I would tend to support your theory because living on islands has a lot of impacts in the long term. Read interesting article (link below) last week that people living thousands of years on small islands in Indonesia became smaller and smaller. Some of the theories: a) When there is shortage of food, it's easier to feed a small body than a big body, b) there were no large predators to stay big for. All that to say that if living on an island can have such an impact on the size of the body, it can have an impact on the size/extent/scope of the culture too :o)