Models of human evolutionary history. In each model, there are K populations, and time runs from the present to the past, with T representing the time of the first population divergence. Widths of regions indicate population sizes. In the serial founder model, a subset of individuals from a source population in Africa (population 1) migrates out and founds a new colony (population 2) approximately 50 thousand years ago. Population 2 experiences a bottleneck, or a period of time with small population size, and then expands to a larger size. Then a subset of individuals from population 2 migrates out and founds population 3, which experiences a bottleneck and then expands to a larger size. This process iterates until all K populations have been founded. In the archaic persistence model, archaic Homo erectus populations populate the world approximately one million years ago. These distinct groups of H. erectus populations exchange genes with neighboring populations (indicated by thin bidirectional arrows). Then, approximately 50 thousand years ago, a wave of individuals (indicated by thick right-pointing arrow) migrates out of a source population in Africa (population 1) and mixes with a neighboring population (population 2). Subsequently, a wave of individuals migrates out of population 2 and mixes with population 3. This wave continues until population K receives a wave of individuals. In the instantaneous divergence model, modern humans populate the world approximately 50 thousand years ago. Populations decrease in size with increasing distance from the source population in Africa (population 1), ensuring that populations farther from the source experience greater genetic drift. Figure modified from DeGiorgio et al. (2009).