I think there is a lot of confusion over the biological reasons for
preventing breeding between close relatives either human or animal.  Human
beings have social and cultural reasons for not marrying and having children
with close relatives.  Our primary justification, of course, is that the
children could be double recessive in some extremely BAD gene.  However, we
have to be careful not to confuse our moral feelings with biology.  If
neither "animal" has any deleterious recessive genes, then the progeny will
be perfectly healthy in every respect.  And many many of us people and
animals are free of horrible recessives.  Those recessives that do appear
are rare, and the odds of finding another are small.  So, what's the big
problem with brothers and sisters marrying?  The truth is that such things
are deleterious to society.  It is actually very common in other cultures
than the dominant Western for cousins to marry.  However, if close relatives
commonly married, it would tend to alienate outsiders, disrupt community
activities, annoy the neighbors, etc.
 
In addition, many, if not most animals will breed happily with a relative if
they happen to be in season.  You can see this in your own domestic pets,
and if you wanted to find it among animal populations, you would not have to
go far.  Many primates (our near animal relatives) have social structures
that minimize inbreeding.  However, the overall breeding populations in
these groups are still closely related.
 
Responsible breeders have been using inbreeding or linebreeding to amplify
*good* recessive traits for thousands of years.  Remember a certain biblical
herd of black goats which was bred from a herd of white goats?  I'm sure
none of these black goats ended up in psychotherapy later.  Breeding
problems arise when any breeder sacrifices the overall health of the animals
for the sake of one or two desirable traits.  This is regardless of whether
the two parents are closely related, or from opposite ends of the Earth.
 
We should not categorically condemn the respectable, and very widely used
practice of linebreeding simply because we think it is icky for brothers and
sisters to marry.  The moral issues do not cause birth defects and
psychological problems.  Genes cause the birth defects --and we can control,
or at least *watch* the genetics-- and SOCIETY causes the psychological
problems.  As for Marshall Farms, they have a lot of ferrets.  A few of them
are bound not to come out right every once in a while.  Anyone who has barn
cats knows that some of the kittens just ain't born right.
 
Catherine Shaffer
Department of Biological Chemistry
The University of Michigan
[Posted in FML issue 1471]