Comment On Genetic Structure Of Human Populations

Rosenberg et al. (1) described the genetic structure of 52 human populations from five continents studied at 377 short tandem repeat (STR) loci. This high-resolution study demonstrated that, using multilocus information only, the individuals of these populations could be subdivided into five stable genetic clusters that correspond to five major geographic regions: sub-Saharan Africa, the Americas, Oceania, EastAsia, and Eurasia (Europe, the Middle East, Central and South Asia). The study also partitioned the total genetic variance into components based upon differences between individuals within populations, between populations within regions, and between these five regions [table 1 in (1)]. Surprisingly, Rosenberg et al. (1) found very small differences between regions— only 4 to 5.7% of total diversity depending on regional sampling intensity, which is roughly half that of previous estimates inferred from molecular markers (2–4) (Table 1). Although the authors attributed that odd result to differences in sampling coverage among studies, we note that they did not base their analysis on the specific stepwise mutation model prevailing at STR loci, which is characterized by recurrent mutations. Ignoring the possibility that the same allelic type found in different individuals or populations may be derived from different evolutionary processes is known to lead to biased estimates of genetic structure (5–7)