chapter 6: adaptations over time - quia · 154 chapter 6 adaptations over time early models of...

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sections

1 Ideas About EvolutionLab Hidden Frogs

2 Clues About Evolution

3 The Evolution of PrimatesLab Recognizing Variation in a Population

Virtual Lab How can naturalselection be modeled?

Adaptation? No problem.Cockroaches have existed for millions ofyears, yet they are still adapted to their envi-ronment. Since they first appeared, manyspecies have disappeared, and other well-adapted species have evolved.

Pick a favorite plant or animal andlist in your Science Journal all the ways it is well-suited to itsenvironment.

Science Journal

Adaptations over Time

Adaptations over Time

B.G. Thomson/ Photo ResearchersB.G. Thomson/ Photo Researchers

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Principles of Natural SelectionMake the following Foldable to help you understand theprocess of natural selection.

Fold a sheet ofpaper in halflengthwise.

Fold paper down 2.5 cm from the top. (Hint: From the tip of your index finger to your middle knuckle is about 2.5 cm.)

Open and drawlines along the 2.5-cm fold andthe center fold. Label as shown.

Summarize in a Table As you read, list the fiveprinciples of natural selection in the left-handcolumn. In the right-hand column, briefly writean example for each principle.

STEP 3

STEP 2

STEP 1

Adaptation for a HunterThe cheetah is nature’s fastest hunter, but itcan run swiftly for only short distances. Its furblends in with tall grass, making it almostinvisible as it hides and waits for prey. Thenthe cheetah pounces, capturing the preybefore it can run away.

1. Spread a sheet of newspaper classified adson the floor.

2. Using a hole puncher, make 100 circlesfrom each of the following types of paper:white paper, black paper, and classified ads.

3. Scatter all the circles on the news-paper on the floor. For 10 s, pick up asmany circles as possible, one at a time.Have a partner time you.

4. Count the number of each kind of papercircle that you picked up. Record yourresults in your Science Journal.

5. Think Critically Which paper circleswere most difficult to find? What can youinfer about a cheetah’s coloring from thisactivity? Enter your responses to thesequestions in your Science Journal.

Start-Up Activities

Preview this chapter’s contentand activities at life.msscience.com

Principles

of Natural

SelectionExample

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154 CHAPTER 6 Adaptations over Time

Early Models of Evolution Millions of species of plants, animals, and other organisms

live on Earth today. Do you suppose they are exactly the same asthey were when they first appeared—or have any of themchanged? A species is a group of organisms that share similarcharacteristics and can reproduce among themselves to producefertile offspring. Many characteristics of a species are inheritedwhen they pass from parent to offspring. Change in these inher-ited characteristics over time is evolution. Figure 1 shows howthe characteristics of the camel have changed over time.

■

Describe Lamarck’s hypothesis of acquired characteristics and Darwin’s theory of natural selection.

■ Identify why variations in organ-isms are important.

■ Compare and contrast gradual-ism and punctuated equilibrium.

The theory of evolution suggestswhy there are so many different living things.

Review Vocabularygene: a section of DNA that contains instructions for makingspecific proteins

New Vocabulary

• species

• evolution

• natural selection

• variation

• adaptation

• gradualism

• punctuated equilibrium

Ideas About Evolution

Figure 1 By studying fossils,scientists have traced thehypothesized evolution of thecamel. Discuss the changes you observein camels over time.

Protylopus56 mya

Poebrotherium35 mya

Procamelus23 mya

Small hump

CamelusPresent day

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SECTION 1 Ideas About Evolution 155

Hypothesis of Acquired Characteristics In 1809, JeanBaptiste de Lamarck proposed a hypothesis to explain howspecies change over time. He suggested that characteristics, ortraits, developed during a parent organism’s lifetime are inher-ited by its offspring. His hypothesis is called the inheritance ofacquired characteristics. Scientists collected data on traits thatare passed from parents to offspring. The data showed that traitsdeveloped during a parent’s lifetime, such as large muscles builtby hard work or exercise, are not passed on to offspring. The evi-dence did not support Lamarck’s hypothesis.

What was Lamarck’s explanation of evolution?

Darwin’s Model of EvolutionIn December 1831, the HMS Beagle sailed from England on

a journey to explore the South American coast. On board was ayoung naturalist named Charles Darwin. During the journey,Darwin recorded observations about the plants and animals hesaw. He was amazed by the variety of life on the GalápagosIslands, which are about 1,000 km from the coast of Ecuador.Darwin hypothesized that the plants and animals on theGalápagos Islands originally must have come from Central andSouth America. But the islands were home to many species hehad not seen in South America, including giant cactus trees,huge land tortoises, and the iguana shown in Figure 2.

Figure 2 This map shows theroute of Darwin’s voyage on the HMS Beagle. Darwin noticed manyspecies on the Galápagos Islandsthat he had not seen along thecoast of South America, includingthe marine iguana. This species isthe only lizard in the world knownto enter the ocean and feed onseaweed.

Azores

Canary Is.Cape Verde Is.

AscensionSt. Helena

MauritiusRio de Janeiro

Bahia

Montevideo

Falkland Is.

Galápagos Is.

ValparaisoTahiti

Sydney

HobartKing George I.

Cocos Is.

Tierra del Fuego

New Zealand

GalápagosIslands

CulpepperWenman

Pinta

MarchenaEquator

Isabela

Fernandina San Salvador

Santa CruzBaltra

San CristóbalSanta

FéSanta Maria

Española

Genovesa

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Darwin’s Observations Darwin observed 13 species offinches on the Galápagos Islands. He noticed that all 13 specieswere similar, except for differences in body size, beak shape, andeating habits, as shown in Figure 3. He also noticed that all theGalápagos finch species were similar to one finch species he hadseen on the South American coast.

Darwin reasoned that the Galápagos finches must have hadto compete for food. Finches with beak shapes that allowedthem to eat available food survived longer and produced moreoffspring than finches without those beak shapes. After manygenerations, these groups of finches became separate species.

How did Darwin explain the evolution of the dif-ferent species of Galápagos finches?

Natural SelectionAfter the voyage, Charles Darwin returned to England and

continued to think about his observations. He collected moreevidence on inherited traits by breeding racing pigeons. He alsostudied breeds of dogs and varieties of flowers. In the mid 1800s,Darwin developed a theory of evolution that is accepted by mostscientists today. He described his ideas in a book called On theOrigin of Species, which was published in 1859.

Figure 3 Darwin observed that the beak shape of eachspecies of Galápagos finch is related to its eating habits.

