Our work on social dominance theory (SDT) has focussed on trying to answer two related questions: Why is group-based social dominance so common, and why is it so difficult to eliminate? In attempting to answer these two questions, we presume that, despite major and sometimes profound differences between societies and cultures, there is also a basic grammar and deep structure of social power that is shared by all societies. Our work on SDT has been devoted to identifying what this grammar and deep structure consist of.

The historical and anthropological record suggests that most human societies contain three distinct but interlocking hierarchical systems: gender, age, and arbitrary sets, that is, the contextually dependent and arbitrarily defined social distinctions based on factors such as ethnicity, race, class, tribe, and nation. We have argued that these three systems of group-based dominance are not interchangeable or equivalent, but rather constitute three interlocking and mutually interdependent structural components of social life. Systems of group-based social dominance occur across a wide variety of historical periods, economies, and technologies. While gender and age hierarchies appear to be essentially universal across all known societies, arbitrary-set hierarchies largely occur only in societies in which people are able to generate and sustain an economic surplus. The consequent social stratification among arbitrary sets then further contributes to gender inequality and the establishment of patriarchy. For example, whe the bush-living !Kung produced only enough to sustain themselves, they had a fairly flat social structure, with few status or power distinctions between men and women, among different groups, or even between adults and children.