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

直立人是人类祖先的一个物种，其头骨厚度是现代人类平均厚度的四倍。这项研究将调查现代哺乳动物颅顶厚度(CVT)是如何发展的，以检验一些化石物种为什么有如此发达的穹隆骨骼的假说。颅顶的功能是保护大脑，并作为许多肌肉的连接点，但分子对其三层骨发育的影响尚不清楚。例如，运动对激素水平的影响是不确定的，这可能反过来影响颅骨发育。对比和实验研究将被用来检验关于CVT增加的假说。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(在70个非人类灵长类动物和10个古人类物种的样本中)与保存在头盖骨中的几个特征相关，如咀嚼肌肉的大小和脑壳的形状。一旦建立了相关性，第二阶段将建立因果关系。在这一阶段，将在一个模式生物(Mus Musculus)中研究人为增加的咀嚼张力和生长激素水平的变化对CVT的影响。该项目的智力优势包括扩大目前对骨骼发育生理过程的了解，更好地了解内分泌对颅顶发育的影响，以及测试假说在整个人类进化过程中骨骼粗壮程度的增加和减少。虽然研究的核心是对古人类学问题的调查，但所使用的方法隐含地涉及现代人、非人灵长类动物和非灵长类哺乳动物的健康和发育主题。因此，这项研究的更广泛影响包括对各种主题的广泛影响，从人类摄入外源激素、创伤性脑损伤治疗、运动和内分泌生理学，以及骨质疏松症。本博士论文的研究将有助于培养和发展一名女研究生。

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.