Game theory

In the wild:

At first glance, the male cleaner wrasse behaves oddly for an animal, in punishing an offender on behalf of a third party, even though he hasn't been wronged himself. That's common practice in human societies but much rarer in the animal world. But Raihani's experiments clearly show that the males are actually doing themselves a favour by punishing females on behalf of a third party. Their act of apparent altruism means they get more food in the long run.