I think the majority of people are very similar as far as natural intelligence goes. In my life I can count on one hand the number of people I have met that are truly bright and perhaps genius---I.e. IQ north of 140 and getting into Good Will Hunting territory. So what helps is more the nurture than the nature aspect--I.e. We're all born with similar intelligence but who was read to as a child, went to good schools, parents were invested in their education etc come out on top.
For reference I was tested as a teenager by PhD psychologist due to suspicion of having ADD and my score was 117. A 117 IQ is better than 85.5% of test takers, I.e. My score is in top 14.5% of test takers. Check this site out to reference meaning of your score.
IQ test scores and percentile calculations. What is your rankings?
At least for me I had to work hard in undergrad to get good grades, but finished with just over a 3.8 GPA. MCAT was 31 with 5 weeks prep and highest score being in verbal. A 140 IQ is extremely rare and the online IQ tests are not valid at all. Keep in mind 130 or above IQ is roughly 2% of the population. But yet the majority of people that ever mention it all mysteriously seem to be at least a 130 IQ which is of course BS. In conclusion I feel as long as you have average level of intelligence you can succeed in medicine as long as you work hard! So don't sweat it...it's all up to you. If you want it bad enough, you can do it!!