Body build and temperature tolerance: an experimental analysis of ecological 'rules'

According to current anthropological theory, the two factors that primarily determine thermoregulation in human populations are body size and body proportions, and they have found their formulation in the ecological 'rules' of Bergmann and Allen. In order to test the validity of these idea, Buffalo and Fisher rats were submitted to various levels of heat and cold. The two strains were chosen because they demonstrate maximum differences in body size and body proportions in domesticated rats. The experiments lead to the conclusion that Allen's rule has only a limited applicability under conditions of heat and none in cold. However, Bergmann's rule is well substantiated by experimental data in heat and in cold. Nutrition is one of the most important factors influencing thermoregulation, but an extremely high degree of individual variation in temperature tolerance is found even under conditions of maximum homozygosity. The basic physiological processes of thermoregulation are sufficiently similar in human and nonhuman homeotherms to justify the extrapolation from one to the other.