From: Smigrodzki, Rafal (SmigrodzkiR@msx.upmc.edu)
Date: Wed Jun 19 2002 - 12:01:49 MDT
Mark Walker wrote:
>
> I am not sure I understand this. Is the idea basically that we should
reason
> that if there were really that easy changes to the brain's factory
settings
> then they would in all probability already be manifest in the gene pool
and
> expressed in our phenotype? Take an example: suppose that a single
homeobox
> mutation would create a human being with a much larger neocortex. I can
see
> reasoning that this mutation is not likely to increase evolutionary
fitness,
> even a few hundred years ago, but I am not sure that we can conclude that
it
> is not an easy means to increase intelligence. One possible explanation
why
> this mutation does not manifest itself is an evolutionary bottleneck not
> directly linked with intelligence, namely, the size of a woman's pelvis.
> That is, we might imagine that this mutation creates babies with heads too
> large for the natural means of birth. Of course, a c-section might get
> around this problem.
### Actually, there is some statistical support for this idea - the children
of tall parents (which to some extend can be taken as a proxy for maternal
pelvic size) tend to be on average slightly more intelligent. A higher birth
weight (in the absence of maternal diabetes, or hydrops fetalis) correlates
with higher IQ. So there might IQ enhancing mutations which are only fully
active in a subset of children lucky enough to have a tall mother, perhaps
explaining part of the Flynn effect. Other explanations are possible, too.
Rafal
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