Bergmann’s rule
There are striking examples in today’s animal world of how a larger body is preferable in cold climates. Bergmann’s rule, known in zoology, states that among closely related species, those living in cold climates are larger, in temperate climates species are smaller and those living in warm climates are the smallest. This rule is not universal and does not apply to some groups, but a really prominent example of this is that of bears.