“Of Moths and Men” by Judith Hooper

It was a world-famous example of evolution in action, and it was rigged. How the case of the peppered moth proved that "scientific fact" sometimes isn't either.

Topics: Evolution, Books,

Almost everyone is familiar with the magnificent story of the peppered moth. In the second half of the 19th century, lepidopterists in Britain began noticing that a dark version of a well-known pale speckled moth, Biston betularia, started appearing in great numbers in the industrialized regions. The more polluted the area, the more they seemed to thrive. Soon, they outnumbered their pale cousins, and Darwinists, eager for a real-life example of evolution at work, suggested the color change might be due to “natural selection.”

Darwin was already in the grave by the time someone first made the connection in 1896. The great man himself had never witnessed a clear-cut case of natural selection and had not expected to. But those who carried the flame were beside themselves with excitement.

The coloring on the typical form of the moth looked a lot like lichen, so on trees in rural areas they could be camouflaged from their predators. But in industrialized areas — so polluted that the lichen died off — this coloring was no longer an asset. Here, where tree trunks were dark with soot, mutant darker forms of the moth had the upper hand, and they survived and multiplied. So the argument went.

But a hypothesis is one thing and real evidence is another. It wasn’t until 1953 that Bernard Kettlewell, an amateur lepidopterist (and erstwhile medical doctor) hired by the Oxford School of Ecological Genetics, set off to test that idea in the field. For a few successive summers, he camped out near industrialized Birmingham or in pastoral Dorset. By releasing marked moths — both dark and light — then counting how many live ones he could lure back, he aimed to show that the dark moths fared better in polluted areas and light ones in pristine areas and that the reason was selective predation.

This is indeed what he “found.” He reported that twice as many darks as lights survived near Birmingham and three times as many lights as darks survived in Dorset. It was marvelous news for evolutionists. The findings were hailed as “Darwin’s missing evidence,” evolution’s “prize horse” and “evolution in action.” The story of the peppered moth became a staple in biology texts and science museums everywhere.



It was almost too good to be true — and, well, it was, as Judith Hooper explores in her new book, “Of Moths and Men: The Untold Story of Science and the Peppered Moth.” She isn’t the first to conclude this, as she readily admits. The first attack on Kettlewell’s methods dates back to 1969, she says, when Ted Sargent at the University of Massachusetts at Amherst pointed out that moths don’t actually choose to rest on colors that match their own. Other exposés appeared everywhere from the New Scientist (1987) to Whole Earth magazine (1999). An entire book on the peppered moth research and its shortcomings, by evolutionary biologist Michael Majerus, came out in 1998. This all does rather raise the question of why a new book was needed, and certainly makes the words “untold story” in the title a tad disingenuous.

Hooper does try to delve into the nitty-gritty of how it all went wrong. She interviewed extensively for the book, read the correspondence between the major players, even did some independent sleuthing. For instance, during Kettlewell’s first summer testing of the peppered moth hypothesis, he wrote to his boss, the formidable professor E.B “Henry” Ford, bemoaning his low recapture rates. Ford replied, innocuously enough, “I do not doubt that the results will be very well worth while.” Oddly, the very next day they suddenly were. After six days of catching only two or three moths per day, Kettlewell suddenly started netting 23 and 34. After asking pointed questions about what could have accounted for this dramatic reversal of fortune — and checking for herself that no significant weather changes happened during that time — Hooper speculates that he might have fudged the numbers.

Hooper is a competent writer, and occasionally she has a nice bite. She enjoys taking the piss out of Darwinists like Ronald Fisher, a mathematician, whose “severe myopia doomed him to lenses the thickness of coke-bottles … It didn’t seem to have occurred to him that in the state of nature, lacking optometrists, he might not have been the fittest of the lot.” Sadly, though, most of the book’s pithy comments come straight from the mouths or pens of others, and are nestled cautiously inside quotation marks, undigested by the author.

Her decision to tell the story chronologically also has some pitfalls. She wants to keep her readers in suspense, so she describes the experiments without pointing out where they were going awry. Consequently, important details often aren’t adequately underscored. For instance, in Dorset, Kettlewell rejigged his procedure partway through and ignored a few days’ data, a big scientific no-no. All decent scientists will immediately see the problems with his work, and wonder why Hooper doesn’t comment on them, while lay readers only find out about the mistakes many pages after they learned the salient details of the experiments in question.

In fact, the list of Kettlewell’s scientific shortcomings is fairly long, and it’s almost all left until Part 3, which doesn’t start until Page 241. For example, he wasn’t “blind” to what he was measuring; that is, he alone decided how dark to score a moth while at the same time knowing the result he wanted to get. Also, he placed many more moths per tree than would be the case in the wild, leading his critics to charge that he simply constructed a bird feeder; in other words, he failed to prove that birds were selectively eating the most visible moths. Somehow the most egregious of all was that photo — impressed on the memories of all young biology students — with two moths side by side on a tree, one nearly invisible because of crypsis, and the other totally obvious. Well, it was a setup. Worse, peppered moths don’t even rest openly on tree trunks that way.

Hooper tells the story right from the beginning — from Darwin’s voyage on the HMS Beagle to present-day critics of Kettlewell’s science. And it is a story well worth reading. But she fails to critically examine many of the important issues this sorry saga brings to light. How did all these flaws pass peer review? Why was this study accepted as gospel before it was replicated? Why did so few people go back and read the original papers before passing the story on?

Clearly, there was a lot at stake. The idea that the fittest survive became more than just a scientific theory — it had huge social implications as well. Many of the experts whose duty it was to cast a critical eye over the work seemed to want so badly for it to be true that they overlooked its glaring deficiencies. But in the case of the moths, only ideology was at stake. What happens when big money enters the picture, and billions of dollars hang on a result? The brave new fields of biotechnology and genomics rush to mind. Hooper quotes researchers saying this sort of thing couldn’t happen today. But reading this cautionary tale makes you wonder not whether it will, but where and when.

Alison Motluk is a freelance writer based in Toronto

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