The original question was:
How do you explain the moths in England changing colour to survive industrial pollution if evolution isn’t true?
Answer by Diane Eager
Peppered Moth History
For many years the Peppered Moth Biston betularia has been used in high school textbooks as the prime example of evolution occurring before our eyes, so let’s look at how this claim came about.
The Peppered Moth occurs in two main colour forms, one pale with black speckles, the other solid black. Before the early 1800’s the black forms were rare, but over the next century they gradually increased in numbers, especially in regions surrounding rapidly industrialising cities like Manchester. At the same time the number of light forms decreased.
The change in proportion of black and speckled moths was believed to be caused by birds eating the moths whose colour did not blend in with the colour of the tree trunks on which the moths rested during the day. The logic was simple: In non-polluted regions the tree trunks were covered in lichen so any speckled moths resting on them were well camouflaged, but black moths on clean trees would have been highly visible, and therefore easily spotted by hungry birds during the day. This left the more speckled moths to breed, and give rise to new generations of the light coloured speckled forms which resulted in more light than dark forms in the moth population. However, in polluted regions the tree trunks became covered with soot, which also killed off the lichens leaving the tree trunks black. In these regions black moths would have been well camouflaged, but the pale speckled moths would be more easily spotted and eaten. In these areas it was argued that more black forms survived to breed and produce generations of black moths so the ratio of dark to light moths increased.
This increase in numbers of black moths was called “industrial melanism,” and has been presented to generations of biology students as a classic example of natural selection, and therefore evolution, since according to Darwin, natural selection produces evolution.
In order to prove that the increasing numbers of black moths was a case of natural selection and hence evolution, Ernest Kettelwell carried out a series of experiments during the 1950s. He released light and dark moths onto tree trunks in two different regions in England, one where the trees were blackened by industrial pollution, and the other an unpolluted area whose trees were covered in lichens. Kettelwell later recaptured moths from both regions and recorded the numbers of each form that had survived. As he expected, more black moths survived in the region with black tree trunks, and more light moths survived in the region with lichen covered tree trunks. Although Kettelwell’s results were often used a proof of evolution, scientists who studied moths recognised serious flaws in Kettlewell’s method.
Cambridge University entomologist Michael Majerus wrote a detailed study of melanism in moths in a book entitled Melanism, Evolution in Action, in which he critiques Kettelwell’s experiments. His criticism is summarised by Jerry Coyne in a review of the book published in Nature Nature, vol 396, pp35-36, 5 Nov 1998, as follows:
“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 (speckled moths) occurred well before lichens recolonized the polluted trees, and that a parallel increase and decrease of the melanic (black) 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.” (From: Jerry A Coyne, Not Black and White, Review of book Melanism, Evolution in Action< by Michael Majerus, Nature, vol 396, pp35-36, 5 Nov 1998)
In 2006 the Manchester Museum had a display on industrial melanism entitled “How did the moth change its spot? By natural selection?”. It contained this statement: “We aren’t sure of the relationship between pollution levels and moth’s colour, but the Peppered Moth reminds us of the complexity of nature and the connections between all life on earth.”
So it seems the link between polluted trees and selection for black moths remains popular but unproven.
Because of the criticisms of Kettelwell’s work Michael Majerus repeated the experiment, but corrected the experimental design. Majerus made his observations over six years in Cambridgeshire, (actually in his own garden there) where trees had never been damaged by pollution, yet both speckled and dark moths existed. Majerus found that birds did eat moths that were less camouflaged, i.e. the black ones more than on the light ones, and this difference in predation rate is enough to change the relative numbers of dark and light forms in succeeding generations given enough time.
Majerus was unable to completely repeat Kettlelwell’s original work on moths by studying the effect on moths of living in soot-blackened areas because anti-pollution laws have resulted in the industrialised regions of England being cleaned up, so trees are no longer soot blackened, and black moths seem to on their way to becoming as rare today as they were in pre-industrial times.
