Principles of Evolution

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Date:______________________ Period:____________________________
“Principles of Evolution” Common Assessment

Review Questions

1. Give a description of natural selection. Give an example of how natural

selection works.

Natural Selection is the process by which individuals that are better suited to their environment survive and reproduce most successfully. In order for this process to work there must be: 1. Genetic Variation within the environment

2. Over- production of offspring

3. Struggle for existence

4. Differential Survival and reproduction

Differential = differing or varying according to circumstances (how well adapted an organism is)
2. Natural selection is also called “survival of the fittest”. What does that

mean? Give an example.

Survival of the fittest means that the best adapted organisms will survive and reproduce = contributing genes to the next generation. It does not necessarily mean the “biggest” or “strongest.” If an organism is not well adapted to their environment, they will not survive and/or reproduce – thus they do not contribute their poorly adapted genes to the next generation.
3. List the four main points of Darwin’s Theory of Evolution
NOTE: Change question to read: “What are the main points of Darwin’s Theory”
Answers could vary – some more thorough than others. Students could discuss the components of natural selection as seen in the answer to #1. Regardless, they must understand that Darwin’s theory of evolution explains DESCENT WITH MODIFICATION BY NATURAL SELECTION.
4. Using natural selection as the basis for your answer, explain why giraffes

have long necks.

In the giraffe population there is genetic variation that determines neck length. Some giraffes have longer necks than others.

There are more giraffes in the population than can be supported by the leaves on trees in the environment.

Giraffes with longer necks will be better able to get food from the trees needed to survive. Giraffes with short necks will not have food and will not survive.

The Giraffes with longer necks will survive to reproduce and pass on their “long neck” trait to their offspring.

5. Use the graph to answer the question below:

Tail length in mice varies within a population. Scientists observed change in the distribution of tail lengths in a mouse population over time. At the genetic level,

what has most likely happened to the allele for the shortest tail lengths?

A. The allele changed from being dominant to being recessive.

B. The allele changed from being autosomal to being sex-linked.

C. The allele became less frequent than the alleles for longer tail lengths.

D. The allele began to code for long tail lengths instead of the shortest ones.

Answer: C
6. What is an adaptation? How can it be inherited?

An adaptation is an inherited characterist that increases an organism’s chance of survival. It is inherited through DNA passed from parent to offspring.

7. Finches on the Galapagos Islands have different beak sizes depending on

which island they are on. What is the reason for this adaptation?

Finches beak size varies based on food source (diet) available to them – insect eater, cactus eater, seed eater, etc..
8. Use the graph to answer the question below:

The graphs illustrate change in a lizard population over time. Which process most

likely led to the change in the lizard population?
A. natural selection acting on a harmful trait

B. natural selection acting on a beneficial trait

C. natural selection acting on a dominant trait

D. natural selection acting on a recessive trait

Answer: B
9. Explain how the founder effect is an example of genetic drift?
The founder effect is a random change in the gene pool that occurs when a small colony is separated / breaks off from a population. This occurs when the gene pool of the colony is not a good representation of the gene pool of the original population.

10. If a species can’t adapt to an environmental change, what can happen to it?

If it doesn’t adapt, it will not survive.
11. The combined genetic information (alleles) of all the members of a particular
population make up the population’s ____gene pool___________________.
12. What is speciation?

Speciation is the formation of a new species.

13. What are the basic steps of speciation, and how does this relate to the

Galapagos Islands and Darwin’s discoveries about the species found on each


  1. Founders arrive

  2. Separation of populations

  3. Changes in the gene pool

  4. Reproductive isolation

  5. Ecological Competition

  6. Continued Evolution

14. What is genetic drift? Give an example.

Genetic drift is a random change in the allele frequencies that occurs in small populations.
15. If the vegetation on an island produces hard seeds, how might that affect the evolution of a species of birds?

If hard seeds are the food source on an island the birds with beaks that are best adapted to crack the hard seeds would be able to survive and reproduce. These beaks would probably be larger/stronger crushing beaks. Those without the large crushing beak would not survive (due to lack of food) and/or not reproduce (due to lack of energy). In the next generation there would be a larger percentage of the population with the large crushing beaks.

16. Speciation can happen if a group of individuals within a population becomes

isolated. What are the three kinds of isolation that can occur and give an

example of each?

