" The evolutionary fusion of hierarchy and reciprocal altruism accounts for a good part of the average human life. Many, if not most, of our swings in mood, our fateful commitments, our changes of heart about people, institutions, even ideas, are governed by mental organs that this fusion wrought. It has done much to form the texture of everyday existence. "

― Robert Wright , The Moral Animal: Why We Are the Way We Are - The New Science of Evolutionary Psychology