After World War II, Kotondo Hasebe and Hisashi Suzuki claimed that the origin of Japanese people was not newcomers in the Yayoi period (300 BCE – 300 CE) but the people in the Jōmon period. However, Kazuro Hanihara announced a new racial admixture theory in 1984 and a "dual structure model" in 1991. According to Hanihara, modern Japanese lineages began with Jōmon people, who moved into the Japanese archipelago during Paleolithic times from their homeland in southeast Asia, followed by a second wave of immigration, from northeast Asia to Japan during the Yayoi period. Following a population expansion in Neolithic times, these newcomers then found their way to the Japanese archipelago sometime during the Yayoi period. As a result, admixture was common in the island regions of Kyūshū, Shikoku, and Honshū, but did not prevail in the outlying islands of Okinawa and Hokkaidō, and the Ryukyuan and Ainu people continued to dominate there. Mark J. Hudson claims that the main ethnic image of Japanese people was biologically and linguistically formed from 400 BCE to 1,200 CE. Currently, the most well-regarded theory is that present-day Japanese are descendants of both the indigenous Jōmon people and the immigrant Yayoi people.