Dienekes links to an abstract calculating that the peoples of Japan are a hybrid population that has issued out of mixtures between the Jomon and Yayoi. Roughly speaking the latter are the most recent arrivals (from Korea, circa 0-500 C.E.), bringing the general cultural core of "Japaneseness," while the Jomon heritage is to be found in remnants among the peoples of Okinawa and the Ainu of Hokkaido.
The study linked estimates that moden Japanese are on average about 25% Jomon and 75% Yayoi as far as genes are concerned. This is in line with most other studies and was the ratio given in Bryan Sykes’ Seven Daughters of Eve. The Ainu and Okinawans are admixed as well, but are more Jomon than Yayoi. The Ainu have sometimes been depicted as "Caucasoid," the pictures here to me indicate they look more "Native American." Clearly they are an ancient Eurasian population that does not exhibit to the same extent the stereotypical features of East Asians, the epicanthic eye-fold (I read once that the Ainu referred to each other as "Men of the same socket"), lack of body hair (ergo, "Hairy Ainu") and low-relief face. It is from the Ainu that the Japanese derive some of their phenotypic diversity, for certainly many Japanese are indistinguishable from Koreans or Chinese, but many also have larger noses and are more hirsute than continental East Asians.
Finally, I wonder if the Yayoi are from Korea why is the Japanese language not more obviously like Korean? I can speak Bengali, and the similaries between it and English (or the Romance languages) are obvious in many words, and the separation between Bengali & the European languages is at least 5,000 years, and more likely 8,000-9,000 years (if the new data is confirmed). The separation between Korean and Japanese should only be 2,000 to 3,000 years. One possible explanation is that before Chinese influence and the rise of the Korean culture in the light of history the peninsula was inhabited by many more diverse ethno-linguistic groups, and the Japanese are derived from one of the groups that were eventually assimilated into Korean culture.
fn1. I am skeptical of the idea of one Jomon language or culture. Certainly if evidence from the New World or much of highland southeast Asia is a clue the Jomon people were culturally and genetically diverse.
Posted by razib at 11:42 PM