Subject: (urth) Re: Digest urth.v013.n010

From: Dan Parmenter <dan at lec.com>
Date: Tue, 16 Jun 1998 07:30:01 +0000

>I think the general explanation that is given in genetics textbooks is
>not that the moths "evolved" a black color and then a white color.
>Rather, there was (and is) a certain amount of genetic variation in the
>moth population.  When pollution made the trees dark, there was
>selective pressure that favored darker colored moths (i.e., birds found
>and ate the light-colored ones).  So, after a while, the population was
>mostly dark-colored, but this didn't mean that the gene for
>light-colored-ness disappeared: it just got less prevalent.  Eventually,
>the pollution was cleaned up and the selective pressure went the other
>way, as the dark moths became more noticeable, so the occasional light
>colored moth was able to reproduce, leaving more light colored moths,
>and so on.

Yes, but as Mantis pointed out, it's often used as a "textbook case"
of evolution.  I remember very well receiving just that explanation in
my eighth grade science class and I was being deliberately provocative
in my post about it by taking the extreme position implied by Mantis'
post.

>If there is some representation of cayenne pepper genes in the moth
>population, then eventually dyeing the trees red will create selective
>pressure favoring red moths.  Otherwise, you're in the position of
>waiting for the moths to mutate at random into red.  This is roughly as
>likely as turning a mouse's tail into a hand by slapping it against a
>tree.

Yes, of course.  Mostly I just wanted to make that stupid pun;
however, such an absurd statement could conceivably follow from an
explanation of evolution given in terms of Peppered Moths, which as
you've pointed out is something of a misconception, though it seems
that the same mechanisms are at work.  

Actually, we didn't get the part about the moths becoming white
again.  I heard about that later, in the context of a later discussion
that touched on the fact that the factories weren't putting out so
much soot any more.  So perhaps my eighth grade teacher wasn't so
off.

Dan

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