New evidence shatters Darwin’s lasting assumptions about male body size

“The males of most species are larger and stronger than the females.” So wrote Charles Darwin in 1871 while laying out his theory of sexual selection in a seminal book called The Descent of Man.

For more than a century, that idea has largely persisted, dominating discussions on mammals especially. At last, arguments against this common male bias are finally being heard.

Three ecologists from Princeton University have now completed a new meta-analysis that includes data from more than 400 species, which, together, cover almost every order of mammal. Their findings suggest that nearly 39 percent of mammal species have males and females with similar mean body masses – a concept known as sexual monomorphism.

By contrast, roughly 45 percent of species had larger males, on average, and 16 percent had larger females.

Even in those cases of sexual ‘dimorphism’, however, most size differences were not extreme.

“While species with larger males were the largest single category, we found that males are not larger than females in most mammalian species, and that sexual size monomorphism was almost as frequent as larger males,” explain the ecologists, led by Kaia Tomback. (Sciencealert) 

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