Majerus died in 2009, but his colleagues have published his results in Biology. Letters 8 Feb 2012, doi: 10.1098/rsbl.2011.1136. They concluded their report with: “The new data, coupled with the weight of previously existing data convincingly show that ‘industrial melanism’ in the peppered moth is still one of the clearest and most easily understood examples of Darwinian evolution in action”.
Has the Moth Evolved?
To answer this question we need to consider what has changed?
Has the moth changed colour?
Historic moth collections show both speckled and black forms existed before the industrial revolution, so the moth has not changed colour – all colours options existed before any selection took place. The only recorded change has been the proportion of speckled and black forms in succeeding generations as the industrial revolution came and went. Although there is confusion about the cause of this. In the USA where industrial pollution of trees has never been a factor, the percentage of colours has changed as in the UK.
Is this natural selection?
Although industrial pollution is not usually regarded as natural, predation by birds is a natural selection force, but birds could only select from moth varieties that already existed.
Selection is the process of choosing something from an already existing set of options, but selection (natural or artificial ) has never been observed to create the options, or change them into something different. It has always resulted in some options being removed and some remaining.
Now, let’s apply this to peppered moths. Wherever black moths were more visible, and birds ate more of the black ones, i.e. selected them out, this definitely would have left more speckled ones to breed. Therefore, the most common form in succeeding generations would be speckled. Therefore, as the trees became soot-blackened and speckled moths became more visible, birds could have more easily have selected them for dinner, leaving a larger number of the black ones to breed, which produced generations of black moths until the trees recovered from the pollution, and the black forms were once more subjected to selection.
Does natural selection produce evolution?
Note well – natural selection did not produce the moths, and it did not produce the moth colours, although it probably did alter the ratio of dark to light moths on clean trees in Cambridgeshire. But natural selection is a actually a destructive process, so if allowed to go to on for too long it could potentially remove the ‘dark gene’ from the population of living things and reduce the gene pool. It has no observed track record of changing living things into new kinds of living things. Natural Selection is a real process, but it cannot produce evolution.
The exact gene that produces the black form of the moth has not yet been found, but scientists are working on it. It seems to be a control switch that regulates the activity of pigment producing genes that produce the colours and patterns of wings in moths and butterflies. (Ref. 2) A change in regulating gene does not add any new pigment genes to the moth. Therefore, the black moth did not come about by the addition of any new genes. We suspect it is the result of a control switch being left on when it should have been turned off, or vice versa. This is not evolution. It is merely the loss of a control system than normally produces patterns, so that it now only produces solid colour.
Postscript – A Moth-er’s Motivation
Prior to his death Majerus admitted that his motive for restoring the peppered moth as an icon of evolution was to campaign against creationism. He claimed: “To have people believe the biology of the planet is controlled by a Creator, I think that’s dangerous”. (Science, 25 June 2004) All students need to know this, along with the fact that now that Majerus has departed this world, he has discovered how much more dangerous it was to reject the Creator of both moths and men.
1. Jerry A Coyne, Not Black and White,, Review of book Melanism, Evolution in Action by Michael Majerus, Nature, vol 396, pp35-36, 5 Nov 1998
2. Van Hof, et. al. Industrial Melanism in British Peppered Moths Has a Singular and Recent Mutational Origin, Science, Vol. 332, pp. 958-960 DOI: 10.1126/science.1203043 20 May 2011 ” … the underlying genetic basis of the difference between the wild-type (light-colored) and carbonaria forms has remained unknown. We have genetically mapped the carbonaria morph to a 200-kilobase region orthologous to a segment of silkworm chromosome 17 and show that there is only one core sequence variant associated with the carbonaria morph, carrying a signature of recent strong selection. The carbonaria region coincides with major wing-patterning loci in other lepidopteran systems, suggesting the existence of basal color-patterning regulators in this region.”
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