New estimates indicate that males are not larger than females in most mammals

Abstract

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 Darwins Descent 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 females when dimorphism occurs, males are not larger 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.