1. It divided Hindus into two (or four) groups - North vs South, and upper-caste vs lower-caste. Viewed from their ideological angle which saw Muslims and Christians as enemies of the Hindus, such internal schisms within Hinduism were an unacceptable weakness.
1. Virtually all groups in India, including those considered to be isolated, have experienced an admixture of two distinct racial groups in the past. There are no "pure" groups today.
2. This admixture took place over a period of time, between 4200 years ago and 1900 years ago.
3. The paper calls these two original racial groups ANI and ASI (Ancestral North Indian and Ancestral South Indian). The ANI group has links to Central Asia, the Middle East and Europe, although the paper takes care to explain that it has no immediate links to Eurasians and hence may have separated from the Eurasian group 12,500 years ago. The ASI group does not have links to any group outside of India, with the closest group being in the Andamans. Hence the ASI group is probably indigenous to India.
4. Present-day Indo-European groups in India (i.e., North Indians) have a higher proportion of ANI genes than ASI. Present-day Dravidian groups (i.e., South Indians) have a higher proportion of ASI genes than ANI.
So far, the data seems consistent with the Aryan Invasion/Migration Theory in that the ASI group indigenous to India seems to correspond to the Dravidians, and the ANI group with links to Central Asia seems to correspond to the Aryans. However, it isn't that straightforward.
5. The dates of admixture are more recent among Indo-European groups than among Dravidian groups. A plausible theory is that Indo-European groups received a second infusion of ANI, making the effective date of the admixture appear more recent. This is backed up by the fact that many North Indian genomes have long stretches of ANI interspersed with stretches that are a mosaic of ANI and ASI, pointing to a more recent admixture on top of an earlier one.
6. "Upper" and "middle" caste people's genomes show multiple waves of admixture compared to "lower" caste genomes. The paper does not offer an explanation for this, but my theory is that lower caste people were less mobile and had fewer opportunities to interact with outside groups, perhaps as a result of social restrictions.
On a matter that can be seen to have a major bearing on our understanding of caste, the paper makes a further surprising claim based on the genetic evidence.
7. An abrupt shift to endogamy (the opposite of cross-breeding) occurred around 1900 years ago. Some groups stopped receiving gene flows from neighbouring groups 3,000 years ago.
Its conclusions are explosive. To cut a long story short, the genetic evidence suggests that the Aryan Invasion Theory is probably on the money. The Out of India Theory stands discredited. What's more, it really was an invasion and not a peaceful migration. Read this commentary in The Hindu which explains the conclusions of the paper in layman's terms.
The research for the first time analyses patrilineal DNA or Y-DNA, whereas previous studies had focused on matrilineal DNA or mtDNA. Previous studies had not detected any genetic infusion into India around the time of the Indus Valley Civilisation, but the newest one does. What's more, the dating of this infusion (around 2000 BCE) matches the collapse of the Indus Valley Civilisation to an astonishing degree.
Let's think about this for a moment. No infusion of matrilineal DNA occurred during the 2000 BCE period, but there was an infusion of patrilineal DNA at that time. In other words, a large group consisting almost exclusively of men entered India at that time. What's the probability that this was an army as opposed to a nomadic community of men, women and children? I'd have to say the evidence very strongly suggests an armed invasion.
Let's think further about the remarkable coincidence that the Indus Valley Civilisation should have collapsed at about the same time that a large group of men (that we have to admit was probably an army) entered the region. What's the probability that these were unrelated events? I'd have to say the evidence strongly suggests a cause-and-effect relationship. An invading army caused the downfall of the Indus Valley Civilisation.
The commentary article in The Hindu is however not bold enough to join these dots as I have above. It echoes the researchers' own circumspection by continuing to talk about a "migration" rather than an "invasion".
To my mind, it's all over but the shouting. The genetic evidence very clearly and strongly suggests an invasion of India by men from Central Asia. The Aryan Invasion Theory was therefore on the money. The ideology of the Hindu right-wing, that Aryan (or "Vedic") culture originated in India, and that all Indians share a single and indigenous genetic heritage, lies in tatters.
None of this should matter to regular Indians, who will probably shrug and carry on with their lives, absolutely untouched by what the evidence says about their past. But to the Hindu right wing, which has made this debate such a point of pride, the latest evidence is devastatingly bad news.
It couldn't happen to a nicer bunch of people.