What do we know about Indian prehistory?

February 05, 2022 [books] #population-genetics #india #steppe #reviews

Book: Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past
Author: David Reich

The past two decades have seen a revolution in population genetics, in no small part due to David Reich's work at Harvard. This revolution, as I understand it, is the ability to extract DNA from ancient bones and to be able to fully sequence it, and by building models of gene frequency dynamics, provide accounts of human migrations. This has allowed reconstruction of population history in more details than had been possible before. Reich's book is a scientist's overview of the field, and a summary of what we know so far about human prehistory.

Reich establishes over many chapters, with examples from Europe, the Americas, Asia that no population group is "pure" in the Nazi sense of the word. Every ethnic group present today is a mixture of many distinct groups from before, and those previous populations themselves were composites. Another fact that he conclusively establishes is that to be human is to migrate, and existing populations in geographic locations often don't have any genetic relation with the ancestors that they remember via cultural memory. Take for example, Britain. Considered to the home of an indigenous Celtic people, who later mixed with the invading Anglo-Saxons. It turns out the Celts themselves are a population group that migrated around three thousand years ago. The Stonehenge, the earliest prehistoric monument in Britain, was built five thousand years ago by a people that no longer exists, before the arrival of ancestors of modern Europeans (and hence Indo-European languages)! Such population replacements have happened many times in human history in many places. A recent example is the genocide and replacement of the Dzungar people by the Han Chinese, Hui muslims and Turkic Taranchis in Xinjiang in the eighteenth century.

The Early Indians

Sintastha Culture Within the Eurasian Steppe

Sintastha Culture within the confines of the Eurasian steppe

Around five thousand years ago, the Yamnaya became the predominant power in the Steppe. To be a superpower back then was to possess two technologies: horses and wheels. The Yamnaya and their descendants migrated in multiple waves to Europe and India, and were so successful that every Indian living today (except the Andamanese) has an Yamnaya as an ancestor. The mitochondrial DNA, a tiny portion of the human genome, is passed along the maternal line from mother to daughter to granddaughter. It can be used to trace the diversity along the female line, and for most population groups, it's very diverse. The Y-chromosome, another portion of the human genome, is a lot less diverse - for all population groups. The Y-chromosome comes only from the male line, passed from father to son. While the Y-chromosome of most Indians show steppe and Iranian farmer ancestry, the mitochondrial DNA of Indians is unique - it's not found outside of the subcontinent. What this indicates is that these migrant groups from the steppes and West Eurasia were in all likelihood composed entirely of men. As it has happened in Americas these past few centuries12, males from a population with more power were more successful in competing for mates and replaced almost entirely the Y-chromosome of the existing population group.

The Yamnaya were Indo-European speakers, and they bought the language with them which later became Old Sanskrit. While it is true that Sanskrit and Hindu mythology developed entirely within the confines of the Indian subcontinent - the oldest layers of the Vedas clearly reflect early Indian geography and memories - there are echoes of the shared Proto-Indo-European past in the most ancient of these myths. Indra and Zeus are gods of thunder and lightening and the kings of their respective pantheon. The Ashvin twins correspond to the Greek twins, Castor and Pollox. One tradition of the Vedic religion was the Asvamedha, horse sacrifice. The Roman religion had its own horse sacrifice ritual, the October Horse.

What population group did the descendants of the Yamnaya encounter during their eastward expansion into India? This was also a composite group, a mixture of ancient Iranian farmers expanding eastwards to the Indus Valley after nine thousand years ago3, and an earlier population group of hunter gatherers. This composite group has been termed the ASI (Ancestral South Indian), and the descendants of the Yamnaya constitute a population group now called ANI (Ancestral North Indian). Every population group in India is a mixture of the ASI and the ANI. There's no purely ASI or purely ANI group in India. Brahmins from Kashmir have as much ASI mixture in them as the members of some of the isolated tribe in deep South India have ANI, about 30%. Indian endogamous groups - jatis - cluster around various blends of ASI to ANI when plotted along a cline.

David Reich's chapter on India ends with some speculation about the Indus Valley Civilization (IVC). Were they Iranian-related farmers, or were they already ASI? Could they be ANI? These were folks at the crossroads of all these movements of people. Since the book was published in 2018, his lab has successfully sequenced a genome from Rakhigiri, an Indus Valley site. To no one's surprise, there's no population group in India that's purely IVC. The IVC folks share more than 75% of their ancestors with people living in ancient pre-Indo-European Iran. About 55% of ASI's ancestry comes from IVC. For ANI, that's 70%. It looks like much of the formation of the ASI and the ANI occurred in the second millennium BCE, a time that also coincides with the decline of the IVC4.


I think we know enough now to tell the story of early Indians, at least something that's more than a speculation. Either all Indians are indigenous or no one is. The Yamnaya gave almost all Indians5 their genes, and their memes. Dravidian/Aryan (~= native/outsider) race-based classification of Indian peoples makes no sense, considering everyone is a composite mixture of ASI and ANI. The AASI6 have been entirely within the borders of the subcontinent for the last ten thousand years, and could be regarded as indigenous to the subcontinent (unless we find evidence otherwise). Every Indian's mitochondrial DNA reflects this heritage.

Regarding the book itself, it's dry as hell. And I mean dry! I am not a fan of Reich's narrative framing - he assumes that the reader has one perspective, explains reasons for the prevailing model and finally leads the reader to what the latest science says. I had no preconceived notions when I started, and these were the parts I found a slog to get through, not to mention confusing. My review covered only those portions that were of interest to me, but Reich has a much larger canvas than just India - he covers the prehistory of Japan, China, the Pacific Islands, the Americas, Africa and Europe. Despite the caveats, this is a book that deserves to be on everyone's shelves. A familiarity with some of its conclusions will only enrich the conversations happening right now about race, caste, nationality and culture.



"Comparison of Y-chromosome and mitochondrial DNA types that are highly different in frequency between African Americans and Europeans also shows that by far the majority of the European ancestry in these populations comes from males, the result of social inequality in which mixed-race couplings were primarily between free males and female slaves." Quoting Reich from this book.


"Andrés Ruiz-Linares and colleagues have documented how in the Antioquia region of Colombia, which was relatively isolated between the sixteenth and nineteenth centuries, about 94 percent of the Y chromosomes are European in origin, whereas about 90 percent of the mitochondrial DNA sequences are of Native American origin. This reflects social selection against Native American men." Quoting Reich from his book.


It's been hypothesized that these expanding farmers brought some form of proto-Dravidian to India. See Elamo-Dravidian languages.


One notable exception: the Pulliyar tribe in South India is almost 100% ASI. All the population groups in the Indian subcontinent can be plotted along a cline, one end of which is 100% ANI (represented by the Kalash of Pakistan's Chitral district), and the other end is 100% ASI, represented by Pulliyar.


Ancient Ancestral South Indian, a ghost population. The Andamanese Islanders are hypothesized to be related to them. They don't have any West Eurasian ancestry.

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