FOOD CHAIN

1
How many moths do you see in . . .
Picture 1 ?
Picture 2 ?
? Picture 3
2
The Peppered Moth
The change in color of the peppered moth after
the Industrial Revolution is a classic example of
evolution in action. In Great Britain there are
two forms of peppered moth--dark and light forms.
When newly industrialized parts of Britain became
polluted in the nineteenth century (1890s),
smoke killed lichens growing on trees and
blackened their bark. Now the pale (light)
colored moths which had been well-camouflaged
before when they rested on tree trunks became
very conspicuous and were eaten by birds.
The rare dark moths, which had been conspicuous
before, were now well camouflaged in the black
background. As birds switched from eating mainly
dark moths to mainly pale moths the large
population of pale (light) moths became
drastically reduced in number. The most common
color of moth color changed to dark. Natural
selection had caused a change in the British moth
population. The moths had evolved. This
hypothesis was proposed by J.W. Tutt in 1896, and
tested by Bernard Kettlewell in the 1950s. It
then became a classic example of Darwinian
evolution in action. Since smoke pollution has
decreased in the UK, the light colored moths have
started to become more common again. The process
which took place after the industrial revolution
is beginning to be reversed. By 2019, the dark
moths are only expected to make up 1 of the
peppered moth population in Britain. Conclusion
Students need to know that the peppered moth
story provides evidence for changes of
frequencies of different types with in a
population, but does not show that large scale
evolution can occur. They should also understand
that the experiments behind the peppered moth
story have widely acknowledged flaws, and are
currently being re-done in a more rigorous
fashion. BibliographyProffitt, F. 2004 In
defense of Darwin and a Former Icon of Evolution.
Science 3041894-1895Majerus, M. 2004 The
Peppered Moth decline of a Darwinian Disciple.
Lecture to the British Humanist Association, 12th
February 2004Updated 01/10/2006