Economic man is self-interested and rational. But in practice, humans often act irrationally and sacrifice their own self-interest for the benefit or detriment of another’s outcome. Rooted in the same fundamental economic principles, is formal game theory, then, a wash? This paper sets out to bring together evidence from recent discussion in behavioral and evolutionary game theory in an attempt to rationalize fair division as a short run equilibrium strategy played by self-interested and rational human beings in the ultimatum game.