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

直立行走是现代人类及其已灭绝的化石亲属（古人类）的定义特征，理解这种独特的运动形式的过渡是古人类学的中心问题。关于如何解释人类化石解剖学的功能意义，特别是关于从原始类人猿祖先保留下来的特征，存在相当大的分歧。一些研究者在重建古人类化石的行为时拒绝原始特征，只考虑衍生特征（如适应两足行走的特征），而另一些研究者则认为早期古人类既有树栖（攀爬）行为，也有两足行为，同时考虑了原始特征和衍生特征。肩膀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是攀爬的。这项研究将集中在肩部解剖，因为以前的工作已经强调了这一地区的运动相似性的基础上形态收敛，也因为几个新的化石保存肩膀填补了人类化石记录的关键空白。为了研究肩关节功能和解剖学之间的关系，本项目将采用1）一种实验方法，用野生型小鼠在两种条件下运动（垂直攀爬和水平奔跑）和考虑转基因，肌肉发达的小鼠，以检查不同运动方式和增加的肌肉组织的形态学效果，2）对灵长类动物进行比较分析，以检查肩部解剖结构的发育如何随生长过程中功能的变化而变化，（3）重新分析早期人类化石，根据实验和个体发育的结果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，以测试长期存在的关于解释早期人类化石解剖中原始特征的假设。除了博士生的培训，该项目将提供研究经验，本科生助理。这项研究具有超越体质人类学的更广泛的意义，因为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对骨骼健康和生物学的理解。此外，探索模型生物和灵长类动物形态发育中运动差异的影响，有可能改变我们对早期人类骨骼解剖进行功能解释的能力。通过研究人类肩部的原始特征是否与运动方式直接相关，该项目将揭示肩部的发育解剖学，并评估有关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.