Founder Effect

The founder effect is the reduction in genetic diversity that occurs when a new population is established by a small number of individuals from a larger source population, so that the new population's entire gene pool is limited to whatever genetic variation happened to be carried by that small founding group. Population geneticist Ernst Mayr formally named and described the effect in his 1942 book Systematics and the Origin of Species, though the underlying statistical logic connects closely to the broader mathematical theory of genetic drift developed slightly earlier by Sewall Wright. Because a small founding group by chance carries only a limited, non-representative sample of the source population's overall genetic variation, certain gene variants can end up substantially over-represented or entirely absent in the new population compared to the population it came from, independent of whether those variants offer any survival advantage. The founder effect is commonly cited to explain elevated rates of certain otherwise rare inherited genetic conditions found in some island populations and other historically isolated human communities descended from a small number of original settlers.