Doctoral Dissertation Improvement: Shoulder Functional Anatomy and Development-Implications for Interpreting Early Hominin Locomotion

直立行走是现代人及其已灭绝的化石近亲(原始人)的特征，理解向这种独特的运动形式的转变是古人类学的一个中心问题。关于如何解释古人类化石解剖学的功能意义，特别是关于原始类人猿祖先保留的特征，人们存在相当大的分歧。一些研究人员在从化石古人类重建行为时拒绝原始特征，只考虑派生特征(如适应两足行走的特征)，而另一些研究人员则同时考虑原始特征和派生特征，断言早期古人类同时实践树栖(攀登)和两足动物行为。肩部的几个特征被认为是原始的，因此可能表明南方古猿属的成员有攀爬的迹象。这项研究将重点放在肩部解剖学上，因为以前的工作强调了该地区基于运动相似性的形态趋同，也因为几个保存肩部的新化石填补了原始人化石记录中的关键空白。为了研究肩功能和解剖学之间的关系，这个项目将使用1)在两种条件下(垂直攀登和水平跑步)锻炼的野生型小鼠的实验方法，并考虑到转基因的高肌肉小鼠来研究不同的运动方式和增加的肌肉对形态的影响，2)对灵长类动物的比较分析来研究肩部解剖的发育如何随着生长过程中功能的变化而变化，以及3)根据实验和个体发育的结果重新分析早期原始人的化石，以提出关于原始特征的功能意义的假说。这些方法将评估运动活动、肌肉解剖和肩部骨骼发育之间的关系，以检验长期存在的关于解释早期古人类化石解剖学中原始特征的假设。除了博士生的培养，该项目还将为一名本科生助理提供研究经验。这项研究除了身体人类学之外，还有更广泛的意义，因为通过实验测试不同运动方式对小鼠肌肉发育和骨骼形状的影响，将有助于我们了解骨骼健康和生物学。此外，探索模式生物的运动差异和灵长类动物的形态发育的影响，有可能改变我们对早期人类骨骼解剖学的功能解释的能力。通过研究人类肩膀上的原始特征是否与运动方式直接相关，这个项目将阐明肩膀的发育解剖学，并将评估关于人类两足动物起源和进化的不同理论。

Upright walking is the defining feature of modern humans and their extinct fossil relatives (hominins) and understanding the transition to this unique form of locomotion is a central problem in paleoanthropology. Considerable disagreement surrounds how the functional significance of hominin fossil anatomy is interpreted, especially with regard to characteristics retained from a primitive, apelike ancestor. Some researchers reject primitive traits when reconstructing behavior from fossil hominins, considering only derived features (such as those adapted for bipedalism), while others consider both primitive and derived traits in asserting that early hominins practiced both arboreal (climbing) and bipedal behaviors. Several characteristics of the shoulder have been cited as primitive and therefore potentially indicative of climbing in members of the genus Australopithecus. This study will focus on shoulder anatomy because previous work has highlighted morphological convergence of this region based on locomotor similarities and also because several new fossils preserving the shoulder fill key gaps in the hominin fossil record. To investigate the relationship between shoulder function and anatomy, this project will use 1) an experimental approach with wild-type mice exercised under two conditions (vertical climbing and horizontal running) and a consideration of transgenic, hypermuscular mice to examine the morphological effects of different locomotor styles and increased musculature, 2) a comparative analysis of primates to examine how the development of shoulder anatomy varies with changes in function during growth, and 3) a reanalysis of early hominin fossils to develop hypotheses about the functional significance of primitive features in light of the experimental and ontogenetic results. These approaches will evaluate the relationship between locomotor activity, muscular anatomy, and shoulder skeletal development to test long-standing hypotheses about interpreting primitive features in early hominin fossil anatomy. In addition to the doctoral student's training, this project will provide research experience to an undergraduate student assistant. This research has broader implications beyond physical anthropology in that experimentally testing the influence of different styles of locomotion on muscle development and bone shape in mice will contribute to our understanding of skeletal health and biology. Moreover, exploring the influence of locomotor differences in a model organism and morphological development in primates has the potential to transform our ability to make functional interpretations of early hominin skeletal anatomy. By examining whether or not primitive features in hominin shoulders are directly related to locomotor style, this project will shed light on developmental anatomy of the shoulder and will evaluate different theories about the origin and evolution of human bipedalism.