This review of Eurasian mtDNA is triggered by some rather interesting debate in this other thread. Not really unexpectedly, the structure of the scatter of mtDNA N is being questioned by an habitual reader, who seems to prefer (without any evidence I know of) a "northern route" for the migration of this haplogroup.
Here I just visually depict the main patterns of earliest scatter of the three pan-Eurasian mtDNA macro-haplogroups: M and N, both directly derived from African L3, and R, derived from N.For that I use exclusively those basal sublineages of these three macro-haplogroups which are one control region (CR) mutation downstream of the main node. Why? For simplicity and because these sublineages are the ones that show, most likely, the earliest sub-expansions of each of the three macro-haplogroups.
Also, if you look at the other sub-lineages, you do not see strong deviations from the general pattern described here and, when that happens, it can and must be attributed to peculiar histories at the stem of those sub-haplogroups. This is for instance case of mtDNA A, a basal sub-lineage of N, which expanded in NE Asia but that shows a rather long stem with 6 CR mutations, indicating a lengthy "invisible" history of its own between the N expansion and that of A.
However I must emphasize that, in spite of the similitude in their spread patterns it is rather likely that the three patterns of diffusion were not simultaneous. At least seen from the viewpoint of the shared ancestral L3 node (East Africa), M is only detached by 3 CR mutations, while N counts 5 and R 6 (the five of N plus one of its own). This is at least suggestive of successive rather than strictly simultaneous process but we cannot totally exclude that the three expansions were more or less simultaneous (or separated only by short periods) because the so-called "molecular clock" is not actually bound to tick with strict regularity but actually has some strong uncertainty.
For the source of the information used to build these maps (ultimately from the reference mtDNA site: PhyloTree), see Leherensuge: Reconstruction of mtDNA spread in Eurasia (again), which shows also a possible time structured sequence based on a hypothetical strict ticking of the "molecular clock" and also those haplogroups derived from M, N and R at longer CR mutation counts (presumably later in time).
What I find most interesting in these three maps is the similitude of the main pattern for all three macro-lineages from NW South Asia to New Guinea, via SE Asia.
The differences are as follows:
- M shows a clear distinct early trend northwards along the East Asian coast, which probably also carried the ancestors of mtDNA A.
- Instead R shows an early trend westwards, which is probably quite more recent than the M expansion, and does include, once you look at more derived sub-lineages (not shown here), three other N subclades (N1, X and W), two other R subclades (U and JT, the one shown is R0), and at least one M subclade (M1). The fact that all these Western lineages are rather derived, also suggests a later time-frame for the expansion of R, some time (10-20,000 years?) after that of M.
It is interesting also that N(xR) shows no scatter peculiarity of its own, in spite of having left a notable legacy. It is also interesting to see that all three macro-haplogroups left an early mark in Melanesia, what suggests that they did indeed have some decent boating skills from early on, and is indeed supportive of the "rapid coastal migration" hypothesis, regardless of whether this model is not needed to explain some other aspects of the Eurasian spread.