Peppered Moth Experiment Confirmed

A target matching a typical moth pinned to a lichen covered tree in woodland in the predation experiments.

Featured news - Study confirms truth behind ‘Darwin’s moth’ - University of Exeter

Just a few days ago, in reply to yet another prediction by a creationist that the Theory of Evolution is a theory in crisis and within a few years scientists will be forced to abandon it in favour of Intelligent Design, because the evidence will be too strong to ignore, I pointed out that there is no evidence whatsoever that the TOE is 'in crisis' and that biomedical scientists regard it as anything less than an established fact and the theory underpinning the whole of biology.

I also said that scientists no longer bother to do experiments to confirm it because it is not seriously disputed.

Then, as thought to prove me wrong, along comes a report by two scientists from Exeter University that does just that. They set out to falsify one of the iconic examples of Darwinian evolution in progress - the evolution of 'industrial melanism' in the Peppered moth, Biston betularia.

Of course, they failed to falsify it and so confirmed it yet again. Not a theory in crisis then, but a theory once again confirmed experimentally.

What the team did was to show how well the moths were camouflaged in the vision of their main predators - birds. They have shown that, to the vision of birds, pale moths are indeed more camouflaged against lichen-covered trees than dark moths – making pale moths less likely to be eaten by birds in unpolluted woodland and giving them an evolutionary advantage.

The team used two methods to demonstrate the improved survival of the lighter moths on lichen-covered trees compared to plain bark trees. Using museum specimens they showed that seen in ultraviolet, visible to birds, they analysed how well pale and dark moths can be seen. They also used baited artificial moths to test predation rates in UK woodlands, mostly in Cornwall. These experiments showed that lighter moths had a 21% higher chance of avoiding predation.

Abstract
Animal defensive coloration has long provided many important examples of evolution and adaptation. Of these, industrial melanism in the peppered moth is the classic textbook example of evolution in action, whereby dark and pale morphs suffer differential predation in polluted and unpolluted woodland based on their camouflage. Despite extensive work, a striking gap remains in that no study has ever objectively quantified their camouflage or related this directly to predation risk. Here we use image analysis and avian vision models to show that pale individuals more closely match lichen backgrounds than dark morphs. Artificial predation experiments in unpolluted woodland show 21% higher survival rates of pale than melanic individuals. Overall, we provide the strongest direct evidence to date that peppered moth morph frequencies stem from differential camouflage and avian predation, providing key support for this iconic example of natural selection.

Walton, O. C., & Stevens, M. (2018).
Avian vision models and field experiments determine the survival value of peppered moth camouflage.
Communications Biology, 1(1), 118. DOI: 10.1038/s42003-018-0126-3

Copyright: © 2018 The Authors
Published Open Access
Reprinted under a Creative Commons Attribution 4.0 International License (CC BY 4.0)

This is one of the most iconic examples of evolution, used in biology textbooks around the world, yet fiercely attacked by creationists seeking to discredit evolution. Remarkably, no previous study has quantified the camouflage of peppered moths, or related this to survival against predators in controlled experiments. Using digital image analysis to simulate bird vision and field experiments in British woodland, we compared how easily birds can see pale and darker moths, and ultimately determine their predation risk.

Our findings confirm the conventional story put forward by early evolutionary biologists – that changes in the frequency of dark and pale peppered moths were driven by changes in pollution and camouflage.

Professor Martin Stevens,
Centre for Ecology and Conservation,
University of Exeter, Penryn Campus, Cornwall.
(Quoted in Exeter University Press Release.

So, in one of those now rare occasions when biologists set out to test the TOE, or in this case one of the iconic examples used to illustrate observed instances of evolution, there is not a hint of a theory in crisis. Quite the opposite in fact. Using new techniques the theory is vindicated and testing one of the assumptions in one of the early experiments - that birds would perceive a difference between the different colour forms - the assumption was confirmed to be valid. Moreover, the improved survival rate has been quantified.

One could even see this as a confirmed prediction of the TOE. The observable fact that there was a change in the allele frequency during industrial pollution which was reversed when the pollution was reduced shows, according to the TOE, that there must have been an improved survival rate due to changes in predation rates and those predation rates must have been due to the perception of predators.

This prediction has now been confirmed.

Crisis? What crisis?

The crisis, of course, is for Intelligent Design which has singularly failed to make any headway as a scientific alternative, is utterly incapable of making testable predictions and still offers nothing by way of an explanatory mechanism. The surprise is that it still survives, albeit only in the minds of those who know little or nothing of science.

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