Jim Holt at the New York Times:
Evolutionary psychologists have come up with four plausible Darwinian reasons for altruism. First, there is “kinship selection,” which is supposed to lurk behind the sacrifices you make for your biological family. It’s based on the percentage of genetic overlap. One biologist, when asked if he would lay down his life for his brother, quipped, no, but he would for two brothers or eight cousins.
Second, there is “reciprocal altruism,” which doesn’t depend on shared genes. Here, the basic idea is: You scratch my back, I’ll scratch yours. Reciprocal altruism is seen not just in humans but in some animal species. Vampire bats, for instance, benefit one another by sharing meals of regurgitated blood.
Kinship and reciprocation are, as Richard Dawkins has written, the “twin pillars of altruism in a Darwinian world.” Neither, however, would appear to be of much use in explaining philanthropy. Bill Gates has no special genetic relationship to the beneficiaries of his foundation. Nor does he expect them to reciprocate by purchasing the next release of Windows.
A third explanation for altruism, the Darwinian advantage of having a reputation for generosity, might look more promising. Nineteenth-century “robber barons” like John D. Rockefeller and Andrew Carnegie had ample reason to amend their reputations by generous benefactions.