Punishment and spite, the dark side of cooperation.

Causing harm to others would hardly seem to be relevant to cooperation, other than as a barrier to it. However, because selfish individuals will exploit cooperators, functional punishment is an effective mechanism for enforcing cooperation by deterring free-riding. Although functional punishment can shape the social behaviour of others by targeting non-cooperative behaviour, it can also intimidate others into doing almost anything. Second-party functional punishment is a self-serving behaviour at the disposal of dominant individuals who can coerce others into behaving cooperatively, but it need not do so. Third-party and altruistic functional punishment are less likely to be selfishly motivated and would seem more likely to maintain norms of cooperation in large groups. These forms of functional punishment may be an essential part of non-kin cooperation on a scale exhibited only by humans. While punitive sentiments might be the psychological force behind punitive behaviours, spiteful motives might also play an important role. Furthermore, functionally spiteful acts might not be maladaptive; reckoning gains relative to others rather than in absolute terms can lead to hyper-competitiveness, which might also be an important part of human cooperation, rather than just an ugly by-product.