Doctoral Dissertation Improvement: Universality and biological mechanisms of subsistence-driven masticatory reduction

农业作为人们获取食物资源的主要手段的出现是人类进化史上最重要的经济转变之一，其生物学后果是进化人类学中经常讨论的主题。这种生存过渡的历史是复杂的，世界上一些地方的农业是由独立的发明产生的，而在其他地方则是由文化和/或人的传播产生的。因此，测试农业的生物后果是由独特的当地生态和历史来更好地解释，还是由农业生存的共同因素来更好地解释的研究，无论在何处采用，都是特别有趣的。在Timothy Weaver博士的指导下，加州大学戴维斯分校的博士生David Katz进行了这项研究，提供了对人类头骨形状的全球分析，以检验关于农业共同后果程度的两个假设。首先，研究人员验证了这样一种说法，即由于早期农民的饮食普遍比他们的狩猎采集祖先更柔软，加工程度更高，从狩猎采集到农业的转变产生了共同的形状变化——主要与尺寸缩小有关——早期农业学家的咀嚼结构。其次，通过研究下颌骨在生长和发育过程中的形状变化，研究人员测试了狩猎采集者和农人之间头骨形状的差异更可能是由于自然选择还是骨骼可塑性——骨骼的能力，特别是在发育过程中，根据一生的行为需求而改变形状。这项研究的结果将直接告知公众对农业转型的生物学后果的理解，也揭示了在人类进化史过程中技术、饮食和解剖学之间的长期关系。此外，这项研究的数据将在互联网上作为教育资源免费提供。

The emergence of agriculture as the predominant means by which people obtain food resources is one of the most significant economic shifts in human evolutionary history, and its biological consequences are a frequent subject in evolutionary anthropology. The history of this subsistence transition is complex, with agriculture emerging by independent invention in some parts of the world, and by the spread of cultures and/or people in others. As a result, studies that test whether the biological consequences of agriculture are better explained by unique local ecologies and histories, or instead by factors common to agricultural subsistence, wherever adopted, are of particular interest. This study by doctoral student David Katz (University of California, Davis), under the supervision of Dr. Timothy Weaver, provides a global analysis of human skull shape in order to test two hypotheses regarding the extent of agriculture's common consequences. First, the investigators test the claim that because the diets of early farmers were universally softer and more heavily processed than those of their hunter-gatherer predecessors, the shift from hunting and gathering to agriculture produced common shape changes - mostly related to reductions in size - in the chewing architecture of early agriculturalists. Second, by studying shape changes in the mandible during growth and development, the investigators test whether differences in skull shape between hunter-gatherers and agriculturalists are more likely due to natural selection or skeletal plasticity - bone's ability, particularly during development, to change shape in response to the demands of lifetime behaviors. The results of the study will directly inform public understanding of the biological consequences of the agricultural transition, and also shed light on the much longer-term relationship between technology, diet, and anatomy over the course of human evolutionary history. In addition, data from this study will be freely available on the internet for use as an educational resource.