A collaborative research team, headed by Jonghyun Kim and Jun Ohashi from the University of Tokyo, has uncovered that the bulk of immigration to the Japanese Archipelago during the Yayoi and Kofun periods (spanning from 3000 BCE to 538 CE) primarily originated from the Korean Peninsula. Through their analysis of an entire genome from a “Yayoi” person, the researchers found that the closest genetic matches, among non-Japanese groups, were to populations from Korea. While it’s already known that contemporary Japanese people have a mixed ancestry, this new information sheds light on specific immigration trends to the archipelago that have previously been unclear to researchers. These findings were published in the Journal of Human Genetics.
Japan today stands as a global center for commerce and tourism. However, this wasn’t always true. The Japanese Archipelago experienced considerable isolation during the Jomon period, which lasted until about 3000 BCE. It was during the subsequent Yayoi and Kofun periods that immigration from continental Asia started taking place.
“Over 80% of the nuclear genomes in the modern Japanese population are related to East Asian and Northeast Asian ancestries,” states Ohashi, the lead investigator of the study. “Yet, the exact origins of these genetic ancestries — in other words, the sources of immigration — remain poorly understood.”
Several hypotheses have been proposed to clarify the genetic diversity seen in the current population. Presently, the leading theories are the two-way and three-way admixture models. The two-way model suggests that one main source of immigration prevailed during both the Yayoi and Kofun periods, while the three-way model posits two distinct sources of migration. To establish which model is more accurate, the researchers examined the complete nuclear genome of an individual excavated from the Doigahama Site, which served as a Yayoi period burial ground in Yamaguchi Prefecture, Japan.
They compared this Yayoi individual’s genome with that of ancient and modern populations from East Asia and Northeast Asia. This analysis showed that the genomes were closely aligned with those from Kofun period individuals, who had a mix of Jomon-related, East Asian-related, and Northeast Asian-related ancestries. Notably, when comparing to modern genomes, it became evident that, aside from contemporary Japanese populations, the Yayoi individual’s genome was most similar to those of current Korean populations, which also display both East Asian and Northeast Asian ancestries.
“Our findings indicate that most immigrants to the Japanese Archipelago between the Yayoi and Kofun periods primarily hailed from the Korean Peninsula,” comments Ohashi. “Additionally, these results suggest that the three-way admixture model—proposing a Northeast Asian group migrating during the Yayoi and an East Asian group during the Kofun—might be incorrect.”
Despite the importance of these results, Ohashi is already contemplating future research.
“Having identified the main sources of these immigrants, our next objective is to analyze the genomes of more Yayoi individuals. This will help us understand why over 80% of the genomic makeup of modern Japanese people is attributed to immigration and how the mixing of continental Asian lineages with indigenous Jomon populations evolved within the Japanese Archipelago.”
