Race-Related IQ

Toby Bradshaw toby at u.washington.edu
Thu Dec 1 11:13:48 EST 1994


In article <mwspitze-301194133515 at phar2.medsurge.hsis.uci.edu>,
matt spitzer <mwspitze at uci.edu> wrote:
>In article <3bi7gc$goa at nntp1.u.washington.edu>, toby at u.washington.edu (Toby
>Bradshaw) wrote:
>
>
>> By this line of reasoning, it would make no sense to measure the
>> heritability of grain yield in maize or stem volume growth in trees,
>...
>
>Actually the reasoning behind IQ is more equivalent to constructing a
>tomato-quality measure by averaging scores on independent tests for total
>yield, disease resistance, drought tolerance and flavor.  Modern plant
>breeders do produce some good "overall" performers, such as the better-boy
>tomato, but they also breed varieties that outperform the generalists under
>specific growing conditions, such as shade-tolerant tomatoes.  No one would
>argue that tomato-quality measures a single heritable trait, or that high
>quality score tomato varieties will be the best producers in all (or any?)
>growing conditions.

I have no problem with this analogy.  Let's say tomato "quality", which
is somewhat nebulous (like "intelligence"), is measured by a weighted
index of yield, disease resistance, etc.  Were we to produce a segregating
population and map QTLs for "quality", we would find QTLs for each component
of the index, with their magnitude of effect proportional to their magnitude
on the "real" trait (i.e., disease resistance) multiplied by the weight
given the trait in the index.

"Yield" itself is just an index, a composite of fruit number, individual
fruit mass, etc.  That doesn't make "yield" impossible to map.  The power
of modern genetics is that the details of the phenotype do not *necessarily*
have to be understood in advance.  The phenotype must be defined, though,
and without question that's the biggest hangup for "intelligence".  We
don't have to agree that the totality of what we call "intelligence" can
be defined, but if we can agree that some component of "intelligence" can
be defined and measured, its genetic basis can be understood if there is
variation for it in human populations.

-Toby Bradshaw
toby at u.washington.edu





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