Bergmann's rule The idea that the size of homoiothermic animals in a single, closely related, evolutionary line increases along a gradient from warm to cold temperatures (i.e. that races of species from cold climates tend to be composed of individuals physically larger than those of races from warm climates). This is because the surface area: body weight ratio decreases as body weight increases. Thus a large body loses proportionately less heat than a small one. This is advantageous in a cold climate but disadvantageous in a warm one. The rule was proposed in 1847 by the German zoologist C Bergmann. See also Allen's rule and Gloger's rule.

Bergmann's rule The idea, proposed by C. Bergmann in 1847, that the size of homoiothermic animals in a single, closely-related, evolutionary line increases along a gradient from warm to cold temperatures, i.e. that races of species from cold climates tend to be composed of individuals physically larger than those of races from warm climates. This is because the surface-area: body-weight ratio decreases as body weight increases. Thus a large body loses proportionately less heat than a small one. This is advantageous in a cold climate but disadvantageous in a warm one. See also ALLEN'S RULE; and GLOGER'S RULE.

Bergmann's rule The idea that the size of homoiothermic animals in a single, closely related, evolutionary line increases along a gradient from warm to cold temperatures—i.e. that races of species from cold climates tend to be composed of individuals physically larger than those of races from warm climates. This is because the surface-area: body-weight ratio decreases as body weight increases. Thus a large body loses proportionately less heat than a small one. This is advantageous in a cold climate but disadvantageous in a warm one. See also ALLEN'S RULE; GLOGER'S RULE.