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1.5.8 Dunbar’s Number, Human Social Groups, and Animal Groups
Primates and other animals often live in groups or “troops” for protection against predators. As social groupings increase in size and complexity, competitors within the aggregation turn on each other. So cliques form for intra-group protection.
The hypothesis of British anthropologist and evolutionary biologist Robin Dunbar is that, in primates other than humans, alliances hold together because members groom each other. Not because everybody in the group is bug-infested. Because grooming feels good. (Same reason humans like massages.)
Those who groom each other also defend each other when conflicts arise. Grooming takes a lot of time and energy, so primate troops that physically groom each other can’t grow beyond a certain size, 50 individuals, tops.
Humans, on the other hand, given sufficient social pressure, can track as many as 150 individuals socially (widely known in anthropology as Dunbar’s number, after Dunbar’s calculations, based on much evidence). So the question is, how come humans can keep track of so many more fellow humans than, say, chimps can of fellow chimps?