Worn, flat occlusal surfaces and anterior edge-to-edge occlusion are ubiquitous among the dentitions of prehistoric humans. The concept of attritional occlusion was proposed in the 1950s as a hypothesis to explain these characteristics. The main aspects of this hypothesis are: 1) the dentitions of ancient populations in heavy-wear environments were continuously and dynamically changing owing to life-long attritional tooth reduction and compensatory tooth migration, 2) all contemporary humans inherit these compensatory mechanisms, and recent reduction in wear severity has resulted in failure to develop attritional occlusion, and 3) this failure leads to an increased frequency of various dental problems in modern societies. Because of the potential significance of this concept, we review and synthesize relevant works and discuss attritional occlusion in the light of current knowledge. Available evidence, on balance, supports the first and second points of the hypothesis. As noted by many workers, the human dentition is basically "designed" on the premise that extensive wear will occur, a conclusion that seems reasonable when one realizes that humans evolved in heavy-wear environments until relatively recently. Some dental problems in contemporary societies appear to reflect the disparity between the original design of our dentition and our present environment, in which extensive wear no longer occurs, but this possibility still needs further investigation.

Temporal changes, within-group variation, and phylogenetic positions of the Early Pleistocene Javanese hominids remain unclear. Recent debate focused on the age of the oldest Javanese hominids, but the argument so far includes little morphological basis for the fossils. To approach these questions, we analyzed a comprehensive dentognathic sample from Sangiran, which includes most of the existing hominid mandibles and teeth from the Early Pleistocene of Java. The sample was divided into chronologically younger and older groups. We examined morphological differences between these chronological groups, and investigated their affinities with other hominid groups from Africa and Eurasia. The results indicated that 1) there are remarkable morphological differences between the chronologically younger and older groups of Java, 2) the chronologically younger group is morphologically advanced, showing a similar degree of dentognathic reduction to that of Middle Pleistocene Chinese H. erectus, and 3) the chronologically older group exhibits some features that are equally primitive as or more primitive than early H. erectus of Africa. These findings suggest that the evolutionary history of early Javanese H. erectus was more dynamic than previously thought. Coupled with recent discoveries of the earliest form of H. erectus from Dmanisi, Georgia, the primitive aspects of the oldest Javanese hominid remains suggest that hominid groups prior to the grade of ca. 1.8-1.5 Ma African early H. erectus dispersed into eastern Eurasia during the earlier Early Pleistocene, although the age of the Javanese hominids themselves is yet to be resolved. Subsequent periods of the Early Pleistocene witnessed remarkable changes in the Javanese hominid record, which are ascribed either to significant in situ evolution or replacement of populations.

A Homo erectus calvarium [Sambungmacan 4 (Sm 4)] was recovered from Pleistocene sediments at Sambungmacan in central Java. Micro-computed tomography analysis shows a modern human-like cranial base flexion associated with a low platycephalic vault, implying that the evolution of human cranial globularity was independent of cranial base flexion. The overall morphology of Sm 4 is intermediate between that of earlier and later Javanese Homo erectus; apparent morphological specializations are more strongly expressed in the latter. This supports the hypothesis that later Pleistocene Javanese populations were substantially isolated and made minimal contributions to the ancestry of modern humans.

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