Dental variation of Ryukyu islanders: a comparative study among Ryukyu, Ainu, and other Asian populations

The presence or absence of 24 nonmetric dental traits was examined to investigate the inter- and intraregional variation of Ryukyu Islanders. We compared the dentition of the Kadena sample from the central district of Okinawa Island in the Ryukyu Island chain to those of samples from Nakijin from the northern district of the same Okinawa Island, Tokunoshima, another island of the Ryukyu Island chain, main-island Japanese in Kagoshima and Tokyo, Hokkaido Ainu, Atayal in Taiwan, and Pashtuns and Tajiks in Afghanistan. Many traits of the Ryukyu Islanders were found to be close to those of the main-island Japanese; however, several were intermediate between those of the main-island Japanese and the Ainu or Atayal. The intraregional variation in the Ryukyu Islanders was comparable to that in the main-island Japanese. This result supports the influence of a complex gene flow to the Ryukyu Islanders, as suggested by some genetic studies. Among the populations compared here, that closest to the Ainu was the population of Tokunoshima.