For decades, scientists believed the Japanese population largely descended from two ancient groups: the Jomon hunter-gatherers who lived in the archipelago for thousands of years, and later migrants from East Asia who brought rice farming and new technologies to Japan. But a major genetic analysis from researchers at RIKEN's Center for Integrative Medical Sciences suggests the picture is far more complicated. Using whole-genome sequencing on more than 3,200 people from across Japan, the team found evidence supporting a third ancestral group tied to northeastern Asia and possibly linked to the ancient Emishi people. The findings, published in Science Advances , add powerful support to the increasingly discussed "tripartite origins" theory of Japanese ancestry. The results also revealed something else surprising: Japan's population is genetically more diverse than many researchers once assumed.…