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

农业作为人类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的一个常见主题。这一生存转型的历史是复杂的，农业在世界某些地区是通过独立发明而出现的，而在另一些地区则是通过文化和/或人口的传播而出现的。因此，特别令人感兴趣的研究是，检验农业的生物后果是由独特的当地生态和历史来解释，还是由农业生存的共同因素来解释。这项研究由博士生大卫卡茨（加州大学戴维斯分校），在蒂莫西韦弗博士的监督下，提供了一个全球分析人类头骨形状，以测试两个假设，关于农业的共同后果的程度。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狩猎采集者的前辈更柔软，加工程度更高，因此从狩猎和采集到农业的转变在早期农业家的咀嚼结构中产生了常见的形状变化-主要与尺寸减小有关。其次，通过研究生长和发育过程中下颌骨的形状变化，研究人员测试狩猎采集者和农业家之间头骨形状的差异是否更有可能是由于自然选择或骨骼可塑性-骨骼的能力，特别是在发育过程中，改变形状以响应终身行为的需求。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，并揭示了人类进化史上技术，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免费提供，用作教育资源。

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.