Ancient DNA has proved to archaeologists that the first farmers in Southeast Asia were migrants from South China.
Researchers extracted DNA from the bones of 18 human bodies found in modern-day Vietnam, Cambodia, Thailand and Myanmar to estimate when new genes started flowing into the indigenous hunter-gatherer populations of the time.
They found an influx of genes from South China coincided with the appearance of agriculture in Southeast Asia around 4,100 to 4,500 years ago, alongside pottery and tools made in the southern Chinese style.
Marc Oxenham, a bioarchaeologist at the Australian National University, is a co-author of the study, which was published in Science journal on Friday.
Oxenham said the genetic analysis gave scientists the "smoking gun" they needed to understand the human dispersal in the region.
"Whether it be piecing together the lifeways of ancient peoples through their pottery ... or exploring their deeper genealogies by way of ancient DNA, [each] provides a series of independent threads that form a greater weave of what it was like to be an ancient Southeast Asian," he said on Friday.
Southeast Asia has a rich and complex history of human occupation, stretching back 1.6 million years ago.
Modern Homo sapiens, that is, those that looked like us, showed up much later, moving in at least 70,000 years ago.
Oxenham said these hunter-gatherer colonists diversified and evolved over tens of thousands of years. "Today we still see their presence, or descendants, as Indigenous Australians, Papuans ... and so forth," he said.
Around 4,500 years ago, farming appeared, along with tools and pottery made in the style of South China populations.
To establish a definite link, Oxenham and his colleagues examined DNA harvested from human remains found at five ancient Southeast Asian sites, ranging from 4,100 to 1,700 years ago.
And when they compared the ancient South-East Asian DNA with that from surrounding areas, they found the distinct genetic signature of Southern China.
So it's likely that farmers from China slowly spread through Southeast Asia between 4,100 to 4,500 years ago, bringing their languages and agricultural, tool-making and pottery technology with them.