New large-scale genome analysis gives insight on details of our way "out of africa"

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Li et al. (2008) conducted a large-scale genome-analysis of 938 humans from 51 populations. He found a clear-cut relationship between haplotype heterozygosity and geography, which not only supports the "out of africa"-hypothesis of a single origin in sub-Saharan Africa. The correlations also indicate our genetical proximity and therefore can show us details on the history of our way out of africa (see Figure 1).


Figure 1: Individual Ancestry Diagram. Each individual isrepresented by a vertical line partitioned into colored segments whose lengths correspond to his/her ancestry coefficients in up to seven inferred ancestral groups.


In detail the findings show that the mean heterozygosity across autosomal haplotypes is negatively correlated with distance from Addis Ababa, Ethiopia, with a correlation coefficient r of –0.91 and a slope of –1.1 × 10−5 per km (see Figure 1). This trend supports a serial founder effect, a scenario in which population expansion involves successive migration of a small fraction of individuals out of the previous location, starting from a single origin in sub-Saharan Africa.


Figure 2: Analysis of molecular variance and correlation between haplotype heterozygosity
and geographic distance.


Source:
Li et al. 2008. Worldwide Human Relationships Inferred from Genome-Wide Patterns of Variation. Science. Vol. 319, pp. 1100-1104