The current thinking about the origin of the Japanese population maintains that the original residents, Jomon's people, were met about 2,500 years ago by a separate group mainly from the Korean Peninsula, the Yayoi people. However, archaeological evidence used to achieve this conclusion is insufficient to tell the final story. Now DNA evidence from Y chromosomes provided the necessary data.
Researchers from the University of Tokyo conducted a census of the Japanese population some 2,500 years ago using Y chromosomes living on the main islands of modern Japan. For the first time, the analysis of modern genomes estimated the size of the ancient human population before they were met by a separate ancient population.
"The evidence in the archaeological excavations was used to estimate the size of ancient human populations, but the difficulty and unpredictability of finding these places is a great limitation. Now we have a method that uses a large amount of modern data, "said associate professor Jun Ohashi, an expert in the field of human evolution genetics and the leader of the research team who carried out the analysis.
Archaeological remains of the Jomon people are recognized by rope patterns pressed into their ceramics. (Chris 73 / CC BY-SA 3.0 )
The current theory regarding the migration of people to Japan is that the original residents, Jomon's people, were met about 2,500 years ago by a separate group mainly from the Korean Peninsula, the Yayoi people.
Archaeologists have identified fewer Jomon sites from the late Jomon period, the era immediately before the arrival of Yayoi. During this period, global temperatures and sea levels have dropped, which could have made life difficult for Jomon hunters-gatherers.
Review of the currently accepted demographic model of the Japanese population on the continent. (University of Tokyo / Permitted use )
When people from Yayoi arrived, they brought wet rice to Japan, which would lead to a more stable supply of food for other Jomon people living with the new Yayoi migrants.
Fewer archaeological remains from the late Jomon period may be evidence of a real decline in the population or simply archaeological excavations have not yet been found.
Ohashi's research team decided to dig a human genome to solve this archaeological mystery. They began by comparing the Y sequence of modern Japanese Y chromosomes with the sequences of Korean and other East Asian men. Y chromosomes are transmitted from father to son with minor changes over generations, so modern Y chromosome sequences can reliably estimate the Y chromosomes of men thousands of years ago.
Sequence analysis of the Y chromosomes reveals a new history of the origin of the Japanese population. ( fancytapis / Adobe Stock)
Researchers used DNA samples taken before 1990. From 345 men whose families came from the three main islands of Honshu, Shikoku and Kyushu in Japan.
The research team identified one group of DNA sequences that only Japanese had. This unique group of sequences probably came from people of Jomon. Researchers identified six groups of sequences common to both Japanese men and men with other East Asian heritage (Korean, Vietnamese, Chinese) that probably came from Yayoi people or other ancestors shared by people from Japan and East Asia.
DNA confirms archeology
Researchers built evolutionary family trees using the Y chromosome sequence and saw a pattern indicating a population decline and a sudden increase: a significant decrease in the number of Y chromosome ancestors around 2,500 years ago.
Interestingly, modern Japanese seem to have a larger percentage of Jomon's ancestry on the Y chromosomes than the rest of their genomes.
Previous genetic analyzes have shown that modern Japanese receive about 12 percent of all genomes from Jomon's ancestors, and the rest from Yayoi's ancestors. Ohashi's research team calculated that one group of identified Jomon sequences accounted for 35.4% of the total Y chromosome, indicating that a specific sequence would be very common in Jomon's men.
Because the sequence becomes easier in a small population, this is another indication that the size of the Jomon population decreased in the late Jomon period before the arrival of the Yayoi people.
"We hope this method can be useful to confirm another ancient human dynamics that is not fully explained by archeology," Ohashi said.
Top image: A new study of the Japanese population reveals the true origin of the Japanese. Source: Monkey's business / Adobe Stock.
The article, originally entitled " Analysis of the entire sequence of the Y chromosome reveals the history of the Japanese population during the Jomon period "It was first published in the Scientific Report
Source: University of Tokyo. Watanabe, Y., Naka, I., Khor, S., Sawai, H., Hitomi, Y., Tokunaga, K. and Ohashi, J. " Archaeological mystery solved with the help of modern genetics: Y chromosomes reveal population bust and bust in ancient Japan . "Scientific reports. Scientific reports , June 17, 2019.