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，人类向两条腿直立行走（两足行走）的过渡，在我们遥远的非灵长类祖先那里得到了促进，因为他们在四条腿行走时越来越依赖后肢。作为人类进化轨迹的关键部分，有人提出，一旦我们祖先的手从行走中解放出来，它们就能用于其他目的，比如使用工具、梳理毛发和搬运东西。先前关于人类祖先向直立行走过渡的研究主要集中在非人类灵长类动物身上。为了更好地理解依靠后肢行走和两足动物的出现之间的关系是否是人类进化所独有的，本博士论文研究项目撒下了广泛的比较网，包括灵长类动物和食肉动物之间的比较。该项目为本科生提供了接触stem学科思想和研究问题的机会，并获得可转移的技术培训和经验。该项目验证了一个假设，即优势肢的发育与非优势肢的形态和功能多样化有关。该项目从三个方面验证了这一假设和相关假设：(1)通过在现存灵长类类群的广泛样本中追踪手和脚骨骼的共同变异，来测试对后肢的依赖程度的增加是否允许前肢的多样化；(2)在独立的哺乳动物分支（食肉目）中评估肢体优势对其功能多样性的影响，该分支被认为在其早期进化中不具有后肢优势的特征；(3)对灵长类动物和哺乳动物食肉动物的手脚骨骼进行大规模比较，追踪两目动物的形状变化率。了解这些群体手脚骨骼的进化方式，有助于更好地理解数百万年前灵长类动物塑造现代人类进化轨迹的潜在过程。本研究采用的广阔视角为更好地理解人类两足动物的进化提供了创新和信息。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.