1Department of Anthropology, University at Albany, 2Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, 3Department of Anthropology, University of Minnesota, 4Integrated Medical Science Department, Florida Atlantic University, 5Forensic Anthropology Center and Department of Anthropology, Texas State University
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Recent analyses of body mass and encephalization quotient (EQ) find that EQ is similar in early Homo erectus and australopiths, and either remains fairly low or increases greatly throughout the Middle Pleistocene. Differences in sample composition and methods make choosing between these conflicting results problematic. In this study, we assembled a large dataset of hominin cranial capacities and body masses in order to assess the tempo and mode of EQ change through time. We calculated EQ for specimens with associated crania and postcrania (EQ1); and for species, using associated (EQ2) and unassociated (EQ3) crania and postcrania, and crania only (EQ4). This study design allowed us to test the effect of different methods and sample composition on EQ. In addition, we used hypothetical growth curves to increase body mass values for key juvenile specimens from Malapa, Dmanisi and West Turkana. New EQ estimates for Dmanisi D2700 and KNM-WT 15000 allow us to reject the hypothesis that EQ does not differ between australopiths and early H. erectus. Systematic differences between EQ estimates calculated in different ways suggest that EQ in Middle Pleistocene Homo has been both under- and overestimated in the recent literature. EQ increases in a step-like fashion in australopiths, early H. erectus, archaic Homo, and Neanderthals and H. sapiens. With the possible exception of H. erectus, EQ seems to remain static within species over long time periods. These results underscore the mosaic nature of brain and body evolution in Pleistocene Homo.