Doctoral Dissertation Research: The shape of hands and feet and the transition to upright walking

长期以来，研究人员一直假设，人类用两条腿直立行走(两足行走)的转变，是因为我们遥远的非灵长类祖先在用四条腿走路时对后肢的依赖增加。作为我们进化轨迹的关键部分，有人提出，一旦我们的祖先的手从行走中解脱出来，它们就能够用于其他目的，如使用工具、梳理和携带。之前关于人类祖先向直立行走转变的研究主要集中在非人类灵长类动物上。为了更好地理解用四条腿走路时对后肢的依赖与两足动物的出现之间的关系是否是人类进化所独有的，这项博士论文研究项目撒下了一个广泛的比较网，其中包括灵长类和食肉动物之间的比较。这个项目为本科生提供了接触STEM学科的想法和研究问题的机会，并接受了可移植的技术培训和经验。本项目检验了优势肢体的发育与非优势肢体的形态和功能多样化有关的假说。该项目通过三种方式测试这一假设和相关假设：(1)通过跟踪现存灵长类动物类群中手骨和脚骨的共同变异，测试是否对后肢的依赖增加允许前肢的多样化；(2)评估肢体优势对独立的哺乳动物支系(食肉目)功能多样性的影响，该支系被认为在早期进化过程中没有后肢优势的特征；以及(3)对灵长类和哺乳动物食肉动物的手骨和脚骨进行大规模比较，以跟踪两个目之间的形状变异率。了解这些群体手部和脚部骨骼的进化方式，有助于更好地理解数百万年前发生在灵长类动物身上、塑造现代人类进化轨迹的潜在过程。这项研究中使用的广阔视角是创新的，为更好地理解人类两足动物的进化提供了信息。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Researchers have long hypothesized that the transition to upright walking on two legs (bipedalism) in humans was facilitated in our distant, non-primate ancestors by an increased reliance on the hind limb while walking on four legs. As a pivotal part of our evolutionary trajectory, it is proposed that once our ancestors’ hands were freed from involvement in walking, they were able to be used for other purposes such as tool use, grooming, and carrying. Previous research on the transition to upright walking in human ancestors has largely focused on non-human primates. To better understand whether the relationship between reliance on hind limbs while walking on four legs and the emergence of bipedalism is unique to human evolution, this doctoral dissertation research project casts a broad comparative net and includes a comparison between primates and carnivores. This project offers opportunities for undergraduate students to gain exposure to STEM-discipline focused ideas and research questions, and to receive transferable technical training and experience.This project tests the hypothesis that the development of a dominant limb is associated with morphological and functional diversification of the non-dominant limb. This project tests this and related hypotheses in three ways: (1) testing if increased reliance on the hind limb allows for diversification of the forelimb by tracking co-variation of hand and foot bones across an expansive sample of extant primate taxa; (2) assessing the effect of limb dominance on functional diversity in an independent mammalian clade (Carnivora) that is thought not to have been characterized by hind limb dominance during its early evolution; and (3) conducting a large-scale comparison of primate and mammalian carnivoran hand and foot bones to track rates of shape variation across both orders. Understanding the ways that the bones of the hands and feet of these groups have evolved helps to elucidate a better understanding of the underlying processes that took place in primates millions of years ago shaping the trajectory of modern human evolution. The broad perspective used in this study is innovative and informative for better understanding of the evolution of bipedalism in humans.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.