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Transcript
The Story of the
Peppered Moth
Laura Candler: Hands-On Science
Peppered moths loved to rest on birch trees. The color of the light gray
moths matched the color of the birch bark almost perfectly. Hungry birds
had a hard time finding the light moths. Instead, the birds ate the dark
moths which were much easier to see against the bark of the birch tree.
Scientists realized that the light gray moths no longer blended in with
the birch bark. The birch trees were black with soot. Hungry birds could
easily spot any light moths resting on the trees. Now the dark moths
blended in with the bark and were able to escape the birds.
The story of the peppered moth began long ago in Manchester,
England. Two types of peppered moths lived there. One was
light gray with dark gray speckles. The other was black all over.
Until the 1850’s, there were more light gray moths than dark
gray ones.
Between 1850 and 1900, England began to change. Factories were built
which pumped tons of black smoke and soot into the air. The leaves and
bark of trees became covered with dark soot. During this time, scientists
noticed that almost all the light gray moths had disappeared. Black
moths became the most common peppered moths in England. What
caused this change?
Fewer and fewer gray moths lived long enough to have light colored
babies. At the same time, more dark moths survived and had dark baby
moths. In less than 50 years, the number of dark moths became greater
than the number of light moths.
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But the story of the peppered moth did not end there. After many years, laws were
passed to clean up England’s pollution. Factories were no longer allowed to pump
smoke into the air. Slowly the rains washed the dark soot from the trees. What do
you think happened to the numbers of dark and light moths?
As you might have guessed, the peppered moth again adapted to its new
environment. Light moths began to survive since hungry birds could not
easily find them. Now light colored moths once again outnumber their
darker relatives.
Is it true??? Did this REALLY happen???
The answer is yes and no. The Story of the Peppered
Moth is used in almost every biology book out thereespecially to teach evolution, however, we are using the
story to teach ADAPTATIONS and CAMOUFLAGE.
The light colored moths didn’t necessarily die out
because of the pollution, but they have to find other
areas to live in order for their species to survive.
Some of the photos you saw were staged with dead moths
so that the story would have graphics. It’s a “lie” per
se, but it’s not totally a lie either. 
No new living species can emerge by way of natural selection. The Industrial
Revolution moths are an excellent example of this. Until the last quarter of the
20th century, tree trunks grew darker in color with the pollution of Industrial
Revolution. Therefore, the light-colored moths alighting on these trees became
more visible to predators, and since they were more easily caught, their numbers
declined. The numbers of dark moths, however, increased.
But this, of course, is not evolution. No new species was formed, and all that
happened was a shift in ratios of variation within an existing species.
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