DISSERTATION RESEARCH: Origins of Population Structure in Modern Humans

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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.