Social dominance orientation (SDO) is a personality trait measuring an individual's support for social hierarchy and the extent to which they desire their in-group be superior to out-groups. SDO is conceptualized under social dominance theory as a measure of individual differences in levels of group-based discrimination; that is, it is a measure of an individual's preference for hierarchy within any social system and the domination over lower-status groups. It is a predisposition toward anti-egalitarianism within and between groups. Individuals who score high in SDO desire to maintain and, in many cases, increase the differences between social statuses of different groups, as well as individual group members. Typically, they are dominant, driven, tough, and seekers of power. People high in SDO also prefer hierarchical group orientations. Often, people who score high in SDO adhere strongly to belief in a "dog-eat-dog" world. It has also been found that men are generally higher than women in SDO measures. A study of undergraduates found that SDO does not have a strong positive relationship with authoritarianism. Social dominance theory SDO was first proposed by Jim Sidanius and Felicia Pratto as part of their social dominance theory (SDT). SDO is the key measurable component of SDT that is specific to it. SDT begins with the empirical observation that surplus-producing social systems have a threefold group-based hierarchy structure: age-based, gender-based and "arbitrary set-based", which can include race, class, sexual orientation, caste, ethnicity, religious affiliation, etc. Age-based hierarchies invariably give more power to adults and middle-age people than children and younger adults, and gender-based hierarchies invariably grant more power to one gender over others, but arbitrary-set hierarchies—though quite resilient—are truly arbitrary. SDT is based on three primary assumptions: While age- and gender-based hierarchies will tend to exist within all social systems, arbitrary-set systems of social hierarchy will invariably emerge within social systems producing sustainable economic surpluses. Most forms of group conflict and oppression (e.g., racism, homophobia, ethnocentrism, sexism, classism, regionalism) can be regarded as different manifestations of the same basic human predisposition to form group-based hierarchies. Human social systems are subject to the counterbalancing influences of hierarchy-enhancing (HE) forces, producing and maintaining ever higher levels of group-based social inequality, and hierarchy-attenuating (HA) forces, producing greater levels of group-based social equality. SDO is the individual attitudinal aspect of SDT. It is influenced by group status, socialization, and temperament. In turn, it influences support for HE and HA "legitimating myths",