Abstract
It is widely accepted that modern humans conform to Bergmann's rule, which holds that body size in endothermic species will increase as temperature decreases. However, there are reasons to question the reliability of the findings on which this consensus is based. One of these is that the main studies that have reported that modern humans conform to Bergmann's rule have employed samples that contain a disproportionately large number of warm-climate and northern hemisphere groups. With this in mind, we used latitudinally-stratified and hemisphere-specific samples to re-assess the relationship between modern human body size and temperature. We found that when groups from north and south of the equator were analyzed together, Bergmann's rule was supported. However, when groups were separated by hemisphere, Bergmann's rule was only supported in the northern hemisphere. In the course of exploring these results further, we found that the difference between our northern and southern hemisphere subsamples is due to the limited latitudinal and temperature range in the latter subsample. Thus, our study suggests that modern humans do conform to Bergmann's rule but only when there are major differences in latitude and temperature among groups. Specifically, groups must span more than 50 degrees of latitude and/or more than 30°C for it to hold. This finding has important implications for work on regional variation in human body size and its relationship to temperature.
Highlights
Bergmann’s rule is an empirical generalization concerning body size in endothermic species
One of the most important of these is that the main studies that have found the correlation between modern human body size and temperature predicted by Bergmann’s rule have employed samples that contain a disproportionately large number of warm-climate and northern hemisphere groups [3,7,8,12,17]
In this paper we have reported the results of a study in which we revisited a long-standing anthropological ‘‘fact’’–namely that modern human body size increases as temperature decreases and conforms to Bergmann’s rule
Summary
Bergmann’s rule is an empirical generalization concerning body size in endothermic species It holds that within such species body size varies such that individuals occupying colder environments tend to be larger than individuals who live in warmer environments [1]. This pattern is usually explained in relation to heat production and loss [2,3,4,5,6,7,8,9]. Given how important the notion that modern humans conform to Bergmann’s rule is for our understanding of contemporary human variation, there is a pressing need to determine whether this is the case
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