Interesting possibility. And Y-hap J* is found in Soqotra off the Arabian coast, as well as in parts of SE Asia. I’m quite convinced that open-water boating is nowhere near as old as the OoA event. In fact it seems to me it was invented somewhere in SE Asia where it made possible the human expansion across Wallace’s Line into New Guinea and Australia. Like most technologies once it had been invented it spread, and that spread carried along several haplogroups.

The Indus River Valley orientation of Y-DNA type L is also striking. If it was ancient South Asian in origin, one would expect a more uniform distribution in South Asia.

“The K is Mesopotamian in origin”

Probably not. Its greatest diversity is wat to the east, east of Wallace’s line in SE Asia, so it probably coalesced there. As to:

“perhaps its sister clade T is also Mesopotamian in origin”

Possibly. But with K in SE Asia it places T’s origin somewhere along the route there. I’m inclined to place its origin somewhere in India, or perhaps it too originated in SE Asia.

“there could be a founder effect in the Harappan society from a small founding Mesopotamian population”.

And I very much suspect that’s associated with Y-hap J, which would also support an Afro-Dravidian connection.

The distribution of T in India lines up well with the South Indian Neolithic culture associated with the early Dravidians, but overlaps very little with the Harappan range, consistent with the lack of archeological association between the two. The K is Mesopotamian in origin, perhaps its sister clade T is also Mesopotamian in origin, and the areas where it is found only thinly in Europe correspond more or less to the earliest Neolithic farming expansion (consistent with ancient DNA from the oldest very early Neolithic Basque and South Scandinavian areas). The Yemeni and Horn of Africa populations fit with long standing early trade by Sumerian/Harappan ocean trade.

So how does it wind up in the Nile River Valley with increasing frequency up the valley and a very high percentage in North Cameroon? What if a founder effect of K in the Harappans is paralleled by a similar founder effect of T in the Nile Valley.

Perhaps the men associated with T are the people who bring the Near Eastern crop package to the Nile Valley. Later influxes of people dilute it significantly in Egypt, but less so in Sudan, and even less so in Northern Cameroon, which is where you end up if you follow the White Nile to its source and hop a very low ancient mountain range to the next river basin over, and which has received only one subsequent influx (R1b – the Atlantic modal type as mostly Chadic speaking herders who are much less diluted).

Why did the T lineage (and the R1B lineage) stop at Northern Cameroon? Because E lineage farmers already filled the rest of the farming niche with non-Near Eastern crops better adapted to the area (this crop set was developed before Sumeria’s). The T people who stayed were stuck reverting to a pastoral lifestyle. But, suppose that these people had remained aware of reports of lands to the East of Harappa and realized that the Sahel crop set was a good fit for that land after some of them have adopted that kind of farming and the African language the T people of Cameroon speak now. They return to Mesopotamia via the Nile Valley (without their women) and from there by boat to Southern India where they have great success and become a large share of the Dravidian population supporting Sergent’s Afro-Dravidian hypothesis which has very strong linguistic and cultural and crop genetic support.

It does have a lot to do with the northern shore of the Mediterranean though. And there is no shortage of rivers north of the Black Sea.

“the distribution in the balkan and central europe suggests (nowhere near certainty) that it is not strongly related with transport over water since there is only little seafaring or boating in these nations”

Not much boating in the Aegean Islands? It seems the islands were not occupied until around 10,000 years ago, but once occupied they would provide easy access to the Balkans and the Black Sea.

“i would guess the northern france branch originates from austriam in the middle and late middle ages”.

I have no doubt that once established in a coastal or riverine region further expansion need not be associated with water or boating at all. However T is very much associated with the Indian Ocean coast, presumably it’s early distribution before it had got anywhere near Europe.

“have you considered a possible link of open-hulled boats (dugouts) and the salt trade”

It’s a possibility but I suspect humans themselves were the main cargo.