The power of Clusters Galore: Iranians and Arabs

The full power of Clusters Galore depends on its ability to infer clusters of arbitrary size, shape, and orientation in a high-dimensional space. It achieves this by using MCLUST over an MDS or PCA representation of dense genomic data.

Nonetheless, we can still see get a sense of it even in a simple 2D representation as the following:

This was produced by applying MDS on 240 individuals (from Behar et al. 2010, HGDP, Xing et al. 2010, and the Dodecad Project).

One can see that the Behar et al. and Dodecad Iranians form a small cluster on the right, together with the Xing et al. Kurds and the single Dodecad Kurd. Arabs are quite more variable: Druze extend to the bottom of the figure, Bedouin form two groups: one similar to other Arabs, the other extending to the left of the figure. There are also a few Arabs stretching to the top.

The variability of the Arabs can be attributed to reproductive isolation, inbreeding, and variable amounts of African admixture. Let's apply MCLUST over these 240 2D points:

The above visual representation shows the centroids and shapes of the 5 inferred clusters. Here are the numbers of individuals from each population assigned to each cluster:

Notice cluster #5: it consists of all Kurds, most Behar et al. Iranians and all Dodecad ones, and the single Dodecad Kurd, plus a Lebanese and a Syrian. It is overall 96% Iranic in composition. It is quite tempting to think that the two Syrian and Lebanese members have some links to Iranian peoples either due to Kurdish ancestry or the Shia form of Islam.

The more variable Arabs are split into multiple clusters: the main, tight, cluster #3 which includes most of the Levantine Arabs, but also some Saudis and Yemenese, the extremely variable African-admixed cluster #1 dominated by some Yemenese but including a few others, the "Arabian" Saudi-Bedouin dominated cluster #2, and the Druze-specific cluster #4.

It seems that just as the distinction between Celto-Germans and Balto-Slavs is not only cultural, but also genetic, so is the distinction between Iranian and Arab. In the case of the Arabs though, religious distinctions (e.g., the Druze), variable African admixture, and quite possibly Arabization of Levantine populations has resulted in a non-homogeneous array of genetic clusters.

PS: Iranic groups are also not homogeneous if one includes some of those from South Asia, as evidenced by this previous genetic map of West Eurasians which analyzed Kurds and Iranians together with Pathans and Balochis.