SCIENCE NEWS-May 17
People who moved out of southern China cultivated big changes across ancient Southeast Asia, a new analysis of ancient human DNA finds.
Chinese rice and millet farmers spread south into a region stretching from Vietnam to Myanmar. There, they mated with local hunter-gatherers in two main pulses, first around 4,000 years ago, and again two millennia later, says a team led by Harvard Medical School geneticist Mark Lipson. Those population movements brought agriculture to the region and triggered the spread of Austroasiatic languages that are still spoken in parts of South and Southeast Asia, the scientists conclude online May 17 in Science.
Over the past 20 years, accumulating archaeological evidence has pointed to the emergence of rice farming in Southeast Asia between 4,500 and 4,000 years ago, accompanied by tools and pottery showing links to southern China. Austroasiatic languages now found from Vietnam to India contain words for rice and agriculture, suggesting that ancient arrivals from southern China spoke an Austroasiatic tongue. Questions have remained, though, about where Austroasiatic languages originated and whether knowledge about farming practices, rather than farmers themselves, spread from China into Southeast Asia.
Now, DNA from ancient Southeast Asians provides “clinching evidence” for the spread of farming via southern Chinese groups, says archaeologist Charles Higham of the University of Otago in Dunedin, New Zealand, who did not participate in the study. The new report aligns with other ancient DNA evidence of culture-changing population movements across parts of Asia starting around 5,000 years ago (SN: 11/25/17, p. 16). “Ancient human DNA is showing that prehistoric people were far more mobile and exploratory than has often been thought,” Higham says.
Lipson’s team obtained DNA from 18 human skeletons unearthed at five Southeast Asian sites dating to between around 4,100 and 1,700 years ago. These sites are located in Vietnam, Myanmar, Thailand and Cambodia.
DNA preserves poorly in such hot, humid regions. A group led by study coauthor Ron Pinhasi, an archaeologist at the University of Vienna, recently found that human DNA survives best in a skull bone surrounding inner-ear structures that has especially dense tissue. In the new study, DNA was extracted from that bone for each ancient individual.
Roughly 4,000-year-old farmers at Vietnam’s Man Bac site displayed a close genetic relationship to present-day speakers of Austroasiatic languages, especially in southern China, Lipson’s group says. About 25 to 30 percent of the Man Bac farmers’ ancestry came from hunter-gatherers, the scientists estimate, perhaps due to interbreeding of rice growers and foragers in southern China before any migrations occurred. Many populations today that speak Austroasiatic languages also display a similar genetic signature. Genetic signs of additional hunter-gatherer ancestry, probably acquired in Southeast Asia, appeared in two of eight Man Bac farmers.
At approximately 2,000-year-old sites in Vietnam and Myanmar, farmers inherited a genetic makeup that differed in some ways from that of the earlier Man Bac crowd, but still closely resembled the DNA of present-day inhabitants of southern China. A second southern Chinese migration into Southeast Asia likely led to those DNA tweaks, the researchers say.
Ancient DNA research in Asia is in the early stages, Pinhasi emphasizes. Further research will likely reveal more human population movements and genetic exchanges among various groups across Asia, he predicts.
