In the following chapters, I offer an evolutionary account of morality and from that extrapolate a version of contractarianism I call consent theory. Game theory helps to highlight the evolution of morality as a resolution of interpersonal conflicts under strategic negotiation. It is this emphasis on strategic negotiation that underwrites the idea of consent. Consent theory differs from other contractarian models by abandoning reliance on rational self-interest in favour of evolutionary adaptation. From this, more emphasis will be placed on consent as natural convergence rather than consent as an idealization. My picture of contractarianism, then, ends up looking more like the relativist model offered by Harman, rather than the rational (or pseudo-rational) model offered by Gauthier, let alone the Kantian brands of Rawls or Scanlon. So at least some of my discussion will dwell on why it is no loss to abandon hope for the universal, categorical morality that rational models promise. In the introduction, I offer the betting analogy that underwrites the remaining picture. There are some bets where the expected utility is positive, though the odds of winning on this particular occasion are exceedingly low. In such cases, we cannot hope to give an argument that taking the bet is rational. The only thing we can say is that those predisposed to take this kind of bet on these kinds of occasions will do better than those with other dispositions, so long as such games occur often enough.