  Selective sweeps affect neutral genetic diversity through hitchhiking. While
this effect is limited to the local genomic region of the sweep in panmictic
populations, we find that in spatially-extended populations the combined
effects of many unlinked sweeps can affect patterns of ancestry (and therefore
neutral genetic diversity) across the whole genome. Even low rates of sweeps
can be enough to skew the spatial locations of ancestors such that neutral
mutations that occur in an individual living outside a small region in the
center of the range have virtually no chance of fixing in the population.
