Monkeying around

The bigger the brain, the stronger chance that a primate will deceive its peers.

University of St Andrews Psychology Professor Richard W Byrne and research assistant Nadia Corp compared the rates of tactical deception across a range of primate species and found that deception is well predicted by the size of the neocortex, a crucial part of the brain which is linked to intelligence.

The study shows, for the first time, that brain size has a direct pay-off in social skill – primates with larger brains are more able to use deception, a subtle technique of social manipulation. It has become widely accepted that primate intelligence originates from a need to deal with the increased social complexity of group living, the so- called “Machiavellian Intelligence¿ theory, but testing the idea is difficult because there is no simple way of measuring social intelligence. Byrne and Corp got round this problem by using a compilation of records of deception, recorded by many expert primatologists over years of study, as a measure of social skill.

The findings are reported in the Proceedings of the Royal Society of London (Biological) today (Wednesday 30 June 2004).

Professor Byrne said, “Monkeys and apes compete more by manipulation than brute force and, for mammals, their brains are relatively large. In this study, we investigated whether these two unusual characteristics are related to each other.

“To manage deception successfully, a primate needs to be able to learn rapidly in social contexts, taking account of many different individuals, their kinship and their past history of friendly and aggressive interactions, and perhaps even what they know about the current situation. Our results show that this rapid social learning is primarily a function of the neocortex of the brain. This supports the influential idea that primate brain enlargement was originally an adaptive response to social complexity, the “Machiavellian Intelligence” hypothesis. Our own, human, brain specialisations may be grounded in the cut-and-thrust of primate social living.”

The researchers compared the rates of tactical deception in a range of primate species with brain measurements for the same species and found that deception was well predicted by neocortex volume. The size of the rest of the brain – the more primitive structures – was much less good at predicting deception usage.

ENDS

NOTE TO EDITORS

Professor Byrne available on 01334 462051.

(The computer-based research was carried out in St Andrews, with the data originating from field studies in which researchers observe animals in the wild).

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