Peppered moths

Arthur V. Chadwick (
Thu, 01 Apr 1999 10:34:42 -0800

Let's see if we can improve the signal-to-noise ratio a little by
crystallizing what it is we are discussing.
I think we would all agree with the following:

1. We do not know where the peppered moths spend their daylight hours, but
we know it is not on the trunks of trees.

2. We do not know what the primary predator of peppered moths is, but since
they fly at night it is most likely something other than birds.

3. We do not know why the moths shifted to darker morphotypes
(simultaneously in U.S. unpolluted areas and Britain polluted areas), but
we know that they did.

4. We do not know why the moths shifted back to the lighter morphotypes,
but we know it is not due to any mechanism we yet understand.

5. We know that the pictures in textbooks were made under circumstances
other than those that would be considered natural, and that their relevance
to the behavior of the peppered moths is thus questionable at best.

Given the above, what can we say about evolution that we have learned from
the peppered moth?

I have omitted at Jonathan's suggestion #4, in order to attempt to find
areas of agreement. He writes:

Mendelian (though not the molecular) genetics of peppered moth morphotypes
is reasonably well understood. (The melanic "carbonaria" allele is
dominant to the light "typica" allele, and there are at least three
intermediate "insularia" alleles.)

Thus industrial melanism in peppered moths DOES (trivially) involve changes
in gene frequencies (as neo-Darwinism claims), it's just that we don't know
what causes those changes. And in the absence of evidence for some
mechanism(s), it's not clear that industrial melanism can even be called
To illustrate this point: let's say that a hole in the northern ozone layer
leads to an increase in solar radiation which causes all the people in
Scandanavia to get a spectacular tan. Then the hole closes, and people
revert to their typical pale skin-color. Is that evolution?

The illustration is not far-fetched: some early workers on peppered moths
proposed that melanism in some insects was induced directly by
environmental pollution, which (they claimed, affected the early embryo.
The induction hypothesis was swept aside by Darwinists after Kettlewell,
but it still remains a theoretical possibility.