Bioscience

Study on the Cambodian Origin of Human Migration into East Asia

Several years ago, during an earlier study on human migration patterns, Su Bing’s group from the Kunming Institute of Zoology, (CAS), found something odd—among the samples taken from some Cambodian males, there was a surprisingly high genetic diversity as compared to the surrounding populations. The most intriguing part is that after eons of settlement in the area, the modern day population of 13.4 million (96% of which belongs to the Khmer ethnic group alongside 20 minority ethnic groups that primarily live in the northeastern provinces) still primarily speaks Austro-Asiatic languages, including the dominant Khmer and nearly all the aboriginal peoples. Fortunately, Su had not abandoned the initial idea from his earlier work. Over the past year, working in cooperation with the Royal University of Phnom Penh, his team from KIZ collected 1,054 unrelated genetic samples, representing 13 aboriginal ethnic populations and one Khmer population from three provinces in northeastern Cambodia. After high-resolution mtDNA diversity analyses of the samples, Su’s group found that Cambodian aboriginal populations still carry ancient sequence polymorphisms in their maternal lineages, suggesting that Cambodia was probably located in the region where the earliest modern human settlers initially populated eastern Asia. In total, analysis yielded eight novel mtDNA lineages in Cambodians, including four basal haplogroups and four sub-branches. Subsequent dating of the mtDNA haplogroups supports the antiquity of Cambodian populations, with most of the estimated haplogroup ages exceeding 25,000 years. Of the newly defined basal haplogroups, named M59, M69, M78 and N7, the age is even more astonishing, with estimates placing them 36,000 to 68,000 years old, directly within the suggested time of the earliest human settlement in the region. The age of the maternal lineages in Cambodians also supports the idea of a Southeast Asia dispersal centre of, an idea consistent with the earlier genetic and linguistic findings that support the southern origin and early northward migrations of modern humans. On the whole, Su’s work alongside that of his predecessors makes a strong case for a new “out-of-Cambodia” expansion. Perhaps what is most significant about this work is not only its potential impact on human genetic research, but in its ability to showcase the advances that science have made in filling in the gaps in academic research by making lasting contributions to studies of culture, linguistics, human migration, demography, and history. The complete study was recently published in Nature Communications Issue 4, Article 2599 (doi: 10.1038/ncomms3599), which is also available for online reading.