Mothballing Evolution's Peppered Moths



A supposed proof of evolution turns out to be flawed.

A number of years ago, I distinctly remember going through some of the supposed "proofs" of evolution in my high school biology class that seemed to be quite convincing at the time.

One of those that caught my attention was the evidence of peppered moths changing their color from light to dark due to industrial pollution. This supposedly shows how natural selection can change a species into another type, and eminent scientists have emphasized the importance of this supposed proof of evolution.

Professor John Maynard Smith stated: "We should expect to find the most rapid evolutionary changes in populations suddenly exposed to new conditions. It is therefore natural that one of the most striking changes which has been observed in a wild population . . . is the phenomenon of 'industrial melanism,' the appearance and spread of dark forms of a number of species of moths" ( The Theory of Evolution, 1966, p. 137).

Sir Gavin De Beer, writing in The Encyclopaedia Britannica, said, "One of the most striking examples of observable evolution is the phenomenon known as industrial melanism" (1974, Vol. 7, "Evolution," p. 14).

As I glanced at a recent biology book, I noticed that the same evidence I read many years ago was still being given today. Here is a summary from the textbook Biology, by John Kimball (online version), updated in 2006:

Many species of moths in the British Isles began to become darker in color in the 19th century.

The best-studied example is the peppered moth, Biston betularia. The moth gets its name from the scattered dark markings on its wings and body.

In 1849, a coal-black mutant was found near Manchester, England. Within a century, this black form had increased to 90% of the population in this region.

The moth flies at night and rests by day on tree trunks. In areas far from industrial activity, the trunks of trees are encrusted with lichens . . . the light form . . . is practically invisible against this background.

In areas where air pollution is severe, the combination of toxic gases and soot has killed the lichens and blackened the trunks. Against such a background, the light form stands out sharply.

The moth is preyed upon by birds that pluck it from its resting place by day. In polluted woods, the dark form has a much better chance of surviving undetected. When the English geneticist H.B.D. Kettlewell . . . released moths of both types in the woods, he observed that birds did, indeed, eat a much higher fraction of the light moths he released than of the dark.

Since pollution abatement programs were put in place after World War II, the light form has been making a comeback in the Liverpool and Manchester areas.

And now, the rest of the story

It is regrettable that much of the information given in this biology textbook and in many others with similar explanations turns out to be grossly inaccurate. It shows why it's so important to get both sides of an argument and not just one. As the Bible says, "The first one to plead his cause seems right, until his neighbor comes and examines him" (Proverbs:18:17).

We will see that this so-called "proof" of the evolution of the peppered moth shows that even supposedly careful and impartial scientists cannot be trusted to leave their bias aside when it comes to teaching Darwinian evolution.

Further investigation on the peppered moth phenomenon has shown Kettlewell's classic experiments with these moths to be deeply flawed. Here is what Jerry Coyne, professor of evolutionary biology at the University of Chicago, explained in a prestigious British scientific journal:

From time to time, evolutionists re-examine a classic experimental study and find, to their horror, that it is flawed or downright wrong . . . The prize horse in our stable of examples has been the evolution of "industrial melanism" in the peppered moth, Biston betularia, presented by most teachers and textbooks as the paradigm of natural selection and evolution occurring within a human lifetime.

The re-examination of this tale is the centrepiece of Michael Majerus's book, Melanism: Evolution in Action. Depressingly, Majerus shows that this classic example is in bad shape, and, while not yet ready for the glue factory, needs serious attention . . .

Majerus notes that the most serious problem is that B. betularia probably does not rest on tree trunks—exactly two moths have been seen in such a position in more than 40 years of intensive search.

The natural resting spots are, in fact, a mystery. This alone invalidates Kettlewell's release-recapture experiments, as moths were released by placing them directly onto tree trunks, where they are highly visible to bird predators. (Kettlewell also released his moths during the day, while they normally choose resting places at night.)

The story is further eroded by noting that the resurgence of typica [light-colored moths] occurred well before lichens recolonized the polluted trees, and that a parallel increase and decrease of the melanic form also occurred in industrial areas of the United States, where there was no change in the abundance of the lichens that supposedly play such an important role.

Finally, the results of Kettlewell's behavioural experiments were not replicated in later studies: moths have no tendency to choose matching backgrounds. Majerus finds many other flaws in the work, but they are too numerous to list here. I unearthed additional problems when, embarrassed at having taught the standard Biston story for years, I read Kettlewell's papers for the first time.

Majerus concludes, reasonably, that all we can deduce from this story is that it is a case of rapid evolution, probably involving pollution and bird predation. I would, however, replace "probably" with "perhaps." B. betularia shows the footprint of natural selection, but we have not yet seen the feet.

Majerus finds some solace in his analysis, claiming that the true story is likely to be more complex and therefore more interesting, but one senses that he is making a virtue of necessity. My own reaction resembles the dismay attending my discovery, at the age of six, that it was my father and not Santa who brought the presents on Christmas Eve. (Source: Nature, Nov. 5, 1998, pp. 35–36.)

"Proof" full of holes

What are the conclusions today about the supposed proof of the evolution of peppered moths?

• Both specimens of moths already existed at the time of the experiments—no new species appeared.

• Only the population ratio of the dark and light moths changed from the 19th and 20th centuries due to a number of conditions, not all well understood. There was no creation of or evolution into a new species.

• The photographs of moths on tree trunks were staged according to inaccurate assumptions, and further investigation showed these moths do not normally perch on trunks.

• The increase of the dark moths and the decrease of the light moths were likely due to various environmental factors, including bird predation, but these examples only show how resilient God's creation is.

• In the beginning of the 20th century, the dark moths predominated due in part to the darkening of the environment through industrial pollution. When the environment was cleaned up, the lighter moths became the dominant type. But there was no change in color or structure of the moths—they both had existed before industrial contamination began.

Regrettably, in their desperation for presenting evidence of their molecule-to-man theory of evolution—which effectively removes from the scene the Creator God described in the Bible—many scientists writing biology books continue to present this myth of evolution to millions of unsuspecting students.

So, given the evidence on both sides, let's mothball another false claim of evolution and, instead, give glory to God for having created a variety of moths that have shown in recent history how they can survive under different circumstances.

For further reading, we recommend our free booklet Creation or Evolution—Does It Really Matter What You Believe? (www.gnmagazine.org/booklets/EV ). You may also want to read Jonathan Wells' Icons of Evolution and Judith Hooper's Of Moths and Men, available through your local library or bookstore. VT


pm

pm's picture

Re: The Peppered Moth.

You say:
start quote
• Both specimens of moths already existed at the time of the experiments—no new species appeared.

• Only the population ratio of the dark and light moths changed from the 19th and 20th centuries due to a number of conditions, not all well understood. There was no creation of or evolution into a new species.
endquote

How are such points supposed to be a problem for evolutionary theory? Darwin himself said that there was variation within species (though he did not know that this was a result of variation in the genes). And evolution is, by definition, just changes in the ratio of the genes (variations) in the population.

The peppered moth situation can be used to as an example of evolution in action but it can not be used as an example of speciation. For one thing, the time line of a a hundred years or so is likely way to short. More importantly if the black moth population returned to a white moth state it is pretty convincing evidence that the black moth population was not yet distinct (in a reproductive sense) from its white moth predecessors. Evolutionary paths are not likely to be reversible. For examples of speciation we are going to have use much longer periods of observation. That, check the fossil records. The evidence there is pretty clear - new species do arise and disappear.



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