Thursday, December 13, 2007

An Icon of ID: Jonathan Wells and the Peppered Moths

Of the books attacking Darwinian science, one of the most popular has been Jonathan Wells' Icons of Evolution. Sponsored by the Discovery Institute as part of its "wedge strategy" for promoting "intelligent design theory," Wells' book argues that some of the best-known examples of evolutionary explanation are actually untrue.

For instance, the evolution of peppered moths in England is often presented in biology textbooks as a clear case of evolution in action. Hundreds of years ago, the typical form of the peppered moth was mostly light gray with some black spots. But during the industrial revolution, pollution turned many tree trunks black. As a result, black "melanic" forms of the moths increased in number, because the lighter colored moths were more easily visible against the black tree trunks and thus most exposed to predation by birds. In the late 1950s, however, legislation that reduced pollution levels allowed trees to return to lighter colored trunks, which favored the return of the lighter colored moths, because now the darker moths were more visible to bird predators. In the 1950s, Bernard Kettlewell became famous for conducting experiments with these moths in the woodlands of England to confirm this Darwinian theory of the evolution of melanic moths.

But then in the 1980s, some researchers began to doubt Kettlewell's reports. The textbooks show Kettlewell's pictures of moths on tree trunks. But some researchers suggested that peppered moths do not rest on tree trunks, but rather they generally hide under horizontal branches. It seemed that the pictures of moths on trees appearing in biology textbooks had actually been staged by researchers who had glued dead specimens onto the trees. Wells could then proclaim this to be an example of scientific fraud. Many critics of Darwinian science have cited this in presentations to public school boards to support their claim that biology textbooks are using fraudulent evidence to advance Darwinian evolutionary theory.

And yet, Wells' presentation of this story is itself fraudulent. The debate over Kettlewell's research was surveyed in Michael Majerus' 1998 book Melanism: Evolution in Action, which Wells cites. But Wells does not accurately present the story in Majerus's book. For example, Wells asserts that "peppered moths don't rest on tree trunks" (148). But this ignores Majerus's reports of peppered moths in the wild found resting on tree trunks (see p. 123 of Majerus's book). Wells asserts that "pictures of peppered moths on tree trunks must be staged" (150). But Majerus' book has unstaged photographs that look no different from staged photographs (146-147).

Since 1998, Majerus has continued to conduct experimental research on peppered moths in England to see if Kettlewell's original claims could be defended against the critics. In recent years, Majerus has published his research confirming that Kettlewell was right after all. For example, in his research, he has shown that a significant proportion of moths (37%) do rest on tree trunks. Moreover, he generally concludes that differential bird predation has been a major factor in determining the common forms of moths, and thus this is a good example of Darwinian evolution in action.

Majerus's research is presented in a book chapter--"The Peppered Moth: Decline of a Darwinian Disciple"--in Insect Evolutionary Ecology, edited by Mark Fellowes et al. The notes for one of Majerus's power point presentations on this research can be found here.

Here then is an example of the experimental testing of Darwinian science. By contrast, as Majerus indicates, creationism and intelligent design are not open to such experimental testing.

1 comment:

oplopanax said...

The paper in Insect Evolutionary Ecology is from 2005 I believe and does not contain the final report on Majerus's long-term experiment which was just completed this year in 2007. Presumably that will be published in a journal somewhere. A fantastic interview of Majerus is online here: