Goodbye, peppered moths
A classic evolutionary story comes unstuck
The ‘textbook story’ of England’s famous peppered moths (Biston betularia) goes like this. The moth comes in light and dark (melanic) forms. Pollution from the Industrial Revolution darkened the tree trunks, mostly by killing the light-coloured covering lichen (plus soot).
The lighter forms, which had been well camouflaged against the light background, now ‘stood out,’ and so birds more readily ate them. Therefore, the proportion of dark moths increased dramatically. Later, as pollution was cleaned up, the light moth became predominant again.
The shift in moth numbers was carefully documented through catching them in traps. Release-recapture experiments confirmed that in polluted forests, more of the dark form survived for recapture, and vice versa. In addition, birds were filmed preferentially eating the less camouflaged moths off tree trunks.
The story has generated boundless evolutionary enthusiasm. H.B. Kettlewell, who performed most of the classic experiments, said that if Darwin had seen this, ‘He would have witnessed the consummation and confirmation of his life’s work.’1
Actually, even as it stands, the textbook story demonstrates nothing more than gene frequencies shifting back and forth, by natural selection, within one created kind. It offers nothing which, even given millions of years, could add the sort of complex design information needed for ameba-to-man evolution.
Even L. Harrison Matthews, a biologist so distinguished he was asked to write the foreword for the 1971 edition of Darwin’s Origin of Species, said therein that the peppered moth example showed natural selection, but not ‘evolution in action.’
However, it turns out that this classic story is full of holes anyway. Peppered moths don’t even rest on tree trunks during the day.
Kettlewell and others attracted the moths into traps in the forest either with light, or by releasing female pheromones—in each case, they only flew in at night. So where do they spend the day? British scientist Cyril Clarke, who investigated the peppered moth extensively, wrote:
‘But the problem is that we do not know the resting sites of the moth during the day time. … In 25 years we have found only two betularia on the tree trunks or walls adjacent to our traps (one on an appropriate background and one not), and none elsewhere.’2
The moths filmed being eaten by the birds were laboratory-bred ones placed onto tree trunks by Kettlewell; they were so languid that he once had to warm them up on his car bonnet (hood).3
And all those still photos of moths on tree trunks? One paper described how it was done—dead moths were glued to the tree.4 University of Massachusetts biologist Theodore Sargent helped glue moths onto trees for a NOVA documentary. He says textbooks and films have featured ‘a lot of fraudulent photographs.’5,6
Other studies have shown a very poor correlation between the lichen covering and the respective moth populations. And when one group of researchers glued dead moths onto trunks in an unpolluted forest, the birds took more of the dark (less camouflaged) ones, as expected. But their traps captured four times as many dark moths as light ones—the opposite of textbook predictions!7
University of Chicago evolutionary biologist Jerry Coyne agrees that the peppered moth story, which was ‘the prize horse in our stable,’ has to be thrown out.
He says the realization gave him the same feeling as when he found out that Santa Claus was not real.5
Regrettably, hundreds of millions of students have once more been indoctrinated with a ‘proof’ of evolution which is riddled with error, fraud and half-truths.8
- H. Kettlewell (1959), ‘Darwin’s missing evidence’ in Evolution and the fossil record, readings from Scientific American, W.H. Freeman and Co., San Francisco, p. 23, 1978. Return to text.
- C.A. Clarke, G.S. Mani and G. Wynne, Evolution in reverse: clean air and the peppered moth, Biological Journal of the Linnean Society 26:189–199, 1985; quote on p. 197. Return to text.
- Calgary Herald, p. D3, 21 March 1999. Return to text.
- D.R. Lees & E.R. Creed, Industrial melanism in Biston betularia: the role of selective predation, Journal of Animal Ecology 44:67–83, 1975. Return to text.
- J.A. Coyne, Nature 396(6706):35–36, 1998. Return to text.
- The Washington Times, p. D8, 17 January 1999. Return to text.
- D.R. Lees & E.R. Creed, ref. 4. Return to text.
- Unfettered by evolutionary ‘just so’ stories, researchers can now look for the real causes of these population shifts. Might the dark form actually have a function, like absorbing more warmth? Could it reflect conditions in the caterpillar stage? In a different nocturnal moth species, Sargent has found that the plants eaten by the larvae may induce or repress the expression of such ‘melanism’ in adult moths (see Sargent T.R. et al. in M.K. Hecht et al, Evolutionary Biology 30:299–322, Plenum Press, New York, 1998). Return to text.
Note: (added January 2008) For a response to an attempt in New Scientist, in late 2007, to ‘rehabilitate’ the peppered moth’s reputation, see More about moths
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