Actually there's an interesting statistical phenomena where at the very top of a hierarchy, the correlation between success and the factor that generally drives

Actually there's an interesting statistical phenomena where at the very top of a hierarchy, the correlation between success and the factor that generally drives success becomes low. For example if you look at NBA players, you'll see that they're on average quite tall, but also that height only has a weak correlation with 'basketball ability' in that sample. That's because those people were already heavily selected on height; and all the not-that-tall people in the sample compensate with the other things that make them good at basketball. So if you want to look at how useful IQ is, you should be looking at the average IQ of successful people vs average IQ of unsuccessful people, and not how successful people are in a relatively high IQ subsample (i.e. all surgeons).