Added: Malcolm Gladwell apparently agrees with me:
LADWELL: It’s a great question. Impossible to answer in the time that I have, but if I can use my favorite subject of running as an example. If you look at times in the marathon today and compare them to times from 30 years ago, we are radically slower today. I’m not talking about the elite level, I’m talking about at the sub-elite level. The number of Americans, for example, who can break three hours in a marathon today is a fraction of what it was in 1980 or 1985. And that goes to this point: In order to extract running talent from the general population, you need to have a really, really broad base and the broad base is gone.
There is still elite running that produces really good, fast runners. But in 1980, there was this many people running the kind of mileage necessary to run a marathon properly, and today there’s this many. And all of our attention and focus is on the 95th percentile. But what we don’t understand is, we’ll never find the next great marathoner until we re-broaden the base. When we had a base this big of mediocre marathoners we had the two greatest marathoners in the world. Now that our base is this big, we got nobody in the top 10.
From an interview here