Couple of things that might be of interest:
1) According to this paper: http://www.krepublishers.com/02-Jou...i-S/IJHG-07-2-167-07-298-Kanthimathi-S-Tt.pdf
, the Iyers and Iyengars of Tamil Nadu were found closest to Veerakodi Vellalars. Found info on veerakudi or karkatha vellalars here: VELLALAR HISTORY
Apparently they were a community of fighters..and it does appear that the time of incoming of medieval cholas coincided with the appearance of the vellalars in the tamil country with ppl in bramanical roles, such as safeguarding things thru rituals: Karkatha-Veera kudi Vellalars
Interestingly, the Thevar sample was found closer to the people of UAE and Pakistan (as intermediaries b/w African and Sahul populations). Kallar sample (as usual) is mentioned as the oldest immigrants to the Indian landscape (of the Neolithic times) with the Mediterranean racial element.
2) According to this paper: http://www.ias.ac.in/jgenet/Vol87No2/175.pdf
, Iyers and Iyengars (esp Iyers) were found related to Bengali Brahmins, who in turn were found related to the Mahisya and Bagdi groups.
3) According to this paper: http://www.ias.ac.in/jgenet/Vol87No2/171.pdf
the Paraiyan, Chakkiliyar and Mutracha were identified as proto-australoid who might have entered Tamil Nadu 15-20K years ago. As usual again, Kallar and Vanniyar were found to display Paleo-Mediterranean and Mediterranean features and it is expected that they entered Tamil Nadu 10K years ago. The Brahmins are suggested to have entered Tamil Nadu 3000 to 5000 years ago. Perhaps it’s the case of same people but different cultures or diff community settings, at different points in time (?).
4) This is a nice recent paper that helps understand the caste-tribe conundrum: http://www.krepublishers.com/02-Jou...a-D-R/IJHG-08-1&2-021-08-323-Silva-D-R-Tt.pdf
Its understood that the current caste system is a fairly ‘recent’ phenomenon, since the ‘aryan’ speakers actually formed the ‘earlier’ caste system which is presently the tribal social and genetic structure. There are several papers, one of them being: AJHG - Polarity and Temporality of High-Resolution Y-Chromosome Distributions in India Identify Both Indigenous and Exogenous Expansions and Reveal Minor Genetic Influence of Central Asian Pastoralists
, that reinforce the point that the distinctive Y-mediated landscape was created not by the recent IE expansions but instead they were dated back, and had happened during the pre-Holocene and Holocene era.
Plus, it is also suggested that the central asian (the one considered as so-called ‘aryan’ in the present time) admixture into existing system at that time was so small, it wud be like mixing a teaspoon of salt into several gallons of water. However, what constitutes ‘central asia’ itself is of much debate, as it seems to have been made up of diff regions at diff points in time.
Everything said and done, all these are matters of subjective or academic interest. Everyone has every right to follow his own way of life.
It may well be possible that not only Iyers, but a good many so-called pucca tamilians, once lived along the gangetic plains or the narmada basin or on the other side of the cauvery. Central india esp is home to very old human dwellings, such as the bhimbetka caves.