Section Surnmary Darwin's Theory

n, te ~ _ Class _

Chapter 7 Changes Over Time • Section 1 Surnmary

Darwin's Theory Key Concepts

• \'\'hat important observations did Darwin make on his \-CY\\lge?

• How did Darwin .iccount for the diversitx of species and the differences bet\Y-een similar species?

• How does natural selection lead to e\'OlUOOll"

In I B31, Charles Darwin left England on bo.ird the H:\IS Eco\'lc. \Vhile on his \'oy,lge, he observed plants and animals he had never seen before. Darwin's important observations included the diversity of organisms, the remains of ancient organisms, and the characteristics of organisms on the Galapagos Islands. Darwin savv man" different species, A species is ,1 gr(llll~

of similar organisms that C,Ul mate with e,lch other and produce fertile offspring. Darwin saw the fossil bones of animals that had died long "g0. A fossil is the preserved remains or traces of all organism th.it Iived ill the past.

In 18.35, the Bt'ilglt· reached the CaL1p"gos Islands in the Pacific Oce.in. Darwin 1I',lS surprised that ll1.any of the plants and animals on the Gal'l1"agos Islands were similar to organisms on mainland South America. However, there were also important differences, Darwin interred that ,1 small number of different species h,K1 come to the islands from the mainland. Eventuallv. their offspring became different from the mainland relatives. The finches on the C'lLip,'g0S Islands were noticeablx different from one island to another. The most obvious differences were tlw varied sizes and shapes of the birds beaks. Beak shape is an example of an adaptation, ,1 trait that helps ,111 orc.mism survive and reproduce. Darwin reasoned that plants or animals that arrived on the Galapagos Islands faced environmental factors that were different from those on the mainland. Perhaps, Darwin hypothesized, the species gradually changed over many generations and became better adapted to the new environments. TIlE' gradual change in ,1 specie5 over time is called evolution. Darwin's idE'<1S are often referred to ,15 the theorv of e\'olution. A scientific theory is ,1 well-tested concept that exphills ,1 wide mnge u: observations.

In his book TheOngiil (lrSpl\Oit'~, Darwin proposed th"t evolution occurs by n.itur.il selection. Natural selection is the process by which individuals that <lre better adapted to their environment Me 1110re likely to survive .ind reproduce than other members of the same species. A number of factors ilffect the process of natural selection: overproduction. competition. and variations. Any difference between individuals of the s,111te species is CLUed a genetic variation. Some variations make certain individuals better ,'c!<'pted to their environment bec\1Use of helpful traits the:' possess. Darwin proposed that, over a long time, natural selection can lead to change. Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear. \ vithout \'"r1<100nS, ,111 members ,)f a species would have the s.une traits. and natural selection would not occur. Onlv traits that are inherited, or controlled by genes, om be acted upon by natural selection,

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Darwin’s Theory

Understanding Main Ideas

Answer the following questions on a separate sheet of paper.

1.

Who was Charles Darwin, and what did he do on the

Beagle’s

voyage?

2.

What is evolution?

3.

Explain how the shape of a finch’s beak is an example of an adaptation.

4.

When members of a species compete, what do they compete for?

5.

What happens when species overproduce offspring?

6.

Suppose a variation makes an individual member of a species better adapted to its environment. How might that variation affect the individual’s reproduction?

7.

How does the environment “select” organisms?

8.

How do helpful variations accumulate in a species over time?

9.

Why can only traits controlled by genes be acted upon by natural selection?

Building Vocabulary

Fill in the blank to complete each statement.

10.

A(n) ________________________ is a group of similar organisms that can mate with each other and produce fertile offspring.

11.

A(n) ________________________ is a trait that helps an organism survive and reproduce.

12.

A scientific ________________________ is a well-tested concept that explains a wide range of observations.

13.

The process by which individuals that are better adapted to their environment are more likely to survive and reproduce is called ________________________.

14.

That some newly hatched turtles can swim faster than others of the same species is evidence of ________________________ within the species.

Changes Over Time

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Review and Reinforce

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Two Theories of Evolution

If you had been a biologist in the 1800s, you would have had to decide between two main theories about how evolution occurred. Consider the long neck of a giraffe. How did that evolve? Read the two explanations below, and then answer the questions that follow.

Theory 1

The ancestors of giraffes had short necks, and there was great competition for the plant food near the ground. Some of the giraffes kept trying to stretch their necks to reach leaves higher in the trees. As they stretched and stretched, their necks became longer. As their necks became longer, they were able to reach more food. Those ancestral giraffes survived to reproduce, while the giraffes that had not stretched their necks died. The offspring of giraffes with stretched necks inherited the longer necks. This process continued for generation after generation. In this way, giraffes evolved with longer and longer necks.

