Peppered Moths

From SkepticWiki

1 Introduction
2 Creationists and Peppered Moths
3 Links and References
4 Related Articles

[edit] Introduction

During the late eighteenth century, a dark variety of the peppered moth arose in industrial areas of England. After the theory of evolution was discovered, It was hypothesized that the dark variety grew prevalent in industrial areas was because mutations which made the moths darker were becoming favored by natural selection because the darker moths were better camouflaged against a landscape blackened by pollution.

This led researchers to test this hypothesis by undertaking a number of experiments to see whether the darker coloring really was advantageous to the moths, by measuring the survival rates of the two different kinds of moth under natural conditions, and by measuring the abilities of birds to find the different kinds of moth under controlled conditions.[1] The results have become a stock example of natural selection in action.

These experiments have recently been repeated over a period of seven years by Professor Michael Majerus, in an unpolluted setting where it was predicted that the light variety of moth would be favored.[2]

[edit] Creationists and Peppered Moths

Misunderstanding the nature of some of these experiments has led creationists to make accusations that these experiments were "fraudulent" because they involved gluing moths to trees. The allegations seem to have originated with the creationist Jonathan Wells, and to have grown in the telling --- we have seen one account in which the errant researchers were jailed for their misdeeds!

While most of the experiments on peppered moths (for example those of Kettlewell, which are most often cited) did not involve glue in any form, some experiments did indeed involve gluing moths to trees.

Of course the reason we know this is because the experimenters said so very clearly in their published papers. The purpose of these experiments was to determine the efficacy of the two different forms of camouflage, which is unaffected by whether or not the moth is glued to the tree. What is affected, of course is the researchers' ability to go to where they left the moth and see if it's been eaten by a bird, which makes the experiment rather easier than the more laborious methods employed by Kettlewell.

To quote one of the researchers involved:

As I am one of the evolutionary biologists who study peppered moths, I feel obliged to comment. Charges of fraud cannot be left unchallenged ... In your paper, Ms. Katrina Rider asserts the peppered moth story is a hoax. She conveys the impression that dead moths were glued to trees as part of a conspiracy of deception. She seems unaware that moths were glued to trees in an experiment to assess the effect of the density (numbers) of moths on the foraging practices of birds. Taken out of the context of the purpose of the experiment, the procedure does sound ludicrous. [3]

These experiments also came under attack in the 1980s, when it was claimed that peppered moths hardly ever sat on tree trunks. This would have invalidated the experiment, since there is no point in testing the adaptive properties of camouflage against a background that the moth never alights on. However, of peppered moths observed in the wild, about a quarter were indeed sighted on tree trunks; they were also found sitting on the bark of branches, where their camouflage would have a similar effect. (see M.E.N. Majerus: Melanism: Evolution in Action, Oxford University Press)

It is difficult to see why creationists bother to attack the peppered moth, since it only demonstrates change within a species, which they call "microevolution" and profess to believe in.