Photo/Illutration The face of a Yayoi man is reproduced based on a skull unearthed from the Doigahama archaeological site in Yamaguchi Prefecture. ((C) Takayuki Matsushita)

The bloodlines of modern Japanese lie with immigrants from the Korean Peninsula who arrived in the archipelago during the Yayoi Pottery Culture Period (1000 B.C.-A.D. 250), new research suggests.

Citing the genome of an individual dating to the Yayoi period, researchers from the University of Tokyo and other institutes speculated that the newcomers mixed with Jomon hunter-gatherers who had inhabited these shores unchallenged since 14500 B.C.

The study debunks a theory put forward three years earlier that the ancestral group of modern Japanese emerged only after the beginning of the Kofun period, named for the distinctive imperial style of earthen burial mounds constructed from the third to seventh century.

The nuclear genome of today’s Japanese population features three distinctive genetic elements: Jomon, East Eurasian and Northeastern Eurasian.

Precisely when these Eurasian migrants reached Japanese shores remains unclear.

A team led by Jun Ohashi, a professor of population genomics at the University of Tokyo, examined the entire genome sequence of an adult Yayoi woman whose skeletal remains were unearthed from the Doigahama archaeological site in Yamaguchi Prefecture.

An analysis of the woman’s remains dating back 2,300 years ago was compared with existing data on Jomon and Kofun populations.

The Yayoi woman, like modern Japanese, was found to possess three genetic components from Jomon, East Eurasian and Northeastern Eurasian peoples. However, her genetic makeup most closely resembled that of the Kofun people, followed by present-day Japanese, ancient Koreans and modern Koreans, Ohashi said.

This outcome is consistent with the traditional “dual structure” model. This asserts that the ancestral group of modern Japanese was born when immigrants with genetic attributes originating from East Eurasia and Northeastern Eurasia mixed with the native Jomon population during the Yayoi period.

A more recent theory also based on genome analysis postulates that the ancestral group did not appear until the Kofun period, instead of the Yayoi period.

The “triple structure” model hypothesizes that immigrants from Northeastern Eurasia and East Eurasia came to Japan separately during the Yayoi and Kofun periods, respectively.

Though the theory garnered considerable attention at the time, it has since been overshadowed by new research.

Asked why the two models differ in their conclusions despite both being grounded in the genome examination of Yayoi remains, Ohashi pointed to the differing quality of the analyses.

“It is wrong to assert that human remains analyzed under a novel model properly represent the Yayoi people,” Ohashi said.

His reasoning is that people in the Yayoi period were divided into a Jomon-derived Yayoi group and the Yayoi population of immigrant origin based on their skeletal features. He noted that their mixing with the Jomon people and the immigrants varied significantly over time across regions.

The remains from the earlier analysis were exclusively from the less-mixed Jomon-Yayoi group. Adding to the problem, not enough genome data on the immigrant-Yayoi group was properly analyzed in the triple structure model.

“A genome analysis of the more-mixed Yayoi population with immigrant origin must have been conducted to trace the roots of foreign-originated people,” Ohashi explained.

The latest analysis involved remains from the Yayoi group with immigrant roots. The survey’s level of precision was said to be above reproach.

The research outcome was published in the Journal of Human Genetics at (https://www.nature.com/articles/s10038-024-01295-w) on Oct. 15.