Sneakiest primates have biggest brains reports more evidence for the “Machiavellian intelligence” theory:
Of all the 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 makes up more than 80% of the mass of the human brain.
Large brains, despite being energetically costly, benefited primates because they conferred complex cognitive skills. But which skills were the priority — was it clever food-finding strategies that were most valuable, for example, or complex social skills?
Now Byrne and Corp have studied a catalogue of observations of deceptive behaviours in wild primates from many researchers over several years up till 1990. They found that the frequency of deception in a species is directly proportional to the average volume of the animal’s neocortex.
Bush babies and lemurs, which have a relatively small neocortex, were among the least sneaky. The most tactically deceptive primates included macaques and the great apes — gorillas, chimpanzees, bonobos and orang-utans — which also have the largest neocortex.
Some examples of deception:
Deception amongst primates is well documented. Sometimes a female gorilla will mate with a male surreptitiously to avoid a beating from a more dominant male. Or monkeys might feign disinterest in tasty food so that others do not come and steal it.
Byrne has himself observed a young baboon dodging a reprimand from its mother by suddenly standing to attention and scanning the horizon, conning the entire troop into panicking about a possible rival group nearby. “We were rather shocked that baboons could do anything quite as subtle as that,” he says.
It’s not just about deception though:
“I’m sure if we could have measured cooperative skill, we’d have found a similar result,” says Byrne. “Cooperation and outwitting are not opposed — they’re both about being socially subtle.”