Theory 2

The ancestors of giraffes had short necks, and there was great competition for the plant food near the ground. Some of the ancestral giraffes naturally had slightly longer necks than others. The individuals with longer necks could reach leaves higher up in trees, and therefore could eat more food. Because those ancestral giraffes ate more food, they survived to produce offspring while the individuals with shorter necks did not. The offspring of giraffes with longer necks inherited the longer necks. This process continued for generation after generation. In this way, giraffes evolved with longer and longer necks.


1.

In Theory 1, what caused the giraffe neck to become longer?

2.

In Theory 2, what caused the giraffe neck to become longer?

3.

According to what scientists now know about genes, could the giraffes’ offspring have inherited longer necks as described in Theory 1? As described in Theory 2? Explain.

4.

Which of the two theories matches Darwin’s theory of evolution? Explain.

Changes Over Time

■

Enrich


Name " _ D" te Cbs",

Chapter 7 Changes Over Time Section 2 Summary

Evidence of Evolution Key Concepts

• 'vVh"t t>\'idence supports the theorv (If evolution?

• How do fossils form?

• Whlt d o scientists learn from fossils?

Modern-d.iv org.misms can provide clues about evolution. Similar bodv structures, patterns of early development, molecular structure, and fossils all provide evidence that organisms have changed over time. B\' comparing org.uusms. scien tists can infer how closelv related the orgunisms ,we in an evolutionarv sense. Scientists compare bod' structures. de\'eJopment before birth, DT\A sequences, .md fossils to determine the evolutionarv relationships ,1lnong org.mism-,

The comparison of the structures of different org.uusms is called comparative anatomy. Fishes. amphibians. reptiles, birds, and mammals all have .in internal skeleton with ,1 backbone This is whv scientists classuv ,111 five groU}'S of animals together ,15 \'ertebl\ltes. Presumablv, these groups .ill inherited these similarities in structure from ,1n e.irlv vertebr ,1 te ancestor th.it thev shared. Similar structures that rel.lted spedes h.ive inherited rrom ,1 c01111non ancestor ,Ire c.illed homologous structures.

Scientists make inferences about e\'olution,u\ relationships by comparing how different species develop before birth. During eurlv development. vertebrates have a tail .uid rows of tiny slits in their throats, suggesting that vertebrate species share " common ancestor. Two species with similar DNA and proteins probablv evolved trom ,1 common ancestor.

Most fossils form when organisms that die become buried ir: sediments. TIle most C01111110n fossils ,1fE' molds .uid C'btS. A mold is ,I hollow urea ill sediment in the sh'lpe of ,111 org,mism A cast is a solid l'l'py of the shape of ,111 org.inism. It is the opposite of .i mold. A fossil may form when the remains of an organism become petrified. Petrified fossils .ire fossils in which minerals rerl<1ce ,1U or part of an orgunism. Trace fossils provide evidence ot the .ictivitv of ancient org.uusms. Preserved rem.un-. such as those preserved in tM ;)1' amber. ,Ire another t\pe of fossil.

A paleontologist is ,1 scientist who studies fossils The fossil record provides evidence about the history of life and past environments on Earth. In addition, scientists use fossils to study the speed at which evolution has occurred. The fossil record shows that life on Earth has evolved. or changed over time, Simple, one-celled org.inisms h.ive gi\'en rise to complex plants and animals. Fossils can show how an en\'ironment 11<1:'> changed [If how Earth's surf.ice has changed.

Scientists ,He not sure how rapidlv spede5 dl,mge, The hypothesis ot gradualism prOp05E'S that evolution occurs slowlv but ste.idilv. The hvpothesis of punctuated equilib ria ,1CC()lmts tor gap5 in the fossil record. It st.ites that species e\'o1\-e quicklv during relatively short periods

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Evidence of EvolutionUnderstanding Main IdeasAnswer the following questions on a separate sheet of paper.

1. Name four kinds of evidence of evolution.2. Describe how a mold is related to a cast.3. What can a paleontologist tell from fossil footprints of a dinosaur?4. What does the fossil record reveal about the evolution of life on Earth?

Building Vocabulary Fill in the blank to complete each statement.

5. The hypothesis that evolution occured slowly but steadily is called ________________________.

6. Similar structures that related species have inherited from a common ancestor are called ________________________.

7. ________________________ provide evidence of the activities of ancient organisms.

8. ________________________ proposes that species evolved quickly during short periods separated by long periods of little to no change.

