What prompted Good King Wenceslas to look out on that feast of Stephen? And why should he have cared that the poor man was gathering winter fuel? Modern evolutionary theory agrees with market economics that we are inherently selfish and unlikely to give if we don't expect to receive. But new research challenges that model.
The origin of altruism goes to the heart of the gene/culture debate that was launched in 1975 with the publication of EO Wilson's Sociobiology and, a year later, Richard Dawkins's The Selfish Gene. Sociobiology claims that human nature - and by extension human society - is rooted in our genes: we are, according to Dawkins, "lumbering robots" created "body and mind" by selfish genes. This is anathema to social scientists and biologists such as Steven Rose, who see human nature as far more malleable.
Altruism is not confined to humans, but when animals give presents it is nearly always to close kin. The mathematical biologist JBS Haldane is credited with discovering the mechanism known as kin selection, when he declared that he would lay down his life for two brothers or eight cousins. Haldane's familial benevolence was based on the fact that two of his brothers or eight of his cousins would carry just about all his genes. So helping your relatives ensures that your (shared) genes live on.
Kin selection may account for pack behavior, but it fails to account for human benevolence, which is often extended well beyond the family. It is not only Blanche DuBois who can depend on the kindness of strangers. Codes of hospitality are a common feature of human societies - from the desert-dwelling Bedouin to the Arctic Inuit.
To explain non-kin-directed altruism, an assortment of gene-based mechanisms has been proposed, ranging from reciprocal altruism (you scratch my back and I'll scratch yours) to signaling theory (conspicuous kindness to attract mates). But none can fully explain human generosity. What did Good King W hope to gain from bringing flesh and wine when the frost was so cruel outside? He could hardly have expected the poor man to reciprocate. And tramping about in all that crisp and even snow was unlikely to improve his mating options.
Kindness and cooperation underpin much of human society. From the Kyoto agreement to arms controls or the state of public toilets, they all depend on individual willingness to commit resources to a common good. But no one has come up with a satisfactory evolutionary explanation of why we do it.
In a recent Nature paper, Ernst Fehr and Urs Fischbacher of the University of Zurich evaluated the evidence from a series of cunning experiments. In the ultimatum game, two subjects are asked to share a pot of money, say £100. One of them (we'll call him Steven) decides the cut - who gets what. The other (we'll call him Richard) can either accept his share or cry foul, in which case neither of them takes any of the money away.
The players play only once so there isn't an opportunity for reciprocal altruism. If Richard is behaving entirely selfishly (programmed by his selfish genes), he should accept whatever Steven is prepared to give. But generally he doesn't. If Steven donates less than £25, Richard generally refuses his share and they both leave the table empty-handed. Richard is prepared to forsake his (albeit smaller) share in order to punish Steven's selfishness.
Another experiment looks at public-good altruism. Here a group of subjects are each given a sum, say £10, which they can either keep for themselves or pay some amount - a tax - towards the public good. The taxman (we'll call him Gordon) is generous enough to double the tax revenue and give an equal share back to each member of the group, whether or not they paid into the tax kitty. It makes sense for the group to donate everything to Gordon who doubles and redistributes it. But instead of getting £20, the group members discover they only take away £12 or £15. Someone's not paying his or her share of the tax but still claiming the reward. At the next round, knowledge that some neighbors are freeloaders prompts group members to reduce the tax they are prepared to pay. The process of cooperation decay continues until nobody is prepared to pay anything.
Avoiding cooperation decay is the aim of governments and international institutions. Fehr and Fischbacher claim that the key to promote what they call strong reciprocity is rewarding generosity with kindness but punishing cheaters, even at the expense of the punisher. This is why Richard refused to accept Steven's offer, though his genes might have been telling him to take the money and run. Similarly, if public-goods experiments allow subjects to punish cheats (even if the punishment is costly for the punisher), cooperation flourishes.
Strong reciprocity promotes kindness and discourages cheats, but is it a product of our genes or in our culture? It can't be entirely genetic, since different human societies (with very similar genes) vary greatly in their tolerance of cheating. Fehr and Fischbacher argue for gene-culture co-evolution: cultural and institutional environments promote social norms that favor the selection of genes that promote cooperation.
Making strong reciprocity work at both a local level (discouraging anti-social behavior) and international level (persuading the Americans to sign the Kyoto agreement) would be beneficial to society and the world. And I for one feel much happier singing Good King Wenceslas's praises when I know he wasn't just a lumbering robot, the slave of his selfish genes.
· Johnjoe McFadden is professor of molecular genetics at the University of Surrey, and author of 'Quantum Evolution'.
© Guardian Newspapers Limited 2003