Dictionary of Human Evolution and Biology

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Allen’s Rule

Tenet that extremities (e.g. legs, ears and tails) of polytypic and homeothermic species tend to be shorter in colder climates than in warmer ones, thereby reducing the surface area of the body. In humans, for example, equatorial peoples such as Nilotics have long and slender arms, whereas arctic peoples such as the Inuit possess shorter arms and legs. This tendency is correlated with the need to conserve heat in colder climates and to radiate heat in warmer climates.

See thermoregulation and crural index.

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