Equilibrium models of isolation by distance predict an increase in genetic differentiation with geographic distance. Here we find a linear relationship between genetic and geographic distance in a worldwide sample of human populations, with major deviations from the fitted line explicable by admixture or extreme isolation. A close relationship is shown to exist between the correlation of geographic distance and genetic differentiation (as measured by F(ST)) and the geographic pattern of heterozygosity across populations. Considering a worldwide set of geographic locations as possible sources of the human expansion, we find that heterozygosities in the globally distributed populations of the data set are best explained by an expansion originating in Africa and that no geographic origin outside of Africa accounts as well for the observed patterns of genetic diversity. Although the relationship between F(ST) and geographic distance has been interpreted in the past as the result of an equilibrium model of drift and dispersal, simulation shows that the geographic pattern of heterozygosities in this data set is consistent with a model of a serial founder effect starting at a single origin. Given this serial-founder scenario, the relationship between genetic and geographic distance allows us to derive bounds for the effects of drift and natural selection on human genetic variation.
Ramachandran S 1,
Deshpande O ,
Roseman CC ,
Rosenberg NA ,
Feldman MW ,
Cavalli-Sforza LL
Affiliations
1 Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA. sohini@stanford.edu
This work was supported by:
NIGMS NIH HHS, United States GrantID: GM28428
NIGMS NIH HHS, United States GrantID: GM28106
NIGMS NIH HHS, United States GrantID: P01 GM028428
This paper reports a striking linear relationship between genetic and geographic distance, using ~800 microsatellites typed in a globally distributed sample of humans.
Diversity levels are best explained by an African origin, in accordance with the findings of Prugnolle et al. (Curr Biol 2005, 15:R159-60 [PMID:15753023]).
Using simulations, the authors show that their results are consistent with a model of spatial expansion and successive bottlenecks, starting at a single origin.
Classifications
New Finding
Cite this Recommendation:
Przeworski M: H1 Connect Recommendation of [Ramachandran S et al., Proc Natl Acad Sci USA 2005 102(44:15942-15947)]. In H1 Connect, 07 Dec 2005;
