Chapter 2: Evolution 195

SKILL: EVALUATING HYPOTHESES

How Did the Deep-SeaAngler Get Its Glow?A fish that uses a fishing pole to catch food might seem odd.However, anglerfish do just that. The fish have a modified spinethat extends from their head, almost like a fishing pole. At the endis a small piece of tissue that is similar in shape to a small worm.The tissue functions like a lure that a fisherman uses to catch fish.The anglerfish wiggles its “lure” to attract prey. If the prey fishmoves in close enough, the anglerfish opens its mouth and swallows the prey whole. The “fishing poles” of abyssal anglerfish,anglerfish that live in the deep sea, have an interesting adaptation.The “lure” actually glows in the dark—it is bioluminescent.

ObservationsFrom laboratory research and field studies, scientists made theseobservations.

There are more than 200 species of anglerfish. Many of

these live in deep water.

Shallow-water species do not have glow-in-the-dark "lures."

Only female abyssal anglerfish have a "pole." They do not

have pelvic fins and are not strong swimmers.

Other deep-sea organisms, including bacteria, jellyfish,

even some squid, are bioluminescent.

HypothesesConsider these hypotheses.

The ancestors of abyssal anglerfish lived in shallow

waters. Some of these fish drifted into deep waters. A

bioluminescent lure helped some survive.

Light does not reach down to the bottom of the deep

sea. Bioluminescence provides an advantage for the

anglerfish because it makes its lure noticeable.

A bioluminescent lure is more valuable to a female

abyssal anglerfish than the ability to swim.

Evaluate Each Hypothesis On Your Own For each hypothesis, think about whether all theobservations support it. Some facts may rule out some hypotheses.Others may support them.

As a Group Decide which hypothesis is the most reasonable.Discuss your thinking and conclusions in a small group and see if the group can agree.

Chapter 6: History of Life 195

196 Unit 2: Life Over Time

Living things, like Earth itself, changeover time.

KEY CONCEPTS SUMMARY

VOCABULARYfossil p. 169unicellular organism p. 172

multicellular organismp. 173

mass extinction p. 174

VOCABULARYevolution p. 177natural selection p. 181

adaptation p. 182speciation p. 184

VOCABULARYancestor p. 189vestigial organ p. 190gene p. 193

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2

3

CONTENT REVIEWCLASSZONE.COM

Chapter Review

Earth has been home to living things for about 3.8 billion years.Fossil records inform humans aboutthe development of life on Earth.Information from fossils can helpscientists reconstruct Earth’s history.

Darwin’s theory of natural selection explains evolution.

The beak of this cactus finch providesan example of an adaptation.

Many types of evidence support evolution.Three different types of evidence provide a bigger picture of evolution

Four principles ofnatural selection

• overproduction

• variation

• adaptation

• selection

biological geneticfossil

Species change over time.

Chapter 6: History of Life 197

8. Which is a possible explanation for massextinctions?

a. Earth had no water.

b. A meteorite collided with Earth.

c. The continents separated.

d. Woolly mammoths left no offspring.

9. Darwin’s theory that species develop new traitsand change over time is known as

a. natural selection c. speciation

b. evolution d. adaptation

10. Which describes Lamarck’s explanation forchanges in the fossil record?

a. Species best suited to their environmentssurvive better than others.

b. Variation within a species can be passed onto offspring.

c. Acquired traits are passed on from one gen-eration to another.

d. Giraffes adapted to their environment.

11. A slight change in a rabbit’s ability to hear itspredators better and help it survive is

a. an adaptation

b. a vestigial structure

c. an aquired trait

d. an isolation

12. Which is necessary for speciation to occur?

a. adaptation

b. mass extinction

c. isolation

d. acquired traits

13. Which of the following statements explain whythe theory of evolution is widely accepted bythe scientific community?

a. It has been proven by experiments.

b. The fossil record is complete.

c. It is supported by genetic evidence.

d. Lamarck’s theory was correct.

14. Genetic evidence is based on the study of

a. embryonic development

b. mutations

c. common ancestors

d. DNA sequences

Reviewing Vocabulary

Draw a triangle for each of the terms below.On the wide bottom of the triangle, write theterm and your own definition of it. Abovethat, write a sentence in which you use theterm correctly. At the top of the triangle,draw a small picture to show what the termlooks like.

1. unicellular organism

2. multicellular organism

3. adaptation

4. vestigial structure

Reviewing Key Concepts

Multiple Choice Choose the letter of the bestanswer.

