Au contraire, at least Malcolm Gladwell has argued all you really need to win a Nobel prize is about an IQ of 120, like supposedly Feynman had an IQ of about that. And because of the Flynn effect it's likely that a 120 in Feynman's day would be a 110 or a 115 now. Hard work out competes genetics any day of the week.
At one time a four minute mile was considered impossible, but right after it was achieved a whole bunch of people started hitting it.
Certainly not everyone is "smart enough" to do certain tasks, but to delimit unnecessarily a whole set of individuals as unable to achieve a goal is Procrustean and unconscionable. I prefer to believe, even if it's slightly unjustified by experience, that the possibility is open to almost everyone to both run a five minute mile and to be a doctor. Why? Because we just don't know what's possible. People are surprising.