Doctoral Dissertation Improvement: Coevolutionary Models and the Evolution of the Anthropoid Honing Complex

两足行走和缩小的犬齿这两个特征，将人类和我们的化石祖先与其他类人猿区分开来。在猴子和猿中，犬齿通常相对较大，并参与在咬合过程中使犬齿锋利的功能复合体；退化的人类犬科动物没有锐化。作为自然选择的结果，功能复合体内的性状预计会共同进化，在非人类类人猿灵长类动物中，该复合体的两个性状已被证明在物种之间是相关的，这表明该复合体的性状确实共同进化。在南方古猿属的早期人类中没有观察到类似的模式。因此，犬的珩磨复合体提供了一个难得的机会来研究一个功能复合体的共同进化和溶解。性状共同进化是不同过程的结果；例如，由于性状之间存在多效性或遗传连锁而产生的遗传相关性，性状可能会共同进化。在物种之间观察到的共同进化，在这种情况下是存在于物种内部的遗传关系的延伸。在没有遗传相关性的情况下，如果性状对选择作出独立的反应，也会发生共同进化，这被称为选择性共变。这个项目将确定珩磨复合体的特征是否共同进化，如果是，通过哪个过程。非人灵长类动物的遗传相关性需要古人类进化过程中复合体的遗传解耦；然而，基因相关性的缺失只需要改变选择压力的来源或强度来破坏复合体。通过研究物种内部和物种之间的共变模式，现存的非人类类人猿将复合体结合在一起的过程将被阐明，这将是古人类复合体分离的过程。这个项目将研究犬类退化的起源，这是人类进化的标志性特征之一。为了解决这个问题，灵长类动物牙列的形态将使用卡尺和基于照片的测量来量化。将对灵长类动物牙齿的广泛样本进行测量，以确保样本在系统发育，体型和社会结构方面是广泛的。

Two features, bipedality and reduced canine size, distinguish humans and our fossil ancestors from other apes. In monkeys and apes the canines are typically relatively large and participate in a functional complex that sharpens the canines during occlusion; the reduced hominin canine is not sharpened. Characters within functional complexes are expected to coevolve as a result of natural selection and, among nonhuman anthropoid primates, two characters of this complex have been shown to be correlated among species, suggesting that characters of the complex do coevolve. A similar pattern is not observed in early hominins of the genus Australopithecus. Thus, the canine honing complex provides a rare opportunity to investigate the coevolution and dissolution of a functional complex. Character coevolution occurs as the result of different processes; for example, characters may coevolve because of genetic correlations, created by pleiotropy or genetic linkage, which exist among characters. Coevolution, observed among species, is in this case an extension of the genetic relationship that exists within species. Coevolution occurs in the absence of genetic correlations as well if characters respond independently to selection, which is termed selective covariation. This project will determine if characters of the honing complex coevolve and, if so, by which process. Genetic correlations in nonhuman primates would require a genetic decoupling of the complex during hominin evolution; however, the absence of genetic correlations would only require a change in the source or strength of selective pressures to break up the complex. By examining patterns of covariation, both within and among species, the process(es) that holds the complex together in extant nonhuman anthropoids will be elucidated as will be the process that decoupled the complex in hominins. This project will investigate the origin of canine reduction, one of the hallmark features of hominin evolution. To address this topic, the morphology of the primate dentition will be quantified using caliper- and photographic-based measurements. Measurements will be taken on a broad sample of primate dentitions to ensure that the sample is broad phylogenetically, in body size, and in social structure.