From: Nick Bostrom (bostrom@ndirect.co.uk)
Date: Wed Nov 25 1998 - 16:07:22 MST
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
http://www.hedweb.com/nickb n.bostrom@lse.ac.uk
Department of Philosophy, Logic and Scientific Method
London School of Economics
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