From the caption:
The segregation of West Eurasian, East Eurasian and South Asian mtDNA pools. Partial map of Eurasia illustrating the spatial frequency distribution of mtDNA haplogroups native to West Eurasia (panel A), South Asia (panel B) and East Eurasia (panel C). . .*
Here we see an image produced by truly ancient (ca 14 billions years old) microwave signals, emanating from every corner of the universe, based on events thought to have taken place ca 380,000 years after the Big Bang. The maps of Figure 11 are strangely analogous in that they too give an idea of the distant past by mapping evidence available in the present. Instead of the echo of distant microwave signals still detectable in space after billions of years, we have the echo of distant mutations, still detectable in our DNA after thousands of years. But the pictures are very different, in the first case relatively uniform, in the other radically disjunct. In fact the genetic maps are described as "The segregation of West Eurasian, East Eurasian and South Asian mtDNA pools."
We found that haplogroup M frequency drops abruptly from about 60% in India to about 5% in Iran, marking the western border of the haplogroup M distribution. A similarly sharp border cuts the distribution of Indian-specific mtDNA haplogroups to the east and to the north of the subcontinent. We therefore propose that the initial mtDNA pool established upon the peopling of South Asia has not been replaced but has rather been reshaped in situ by major demographic episodes in the past and garnished by relatively minor events of gene flow both from the West and the East during more recent chapters of the demographic history in the region (my emphasis).
What could this event have been? It's time to take another look at yet another map, one we've seen before:
(to be continued . . . )
*Though tribal populations constituted roughly 50% of the 2572 total sample for India (4600 samples for Asia overall were analyzed, and considerably more added for Figure 11), they are, very unfortunately, not represented on the isofrequency maps (A, B and C), for reasons explained in the "methods" section:
In relatively small and isolated groups (e.g. tribal groups) random genetic drift might seriously affect the haplogroup frequencies, which may become uninformative when a whole region (e.g. state) is considered . . . Therefore, the tribal data were excluded from the haplogroup isofrequency maps calculation. When illustrating the spread of mtDNA haplogroups native to West Eurasia, East Eurasia and India (Figure 11, panel D) we present these data as pie diagrams. The respective sample size and origin are indicated adjacent to the diagrams.The effect of the tribal data on maps A, B and C may, to some extent, be inferred from the pie charts in map D. And, indeed, the picture they present, of a major division between South and Southeast Asia, is consistent with what we see in the maps above.