall brain size. The neocortex is connected with cognitive functions, such as learning, memory and more complex thought. In monkeys, species with large neocortices typically live in groups of 25-50 animals, whereas species with small neocortices live in groups of 10-20 individuals.  Species with larger neocortices are able to maintain larger social groups because they can balance a few very intimate friendships against many less close acquaintances. In contrast, species with smaller neocortices cannot manage this, and so have groups that fragment more easily.

The study therefore suggests that, while bigger brained female monkeys concentrate their social effort on core partners in smaller cliques in order to minimize the costs of harassment from other members of the group, their enhanced social skills allow them to exploit weak social links with others in the wider network and maintain good social relations outside their own close-knit groups. Lead author Dr Julia Lehmann, from the Centre for Research in Evolutionary Anthropology at Roehampton University, the UK's number one university in biological anthropology research, said: ' 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.

Professor Robin Dunbar, from the Institute of Cognitive and Evolutionary at Oxford University, said: 'These findings give us glimpses into how humans manage the complex business of maintaining coherence in social groups that are much larger than those found in any other primate species. 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.

For more information, please contact the University of Oxford Press Office on 01865 280534 or press.office@admin.ox.ac.uk.

Or contact Roehampton University Press Office on 020 8392 3181/ 07825 805833 or m.nicholson@roehampton.ac.uk