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The Wikipedia entry for Y-chromosome haplogroup T claims:

“The distribution of haplogroup T in most parts of Europe is spotty or regionalized”. As it is through much of the rest of the world.

http://en.wikipedia.org/wiki/Haplogroup_T_(Y-DNA)

However from the map at Wiki we can see that Y-hap T is largely distributed along coastlines and up major river systems.

Y Hap T wiki

Haplogroup T
Time of origin 25,000-30,000 years BP
Place of origin Asia[1]
Ancestor K
Defining mutations USP9Y+3178=M184, M70, M193, M272
Highest frequencies Saccensi/Sicilians, Fulbe, Eivissencs, Stilfser/Tyroleans, Xibe, Egyptians, Gaditanos

I realise it’s risky to draw conclusions about ancient migrations from modern haplogroup distribution, but I believe that if we consider the possibility that Y-hap T was originally associated with some sort of a boating expansion we are easily able to explain the spotty distribution.

Perhaps we should start at the ‘beginning’ and examine the (doubtful) possibility that T, and boating, originated in Africa. So we’ll first visit the ‘easily crossed’ Bab al Mandab.

Y-hap T is well established to the south, on the African side. For some reason it was able to spread easily through the whole Horn, and even into the Ethiopian Highlands, probably by moving up the rivers flowing down from them. And perhaps then on down the Nile. Note that Y-hap T is not found through the Red Sea though. This suggests that the Bab al Mandab is not so easily crossed, or entered, after all. And T is virtually absent from the ‘inviting’ Yemeni coastline, for some reason or other. It’s not until we reach the actually much more benign Oman coast that we find T well established again. So T probably crossed the Gulf of Aden east of the Bab al Mandab. Is T, as well as Y-hap J, found on Socotra?

Y-hap T makes a substantial contribution to populations right around both the Gulf of Oman and the Persian Gulf. And way upstream through Mesopotamia, the region that later developed into a major urban culture. This later development was probably related to Eurologist’s comment at Dienekes blog about transporting commodities efficiently: “Another big problem with large-scale shepherding is the transport of final products and exchange for foodstuff like cereals”.

http://dienekes.blogspot.com/2010/01/migrants-introduced-farming-to-britain.html

Anyway the urban culture that developed in Mesopotamia was based on controlling the water that flowed through the region from the Anatolian highlands. So the place was wet. Ideal for boats.

In keeping with the boating connection there is, naturally, a hiatus between the Mesopotamian and Mediterranean Y-hap Ts. We would expect a boat-adapted population to find little of interest as they crossed what has become known as ‘the Fertile Crescent’. However the technology would be easily transported to the Mediterranean without necessarily transporting the actual boats. And Y-hap T and the technology could have entered the Mediterranean from the Nile. Or from both places. Technological hybrid vigour? A similar hiatus in Y-hap T’s distribution also occurs to the north, between Mesopotamia and the Caspian Sea. But a similar explanation suffices, as it does for the more distant T around lakes in Central Asia.

So Y-hap T entered the Mediterranean. It’s found in Crete and Greece, which makes sense. The islands through the Aegean would have been chickenfeed for any substantial boating technology. T also entered the Adriatic, but didn’t establish a foothold in the Dalmatian islands. Perhaps they were already occupied? T got a better reception across the Adriatic in Italy. Y-hap T and boating also set up home on the Tunisian coast, around the Ebro and on many Mediterranean islands, ultimately reaching the Atlantic coast of Spain/Portugal.

But did Y-hap T originate in Africa? I doubt it. It’s also found in India. As is its closest relation L. This particular haplogroup is spread along the Indus valley as well as south right along the west coast:

http://en.wikipedia.org/wiki/Haplogroup_L_(Y-DNA)

Hap group L

Haplogroup L
Time of origin 25,000-30,000 years BP
Place of origin South Asia[1]
Ancestor K
Defining mutations M20
Highest frequencies Indians, Pakistanis

But we find another Y-hap T hiatus along the ‘easily navigated’ Makran coast. T reappears in the Indus Delta and a little way down the west coast of India from there. But T’s distribution in India looks much more likely to be the product of a first arrival on the east coast and subsequent movement up the rivers flowing into the Bay of Bengal.

What is the possibility that L and T originate even further east? Y-haps N/O and P have become so widespread it’s possible to come up with almost any theory concerning their place of origin. But among L and T’s other close relations are S and M. Found in New Guinea, Melanesia and Australia, a region we know people must have reached using boats of some sort a very long time ago.

So we have evidence for a southern coastal migration. But not from Africa. The migration is into that continent. The fact that Y-hap T, along with L to some extent, appears to have effortlessly established itself in all the desirable coastal and riverine ecosystems along the southern Eurasian margin suggests that this habitat was actually unoccupied until T’s expansion. And that argues against any other more ancient great southern coastal migration.

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