Adaptation and Natural Selection in Peppered Moths
Charles Darwin collected many facts to support his theory of evolution by
natural selection. Although the evidence for evolution in the fossil record
is very compelling, at the time of Darwin no one had observed evolution actually
taking place. Darwin pictured the process of evolution as requiring vast amounts
of time, far greater than a person's life span. Although Darwin was unaware
of it, remarkable examples of evolution were going on around him in the countryside
of his native England. One example of this evolution was happening to a species
of moth known as the peppered moth, Biston betularia. The Industrial
Revolution began in England in the middle of the eighteenth century. Since then,
tons of factory soot has been deposited in the countryside around industrial
areas in England. The soot has discolored and generally darkened the trees,
rocks, and other natural features of the landscape. Before the Industrial Revolution,
the wild type peppered moth was mostly light colored. A very rare form of the
moth that was covered with gray spots was generally dark in appearance. In contrast,
today the situation has reversed. Today in some areas over 90% of the peppered
moths are dark in color. More than 70% of other moth species in England have
also changed from a light to darker phenotype. Similar observations have been
made in other industrial nations including the United States. How has this striking
change come about? In this investigation, you will perform an experiment and
use your data to offer and support an explanation.
In this investigation, you will simulate a predator/prey relationship. You
will determine whether color contrast has an effect on the ability of a predator
to rapidly locate prey. You will observe the impact on predation in a population
of peppered moths living just outside an industrial city. Birds are the moth's
- You will use one-inch squares of white and newsprint paper to represent
the light and dark colored moths. Each team should cut out thirty pieces
of white paper and newspaper about one inch square. It is important to make
sure all the squares are approximately the same size.
- Place a piece of white butcher paper on your lab bench to represent the
- Roll a pair of dice to see how many generations that the tree bark remains
- A person with a watch with a second hand should be designated as the timekeeper.
- While teammates are looking away, the timekeeper scatters the thirty white
and thirty dark squares of paper moths all around the white paper tree.
- When your partner is ready with the forceps, which will represent the
bird's beak, let the hunt begin! Start timing 15 seconds. During this time,
the predator bird picks up moths one at a time using only one hand and the
forceps, and places the moth in a nest (aside). The object is to collect
as many moths as you possibly can.
- When the 15 seconds are up, count the number of light and dark moths captured
and enter the numbers into the data table. Each surviving moth not captured
gets to pass on their genes by breeding once, so place a new dark or light
square for each moth left on the newspaper tree.
- Repeat this process for the number of generations, represented by the
roll of the dice.
- Then replace the white butcher paper with newspaper. The newspaper will
represent the soot-covered trees.
- A repeat step 5 to 7 for another 4 to 5 turns or until everyone in your
group has had a chance to hunt during this second round.
III. Data Analysis and Questions
Each person in your group will answer at least one of the following questions,
but all of the questions must be answered. The group will share their
answers with the group's members. But each person must turn in his or her own
- Make a bar graph that shows the changes in size of the two populations
of moths over at least a five-generation period. See example on the board.
- How did the appearance of the light colored peppered moth compare to that
of the tree trunks before the Industrial Revolution?
- How did the appearance of the dark colored moths compare to that of the
tree trunks as the Industrial Revolution progressed?
- Based on the data you graphed, how did the population of moths change
over five generations?
- What caused the change in the moth population?
- How would Lamarck account for the changes that took place in the moth
population over five generations?
- How would Darwin account for these changes?