I guess, humans must be an exception! 😊
"Human males are typically about 15% taller and heavier than females. Similarly, male lions and gorillas are much larger and stronger than their female counterparts. Since the days of Charles Darwin, the assumption has been that males are typically larger than females across the mammalian kingdom. However, a new study that compared male and female body masses across 429 species in the wild challenges this bias.
In the vast majority of cases, males aren’t larger than females. In fact, in many species, males and females are about the same size. There are examples of males larger than females and females larger than males (like in the case of the northern elephant seal), but neither is the norm. ..."
From the abstract:
"Sexual size dimorphism 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’s Descent of Man—still dominates today, supported by meta-analyses that use coarse measures of dimorphism and taxonomically-biased sampling. With newly-available datasets and primary sources reporting sex-segregated means and variances in adult body mass, we estimate statistically-determined rates of sexual size dimorphism in mammals, sampling taxa by their species richness at the family level. Our analyses of wild, non-provisioned populations representing >400 species indicate that although males tend to be larger than females when dimorphism occurs, males are not larger in most mammal species, suggesting a need to revisit other assumptions in sexual selection research."
Fig. 1: Estimated rates of sexual dimorphism in body mass in mammals.
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