Peppered myths

It's amazing how little critical thought is brought to bear on the subject of evolution. Most people pick one side or the other of the argument, knowing next to nithing about it. Even worse, they may have picked up some caricature of the subject and think they have real knowledge about it.

Even more amazing to me is how many of those who emphasize the need for critical thought apply it in only one direction.

Here's a case in point.

Norm Weatherby is hammering away at the peppered moth (Biston betularia) and industrial melanism.

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On January 17, 1999 The Washington Times reported that this "icon for evolution" is being disputed not by creationists, but evolutionists. Biologist Theodore Sargent admitted that he helped glue moths onto trees for a NOVA documentary about the peppered moth. The Washington Times reported that, "Mr. Sargent wrote in 'Evolutionary Biology' last year [1998] that subsequent studies have all found they change under many conditions, and do not really live on tree trunks." Jerry Coyne, a biologist at the University of Chicago, "agreed that the moth illustration of evolution had to be thrown out." Coyne wrote in the journal Nature, "My own reaction resembles the dismay attending my discovery, at age six, that it was my father and not Santa who brought the presents on Christmas Eve."

OK, sounds terrible. However, one of the neat things about science is that the court never adjourns. Any time a witness comes forward with new testimony, there's always time to power up the investigation and check out the details. For example, here's a link to a discussion on the peppered moth.

Now we have a number of statements of purported fact in the above, including:

• Peppered moths don't really live on tree trunks.
• Moths were glued to tree trunks.
• "They" (I assume this means peppered moths) change under many conditions.

The first statement, "Peppered moths don't really live on tree trunks." (No, dummy, they fly around at night, looking for mates. They may very well sleep on tree trunks.) Even stipulating that the Washington Times writer meant to say the moths don't "rest on tree trunks" as Wells did in his book, it's still wrong.

First, several of Wells's worst distortions must be dealt with directly.

The natural resting locations of peppered moths – Majerus' data. On page 148, Wells discusses the natural resting places of peppered moths, under the heading "Peppered moths don't rest on tree trunks." But they do, at least sometimes. Here are the relevant datasets, which Wells does not quote or cite for his readers:

Location of resting moths	Natural	Near traps
Branches	31.9%	9.9%
Exposed trunk	12.8%	23.6%
Unexposed trunk	12.8%	10.8%
Trunk/branch joint	42.6%	32.5%
Foliage	0%	10.8%
Man-made surfaces	0%	12.3%

Hmmm... This data never seems to make it into the critiques of the peppered moth story. I wonder what else isn't being mentioned.

The second statement may be relevant, or it may not. Certainly, articles in science journals may include photographs and illustrations that show organisms in contrived situations. A dissected animal is very definitely contrived. You never find an animal in the wild splayed out on a tray, with its skin cut open and pinned back, and with innards moved conveniently out of the way for easy viewing.

In this case, it seems to be much ado about nothing.

...textbook photos are used to show relative crypsis of moth morphs, not to prove that peppered moths always rest in one section of the trees. And third, Majerus himself has taken unstaged photos of peppered moths on matching tree trunk backgrounds, and these are not significantly different than staged photos; this eviscerates whatever vestige of a point Wells thinks that he has.

Yes, moths do rest on tree trunks. (At least a quarter of the time, based on the survey in the wild. Add the trunk/branch joint, which in my experience bears a surface appearance strikingly similar to the nearby trunk, which is about four tenths of the cases observed in the wild. This adds up to more than half of the observed moths. And I'm inclined to wonder how far up branches the lichin pattern extends.)

Dr. Bruce Grant, in his review of Wells' work, said pretty much the same thing:

No one who reads Kettlewell's paper in which the original photos appeared would get the impression from the text that these were anything but posed pictures. He was attempting to compare the differences in conspicuousness of the pale and dark moths on different backgrounds. Nobody thought he encountered those moths like that in the wild.

Yes, the original photos were staged, almost certainly because it was easier than dragging photographic equipment over to every example for which an illustrative case was desired.

Guess what – when someone went to the trouble of photographing moths where they actually landed, the photos were pretty darn similar.

Somehow, though, that never gets mentioned. It makes a fellow wonder what else isn't being mentioned.

The third statement is incoherent. A professional writer should be able to turn out something a little bit clearer. (I would hope!)

In the spirit of good sportsmanship, I'll attempt to divine what the writer was getting at with the statement that "they change under many conditions".

It happens that moths, and indeed most living things, will exhibit variations in their features. Even in the absence of pollution, you'll find occasional melanic moths, just as you find the occasional albino snake or other animal appearing in the wild. The thing is, they tend not to last very long in the wild unless they're very lucky.

There have been discussions about the relative importance of predation by birds on the observed changes in the abundance of light and dark forms of the peppered moth. However, the notion that birds have something to do with it is not based on just one piece of data.

Kettlewell showed that the dark, or melanic, form of the moth predominated primarily because of predation by birds. He did not think that predation was the only cause of industrial melanism and in fact speculated as to the relative strengths of other causes. Briefly, he performed a number of experiments: 1. Release-recapture experiments 2. Direct observation and filming 3. Ranking of camouflage 4. Correlation of geographical distributions with industrialization

Word of the researcher who took the time to photograph peppered moths in their natural resting spots, Michael Majerus, must have gotten back to Wells, because Wells wrote a response. He called Majerus a liar.

In his response, Majerus mentioned that he had read some 500 papers, adding up to about 8000 pages (average of 16 pages per paper). They all support the hypothesis of selective predation.

And indeed, this is characteristic of sound science. It hangs together and it meshes with other results that turn up elsewhere. In particular, people who look for side-effects of evolution in action will find it. Geographic distributions will work out right, as will the timing of population changes. Similar cases can be expected to behave in similar ways. Analogous cases can be expected to behave in analogous ways. (E.g., soot on tree trunks might similarly favor darker varieties of predatory insects. Predators need to remain un-noticed until they're close enough to pounce.)

I wonder if either Dr. Wells or Mr. Weatherby would be willing to bet that industrial melanism has never shown up in predators.