Our picture of global genetic variation becomes ever more clear. In this study -the supplementary material of which are online- the researchers studied 240K loci in 554 individuals from 27 populations.
From the paper:
The African, East/Southeast Asian, European, and Indian individuals are correctly assigned to their self-identified continental groups without exception.
Some individuals show evidence of membership in multiple groups. South Indian upper- and lower-caste populations have ∼30% and 10% membership in the inferred European group, respectively. South Indian tribal Irula have a relatively high probability of membership in the inferred Indian cluster. Southeast Asians (Iban, Cambodians, and Vietnamese) have ∼10% membership in the inferred Indian cluster, and the African Hema cluster shares ∼15% membership with the inferred European cluster.
The Hema are Nilotic-speaking pastoralists from the Congo. The Alur, from the same region were also studied.
Social stratification based on "European" (more properly extra-Indian Cauasoid) ancestry in South Indian populations is not surprising; see my post on the Origin of Hindu Brahmins. Differential -based on caste- admixture with an exogenous element is not really compatible with an indigenous creation of the caste system, and is more in accord with the traditional theory of an exogenous origination of the upper caste populations.
The study also includes populations from the Caucasus (Stalskoe and Urkarah) from Daghestan, which group with HGDP Adygei (see Figure S3C) and are clearly (FRAPPE analysis in Figure 4, reproduced top left) transitional (as mentioned in my previous post) between European and Indian Caucasoids, although quite clearly more on the European side.
Genome Research doi:10.1101/gr.085589.108
Fine-scaled human genetic structure revealed by SNP microarrays
Jinchuan Xing et al.
We report an analysis of more than 240,000 loci genotyped using the Affymetrix SNP microarray in 554 individuals from 27 worldwide populations in Africa, Asia, and Europe. To provide a more extensive and complete sampling of human genetic variation, we have included caste and tribal samples from two states in South India, Daghestanis from eastern Europe, and the Iban from Malaysia. Consistent with observations made by Charles Darwin, our results highlight shared variation among human populations and demonstrate that much genetic variation is geographically continuous. At the same time, principal components analyses reveal discernible genetic differentiation among almost all identified populations in our sample, and in most cases, individuals can be clearly assigned to defined populations on the basis of SNP genotypes. All individuals are accurately classified into continental groups using a model-based clustering algorithm, but between closely related populations, genetic and self-classifications conflict for some individuals. The 250K data permitted high-level resolution of genetic variation among Indian caste and tribal populations and between highland and lowland Daghestani populations. In particular, upper-caste individuals from Tamil Nadu and Andhra Pradesh form one defined group, lower-caste individuals from these two states form another, and the tribal Irula samples form a third. Our results emphasize the correlation of genetic and geographic distances and highlight other elements, including social factors that have contributed to population structure.