I think it is difficult to consider ethnic groups to be the same anthropologically. People living in mainland Japan and Okinawa Islands are similar but have some differences, though they are surely very close to each other.
The Ainu people, who once lived widely in the northern island, Hokkaido, uses quite different languages and is no doubt different peoples from the Japan (Yamato) people. The Yamato people, who makes up the majority of the Japanese, made a full-scale entry into Hokkaido in the mid-19th century. Then no one speaks the Ainu language on a daily basis now.
The same thing happened anywhere in the word. This is very similar to wildlife conservation. After it’s no longer possible for them to recover, people say that the diversity is important.
In the past, the Ainu people were considered to belong to the Caucasian race. Certainly, the features are a little like Europeans and the language seems to be very different from Japanese. However, an analysis tells to show that both languages are derived from the common proto-language.
Some say that the Ainu people once lived widely in mainland Japan about 5,000 years ago. They say that the potteries from the ruins around this time are produced by the Ainu people. Furthermore, there is a claim that place names, not only in eastern Japan but also in western Japan, can be interpreted in Ainu language.
Though it is a story of a very old age with no textual material, there is no choice but to collect and verify this and that evidence.