Finches with medium-sized beakseat a variety of foods includingseeds and insects.

Finches that feed on insects havelong, slender beaks for probingbeneath tree bark.

Finches that eat nuts and seedshave short, strong beaks for breaking hard shells.

Topic: Darwin’s FinchesVisit for Web links to informationabout the finches Darwinobserved.

Activity In your Science Journal,describe the similarities and dif-ferences of any two species ofGalápagos finches.

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Darwin’s Theory Darwin’s observations led manyother scientists to conduct experiments on inheritedcharacteristics. After many years, Darwin’s ideas becameknown as the theory of evolution by natural selection.Natural selection means that organisms with traits bestsuited to their environment are more likely to surviveand reproduce. Their traits are passed to more offspring.All living organisms produce more offspring than sur-vive. Galápagos finches lay several eggs every few months.Darwin realized that in just a few years, several pairs offinches could produce a large population. A population isall of the individuals of a species living in the same area.Members of a large population compete for living space,food, and other resources. Those that are best able to sur-vive are more likely to reproduce and pass on their traitsto the next generation.

The principles that describe how natural selectionworks are listed in Table 1. Over time, as new data wasgathered and reported, changes were made to Darwin’soriginal ideas about evolution by natural selection. Histheory remains one of the most important ideas in thestudy of life science.

Alejandro raises tropical fish as a hobby.Could the observations that he makes

over several weeks illustrate the principles of natural selection?

Identifying the ProblemAlejandro keeps a detailed journal of his

observations, some of which are given in thetable to the right.

Solving the ProblemRefer to Table 1 and match each of

Alejandro’s journal entries with the princi-ple(s) it demonstrates. Here’s a hint: Someentries may not match any of the principles ofnatural selection. Some entries may matchmore than one principle.

Does natural selection take place in a fish tank?

Fish Tank Observations

Date Observation

June 6 6 fish are placed in aquarium tank.

July 22 16 new young appear.

July 24 3 young have short or missing tail fins. 13 young have normal tail fins.

July 28 Young with short or missing tail fins die.

August 1 2 normal fish die—from overcrowding?

August 12 30 new young appear.

August 15 5 young have short or missing tail fins. 25 young have normal tail fins.

August 18 Young with short or missing tail fins die.

August 20 Tank is overcrowded. Fish are divided equally into two tanks.

Table 1 The Principles of Natural Selection

1. Organisms produce more offspring than can survive.

2. Differences, or variations, occur among individuals of a species.

3. Some variations are passed to offspring.

4. Some variations are helpful. Individuals with helpful variations survive and reproduce better than those without these variations.

5. Over time, the offspring of individuals with helpful variations make up more of a population and eventually may become a separate species.

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Variation and AdaptationDarwin’s theory of evolution by natural selection empha-

sizes the differences among individuals of a species. These dif-ferences are called variations. A variation is an inherited traitthat makes an individual different from other members of itsspecies. Variations result from permanent changes, or muta-tions, in an organism’s genes. Some gene changes produce smallvariations, such as differences in the shape of human hairlines.Other gene changes produce large variations, such as an albinosquirrel in a population of gray squirrels or fruit without seeds.Over time, more and more individuals of the species mightinherit these variations. If individuals with these variations con-tinue to survive and reproduce over many generations, a newspecies can evolve. It might take hundreds, thousands, or mil-lions of generations for a new species to evolve.

Some variations are more helpful than others. An adaptationis any variation that makes an organism better suited to its envi-ronment. The variations that result in an adaptation can involvean organism’s color, shape, behavior, or chemical makeup.Camouflage (KA muh flahj) is an adaptation. A camouflagedorganism, like the one shown in Figure 4, blends into its envi-ronment and is more likely to survive and reproduce.Figure 4 Variations that

provide an advantage tend toincrease in a population overtime. Variations that result ina disadvantage tend todecrease in a population over time.

Albinism can prevent an organism from blending into its environment.Infer what might happen to an albino lemur in its natural environment.

Camouflage allows organisms to blend into their environments. Infer how its coloration gives this scorpion fish a survival advantage.

Evolution of EnglishIf someone fromShakespeare’s time wereto speak to you today,you probably would not understand her.Languages, like species,change over time. In yourScience Journal, discusssome words or phrasesthat you use that yourparents or teachers donot use correctly.

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Changes in the Sources of Genes Over time, the geneticmakeup of a species might change its appearance. For example,as the genetic makeup of a species of seed-eating Galápagosfinch changed, so did the size and shape of its beak. Many kindsof environmental factors help bring about changes. When indi-viduals of the same species move into or out of an area, theymight bring in or remove genes and variations. Suppose a fam-ily from another country moves to your neighborhood. Theymight bring different foods, customs, and ways of speaking withthem. In a similar way, when new individuals enter an existingpopulation, they can bring in different genes and variations.

Geographic Isolation Sometimes mountains, lakes, orother geologic features isolate a small number of individualsfrom the rest of a population. Over several generations, varia-tions that do not exist in the larger population might begin to bemore common in the isolated population. Also, gene mutationscan occur that add variations to populations. Over time, the twopopulations can become so different that they no longer canbreed with each other. The two populations of rabbits shown inFigure 5 have been geographically isolated from each other forthousands of generations.

Figure 5 About 600 years ago, European rab-bits were introduced to the Canary Islands froma visiting Portuguese ship. The Canary Islandsare in the Atlantic Ocean off the northwest coastof Africa. Over time, the Canary Island rabbitsbecame a separate species.

Canary Island rabbits feed during the night. Explain why large eyes might be considered a helpful adaptation in Canary Island rabbits.

European rabbits, like the one above, feedduring the day and are fairly large.

Relating Evolution toSpeciesProcedure1. On a piece of paper, print

the word train.2. Add, subtract, or change

one letter to make a newword.

3. Repeat step 2 with thenew word.

4. Repeat steps 2 and 3 twomore times.

5. Make a “family tree” thatshows how your first wordchanged over time.

Analysis1. Compare your tree to those

of other people. Did youproduce the same words?

2. How is this process similarto evolution by naturalselection?

(l)Darek Karp/Animals Animals, (r)Vonorla Photography

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The Speed of EvolutionScientists do not agree on how quickly evolution occurs.

Many scientists hypothesize that evolution occurs slowly, per-haps over tens or hundreds of millions of years. Other scientistshypothesize that evolution can occur quickly. Most scientistsagree that evidence supports both of these models.

