Researchers at the University of Tokyo found that the immigrants who poured into the Japanese archipelago during the Yayoi and Jomon periods were mainly from the Korean Peninsula. The discovery, based on genome analysis of ancient individuals, challenges previous models of admixture and refines our understanding of Japanese ancestry.
A research team led by Jonghyun Kim and Jun Ohashi of the University of Tokyo found that during the Yayoi and Jomon periods (3000 BC to AD 538), most immigrants to the Japanese archipelago came from the Korean Peninsula. Their study analyzed the complete genome of a "Yayoi" individual and found that among non-Japanese populations, the genetic makeup was most similar to that of the Korean population.
Although modern Japanese are generally believed to be of dual ancestry, the discovery provides insight into details of immigration patterns in the Japanese archipelago that previously baffled researchers. The findings are published today (October 14) in the Journal of Human Genetics.
Today, Japan has become an international center for business and leisure. However, this is not always the case. During the Jomon period before about 3000 BC, the Japanese archipelago was relatively isolated from the outside world. Then, during the Yayoi and Komon periods, immigration to the archipelago began from mainland Asia.
"Ancestors related to East and Northeast Asia account for more than 80% of the nuclear genome of the modern Japanese population. However, how the Japanese population acquired these genetic ancestors, that is, the origin of immigration, is not fully understood."
Various theories have been proposed to explain the genetic diversity of modern populations. Currently, the two-way hybrid model and the three-way hybrid model are the two major contenders. According to the two-way model, the main sources of immigrants during the Yayoi and Jomon periods were the same, while the three-way model assumes two different sources. To investigate which model was more appropriate, the researchers analyzed the complete nuclear genome of an individual from the Doihama site in Yamaguchi Prefecture, Japan, an archaeological site of a Yayoi period cemetery in Japan.
The researchers compared the genomes of individuals from this Yayoi period to those of ancient and modern populations in East and Northeast Asia. The comparison results show that this Yayoi-era individual is very similar to the Komon-era individual, and its ancestors are related to Jomon, East Asia, and Northeast Asia respectively. However, comparisons with modern genomes also show that apart from modern Japanese, Yayoi individuals are closest to modern Koreans, who also have East Asian-related and Northeast Asian-related ancestors.
"Our results indicate that most of the immigrants to the Japanese archipelago between the Yayoi and Jomon periods came primarily from the Korean Peninsula," Ohashi said. "These results also mean that the tripartite hybrid model, which suggests that Northeast Asian groups immigrated to the Japanese archipelago during the Yayoi period and East Asian groups immigrated to the Japanese archipelago during the Kai period, is incorrect."
As significant as these findings are, the bridge is already looking to the future.
"Now that our study has identified the main source of immigrants, the next goal is to study the genomes of more Yayoi individuals to understand why more than 80% of the genome of the modern Japanese population comes from immigrants, and how interbreeding between mainland Asians and the indigenous Jomon people developed within the Japanese archipelago."
Compiled from/SciTechDaily