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各样的人口统计学模型来解释人类群体差异的起源，但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将基因流动作为一种将占据热带和温带旧大陆部分地区的种群联合起来的方式，但它不能解释低遗传多样性，除非存在遗传多样性减少的瓶颈，或者通过连续的种群灭绝和在地方一级的重新定居来维持低遗传多样性。相比之下，现代人类起源的近代非洲起源模型可以解释在现代人类中观察到的低遗传多样性，但传统上该模型没有纳入人口结构。最近非洲起源模型的两种变体是分裂伊甸园模型和巴别塔模型，它们假设有效人口规模较小，但提出了人口结构产生的机制。在分裂伊甸园模型中，在上更新世，种群分裂先于种群的急剧扩张。巴别塔模型假设现代人类的人口结构是连续殖民瓶颈的结果。这三种模式都有潜力。然而，还没有人用现有的基因数据系统地测试过它们。本项目的目的是基于聚结理论，利用计算机模拟系统地测试人口统计模型。模拟结果将与由多个基因座组成的五个数据集进行比较，以确定每种人口统计学模型的参数值与观测数据相匹配。这些结果不仅将揭示哪些模型可以解释现代人类人口结构的起源，而且还将提供有关人类人口历史的信息。还将进行功效分析，以确定进一步完善人口统计模型还需要多少个基因座。

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.