The Japanese people (日本人 Nihonjin) are an ethnic group native to Japan. Japanese make up 98.5% of the total population of their country. Worldwide, approximately 130 million people are of Japanese descent; of these, approximately 127 million are residents of Japan. People of Japanese ancestry who live in other countries are referred to as Japanese diaspora (日系人 Nikkeijin). The term ethnic Japanese may also be used in some contexts to refer to a locus of ethnic groups including the Yamato, Ainu, and Ryukyuan people.
A new study published in the journal Molecular Biology and Evolution provides more support for the hypothesis that modern Japanese are an admixed population between the Jomon and the Yayoi people.
According to this hypothesis, called the ‘hybridization hypothesis,’ Neolithic hunter-gatherers known as Jomon, who are assumed to have originated in southeast Asia and lived in the Japanese archipelago more than 10,000 years ago, admixed with an agricultural people known as Yayoi, whom were migrants from the East Asian continent 2,000-3,000 years ago.
Meanwhile, some scientists propose that rather, morphological differences between the Jomon and Yayoi people can be explained by microevolution following the lifestyle change.
To resolve this controversy, a team of scientists co-led by Dr Hiroki Oota from Kitasato University School of Medicine in Kanagawa and Dr Shuhei Mano from the Institute of Statistical Mathematics in Tokyo identified the genetic differences between the Ainu people (direct descendants of indigenous Jomon) and the Chinese from Beijing (same ancestry as Yayoi).
Their results strongly support the hybridization hypothesis as the best fit for Japanese population history.
“An initial divergence between the Ainu and Beijing group was dated to approximately 20,000 years ago, while evidence of genetic mixing occurred 5,000 to 7,000 years ago, older than estimates from the archaeological records, probably due to the effect of a further sub-population structure of the Jomon people,” the scientists said.
They caution that further studies will need to be undertaken – especially ancient genome analysis of Jomon and Yayoi skeletal remains and genomic analysis of northeast Asians – to untangle the true evolutionary history of Japanese, in particular, the origins of the Jomon and Yayoi people and the source of gene flow to the Ainu.
Shigeki Nakagome et al. Model-based verification of hypotheses on the origin of modern Japanese revisited by Bayesian inference based on genome-wide SNP data. Mol Biol Evol, published online March 10, 2015; doi: 10.1093/molbev/msv045