Support from the relationship of genetic and geographic distance in human populations for a serial founder effect originating in Africa

doi:10.1073/pnas.0507611102

Support from the relationship of genetic and geographic distance in human populations for a serial founder effect originating in Africa

Departments of ^*Biological Sciences and ^‡Computer Science, Stanford University, Stanford, CA 94305; ^§Department of Anthropology, University of Illinois at Urbana-Champaign, 209 Davenport Hall, 607 South Matthews Avenue, Urbana, IL 61801; ^¶Department of Human Genetics, Bioinformatics Program and Life Sciences Institute, University of Michigan, 2017 Palmer Commons, 100 Washtenaw Avenue, Ann Arbor, MI 48109-2218; and ^∥Department of Genetics, School of Medicine, Stanford University, Stanford, CA 94305-5120

Contributed by L. Luca Cavalli-Sforza, September 2, 2005

Abstract

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.

Footnotes

↵ † To whom correspondence may be addressed. E-mail: sohini{at}stanford.edu or cavalli{at}stanford.edu.
Author contributions: S.R., M.W.F., and L.L.C.-S. designed research; S.R., O.D., and C.C.R. performed research; S.R., C.C.R., and N.A.R. analyzed data; and S.R., O.D., C.C.R., N.A.R., M.W.F., and L.L.C.-S. wrote the paper.
Abbreviation: HGDP-CEPH, Human Genome Diversity Project-Centre d'Etude du Polymorphisme Humain.