Re: Famous thinkers and their IQs

Nick Bostrom (
Wed, 25 Nov 1998 23:07:22 +0000

Remi Sussan wrote:

> Nick Bostrom wrote:
> >
> >
> > BTW, contrary to what was said on another thread some weeks back,
> > there seems to be a fairly substantial correlation between IQ and
> > brain size. I've heard figures of correlation coefficients of up
> > to .4. It would be interesting to try correlate the size and
> > complexity of specific cortical areas with performance measures of
> > the sort of activity they are thought to be responsible for. Maybe
> > one could find even greater coefficients then.
> This is probably a stupid question, but how to explain this Brain
> size/I.Q correlation if we admit that the I.Q level has
> significantly risen in one century?

A .4 correlation leaves a huge scope for other factors, so I don't see any difficulty here. (It's also possible to imagine that better nourishment during childhood could have increased average brain size.)

One has to be careful before jumping to conclusions from a weak correlation. After all, shoe size also correlates positively with IQ (though less than brain size I think). Couldn't head size simply be correlated with body size, which in turn may be correlated with intelligence because the best mates prefer to mate people who are both tall and intelligent?

I don't think that's the whole explanation in this case however. Because (1) I think IQ correlates (slightly) more strongly with brain size than head size, and (2) a big brain is costly (risks at birth with big head; heavy to carry around; consumes lots of energy) so there must be some strong reward for having a big head, and it's hard to see what that could be except intellectual performance.

Nick Bostrom Department of Philosophy, Logic and Scientific Method London School of Economics