Evrim Yazgin
Cosmos science journalist
The genome extracted from a 2,300-year-old skeleton has helped map out ancient immigration to the Japanese archipelago.
Japan has been inhabited by people since about 35,000 years ago. Roughly 16,500 years ago a group of Neolithic hunter-gatherers, referred to as the “Jomon” culture, developed a complex society including the production of pottery and jewellery.
About 3,000 years ago, rice cultivation in paddy fields was introduced to Japan. This saw the beginning of the Yayoi period which ended around the year 300 CE. After the Yayoi came the Kofun period (300–538 CE).
The new research, published in the Journal of Human Genetics, sought to understand the population dynamics behind this shift.
“There were various hypotheses to explain the history of the Japanese,” the authors write.
“For example, the ‘transformation model’ posits that only culture, not people, came from the continent. The ‘replacement model’ suggests a complete replacement of indigenous Jomon people by the Yayoi people, while the ‘hybridization model’ proposes admixture between indigenous Jomon people and continental immigrants.”
The authors note that the current consensus based on DNA evidence from modern Japanese people is that there was 2 or 3-way mixing between the indigenous Jomon people and 1 or 2 other sources of immigration to the archipelago during the Yayoi and Kofun periods.
“East Asian-related and Northeast Asian-related ancestries account for over 80% of nuclear genomes of the modern Japanese population,” explains principal investigator of the new study Jun Ohashi from the University of Tokyo. “However, how the Japanese population acquired these genetic ancestries – that is, the origins of the immigration – is not fully understood.”
Ohashi’s team analysed the complete nuclear genome of an individual dug up at a Yayoi period cemetery in the Doigahama archaeological site. The site is on the far southwest of Japan’s main island Honshu, about 800km from Tokyo.
The genome was compared with those of modern and ancient populations in other parts of East and Northeast Asia.
Researchers found close similarity between the Yayoi individual and Kofun individuals who have distinct Jomon, East Asian and Northeast Asian ancestries.
Among modern populations, the Yayoi genome most closely resembled – apart from modern Japanese people – Korean populations.
“Our results suggest that between the Yayoi and Kofun periods, the majority of immigrants to the Japanese Archipelago originated primarily from the Korean Peninsula,” says Ohashi.
“The results also mean the 3-way admixture model, which posits that a Northeast Asian group migrated to the Japanese Archipelago during the Yayoi period and an East Asian group during the Kofun period, is incorrect.
“Since our study has identified the primary origins of the immigrants, our next goal is to examine the genomes of more Yayoi individuals to clarify why more than 80% of the genomic components of the modern Japanese population are derived from immigration and how the admixture between continental Asian and indigenous Jomon people progressed within the Japanese Archipelago.”
