Genomics of India

Arun and his commentators have linked to and discussed an important new paper on the genomics of India by David Reich and the Harvard collaboration. This paper bears on a number of points dear to my interests, including the origins of the Indo-European languages. Among the zillions of theoretical locations for the PIE Urheimat, only three still seem to have any substantial support, with the Eurasian steppe near the Black Sea the overwhelming favorite. Number two seems to be the Iranian highlands, with the Out of India (OIT) theory championed almost exclusively by Indian nationalists.

I'm not ready to discuss the paper yet, though I have read it, the broad conclusions suggest that the modern Indian population was formed by two major migrations mixing with the existing population, which may well have been there since the earliest spread of modern humans from Africa, and which has the Andaman Islanders and Australians as their closest relatives. The first major wave of immigrants were Neolithic Iranian farmers and the second were Bronze Age pastoralists from the steppe. These migrations closely parallel what is far better documented in Europe: indigenous hunter-gatherers largely displaced by Anatolian farmers, who were in turn displaced by the same steppe pastoralists.

The genetic data provides strong circumstantial evidence for the classical Aryan immigration theory for the arrival of the IE languages in India - the notion that steppe immigrants, who clearly brought IE languages to Europe (and even parts of China), arriving near the end of the Indus Valley Civilization, also brought the related languages to India (and Iran). I call the case circumstantial, because we lack ancient DNA from India, a lack we hope will be alleviated if the Rakhigarhi data is ever published.

This new information does not appear to sit well with the Indian nationalists, who want Indian Civilization to be wholly autochthonous, and hate the idea that Sanskrit might be a foreign import, even if it happened 4000 years ago.

Here is Arun quibbling:

The life expectancy at birth in the Paleolithic is estimated to be 33 years per Wiki. The per generation time of 28 years means that the average age of a woman relative to the birth of her children is 28 years. E.g., if women uniformly bore children at ages 20, 24, 28, 32 the generation time would be (20 + 24 + 28 + 32)/4 = 26. You can see that women would be bumping up into the life expectancy. On the other hand, what is important is actually the conditional life expectancy, which is the life expectancy of women who survived up to at least one live birth, which may be better than that 33 years. Still, one would think that in the Paleolithic, women in the 18-28 age group would have more children than the women 28-38 age group, if only for the reason that there's more of them.

Arun is a very smart fellow, and I'm sure that he knows that a life expectancy at birth of 33 years doesn't mean that people live until 33 and then die. What it means is that there is high infant and perhaps childhood mortality, and that those who reach their teens are only slightly less likely to make it to sixty than their modern counterparts. Biologically, humans 15,000 years ago were as capable of living to 70, 80, or more as our contemporaries, though they might have lived more dangerous and difficult lives. In any case, India was far from Paleolithic 6000 years ago. Agriculture had already existed there for thousands of years.

This would probably more appropriate as a comment on his blog, but I don't seem to be able to comment there any more.