Explaining altruistic behaviour in humans

This article presents evidence supporting strong reciprocity. It explains why, under conditions plausibly characteristic of the early stages of human evolution, a small fraction of strong reciprocators could invade a population of self-regarding types, and why strong reciprocity is an evolutionarily stable strategy. It uses the term 'self-regarding' rather than the more common term 'self-interested' to avoid the question as to whether it is selfish to help others if that is how one 'maximizes utility'. Although most of the evidence it reports is based on behavioural experiments, the same behaviours are regularly observed in everyday life, and of great relevance for social policy. Despite the fact that strong reciprocity is altruistic, its results do not contradict traditional evolutionary theory. A gene that promotes self-sacrifice will die out unless those who are helped carry the mutant gene, or its spread is otherwise promoted.