Inter-caste marriages are good for health of Indians. That’s what DNA testing tells us

Representational image of a wedding ceremony | Commons

Around 70 generations ago, Indians stopped inter-marrying and created endogamous caste groups.

Among the most exciting discoveries in recent years has been in the field of genetics and genomics, as the deciphering of the Indian genetic code has yielded fascinating insights into, “Who We Are and How We Got Here”. That’s the title of Harvard scientist David Reich’s recent book on human origins as pieced together from our DNA.

I may be biased, but the chapters about India — based on the work of Priya Moorjani, K. Thangaraj, Lalji Singh, Vagheesh Narasimhan and numerous other collaborators — are the most fascinating. Over the past decade, these scientists have uncovered compelling evidence showing that most people in India arose from a mixture of two ancestral populations that they call Ancestral North Indian (ANI) and Ancestral South Indian (ASI), and that the ANI component tends to be higher among upper-caste and northern Indians. Other researchers have added greater detail to the picture, showing that in addition to ANI and ASI, Andaman and Nicobar Islanders, Tibeto-Burmans and Austro-Asiatic groups contribute to the great Indian population mix.

Of course, the biggest mystery that ancient DNA can help solve is identifying the Harappans and telling us what happened to them. One 4,500-year-old skeleton from Rakhigarhi is proving to be crucial in this puzzle as the person who it belonged to carried ASI genes, and none from ANI. The coming years will see a lot more discoveries as geneticists and archaeologists get to know each other better, and as polemicists and ideologues reckon with greater and more incontrovertible evidence about our origins.

Here’s what our DNA tells us: More than 4,000 years ago, ANI and ASI didn’t intermarry much. For roughly the next 2,000 years, they widely intermarried, resulting in almost all their descendants (that is, us) being a mixture of ANI and ASI. Then, around 70 generations ago, our ancestors stopped inter-marrying and created endogamous groups that we know as castes. Indians started marrying within their own caste groups around 2,000 years ago.

Who the Harappans were might be of academic and political interest, but the genomics of caste has immense utility for public health and indeed, for how we want to shape our future.

Reich puts it very well. India, he writes, “is composed of a large number of small populations”. He points out that caste groups living side by side in the same village for hundreds of years are two to three times more genetically differentiated compared to people living at the opposite ends of Europe.

Thangaraj and his co-researchers found that of the 263 endogamous groups they studied, more than 81 had greater “identity by descent” scores than the Askhenazi Jews and Finns, among the world’s best-known endogamous groups. Of these, 14 groups had estimated populations of over a million. Now, because certain types of genetic diseases arise because of endogamy — either because people marry close relatives or because they have descended from common ancestors — we can identify and reduce the risk of their occurrence. He cites the example of how diseases like Tay-Sachs syndrome, once widely prevalent among Ashkenazi Jews, have virtually disappeared after the introduction of a community genetic testing programme.

Potential couples can query a genetic database to know the risks of known genetic diseases in their offspring.

Simple genetic testing is now almost as affordable as an MRI scan. The challenge though is to know what to look for. Ashkenazi Jews have identified a list of diseases that their community is particularly prone to. That list, though, won’t work for other populations. We have around 5,000 endogamous groups in India — which means we need to create 5,000 lists of diseases. To create a list, we must sequence the genomes of 200 individuals from each group and correlate them with observations of genetic diseases prevalent in that community. If we have a national genomic database for all 5,000 communities, a simple genetic test will help uncover any risk of genetic diseases that the individual or couple can expect. Setting up a national genomic database ought to be a part of India’s public health policy.

So, public health is yet another reason to dissolve caste. Inter-caste marriages are a good thing. We, Indians, were forged when the ANI, ASI and others mixed freely for 2,000 years. Then came caste, and divided us into numerous small populations.

Will this change? The bad news is that across India, only 5-6 per cent of marriages are inter-caste. The Indian Human Development Survey, which covers over 42,000 households across India, found that this number hadn’t changed much between 2004-5 and 2011-12. Mizoram (55 per cent), Meghalaya (46 per cent), Sikkim (38 per cent), Jammu & Kashmir (35 per cent) and Gujarat (13 per cent) had the highest inter-caste marriage rates, while Madhya Pradesh (1 per cent), Himachal Pradesh, Chhattisgarh and Goa (2 per cent each) and Punjab (3 per cent) had the lowest. Another survey, conducted by the Lok Foundation and CMIE, shows that while south Indian states have higher inter-caste marriage rates compared to the national average, Tamil Nadu stands out with only 3 per cent.

But there is some good news. The Lok Foundation survey reveals that more Indians are accepting inter-caste marriages for their children. Interestingly, of all factors, women with more years of education tend to be more accepting of inter-caste marriages for their children. So if you are thinking of marrying someone outside your caste, your chances improve if your would-be mother-in-law is educated.

(Disclosure: A member of my immediate family works for a company that provides genetic testing services)

The author is the director of the Takshashila Institution, an independent centre for research and education in public policy.