[dagw]

I basically agree, but only to a degree. I agree that essentially everybody is smart enough to get to PhD level in any subject. I've seen a couple of examples myself of people with no innate ability and average intelligence get a PhD in math simply by working really hard and really wanting it.

That being said I think it takes some sort of innate smarts to take it several levels above that. To be the person who comes up with the sort of fundamental breakthrough that only shows up once a decade or so. That takes something beyond simply putting in the work, and I don't think everybody has that potential.