Gradualism Darwin hypothesized that evolution takes placeslowly. The model that describes evolution as a slow, ongoingprocess by which one species changes to a new species is knownas gradualism. According to the gradualism model, a continu-ing series of mutations and variations over time will result in anew species. Look back at Figure 1, which shows the evolutionof the camel over tens of millions of years. Fossil evidence showsa series of intermediate forms that indicate a gradual changefrom the earliest camel species to today’s species.

Punctuated Equilibrium Gradualism doesn’t explain theevolution of all species. For some species, the fossil record showsfew intermediate forms—one species suddenly changes toanother. According to the punctuated equilibrium model, rapidevolution comes about when the mutation of a few genes resultsin the appearance of a new species over a relatively short periodof time. The fossil record gives examples of this type of evolu-tion, as you can see in Figure 6.

Figure 6 The hypothesized evo-lution of bears illustrates the punc-tuated equilibrium model ofevolution. Discuss how the six species on thefar right are explained better bypunctuated equlibrium.

Common ancestor

about 40 millionyears ago

15-20 millionyears ago

2 millionyears ago

RaccoonRed

pandaGiantpanda

Polarbear

Spectacledbear

Slothbear

Blackbear

Brownbear

Sunbear

(l)Joe McDonald/Animals Animals, (c)Tom McHugh/Photo Researchers, (r)Tim Davis/Photo Researchers

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Self Check1. Compare Lamarck’s and Darwin’s ideas about how evo-

lution takes place.

2. Explain why variations are important to understandingchange in a population over time.

3. Discuss how the gradualism model of evolution differsfrom the punctuated equilibrium model of evolution.

4. Describe how geographic isolation contributes to evolution.

5. Think Critically What adaptations would be helpful foran animal species that was moved to the Arctic?

6. Concept Map Use information given in Figure 6 tomake a map that shows how raccoons, red pandas,giant pandas, polar bears, and black bears are relatedto a common ancestor.

SummaryEarly Models of Evolution

• Evolution is change in the characteristics of aspecies over time.

• Lamarck proposed the hypothesis of inheritedacquired characteristics.

Natural Selection

• Darwin proposed evolution by natural selec-tion, a process by which organisms bestsuited to their environments are most likely tosurvive and reproduce.

• Organisms have more offspring than can sur-vive, individuals of a species vary, and manyof these variations are passed to offspring.

Variation and Adaptation

• Adaptations are variations that help an organ-ism survive or reproduce in its environment.

• Mutations are the source of new variations.

The Speed of Evolution

• Evolution may be a slow or fast processdepending on the species under study.

7. Use Percentages The evolution of the camel can betraced back at least 56 million years. Use Figure 1 toestimate the percent of this time that the moderncamel has existed.

Punctuated Equilibrium Today Evolution by the punctu-ated equilibrium model can occur over a few thousand or mil-lion years, and sometimes even faster. For example, manybacteria have changed in a few decades. The antibiotic penicillinoriginally came from the fungus shown in Figure 7. But manybacteria species that were once easily killed by penicillin nolonger are harmed by it. These bacteria have developedresistance to the drug. Penicillin has been in use since1943. Just four years later, in 1947, a species of bacteriathat causes pneumonia and other infections already haddeveloped resistance to the drug. By the 1990s, several dis-ease-producing bacteria had become resistant to peni-cillin and many other antibiotics.

How did penicillin-resistant bacteria evolve soquickly? As in any population, some organisms have vari-ations that allow them to survive unfavorable living con-ditions when other organisms cannot. When penicillinwas used to kill bacteria, those with the penicillin-resist-ant variation survived, reproduced, and passed this trait totheir offspring. Over a period of time, this bacteria popu-lation became penicillin-resistant.

Figure 7 The fungus growing inthis petri dish is Penicillium, theoriginal source of penicillin. It pro-duces an antibiotic substance thatprevents the growth of certainbacteria.

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Through natural selection, animals becomeadapted for survival in their environment.Adaptations include shapes, colors, and eventextures that help an animal blend into its sur-roundings. These adaptations are called camou-flage. The red-eyed tree frog’s mint green bodyblends in with tropical forest vegetation asshown in the photo on the right. Could youdesign camouflage for a desert frog? A temper-ate forest frog?

Real-World QuestionWhat type of camouflage would best suit a frogliving in a particular habitat?

Goals■ Create a frog model camouflaged to blend

in with its surroundings.

Materials (for each group)cardboard form of a frog gluecolored markers beads crayons sequinscolored pencils modeling clay

Safety Precautions

Procedure1. Choose one of the following habitats for

your frog model: muddy shore of a pond,orchid flowers in a tropical rain forest, mul-ticolored clay in a desert, or the leaves andbranches of trees in a temperate forest.

2. List the features of your chosen habitat thatwill determine the camouflage your frogmodel will need.

3. Brainstorm with your groupthe body shape, coloring, andskin texture that wouldmake the best camou-flage for your model.Record your ideas inyour Science Journal.

4. Draw in your Science Journal samples ofcolors, patterns, texture, and other featuresyour frog model might have.

5. Show your design ideas to your teacher andask for further input.

6. Construct your frog model.

Conclude and Apply1. Explain how the characteristics of the

habitat helped you decide on the specific frog features you chose.

2. Infer how the color patterns and otherphysical features of real frogs develop innature.

3. Explain why it might be harmful to releasea frog into a habitat for which it is notadapted.

Create a poster or other visual display thatrepresents the habitat you chose for thisactivity. Use your display to showclassmates how your design helpscamouflage your frog model. For morehelp, refer to the Science Skill Handbook.


Hidden FrMgs

Frans Lanting/Minden Pictures

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SECTION 2 Clues About Evolution 163

Clues from FossilsImagine going on a fossil hunt in Wyoming. Your compan-

ions are paleontologists—scientists who study the past by col-lecting and examining fossils. As you climb a low hill, you noticea curved piece of stone jutting out of the sandy soil. One of thepaleontologists carefully brushes the soil away and congratulatesyou on your find. You’ve discovered part of the fossilized shell ofa turtle like the one shown in Figure 8.

The Green River Formation covers parts of Wyoming, Utah,and Colorado. On your fossil hunt, you learn that about 50 mil-lion years ago, during the Eocene Epoch, this region was coveredby lakes. The water was home to fish, crocodiles, lizards, and tur-tles. Palms, fig trees, willows, and cattails grew on the lakeshores.Insects and birds flew through the air. How do scientists knowall this? After many of the plants and animals of that time died,they were covered with silt and mud. Over millions of years,they became the fossils that have made the Green RiverFormation one of the richest fossil deposits in the world.

Clues About Evolution

■ Identify the importance of fossilsas evidence of evolution.

