Significance of the Peppered Moth Argument


Dr. Wells:

I've got a question regarding the Peppered Moth data that you discuss in your new book Icons of Evolution

What does one say to a Darwinist when she points out that we are making a big fuss about nothing. Sure, students should know that the pictures were faked. But this does nothing to falsify it as a core example of natural selection and really does not undermine Darwin's theory. In fact, the actual phenomenon of dark moths surviving is true.

Basically, I'm asking whether your insights make the peppered moth example irrelevant or simply require that it be retold truthfully. I'm having trouble convincing others that this revelation makes the story irrelevant. Most agree that it should be told according to the facts.

Micah Sparacio


Dear Micah,

My comments are organized around four specific points in your question. Starting with the last:

1. "the actual phenomenon of dark moths surviving is true": Yes, it is certainly true that dark (melanic) forms of peppered moths became much more prevalent during the industrial revolution.  The same thing happened in many other species of moths, ladybird beetles, and even some birds.  But it is clearly not the case that melanism in all of these species was due to camouflage and selective predation.  Ladybird beetles, for example, are extremely distasteful to birds, who do not eat them.  Theory has it that dark ladybird beetles became more prevalent because of "thermal melanism" -- in which dark forms supposedly absorb more heat from the subdued sunlight in polluted environments.  In other words, the fact that industrial melanism occurred does not tell us what caused it.

2. "this ... really does not undermine Darwin's theory": It is true that, logically speaking, no theory is refuted simply by removing one piece of supporting evidence.  Anyway, there are examples of natural selection in the wild that (unlike the peppered moth) have been clearly established -- slight reversible changes in the beaks of Galapagos finches are one example.  Surprisingly, however, there have been remarkably few good demonstrations of natural selection.  And none of them show anything approaching the dramatic changes within species that breeders had been producing in domestic plants and animals for hundreds of generations before Darwin.  (Even if the peppered myth were true, it would be utterly trivial when it comes to explaining the origin of species or of new body plans.) So although discrediting the peppered moth story does not logically undermine Darwin's theory, it emphasizes how little empirical support there really is for it.  For a theory that pretends to be supported by "overwhelming evidence" -- and thus undeniable except by fundamentalist fanatics -- this looks a lot like undermining to me.

3. "this does nothing to falsify it as a core example of natural selection":  Again, while it is logically true that invalidating Kettlewell's experiments does not falsify the camouflage-predation explanation (which could still, in theory, be true), no scientist with any integrity would point to the peppered myth as "a core example of natural selection."  Without evidence, the assertion that melanism in peppered moths was due to natural selection is a faith-statement, not a scientific inference.  The phenomenon might have been due to any number of selective factors, or to none at all.  The most honest answer is that we don't know the reason the shift in the color of the population coincided with the increase of pollution in the area.

When evolutionary biologist John Endler wrote his now-classic book, "Natural Selection in the Wild," in 1986, he declared that "the time has passed for 'quick and dirty' studies of natural selection."  Although most researchers are "satisfied in demonstrating merely that natural selection occurred," Endler wrote, "this is equivalent to demonstrating a chemical reaction, and then not investigating its causes and mechanisms.  A strong demonstration of natural selection combined with a lack of knowledge of its reasons and mechanisms is no better than alchemy."  So even if industrial melanism in peppered moths were a demonstrated case of natural selection (which it isn't), without identifying the selective agent(s) it would still be "no better than alchemy."

4. "students should know that the pictures were faked": This goes without saying.  Since biologists have known since the 1980s that peppered moths do not normally rest on tree trunks, not to tell students that the pictures were staged (in many cases by gluing or pinning dead moths to desired backgrounds) constitutes as clear a case of scientific fraud as any on record.  Yet I'm aware of no sincere efforts by Darwinists to inform students of this -- despite their pious declarations of good intentions. Almost all recent (1998-2000) biology textbooks use such photos without any indication that they were staged.  As a scientist, I find this absolutely
inexcusable.  If dogmatic Darwinists were as smart as they pretend to be, they would be actively campaigning -- for their own good! -- to rid textbooks of this fraud.  Acquiescence in scientific misconduct will not look good on their resumes.

Jonathan Wells, Ph.D.
Center for the Renewal of Science & Culture
Discovery Institute, Seattle