See first two paras in wikipedia https://en.wikipedia.org/wiki/Caste_system_in_India

Excerpt:

The British Raj furthered this development, making rigid caste organisation a central mechanism of administration. Between 1860 and 1920, the British formulated the caste system into their system of governance, granting administrative jobs and senior appointments only to Christians and people belonging to certain castes.

The word does not exist in any Indian language.

To justify the "pre-date", proponents combine highly distorted theory of jatti and varna to artificially synthesize Indian caste system.

The connection of caste with Europe is much more solid and meaningful given the monopoly of church over God and the king as the representative of God.

That's pretty broad conclusions for Razib Khan to be drawing from scant (and biased) data. (The population of Indians in the United States in a non-random sampling of the Indian genome, especially since our immigration policy is largely selected on the basis on already having family networks based in the US. I would expect to see a lot more clustering than in an Indian sampling).

This is a better and more holistic description. I'd quibble withs some aspects of its framing but it's mostly nitpicks. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3514343/

The gist of it is that there are a lot of discrete, endogamous subgroups within India formed by successive waves of migration by different groups to where they are functionally distinct ethnic populations. So it wouldn't be all that different from racial differences in a plural society like the United States. What's remarkable is the maintenance of this plurality, as well as in-group social norms, over a very long span of time rather than it becoming a genetic melting pot as we might have expected from experiences with Europe. But even there you still have distinct groups with strong endogamy norms (e.g. Ashkenazi Jews).

There's also additional complexity because in many places there isn't just a norm of endogamy, but consanguinity (cousin-marriage). Which is certainly going to make groups look more endogamous even though it would lead us to draw subtly different conclusions about what that means in terms of historic cultural norms.

TL;DR it's a really complicated matter that doesn't lend itself to summarization into a single, clean, generalizable narrative.

The person you’re replying to has a history of denying known issues with Indian society and blaming the britishers and/or Islamic invaders like the Mughals for all of India’s issues. I tangled with them not so long ago. Wasn’t worth the effort, imho.

I think vedic period had "varna" which is different from "jati" or castes of today.

Vedic scriptures is very clear (rig veda) and prohibits any move. Even "Richard Stallman" (RMS) understands this https://stallman.org/articles/ramayana.html which native indian people act like they don't understand. I can site recent and better example that happened in TamilNadu (https://www.indiatoday.in/india/story/tamil-nadu-dmk-temples...). 120 or so priests were appointed who were not from priest families. This is not allowed by the vedas(the hindu book). It is because government intervened and fought against the temples decisions. There is some progressive things happening in these states. Thanks to Periyar.