Razib Khan is a definitive source on Indian genetic makeup and has written almost too prolifically about it. Razib is a population genomics researcher, but a lot of his content is gated behind publications and substack. I'll try to quote what is available to me right now. But, for a more detailed explanation, I'd recommend drinking straight from the source.
The Indian genetic make up can be entirely summarized as a combination of 3 independent groups.
We can place every Indian on a chart that estimates their contribution from the three ancestral streams: steppe (agro-pastoralists who ranged between modern Ukraine and modern Tajikistan), IVC (indus valley civilization), and “Ancient Ancestral South Indian” (AASI).
or this image.
NOTE: The AASI has nothing to do with south indians as we know the today.
upper-caste Hindus were Indo-Aryan and lower-caste/dalit Hindus were not
That is a moderately incorrect statement. All Indians have sufficient amounts of all 3 genetic groups such that no straight lines can drawn from indo aryan -> upper caste. But, AASI percentage does go up as you go from Brahmin to non-Brahmin Tamilians.
To a great extent, the algebra of genetic composition across South Asia can be thought of as modulating these three components, farmer, steppe, and AASI.
Consider:
- Bhumihar people in Bihar tend to have more steppe than typical, but not more farmer than typical, and average amounts of AASI.
- Sindhi people in Pakistan tend to have lots of farmer, some steppe, and not much AASI.
- Reddy people in South India have lots of farmer, very little steppe, and average amounts of AASI.
- Kallar people in South India have some farmer, very little steppe, and lots of AASI [link]
Hope that helps with getting some grounding.
the expansion and dominance of Dravidian-speaking agricultural societies in much of South India in the form we recognize them today does not predate the arrival of Indo-Aryans by much if at all. Rather than thinking of Indian culture as the application of Indo-Aryan elements atop a Dravidian base, it is more accurate I think to consider them a synthesis that developed simultaneously. Though it is quite likely that the IVC language was related to that of the Dravidians, the impact of the Indo-Aryans shapes most Dravidian-speaking societies both culturally and genetically. [link]
Dravidian culture as we understand it today is not non-aryan. Infact, they appear to have developed together. So, the idea of Dravidians as a group distinct from Indo-Aryans might be a flawed assumption. Also, Indo-Aryans (Steppe people) do not form a nearly as big portion of the Indian ancestry as we think. (In this image, Iranians are not Iranian/Anatolian people as we know them. They are pre-indus valley people that resided in that region)
presence of Brahmins amongst Dravidians today, like Iyers, Iyengars, Madhvas, etc?
Does that mean we are all genetically the same and that the difference in melanin is purely for show ? No. It is a matter of proportions. At one level, you may say we're splitting hairs, IE. The different Indian sub-groups are far far more similar to each other than any other non-Indian group. At the same time, the lines that divide these subgroups are discernable in a way that is not true in more integrated nations.
We know that Tamil Brahmins are genetically closer to UP Brahmins than their fellow Tamilians.
If you disregard Razib's non-historian like tone, he parses the scientific literature pretty directly to conclude :
But how do they relate to other South Indians and other Brahmins? This is a question that is politically fraught. I really don’t care though, because I’m not Indian, and even if I was, I still wouldn’t care. I don’t have Zack’s data set, but I do have three Tamil Brahmin genotypes. You can see them on the PCA plot above. The North Indian data set is all Punjabi, while the South Indians are a mix of non-Brahmin Tamils and Telugus, from the 1000 Genomes. The rest is from the Estonian Biocentre data. The results are clear, you can see that Tamil Brahmins are strongly shifted toward the North Indian cluster but in comparison to Uttar Pradesh Brahmins they are South Indian skewed. The most parsimonious explanation taking into account their generally agreed upon communal history of migration from northern India is that they are predominantly a northern origin caste with some admixture from the local substrate. This seems entirely reasonable with how we know demographic processes work.
Your exact question was the most upvoted question asked to him in his AMA last year and he answered in his trademark rude-curt style. So, I'll directly quote that,
Q : Hey Razib, firstly I'd like to thank you for taking time out and doing this. I've three questions. 1) Could you shed some light on Tamil Brahmin (Iyer) genetics? 2) What are the communities they're similar and dissimilar to ? 3) Is there a specific migration that happened to the south that actually put them there?
A : they look 75% up brahmin and 25% generic tamil. mostly mtdna is native. brahmins in 4 southern states look similar
Q : That hints toward migration from the north and mixing to some extent with local populace, correct? Also mtDNA is passed down only by the mothers right? I've little to no understanding in genetics, so just trying to clarify and see if I'm understanding everything properly.
A : i think they migrated from the north and married local women. since 75% is northern perhaps several waves of men. they took local wives. the half-brahmin daughters of the 1st wave perhaps married the full-brahmin 2nd wave migrants. you get 3/4 northern ppl. iyers are all pretty similar genetically.
Q : Makes sense. Would the same apply for the Kerala sect of Iyers as well? The caste history dictates they migrated to Kerala a few centuries ago, but have mostly remained an endogamous group, retaining their Tamil identity and culture.
A : an iyer is an iyer is an iyer
Paywalled primary & secondary sources.
[2] The stark truth about Aryans P1, P2
[3] Reich Lab @ Harvard - Reconstructing Indian population history
