Based on the research on skeleton, there is a theory in anthropology that a group of toraijin (settlers) from northern east of Asia settled down in the northern Kyushu (northern Fukuoka Prefecture, northern Saga Prefecture, western Yamaguchi Prefecture) after the middle of Yayoi period, and conquered or mixed with Jomon-jin people who lived in the Japanese islands, extending their influences across the west Japan little by little, and finally spread to the Kinki region by the Kofun period (tumulus period) (hypothesis by Kazuro HANIWARA).
人類学では骨格の研究により、北部九州（福岡県北部、佐賀県北部、山口県西部）に東北アジア系の渡来人集団が弥生時代中期以後定住し、徐々に勢力を西日本一帯に拡大し、それまで日本列島で暮らしていた縄文系の人々を征服し、あるいは混血しつつ古墳時代までには近畿地方まで広がったとする説（≒埴原和郎の仮説）がある。