From: allens@yang.earlham.edu (Allen Smith)
Newsgroups: alt.sex,sci.bio
Subject: Re: incest
Date: 6 Apr 92 20:15:56 GMT
 <1992Mar25.100724.23445@deeptht.santa-cruz.ca.us> <bruce.701664143@harry> <1992Apr03.091936.11548@deeptht.santa-cruz.ca.us>
Organization: Earlham College, Richmond, Indiana

In article <1992Apr03.091936.11548@deeptht.santa-cruz.ca.us>, rstevew@deeptht.santa-cruz.ca.us (Richard Steven Walz) writes:
> In article <bruce.701664143@harry> bruce@harry.ugcs.caltech.edu (Bruce J Bell) writes:
>>rstevew@deeptht.santa-cruz.ca.us (Richard Steven Walz) writes:
>>
>>
>>[...]
>>
>>>I think that the various tribes of the world and the various ruling
>>>monarchies in history and the same genetics which apply to breeders of
>>>improved animals will tell you that incest won't really hurt a breed
>>>of animals or humans unless you happen on a gene which has a delayed
>>>effect during the life of the animal and you duplicate them through
>>>enforced interbreeding, like the Pharoahs and the European Royalty.
>>
>>The reason inbreeding won't likely hurt a well-defined breed of domestic
>>animals is that all such breeds are *already* extremely inbred, so
>>that all the deadly/disease-causing recessives have been bred out.
>>The inbreeding causes each animal to have identical copies of every
>>gene, so that the results of mating within the breed is predictable.
>>
>>Humans, on the other hand, are genetically "wild", with thousands of
>>harmful recessives, most of which are extremely rare.  However, incest
>>makes it much more likely for these recessives to be expressed.  Thus,
>>a product of incest is likely to have *extreme* genetic problems.  If
>>a group of humans is willing to ignore the incest taboo and sacrifice
>>a few generations of their offspring, they might be able to produce a
>>breed of humans which could commit incest with impunity, but I don't
>>think that is particularly likely, or particularly desirable...
>>
>>BTW, I believe some wild species have undergone population crises so
>>extreme as to have a similar effect to human breeding.  Cheetahs are
>>almost genetically identical to each other, so inbreeding doesn't have
>>as severe an effect on them as many other species.  (I vaguely remember
>>this from a Scientific American way back in the misty past, so don't
>>count on this; look it up instead).

	As I recall, Cheetahs may not have much impact from further 
inbreeding since they're already rather inbreed (it appears that there was 
a genetic bottleneck a bit back, and transplants from one cheetah to 
another, for instance, will not be rejected). BTW, I am not sure if this 
applies to all cheetahs, or just one population of them. Cheetahs have 
rather high sterility, miscarriage, and infant mortality rates due to 
genetic disorders.
>>
>>At any rate, there was, and is still, a very good reason to avoid incest.
>>Don't knock the primitives until you have a very good handle on your facts...
>>
>>
> 
> Bruce:
> These aren't my facts. They are from a project paper I did one time on
> the incest taboo in anthropology. I discovered that numerous
> geneticists had been trying for years to get the ear of the amateur
> geneticists out there who have been giving us the wrong ideas about
> the "dangers" of incest. The quote from a group of them went something
> like: Humans would have to enforce inbreeding every generation to
> really get into trouble. Humans could in-breed every other generation
> as an average without getting into trouble. Also. We share so many
> genes which are fatal to the fetus when duplicated that only our level
> of miscarriages might rise very slightly over the current level, and a
> living duplication which was bad would be fairly rare. However,
> enforced in-breeding would make the problem go exponentially critical
> unless your family was free of survivable genetic disease. Please,
> you look up your facts and get a handle on them. I already have. -

	I don't doubt what you say, but I'd be interested in seeing the 
original papers on the subject. I can see humans having problems w/incest 
because of our habit of preserving and allowing to breed (in the case of 
royal families, encouraging) those with genetic defects. One could make an 
argument for eugenics, but fortunately germ line gene therapy (my intended 
field) is emerging as an alternative.
	-Allen