Craniofacial variation in Homo habilis: an analysis of the evidence for multiple species

The question of heterogeneity in the Homo habilis sample continues to be controversial. Various lines of evidence have been used to reject the null hypothesis of intraspecific variation. This evidence derives from analyses of endocranial volume variation, probability estimates of sexual dimorphism, facial variation, cranial angles, CV analysis of craniofacial variation, the multivariate pattern of sexual dimorphism, the pattern of variability (CV) profiles, distance data using exact randomization methods, and various kinds of quantitative ordinations of fossils. Although consensus is lacking as to how the H. habilis sample is to be split, there is a growing perception that the degree of variation among the fossils is too great and the pattern of variation is too different to be explained by intraspecific variation. This has resulted in the recognition of new species such as "Homo rudolfensis." The present study critically examines the evidence commonly cited as the basis for recognizing multiple species in the extended H. habilis hypodigm. Reanalysis and reinterpretation of these data indicates that: (1) the degree of variation in the H. habilis sample is typical of modern hominoids, and (2) the pattern of variation among specimens of the H. habilis sample is consistent with intraspecific variation. Thus, at present, there is no sound basis to reject the null hypothesis of intraspecific variation as an adequate explanation of the morphological variation seen among specimens of the extended H. habilis sample. If multiple species are indeed represented, then their presence has not yet been satisfactorily demonstrated.