# Digest urth.v013.n010

*The Urth list — 1 messages, 1 voices, 16 Jun 1998*

<https://urth.darkrealm.vip/thread/urth/808>

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### Dan Parmenter
*16 Jun 1998, 07:30*

> From: David_Lebling at avid.com
> 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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