Severine Hex

Sexual size dimorphism (SSD) has motivated a large body of research on mammalian mating strategies and sexual selection. Despite some contrary evidence, the narrative that larger males are the norm in mammals – upheld since Darwin’sDescent of Man– still dominates today, supported by meta-analyses that use crude measures of dimorphism and taxonomically-biased data. With newly-available datasets and primary sources reporting sex-segregated means and variances in adult body mass, we estimated statistically-determined rates of SSD in mammals, sampling taxa by their species richness at the family level. Our analyses of >400 species indicate that although males tend to be larger than femaleswhendimorphism occurs, males arenotlarger in most mammals, and suggest a need to revisit other assumptions in sexual selection research.One-Sentence SummaryTaxonomically-balanced estimates of rates of sexual size dimorphism in mammals refute the ‘larger males’ narrative.