re: Is there any historical evidence of diversity working out?

American educational system = so far = but on death bed.

BUT - diversity ONLY works when left to survive on its own. Nature itself has taught us that it is GREAT to allow all sorts of 'diversity' enter the gene pool, but it is axiomatic that it only works when you allow unworkable species to become extinct.

otherwise we'd still all be in some sort of multi-colored slime existence - each depending on the waste output of the other colors.