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From: mkkuhner@codon1.berkeley.edu (Mary K. Kuhner;335 Mulford)
Newsgroups: sci.bio
Subject: Re: Hybrid vigor
Message-ID: <1989Aug10.003610.14496@agate.berkeley.edu>
Date: 10 Aug 89 00:36:10 GMT
References: <4869@drivax.UUCP> <3411@internal.Apple.COM> <5983@lynx.UUCP>
Reply-To: mkkuhner@codon1.berkeley.edu.UUCP (Mary K. Kuhner)
Distribution: usa
Organization: University of California, Berkeley
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Hybrid vigor is well known in plants and animals--when two inbred 
stocks are crossed, the offspring are often more vigorous because
(a) they are not homozygous for as many deleterious recessives, and
(b) they are possibly heterozygous for genes where the heterozygote
is the most vigorous type.

Human races are not inbred.  The difference between an 'average'
Caucasian and an 'average' Negro is less than the difference between
individuals of each race.  There is no obvious reason why racial
hybrids would show hybrid vigor.

Selection for vigor in African-Americans is another matter which
has nothing to do with 'hybrid vigor' as plant or animal breeders
understand it.  I am not sure how this hypothesis could practicably
be tested, but there's nothing wrong with trying to think of a way
to do it. 

Why the yells of 'racist'?  Human races may not be as differentiated
as has been thought, but surely the way to prove this is to study
them, not to push the whole topic under the rug.

Some geneticists may find it useful to group all humans together
without regard to race, but in the population genetics of disease
it is vital to match the control and disease populations by race.
The occurence of juvenile diabetes in African-Americans, for example,
correlates quite exactly with the proportion of Caucasian admixture,
and Africans almost never get this disease.
 
Mary Kuhner
mkkuhner@enzyme.berkeley.edu