A landmark genomic study has identified a previously overlooked third ancestral group in the Japanese population, challenging the long-accepted "dual origins" model of Japanese ancestry that has dominated the field for decades.¹² The research, published in Science Advances, analysed the complete genomes of 3,256 individuals drawn from across Japan — generating 3,000 times more genetic data per person than previous large-scale studies — and found evidence of a distinct northeastern Asian lineage not accounted for by the existing two-population framework.¹⁵

The new ancestral signal is strongest in northeastern Japan and shares genetic characteristics with the ancient Emishi people, a historically documented group who occupied the Tohoku region and resisted incorporation into the centralised Japanese state during the Nara and Heian periods (710-1185 CE).²³ The findings build on years of growing genetic evidence that Japanese origins are more complex than the traditional model — which described the modern Japanese population as a blend of the indigenous Jomon people and Yayoi migrants from the Asian continent — suggests.⁴

How the study was done

The research team created the Japanese Encyclopedia of Whole-Genome/Exome Sequencing Library, or JEWEL — a high-depth whole-genome sequencing dataset comprising the 3,256 participants.¹ Whole-genome sequencing determines virtually all three billion base pairs that make up a person's DNA, compared with the DNA microarray technology used in earlier population genetics studies, which samples only a small fraction of the genome at known variable positions.⁵⁶ This 3,000-fold increase in data density allows researchers to detect subtle genetic patterns that would have been invisible in smaller datasets, including the signal from a third ancestral group whose contribution to any single genome is modest but consistent across the northeast of the country.¹³

What the genomes show

The analysis confirmed and refined established patterns of regional genetic variation across Japan. Jomon ancestry — the contribution from Japan's indigenous pre-agricultural population — makes up approximately 28.5% of the genome in people from Okinawa but only around 13.4% in western Japan, reflecting the historical pattern of continental migration that was more intense in the western islands closest to the Korean peninsula and China.¹⁴ Western Japanese populations show stronger genetic similarity to Han Chinese peoples, consistent with documented migrations between approximately 250 and 794 CE.¹

The newly identified third ancestral component appears predominantly in the northeastern islands, consistent with the historical geography of the Emishi and their successors in the Tohoku region.²³ The team characterised this component as distinct from both the Jomon and Yayoi-continental contributions, suggesting it represents a separate migratory event or a population that maintained relative genetic isolation in northeastern Japan for an extended period.¹⁵

Ancient DNA: Neanderthals, Denisovans, and disease risk

Beyond the three-population structure, the JEWEL dataset also allowed the team to quantify inherited ancient DNA in the modern Japanese genome. Participants carry measurable quantities of Neanderthal and Denisovan DNA — remnants of ancient interbreeding events that occurred tens of thousands of years ago as anatomically modern humans spread out of Africa and encountered archaic populations.¹⁶ The researchers linked specific segments of this ancient DNA to elevated risks for conditions including type 2 diabetes, heart disease, and certain cancers — adding a medical dimension to what began as a historical and anthropological inquiry.¹

Broader significance

The study is one of the largest whole-genome sequencing projects ever conducted on a single national population and demonstrates the power of comprehensive genomic sequencing over earlier genotyping approaches for resolving population history.⁵⁷ It adds to a growing body of evidence from across East and Southeast Asia suggesting that population origins in this region are substantially more complex than the models developed in the 1990s and 2000s, when far less genetic data was available.⁴⁸ The JEWEL dataset itself is expected to be a resource for follow-up studies on genetic risk factors specific to the Japanese population, which are currently underrepresented in global genomic databases dominated by European ancestry cohorts.¹³

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Whole-Genome Study of 3,256 Japanese People Uncovers a Hidden Third Ancestral Group Linked to the Ancient Emishi