Biology Now, 2e

Battling Resistance ■ 217

Predatory

bird

Predatory

bird

Predatory

bird

Before the industrial revolution

of the nineteenth century, there

was a wide distribution of colors

in the peppered moth.

Upon the darkening of tree bark

by industrial pollution, dark-

colored moths increased in

frequency and all other moths

decreased.

After clean-air legislation was

enacted in the twentieth century,

the bark color of trees became

lighter, and so did the frequency

of lighter-colored moths.

Phenotype

Frequency inpopulation (%)

Frequency inpopulation (%)

Frequency inpopulation (%)

Phenotype

Phenotype

Original

population

Industrial-pollution

population

Clean-air

population

Light- and dark-colored

moths on dark tree bark

Light- and dark-colored

moths on light tree bark

Figure 12.7

The peppered moth has undergone directional selection two different times in the last 200 years

The industrial revolution of the nineteenth century caused extreme air pollution in both England and the United States, due mostly

to soot from the mass burning of coal.

Q1: If one extreme phenotype makes up most of a population after directional selection, what happened to the individuals

with the other phenotypes?

Q2: What do you think would happen to the phenotypes of the peppered moth if the tree bark was significantly darkened

again by disease or pollution?

Q3: What do you think would happen to the phenotypes of the peppered moth if the tree bark became a medium color,

neither light nor dark? (You will need to read the next paragraph to answer this question.)