Sunday, September 25, 2016

New indications on the peopling of India

The NYT reports:
In the journal Nature, three separate teams of geneticists survey DNA collected from cultures around the globe, many for the first time, and conclude that all non-Africans today trace their ancestry to a single population emerging from Africa between 50,000 and 80,000 years ago.
The three teams are led by Eske Willersley of the University of Copenhagen (A genomic history of aboriginal Australia), David Reich of Harvard University (The Simons Genetic Diversity Project: 300 genomes from 142 diverse populations), and Mait Metspalu of the Estonian Biocentre (Genomic analyses inform on migration events during the peopling of Eurasia).

Unfortunately all the articles are behind a paywall, and a visit to the nearby university library is not in the plan for now.  The article with the most to do about anything Indian is the Reich article.

Some observations follow.

About the dates:

There were tool-making hominids in India at the time of the Toba supervolcano eruption 74,000 years ago. Was India repeopled by this "single population" mentioned above; or had this population already arrived in India at that time?

Figure 1 from the Reich article:
It looks like this:

The neighbor-joining algorithm is described in this wiki article.  Given a set of N points with the distances between every pair of points, the neighbor-joining algorithm joins the two closest points into a new point, computes an effective distance of this new point from the other points, and then runs  the neighbor-joining algorithm on the N-1 points (1 new point and N-2 untouched points). It runs until all the points are joined.  Wiki tells us that this algorithm gives a good approximation to an optimized 'balanced minimized evolution' tree (whatever that means).

PS: How do two population groups get to be closely related?   One is that they intermarry; the other is that though endogamous they share recent common ancestors.

With this under our belt, let's look at some of the diagram, showing the Indian sub-populations:

Remember how to read this.  Neighbor-joining found Mala and Relli to be the most closely related of all these groups.  In the subsequent graph, the Madiga- (Mala-Relli) relationship was the closest. Irula-Kappu is next.  and the next is the (Irula-Kappu)-(Madiga-(Mala-Relli)).  And so on.

No big surprises here.  We kind of see the ASI/ANI gradient reflected here. ASI=Ancestral South Indian, ANI=Ancestral North Indian, which are the two principal components of variation in the Indian population.

The surprise comes in what the Indian group is most closely related to.

The Indian group + the Tajik are most closely related to a group that includes the Saami, Mansi, Tlingit, Aleut, etc.  The Saami are the northern-most indigenous people of Europe, today living in far north Finland, Norway, Sweden, the Kola peninsula of Russia.  The Mansi are a Uralic people.  The rest are indigenous peoples of the Americas, who separated from old world populations at least 16,000 years ago.

Where are the Indo-European group?  Largely here in the pink group.

Notice that Iranians are not as close to the people who live at and around the Indus valley - the Brahui, Makrani, Balochi, Kalash, Burusho, Pathan, Sindhi, Punjabi as the entire indigenous American group, as per this tree.  Wherever agriculture came from to the Harappan civilization,  it did not bring any significant Iranians or Iranian population explosion with it.

Notice that the whole ANI/ASI mixture of two-components population nevertheless places ANI closer to indigenous Americans than to any Indo-European speaking group.  We see the problem with the genetic studies that use as a reference point for Indians the East European genomes.  They have pre-determined the story they want to tell, of an Indo-European incursion into India from the west.  But if this tree is correct, shouldn't ANI be looked at with an Amerindian reference point? I.e., two waves of people entered India many tens of thousands of years ago, first the ancestors of the ASI component, and then the ancestors of the ANI component, a branch of which also made their way over generations all the way east across Asia and into the Americas?

The Yamnaya invasion/migration story might help explain how all the non-Indian Indo-European speaking groups are related.  The Brahmins, the age-old upholders of the Vedic culture, and the preservers of the oldest extant Indo-European literature, the Rg Veda, are solidly within ANI/ASI spectrum, and not as close to any of the other IE groups as they are to within-India groups.  Whether ancient Sanskrit entered India or left India, it did so with no movement of people significant enough to leave a trace on the above tree.

IMO,  on the face of it, this chart supports an independent agro-pastoralism in India and Robin Bradley Kar's ideas about proto-IndoEuropean. 

In any case, there was no population explosion of outsiders bearing agriculture or horses relative to the native population of India.  The idea of a civilization, that of the Saraswati-Sindhu whose language spread through cultural influence all the way from the Indus into the steppes without significant movement of people might be borne out.