Over at my other weblog I put up a post, Indian Ancestry In Southeast Asia Is Older Than Statistical Genetic Tests Suggest. If you look at two populations in Southeast Asia and find one has Indian ancestry you often can’t find the admixture older than 1000 A.D. (in peninsular Malaysia there is more recent intermarriage between Muslim Indians and Malays too). This seems far too recent. My explanation is simple: these dates reflect the assimilation of a hybrid Indian-Southeast Asian population across much of Southeast Asia. I have done the analyses myself, and in Cambodia, I get dates around 1000 A.D. Cambodia is not close to India and there isn’t evidence of a large Diaspora in recorded history. But, we know that Hinduism was a major influence in the region, and the Vietnamese Cham are still predominantly Hindu.
The kingdom of Funan, known mostly from Chinese accounts, flourished in Cambodia for the first five centuries of the common era or so. There is an inscription in Sanskrit from the region dated to the 5th century A.D. that refers to the moon of the Kauṇḍinya line (… kauṇḍi[n]ya[vaṅ]śaśaśinā …) and chief “of a realm wrested from the mud”. The text is in the Grantha script.
Further west, Dvaravati also had a strong Indic influence, no later than the 5th century A.D.
The genetic results indicate on the order of 10-20% of the ancestry of people in central Thailand is broadly Indian. This is not a trivial fraction. Who were these people? How early did they come?
On a minor editorial note, I’ll observe there is lots of discussion about possible Indian gene flow to the north and west (into Iran and Turan), but the data on Southeast Asia is clear and of greater magnitude. But there is far less discussion and exploration of this.