there is no such thing as intelligence when it comes to education, just different speeds at which people understand stuff. Real intelligence in a subject comes when making an original contribution, figuring out something that no one has figured out before. This isn't done by students, students just go over things that have already been laid out well in advance by other people. It's painting by numbers. Grades are just a question of the amount of time someone is willing to put in, it's not like there's anyone studying, say, sociology, that couldn't do medicine if they wanted.