Message posted at IndianCivilization (Yahoo egroups):
I went through the above article. The article seems to be transcript of Prof. Lynn Jorde’s oral presentation. The slides are missing so little can be said about it. (Lynn Jorde is Professor of Human Genetics at the University of Utah. He has been involved in a collaborative effort between geneticists, physical anthropologists, and indigenous populations in India.)
It is my conclusion that the data presented by Prof. Jorde fits the OIT better than the AIT/AMT. Here is my analysis of the article.
Early in the article Prof. Jorde presents the picture that he wants to research (in Prof. Jorde’s words):
“So here are some of the research questions that we’ve been addressing in our studies in south India. First of all, is there significant between-population genetic variation, and we’ve been looking thus far primarily at caste variation, and what is the pattern of between-caste genetic distances? What are the likely origins of south Indian castes and tribal populations? And finally, is there evidence of a sex-biased gene flow between castes? And this is essentially the system that we were testing with mitochondrial and Y-chromosome genetic markers, and I’ll talk a little bit more about that as we go along.”
Later he builds his premise to test out the data he collected.
“Now, we can summarize — and this is a very, very oversimplified summary of major historical events in India, but it gives us at least a framework from which to proceed — Paleolithic settlement of probable African origins, migrations of proto-Dravidian speakers from the Fertile Crescent area about nine or ten thousand years ago. And then most recently, a third major event, migrations of Indo-European-speaking, so-called Aryans from West Asia, about 3500 years ago, and it was these individuals who established, who are thought to have established, the caste system. And I’ll be referring to these waves of migration as we go through the talk.”
It is clear that the premise of Prof. Jorde’s research is based on the AIT/AMT.
So, strictly speaking, this presentation cannot be taken as a proof of migration. This presentation can be limited to what Prof. Jorde set out to prove namely: Genetic variation and caste. However, lets see how it all goes.
Prof. Jorde first shows that genetic variations across the caste exists. A loose summary goes like this: The transmission of mitochondrial DNA across generations is associated with the female of the species while Y chromosomal DNA is associated with the male. It is observed that females had greater mobility across the castes as opposed to males. The more homogenous nature of the mitochondrial DNA across the castes shows this, while a 6-7 times higher variation in Y-chromosomal DNA in males of the population shows their lower mobility across the castes.
For the “critical” conclusions, which “prove” AIT/AMT, I’ll use Prof. Jorde’s words:
“Now, we can also look at — and this is some fairly new work that hasn’t yet been published — mitochondrial DNA, genetic distances between various caste groups and continental populations. And one of the things we see here is that all of the castes are most similar to groups of Asian populations. And that’s expected, given the origins of the proto-Dravidian populations, so that we see much, much smaller distances between Asian populations and each of the caste groups for the mitochondrial DNA.”
Comments: Given the geographical isolation of the sub-continental population for long periods of time and the female mobility across castes, a homogeneity in mitochondrial DNA is not totally unexpected, even according to Prof. Jorde’s analysis. IOW, assumption of the existence of a proto-Dravidian population is unnecessary.
Further Prof. Jorde says:
“When we look at Y chromosome DNA, we again see a somewhat different pattern. For the upper castes, they actually have slightly greater genetic affinity (smaller distances) for European populations than for any other population. The middle castes, a little bit smaller distance between them and Europeans, and the lower castes instead have the greatest affinity to Asian populations.”
Comments: “…..greatest affinity to Asian populations”? This is ambiguous. If it refers to the Dravidian population as Prof Jorde previously alluded, then it is fictitious comparison since, then he is comparing the supposed “lower caste” with themselves and obviously a good match will be found.
OTOH, it would be naive to imagine that the population across whole of Europe has very low variation in Y-chromosomal DNA. It would be interesting to see which European population set has the maximum affinity to the “upper caste”.
And then he concludes;
“Now, if we think back about the history of the population, the most recent wave, and the one that is the most recent wave of migrants, the one that instituted the caste system is thought to have come from West Asia, Eurasia, and those individuals would likely have been more similar to individuals from Europe. And as those individuals who began the caste system, they also likely appropriated the highest positions in the system. So, a very interesting historical insight, again consistent with some historical hypotheses that the invaders who came in about 3500 years ago, established the system, and primarily who were male, so we see the Y chromosome versus mitochondrial difference, we can still see that signature in today’s genes.”
Comments: Prof. Jorde started with a premise and his data set proves it. If Prof. Jorde had started with a different premise, will the data-set disprove the different and incorrect premise? Theoretically, it should. Let see how the data set fits for example the OIT. We take OIT because, it runs diametrically opposite to AIT/AMT.
But, first, let us re-build the premise.
In 3500 BP or so the life-sustaining ability of river Saraswathi was on decline. Migrations of population from its banks began. It is well known that the “upper caste” brahmin population migrated down the coast upto Kerala, populating the regions all along the way. The saraswath brahmins the tulu-brahmins the namboodris are examples and there is hardly any dispute in this. The other wave moved across to the gangetic plains and upto Brahmaputra. I am afraid I have little to go on here. (Can somebody tell me more?) But what about the other castes? Did they move along with them? What artefacts have they left behind I have no idea. However, it is tempting to assume that the “upper class” mobility was much higher. As it turns out, this is the ONLY assumption one has to make to fit Prof Jorde’s data-set to OIT! Lets see how.
Now, it is downright silly to assume that R. Saraswathi was populated only on the Eastern bank! What happened to those who lived on the west side? Did they die out as the Saraswathi dried up? Likely no. They too migrated? Very possible. Where did they migrate to? Did they run across the river and into the eastern side? Possible too. But, did they moved out to present-day Afghanistan and beyond, through to Middle-East and to Europe!! Lets pick up this possibility and see how Prof Jorde’s data fits.
No disputes about the variation of the Y-chromosomal DNA and similarities of the mitochondrial DNA across the castes in the sub-continent. The issue is the similarity of the Y-Chromosomal DNA of the European population with that of the “upper caste” with gradually decreasing similarities with other castes. This can easily be explained as a representation of the mobility pattern. The “upper caste” had a higher mobility and moved to Europe. The homogenization of the Y-Chromosome can be explained as the lack of “caste-system” and it is no surprise that this homogenized population’s Y-Chromosome DNA shows greater similarity to the population that showed the greatest mobility – namely – the “upper caste”.
So, as compared to Prof. Jorde’s premise, where he had to make several assumptions (the Aryan invasion into India, mostly male, formation of caste system by them, appropriation of the “higher caste” by these invaders etc.), one has to use just one simple and probably very likely assumption that the so called “upper caste” had higher mobility and the premise of “OIT” fits much better.
Guess, the idea is, the lesser the assumptions one has to make to fit a data-set, the higher the probability of the theory to be true.