Recent research and theorizing suggest that desires for group-based dominance underpin biases towards both human outgroups and (non-human) animals. A systematic study of the common ideological roots of human-human and human-animal biases is, however, lacking. Three studies (in Belgium, UK, and USA) tested the Social Dominance Human-Animal Relations Model (SD-HARM) proposing that Social Dominance Orientation (SDO) is a key factor responsible for the significant positive association between ethnic outgroup attitudes and speciesist attitudes towards animals, even after accounting for other ideological variables (that possibly confound previous findings). Confirming our hypotheses, the results consistently demonstrated that SDO, more than right-wing authoritarianism (RWA), is a key factor connecting ethnic prejudice and speciesist attitudes. Furthermore, Studies 2 and 3 showed that both SDO and RWA are significantly related to perceived threat posed by vegetarianism (i.e. ideologies and diets minimizing harm to animals), but with SDO playing a focal role in explaining the positive association between threat perceptions and ethnic prejudice. Study 3 replicated this pattern, additionally including political conservatism in the model, itself a significant correlate of speciesism. Finally, a meta-analytic integration across studies provided robust support for SD-HARM and offers important insights into the psychological parallels between human intergroup and human-animal relations. Copyright (C) 2016 European Association of Personality Psychology