That's something else. I never heard such a theory but the guy is prolly at least 50% right. Thanks much! Island people means insular people. This applies to all of Japan back then. You hear about the Palestinians and Arabs being clannish. The Japs of the past were many times more so. All due to being on islands. Brits are the same to a lesser extent. Most real Brits are blood related even if just a bit. All comes from being on an island. A few islands.
Island = isolated= insular= inbred