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Natural Selection Introduction
In the 1800’s, naturalists in England were familiar with the peppered moth. This moth
gets its name from its speckled, light-colored wings. The peppered moths that naturalists had
observed all looked similar and were usually found on lichen-covered tree trunks and rocks.
These tree were a light brown. Then in 1845, one black speckled moth was caught in
Manchester, England. At that time England was becoming industrialized. Manchester, like
many other cities, had factories pouring out smoke and soot and other forms of pollution. The
pollution spread to the surrounding countryside and killed the lichens. The soot covered tree
trunks, rocks and even the ground, making everything black. During this time, more and
more black peppered moths were found. By 1950 very few light-colored moths could be
found – almost all were black.
How did the peppered moth change so much in just 100 years? The
moth had changed as its surroundings had changed. Trees and rocks covered
with lichens had been light colored. Covered with soot, they became black.
Against the light background, the light-colored moths were hard to see. But
against the dark background, they were easy for birds to find and eat. In these
new dark surroundings, the dark moths more often survived, and produced
offspring. Thus, within 100 years the peppered moth totally changed color.
1. Describe how the environment changed after Manchester became industrialized.
2. Use the reading and pictures above to explain why the light peppered moths started to disappear after the
industrial change.
3. No black peppered moths had been found before 1845.
Where did this black moth come from? Why was a black moth not
found before? Use the image to explain your answer.
The peppered moth is a classic demonstration of natural selection. Natural selection is the process in which
some organisms live and reproduce and others die before reproducing.
Some life forms survive and reproduce because they are better suited to environmental pressures, ensuring
that their genes are passed to their offspring. Their adaptation (beneficial variation in a behavior or trait that
an individual is born with) allow them to survive in their environment.
4. Define natural selection in your own words.
5. Define adaptation in your own words.
6A. Which moth is better adapted to the unpolluted birch forest? ________
6B. What will happen to each moth population in the unpolluted birch forest over
time?

The light moth population will (increase/decrease).

The dark moth population will (increase/decrease).
7A. Which moth is better adapted to the polluted birch forest? __________
7B. What will happen to each moth population in the polluted birch forest over
time?

The light moth population will (increase/decrease).

The dark moth population will (increase/decrease).
8. Explain how natural selection occurred in the moth population from 1845-1950.
The Leaf Frog
This species is found on the Solomon Islands and Bougainville and Buka Island, Papua New Guinea. The pointed snout,
projections over the eyes, and ridged “veins” running down its back gives this frog the option of disappearing into the
leaves that litter the ground.
Answer the following questions based on the reading above:
9. What adaptations does the leaf frog have?
10. Describe how a species like this arises using Darwin’s factors of natural selection.
11. Do you think that this type of frog could be successful in the U.S. Why or why not?
12. Explain how a mutation could have created this leaf frog.
The Scientist behind the Theory of Evolution
The theory of evolution emerges from different lines of evidence, such as fossil records, modification by descent,
and the evidence from biogeography, genetics and other forms of evidence. Jean-Baptiste Lamarck (1744-1829) and
Charles Darwin (1809-1882) had different theories about how life on earth got to be the way it is now.
Jean-Baptiste Lamarck (1744-1829)
Lamarck was a French biologist who is best known for his Theory of Inheritance of Acquired
Characteristics, first presented in 1801. He believed that evolution was the “acquired traits” of
a species that is inherited by its offspring. His theory was that if an organism continually used
a structure to carry out a certain task, the structure used would become physically modified
over time to make the task easier This modified structure would then be passed on to any
offspring. For example, if a short-nosed elephant was continually stretching out its trunk to try
to reach the leaves high up in trees, it’s trunk would stretch and become longer over time, and
any babies that it had would be born with longer trunks. Lamarck also believed that when body parts were not
being used, such as the human appendix, they gradually disappear. Eventually, people will be born without these
parts. Lamarck believed that evolution happens according to a prearranged plan and that the results have already
been decided.
13. Summarize Lamarck’s Theory using words and/or images
Charles Darwin (1809 -1882)
Charles Darwin is famous for the theory of evolution and Natural Selection, or ‘Survival of the
Fittest’. He dedicated his life to studying plants and animals and believed that the desires of
animals have nothing to do with how they evolve. He said that organisms, even of the same
species, are different in some ways, and over time those creatures which are adaptable,
survive, while those that do not adapt to changing conditions, such as climatic and
environmental change, do not live to breed and pass on their genes. He came to the conclusion
that there was a variation of physical and behavioral features within a species. Organisms which
had features that helped them to adapt to their environment and circumstances had a better chance of survival
than individuals who lacked these features. These adaptable organisms survived to breed and produce offspring
which generally inherited the ‘successful’ features of their parents. He called this process ‘natural selection’.
14. Summarize Darwin’s theory using words and/or images.
15. Whose theory was correct? ____________________________________