Although it seems logical that we would help people we are related to or those we perceive as similar to us, why would we ever help people to whom we are not related? One explanation for such behavior is based on the principle of reciprocal altruism (Trivers, 1971). Reciprocal altruism is the idea that if we help other people now, they will return the favor should we need their help in the future. Thus by helping others, we both increase our chances of survival and reproductive success and help others increase their chances of survival too. Over the course of evolution, those who engage in reciprocal altruism should be able to reproduce more often than those who do not, thus enabling this kind of altruism to continue. Reciprocal altruism means that people even may help total strangers, based on the assumption that doing so is useful because it may lead others to help them (when help is most needed) in the future.
One fact that might help convince you that altruism is in fact evolutionarily adaptive is that many animals also engage in reciprocal altruism. Birds emit an alarm to nearby birds to warn them of a predator even at a potential cost to themselves. Dolphins may support sick or injured animals by swimming under them and pushing them to the surface so they can breathe. Male baboons threaten predators and guard the rear of the troop as it retreats. And even bats have a buddy system in which a bat that has had a successful night of feeding will regurgitate food for its less fortunate companion (Wilkinson, 1990).
Altruism can even be found in low-level organisms, such as the cellular slime molds (Figure 8.4). Slime molds are groups of cells that live as individuals until they are threatened by a lack of food, at which point they come together and form a multicellular organism in which some of the cells sacrifice themselves to promote the survival of other cells in the organism. Altruism, then, is truly all around us.
Reciprocal altruism is one example of the general principle of social exchange. We frequently use each other to gain rewards and to help protect ourselves from harm, and helping is one type of benefit that we can provide to others. In some cases, this exchange reflects overt cooperation, such as when two students take notes for each other in classes that they miss or when neighbors care for each other’s pets while one of them is away. In other cases, the exchange may be more subtle and indirect: for instance, when we help someone we don’t really know, with the expectation that someone else may help us in return someday.