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Wells' third reply
QUESTION: Do peppered moths normally rest on exposed tree trunks in the wild?

Ian Musgrave re-analyzes the data and concludes that "around one in 10 moths are found on exposed trunks."

Musgrave argues that the distinction between exposed and unexposed positions is not significant, because moths in unexposed positions are still subject to bird predation and thus protected by camouflage. This second claim, however, is not the question being addressed here. Furthermore, before it can be persuasive it will need more experimental support than the "pilot experiment" by Howlett and Majerus that Musgrave cites.

The question, then, is whether "one in 10" supports the claim that peppered moths normally rest on exposed tree trunks in the wild. In my opinion, to call 10% "normal" is to misuse the word. Where else in science (or in normal English usage, for that matter) would 10% qualify as normal? I doubt that continued discussion will shed any further light on the question with which we began. I will rest my case by repeating the major conclusions of the published empirical studies on the normal resting places:

"[T]he species probably only exceptionally rests on tree trunks." Thus "the results of Kettlewell (1955, 1956) fail to demonstrate the qualitative predation of the morphs of the Peppered Moth by birds or other predators in natural conditions." Kauri Mikkola, Biological Journal of the Linnean Society 21 (1984): 416, 418.

"We are, however, convinced that exposed areas of tree trunks are not an important resting site for any form of B. betularia." Rory J. Howlett and Michael E. N. Majerus, Biological Journal of the Linnean Society 30 (1987): 40.

"We agree with Mikkola's critique of field experiments to estimate the relative fitness of the phenotypes of B. betularia by using moths exposed on tree trunks. Such predation experiments must take into account the full range of the moth's resting sites in more. or less exposed positions." Tony G. Liebert and Paul M. Brakefield, Biological Journal of the Linnean Society 31 (1987): 145.

"[P]eppered moths do not naturally rest in exposed positions on tree trunks." Michael E. N. Majerus, Melanism: Evolution in Action (Oxford, 1998), p. 121.

Jonathan Wells
Discovery Institute, Seattle

Dr Musgrave has replied to the above.