Unpopular to hear, but it needs to be said more. While I believe that the US still has a ways to go to truly achieve equality of opportunity (and then equality of outcome really would be based on culture, I would think), culture is such an important factor in peoples' personalities and therefore an important factor in peoples' outcomes. I can't speak to other life forms, but culture (nurture) is a powerful force in humans that can rival genetic dispositions (nature).