■ Explain how relative and radio-metric dating are used to esti-mate the age of fossils.

■ List examples of five types of evidence for evolution.

The scientific evidence for evolutionhelps you understand why this theory is so important to the study of biology.

Review Vocabularyepoch: next-smaller division ofgeological time after a period; ischaracterized by differences inlife-forms that may vary regionally

New Vocabulary

• sedimentary rock

• radioactive element

• embryology

• homologous

• vestigial structure

Figure 8 The desert of the Green River Formation is home to prong-horn antelope, elks, coyotes, and eagles. Fossil evidence shows thatabout 50 million years ago the environment was much warmer and wetter than it is today.

The turtle Cistemum undatum is from thesame fossilformation.

The most abundantfossils are of a fresh-water herring, Knightiaoecaena, which isWyoming’s state fossil.

(l)Dominique Braud/Earth Scenes, (c)Carr Clifton/Minden Pictures, (r)John Cancalosi/DRK Photo

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Types of FossilsMost of the evidence for evolution comesfrom fossils. A fossil is the remains, an

imprint, or a trace of a prehistoric organism. Several types of fos-sils are shown in Figure 9. Most fossils are found in sedimentaryrock. Sedimentary rock is formed when layers of sand, silt, clay,or mud are compacted and cemented together, or when mineralsare deposited from a solution. Limestone, sandstone, and shaleare all examples of sedimentary rock. Fossils are found moreoften in limestone than in any other kind of sedimentary rock.The fossil record provides evidence that living things haveevolved.

Figure 9 Examples of several differenttypes of fossils are shown here. Infer which of these would most likely be foundin a layer of sedimentary rock.

Fossils in amber When the sticky resin of certaincone-bearing plants hardensover time, amber forms. Itcan contain the remains oftrapped insects.

Frozen fossils Theremains of organisms likethis mammoth can betrapped in ice that remainsfrozen for thousands of years.

Mineralized fossilsMinerals can replace wood orbone to create a piece of pet-rified wood as shown to theleft or a mineralized bonefossil. Imprint fossils

A leaf, feather,bones, or eventhe entire bodyof an organismcan leave animprint on sedi-ment that laterhardens tobecome rock.

Cast fossils Mineralscan fill in the hollowsof animal tracks, asshown to the right, amollusk shell, or otherparts of an organism to create a cast.

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Determining a Fossil’s AgePaleontologists use detective skills to determine the age of

dinosaur fossils or the remains of other ancient organisms. Theycan use clues provided by unique rock layers and the fossils theycontain. The clues provide information about the geology,weather, and life-forms that must have been present during eachgeologic time period. Two basic methods—relative dating andradiometric dating—can be used, alone or together, to estimatethe ages of rocks and fossils.

Relative Dating One way to find the approximate age of fos-sils found within a rock layer is relative dating. Relative dating isbased on the idea that in undisturbed areas, younger rock layersare deposited on top of older rock layers, as shown in Figure 10. Relative dating provides only an estimate of a fossil’sage. The estimate is made by comparing the ages of rock layersfound above and below the fossil layer. For example, suppose a 50-million-year-old rock layer lies below a fossil, and a 35-million-year-old layer lies above it. According to relative dating,the fossil is between 35 million and 50 million years old.

Why can relative dating be used onlyto estimate the age of a fossil?

Radiometric Dating Scientists can obtain a more accurateestimate of the age of a rock layer by using radioactive elements.A radioactive element gives off a steady amount of radi-ation as it slowly changes to a nonradioactive element.Each radioactive element gives off radiation at a differentrate. Scientists can estimate the age of the rock by com-paring the amount of radioactive element with theamount of nonradioactive element in the rock. Thismethod of dating does not always produce exact results,because the original amount of radioactive element inthe rock can never be determined for certain.

Figure 10 In Bryce Canyon, ero-sion by water and wind has cutthrough the sedimentary rock,exposing the layers. Infer the relative age of rocks in thelowest layers compared to the toplayer.

Topic: Fossil FindsVisit for Weblinks to information about recentfossil discoveries.

Activity Prepare a newspaperarticle describing how one of thesediscoveries was made, what itreveals about past life on Earth,and how it has impacted ourunderstanding of what the pastenvironments of Earth were like.

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John

Kie

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Pet

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nc.

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Figure 11

Earth is roughly 4.5 billion years old. Asshown here, the vast period of time fromEarth’s beginning to the present day has

been organized into the geologic time scale. Thescale is divided into eras and periods. Dates onthis scale are given as millions of years ago (mya).

Reptiles

Humans

Amphibians

Mammalsand birds

CENO

ZOIC

MES

OZOI

C

PALE

OZOI

C

PREC

AMBR

IAN

Bacteria

Trilobites

Fish

Landplants

Himalaya rise

Floweringplants

570 mya

245 mya

65 mya

QUATERNARY

JURASSIC

DEVONIAN

CAMBRIAN

TERTIARY

CRETACEOUS

TRIASSIC

SILURIAN

PENNSYLVANIAN PERMIAN

MISSISSIPPIAN

ORDOVICIAN

PRECAMBRIAN

ORIGIN: 4.5 billion years ago

166

VISUALIZING THE GEOLOGIC TIME SCALE

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Fossils and EvolutionFossils provide a record of organisms that lived in the past.

However, the fossil record is incomplete, or has gaps, much likea book with missing pages. The gaps exist because most organ-isms do not become fossils. By looking at fossils, scientists con-clude that many simpler forms of life existed earlier in Earth’shistory, and more complex forms of life appeared later, as shownin Figure 11. Fossils provide indirect evidence that evolution hasoccurred on Earth.

Almost every week, fossil discoveries are made somewhere inthe world. When fossils are found, they are used to help scien-tists understand the past. Scientists can use fossils to make mod-els that show what the organisms might have looked like. Fromfossils, scientists can sometimes determine whether the organ-isms lived in family groups or alone, what types of food they ate,what kind of environment they lived in, and many other thingsabout them. Most fossils represent extinct organisms. From astudy of the fossil record, scientists have concluded that morethan 99 percent of all organisms that have ever existed on Earthare now extinct.

More Clues About EvolutionBesides fossils, what other clues do humans have about evo-

lution? Sometimes, evolution can be observed directly. Plantbreeders observe evolution when they use cross-breeding toproduce genetic changes in plants. The development of antibi-otic resistance in bacteria is another direct observation of evolu-tion. Entomologists have noted similar rapid evolution ofpesticide-resistant insect species. These observations providedirect evidence that evolution occurs. Also, many examples ofindirect evidence for evolution exist. They include similarities inembryo structures, the chemical makeup of organisms includ-ing DNA, and the way organisms develop into adults. Indirectevidence does not provide proof of evolution, but it does sup-port the idea that evolution takes place over time.

