Amusing. I always find it amusing when someone tells me about purity of a culture, of a nation, of a "race." For the record, I'll say that these are hogwash. Every culture has both original facets and borrowed facets. It's just a fact, and it's all around us. But the denial about loaned cultural aspects continues, and I don't really hold it against anyone who fancies his ancestral homeland as one of greatness. I just laugh about assertions of purity.
Take Japan. With all the historical evidence in place, we know that the Jamon culture preceded the Yayoi. There are artifacts throughout Japan with the exception of Hokkaido and Ryukyu (Okinawa). Rice is widely believed to have been imported from central China, not just as a product, but as a skill that revolutionized ancient Japan and fostered population explosion.
Migration of people from the Korean peninsula is also a given. I know there are people today who cringe at the fact that they have Korean and Chinese blood coursing through their veins, but that's just the fact. Live with it, I say, and be thankful that the skill it takes to grow rice was given freely to the original settlers of Japan.
Professor Charles T. Keally breaks it down well: Yayoi Culture
The originals, the Jomon, supposed shared more physical characteristics with Southeast Asians, while the Yayoi resembled Northeast Asians. I wonder why there was migration to Japan from China and Korea, and not so much from Southeast Asia. Was overpopulation more of a crisis issue in those regions?
Kyushu, like Ryukyu and Hokkaido, fascinate me in terms of travelers. Kyushu's location made it much more accessible to mainland peoples and faraway travelers by ship. Does this mean there was a multicultural society there to some degree? I don't know, but if the info is out there, any kind of proof, I hope to find it soon.
One thing that Keally doesn't delve into with this analysis is whether the Ainu are more closely related to the Jomon, the Yayoi or anyone else. Whether the Ainu were simply pushed by warfare or politics to the northern, cold region of Japan, and whether they are related to the Ryukyu people, I also want to know.
Here's a cool site (PDF) with a series of pics in lectures by Prof. John C. Huntington
Early Jomon artifacts
Late Jomon and Yayoi period artifacts, housing technology