Dual origin hypothesis Previous studies showed genetic affinities between the Ainu and Ryukyu peoples,who live in the north and south ends of Japan, respectively, and who are thought to be descendents of the Jomon people. These observations are consistent with the “dual-origin hypothesis”, which states that the ancestral Japanese populations were brought by two major migration events. Archeological studies have suggested that the Jomon period (the Japanese Neolithic age) started about (14000 - 300 BC), when the Yayoi period(300 BC - 250 AD), a rice-farming and metal-using age, started. In the Yayoi period, immigrants from the Asian continent had moved to western Japan via Korea or China and expelled or mixed with the Jomon people. Our observations of the two main clusters and genetic differentiation among geographic regions are not discordant with the dual-origin hypothesis, although most of the Hokkaido individuals in this study are probably different from the indigenous Ainu people...