Sexual dimorphism: a comparative study between the prehispanic inhabitants from El Hierro and other populations of the world

Sex estimation based on tibial measurements can be achieved using discriminant functions combining several parameters. However, functions differ from one population to another, because sexual dimorphism may be more or less marked among different ancestry or ethnic groups. Calculation of one of these functions with the dimensions of populations other than that from which the function was obtained may misclassify a different proportion of males or females than when calculated with the dimensions of the original population. By dividing the proportions of correctly classified individuals when the function was applied to the population from which it derived and that of El Hierro (Canary Islands), we can calculate an index of male trait expression and an index of female trait expression, and, by addition of both indices, an index of sexual dimorphism. Therefore, it is possible to compare the degree of sexual dimorphism among several populations, at least regarding those measurements included in the function. Based on this fact we have calculated several functions (reported in the scientific literature), obtained from tibiae of modern black, white, and Japanese populations, and from medieval Croatians and prehispanic inhabitants of Gran Canaria (ap. 1000 BP), with the dimensions of the prehispanic population of El Hierro, genetically sexed, also with an antiquity of ap. 1000 BP. Despite the different antiquity, the population of El Hierro was more dimorphic that the modern Japanese one, but less dimorphic than most of the other groups with which it was compared, especially when functions including distal epiphyseal breadth and minimum shaft perimeter (near the distal end of the tibiae) were calculated: in these cases, dimorphism was lower for the population of El Hierro, due to the fact that, although male trait expression index was higher, many females of El Hierro were misclassified as males because of the abnormally thick distal diaphyseal and epiphyseal breadths of El Hierro inhabitants.