Dispersion dimorphism in human populations

The aim of this paper is to verify the existence of dispersion (or variability) dimorphism in several anthropometric traits, i.e., some skeletal, muscular, and adipose dimensions, and to provide an evaluation of this scarcely considered aspect of sex differences. This research focuses on two human samples from two different European regions, Sardinia (Italy) and the Basque Country (Spain). Twenty-three anthropometric measurements were taken. A first qualitative analysis was carried out comparing the profiles of the coefficients of variation of each variable in both sexes. Secondly, the equality of variability was verified with different tests. In the normal case, Student's t-test, as proposed by Sokal and Braumann ([1980] Syst. Zool. 29:50-63), was applied. In the more general case, it was necessary to resort to resampling techniques. A suitable bootstrap test was constructed and the results were compared, when possible, with those obtained by other methods. The measurements showed parallel trends in the two populations. In particular, subcutaneous skinfolds showed significant dispersion dimorphism, with the greatest coefficients of variation in men. We suggest that this result was linked to stronger canalization in female dimensions related to the reproductive function and influenced by sociocultural factors. We also suggest defining dispersion dimorphism, whose existence is confirmed by the results presented in this paper, as a descriptive pattern of phenotype variability in both sexes that can be specific of a given class of anthropometric traits.