Punish or perish? Retaliation and collaboration among humans.

A spate of recent investigations on reciprocation and social enforcement in humans has brought together (and sometimes divided) economists, psychologists, anthropologists, social scientists and evolutionary biologists, in addition to neurologists and students of animal behavior. Experimental work on public goods and social incentives has addressed a wealth of questions on the emotional and cognitive (proximal) factors, and also on the genetic and cultural (ultimate) evolutionary mechanisms involved in this essential aspect of human nature.