the claim that humans have a passion for equality may raise an eyebrow among some readers. Indeed, inequality not only pervades our own postindustrial civilization but also seems to have been part and parcel of all previous societies, as expressed in feudalism, slavery, gender inequality, and the like. However, to say that we have a passion for equality is not to say that it is our only passion. The human mind is complex, and many competing motives struggle to determine our behavior. Moreover, calls for equality can be based on motives (envy, spite, malevolence) that have little to do with equality as such.

The natural history that I propose is one in which the passion for equality has force in the human lineage, but remains in competition with other motives to produce societies as diverse as small foraging bands and continental empires. In the following chapters, I argue that egalitarian social arrangements in Homo sapiens and extinct human species should not be explained as the direct outcome of a passion for equality, but rather in the broader context of the evolution of the motivational and cognitive mechanisms underlying norm following and sanctioning. In the proper circumstances, these very mechanisms are also likely to permit the evolution of hierarchical and inegalitarian arrangements. Before I get into the phylogenetic and historical debate on the origins of hierarchies, however, I want to discuss Homo sapiens as we know it today.