Darwin is a classic example of an above average guy who became a genius.
His IQ would have probably scored in the 130 range (i.e. an intelligence slightly above average) on a standard IQ test.
And yet there he is, buried next to the calculus-inventing genius Isaac Newton (estimated IQ of 190!) in Westminster Abbey. (As Charlie Munger often notes.)
What thinking habits made this above-average man a genius?
Well this extract from Darwin’s autobiography gives us a clue:
I think that I am superior to the common run of men in noticing things which easily escape attention, and in observing them carefully.
My industry has been nearly as great as it could have been in the observation and collection of facts. What is far more important, my love of natural science has been steady and ardent …
From my early youth I have had the strongest desire to understand or explain whatever I observed, that is, to group all facts under some general laws. These causes combined have given me the patience to reflect or ponder for any number of years over any unexplained problem.
As far as I can judge, I am not apt to follow blindly the lead of other men. I have steadily endeavored to keep my mind free so as to give up any hypothesis, however much beloved (and I cannot resist forming one on every subject), as soon as facts are shown to be opposed to it.1