If we are too look at this from a scientific perspective it is mainly via our Y-Chromosome by which we claim our Brahmin lineage. Our community so as to speak is rather patriarchal, thus for us it is our y-dna that is of utmost importance and not our mt-DNA, which is arguablly of a local origin. We can safely say our existence is based on our Y-DNA. It is general knowledge that the first wave of Brahmins took local females as their wives. Local females sought Brahmin males as their husbands, what we could call 'upwardly mobile'. However, it was never the other way around. Thus most Brahmins claim their 'Aryan' lineage from their paternal side and any intermixing with the locals is strictly maternal. I did a search for something related and this is apparently the I&I 21 ydna composition. If anyone can further explain what this exactly means that'd be great. What I can make of it now, is that R1a and J2 Y-DNA are the strongest markers for I&I and Brahmins in general as far as paternal lineage goes.
I&I 21 Y-DNA haplogroup compositon ~ Iyer: (J2a, R1a1, R1a1, L1, L1, R2, J2b2, L1, H1, R1a1, G2, R*, L1, R2, L1, J2a, R1a1, R1a1, R2, G2, C5, J2a, G2, R1a1, H, R1a1, C5, J2a, R1a1) Iyengar: (R1a1, R1a1, R2, R1a1, R2, R1a1, H1, J2a1e, H1, R1a1, R2, R1a1, R1a1, J2a, G2, L1, R1a1, L1, J2a, J2b2, L1, J2a, R1a1, G2, H1, G2, J2a, L1, L1, G2). _______________ Iyer: (Dravidian speaking Brahmin) 2/29 = 6.9% C5-M356 3/29 = 10.3% G2a-P15 1/29 = 3.4% H-M69 1/29 = 3.4% H1-M52 4/29 = 13.8% J2a-M410 1/29 = 3.4% J2b2-M241 5/29 = 17.2% L1-M76 1/29 = 3.4% R*-M207 8/29 = 27.6% R1a1a-M17 3/29 = 10.3% R2-M124 Iyengar: (Dravidian speaking Brahmin) 4/30 = 13.3% G2a-P15 3/30 = 10.0% H1-M52 4/30 = 13.3% J2a-M410 1/30 = 3.3% J2a1d-M158 1/30 = 3.3% J2b2-M241 5/30 = 16.7% L1-M76 9/30 = 30.0% R1a1a-M17 3/30 = 10.0% R2-M124 ________________ Sengupta et al Y-DNA haplogroup frequency among Southern castes. I think 'middle castes' must refer to Vaishyas and socially dominant Shudras, but really there is no middle caste as per the sacred texts as there is only dwija/twice born.