Few serious thinkers see Homo sapiens as being fundamentally distinct from the animal kingdom. Language, culture and cooperation are being identified in increasing numbers of animals, to varying degrees of sophistication. It would take a truly close-minded anthropocentric to believe that the rules governing social behaviour in humans are entirely dissimilar to those we have studied in animals. The modern view amongst zoologists is that individual animals act in a way to benefit themselves through maximising their lifetime reproductive success; if this means that other individuals suffer, then so be it.

Yet, when we look around us we see a society where theft and deceit are 'abnormal' behaviours, and people constantly seem to sacrifice aspects of their own self-interests for the 'good of the community'. How can the view of individuals as essentially selfish entities be compatible with the cooperation and altruism we widely observe?

Robert Trivers's theory of reciprocal altruism vindicates altruistic behaviour between unrelated individuals by suggesting that the favour will be returned on a later occasion. There is much evidence for the action of this system in organisms as distantly related as vampire bats and stickle-back fish. Could this mechanism be acting in human populations?

Could this explain the puzzles of human sociality, such as why people are generally ruder to those they meet in large cities than their neighbours in small towns? It is well established that we are kinder to those we are likely to meet again. If, for now, we accept that humans act in self-interest according to some form of altruistic reciprocity, what are the implications for economic and environmental policy? If we could 'tap in' to this aspect of human nature, rather than plea for people to change their nature and act selflessly, we may be able to structure our economies in ways that reward environmentalism. This task may seem difficult, but certainly less so than systematically altering the innate behaviour of billions of people.

Economists, mathematicians and biologists alike have shown that the rational man will grasp a resource (oil, water, land, elephants etc.) while he can, otherwise risking playing into the hands of his opportunist neighbour. We need only glance at the plethora of examples of valuable species going extinct through overexploitation to realise this, a dilemma is often referred to as the 'tragedy of the commons'. How can we stop the rational man from shooting the last rhinoceros? Many environmentalists point to government intervention and nationalization of resources as solutions. But time and time again, history shows us that this does not work. People often need direct, personal motivation not to over-exploit resources, and avoid free-for-alls which rapidly exhaust a useful resource.

Near Fowler, Kansas, in the Artesian valley, there was a state-owned creek from which anyone could consume as much water as they liked. Steadily, the resource was diminished, and whilst the inhabitants knew that limiting their usage would help sustain the supply, it was not in their immediate personal interest to do so. Exercising restraint would simply play into the hands of the next person. Contrast this with the Turia river near Valencia, which is shared by some 15,000 farmers, each of whom take their turn to take water from it. Cheating (i.e. taking out of turn) is discouraged by the watchful eyes of the other farmers, and any misdemeanours are reported to the Tribunal de las Aguas, the records of which go back to the 15th century and suggest that cheating is very rare indeed. Moreover, the area is highly lucrative, and produces two harvests per year. These examples illustrate that the self-interest that we all naturally harbour will, if allowed to do so, strive for short-term personal gain over the long-term benefits to the wider community. Two water sources, two different approaches to their regulation, two very different outcomes.

I am not under the illusion that an evolutionary approach to economic policy can solve all of the problems in our society, but it can surely offer some interesting insights. As Ridley and Low put it, "We are merely asking governments to be more cynical about human nature. Instead of being shocked that people take such a narrow view of their interests, use the fact." At first it seems that nationalization of resources is the sensible, humanitarian and environmentally-friendly thing to do, but a peer into the human psyche suggests that we may not like the result as much as we had first supposed.