Re: Is the human race with modern medecine not evolving downward?

Dave wrote:

>Could someone on the list please explain to me why at least for
>humans, descent is not true in both senses. Both modern medicine
>and things like controlled environments seem to be allowing
>individuals to survive to have children that in the past would not
>have occurred. I realize that controlled environments are a mixed
>blessing, but at least having heat when the temperature is -30 out,
>does help lung conditions. . For example I have serious asthma and
>have had so since at least 5 years of age. In my senior year of
>high school we were at emerg at least two nights of most weeks
>getting adrenaline shots and that was when my atomizer, pills and
>allergy shots failed to control things. Between ages of 16 and 23 I
>was determined not to have children and still at times wonder if I
>did right when I see allergies in my children and grandchildren.
>

I knew I had a reference somewhere that was relevant to this, but it
took me until now to find it. Crow argues that we have probably been
accumulating mildly deleterious mutations for several centuries, but
that the effect is not too serious at this point. We have time to get
a better much better understanding before doing anything about it.
This article is available free at the url below.

Preston G.

http://www.pnas.org/cgi/content/abstract/94/16/8380

Proc Natl Acad Sci U S A. 1997 Aug 5;94(16):8380-6.
   
The high spontaneous mutation rate: is it a health risk?
Crow JF.
Genetics Laboratory, University of Wisconsin, Madison, WI 53706, USA.

The human mutation rate for base substitutions is much higher in
males than in females and increases with paternal age. This effect is
mainly, if not entirely, due to the large number of cell divisions in
the male germ line. The mutation-rate increase is considerably
greater than expected if the mutation rate were simply proportional
to the number of cell divisions. In contrast, those mutations that
are small deletions or rearrangements do not show the paternal age
effect. The observed increase with the age of the father in the
incidence of children with different dominant mutations is variable,
presumably the result of different mixtures of base substitutions and
deletions. In Drosophila, the rate of mutations causing minor
deleterious effects is estimated to be about one new mutation per
zygote. Because of a larger number of genes and a much larger amount
of DNA, the human rate is presumably higher. Recently, the Drosophila
data have been reanalyzed and the mutation-rate estimate questioned,
but I believe that the totality of evidence supports the original
conclusion. The most reasonable way in which a species can cope with
a high mutation rate is by quasi-truncation selection, whereby a
number of mutant genes are eliminated by one "genetic death."
Received on Wed Apr 5 00:20:41 2006