Allen's rule

Etymology
Formulated by Joel Asaph Allen in 1877.

Proper noun

 * 1) An ecogeographic principle broadly stating that animals adapted to cold climates have relatively short limbs. Specifically, homeothermic animals in hot climates have low volume-to-surface ratios, and homeothermic animals in cold climates have high volume-to-surface ratios, due to thermal adaptation.