From BBC News:
The popular view of our ancient ancestors as hunters who conquered all in their way is incorrect, scientists have told a conference in St Louis, US. Instead, they say, early humans were on the menu for predatory beasts. This may have driven humans to evolve increased levels of co-operation, according to their theory. Despite humankind’s considerable capacity for war and violence, we are highly sociable animals, according to anthropologists. James Rilling at Emory University in Atlanta, US, has been using brain imaging techniques to investigate the biological mechanisms behind co-operation. He has imaged the brains of people playing a game under experimental conditions that involved choosing between co-operation and non-co-operation.
From the parts of the brain that were activated during the game, he found that mutual co-operation is rewarding. People also reacted negatively when partners do not co-operate. Dr Rilling also discovered that his subjects seemed to have enhanced memory for those people that did not reciprocate in the experiment. By contrast, our closest relatives – chimpanzees – have been shown not to come to the aid of others, even when it posed no cost to themselves. “Our intelligence, co-operation and many other features we have as modern humans developed from our attempts to out-smart the predator,” said Robert Sussman of Washington University in St Louis.
More here.