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

Abstract

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 ideas, 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.

Ecological factors affecting body size of Japanese adolescents

“…Therefore the apparent phenomenon of larger body size in colder climates probably comes from the consumption of more calories per capita in colder regions than in warmer regions. This supports the nutritional theory that Bergmann's phenomenon in humans is to be interpreted in terms of geographical differences in nutritional factors rather than the temperature itself (Walter, 1976;Riesenfeld, 1980). It may be that cold weather necessitates more energy intake, or that it stimulates the appetite (Newman and Munro, 1955), resulting in larger body size.…”

“…However, some of the populations studied were not homogeneous enough, either genetically (different breeding populations) or socioeconomically (different countries) to afford a reliable test of the rule. Further, some investigators (Walter, 1976;Riesenfeld, 1980) have speculated that this phenomenon in humans is to be interpreted as the result of geographical differences in nutritional factors such as protein and energy intake, rather than as reflecting genetic differences produced by natural selection.…”

Physical growth of St. Lawrence Island Eskimos: Body size, proportion, and composition

“…The above suggests that the adaptive response of the children and youth of the St. Lawrence sample is a metabolic one, represented by increased amounts of heat-producing tissue, rather than an insulative one that would have been seen in increased levels of body fatness. The interaction between weight, lean body mass, nutrient intake, and adaptation to cold stress has been demonstrated pre-viously in rats by Riesenfeld (1980). While we do not have data on the diets of our subjects, and while studies that have been carried out suggest that mild nutritional deficiencies may occur among Eskimos (Mann et al, 1962;Beaton, 1975).…”