Genealogical trees derived from simulated sequences at varying population sizes. In each case, sequence evolution was simulated using a neutral Wright-Fisher model, and approximately 200 samples were taken over the course of 10,000 generations (sampled at a Poisson rate of 0.02 per generation). In each frame, the x-axis is shown as intervals of 5000 generations, so that the temporal scale increases with N. As population size N increases, the time it takes for two lineages to coalesce increases proportionally, so that larger populations show a deeper most recent common ancestor. Population dynamics result in rapid coalescence when there are many contemporaneous lineages and slower coalescence when there are few, a detail especially apparent at larger population sizes.
Bedford et al. BMC Evolutionary Biology 2011 11:220 doi:10.1186/1471-2148-11-220