Department of Human Evolutionary Biology, Harvard University
March 27, 2015 , Archview Ballroom
Reduced dental and jaw size in the genus Homo suggests a shift to foods that require less masticatory effort to consume. Here we test the hypothesis that the adoption of early food processing techniques such as roasting, and slicing or pounding with a stone tool reduce chewing forces, and thus altered selection pressures on masticatory adaptations in Homo. Additionally, we test the degree to which the material properties of raw and processed foods can be used to predict chewing performance. 14 subjects (7F/7M) were fed size-standardized samples of three USOs (carrots, yams, beets) that were raw, sliced, pounded with a stone tool, or roasted. As the subjects chewed, surface EMG data were collected from the masseter muscle and then used to estimate forces. While slicing had no effect (p>0.05; Wilcoxon signed rank test), both pounding, and to a greater extent roasting, reduced the average masticatory force used to consume the foods (~11% and 20% reduction respectively; p<0.01; Wilcoxon signed rank test). These masticatory changes were strongly associated with the toughness and stiffness of the USOs (r2=0.50 and 0.95, respectively). These results suggest that stone-assisted food processing may have allowed for early reductions of dental and jaw size within Homo, with further reductions being allowed by the adoption of cooking. Additionally, the strong relationship between material property and masticatory changes highlight the utility of measuring food properties to model hominin diets.
This study was funded by the National Science Foundation (DDIG # 0925688).