Wednesday, April 1, 2009
In the second post of this mini-series, I suggested to do some fine tuning experiments in regard with my Y-DNA timeline analysis, by comparing the general graph (which shows pattern and proportions) with actual climatic data.
I have done some of it, mirroring the glaciar climatic data in order to make it fit with the left to right orientation of my graph, and stretching it at different escales until it fit as well as I could figure with the apparent demic expansions' pattern.
The result is as follows:
I am pretty much satisfied with this result but I welcome alternative proposals if you think you can find something better. Just in case I tried to find other possible fittings between the two graphs and the best I could come up with was this:
Unlike in the previous case this alternative does not satisfy me, nor I think it will anybody else. Even if the oldest dates could fit better with some usual assumptions (OOA at 80-70 kya, main Eurasian expansions at 60-40 ka), it makes the "recent past" final line to be way too distant from the present, well in the Magdalenian period and in the middle of a cold phase. There are many other inconsistencies that suggest that this "short chronology" version is wrong.
But feel free to experiment yourself: maybe you can come up with some improved chronology that I have missed.
So I am sticking to the first graph, which I am pretty much satisfied with. What revised conclusions can we come up with?
1. The Y-DNA root and the OOA (CF split) epysode are close in time. It suggests that the whole process of Y-DNA diversification at high levels happened in an expansive phase that culminated in the OOA. It fits well with a climatic high and also with archaeological data, recently ratified with the datation of North African Aterian to c. 95,000 BP. It suggests that the OOA route was not via southern Arabia but via the Fertile Crescent instead, where the oldest Eurasian AMH fossils are found.
2. The DE split (OOA chapter 2) is the only anomalous reference point, as it is in a climatic low. Nevertheless this may well be due to the normal margin of error in the estimate and could have happened in the previous or subsequent climatic highs perfectly.
3. The F-K (or F-IJK-K-NOP) supernode (first expansion) is in the 80-70,000 BP window. It may have got the Toba epysode in between (sharp valley between two climatic peaks) or right after it (much larger and also deep climatic low). Whatever the case, it fits well with the evidence of South Asian cultural continuity at Jawalpura under and over the Toba ash layer.
Of some interest is that the first and second nodes in this supernode show divisions with West Eurasian exclusive subclades, as are G adn IJ, as well as South Asian only (H). It suggests that "the F clan" was estabilished between West and South Asia at the time.
A parallel expansion is that of macrohaplogroup D, which shows an East Asian distribution nowadays (from Andaman to Siberia). It is possible that D lineages represent, in the Y-DNA, the oldest Eastern Eurasian signature.
In Africa, haplogroup B seems also to have expanded in this window.
4. The second expansion corresponds to a better accepted period: that between 60 and 50,000 BP for the Eurasian expansion.
The expansion of macrohaplogroup C may have happened then (though there is great uncertainty, because this clade is not sufficiently well studied). A possible center for this haplogroup could have been SE Asia, though South Asia is also a possibility.
Other splits happening in this phase are (seemingly) those of H, IJ, NO and P (Q and R). It clearly seems an already regionalized expansion in South Asia, West Asia, East Asia and Central/South Asia respectively. Some time before, Melanesian clade M expanded too, what surely means that people were already thriving in New Guinea at that time.
In Africa, haplogroup E also began its early expansion at this time.
5. Another moment of particular interest is c. 41,000 BP, where the graph places the split between I2a and I2b, as well as of J1 and J2. This is so strictly coincident with Aurignacian expansion that I can't but take it as proof that the graph is well calibrated (as this was not taken in account initially at all). Further division of these clades happened closer to the Gravettian timeline, what makes me wonder if some J2 subclades, rare in West Asia but common in Europe and South Asia, are not pre-Neolithic signature as well.
Other clades expanding in this period (roughly 45-30,000 BP) are C2 (Melanesia), G (West Eurasia), N (East and North Eurasia), O (East and SE Asia), Q (South, Central and North Asia), R (South, Central and West Eurasia) and S (Australia).
In Africa, it is also the time of expansion of E1b1 and E1b1b (but not yet of E1b1a), as well as that of E2 (but not yet of E1a).
6. The last mark in cyan color in the graph is for the formation of the West European R1b1b2a1, dated to some 19,000 years ago. It really makes it look like a Solutrean or Magdalenian founder effect. A matter that surprises me but that I am going to research as much as I can, looking for possible precursors of either of these cultures in West Asia, where R1b coalesced almost without doubt since some 30-28,000 years ago. This date for R1b as a whole is nevertheless most intriguing, as it is oddly coincident with Gravettian expansion. I can only scratch my head at the moment, as the structure of R1b is only relatively well understood with many blanks in our knowledge of non-European (and even European) subclades.
The formation of the (rather rare) R1b1b1a subhaplogroups would still fall within a late Magdalenian (or early post-Magdalenian at most) time frame.
Other expansions at this "late" moment are those of E1a and E1b1a (Africa), C1 (Japan), L (South and Central Asia), T (West Eurasia), and probably R1a1 towards the easternmost edge of Europe.
7. The "recent past" final line of (relative) stability is dated to some 9,000 years ago, in the Epipaleolithic or early Neolithic (depending on the region). This may seem a little early to some but it's what the excercise of fine tuning has produced on its own. It does anyhow fit with a climatic high, what makes sense.
That's all, folks.
Previous post of the Y-DNA timeline series: 1, 2, 3.
Related R1b structure post.
MtDNA miniseries: 1, 2, 3.