Embryology The study of embryos and their development iscalled embryology (em bree AH luh jee). An embryo is the ear-liest growth stage of an organism. A tail and pharyngeal pouchesare found at some point in the embryos of fish, reptiles, birds,and mammals, as Figure 12 shows. Fish develop gills, but theother organisms develop other structures as their developmentcontinues. Fish, birds, and reptiles keep their tails, but manymammals lose theirs. These similarities suggest an evolutionaryrelationship among all vertebrate species.

Figure 12 Similarities in theembryos of fish, chickens, and rab-bits show evidence of evolution.Evaluate these embryos as evi-dence for evolution.

Pharyngealpouches

Pharyngealpouches

Tail

TailFish

Chicken Rabbit

Evolution in Fossils Manyorganisms have a historythat has been preserved insedimentary rock. Fossilsshow that the bones of ani-mals such as horses andwhales have becomereduced in size or numberover geologic time, as thespecies has evolved. Inyour Science Journal,explain what informationcan be gathered fromchanges in structures thatoccur over time.

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Homologous Structures What do the structures shown inFigure 13 have in common? Although they have different func-tions, each of these structures is made up of the same kind ofbones. Body parts that are similar in origin and structure arecalled homologous (hoh MAH luh gus). Homologous struc-tures also can be similar in function. They often indicate thattwo or more species share common ancestors.

What do homologous structures indicate?

Vestigial Structures The bodies of some organisms include vestigial (veh STIH jee ul) structures—structures thatdon’t seem to have a function. Vestigial structures also provideevidence for evolution. For example, manatees, snakes, andwhales no longer have back legs, but, like all animals with legs,they still have pelvic bones. The human appendix is a vestigialstructure. The appendix appears to be a small version of thececum, which is an important part of the digestive tract of manymammals. Scientists hypothesize that vestigial structures, likethose shown in Figure 14, are body parts that once functionedin an ancestor.

Figure 14 Humans have three smallmuscles around each ear that are vestigial.In some mammals, such as horses, these muscles are large. They allow a horse to turn its ears toward the source of a sound. Humans cannot rotate their ears, but some people can wiggle their ears.

Figure 13 A porpoise flipper,frog forelimb, human arm, and batwing are homologous. These struc-tures show different arrangementsand shapes of the bones of theforelimb. They have the samenumber of bones, muscles, andblood vessels, and they developedfrom similar tissues.

Porpoiseflipper

Frog forelimb Humanarm

Bat wing

(l)Kees Van Den Berg/Photo Researchers, (r)Doug Martin

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Self Check1. Compare and contrast relative dating and radiometric

dating.

2. Discuss the importance of fossils as evidence of evolu-tion and describe five different kinds of fossils.

3. Explain how DNA can provide some evidence of evolution.

4. List three examples of direct evidence for evolution.

5. Interpret Scientific Illustrations According to data inFigure 11, what was the longest geologic era? What wasthe shortest era? In what period did mammals appear?

6. Think Critically Compare and contrast the five types ofevidence that support the theory of evolution.

SummaryClues from Fossils

• Scientists learn about past life by studyingfossils.

Determining a Fossil’s Age

• The relative date of a fossil can be estimatedfrom the ages of rocks in nearby layers.

• Radiometric dating using radioactive ele-ments gives more accurate dates for fossils.

Fossils and Evolution

• The fossil record has gaps which may yet befilled with later discoveries.

More Clues About Evolution

• Homologous structures, similar embryos, orvestigial structures can show evolutionaryrelationships.

• Evolutionary relationships among organismscan be inferred from DNA comparisons.

7. Use Percentages The Cenozoic Era represents about65 million years. Approximately what percent ofEarth’s 4.5-billion-year history does this era represent?

DNA If you enjoy science fiction, you prob-ably have read books or seen movies in whichscientists re-create dinosaurs and otherextinct organisms from DNA taken from fos-sils. DNA is the molecule that controls hered-ity and directs the development of everyorganism. In a cell with a nucleus, DNA isfound in genes that make up the chromo-somes. Scientists compare DNA from living organisms to iden-tify similarities among species. Examinations of ancient DNAoften provide additional evidence of how some species evolvedfrom their extinct ancestors. By looking at DNA, scientists alsocan determine how closely related organisms are. For example,DNA studies indicate that dogs are the closest relatives of bears.

Similar DNA also can suggest common ancestry. Apes suchas the gorillas shown in Figure 15, chimpanzees, and orangutanshave 24 pairs of chromosomes. Humans have 23 pairs. Whentwo of an ape’s chromosomes are laid end to end, a match forhuman chromosome number 2 is formed. Also, similar proteinssuch as hemoglobin—the oxygen-carrying protein in red bloodcells—are found in many primates. This can be further evidencethat primates have a common ancestor.

Figure 15 Gorillas have DNAand proteins that are similar tohumans and other primates.

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Primates Humans, monkeys, and apes belong to the group of mam-

mals known as the primates. All primates have opposablethumbs, binocular vision, and flexible shoulders that allow thearms to rotate. These shared characteristics indicate that all pri-mates may have evolved from a common ancestor.

Having an opposable thumb allows you to cross your thumbover your palm and touch your fingers. This means that you cangrasp and hold things with your hands. An opposable thumballows tree-dwelling primates to hold on to branches.

Binocular vision permits you to judge depth or distance withyour eyes. In a similar way, it allows tree-dwelling primates tojudge the distances as they move between branches. Flexibleshoulders and rotating forelimbs also help tree-dwelling pri-mates move from branch to branch. They also allow humans todo the backstroke, as shown in Figure 16.

Primates are divided into two major groups. The first group,the strepsirhines (STREP suh rines), includes lemurs and tar-siers like those shown in Figure 17. The second group, hap-lorhines (HAP luh rines), includes monkeys, apes, and humans.

The Evolution of Primates

■ Describe the differences amongliving primates.

■ Identify the adaptations of primates.

■ Discuss the evolutionary historyof modern primates.

Studying primate evolution will help you appreciate the differencesamong primates.

Review Vocabularyopposable: can be placed againstanother digit of a hand or foot

New Vocabulary

• primate • Homo sapiens

• hominid

Figure 16 The ability to rotate the shoulderin a complete circle allows humans to swimthrough water and tree-dwelling primates totravel through treetops.

