Southeast Asians are far more diverse than previously thought, according to new research done by experts examining the ancient origins of man in this region.

The latest study reveals that modern-day Southeast Asians are the direct descendants of at least four prehistoric populations that mingled with one another from the Late Stone Age to the Iron Age.

The findings tie up a significant loose thread in the debate on the origins of Southeast Asians that has been raging on for at least a hundred years.

Ancient DNA Analysis In Southeast Asia

Southeast Asia is one of the most under-represented regions in the field of ancient DNA. The tropical region is characterized by a hot and humid climate, which makes DNA preservation and extraction a challenge for experts.

In new research published in the journal Science, a team of international scientists has finally collected enough samples gathered from a variety of places in the region to conduct a thorough analysis of ancient DNA found in the area.

The analysis shows there were two waves of mingling between ancient populations. The first wave came 4,500 years ago when the Hoabinhians, a hunter-gatherer society characterized by their special stone tools, mingled with the rice farmers coming from China.

The second wave took place during the Bronze Age when migrants from China and areas further up north settled in Vietnam and other parts of Southeast Asia.

Previous Theories Debunked

The results of the study turn the tables on the two most popular theories on the origins of Southeast Asians. The first theory proposes that present-day Southeast Asians are descendants of the Hoabinhians, who appeared in the region sometime 44,000 years ago.

The Hoabinhians are defined by their use of the sumatralith, a broad, flat, and long stone tool carved from river stones. Proponents of this theory say the Hoabinhians developed the agricultural methods without input from outsiders.

Contrary to the first theory, the second theory suggests that rice farmers from Eastern China supplanted the Hoabinhians and introduced agriculture in the region 4,500 years ago.

"We have shown that neither interpretation fits the complexity of Southeast Asian history," says Hugh McColl, a Ph.D. researcher at the Natural History Museum of Denmark's Centre for GeoGenetics at the University of Copenhagen. "Both Hoabinhian hunter-gatherers and East Asian farmers contributed to current Southeast Asian diversity, with further migrations affecting islands in South East Asia and Vietnam."

Samples Gathered From Various Places

The researchers studied the DNA of a wide variety of human fossils unearthed in Indonesia, Laos, Malaysia, the Philippines, Thailand, and Vietnam. The oldest of these dates as far back as 8,000 years ago.

Most of the samples are part of The Duckworth Collection at the University of Cambridge. This is one of the biggest repositories of ancient human remains in the world. The researchers also analyzed DNA extracted from Hoabinhian fossils and DNA from the remains of a Jomon man found in Japan.

All in all, the researchers sequenced a total of 26 human genomes. These were later compared with DNA samples from modern-day Southeast Asians from throughout the region.

"We put a huge amount of effort into retrieving ancient DNA from tropical Southeast Asia that could shed new light on this area of rich human genetics," says lead author Eske Williams of the University of Cambridge, University of Copenhagen, and St. John's College. "The fact that we were able to obtain 26 human genomes and shed light on the incredible genetic richness of the groups in the region today is astonishing."

First Whole-Genome Analysis Of Southeast Asian Ancestor

The findings are consistent with earlier research done by a separate group of scientists from the Harvard Medical School and the University of Vienna.

In May 2018, the researchers completed the first successful genome sequencing of ancient DNA obtained in Southeast Asia. By analyzing the DNA of 18 ancient human remains as old as 4,100 years, they concluded that ancient peoples populated Southeast Asia in three waves.

The first wave began when a hunter-gatherer population arrived 45,000 years ago, around the same time as the appearance of the Hoabinhians. This was followed by a second wave 4,500 years ago composed of Chinese farmers that drifted to the region and mixed with the hunter-gatherers of the Neolithic period.

The third wave came some 3,000 years ago during the Bronze Age. This was characterized by populations from China speaking in different languages settling in Myanmar, Vietnam, and Thailand.

The researchers say large portions of the modern-day populations in Malaysia, the Philippines, Thailand, and the Andaman Islands came directly from the ancient foraging populations. In contrast, Europeans trace only a very small portion of their ancestry to the hunter-gatherers.

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