Shop Windows to the Universe

Learn about planets outside our solar system through Exoplanets and Alien Solar Systems by Tahir Yaqoob, Ph.D., a book in our online store book collection.

Evidence of Evolution

Forested English countryside is an ideal habitat for peppered moths.
Click on image for full size

Peppered Moths: An Example of Natural Selection

A species of moth in England called the peppered moth is found in two varieties: light gray and dark gray. The light gray version used to be far more common, but researchers observed that between 1848 and 1898 the dark colored ones were becoming more common. In fact, only 2% of the moths near one industrial city were light gray.

This change in moth coloration occurred at the same time that coal was becoming a major source of power in England. Coal is not a very clean energy source and burning vast quantities of it put large amounts of soot into the air in and near London and other industrial cities. The soot would settle over the land, buildings and even the trunks of trees. Tree trunks turned from light gray to black. Peppered moths are active at night but rely on places where they can blend in, avoiding predators, during the day. Light-colored peppered moths were no longer well camouflaged on the darkened tree trunks. The dark colored moths, however, were well camouflaged. Because predators were able to spot the light moths more easily, the dark moths were more likely to survive and reproduce. Eventually, moths in industrialized areas of England were predominantly the dark variety and moths in the non-industrialized regions (where tree trunks were still light in color) remained predominantly light gray in color.

Several scientific studies have tested the hypothesis that peppered moth coloration was due to natural selection. For example, a scientist named Kettlewell bred both varieties of moths and marked them so that he would know when he found them again. Then, he released some of each variety into a region where pollution was high, and some of each variety into a region where pollution was low. Kettlewell later went out to recapture as many of the moths as he could from both areas. He found more dark moths in the polluted area and more light gray moths in the low pollution area, suggesting that more of the dark ones survived in the soot covered industrial setting and more of the light colored ones survived where the tree trunks remained light in color. This supports the hypothesis that the change in moth color was caused by natural selection.

The peppered moth case is an example of natural selection. In this case, changes in the environment caused changes in the characteristics that were most beneficial for survival. The individuals that were well adapted to the new conditions survived and were more likely to reproduce. This particular type of natural selection, when amounts of genes varieties shift in a particular direction in response to a new factor in the environment, is called directional selection.

Last modified May 16, 2005 by Lisa Gardiner.

Shop Windows to the Universe Science Store!

Our online store includes fun classroom activities for you and your students. Issues of NESTA's quarterly journal, The Earth Scientist are also full of classroom activities on different topics in Earth and space science!

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

ExploraTour - Looking at the World in a Different Light

Even though the sleeping man is no longer on the bed, you can still see where he was lying down. The heat from his body warmed up the bed sheets which are now radiating infrared light toward your eyes....more

ExploraTour - Looking at the World in a Different Light

All warm objects (not just people) radiate in the infrared. Warmer objects give off more infrared radiation. Very hot objects radiate other types of light in addition to infrared. Click on the picture...more

ExploraTour - Looking at the World in a Different Light

Your eye is a wonderful detector of visible light. Different frequencies of light produce different sensations in the eye which we interpret as colors. Our eyes detect light by using light sensitive components...more

ExploraTour - Looking at the World in a Different Light

Imagine you found a pair of special glasses that not only gave you telescopic vision but gave you the ability to see all forms of radiant energy. The universe in visible light contains all the familiar...more

ExploraTour - Looking at the World in a Different Light

This is a volcano on the island of Miyake in Japan. It has erupted, sending hot lava and ash into the air, a total of ten times. The time after one eruption until the next occurred was about twenty years...more

ExploraTour - Looking at the World in a Different Light

This is a picture of a galaxy in visible light. A galaxy is a large number of stars, some like our sun, some bigger, some smaller and all moving together through space. This galaxy is called Centaurus...more

ExploraTour - Looking at the World in a Different Light

This is a plant in Gary, Indiana where power is made. We use power to run things like television sets, radios, lights, and microwave ovens. The picture looks very strange because it was taken in infrared....more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA