I just read Fred Reed's column about intelligence, in which he takes on the prevailing theories about what intelligence is and how it is proliferated. (Supposedly it is largely genetic.)
I think there are a lot of factors to intelligence, but heredity is only a part of the mystery. For instance, compared to my father I am downright sluggish between the ears, yet according to theory by this time I should be inventing a new atom. That's if high intelligence is always passed on.
I agree that there's way more to intelligence than just genetics. (Although, I'm sure it does play a rather large part.) But I think nurture is also a big deal.
I heard a story once (and granted, it could just be a feel good urban legend, but even if it was, I think the point is on target) about two groups of kids who were determined, through computer testing, to be dumb and smart, respectively. Thing was, the "dumb" kids accidentally ended up being labeled "smart" by mistake and the "smart" kids "dumb." Well they sent the supposedly "smart" kids off to class and the teachers found they had difficulty with the children actually learning anything. Now, here's the kicker, they got together and said, "Wow, what is going on? These are smart kids. If they're not learning, then maybe we're teaching them the wrong way
. We'll have to find different ways of teaching." And lo, behold, they changed their methods, and the kids started learning.
Again, the whole story could just be an allegory, but I personally know some people who've been told they were "dumb" and "stupid" and since they believed it, they never would try and thus, the whole thing became a self-fulfilling prophecy.