Razib Khan One-stop-shopping for all of my content

April 18, 2017

Women hate going to India

Filed under: Anthroplogy,Genetics,Human Genetics,India,Parsi — Razib Khan @ 9:11 pm


For some reason women do not seem to migrate much into South Asia. In the late 2000s I, along with others, noticed a strange discrepancy in the Y and mtDNA lineages which trace one’s direct male and female lines: in South Asia the male lineages were likely to cluster with populations to the north an west, while the females lines did not. South Asia’s females lines in fact had a closer relationship to the mtDNA lineages of Southeast and East Asia, albeit distantly.

One solution which presented itself was to contend there was no paradox at all. That the Y chromosomal lineages found in South Asia were basal to those to the west and north. In particular, there were some papers suggesting that perhaps R1a1a originated in South Asia at the end of the last Pleistocene. Whole genome sequencing of Y chromosomes does not bear this out though. R1a1a went through rapid expansion recently, and ancient DNA has found it in Russia first. But in 2009 David Reich came out with Reconstructing Indian population history, which offered up somewhat of a possible solution.

What Reich and his coworkers found that South Asia seems to be characterized by the mixture of two very different types of populations. One set, ANI (Ancestral North Indian), are basically another western or northwestern Eurasian group. ASI (Ancestral South Indian), are indigenous, and exhibit distant affinities to the Andaman Islanders. The India-specific mtDNA then were from ASI, while the Y chromosomes with affinities to people to the north and west were from ANI. In other words, the ANI mixture into South Asia was probably through a mass migration of males.

But it’s not just Y and mtDNA in this case only. A minority of South Asians speak Austro-Asiatic languages. The most interesting of these populations are the Munda, who tend to occupy uplands in east-central India. Older books on India history often suggest that the Munda are the earliest aboriginals of the subcontinent, but that has to confront the fact that most Austro-Asiatic language are spoken in Southeast Asia. There was no true consensus where they were present first.

Genetics seems to have solved this question. The evidence is building up that Austro-Asiatic languages arrived with rice farmers from Southeast Asia. Though most of the ancestry of the Munda is of ANI-ASI mix, a small fraction is clearly East Asian. And interestingly, though they carry no East Asian mtDNA, they do carry East Asian Y. Again, gene flow mediated by males.

The same is true of India’s Bene Israel Jewish community.

A new preprint on biorxiv confirms that the Parsis are another instance of the same dynamic: The genetic legacy of Zoroastrianism in Iran and India: Insights into population structure, gene flow and selection:

Zoroastrianism is one of the oldest extant religions in the world, originating in Persia (present-day Iran) during the second millennium BCE. Historical records indicate that migrants from Persia brought Zoroastrianism to India, but there is debate over the timing of these migrations. Here we present novel genome-wide autosomal, Y-chromosome and mitochondrial data from Iranian and Indian Zoroastrians and neighbouring modern-day Indian and Iranian populations to conduct the first genome-wide genetic analysis in these groups. Using powerful haplotype-based techniques, we show that Zoroastrians in Iran and India show increased genetic homogeneity relative to other sampled groups in their respective countries, consistent with their current practices of endogamy. Despite this, we show that Indian Zoroastrians (Parsis) intermixed with local groups sometime after their arrival in India, dating this mixture to 690-1390 CE and providing strong evidence that the migrating group was largely comprised of Zoroastrian males. By exploiting the rich information in DNA from ancient human remains, we also highlight admixture in the ancestors of Iranian Zoroastrians dated to 570 BCE-746 CE, older than admixture seen in any other sampled Iranian group, consistent with a long-standing isolation of Zoroastrians from outside groups. Finally, we report genomic regions showing signatures of positive selection in present-day Zoroastrians that might correlate to the prevalence of particular diseases amongst these communities.

The paper uses lots of fancy ChromoPainter methodologies which look at the distributions of haplotypes across populations. But some of the primary results are obvious using much simpler methods.

1) About 2/3 of the ancestry of Indian Parsis derives from an Iranian population
2) About 1/3 of the ancestry of Indian Parsis derives from an Indian popuation
3) Almost all the Y chromosomes of Indian Parsis can be accounted for by Iranian ancestry
4) Almost all the mtDNA haplogroups of Indian Parsis can be accounted for by Indian ancestry
5) Iranian Zoroastrians are mostly endogamous
6) Genetic isolation has resulted in drift and selection on Zoroastrians

The fact that the ancestry proportion is clearly more than 50% Iranian for Parsis indicates that there was more than one generation of males who migrated. They did not contribute mtDNA, but they did contribute genome-wide to Iranian ancestry. There are wide intervals on the dating of this admixture event, but they are consonant oral history that was later written down by the Parsis.

So there you have it. Another example of a population formed from admixture because women hate going to India.

Citation: The genetic legacy of Zoroastrianism in Iran and India: Insights into population structure, gene flow and selection.
Saioa Lopez, Mark G Thomas, Lucy van Dorp, Naser Ansari-Pour, Sarah Stewart, Abigail L Jones, Erik Jelinek, Lounes Chikhi, Tudor Parfitt, Neil Bradman, Michael E Weale, Garrett Hellenthal
bioRxiv 128272; doi: https://doi.org/10.1101/128272

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