In Jensen's study, chimpanzees from the Wolfgang Koehler Primate Research Centre in Leipzig were given a choice; by pulling on a rope they could either deliver food to another chimpanzee or they could deliver it to an empty room. In both cases, the chimpanzee pulling the rope did not receive any food itself. Contrary to initial expectations the chimpanzees behaved neither altruistic nor spiteful. According to the researchers, both characteristics therefore seem to be human-specific.
An altruistic chimpanzee would give food to its neighbour, despite the effort in pulling the food, and a spiteful chimpanzee would prevent its neighbour from having the food by delivering it to the empty room.
'I predicted chimps would be spiteful. I thought if they knew they couldn't have the food, they wouldn't let anyone else have it.' Jensen found that half the time, the chimpanzees did nothing. A quarter of the time they delivered food to their neighbour, then a quarter of the time to the empty room. This demonstrated neither altruism nor spite.
'They didn't seem to care about the other guy one way or the other. All that concerned them was getting the food and they were completely focused on that. Even when they knew they couldn't have the food, they didn't help the other chimp but they weren't spiteful either.'
In contrast, humans are obviously altruistic. We give blood, we donate money to charity, and we volunteer to help strangers. This kind of altruism has never been demonstrated in any other animal except for humans and some believe it is one of the characteristics that makes us human. But Jensen says spite is just as important. As a form of punishment, spite can encourage cooperative behaviour by penalising cheaters.
'Punishing others is usually costly to yourself, whether that's the taxpayer or the lawmakers but punishment is still a natural part of modern society. We punish theft, murder and countless other crimes to keep the fabric of society together. Perhaps human society is where it is today because spite exists and there is a mechanism to punish cheaters.'
If altruism and spite are unique to humans and are not present in chimpanzees, then it is likely that these characteristics have arisen in the last 6 million years since humans and chimpanzees shared a common ancestor. Humans' intense regard for each other, either positive or negative, may have made an important contribution to our ability to cooperate, our sense of fairness, and the morality that defines today's society.