The following are excerpts from Nasrine Bendjilali et al., “Who Are the Okinawans? Ancestry, Genome Diversity, and Implications for the Genetic Study of Human Longevity From a Geographically Isolated Population,” The Journals of Gerontology: Series A, Volume 69, Issue 12, 1 December 2014, Pages 1474–1484.

 The earliest human remains in Japan (from the Yamashita site in Okinawa) date to about 30,000 years ago and are thought to be ancestors of the Jomon people, whose pottery appeared throughout the Japanese archipelago as far north as Siberia by about 13,000 years ago. New migrants, called the Yayoi people, arrived in Japan from the Korean peninsula about 2,000 years ago causing admixture of the two populations (19,23) but appearing not to have had a major genetic influence in outlying regions such as Okinawa or Hokkaido (21,22).  

 However, performing PCA using only the Okinawan and the Asian HapMap samples suggested that the Okinawan population is a homogeneous group and was distinct from the Japanese and the Chinese.

 We found that the Okinawans clustered consistently with East Asians, with individual ancestry estimates (ie, the estimated membership coefficients for each individual in each of the seven predefined world regions) ranging from 0.928 to 0.997. No other world population present in the reference dataset had a significant contribution to the Okinawan participants.

 On average, the Okinawans were found to share 80.8% (±11.2 SD) admixture with Japanese and 19.2% (±11.2 SD) admixture with Chinese suggesting that the Okinawans and the Japanese share substantial common ancestry.

 On average, the Okinawans were found to share 80.8% (±11.2 SD) admixture with Japanese and 19.2% (±11.2 SD) admixture with Chinese. Individual admixture estimates were quite variable and ranged from 5.84% to 57.82% Chinese admixture (Figure 4B).

 Okinawans are an isolate with limited gene flow from outside populations, and are likely descended from an original, older ancestral population called the Jomon who already possessed a high degree of differentiation from Paleolithic times.

 One limitation [of this study] is the small sample size. We studied 24 Okinawan centenarians and 26 middle-aged Okinawans.

 In conclusion, we have demonstrated that the Okinawans are relatively homogeneous at the genetic level, Okinawan centenarians tend to cluster into an even more homogeneous group suggesting some shared genetic mechanisms for longevity, and that Okinawan centenarian siblings show a high relative risk of longevity.