Dual structure model for the population history of the Japanese

This paper proposes a 'dual structure model' to explain the population history of Japanese, including the Okinawa islanders (Ryukyus) and Ainu under a single hypothesis. The model assumes that the first occupants of the Japanese Archipelago came from somewhere in Southeast Asia in the Upper Palaeolithic age and they gave rise to the people in the Neolithic Jomon age, or Jomonese; then the second wave of migration from northeast Asia took place in and after the Aeneolithic Yayoi age; and the populations of both lineages gradually mixed with each other. The 'dual structure model' also assumes that the population intermixture is still going on and the dual structure f the Japanese population is maintained even today. Thus, several regional differences such as those between east and west Japan in physical as well as cultural characteristics can be explained by the varying rates of intermixture from region to region. In general, this model agrees well not only with physical and cultural evidence but also with non-human evidence as revealed by Japanese dogs, mice, etc. At the same time, the model provides a reasonable way of explanation in regard to the relationships among the Japanese main islanders, Ryukyus, and Ainu.