I think Vladimir has the right of it - it's neither clear how best to measure 'intelligence' nor how what-is-measured-by-IQ is 'naturally' distributed.

As I understand it, we see what seems to be higher levels of separation between, say, IQs of 100 and 110 than between 160 and 170. This suggests to me that the scale is 'stretched' at the high end (though not at the low end?).

It's an interesting question!