(l)M

ark

E.

Gib

son,

(r)

Ger

ard

Lacz

/Ani

mal

s A

nim

als

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SECTION 3 The Evolution of Primates 171

Hominids About 4 million to 6 million years ago, humanlikeprimates appeared that were different from the other primates.These ancestors, called hominids, ate both meat and plants andwalked upright on two legs. Hominids shared some characteris-tics with gorillas, orangutans, and chimpanzees, but a largerbrain separated them from the apes.

African Origins In the early 1920s, a fossil skull was discov-ered in a quarry in South Africa. The skull had a small space forthe brain, but it had a humanlike jaw and teeth. The fossil,named Australopithecus, was one of the oldest hominids discov-ered. An almost-complete skeleton of Australopithecus wasfound in northern Africa in 1974. This hominid fossil, shown inFigure 18, was called Lucy and had a small brain but is thoughtto have walked upright. This fossil indicates that modernhominids might have evolved from similar ancestors.

Figure 17 Tarsiers and lemurs areactive at night. Tarsiers are commonlyfound in the rain forests of SoutheastAsia. Lemurs live on Madagascar andother nearby islands.List the traits that distinguish theseanimals as primates.

Figure 18 The fossil remains of Lucy are esti-mated to be 2.9 million to 3.4 million years old.

TarsierLemur

Living Without ThumbsProcedure1. Using tape, fasten down

each of your thumbs nextto the palm of each hand.

2. Leave your thumbs tapeddown for at least 1 h.During this time, do thefollowing activities: eata meal, change clothes,and brush your teeth. Becareful not to try anythingthat could be dangerous.

3. Untape your thumbs, then write about yourexperiences in your Science Journal.

Analysis1. Did not having use of your

thumbs significantly affectthe way you did anything?Explain.

2. Infer how having opposablethumbs could have influ-enced primateevolution.

(l)Michael Dick/Animals Animals, (r)Carolyn A. McKeone/Photo Researchers

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Early Humans In the 1960s in the region ofAfrica shown in Figure 19, a hominid fossil,which was more like present-day humans thanAustralopithecus, was discovered. The hominidwas named Homo habilis, meaning “handy man,”because simple stone tools were found near him.Homo habilis is estimated to be 1.5 million to 2million years old. Based upon many fossil com-parisons, scientists have suggested that Homohabilis gave rise to another species, Homo erectus,about 1.6 million years ago. This hominid had alarger brain than Homo habilis. Homo erectustraveled from Africa to Southeast Asia, China,and possibly Europe. Homo habilis and Homoerectus are thought to be ancestors of humansbecause they had larger brains and more human-like features than Australopithecus.

Why was Homo habilis giventhat name?

Humans The fossil record indicates that Homo sapiens evolved about

400,000 years ago. By about 125,000 years ago, two early humangroups, Neanderthals (nee AN dur tawlz) and Cro-Magnonhumans, as shown in Figure 20, probably lived at the same timein parts of Africa and Europe.

Neanderthals Short, heavy bodies with thick bones, smallchins, and heavy browridges were physical characteristics ofNeanderthals. Family groups lived in caves and used well-madestone tools to hunt large animals. Neanderthals disappearedfrom the fossil record about 30,000 years ago. They probably arenot direct ancestors of modern humans, but represent a sidebranch of human evolution.

Figure 19 Many of the oldesthumanlike skeletons have beenfound in this area of east Africa.

Figure 20 Compare theskull of a Neanderthal with the skull of a Cro-Magnon.Describe what differences youcan see between these twoskulls.

Skull of a Cro-Magnon

ETHIOPIA

KENYA

TANZANIA

SUDAN

AFRICA

SOMALIA

Omo

UGANDA

Hadar

Koobi ForaLothagam

Kanapoi

Laetoli

Olduvai Gorge

Skull of aNeanderthal

(l)John Reader/Science Photo Library/Photo Researchers, (r)Archivo Iconografico, S.A./CORBIS

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SECTION 3 The Evolution of Primates 173

Self Check1. Describe three kinds of evidence suggesting that all pri-

mates might have shared a common ancestor.

2. Discuss the importance of Australopithecus.

3. Compare and contrast Neanderthals, Cro-Magnonhumans, and early humans.

4. Identify three groups most scientists consider to bedirect ancestors of modern humans.

5. Think Critically Propose a hypothesis to explain whyteeth are the most abundant fossil of hominids.

SummaryPrimates

• Primates are an order of mammals character-ized by opposable thumbs, binocular vision,and flexible shoulder joints.

• Primates are divided into strepsirrhines andhaplorhines.

• Hominids are human ancestors that firstappeared in Africa 4–6 million years ago.

• Hominids in the genus Homo first used toolsand had larger brains than previous primates.

Humans

• Homo sapiens first appeared about 400,000years ago.

• Cro-Magnon humans and Neanderthals coex-isted in many places until Neanderthals disap-peared about 30,000 years ago.

• Homo sapiens looked like modern humansand are believed to be our direct ancestors.

6. Concept Map Make a concept map to show in whatsequence hominids appeared. Use the following: Homosapiens sapiens, Neanderthal, Homo habilis, Australo-pithecus, Homo sapiens, and Cro-Magnon human.

7. Write a story in your Science Journal about what lifemight have been like when both Neanderthals andCro-Magnon humans were alive.

Cro-Magnon Humans Cro-Magnon fossils have been foundin Europe, Asia, and Australia and date from 10,000 to about40,000 years in age. Standing about 1.6 m to 1.7 m tall, the phys-ical appearance of Cro-Magnon people was almost the same asthat of modern humans. They lived in caves, made stone carv-ings, and buried their dead. As shown in Figure 21, the oldestrecorded art has been found on the walls of caves in France,where Cro-Magnon humans first painted bison, horses, andpeople carrying spears. Cro-Magnon humans are thought to bedirect ancestors of early humans, Homo sapiens, which means“wise human.” Evidence indicates that modern humans, Homosapiens sapiens, evolved from Homo sapiens.

Figure 21 Paintings on cavewalls have led scientists to hypoth-esize that Cro-Magnon humanshad a well-developed culture.

life.msscience.com/self_check_quizFrancois Ducasse/Rapho/Photo Researchers

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Design Your OwnDesign Your Own


Real-World QuestionWhen you first observe a flock of pigeons, you might think all thebirds look alike. However, if you look closer, you will notice minor differences, or variations, among the individuals. Different pigeonsmight have different color markings, or some might be smaller orlarger than others. Individuals of the same species—whether they’rebirds, plants, or worms—might look alike at first, but some variationsundoubtedly exist. According to the principles of natural selection,evolution could not occur without variations. What kinds of variationshave you noticed among species of plants or animals? How can youmeasure variation in a plant or animal population?

