Laird Myra F, Vogel Erin R, Pontzer Herman
Department of Anthropology, New York University, New York, NY, USA; New York Consortium of Evolutionary Primatology, New York, NY, USA.
Department of Anthropology and the Center for Human Evolutionary Studies, Rutgers University, New Brunswick, NJ, USA.
J Hum Evol. 2016 Apr;93:1-11. doi: 10.1016/j.jhevol.2015.11.005. Epub 2016 Feb 6.
The reduction of occlusal dimensions in early Homo is often proposed to be a functional adaptation to diet. With their smaller occlusal surfaces, species of early Homo are suggested to have reduced food-processing abilities, particularly for foods with high material properties (e.g., increased toughness). Here, we employ chewing efficiency as a measure of masticatory performance to test the relationships between masticatory function and food properties. We predicted that humans are more efficient when processing foods of lower toughness and Young's modulus values, and that subjects with larger occlusal surfaces will be less efficient when processing foods with higher toughness and Young's modulus, as the greater area spreads out the overall bite force applied to food particles. Chewing efficiency was measured in 26 adults using high-speed motion capture and surface electromyography. The dentition of each subject was cast and the occlusal surface was quantified using dental topographic analysis. Toughness and displacement-limited index were negatively correlated with chewing efficiency, but Young's modulus was not. Increased occlusal two-dimensional area and surface area were positively correlated with chewing efficiency for all foods. Thus, larger occlusal surface areas were more efficient when processing foods of greater toughness. These results suggest that the reduction in occlusal area in early Homo was associated with a reduction in chewing efficiency, particularly for foods with greater toughness. Further, the larger occlusal surfaces of earlier hominins such as Australopithecus would have likely increased chewing efficiency and increased the probability of fracture when processing tough foods.
早期人类咬合尺寸的减小通常被认为是对饮食的一种功能适应。早期人类物种的咬合面较小，这表明它们的食物加工能力有所下降，尤其是对于具有高材料特性（如韧性增加）的食物。在这里，我们采用咀嚼效率作为咀嚼性能的衡量指标，以测试咀嚼功能与食物特性之间的关系。我们预测，人类在处理较低韧性和杨氏模量值的食物时效率更高，而咬合面较大的受试者在处理较高韧性和杨氏模量的食物时效率较低，因为更大的面积会分散施加在食物颗粒上的整体咬合力。使用高速动作捕捉和表面肌电图对26名成年人的咀嚼效率进行了测量。对每个受试者的牙列进行了铸造，并使用牙科地形分析对咬合面进行了量化。韧性和位移限制指数与咀嚼效率呈负相关，但杨氏模量并非如此。对于所有食物，咬合二维面积和表面积的增加与咀嚼效率呈正相关。因此，在处理韧性更大的食物时，较大的咬合面更有效率。这些结果表明，早期人类咬合面积的减小与咀嚼效率的降低有关，尤其是对于韧性更大的食物。此外，像南方古猿这样的早期古人类较大的咬合面可能会提高咀嚼效率，并增加处理韧性食物时骨折的可能性。
