Thursday April 17

• Essential Question: What is a selective pressure? What are some examples?

• Today Peppered Moth Case Study. For Full points Answer Questions in complete sentences.

• Finish Study Guides

The Peppered MothThe Peppered Moth

The "typica" form of the moth (light-colored)

The "The "carbonariacarbonaria" " form (dark-colored)form (dark-colored)

The Peppered Moth has 2 variationsvariations: light graylight gray and dark graydark gray.

The peppered moth lives in a forest The peppered moth lives in a forest in England.in England.

The trees in the forest are covered The trees in the forest are covered with with lichenlichen..

If you were a If you were a hungry bird, hungry bird,

which of which of these these

peppered peppered moths would moths would you grab for you grab for

lunch?lunch?

The black mothsblack moths were easy to see against the lichen, but the light mothslight moths blended in and were hard to see.

Birds ate more of the dark dark mothsmoths, until there were a lot of light moths and very few dark ones.

Ha ha! You can’t see

me…

One day factories moved into the area, and released pollutionpollution into the air.

The trees were blackened with

sootsoot..

What do you think happened to the moths?What do you think happened to the moths?

You’re right!You’re right!

The birds ate more of the light mothslight moths because they were now easier to see than the dark mothsdark moths.

Eventually there were a lot of dark mothsdark moths and very few light oneslight ones.

Peppered Peppered moths on a moths on a normal normal tree tree backgrounbackgroundd

Peppered Peppered moths on a moths on a tree tree darkened darkened by sootby soot

When the monster came, Lola, like the

peppered moth and the arctic

hare, remained motionless and

undetected. Harold, of

course, was immediately devoured.

Peppered moths have lived in the forests of England for thousands of years. They rest on the trunks of trees during the day, and are a source of food for many birds.

Peppered moths vary in color, from light-colored to dark-colored. These color variations are genetic.

Before the Industrial Revolution, the tree trunks were light-colored. The trunks and branches were also covered with silvery-white lichens. As industry grew, pollution killed the lichens and blackened the tree bark.

In the 1950s, Oxford University professor H.B.D. Kettlewell and his students performed an experiment. They released the same number of light and dark-colored moths in two areas. One was an unpolluted area that had lichen-covered unpolluted area that had lichen-covered oak treesoak trees;; the other was a wooded area that had wooded area that had experienced pollution for many yearsexperienced pollution for many years.

After a certain amount of time, they recaptured as many moths as they could, and counted them.

What do you think the results of the experiment were?

You’re right!

In the unpollutedunpolluted area (light-colored tree light-colored tree trunkstrunks), moremore light-colored mothslight-colored moths

survivedsurvived.

In the polluted area (polluted area (dark-colored tree dark-colored tree trunkstrunks), moremore dark-colored mothsdark-colored moths

survivedsurvived.

How does this experiment show the process of natural selectionnatural selection?

Note that this example illustrates Darwin's four Darwin's four points:points:

moth eggs are over-produced;over-produced; many moths will not survive to reproduce. there is variationvariation among individuals -- some are black in color, others are light gray the variation is geneticgenetic –black moths have different alleles for color than do gray moths the different colors differ in advantageadvantage-- in industrial environments, black moths survive to reproduce better than gray moths do. In unpolluted environments, the opposite is true.