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Archiver > GENEALOGY-DNA > 2002-09 > 1031195700


From: "John F. Chandler" <>
Subject: Re: [DNA] Toba bottleneck
Date: Wed, 4 Sep 2002 23:15 EDT
In-Reply-To: gbonner@smhrimsx.mhri.med.umich.edu message <2449F3F867FBD211936600C04F68569EA3CC74@smhrimsx.mhri.med.umich.edu> of Wed, 4 Sep 2002 20:59:27 -0600


Gregg wrote:
> Consider the American human population as a whole. Imagine the
> sub-population that is routinely having 5 children. Now imagine the
> sub-population that is having 2 children.

Need I point out that it's more complicated than that? Among other
things, family size is primarily cultural rather than genetic, as long
as basic nutritional needs are met.

> And finally, about antibiotics, I must agree with the original sentiment.
> What is the alternative - not prescribe them? What is the point of having
> them if you can not use them? To say that they lead to resistant bacteria is
> to claim that antibiotics are mutagenic, otherwise the mutation is naturally
> occurring, and not the result of the drug.

That's a misrepresentation of the argument, which is twofold. First,
there is outright misuse of antibiotics by giving them in low doses
or incomplete treatments (to farm animals and difficult humans). Such
treatments kill many bacteria, but are optimal for selecting strains
with marginal resistance. Since bacteria exchange genes by conjugation,
it is entirely possible for two marginally resistant strains to thrive
in this environment and so get together and become truly resistant.
(Note: this is a little like the cross-over between pairs of chromosomes,
which is the reason why only Y DNA testing has caught on for genealogy
as far as nuclear DNA is concerned. -- There! That's the point that
makes this digression on-topic for this list!)

Second, antibiotics are routinely used for treating viral infections,
even though they have absolutely no effect on a virus, but just in case
there is some secondary bacterial infection. This is a gray area
where the treatment probably doesn't hurt, but probably doesn't help
either. (In a way, this is like the debate over 12 loci vs. 25 loci.
Cost really does enter into the decision-making process, but it depends
a lot on who is paying.)

John Chandler

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