A Genetic Mechanism for Convergent Skin Lightening during Recent Human Evolution.

Skin lightening among Eurasians is thought to have been a convergence occurring independently in Europe and East Asia as an adaptation to high latitude environments. Among Europeans, several genes responsible for such lightening have been found, but the information available for East Asians is much more limited. Here, a genome-wide comparison between dark-skinned Africans and Austro-Asiatic speaking aborigines and light-skinned northern Han Chinese identified the pigmentation gene OCA2, showing unusually deep allelic divergence between these groups. An amino acid substitution (His615Arg) of OCA2 prevalent in most East Asian populations-but absent in Africans and Europeans-was significantly associated with skin lightening among northern Han Chinese. Further transgenic and targeted gene modification analyses of zebrafish and mouse both exhibited the phenotypic effect of the OCA2 variant manifesting decreased melanin production. These results indicate that OCA2 plays an important role in the convergent skin lightening of East Asians during recent human evolution.

Y-chromosome diversity suggests southern origin and Paleolithic backwave migration of Austro-Asiatic speakers from eastern Asia to the Indian subcontinent.

Analyses of an Asian-specific Y-chromosome lineage (O2a1-M95)--the dominant paternal lineage in Austro-Asiatic (AA) speaking populations, who are found on both sides of the Bay of Bengal--led to two competing hypothesis of this group's geographic origin and migratory routes. One hypothesis posits the origin of the AA speakers in India and an eastward dispersal to Southeast Asia, while the other places an origin in Southeast Asia with westward dispersal to India. Here, we collected samples of AA-speaking populations from mainland Southeast Asia (MSEA) and southern China, and genotyped 16 Y-STRs of 343 males who belong to the O2a1-M95 lineage. Combining our samples with previous data, we analyzed both the Y-chromosome and mtDNA diversities. We generated a comprehensive picture of the O2a1-M95 lineage in Asia. We demonstrated that the O2a1-M95 lineage originated in the southern East Asia among the Daic-speaking populations ~20-40 thousand years ago and then dispersed southward to Southeast Asia after the Last Glacial Maximum before moving westward to the Indian subcontinent. This migration resulted in the current distribution of this Y-chromosome lineage in the AA-speaking populations. Further analysis of mtDNA diversity showed a different pattern, supporting a previously proposed sex-biased admixture of the AA-speaking populations in India.

Analysis of mitochondrial genome diversity identifies new and ancient maternal lineages in Cambodian aborigines.

Cambodia harbours a variety of aboriginal (and presumably ancient) populations that have largely been ignored in studies of genetic diversity. Here we investigate the matrilineal gene pool of 1,054 Cambodians from 14 geographic populations. Using mitochondrial whole-genome sequencing, we identify eight new mitochondrial DNA haplogroups, all of which are either newly defined basal haplogroups or basal sub-branches. Most of the new basal haplogroups have very old coalescence ages, ranging from ~55,000 to ~68,000 years, suggesting that present-day Cambodian aborigines still carry ancient genetic polymorphisms in their maternal lineages, and most of the common Cambodian haplogroups probably originated locally before expanding to the surrounding areas during prehistory. Moreover, we observe a relatively close relationship between Cambodians and populations from the Indian subcontinent, supporting the earliest costal route of migration of modern humans from Africa into mainland Southeast Asia by way of the Indian subcontinent some 60,000 years ago.