Bergmann'srule

Berg·mann's rule (bûrgʹmənz) n.

The principle holding that in a warm-blooded, polytypic, wide-ranging animal species, the body size of the members of each geographic group varies with the average environmental temperature. According to this principle, warm-blooded animals living in cold climates tend to be larger than animals of the same species living in warm climates.

  [After Karl Bergmann (died 1865), German biologist.]

* * *