India, March 14 -- Male-biased size dimorphism was found in only 28% of 429 mammal species examined

Males are bigger than females, right? Generally, this is true of humans - imagine the extremes of Dwayne "The Rock" Johnson and singer Kylie Minogue. It is also true of other familiar mammals including pets, such as cats and dogs and livestock such as sheep and cows.

But a new study by United States scientist Kaia Tombak and colleagues found that, in many mammal species, males are not larger than females. In fact, in a comparison of 429 species in the wild, 50 per cent of species including rodents and some bats - which make up a large proportion of all mammal species - showed no difference in body size between the sexes. Male-biased size ...