Biston betularia

[Patrick Foley]

Dear Leppers

     It appears from papers by K. Mikkola (1979 Acta Entomologica Fennici
45:81-87, 1984 Biol. Journal Linnean Society 21: 409-421) and from the recent book
by M E N Majerus(1998. Melanism. Oxford University Press) that Kettlewell's
careful experiments with bird predation on peppered moths on tree trunks were
somewhat artificial. The moths rest in more obscure places on the trees, such as
the underside of branches near nodes. IN fact we are not sure exactly where they
rest during the day, so it is hard to extrapolate Kettlewell's experiments to
"natural " selection in a precise way. Majerus reviews the issue, points out the
problems, but concludes that the main thrust of Kettlewell's study is still sound.
Some reviewers (such as Jerry Coyne) are now troubled by the whole case, but I
think the peppered moth study is still a great example of microevolution.
    It is worth remembering that science does not proceed like a movie courtroom
trial. We don't throw out theories because we haven't proved beyond a shadow of
doubt every feature of a case. If the "holes" in Kettlewell's story make you
chortle with glee, you should read Majerus' book. The evidence for naturally
selected melanism would seem overwhelming. And it should be noted that scientists,
not creation "scientists" are the ones finding the holes _and_ deepening our
understanding of nature.

Patrick Foley
patfoley at csus.edu