The study, appearing today in the journal Science, suggests that groups with few rules attract many exploitative people who quickly undermine cooperation. By contrast, communities that allow punishment, and in which power is distributed equally, are more likely to draw people who, even at their own cost, are willing to stand up to miscreants.
(via dm)
I'm not surprised. This kind of behavior is observable in animals other than humans. Wolves and other pack animals hunt as groups of cooperating individuals. When chimps have been observed stalking and attacking prey, such as a monkey, they are clearly cooperating with each other. There's a lot of cooperation going on, also, among female chimps, their offspring, and each other.
I've no way of knowing if this behavior is instinctive or conscious. However, I suspect an adult chimp is quite capable of opting out of whatever it is that the rest of the clan is cooperating on.
It seems reasonable, then, that early humans -- given the ability to plan and to communicate -- sought ways to cooperate when threatened by local miscreants.