Form a HypothesisMake a hypothesis about the amount of variation in the fruit andseeds of one species of plant.

Goals■ Design an experiment

that will allow you tocollect data about vari-ation in a population.

■ Observe, measure,and analyze varia-tions in a population.

Possible Materialsfruit and seeds from one

plant speciesmetric rulermagnifying lensgraph paper

Safety Precautions

WARNING: Do not put anyfruit or seeds in your mouth.

Recognizing Variation ina PrpulatiHn

(t)Aaron Haupt, (b)Kenneth W. Fink/Photo Researchers

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LAB 175

Test Your HypothesisMake a Plan1. As a group, agree upon and write out the prediction.

2. List the steps you need to take to test your prediction. Be specific. Describe exactly what you will do at each step. List your materials.

3. Decide what characteristic of fruit and seeds you will study. For example, you could measure the length of fruit and seeds or count the number of seeds per fruit.

4. Design a data table in your Science Journal to collect data about two variations. Use the table to record the data your group collects.

5. Identify any constants, variables, and controls of the experiment.

6. How many fruit and seeds will you examine? Will your data be more accurate ifyou examine larger numbers?

7. Summarize your data in a graph or chart.

Follow Your Plan1. Make sure your teacher approves your plan before you start.

2. Carry out the experiment as planned.

3. While the experiment is going on, write down any observations you make andcomplete the data table in your Science Journal.

Analyze Your Data1. Calculate the mean and range of variation in your experiment. The range is the

difference between the largest and the smallest measurements. The mean isthe sum of all the data divided by the sample size.

2. Graph your group’s results by making a line graph for the variations you meas-ured. Place the range of variation on the x-axis and the number of organismsthat had that measurement on the y-axis.

Conclude and Apply1. Explain your results in terms of natural

selection.

2. Discuss the factors you used to determine theamount of variation present.

3. Infer why one or more of the variations you observed in this activity might be helpful to the survival of the individual.

Create a poster or other exhibit thatillustrates the variations you and yourclassmates observed.

Aaron Haupt

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The first cases of AIDS, or acquiredimmune deficiency syndrome, in humanswere reported in the early 1980s. AIDS is

caused by the human immunodeficiency virus,or HIV.

A major problem in AIDS research is therapid evolution of HIV. When HIV multipliesinside a host cell, new versions of the virus areproduced as well as identical copies of the virusthat invaded the cell. New versions of the virussoon can outnumber the original version. Atreatment that works against today’s HIV mightnot work against tomorrow’s version.

These rapid changes in HIV also mean thatdifferent strains of the virus exist in differentplaces around the world. Treatments developedin the United States work only for people whocontracted the virus in the United States. Thisleaves people in some parts of the world withouteffective treatments. So, researchers such asgeneticist Flossie Wong-Staal at the University ofCalifornia in San Diego, must look for new waysto fight the evolving virus.

Working BackwardsFlossie Wong-Staal is taking a new approach.

First, her team identifies the parts of a human cellthat HIV depends on and the parts of the humancell that HIV needs but the human cell doesn’tneed. Then the team looks for a way to remove—or inactivate—those unneeded parts. This tech-nique limits the virus’s ability to multiply.

Wong-Staal’s research combines threeimportant aspects of science—a deep under-standing of how cells and genesoperate, great skill in thetechniques of genet-ics, and great ideas.Understanding,skill, and greatideas are thebest weaponsso far in thefight to con-quer HIV.

For more information, visitlife.msscience.com/time

SCIENCEAND

HISTORYSCIENCE

CAN CHANGE THE COURSE OF HISTORY!

Research Use the link to the right and other sources todetermine which nations have the highest rates of HIV infection.Which nation has the highest rate? Where does the U.S. rank? Next,find data from ten years ago. Have the rankings changed?

Wong-Staal was on one of the two teams that first identified HIV as the virus that causes AIDS.

Fighting HIVFighting HIV

(t)Oliver Meckes/E.O.S/Gelderblom/Photo Researchers, (b)Lara Jo Regan/Saba

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http://life.msscience.com/time

Copy and complete the following spider map on evolution.

Ideas About Evolution

1. Evolution is one of the central ideas ofbiology. It explains how living things havechanged in the past and is a basis for predicting how they might change in the future.

2. Charles Darwin developed the theory ofevolution by natural selection to explainhow evolutionary changes account for thediversity of organisms on Earth.

3. Natural selection includes concepts of varia-tion, overproduction, and competition.

4. According to natural selection, organismswith traits best suited to their environmentare more likely to survive and reproduce.

Clues About Evolution

1. Fossils provide evidence for evolution.

2. Relative dating and radiometric dating can be used to estimate the age of fossils.

3. The evolution of antibiotic-resistant bac-teria, pesticide-resistant insects, and rapidgenetic changes in plant species providesdirect evidence that evolution occurs.

4. Homologous structures, vestigial structures,comparative embryology, and similarities in DNA provide indirect evidence ofevolution.

The Evolution of Primates

1. Primates include monkeys, apes, andhumans. Hominids are humanlike primates.

2. The earliest known hominid fossil isAustralopithecus.

3. Homo sapiens are thought to have evolvedfrom Cro-Magnon humans about 400,000years ago.

CHAPTER STUDY GUIDE 177

Evolution

Competition

Genetic changes in plants Vestigial structuresindirect evidence

principles of natural selection

direct evidence

life.msscience.com/interactive_tutor(l)Koster-Survival/Animals Animals, (r)Stephen J. Keasemann/DRK Photo

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Fill in the blanks with the correct vocabularyword or words.

1. _________ contains many different kinds of fossils.

2. The muscles that move the human earappear to be _________.

3. Forelimbs of bats, humans, and seals are_________.

4. Opposable thumbs are a characteristic of_________.

5. The study of _________ can provide evi-dence of evolution.

6. The principles of _________ include varia-tion and competition.

7. _________ likely evolved directly fromCro-Magnons.

Choose the word or phrase that best answers the question.

8. What is an example of adaptation?A) a fossilB) gradualismC) camouflageD) embryo

9. What method provides the most accurateestimate of a fossil’s age?A) natural selectionB) radiometric datingC) relative datingD) camouflage

10. What do homologous structures, vestigialstructures, and fossils provide evidence of?A) gradualism C) populationsB) food choice D) evolution

11. Which model of evolution shows changeover a relatively short period of time?A) embryologyB) adaptationC) gradualismD) punctuated equilibrium

12. What might a series of helpful variationsin a species result in?A) adaptation C) embryologyB) fossils D) climate change

Use the following chart to answer question 13.

