Genetic Differences Within and Between Populations of the Major Human Subgroups

An extensive array of gene frequency data for 18 polymorphic genetic systems has been extracted from Mourant et al. (1976), representing more than 178 human tribes or nationalities from six major geographic groups, each divided into regional subgroups. Estimates have been derived of the proportion of genes at these loci that differ in two randomly chosen individuals within the same tribe or nationality, by comparison with two individuals chosen from different tribes within the same region, from different regions within the same geographic group, or from different geographic groups. The formulas necessary for calculation of these proportions for genotypic arrays which are not in Hardy-Weinberg equilibrium are given. This measure of genetic distance has the advantages of being readily interpreted by biologist and layman alike, being equally applicable to comparisons within and between populations, and being completely model free. The major component of genetic diversity as measured by this statistic falls within populations, accounting for 83.8% ± 2.8% of the total variation within the species. This conclusion is almost identical to that reached by Lewontin (1972) from an analysis based on the Shannon information measure. A study of the variation within each of the six geographic groups has demonstrated a significantly higher level of genetic variability in the Caucasian groups (Europe, Near East and Indian region) than in Africa, East Asia, America, and Oceania, amounting to a 22% increase at the between-region level. For each geographic group except Oceania, the component of variation between populations within a region has in addition been shown to be far greater than that due to differences between regions within a group. Finally, an analysis of all 15 pairwise comparisons among the geographic groups has shown the genetic divergence between major racial groups to be no more than a modest extension of the differences to be found between regions of the same group, accounting for only 51.6 ± 5.1% of the total between-population diversity.