If one goes by the AIT (or, if you prefer to be more politically correct, AMT), caste stratification developed quite early after waves of Aryan settlers came to northwestern India.
There's little evidence for either of those statements.
Au contraire, there is plenty of evidence. All you have to do is travel all throughout India by train and keep clicking pictures of people on the crowded railway stations. The sample size will be at least one million, if you happen to travel by trains that stop at many places. If the massive genetic diversity of India is not evidence enough, then no evidence will be enough. One can point out, but one cannot force one to acknowledge what one sees with his own eyes.
Caste stratification seems to have become especially rigid starting in the Gupta period. As for the "Aryan invasion", the actual number of foreigners to arrive in India in the 2nd millennium B.C.E. was probably quite small. So small, that it had hardly any impact on Indian demographics of the time.
There is no evidence to prove that migration was in small numbers. The current genetic stock of Indians indicates towards quite the opposite, i.e. an eclectic influx in large numbers.
The main consequence of the "Aryan invasion" was not a massive influx of new genes (for which there is little evidence), but the spread of a new language and culture across North India by Aryanized Indian (probably mostly Harappan) settlers.
Again, as I have already said, and as
@Known_Unknown has given pictures, there is more evidence to support the Aryan Migration/Invasion Theory than to support this Indigenous Stock Theory.
Secondly, please define what you mean by Harappan Settlers.
For similar cases in other parts of the world, see the Germanization of post-Roman Britain and the Indianization of Southeast Asia. The actual numbers of Germans (Anglo-Saxon) and Indians to arrive in Britain and SE Asia was probably quite small, but their cultural impact was huge relative to their size, mainly because large numbers of natives (Celtic Britons and Austro-Asiatic SE Asians) adopted the foreign culture.
I have something to share about what exactly happened when the Anglo-Saxons migrated to what today would be the "land of the Angels," i.e. England.
Migration of the Germanic speaking people
When Britain gained "independence" from Rome in the year 410ce, the Roman legions withdrew leaving the country vulnerable to invaders. Soon after the withdrawal of Roman troops, inhabitants from the north began attacking the Britons. In response to these attacks, individual towns sought help from the Foedarati, who were Roman mercenaries of German origin, for the defense of the northern parts of England. As the legend has been told, a man named Hengest arrived on the shores of Britain with "3 keels" of warriors in 450ce. This event is known in Latin as the "adventus Saxonum," or the coming of the Saxons. At this time, the Foedarati stopped defending Britain and began conquering the territories on the southern and eastern shores of the country. These invaders drove the Britons to the north and west. The Saxons called the native Britons, 'wealas', which meant foreigner or slave, and from this term came the modern word Welsh. Eight to ten years later many British aristocrats (Celts) and city dwellers began migrating to Brittany, an event known as the second migration.
Full Article:
Anglo-Saxon England
Please read the full article. There is a list of different tribes that got clubbed under "Germanic
speaking people." (Linguistic Anthropology)
I think something similar happened with regards to the "Aryans" and the "native" Indians.
The alternative is also quite possible - indigenous Indians, such as the sedentary civilized IVC people, were driven out by the invaders or migrants from Central Asia and/or Caucasia, who were more nomadic and aggressive.
You still haven't explained why there is a higher prevalence of fair skin and coloured eyes among Brahmins compared to lower castes.
I have.
People with such traits (fair skin, colored eyes and hair, etc.) were probably favored among certain communities, especially those of the higher castes, and endogamous marriage ensured that a fairly high concentration of these traits remained in those communities (compared to other communities).
If the mixing was fairly random (as it would be, if the early caste system is assumed to be flexible), then there would be a far higher proportion of fair skinned and blue eyed individuals among the lower castes as well.
Not really, given that there has been at least ~1,500 years of rigid social stratification to ensure disproportionate concentrations of physical attributes.
for every example you give of a lower caste individual with fair skin, I can give you 5 KoBras.
I'm sure you could, since as I already stated, there is a higher concentration of such individuals in higher castes. Though you haven't explained why there exist shudras who are lighter and taller than KoBras at all.
Apropos the emboldened part, agreed, but then, to even achieve a "high concentration of these traits" [
sic.], we would have to begin somewhere, with those very genes that reflect those traits. We cannot have a tree if there was no seed in the first place.