Fig. 2.

Genetic processes in spatially expanding populations are effectively well mixed on time scales larger than the mixing time of the front. (A) The distribution of initial locations from which the ancestor position was tracked backward in time. Due to the stochastic nature of the front, the distribution of sampling locations has a finite width with respect to the average front profile shown in gray. (Inset) The final front from 30 independent runs used to generate histograms in A. For each run, two subpopulations were chosen, one close to the bulk (blue) and another close to the edge of the front (orange), and the locations of their ancestors were recorded at different times in the past (see SI Appendix, section 5 for exact sampling procedure). (B) Distribution of locations of ancestors of individuals shown in A from 100 generations in the past.