tag:blogger.com,1999:blog-7785493.post3380553304978283460..comments2024-01-04T04:11:55.717+02:00Comments on Dienekes’ Anthropology Blog: Genetic traces of east-to-west human expansion waves in EurasiaDienekeshttp://www.blogger.com/profile/02082684850093948970noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-7785493.post-71304786870091267032008-03-12T15:33:00.000+02:002008-03-12T15:33:00.000+02:00OK, thanks for sending the paper. I don't follow t...OK, thanks for sending the paper. <BR/><BR/>I don't follow the authors' logic here:<BR/><BR/><I>Indeed, our data point to Central Asia as having played<BR/>first a role of receiver of genetic diversity coming from<BR/>the Far East, and subsequently, a role of starting point<BR/>of expansion waves toward western regions. Such scenario<BR/>could explain the current distribution of mtDNA<BR/>haplogroups in Eurasia, showing a clear distinction<BR/>between eastern and western haplogroups and a mixture<BR/>of these geographically-distinct haplogroups in Central<BR/>Asia (Comas et al., 1998, 2004; Quintana-Murci et al.,<BR/>2004; Derenko et al., 2007).</I><BR/><BR/>No, the "clear distinction between eastern and western haplogroups" is strong evidence <I>against</I> the scenario propounded here. There is simply no way to interpret the mtDNA phylogeographic data as supporting an east-west demic diffusion <I>starting in China</I>.<BR/><BR/>The basic idea behind the study (looking at "LIC") seems reasonable to me, at least on the surface. But I haven't reviewed in detail all the assumptions underlying it. <BR/><BR/>The results on the Y chromosome are broadly in line with the phylogeographic evidence:<BR/><BR/><I>Regarding Y chromosome data, the proportions of LIC<BR/>observed between China and western Eurasia were high<BR/>(76% and above) and such high percentages of LIC are<BR/><B>compatible with the existence of independent expansion<BR/>events in China on one hand and in western Eurasia on<BR/>the other hand</B>, although the percentage of LIC between<BR/>China and Central Asia (76%) could also correspond to<BR/>an extreme case of a diffusion of expansion through<BR/>migrations with an old divergence age between the two<BR/>regions (about 1,700 generations), a migration rate not<BR/>higher than 0.0005 and a size before expansion N0 equal<BR/>to at least 500.</I><BR/><BR/>Exactly where they go wrong on the mtDNA side, I can't immediately say. The authors themselves mentions one possible confounding factor:<BR/><BR/><I>However, given that<BR/>the two genetic systems investigated here represent only<BR/>two realizations of evolution and are both <B>putative candidates<BR/>for the action of natural selection</B> (McElreavey<BR/>et al., 2000; Mishmar et al., 2003; Bazin et al., 2006),<BR/>sequence-based data from independent noncoding regions<BR/>of the human genome would be useful to obtain a<BR/>more robust view of Eurasian demographic history.</I><BR/><BR/>Admixture may be the biggest issue, though the authors downplay the possibility:<BR/><BR/><I>This approach has been criticized for being sensitive to a<BR/>couple of phenomena: (i) the heterogeneity of mutation<BR/>rates (Aris-Brosou and Excoffier, 1996) and (ii) past<BR/><B>admixture events, which can both affect the shape of the<BR/>mismatch distributions</B>. However, there is no objective<BR/>reason why these processes should affect the eastern<BR/>and western populations differentially. Moreover, our<BR/>simulation study comforts us in the validity of our<BR/>approach, in particular since we took into account the<BR/>heterogeneity of mutations rate in these simulations,<BR/>this heterogeneity having little impact of the LIC proportions.<BR/>Finally, the high proportion of observed unimodal<BR/>mismatch distributions suggests that admixture events<BR/>between genetically differentiated populations have been<BR/>rare enough not to affect substantially the genetic landscape<BR/>of Eurasian populations.</I><BR/><BR/>In fact, both the Chinese and Central Asians are most likely products of "admixture events between genetically differentiated populations".n/ahttps://www.blogger.com/profile/02378473351485233448noreply@blogger.comtag:blogger.com,1999:blog-7785493.post-16302691499181182842008-03-10T12:54:00.000+02:002008-03-10T12:54:00.000+02:00There is ample evidence (archaeological and geneti...There is ample evidence (archaeological and genetic) of ancient expansions from Central Asia into Europe. There is none I'm aware for expansion from China (besides, some would claim, Y haplogroup N).<BR/><BR/>Did the authors completely ignore phylogeny and focus purely on diversity? That's the impression I get from the abstract and supplementary material.<BR/><BR/>I have no access to AJPA at the moment, but send me a copy of the pdf and I'll comment further.<BR/><BR/>rhenotes@gmail.comn/ahttps://www.blogger.com/profile/02378473351485233448noreply@blogger.comtag:blogger.com,1999:blog-7785493.post-23259674762563145922008-03-10T09:16:00.000+02:002008-03-10T09:16:00.000+02:00Here is a passage from the discussion section of t...Here is a passage from the discussion section of the paper.<BR/><BR/>"If we extend these results to other parts of Eurasia, which always show proportions of LIC equal to 39% or less, our mtDNA results support a scenario in which<BR/>the expansion diffused westward from the Far East (China and Mongolia) to Europe through recurrent gene flows and/or massive and sudden moves of people."arboristhttps://www.blogger.com/profile/02052958024189486731noreply@blogger.comtag:blogger.com,1999:blog-7785493.post-39742702190657045292008-03-10T07:21:00.000+02:002008-03-10T07:21:00.000+02:00No, they aren't (or at least I highly doubt it). H...No, they aren't (or at least I highly doubt it). Have you read the paper?n/ahttps://www.blogger.com/profile/02378473351485233448noreply@blogger.comtag:blogger.com,1999:blog-7785493.post-4183547789108007862008-03-10T04:08:00.000+02:002008-03-10T04:08:00.000+02:00I am surprised that this did not draw more interes...I am surprised that this did not draw more interest. They are saying that people moved from China to Central Asia and then to the Middle East and Europe.arboristhttps://www.blogger.com/profile/02052958024189486731noreply@blogger.com