[dog breath]

These bones are not ancestral to the majority of Japanese. The ancestors of most Japanese apparently came from the Korean peninsula at some point, but they might be ancestors of the Ainu, who are descended from earlier peoples, and those Japanese who picked up some of their genes through the centuries of contact. Somewhat similar in a sense to how the American population has absorbed some American Indian bloodlines into the larger population.

[DNA.2012]

The ancestors of most Japanese apparently came from the Korean peninsula at some point

What evidence is there for that assertion?