MONKEYS and apes that most often deceive their peers also have the biggest brains relative to their body size. The finding backs the 鈥淢achiavellian intelligence鈥� theory, which suggests that the evolution of large primate brains was driven by the benefits of complex social skills.
Of all terrestrial mammals, primates have by far the largest brains relative to their body size, with humans having the largest of all. The enlargement is almost exclusively in the neocortex, which in humans makes up more than 80 per cent of brain mass.
Psychologists Richard Byrne and Nadia Corp at St Andrews University in the UK, who examined published studies of primate behaviour in the wild, have now found that the frequency of deceptive behaviour in primate species is directly proportional to the average volume of that species鈥� neocortex. Bushbabies and lemurs, which have a relatively small neocortex, were among the least sneaky. The most tactically deceptive primates included macaques and the great apes 鈥� gorillas, chimpanzees, bonobos and orang-utans 鈥� which have the largest neocortex.
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That is consistent with the idea that natural selection favoured larger brains for sophisticated social interactions, including behaving in a way designed to deceive others (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2004.2780).