How did we evolve from amoral apes to moral humans?

In Moral Origins, social anthropologist Christopher Boehm argues that our ancestors were "preadapted" for morality. Like today's chimps and bonobos, they had a sense of self and of fairness, a tendency for young to learn appropriate behaviour from their mothers, and the potential for collective action, giving subordinates some power over dominant individuals. The first step was to develop a conscience, or what Boehm describes as a "Machiavellian risk calculator". At first, this controlled selfish urges through fear of punishment, but morality began to emerge when our ancestors learned to internalise their society's social rules, connecting them with emotions such as shame and honour. Finally, he says, altruistic genes got a boost as societies came to value generosity and punish selfishness. Our egotistic and nepotistic tendencies still far outweigh the altruistic ones, but by social selection we have unwittingly made our own gene pool more virtuous.