High Quality Content by WIKIPEDIA articles! In zoology, Bergmann's rule is an ecogeographic rule that correlates latitude with body mass in animals. Broadly it asserts that within a species the body mass increases with latitude and colder climate, or that within closely related species that differ only in relation to size that one would expect the larger species to be found at the higher latitude. The rule is named after a nineteenth-century German biologist, Christian Bergmann, who first formulated the rule in 1847. The rule is often applied only to mammals and birds (endotherms), but some researchers have also found evidence for the rule in studies of ectothermic species. Bergmann's rule is controversial amongst researchers and its validity has been called into question, and there is division amongst scientists about whether the rule should be interpreted to be within species variation or among species variation. Although several mechanisms have been suggested to explain the rule there is no clear explanation for why the pattern exists.

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