Abstract

My answer to the question why? is relatively uncontroversial among anthropologists. Sharing food makes good evolutionary sense, because animals who share food thereby insure themselves against hunger. It is for this reason that sharing food is thought to be so common in the natural world. The vampire bat is a particularly exotic example of a food-sharing species. The bats roost in caves in large numbers during the day. At night, they forage for prey, from whom they suck blood if they can, but they aren’t always successful. If they fail to obtain blood for several successive nights, they die. The evolutionary pressure to share blood is therefore strong. The biologist Wilkinson [59] reports that a hungry bat begs for blood from a roostmate, who will sometimes respond by regurgitating some of the blood it is carrying in its own stomach. This isn’t too surprising when the roostmates are related, but the bats also share blood with roostmates who aren’t relatives. The behaviour is nevertheless evolutionarily stable, because the sharing is done on a reciprocal basis, which means that a bat is much more likely to help out a roostmate that has helped it out in the past. Bats that refuse to help out their fellows therefore risk not being helped out themselves in the future. Vampire bats have their own way of sharing, and we have ours. We call our way of sharing “fairness”. If the accidents of our evolutionary history had led to our sharing in some other way, it would not occur to us to attribute some special role to our current fairness norms. Whatever alternative norms we then..