The relationship between Homo erectus and Homo sapiens is critical to understanding the origin of modern humans. Two schools of thought exist, one that sees regional evolution of Homo sapiens from local populations of H. erectus throughout the Old World, and another that sees H. sapiens originating in Africa and ultimately replacing local H. erectus populations. Both schools use cranial characters to examine the degree of continuity in a geographic region but differ on their interpretations of the significance of these characters. Both agree that the best case for such continuity can be made in Australasia. This study uses comparative human anatomy to explicitly test whether the characters used to link Indonesian H. erectus and Australian modern humans are likely to be good indicators of genetic relatedness. The hypotheses to be tested are: 1) are the linking features functionally associated with a robust masticatory (chewing) pattern in modern Australians, 2) are features of the neurocranium (braincase) structural consequences of growth universal to long-headed individuals but not necessarily of genetic valence, and 3) are cranial keels structurally similar across taxa. These hypotheses are tested using 15 geographically diverse modern human samples, metric and nonmetric traits, and Computed Tomography. Answers to each of these three questions are critical to evaluating whether the linking features are likely to reflect genetic relatedness or some other shared environmental or developmental condition. Without explicit evaluation of the sources of these features, the simple enumeration of features in modern and fossil samples is not phylogenetically interpretable.