Homo habilis

Homo erectus

?

Homo sapiens

13. Which of the following correctly fills the gapin the line of descent from Homo habilis?A) NeanderthalB) AustralopithecusC) Cro-Magnon humanD) chimpanzee

14. What is the study of an organism’s earlydevelopment called?A) adaptation C) natural selectionB) relative dating D) embryology

➝➝

➝

178 CHAPTER REVIEW

adaptation p. 158embryology p. 167evolution p. 154gradualism p. 160hominid p. 171Homo sapiens p. 172homologous p. 168natural selection p. 157

primate p. 170punctuated equilibrium

p. 160radioactive element p. 165sedimentary rock p. 164species p. 154variation p. 158vestigial structure p. 168

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15. Predict what type of bird the foot pictured at right would belong to.Explain your reasoning.

16. Discuss how Lamarck and Darwin would have explained the large eyes ofan owl.

17. Explain, using an example, how a newspecies of organism could evolve.

18. Identify how the color-changing ability ofchameleons is an adaptation.

19. Form a hypothesis as to why ponds are not overpopulated by frogs in summer.Use the concept of natural selection tohelp you.

20. Sequence Make an events-chain concept mapof the events that led Charles Darwin to histheory of evolution by natural selection.

Use the table below to answer question 21.

21. Interpret Data Each letter above represents achemical found in a species of bacteria.Which species are most closely related?

22. Discuss the evidence you would use todetermine whether the evolution of agroup were best explained by gradualism.How would this differ from a group thatfollowed a punctuated equilibrium model?

23. Describe the processes a scientist would useto figure out the age of a fossil.

24. Evaluate the possibility for each of the fivetypes of fossils in Figure 9 to yield a DNAsample. Remember that only biologicaltissue will contain DNA.

25. Collection With permission, collect fossilsfrom your area and identify them. Showyour collection to your class.

26. Brochure Assume that you are head of anadvertising company. Develop a brochureto explain Darwin’s theory of evolution bynatural selection.

Chemicals Present in Bacteria Species 1 A, G, T, C, L, E, S, H

Species 2 A, G, T, C, L, D, H

Species 3 A,G, T, C, L, D, P, U, S, R, I, V

Species 4 A, G, T, C, L, D, H

CHAPTER REVIEW 179

27. Relative Age The rate of radioactive decay ismeasured in half-lives—the amount of time ittakes for one half of a radioactive element todecay. Determine the relative age of a fossilgiven the following information:

• Rock layers are undisturbed.

• The layer below the fossil has potassium-40with a half-life of 1 million years and onlyone half of the original potassium is left.

• The layer above the fossil has carbon-14 witha half-life of 5,730 years and one-sixteenth ofthe carbon isotope remains.

Use the graph below to answer question 28.

28. First Appearances If Earth is 4.5 billion yearsold, how long ago did the first many-celled life-forms appear?

4.5 Billion Years

None or only

one-celled life

Many-celled life

89

19

life.msscience.com/chapter_reviewTom Tietz/Stone/Getty Images

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Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

1. A species is a group of organismsA. that lives together with similar

characteristics.B. that shares similar characteristics and

can reproduce among themselves to pro-duce fertile offspring.

C. across a wide area that cannot reproduce.D. that chooses mates from among

themselves.

2. Which of the following is considered animportant factor in natural selection?A. limited reproductionB. competition for resourcesC. no variations within a populationD. plentiful food and other resources

3. The marine iguana of the Galápagos Islandsenters the ocean and feeds on seaweed.What is this an example of?A. adaptationB. gradualismC. survival of the fittestD. acquired characteristic

Use the illustration below to answer question 4.

4. According to Lamarck’s hypothesis ofacquired characteristics, which statement bestexplains the changes in the camel over time?A. All characteristics developed during an

individual’s lifetime are passed on to offspring.

B. Characteristics that do not help the ani-mal survive are passed to offspring.

C. Variation of the species leads to adaptation.D. Individuals moving from one area

to another carry with them new characteristics.

Use the illustrations below to answer question 5.

5. What, besides competition for food, con-tributed to the evolution of the species ofDarwin’s finches?A. predationB. natural disasterC. DNAD. variation in beak shapes

6. Some harmless species imitate or mimic apoisonous species as a means for increasedsurvival. What is this an example of? A. acquired characteristicsB. adaptationC. variationD. geographic isolation

Tool-usingfinch

Seed-eatingfinch

Cactus-eatingfinch

Plant-eatingfinch

Insect-eatingfinch

Protylopus56 mya

mm

Procamelus23 mya

Small hump

CamelusPresent day

Poebrotherium35 mya

180 STANDARDIZED TEST PRACTICEGregory G. Dimijian, M.D./Photo Researchers

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Never Leave Any Answer Blank Answer each question as bestyou can. You can receive partial credit for partially correct answers.

Question 16 If you cannot remember all primate characteristics,list as many as you can.

STANDARDIZED TEST PRACTICE 181

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

7. How does camouflage benefit a species?

Use the photo below to answer question 8.

8. Describe an environment where the albinolemur would not be at a disadvantage.

9. Variation between members of a speciesplays an important role in Darwin’s theoryof evolution. What happens to variation inendangered species where the number ofindividuals is very low?

10. Describe what happens to an endangeredspecies if a variation provides an advan-tage for the species. What would happen ifthe variation resulted in a disadvantage?

11. Using the theory of natural selection,hypothesize why the Cro-Magnon humanssurvived and the Neanderthals disappeared.

Record your answers on a sheet of paper.

12. What are the two groups of early humansthat lived about 125,000 years ago inAfrica and Europe? Describe their generalappearance and characteristics. Comparethese characteristics to modern humans.

13. Explain how bacterial resistance to antibiotics is an example of punctuatedequilibrium.

14. Why are radioactive elements useful indating fossils? Does this method improveaccuracy over relative dating?

Use the illustrations below to answer question 15.

15. Why would scientists study embryos?What features of these three embryos sup-port evolution?

16. How does DNA evidence provide supportthat primates have a common ancestor?

Pharyngealpouches

Pharyngealpouches

Tail

TailFish

Chicken Rabbit

life.msscience.com/standardized_testPatti Murray/Animals Animals

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chapter 6: adaptations over time - quia · 154 chapter 6 adaptations over time early models of...

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