Bottlenecks, soft selection, and Phase III of Wright's ?Shifting Balance? theory

Abstract

An argument is presented, using the spread of the African honeybee through the American tropics, Mexico, and into the southern United States, that the geographic spread of a novel, highly successful gene combination does not necessarily occur as commonly viewed under Phase 3 of Wright's shifting-balance theory. Rather, migrants from the deme possessing the new genetic system may populate sites previously left vacant and subsequently, when their numbers have swelled, overwhelm the populations in previously occupied sites. The outcome, the argument continues, gives the (false) appearance of the species having gone through a bottleneck.