Hard lessons for soft selection.

The relative stringencies of hard and soft selection in protecting an allele in a geographically structured population is an important question in the maintenance of genetic variability. It is shown for the generalized two-deme case that hard selection is expected to be less stringent than soft selection roughly half of the time, in sharp contrast to the widely held view that hard selection is almost always more stringent than soft selection. Hard selection is usually expected to be less stringent than soft selection in the n-deme case when those demes in which the allele is favored are more fit than in those demes where the allele is at a disadvantage. This results from reduced migration into the favored demes under hard selection compared with soft selection, enhancing the protection of the allele. -Author