Anthropology.net

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.

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)

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.

Dienekes, Blaine, Razib, and Simon have all chimed in introducing us to a new paper from the American Journal of Human Genetics. It seems like a really interesting one, one that takes mtDNA to construct a phylogeny used to investigate what was happening to early Homo sapiens genetic diversity and populations within Africa. This study focuses on what was going on before the migrations out of Africa. The paper is titled, “The Dawn of Human Matrilineal Diversity,” and is open access. The research has already made it all the way onto some of my favorite news sources, such as Digg and Slashdot, but the big timers like CNN, BBC, the Economist, and the AFP are also carrying word.

The researchers constructed a mitochondrial phylogeny of 624 sub-Saharan individuals. They paid close attention to what’s going on with the phylogeny of the Khoisan, because previous research like Knight et al.‘s study on another loci, the Y-chromosome has shown that the Khoisan are carriers of oldest-diverging Y haplogroup, the Y-haplogroup A, indicating they may represent the deepest clade of modern humans. Recent research identified that the pygmy Khoisan populations share an ancestral and indigenous lineage of mtDNA with a neighboring population, the Bantu and this new study confirmed this.

The phylogenetic tree in this newer study is really informative. I’ve included it to the right. The researchers honed in on the mitochondrial haplogroup L, which is one of the oldest mtDNA haplogroups out there. The tree shows that early humans split into two small groups, demarcated by the L0 branch splitting from the L1’5 branch around 140,000 years ago. Based upon these two branches, the researchers were able to identify that one group was concentrated around eastern Africa (the L1’5 branch), while the other, the Khoisan’s L0 branch, in southern Africa. The sub-branches within the L1’5 clade represent all of the other L haplotypes in the entire remainder of humanity, including haplogroups of those that left Africa… further suggesting east Africa peoples were the main migrators out of Africa.

How could this happen? As populations of early humans migrated within Africa and reached southern Africa, they were cut off from the eastern African populations for a significant period of isolation to diverge into two separate clades. From ScienceDaily,

“Recent paleoclimatological data suggests that Eastern Africa went through a series of massive droughts between 135,000-90,000 years ago. It is possible that this climatological shift contributed to the population splits.”

The press is suggesting that this phenomenon indicated humans “started down the path of evolving into two separate species.” But that’s not true, they missed the part of the paper where populations came back together as a single, pan-African population about 40,000 years ago.

But, something is a little fishy, because as I already indicated, the coalescence calculations in this new paper indicate the Khoisan matrilineal ancestry diverged from the rest of the human mtDNA pool about 140,000 years ago. At that time, the five additional, currently extant maternal lineages (Haplogroups L1’5) existed in Eastern Africa, before the emergence of L0 branch. Looking at the phylogenetic tree, these haplogroups are more ancestral to the haplogroup L0 branch by at around 40,000 years, implying that the Khoisan may not be the deepest clade of living humans alive. This doesn’t match the Y-chromosome data, but we know already that mtDNA and Y-chromosome coalescent times aren’t the same… but this doesn’t match scores of other studies that indicate the Khoisan are a basal group of humans based off of their linguistic and cultural traits.

What this ultimately indicates is that eastern Africa may have truly been the cradle of humanity, at least the maternal cradle of modern humans. Which matches the fossil record, since some of the oldest remains of early human remains are also found in Eastern Africa, such as BOU-VP-16/1 and Omo 1 from Ethiopia.

BEHAR, D., VILLEMS, R., SOODYALL, H., BLUESMITH, J., PEREIRA, L., METSPALU, E., SCOZZARI, R., MAKKAN, H., TZUR, S., COMAS, D. (2008). The Dawn of Human Matrilineal Diversity. The American Journal of Human Genetics DOI: 10.1016/j.ajhg.2008.04.002

KNIGHT, A. (2003). African Y Chromosome and mtDNA Divergence Provides Insight into the History of Click Languages. Current Biology, 13(6), 464-473. DOI: 10.1016/S0960-9822(03)00130-1

Quintana-Murci, L., Quach, H., Harmant, C., Luca, F., Massonnet, B., Patin, E., Sica, L., Mouguiama-Daouda, P., Comas, D., Tzur, S., Balanovsky, O., Kidd, K.K., Kidd, J.R., van der Veen, L., Hombert, J., Gessain, A., Verdu, P., Froment, A., Bahuchet, S., Heyer, E., Dausset, J., Salas, A., Behar, D.M. (2008). Maternal traces of deep common ancestry and asymmetric gene flow between Pygmy hunter-gatherers and Bantu-speaking farmers. Proceedings of the National Academy of Sciences, 105(5), 1596-1601. DOI: 10.1073/pnas.0711467105