Doctoral Dissertation Improvement: Comparative and Experimental Investigations of Cranial Robusticity in Homo Erectus

直立人是人类的祖先，其头骨比现代人类平均头骨厚四倍。这项研究将调查现代哺乳动物的颅穹窿厚度（CVT）是如何发展的，以测试为什么一些化石物种有如此发达的穹窿骨的假设。颅穹窿的功能是保护大脑，并作为许多肌肉的附着部位，但对其三层骨发育的分子影响尚不清楚。例如，运动对激素水平的影响可能反过来影响颅骨发育，这是不确定的，比较和实验研究将被用来测试CVT增加的假设。以前的研究将CVT的测量限制在总厚度上;本研究测量了骨的所有三层。这些测量将与保存在头盖骨中的几个特征（如咀嚼肌的大小和脑的形状）相关联（在70个非人类灵长类动物和10个人类物种的样本中）。一旦建立了相关性，第二阶段将建立因果关系。在这一阶段，将在模型生物中研究人工增加咀嚼张力和生长激素水平变化对CVT的影响（小家鼠）。该项目的智力价值包括扩大目前对骨骼发育生理过程的认识，更好地了解内分泌对颅穹窿发育的影响，以及测试在整个人类进化过程中骨骼健壮性增加和减少的假设。虽然这项研究的核心是对一个古人类学问题的调查，但所使用的方法与现代人类、非人类灵长类动物、和非灵长类哺乳动物的健康和发育。因此，该研究的更广泛影响包括对人类消耗外源性激素、创伤性脑损伤治疗、运动和内分泌生理学以及骨质疏松症等各种主题的广泛影响。 本博士论文的研究将有助于女研究生的培养和发展。

Homo erectus, a species of human ancestor, has skull bones four times thicker than themodern human average. This research will investigate how cranial vault thickness (CVT) develops in modern mammals in order to test hypotheses for why some fossil species had such well developed vault bones. The function of the cranial vault is to protect the brain and to serve as an attachment site for many muscles, but molecular influences on the development of its three layers of bone are not well understood. For example, the effect of exercise on hormone levels, which may in turn influence cranial bone development, is uncertain.Both comparative and experimental studies will be used to test hypotheses for increased CVT. Previous studies have limited their measurement of CVT to total thickness; this study measures all three layers of the bone. These measures will be correlated (in a sample of 70 nonhuman primate and 10 hominin species) with several characters preserved in the cranium such as the size of chewing muscles and brain case shape. Once correlations are established, a second phase will establish causative relationships. For this phase, the effects of artificially increased masticatory strain and variation in growth hormone levels on CVT will be investigated in a model organism (Mus musculus).Intellectual merits of this project include expanding current knowledge of physiological processes in osteological development, providing a better understanding of endocrinological influences on cranial vault development, and testing hypotheses for increased and decreased skeletal robusticity throughout human evolution.While the heart of the study is an investigation of a paleoanthropological question, the methods used implicitly relate to topics of modern human, non-human primate, and non-primate mammalian health and development. Thus, the broader impacts of the study include widereaching implications for subjects as varied as human consumption of exogenous hormones, traumatic brain injury treatment, exercise and endocrine physiology, and osteoporosis. This doctoral dissertation research will contribute to the training and development of a female graduate student.