Doctoral Dissertation Improvement Grant: Three-dimensional morphometrics and kinematics of the anthropoid wrist and the evolution of knuckle-walking

重建人类两足动物进化之前的运动形式是古人类学的一个关键目标。指关节行走(一种半陆地运动形式，重量在中手指骨的背部承担)是一个合理的候选方案，因为它是非洲猿类的练习，非洲猿类是人类现存最接近的亲戚。然而，支持人类进化血统的指节行走祖先的论点依赖于对黑猩猩、大猩猩和早期人种(比黑猩猩更接近人类的化石物种)某些解剖特征的准确解释，以适应指节行走。这项拟议中的项目将由Caley Orr在亚利桑那州立大学的Mary Marzke博士和Mark Spencer博士的指导下进行，将使用比较方法来测试这些特征适应指节行走的假说。这个跨学科的项目将整合人类学、计算机科学和生物工程领域的创新技术。类人灵长类动物的手腕关节形状将通过激光扫描得出的三维数字模型进行量化。此外，将使用灵长类身体的连续计算机断层扫描来分析腕骨的三维运动，以测试关于不同物种之间关节形状差异的功能后果的具体假设。指节行走的非洲类人猿将与数字级别的狒狒进行比较，后者也使用“垂直手掌”的运动形式，在移动过程中，当将手掌放在底物上时，手掌垂直握住。这些物种将与几种能够使用手腕伸展手掌姿势的灵长类动物形成对比，在这种姿势下，手掌通常会放在底物上。非洲类人猿和狒狒独有的关节机制将被支持作为保持垂直手部姿势的适应，这些特征可以用来推断化石物种的这种手部姿势。这项研究的科学价值在于其新颖的综合和定量的方法有助于识别适应垂直手部姿势的特征。这些特征在早期人类中的出现支持了指关节行走祖先的假说。如果要证明人类进化的一个指节行走阶段，它将限制对两足动物起源的适应性解释，仅限于那些与半陆地祖先一致的解释。该项目的广泛影响是它对各级学生的教育价值及其临床和学术应用。首先，3D激光扫描模型和开发的分析软件将通过在线数据库共享，以促进进一步研究。这些数据和软件将对人类学、古生物学、解剖学和整形外科等生物医学领域的研究人员和教育工作者有用。其次，该项目将为帮助数据处理和分析的本科生提供研究经验。最后，该项目将为Caley Orr提供人类学、解剖学、生物工程和计算机可视化技术方面的跨学科培训机会，这将促进他未来的研究并加强他在大学层面的教学。

Reconstructing the form of locomotion that preceded the evolution of human bipedality is a key goal of paleoanthropology. Knuckle-walking (a semi-terrestrial form of locomotion in which weight is borne on the backs of the middle hand phalanges) is a plausible candidate because it is practiced by the African apes, which are humans' closest living relatives. However, arguments for a knuckle-walking ancestor for the human evolutionary lineage rely on accurate interpretations of certain anatomical features in chimpanzees, gorillas, and early hominins (fossil species more closely related to humans than chimpanzees) as adaptations to knuckle-walking. The proposed project, to be conducted by Caley Orr under the direction of Dr. Mary Marzke and Dr. Mark Spencer at Arizona State University, will test the hypothesis of adaptation to knuckle-walking for such features using the comparative method. The interdisciplinary project will proceed by integrating innovative techniques from the fields of anthropology, computer science, and bioengineering. Wrist joint shape in anthropoid primates will be quantified from laser scan-derived three-dimensional digital models. In addition, the three-dimensional movements of the wrist bones will be analyzed using serial computed tomography scanning of primate cadavers to test specific hypotheses about the functional consequences of differences in joint shape between species. The knuckle-walking African apes will be compared with the digitigrade baboons, which also use a "vertical manus" form of locomotion, during which the palm is held vertically when placed onto the substrate. These species will be contrasted with several primates capable of using extended-wrist palmigrade hand positions during which the palm is typically placed onto the substrate. Joint mechanisms shared exclusively by the African apes and baboons will be supported as adaptations to maintaining vertical manus postures, and these features can be used to infer such hand postures in fossil species.The scientific merit of this study is that its novel integrative and quantitative approach facilitates the identification of features adapted to vertical manus postures. The appearance of these features in early hominins would support the hypothesis of a knuckle-walking ancestor. If a knuckle-walking phase in human evolution were to be demonstrated, it would limit adaptive explanations for the origins of bipedality to those consistent with a semi-terrestrial ancestor.Broader impacts of the project are its value for education of students at all levels and its clinical as well as academic applications. First, the 3D laser-scan models and developed analytical software will be shared via an online database to facilitate further research. The data and software will be useful for researchers and educators in anthropology, paleontology, anatomy, and biomedical fields such as orthopedics. Second, the project will provide a research experience for an undergraduate student who will assist with data processing and analysis. Finally, the project will provide an interdisciplinary training opportunity for Caley Orr in techniques from anthropology, anatomy, bioengineering, and computer visualization that will facilitate his future research and enhance his teaching at the university level.