1Anthropology, University of Texas-Austin, 2Ankoatsifaka Research Station, Kirindy Mitea National Park, 3Evolutionary Anthropology, Duke University
April 20, 2017 9:00, Studio 1/2/3
Sex-based power inequality is pervasive in primates. We hypothesized that both dominance and leverage influence sex-based power. If sexual dimorphism causes intersexual dominance, we predicted that highly dimorphic species are constrained to be male dominant, and low dimorphism species are free to demonstrate any pattern of power. If market effects influence intersexual leverage, we predicted that females have more power when social group sex ratios are more female-biased and estrus is asynchronous. We analyzed intersexual dominance status, body mass and canine ratio, expected estrous overlap, reproductive seasonality, and sex ratio data for 79 primate species using phylogenetic logistic regression and ancestral state reconstructions (ASRs). While male dominance is most common in primates, every major extant clade includes at least one species that is not male dominant. Male dominance was significantly associated with greater dimorphism in body mass and canine length and with female-biased sex-ratios. Very low expected estrus overlap was significantly associated with female dominance and co-dominance. Based on multiple ASR analyses, male dominance was not necessarily the ancestral condition for primates, strepsirrhines, or haplorhines. The anthropoid last common ancestor (LCA) was probably male dominant but likely did not exhibit high sexual dimorphism. High dimorphism probably characterized the catarrhine LCA, which constrained dominance relationships within this clade and helps explain why living catarrhines are primarily male dominant. Male dominance evolved multiple times in primates and is probably common because multiple traits are linked to male dominance but fewer traits are associated with female dominance or co-dominance.