5. Which is not part of the fossil record?

a. fossil bones

b. preserved remains

c. living unicellular organisms

d. imprints

6. Whether a fossil formed before or after another fossil is described by its

a. relative age

b. absolute age

c. fossil record

d. radioactive age

7. The earliest multicellular organisms were

a. jellyfish

b. simple plants

c. fungi

d. tiny seaweeds

Fossils of shellscan be preserved

in rock.

A fossil is the imprint or remains of

a once-living organism.

198 Unit 2: Life Over Time

25. ANALYZE How is geographic isolation relatedto the formation of a new species?

26. EVALUATE Pandas were once considered to beclosely related to raccoons and red pandasbecause of their physical similarities. Today, scientists have learned that pandas are moreclosely related to bears than to raccoons andred pandas. What evidence might scientistshave used to draw this conclusion? Explain.

27. INFER What does the presence of similar struc-tures in two organisms—such as a dolphin’sflipper and a lizard’s forelimb—indicate?

28. INFER Look again at the picture on pages166–167. Now that you have finished the chap-ter, how would you change or add details toyour answer to the question on the photograph?

29. SYNTHESIZE The beaks of hummingbirds areadapted to fit into long, thin flowers.Hummingbirds can feed on the nectar insidethe flower. Write an explanation for this adaptation that Lamarck might have proposed. Then write an explanation for thisadaptation based on Darwin’s ideas. Use theterms acquired traits and natural selection inyour answer.

If you are doing a unit project, make a folder foryour project. Include in your folder a list of theresources you will need, the date on which theproject is due, and a schedule to track yourprogress. Begin gathering data.

15. Genetic information that cells use to controlthe production of new cells is located in

a. embryos

b. genes

c. the environment

d. vestigial structures

Short Answer Write a short answer to eachquestion.

16. Describe how the relative age of a fossil isdetermined by studying layers of rock.

17. Explain the difference between artificial selection and natural selection.

18. How does common ancestry between twospecies support evolution?

Thinking Critically

19. COMMUNICATE What have scientists learnedabout past life on Earth from the fossil record?

20. PROVIDE EXAMPLES Explain the principle ofoverproduction. Give an example.

21. SYNTHESIZE How might the mass extinction ofdinosaurs enable many new species of mam-mals to develop?

22. EVALUATE How would natural selection haveled to the development of giraffes with longnecks as opposed to giraffes with short necks?

23. PROVIDE EXAMPLES How are variation andadaptations related to natural selection? Givean example.

24. PREDICT In Africa’s Lake Tanganyika differentpopulations of cichlids became isolated fromeach other. Based on what you already learned,predict how the changing water level helpedthe cichlid population to change. How do youthink the development of new cichlid speciesaffected other living things in the lake?

Chapter 6: History of Life 199

Standardized Test Practice TEST PRACTICECLASSZONE.COM

For practice on yourstate test, go to . . .

Interpreting DiagramsChoose the letter of the best answer.

This diagram shows how groups of carnivores arerelated to one another. Each Y in the diagram indicates a common ancestor.

1. Hyenas are most closely related to which group?

a. cats

b. civets

c. mongooses and meerkats

d. raccoons and kinkajous

2. Weasels, otters, and ferrets are most closely related to

a. bears and giant pandas

b. sea lions and fur seals

c. raccoons and kinkajous

d. mongooses and meerkats

3. Sea lions and fur seals share their closest commonancestor with

a. walruses and earless seals

b. raccoons and kinkajous

c. mongoose and muskrats

d. civets

4. Which statement is true based on the informationin the diagram?

a. Dogs, wolves, and coyotes do not share a com-mon ancestor with any of the groups.

b. Raccoons are more closely related to weaselsthan they are to giant pandas.

c. None of the groups shown in the diagram sharea common ancestor.

d. Mongooses and meerkats are the same ascivets.

5. The branches on the diagram indicate where

a. mass extinctions might have occurred

b. speciation took place

c. groups acquired traits and passed them ontotheir offspring

d. there are gaps in the line of evolution

Extended Response6. A scientist has discovered a new type of animal in

the tundra area near the North Pole. Write a para-graph describing the type of evidence the scientistmight use to classify the animal by its evolutionaryhistory in the chart shown. Use these terms in yourparagraph. Underline each term in your answer.

7. Write a paragraph in which you describe the traitsof one of the animals named in the diagram.Choose several traits and describe how these traitsmight help the animal survive. Then describe howthese might have been the result of adaptationsand natural selection.

embryo DNA sequencesvestigial structures common ancestor

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Mon

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Dogs

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coyo

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s

Wea

sels,

ott

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ferr

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Racc

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, kin

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us

Wal

ruse

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sea

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Sea

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