"By describing adultery as a force that shaped our mating system, I am not “justifying” it. Nothing is more “natural” than people evolving the tendency to object to being cuckolded or cheated on, so if my analysis were to be interpreted as justifying adultery, it would be even more obviously interpreted as justifying the social and legal mechanisms for discouraging adultery. What I am claiming is that adultery and its disapproval are both “natural.”"