The current thinking on the origins of the Japanese population holds that the original inhabitants, the Jomon people, were met about 2,500 years ago by a separate group coming mainly from the Korean Peninsula, the Yayoi people. However, the archaeological evidence used to reach this conclusion is insufficient to tell the definitive story. Now DNA evidence from Y-chromosomes has provided the data needed.
Researchers at the University of Tokyo conducted a census of the Japanese population around 2,500 years ago using the Y chromosomes of men living on the main islands of modern-day Japan. This is the first time analysis of modern genomes has estimated the size of an ancient human population before they were met by a separate ancient population.