Peppered Moths

Yesterday, I shared about an artificial (and rather poor) illustration of natural selection in action ("Green Toothpicks"). The most famous (and much-cited) example of natural selection in the wild is the changes in coloration of the Peppered Moth, changes that occurred as a result of industrialization in Great Britain. These changes were noticed throughout the 19th and early 20th centuries, as Peppered Moth populations went from being mostly white (with a few melanistic individuals) to mostly dark (with a few light individuals). In the 1950's, Bernard Kettlewell, a British biologist and physician, began a series of experiments that led him to believe that this change could be explained as a result of natural selection. He concluded that the moths were eaten by birds (visually-oriented predators) as they rested on tree trunks during the day. Kettlewell reasoned that before industrialization, light-colored moths were more prevalent because they were better comouflaged on the light-colored (and lichen-covered) tree trunks. But with increasing pollution, tree trunks became darker (and lichens died), light-colored moths were less camouflaged than darker ones, and the phenotype of the population became predominantly that of the dark individuals. This elegant example from the wild remains to this day the classic textbook example of natural selection at work.

Subsequent research has cast a great deal of doubt on this entire scenario. It turns out that Peppered Moths don't normally rest on tree trunks but in the crown of the trees, that researchers (including Kettlewell) released moths by day (even though they are a nocturnal species), that many (not including Kettlewell) in fact pinned dead moths to trunks rather than use live ones in their capture-recapture experiments. In addition, neither the distribution of the various color morphs nor that of the lichens fit the patterns predicted by pollution rates, either during the industrialization or following emission controls (when white moths made a comeback in some regions). The problems unearthed have been so serious that what had been called "Darwin's missing evidence" has been deemed invalid even by evolutionary scientists. (For a summary of these problems, the reader is referred to chapter 7 of Jonathan Wells' Icons of Evolution.) Nonetheless, since evidence for the evolutionary paradigm is so scant, this invalidated tale is still a prominent feature in most modern textbooks (with no mention of its problems).

But again, suppose we ignore (for the sake of argument) the fact that subsequent research has shown that the Kettlewell scenario does not provide the evidence for which Darwinists hope. Let us be generous and grant that perhaps further research will discover a mechanism (consistent with natural selection) that explains the change in Peppered Moths. Then, as evidence for macroevolution, we have the same problem here as we had with the green toothpicks. We have--at the end of the experiment--merely a different frequency of the same phenotypes already present at the beginning. Phillip Johnson has stated the problem well (in Darwin on Trial)...

Why do other people, including experts whose intelligence and intellectual integrity I respect, think that evidence of local population fluctuations confirms the hypothesis that natural selection has the capacity to work engineering marvels, to construct wonders like the eye and the wing? Everyone who studies evolution knows that Kettlewell’s peppered moth experiment is the classic demonstration of the power of natural selection, and that Darwinists had to wait almost a century to see even this modest confirmation of their central doctrine. Everyone who studies the experiment knows that it has nothing to do with the origin of any species, or even any variety, because dark and white moths were present throughout the experiment. Only the ratios of one variety to the other changed. How could intelligent people have been so gullible as to imagine that the Kettlewell experiment in any way supported the ambitious claims of Darwinism?

At least two pitfalls (obstacles to objective truth) can be seen in the Peppered Moth story. First, moth researchers used invalid methods and jumped to wrong conclusions primarily because of an inordinant desire to provide evidence for a popular--but evidentially-impoverished--theory. Second, had their conclusions not been spurious, these same researchers (and their popularizers, including textbook editors still today) have been guilty of failing to see the scalar limitations of their results. Evidence of natural selection working at the level of a species quite simply is irrelevant as evidence for macroevolution.

As a scientist, I only hope that the Peppered Moth may serve as a reminder to avoid these pitfalls long after it has been finally discarded as a significant piece of evidence for Darwinian evolution.