Peppered Moths: We Told You So

The ID movement hasn’t had many successes, but one area where they did pretty much succeed in causing considerable havoc was the classic textbook example of natural selection in action: the change in color of peppered moths (Biston betularia) from peppered white, to black, and back to peppered white again. Through a series of accidents that is still difficult to understand, the idea got started in the late 1990s that leading peppered moth researcher Michael Majerus had debunked Bernard Kettlewell’s famous study confirming the old hypothesis that the change in peppered moth color was due to selective predation of conspicious moths by birds.

This confusion, minor by itself, was massively magnified when the ID/creationists picked it up and spread it far and wide. In the 1970s-1980s, creationists used to just resort to traditional obfuscation when confronted with natural selection producing a the “designed-looking” adaptation of moth camouflage to match their changing background – creationists would just reply “they’re still moths”, purposely avoiding the point of the peppered moth example. But once they heard that Kettlewell’s research and hypothesis were in trouble, they declared the example a fraud, the illustrative photos a dastardly fraud, and told the world that the biology textbooks were lying to the children and that the ID movement’s quack science should be given a place in schools to balance things out. I think Jonathan Wells probably considered the alleged downfall of the peppered moth his career achievement.

Science journalists, forgetting the maxim “If a creationist declares victory, it doesn’t necessarily mean that they’ve actually won” breathlessly and almost entirely uncritically repeated the basic “peppered moths debunked” storyline, almost completely neglecting the horrified objections of the actual people who knew something about the subject, the peppered moth researchers like Bruce Grant and Michael Majerus himself. Piling on was the (2002) book Of Moths and Men by New-Ager science journalist Judith Hooper, who naively took all the hubbub as an indication of reality, and added her own rumor-mongering and uninformed speculation to the mix, for example by postulating that maybe night-feeding bats somehow magically selectively predated one color of moth, and, most egregiously, inventing the idea that Kettlewell had actually deliberately faked his results, a conclusion which Hooper based on nothing but clueless armchair analysis of a few datapoints and a magical letter that somehow influenced Kettlewell the day before he actually received it (see debunking of this).

Well, the press was against Kettlewell’s Bird Predation Hypothesis. More than a few scientists (outside of the peppered moth community) looked askance at it. And the creationists were crowing for years. In addition, while I haven’t done a systematic analysis, my sense of it is that the poor peppered moth took a serious hit in coverage in the textbooks. The only defenders, basically, were the peppered moth guys themselves, and, well, us PT/talkorigins/NCSE folks. We defended the old Biston example through thick and thin, based mostly on the novel idea that one ought to read the original research and the actual experts to get a sense of what the most likely reality is. You can see most of this long-live-the-peppered-moth stuff here, here, here, and here.

It’s all well and good to argue about old studies, but for the last five years or so, Michael Majerus has been working on a long-term, answer-all-the-critics experiment to re-test (yet again) the idea that selective bird predation on conspicuous moths is the primary cause of the change in color morphs of the peppered moth. It looks like he’s finally finished:

Majerus Lab Evolutionary Genetics Group

STOP PRESS - The text of Mike Majerus’ talk given at Uppsala on 23 August is now available as a pdf file - The Peppered Moth: The Proof of Darwinian Evolution

I have emailed Majerus, he says that he will put up the powerpoint slides and photos when he gets back from a meeting next week. (So please, don’t flood his email asking for these.)

Here is the news story on his talk:

Moth study backs classic ‘test case’ for Darwin’s theory

For more than a century it has been cited as the quintessential example of Darwinism in action. It was the story of the peppered moth and how its two forms had struggled for supremacy in the polluted woodlands of industrial Britain.

Every biology textbook on evolution included the example of the black and peppered forms of the moth, Biston betularia. The relative numbers of these two forms were supposed to be affected by predatory birds being able to pick off selectively either the black or peppered variety, depending on whether they rested on polluted or unpolluted trees.

It became the most widely cited example of Darwinian natural selection and how it affected the balance between two competing genes controlling the coloration of an organism. Then the doubts began to emerge.

Critics suggested that the key experiments on the peppered moth in the 1950s were flawed. Some went as far as to suggest the research was fraudulent, with the implication that the school textbooks were feeding children a lie.

Creationists smelt blood. The story of the peppered moth became a story of how Darwinism itself was flawed - with its best known example being based on fiddled data.

Now a Cambridge professor has repeated the key predation experiments with the peppered moth, only this time he has taken into account the criticisms and apparent flaws in the original research conducted 50 years ago. Michael Majerus, a professor of genetics at Cambridge University, has spent the past seven years collecting data from a series of experiments he has carried out in his own rambling back garden. It has involved him getting up each day before dawn and then spending several hours looking out of his study window armed with a telescope and notepad.


In a seminal description of his results to a scientific conference this week in Sweden, Professor Majerus gave a resounding vote of confidence in the peppered month story. He found unequivocal evidence that birds were indeed responsible for the lower numbers of the black carbonaria forms of the moth. It was a complete vindication of the peppered month story, he told the meeting.


While the professor has also described drawbacks to Kettlewell’s methodology, he was able to address all of these concerns and even tested an idea that Hooper had raised in her book - that it was bats rather than birds responsible for moth predation - a suggestion he dismissed altogether.

Professor Majerus compiled enough visual sightings of birds eating peppered moths in his garden over the seven years to show that the black form was significantly more likely to be eaten than the peppered.

A statistical analysis of the results revealed a clear example of Darwinian natural selection in action.

“The peppered moth story is easy to understand, because it involves things that we are familiar with: vision and predation and birds and moths and pollution and camouflage and lunch and death,” he said. “That is why the anti-evolution lobby attacks the peppered moth story. They are frightened that too many people will be able to understand.”

Barring the unlikely possibility of a dramatic change in the conclusions before Majerus’s official publication of his results (which, we must remember, will be the official, authoritative presentation of the work), let me say it again. We Told You So.

I do think that this case should be a cause of some reflection on the part of journalists and textbook publishers. Is it possible that these groups, normally skeptical of creationists, let themselves get stampeded into the “bird predation is dead!” meme by creationist propaganda?

At any rate, as sure as night follows day, the ID/creationists, craven as always, are already refusing to admit they were wrong, and are instead trying to crawl unnoticed back to their old hole: “Sure it’s natural selection, but they’re still just moths!” A case in point:

IMHO…a couple of issues with the most recent peppered moth study. It’s still a moth, and the evolution is an oscillation of populations, just like the finches of Galapagos

There it is, in black and white.