People still debate whether humans are genuinely altruistic by natureIf you believe there is no such thing as altruism, you are in good company. In The Selfish Gene, Richard Dawkins writes that we must “try to teach generosity and altruism, because we are born selfish”. Even if we are nice to members of our family, that doesn’t count because there is a pay-off, at least in biological terms: they share some of our genes, so by helping them we indirectly further our own genetic immortality. Meanwhile, other acts of seeming altruism are often just reciprocity. If you scratch my back, then I scratch yours – no matter how much later – that’s not selfless either. This all makes good evolutionary sense, since spending time and energy helping someone without any return puts you at a distinct disadvantage in the survival stakes. The only trouble is that in recent years evidence has amassed that people do commit acts of genuine altruism. In experimental game-playing situations, for example, many people will share money with a stranger even when there is nothing in it for them. This has led biologists to conclude that altruism is a part of human nature. What they cannot decide is how or why it evolved.