Evolutionary theorist Robert Trivers

Nice Guardian profile. Trivers linked the evolution of altruism to that of an ability to detect cheaters.

...There are less dramatic examples, however, which include sharing food, helping the sick, the very young, and the old, even when we are not related to them, and sharing tools and knowledge. All these are nearly universal human habits; in fact we describe societies where they don't happen as inhuman.

This kindliness became part of human nature, Trivers argued, because kind instincts were rewarded and this happened because our ancestors lived sufficiently long lives in small stable groups to keep track of who owed whom favours. The great originality of the theory is not that it says that we are under certain circumstances naturally benevolent. Plenty of people had made that observation before. What no one had seen was that this benevolence requires a very strong sense of fairness if it is to become an established instinct. Fairness, or justice, has its roots for Trivers in the determination to see that other people are not cheating us, and taking favours without giving anything in return.

From abstract notions about the flow of genes he had come up with concrete and testable ideas about the ways our minds work; and it turned out to be demonstrably true that we find it much easier to solve logical puzzles if they are framed as if they are about cheating rather than an emotionally neutral subject, even though the two ways of putting the problem are logically equivalent.

The paper on reciprocal altruism, written before he had even gained a doctorate, has been enormously influential. Robin Dunbar, the professor of behavioural ecology at Liverpool University, says Trivers played a fundamentally important role in the development of modern evolutionary studies of behaviour and ecology. His four key early papers spawned (and continue to spawn) research in the study of both animals and humans. The importance of his contribution is beyond question. The modern field of behavioural ecology (the name under which sociobiology now travels) would simply not have been the same had he not written these papers.