In the varNa system all knowledge providers to society are brahmins. Every scientist, researcher, technologist, teacher are all brahmins only.
In the jAti system, those who do veda raksanam are brahmana jAti. The sole aim and purpose of brahmana jAti was veda raksanam. Veda raksanam is reading, reciting all vedic scriptures by memory, transmission to next generation and along with it provide mental work to society for society's progress. It's like they do 90% veda raksanam, but since society takes care of them provide knowledge services to society for 10% of their time.
Even in the pre-sangam era, ancient tamil kings had fascination for vedic culture, its knowledge and customs and hence brought in these brahmins from all over, settling them locally in different regions of the land.
Chozhiyars (brought in by the very ancient cholas as they were the ones in touch with North due to their kingdom proximity) came in probably in the pre-sangam era and interbred with local population and were called the 'anthanars' or 'vediyars'. Their influence spread across all 3 tamil kingdoms of chera, chola, pandiyas.
But with kalabhra's invasion, for several centuries, they lost the support of kings and were marginalized or annihilated. Buddhism and jainism were the favorite dharma for the kings.
With the bhakti movement of Nayanmars, Alwars, vedic culture got back its feet in the south and Sankara took it to North also. Vedic culture started influencing the kings again.
When the cholas came back winning over kalabhras, they brought in the brhatcharanams, the 'large-footed' brahmins from the North and settled in their kingdom, to help them with warfare knowledge of the North, primarily. Warfare knowledge involved weapons, army formations, astronomy, astrology, reading natural signs etc.
Much later on a set of brahmins from the North were settled for music during the Pandya times and they were called vaathimas.
Much later on during the later cholas period (who were essentially the chalukyas as rajendra chola adopted paternal grandson) , telugu brahmins from tungabhadra were settled all over chola empire to guide on agricultural practices. They were the vadamas.
Similarly all Southern kings, be it chalukyas, hoysalas, rashtrakutas, all of them settled brahmins from North in their kingdoms (like the chola, chera, pandyas).
Wherever these southern brahmins went they had some service to society, but their core aim and purpose in life was veda raksanam.
When the Islamic kings came in, the first to reach out to them for patronage were the Southern Brahmins Madhvacharya went to Jalaludin khilji and proclaimed allah and vishnu are same (as in the Madhva vijayam).
Because southern brahmins primary aim and purpose is veda raksanam, they simply allied with whoever was ruling, got their support and propagated vedic scriptures to their descendants.
It was easy to do veda raksanam with big aristocracies than to do with small kings and hence they favored such big aristocracies.
Veda raksanam is a non-productive work for the society and needed society's support. Brahmins used temples for survival. They minimized their living needs by unjaviruthi. Thus they minimized their support for society and provide more energy for veda raksanam, which was a huge task by itself.
But as Indian kingdoms splintered, a lot of southern brahmins moved away from veda raksanam for life sustenance. With big aristocracies, if 20% of brahmins spent on other services to society and 80% were in veda raksanam, this inverted with splintered kingdoms. Now 20% were only in veda raksanam.
When Dutch, Portugese or the British came, the first ones to ally with them were Southern Brahmins. They had no qualms in absorbing or digesting some elements of their beliefs and practices, as long as they were able to dedicate some part of their community energy for veda raksanam. But by this time, the percentage of southern brahmins doing veda raksanam had significantly declined to say 10%.
The primary reason for southern brahmins not to cross the ocean was that they will fail to do veda raksanam in foreign lands, But since foreign forces, thoughts and knowledge took over our society by storm, it's like they crossed the ocean, even while residing in their own land. With industrial, technological revolution and more integration of the world, the percentage of southern brahmins involved in veda raksanam has fallen down to low single digits now.
Ofcourse significant number of southern brahmins are still knowledge providers or follow the varNa. Except very few, all the southern brahmins do not belong the brahmana jAti as we don't do veda raksanam.
Even most vaathiyaars (many of them have not attended full-fledged veda patasalas) today don't do veda raksanam, as their primary aim to survive by their laugiga prayogams. Even there due to paucity of time, vaathiyaars and knowledge, many samskaras have reduced to an abridge version, a namesake formality.
So the brahmin community has been in cross-roads for last few centuries. Will veda raksanam eventually move out from human memory transmission to machine recorders..? Will even the laugiga prayogams come down and down and eventually lose it all completely..?
Southern brahmins (and all brahmins in general) had a flair for knowledge because they were reading, reciting and researching (mental work). This is the genetic, social environmental advantage they passed on. With all communities reading, reciting, researching, this differentiation no longer exists. So there's no long term genetic differentiation as proclaimed.
So what does this southern brahmin jAti has with it, to differentiate itself or stand separately, say in 50 or 100 years from now..?
Nothing.
In fact it's time now that the brahmin jAti expands by bringing in all kinds of people into their fold for veda raksanam, by bringing in people of all castes into veda patasalas at an early age, by devising great financial support for veda raksanam.
Without veda raksanam, there is no brahmin jAti.
