Genetic analysis of an individual from the Yayoi period reveals immigration patterns from the Korean Peninsula.
Researchers at the University of Tokyo have revealed that the primary influx of immigrants to the Japanese Archipelago during the Yayoi and Kofun periods primarily originated from the Korean Peninsula. This discovery, based on genome analysis of ancient individuals, challenges previous admixture models and refines our understanding of Japanese ancestry.
Ancient Origins: Unveiling the Genetic Journey to the Japanese Archipelago
A research team led by Jonghyun Kim and Jun Ohashi from the University of Tokyo has found that during the Yayoi and Kofun periods (3000 BCE to 538 CE), the majority of immigrants to the Japanese Archipelago came from the Korean Peninsula.
Their study analyzed the complete genome of a “Yayoi” individual and found that, among the non-Japanese populations, the results showed the genetic makeup most closely resembled that of Korean populations.
Although it is widely accepted that modern Japanese populations have a dual ancestry, the discovery provides insight into the details of immigration patterns to the archipelago that had previously puzzled researchers. The findings were published today (October 14) in the Journal of Human Genetics.
Isolation and Immigration: From Jomon to Yayoi Period
Today, Japan is an international hub for both business and pleasure. However, this was not always the case. The Japanese Archipelago was relatively isolated during the Jomon period until around 3000 BCE. Then, during the Yayoi and Kofun periods, immigration to the islands from continental Asia began.
“East Asian-related and Northeast Asian-related ancestries account for over 80% of nuclear genomes of the modern Japanese population,” explains Ohashi, the principal investigator of the study. “However, how the Japanese population acquired these genetic ancestries—that is, the origins of the immigration—is not fully understood.”
Genetic Theories of Japanese Ancestry
Various theories have been proposed to explain the genetic variety in the modern population. Currently, the two contenders are the two-way and three-way admixture models. According to the two-way model, the main source of immigration was the same during the Yayoi and Kofun periods, while the three-way model assumes two different sources. To investigate which model was the better fit, the researchers analyzed the complete nuclear genome of an individual from the Doigahama Site, the archeological site of a Yayoi period cemetery in Yamaguchi prefecture, Japan.
The researchers compared the genome of this Yayoi-period individual with the genome of ancient and modern populations in East Asia and Northeast Asia. The comparison showed close similarity to Kofun period individuals with distinct Jomon-related, East Asian-related, and Northeast Asian-related ancestries. However, a comparison with modern genomes also revealed that the Yayoi individual, except for modern Japanese populations, was the closest to modern Korean populations, which also have both East Asian-related and Northeast Asian-related ancestries.
Korean Peninsula As the Primary Source of Immigration
“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 three-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.”
Future Research Into Japanese Population Genetics
Despite the significance of these findings, Ohashi is already looking ahead.
“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.”
Reference: “Genetic analysis of a Yayoi individual from the doigahama site provides insights into the origins of immigrants to the Japanese archipelago” 14 October 2024, Journal of Human Genetics.
DOI: 10.1038/s10038-024-01295-w