There is a lot of historical evidence, that deep knowledge and long tail expertise in specific industries is carried in groups of people with a close knit subculture.

Such knowledge can also be transmitted from one subculture to another, with varying degrees of success. In order to bring in new people, one must either bring in a few beginners into a majority competent population, or have one subculture highly motivated to absorb and replicate the success of another.

This is well covered in Migrations And Cultures: A World View by Thomas Sowell.