NEW YORK – Genetically distinct populations from the northern reaches of East Asia appear to have expanded into southern Asia since the Stone Age, or Neolithic, according to a new ancient DNA analysis.
As they reported in Science on Thursday, researchers from China, Germany, and other international centers used targeted nuclear DNA capture and sequencing to assess some 1.2 million SNPs in the genomes of more than two-dozen ancient individuals going back 300 to 9,500 years from sites in northern and southern parts of East Asia. Along with previously unappreciated levels of genetic differentiation in the historical populations, their results pointed to post-Neolithic mixing between individuals moving from the northern to southern East Asia.
"Genetic differentiation was higher in the past than the present, reflecting a major episode of admixture involving northern East Asian ancestry spreading across southern East Asia after the Neolithic, transforming the genetic ancestry of southern China," senior author Qiaomei Fu, a vertebrate evolution and human origins researcher affiliated with the Chinese Academy of Sciences' Institute of Vertebrate Paleontology and Paleoanthropology and its Center for Excellence in Life and Paleoenvironment, and their colleagues wrote.
Despite the size and diversity of populations in China, Mongolia, the Korean peninsula, and the other islands that make up East Asia, the team explained, much of the genetic data that is currently available from the region comes from Han Chinese and other selected populations living in East Asia today.
Even so, the authors noted, "the archeological record highlights that East Asians may have been more diverse in the past than today."
"A craniometric study on past and present humans suggest that human history in Asia is characterized by two 'layers' of ancestry — a 'first layer' composed of pre-Neolithic hunter-gatherers with a 'second layer' of northern East Asians spreading across Asia from the Early Neolithic to the present, contributing ancestry to many East Asians today," they explained.
In an effort to explore East Asia's historical genetic diversity, the researchers looked at 26 ancient samples from Inner Mongolia and Shandong in northern China, along with Fujian, a province in southern China, and sites from two islands in the Taiwan Strait, ultimately generating informative data from 24 of the ancient samples.
The team did not find genetic evidence that lined up with the proposed 'two layer' population model when it analyzed these sequences in the context of other available data from ancient and present-day East Asians.
Instead, samples with 'first layer' cranial features appeared to cluster genetically with other East Asian samples, the investigators reported, though distinct populations turned up in northern and southern parts of East Asia during the Early Neolithic — populations that appear to have met and mixed when populations subsequently started moving south, followed by broader back and forth mixing between northern and southern populations.
"While we did not find evidence of a 'first layer' population in coastal southern East Asia by 8,400 years ago, we do observe increased northern influences in southern East Asia between the Early Neolithic and today," the authors wrote. "Thus, the argument for the spread of a 'second layer' associated with northern East Asian ancestry is still an important model to explore in the context of East Asian prehistory."