Xref: utzoo sci.research:610 sci.bio:1806
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From: hes@ecsvax.uncecs.edu (Henry Schaffer)
Newsgroups: sci.research,sci.bio
Subject: Re: animal research
Summary: gene frequency changes take time
Message-ID: <6317@ecsvax.uncecs.edu>
Date: 2 Feb 89 13:51:29 GMT
References: <1252@meccsd.MECC.MN.ORG>
Distribution: na
Organization: NC State Univ.
Lines: 56

In article <1252@meccsd.MECC.MN.ORG>, scj@meccsd.MECC.MN.ORG (Scotian) writes:
> Alan Morimoto writes:
> |We end up with a lot of sick people that would not survive
> |without medical help.  [..] I can imagine that countries that are
> |not as medically advanced inherit a stronger gene pool of people simply
> |because the weak will perish.  ...
> 
> I have come to the same conclusion when pondering the future of the
> human race, and it is rather disconcerting.  However, I do not see
> this is a case against animal experimentation.  ...
> -- 
> Scott C. Jensen

  Two topics intermixed - animal experimentation and genetic consequences
of medical intervention.

  1)If the argument is correct that animal intervention makes for more
effecive medical treatments and that leads to increased gene frequencies 
of deleterious genes, that seems to be admitting the effectiveness of
animal experimentation in developing medical treatments!  (If we really
want to stop saving lives, it would be *much* more efficient to just
stop applying medical treatments, rather than to stop animal experimentation
and hope that medicine will stop improving.)

  2)While medical intervention clearly leads to changes in gene frequencies
(as do *many* other changes in the selective nature of the environment)
there still is a question of how much and how fast.  If an illness/condition
was caused by purely environmental effects, with no genetic component, then
medical intervention does not make any change in gene frequencies.  (I'm
thinking of things like automobile and other accidents.  There may be a
second order genetic effect - e.g. that good genes for nimbleness will help
one keep from being hit by cars, but I'll ignore that as being second
order.)

  Also illnesses which occur after reproductive years do not affect gene
frequencies.  Whether or not medical intervention saves a life at that
time does not affect whether or not the genetic basis of that illness
has been passed on.

  Then for illnesses which have a genetic basis, and which affect the
reproductive potential of the individual, medical intervention has a
genetic effect on the population - which depends on how much it changes
the survival rate.  (I.e., if the base rate is 80% survival, and medicine
changes it to 90%, that is not a dramatic change in the selective
situation.)  Even if medicine changes a lethal condition to complete
survival (the most extreme example possible) how fast will the population
gene frequencies change?

  The medical intervention does not in itself *increase* the frequencies
of deleterious genes.  It just stops the selection against them, and allows
mutation to increase the frequencies.  Mutation is a slow process, with
rates often found in the 10**-5 to 10**-6 range.  For deleterious recessive
genes gene frequencies are often found to be in the area of 10**-1, and
so it takes *many* generations for an appreciable change.

--henry schaffer  n c state univ