A widely documented sex difference in political psychology is that men have higher social dominance orientation than women. Social Dominance Theory claims that this phenomenon reflects the different adaptational challenges men and women faced in the evolutionary history of the human species. Thus, according to the invariance hypothesis, all things being equal, men should have a higher level of social dominance orientation than women. The biological emphasis of Social Dominance Theory was criticized by Social Identity and System Justification theorists, who argued that gender differences stem from social and contextual factors. In this paper, I systematically reviewed the studies that test the invariance hypothesis or alternative explanations of sex differences in social dominance orientation. To this, I searched two online databases for relevant studies published after the invariance hypothesis is proposed and identified 21 studies in 17 articles. The literature indicates that there is considerable evidence that contradicts the invariance hypothesis. Age, academic major, gender identification, gender roles and stereotypes, and intergroup status emerged as alternative explanatory variables. I discussed the implications of these findings for Social Dominance Theory and its alternatives.