Arguing from a sociobiological perspective, Sidanius and Pratto (1999) have shown that the male/female difference in social dominance orientation (SDO) is largely invariant across cultural, situational and contextual boundaries. The main objective of this study was to test the validity of Social Dominance Theory (SDT) by contrasting it with a model derived from Social Identity Theory (SIT). More specifically, while SIT predicts that gender identification mediates the effect of gender on SDO, SDT predicts the reverse. According to SDT, the degree to which men and women endorse status legitimizing ideology should determine to what extent they identify with their gender group. Using structural equation modelling, the results provide strong support for the SIT model and no support for SDT predictions. Implications of these results for social dominance theory and its sociobiologically based invariance hypothesis are discussed.