In short, my answer would be "yes, but not exclusively".
The environment in which one is raised plays a role which is no
less important, although admittedly, if you put two people of
different levels of intelligence level in the same
environment(imagine twins or siblings in the same family having an
equal access to opportunity) and should they attain different
levels of success, that should answer your question.
At the end of the day, exceptional academic ability, in my opinion,
is no different from extraordinary musical or athletic ability -
quite simply, not everyone is born to be a Stephen Hawking, Michael
Jordan or Beethoven even if they were prepared to work hard...
