You’ve heard of the Flynn effect, right? The point that IQ scores seem to be getting higher with each passing generation?
Myself, I’ve always thought it was down to nutrition. We know that bad nutrition in the womb and childhood reduces mental capacity, we also know that (whatever the hysteics are screaming about now on obesity) said nutrition has become immeasurably better in the last few centuries. I mean ricketts for God’s sake, a simple calcium deficiency, was common enough in England pre-WWII.
I am rather ashamed to note that I was not thinking clearly enough myself (Mum? What were you feeding me those years ago?). Go read this quite stunningly good take on the subject from Stumbling and Mumbling. You should also read the rest of the blog. Going on my blogroll right away.