A comment I made on an e-mail thread that was well-received:
Intelligence is the product of basic brainpower, passion, and education. The brain is like a car engine: whether you have a little two-stroke or a V-12 you still aren’t going to get anywhere without some passion fuel, and the going will be really tough without some nice, smooth educational asphalt to help guide you to where you want to go.
Also, to those endlessly debating nature-versus-nurture, the answer is usually “both” . . . you start with a certain genetic baseline, then a childhood you don’t have much control over, and you make of your life what you will. Some folks receive a terrible start in life and are going to have it hard whatever they do, but most people have something they can work with, and with the right sort of ambition, positive attitude, and tenacity, can achieve some sort of success in life.