Prezygotic Barriers:

Students could offer more than 3 isolating mechanisms: The could could be:

Behavioral Isolation – courtship rituals

Geographic/Habitat Isolation – living in separate regions

Temporal Isolation – mating at different times

Mechanical Isolation – reproductive parts don’t “fit”

Gametic Isolation – sperm of one species is unable to fertilize the egg of the other

Postzygotic barriers:

Hybrid Inviability – offspring are weak and may not surprise

Hybrid Sterility – offspring are sterile (donkeyXhorse = mule which is sterile)

Hybrid breakdown – 1st generation survives to reproduce but the following generations become successively weaker and eventually may become sterile

Ultimately these isolating barriers could result in reproductive isolation.
17. In North America, the eastern spotted skunk mates in late winter, and the

western spotted skunk mates in late summer. Even though their geographic

ranges overlap, the species do not mate with each other. What most likely

prevents these two species from interbreeding?

A. habitat isolation

B. gametic isolation

C. geographic isolation

D. reproductive isolation

Answer: D

If this were an open-ended, temporal isolation would be the best answer.

18. What is meant by natural (genetic) variation? What two things cause it?

Natural variation/genetic variation is shown in the diversity of traits seen in the population. Variation that is inheritable provides the raw materials for natural selection. Variation allows some organisms to be better adapted to their environment allow them to survive to reproduce.

Cause of variation:

  1. Mutations (helpful, harmful, and neutral) – major source of variation in asexual reproducers/prokaryotes

  2. Sexual reproduction – events of meiosis (crossing over, independent assortment, & segregation of alleles) and random fertilization

19. A mutation occurs in a certain group of finches. The finches develop

narrower beaks in order to eat the insects that live in trees. What will

determine if the frequency of this new allele will increase in the finches?

If the mutation increases the fitness of the finch, then it will be better able to survive and reproduced. This would ultimately lead an increase in the frequency of the new allele in the gene pool.

If the mutation decreases the fitness, then it will not become more frequent in the gene pool.
20. Why are mutations in the ovaries and testes more likely to influence

evolution than mutations that occur in other parts of the body?

These cells contain the DNA that will be passed on to the next generation.
21. A mutation occurs in the genes that code for coat color in deer. Which

change will most likely result from this mutation?

A. a change in the selection pressures acting on coat color

B. a change in the coat-color genes of deer predator species

C. an increase in coat-color diversity in the population

D. an increase in the number of genes for coat color in the population

Answer: C
22. Charles Darwin took a journey around the world on the HMS Beagle.

Where did he go and how did this lead him to develop his theory of


Darwin’s 5 year voyage took him around the world through the Atlantic Ocean around the coast of South America through to the Galapagos Islands and around the coast of Australia, through the Indian Ocean and around the southern tip of Africa, back through the Atlantic Ocean to the British Isles.

On his voyage he saw a vast array of diverse organisms, he collected evidence (specimens of living organisms & fossils remains), he made drawings of his observations, he saw the impacts of geologic events (earthquakes and volcanoes) and he read the work of Charles Lyell (a geologist who influenced Darwin concerning the age of the earth). The Galapagos were a major influence – he was fascinated by the unique creatures and how well adapted they were to island life.

This voyage helped him appreciate the vast diversity of organisms in the world. The voyage made him question the divine creation of all organisms and the age of the earth.

13. A vestigial organ is an organ that served a purpose in the distant ancestor of

an organism, but is not longer needed in the presently existing, recently

evolved, organism. Give an example of a human vestigial organ and explain

how it suggests common ancestry.

The appendix – this narrow, muscular tube attached to the large intestine served as a special area to digest cellulose when the human diet consisted more of plant matter than animals protein.

Wisdom teeth – early humans had to chew a lot of plants to get enough calories to survive, making another row of molars helpful

Erector pili - are bundles of smooth muscle fibers that allow animals to puff up their fur for insulation or to intimidate others. Humans retain this ability. They are often called goose bumps.
24. Modern whales resemble extinct land mammals in several characteristics.

What does this similarity suggest about the evolution of modern whales?

They evolved from a mammal that walked on land.
25. What are homologous structures? Give an example.

Homologous structures are structures that have different mature forms in different organisms but develop from the same embryonic tissues.

The forelimb of birds, bats, whales, dogs, humans, horses, etc… have the same number and type of bones.
26. The frequency of an allele in a fly population changes from 89% to 20%

after three generations. Which other events most likely occurred during the

same time period?
A. an environmental change and a fly population increase

B. an environmental change and a fly population decrease

C. interbreeding of flies with an invasive species and fly population


D. interbreeding of flies with an established local species and fly

population speciation

Answer: B

27. Use the table below to answer the following question:

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