Girard had a less fanciful explanation. Early societies, he argued, did not yet have a legal system – laws, courts, prisons and punishments – to enforce order. Instead they practised reciprocity, the rule of Tit-for-Tat that, as we saw, was the first principle to emerge from computer simulations of the Iterated Prisoner’s Dilemma. They acted generously to others until they encountered a hostile response.
