Sunday, 25 October 2009

Genetic history of Muslims in India: Islam spread through cultural conversion, and not through human invasion

By Syed Akbar
Hyderabad, Oct 23: The spread of Islam in India was predominantly a cultural conversion associated with minor but detectable levels of gene flow primarily from Iran and Central Asia, and not directly from the
Arabian peninsula, according to a new research study collaborated by the city-based Centre for Cellular and Molecular Biology.

The study also found that most of the Indian Muslim populations received their major genetic input from geographically close non-Muslim populations. "However, we have also observed low levels of likely sub-Saharan African, Arabian and West Asian admixture among Indian Muslims. We rule out significant gene flow from Arabia," CCMB senior scientist Dr K Thangaraj told this correspondent.

According to historical evidence, the Indian Subcontinent has been exposed to several waves of human migrations from the Arabian Peninsula and Iran, the homelands of Indian Muslim rulers Arabian Peninsula (where Islam was propagated) served as a hub for human migrations, hence the merged genetic signatures of Eurasian and African origin, which has been detected in both maternal and paternal lineages from the region. Besides Arabia, Iran is a second plausible genetic source for Indian Muslims. It is positioned in the tricontinental nexus and its populations genetically show close proximity to those from the Near East, lthough with a lesser genetic input from Africa than from the populations of the Arabian Peninsula.Besides mtDNA and the Y chromosome, which show relatively low levels of differentiation between these two potential sources, recentstudies of lactose tolerance have revealed that Iranian and Arabian populations differ significantly in genetic patterns at this locus.
The CCMB took up the study in collaboration with the National DNA Analysis Centre of the Central Forensic Science Laboratory, Kolkata, State Forensic Laboratory, Lucknow, Leverhulme Centre for Human
Evolutionary Studies of University of Cambridge, UK, Department of Evolutionary Biology of Estonian Biocentre and Tartu University, Estonia, and the Wellcome Trust Sanger Institute, UK.

To estimate the contribution of West Asian and Arabian admixture to Indian Muslims, the team assessed genetic variation in mitochondrial DNA (mother's lineage), Y-chromosomal (father's lineage) and genetic
markers representing six Muslim communities from different geographical regions of the country.

"Most Indian Muslims are closely related to their neighbouring non-Muslim populations and this suggests that they descend primarily from local Hindu converts. The exception to this are some northern and north-western Indian Muslims, who differ from indigenous Hindu populations, likely because of a higher proportion of genetic lineages of external origin," the study pointed out.

The researchers used as many as 472 Indian Muslim mitochondrial DNAs, 431 Indian Muslim Y chromosomes and 747 Indian Muslim and non-Muslim gene (MCM6) profiles for the study. "There is a notable variation between different Indian Muslim populations, some being highly similar to local Indian populations and others having similarities with external populations, so that when they are all grouped
together as ‘Indian Muslims’, the group difference is statistically insignificant from that of non-Muslims," Dr Thangaraj said.
Shia, Sunni, Dawoodi Bohras from Gujarat and Mappla from Kerala are found to cluster together with Indian non-Muslim populations, whereas Dawoodi Bohras from Tamil Nadu seem to be an outlier. In the Y-chromosomal plot too, Shia, Sunni, Dawoodi Bohras from Gujarat and Mappla form a group with their neighbouring Indian non-Muslim populations and Europeans, whereas the Dawoodi Bohras from Tamil Nadu, again found as an outlier.

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