What's the fastest a human could run?

We put this question to Professor Chris Cooper:

The cynical answer is to say we know that because we have Tim Montgomery as an example of somebody but then he'd been beaten by Usain Bolt! I think it's quite a difficult question to answer. The world record now is 9.72 [men's 100m] and no evidence that's been done illegally. You can sort of extrapolate form that where you might get. I think increasingly we're going to see genetic anomalies, people who've got a genetic aberration that makes them perform better and that's going to be what makes the difference. A classic example was a Finnish cross-country skier who had a naturally active EPO system. He made in his body large amounts of red blood cells because he had a gene defect. It wasn't a defect, of course! I think you'll see these step changes by people who happened to have had a mutation. It's difficult to therefore extrapolate.