DISSERTATION RESEARCH: Origins of Population Structure in Modern Humans

与其他物种相比，人类的遗传多样性水平较低，种群之间的差异也很小。研究人员提出了各种人口统计学模型来解释人类群体差异的起源，但还没有人对它们进行系统的测试。例如，现代人类起源的多区域模型明确地援引基因流作为一种方式来联合占据热带和温带东半球部分地区的种群，但它不能解释低遗传多样性，除非存在一个瓶颈，即遗传多样性减少或低遗传多样性是通过在地方一级连续的种群灭绝和重新殖民来维持的。相比之下，最近的现代人类起源的非洲起源模型可以解释在现代人中观察到的低遗传多样性，但传统上该模型没有纳入种群结构。最近的非洲起源模型的两个变种是分裂的伊甸园模型和巴贝尔模型，它们假定有效人口规模较小，但提出了产生人口结构的机制。在分裂的伊甸园模型中，人口分裂先于上更新世人口的戏剧性扩张。巴别尔模型假设，现代人的人口结构是连续的殖民瓶颈的结果。这三种模式都有潜力。然而，还没有人用现有的基因数据对它们进行系统的测试。本项目的目的是使用基于合并理论的计算机模拟来系统地测试人口模型。模拟结果将与由多个位置组成的五个数据集进行比较，以确定每种类型的人口模型的哪些参数值符合观测数据。这些结果不仅将揭示哪些模型解释了现代人的人口结构起源，还将提供关于人类人口历史的信息。还将进行能力分析，以确定还需要多少个基因座才能进一步完善人口模型。

Compared to other species, humans have low levels of genetic diversity and a small amount of differences among populations. Investigators have proposed a variety of demographic models to explain the origins of differences among human populations but no one has systematically tested them. For example, the Multiregional model of modern human origins explicitly invokes gene flow as a way to unite populations occupying parts of the tropical and temperate Old World, but it cannot account for the low genetic diversity unless there was a bottleneck that reduced genetic diversity or low genetic diversity was maintained by successive population extinctions and recolonizations at the local level. In contrast, the Recent African Origin model of modern human origins can account for the low genetic genetic diversity observed in modern humans, but traditionally the model has not incorporated population structure. Two variations of the Recent African Origin model that assume a small effective population size but propose mechanisms by which population structure can arise are the Divided Eden model and the Babel model. In the Divided Eden model, population division preceded a dramatic population expansion in the Upper Pleistocene. The Babel model hypothesizes that population structure in modern humans is the result of successive colonization bottlenecks. All three of these models have potential. However, no one has systematically tested them with available genetic data. The purpose of this project is to test systematically demographic models using computer simulations based on coalescence theory. Simulation results will be compared to five datasets consisting of multiple loci to determine which parameter values for each type of demographic model fit the observed data. These results will not only reveal which models explain the origins of population structure in modern humans but also provide information on human demographic history. A power analysis will also be performed to determine how many more loci will be necessary to further refine the demographic models.