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From "Melanism: Evolution in Action"
By Michael E. N. Majerus
Oxford University Press, 1998
Quotations on peppered moth melanism selected by Arthur S. Lodge
Quotations from Dr Majerus' book are given in italics.
Importance that has been attached to peppered moth melanism
Preface, p.vi, paragraph 3: …this most famous example of evolution in action….
p.97, paragraph 1: As the renowned evolutionary geneticist, Professor Sewall Wright, wrote in 1978 of the peppered moth story, it is: `the clearest case in which a conspicuous evolutionary process has actually been observed'.
p.115, paragraph 2: Bernard Kettlewell's observational and experimental work on the peppered moth had a considerable influence on the subject of evolution, for it moved the primary perceived mechanisms of biological evolution from theory to fact.
Non-existence of important bird predation evidence
p.125, paragraph 2: …observations of peppered moths being taken from natural resting positions are still lacking and are urgently needed,….
Dr Majerus started this sentence with the word Although and ended with the words: it is highly probable that predation levels are significant. On May 7, 2002, I sent Dr Majerus an e-mail asking: why is it highly probable? I have not yet received a reply.
Scarcity of data on resting sites in the wild
Preface p.v, paragraph 2: …one of the slowest accumulating data sets I have compiled: …a data set that comprises notes on 47 moths found over 34 years.
p.121, paragraph 4: Data on the natural resting sites of the peppered moth are pitifully scarce…
…the number of published records of peppered moths being found on tree trunks is negligible..
This is emphasized in an admission by Sir Cyril Clark (Clark et al., 1985): `all we have observed is where the moths do not spend the day. In 25 years we have found only two betularia on the tree trunks or walls adjacent to our traps…and none elsewhere.'
p.121, paragraph 5: The largest data set of wild pepper moths found in truly natural positions …is of just 47 moths found over a period of 34 years (Howlett and Majerus, 1987)
Not NDT, but EDM?
The above quotations cast serious doubt on the validity of the conventional interpretation of peppered moth melanism in terms of the NDT. An alternative possibility is EDM - environmentally directed mutation. Photographs of melanic and non-melanic moths taken against matching backgrounds are remarkable not only in regard to color matching but also (particularly for non-melanics) for pattern matching. Moths appear to be as good as chameleons in their ability to match backgrounds. Of course, there is the important difference that moths do not change during their lifetime, but is it conceivable that some variant of the chameleon's genetic code could exist in the peppered moth that would enable the moth to alter the code of its offspring in such a manner that successive generations could attain closer and closer matches to the appropriate background?
Not NDT, but ETMC?
On p.68, Majerus discusses yet another mechanism of evolutionary change in connection with certain other lepidoptera, ending with the following paragraph:
In cases of this type, melanism is a product of an interaction between genetic factors and the environment. Some or all members of a population will carry the necessary genes to produce melanism, but these genes are only expressed if triggered by some environmental cue.
It seems reasonable to call this process "Environmentally-Triggered Mutations Change", or ETMC, for short. If peppered moth melanism falls under this category, then the NDT cannot apply to it, because random, spontaneous mutation is an essential part of the NDT.