View Full Version : Divergence of East Asians and Europeans

18-02-15, 20:00
I stumbled across this study, estimating the divergence of East Asians and Europeans. http://gbe.oxfordjournals.org/content/6/3/466.full
I'm posting hereafter some interesting excerpts. I highlighted the parts I found more interesting.
For the male lineages, we used the Y-STR markers for 453 individuals covering Japanese, Korean, Mongolian (Khalkh), American, and European people. We determined the evolutionary distances (RST) among them, and constructed a phylogenetic tree using the NJ method (Saitou and Nei 1987 (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-32)), as shown in figure 1 (http://gbe.oxfordjournals.org/content/6/3/466.full#F1). The Y-STR tree revealed that the male ancestral lineage contained two clades (Yap-A and Yap-B). While Yap-A clade includes the East Asian individuals only, Yap-B clade contains the East Asian and European individuals together. Surprisingly, the European males never formed an independent clade. Instead, they formed separate clades within Yap-B.
We then constructed a phylogenetic tree (Mt tree) for the 72 complete mtDNAs including the four ethnic groups, as shown in figure 2 (http://gbe.oxfordjournals.org/content/6/3/466.full#F2). We used Kimura’s two parameter method (Kimura 1980 (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-23)) for computing evolutionary distances among them and the NJ method for the tree construction. The Mt tree revealed two female descendant clades (Mt A and Mt B). Mt B consisted of the East Asian females only, while Mt A contained the East Asian and European females together. As in the case of males, the European females did not form an independent clade, but comprised several groups within the Mt A tree. As the Mt A cluster includes roughly as many European individuals as East Asian individuals, it is not clear which of them is ancestral to the other. The node marked with the blue circle in figure 2 (http://gbe.oxfordjournals.org/content/6/3/466.full#F2) suggests that the East Asians are ancestral to the Europeans. The bootstrap value of the node is 99%. Therefore, both male and female lineages suggest that Europeans diverged from within East Asian ancestors or that they interbred with East Asian individuals up to a certain divergence time.
Our next question was thus to estimate the divergence time of the European clade within the East Asian lineage, for males and females separately. To address that question, we computed the evolutionary distance (RST) between every pair of the male individuals to construct the Y-STR tree in figure 1 (http://gbe.oxfordjournals.org/content/6/3/466.full#F1). The RST value between the bottom and root of A and B clades in the tree was 16.91, while that between the bottom and root of the European male clade in the B clade was 12.31. Based on a divergence of East Asians from Africans of 55,000 years ago (Nei and Roychoudhury 1974 (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-29), 1993 (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-28)), and assuming that RST is proportional to time, we can estimate the evolutionary rate of Y-STR by using the Y-STR tree. In the tree the RST value between the deepest root and the bottom is 16.91, and that between the common ancestor of Europeans males and the bottom is 12.31. The rate is thus estimated as 16.91/55,000 = 3.07 × 10−4 per repeat per year, which leads us to the conclusion that the divergence time of the European males is ∼40,100 years ago. [...]
Both the Y-STR and mtDNA trees consistently show that Europeans diverged from East Asian ancestors ∼41,000 years ago. Population genetic theory indicates that 41,000 years, or about 2,000 generations, are long enough to accumulate SNPs in the same loci in each lineage (Kimura 1983 (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-22);Nei 1987 (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-27)) to account for the present genetic and phenotypic differences between the East Asians and Europeans, but too short to acquire independent loci between them. Recently, Liu (2012) (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-25) reported on five genes responsible for the facial morphology of European people. The East Asian people must have the counterparts that differ at the SNP level from those in the European people. As our phylogenetic trees demonstrate, the European alleles at the five loci have diverged from the ancestral East Asian alleles.
Our result contrasts with the traditional view that Europeans and East Asians simultaneously diverged from African ancestors 55,000 years ago. It is noteworthy, however, that Shinoda (2007) (http://gbe.oxfordjournals.org/content/6/3/466.full#ref-34) investigated into the haplogroups of mtDNA, and revealed a number of evolutionary haplotype lineages. The lineages include L3 (African), N (East Asian), W (European), and L3 to N to R (East Asian) and then HV (European) among others. Though they did not explain their results, their haplotype lineages can now be understood by our finding that the Europeans diverged from the East Asians.

18-02-15, 22:14
Okay, even someone like myself who knows little about the science of genetics knows that Paleolithic Europeans shared some ancestry with the people who became East Asians. But is it really accurate to refer to that common ancestry as East Asian? More like not yet differentiated, I would think.

19-02-15, 11:08
What puzzles me is that east asians should have less genetic variation than europeans. The more a population is far from the "source" (Africa), the less it bears genetic variations. So, how come we euros have more variations than our supposed source population (east asians, or more likely, their ancestors)?

20-12-18, 19:00
Cool stuff