Body Size, Size Variation, and Sexual Size Dimorphism in EarlyHomo

Abstract

Size variation provides important clues about the taxonomy, morphology, behavior, and life history of extinct species. Body size variation in living species is commonly attributed to Bergmann’s rule, resource availability, nutrition, local selection pressures, and sexual size dimorphism. While our understanding of the mechanisms producing size variation in living species has grown more sophisticated in recent years, our ability to apply this knowledge to the fossil record is limited by the quality of the available fossil and extant comparative samples. New discoveries of fossil Homo have expanded the known range of size variation and provide hints of geographic and temporal variation in size within and between named taxa and possible strong sexual size dimorphism. Even so, the range of size variation in Homo habilis/rudolfensis and Homo erectus matches or even is less than that seen in geographically restricted samples of living anthropoid primates. These observations dictate caution in interpreting the meaning of variation in early Homo but also underscore the critical necessity of improving comparisons of size among fossils and establishing an adequate comparative database of living species that allows us to discriminate between the effects of epigenetic and selective factors on the expression of variation.