9. Fossils in which minerals replace part or all of an organism are called ________________________.

10. The comparison of the structures of different organisms is called ________________________.

Changes Over Time ■ Review and Reinforce



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Traces of TracksPaleontologists can learn a lot from trace fossils. The figure below shows fossil footprints. The larger prints were made by a dinosaur. The smaller prints were made at the same time by a small mammal. Can you infer what happened?


1. What are trace fossils?2. When these animals made the prints, was the soil moist or dry? Explain.3. How did the prints become trace fossils?4. From which direction did the dinosaur come? From which direction did

the mammal come?5. Did either animal change its speed? How can you tell?6. What prints lead away from the meeting of these animals?7. How do you interpret these trace fossils? Tell what happened.

Changes Over Time ■ Enrich


[h te Cbs"' _r"me ~~~-~~------ ---------

/Chapter 7 Changes Over Time Section 3 Summary

IEvolution of Species Key Concepts

I. vVhat bctors h.ive contributed to the diversirx of 'Species:'

I. How do new species torm?

I•• How do 'Scientists infer evolntion.irv H'btionshIp" among species'

vVh.1t causes the extinction of species'

Over time, different environments and genetic variation have produced, through natural selection, the variety of organisms that exist today. Over millions of ye,lrs, natural selection h,15produced different :-;pecies, each with l'ldapt.1tions enabling it tolive in ,1 specific habitat. An organism's habitat is the specific environment rha t produces the things the organism needs to live. grov..r, ,1nd reproduce,

Organisms within the same species do not all h,1\e identical traits, Some genetil' differences, or variations. m.iv result from mutations in DNA, Others may be caused by "reshuffling" of genl?s during meiosis. All the g0netic variations In ,1 spl?cil?S make up the total gene "pool" of that sppc'ies. I\I.U1\ species haH' ,1 lot of varietv ill their gl:'ne pools. These species can often adapt to ch.uiges in the environment beClllS0 some individuals will have traits that let them survive in the new conditions. In some s}'ecies, however, most of the org.misms elre similar gt'netic,l11y, Those species rna v h,1\'0 difficult SUJli\'ing el1\ 'iron nlen tal change

A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits. Isolation. or complete separation, happens when some members of ,1 species beconw cut off from tht:'rest of thE' specit's, Once a group becomes isoluted, members of the isolated group em no longer mate with the rest ot the species.

Scientists have combined the evidence from DNA, protein structure, fossils, early development, and body structure to determine the evolutionary relationships among species, Scientists infer th.it species that h'1\e similar bodv S trucrures and de\ elopment P,l tten15 111hen ted manx U

the 5,l11W genes from ,I common ancestor. B~' comparing the sequence of ni trogen b,lses in the D:'J i\ of different spec'ie"" scientists c.ui infer h01\'

closelv related two species .ire. The more similar the D0:A sequences, the more closely related the species .ue. In most e,15es, P\ idenc0 from DNA and protein structures has confirmed hvpotheses b.ised on fossils. embrvos. and bodv structure.

Aspecies is extinct if no members of th.1 t species .1fe still alive. Extinction is caused by a change in a species' environment. The members of the species may not have adaptations that allow them to survive and reproduce in the changed environment. An environment's climate can change, Climate changes CUI destrov so me orsanisllls' habitats. Environmental change does not ,11\\"WS lead tel extindion, SUIne organisms in ,I species mav have traits that help them survive in ,I ch.uured el1,j rorunent.

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Evolution of SpeciesUnderstanding Main IdeasAnswer the following questions in the spaces provided.

1. What accounts for the diversity of millions of species on Earth?____________________________________________________________________________

____________________________________________________________________________

2. Explain how a new species can form.____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

3. What types of evidence do scientists use to determine evolutionary relationships among groups?____________________________________________________________________________

____________________________________________________________________________

4. What do similarities in the early development of organisms suggest?____________________________________________________________________________

____________________________________________________________________________

5. What causes extinction?____________________________________________________________________________

____________________________________________________________________________

6. Explain how changes in the environment affect species.____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________




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Species Relationships

Use the figure above to answer the following questions. Write your answers on a separate sheet of paper.

1. What types of evidence did scientists use to make this diagram?2. Did amphibians evolve from reptiles? Give evidence for your answer.3. Are birds more closely related to mammals or to reptiles? Explain your

answer.4. What could cause scientists to change the information on this diagram in

the future?

Mammals

Birds

ReptilesAmphibians

Bony fishes

Jawlessfishes

Sharks andtheir relatives



D" tf' ~ _

Chapter 7 Changes Over Time • Section 4 Summary

Classifying Organisms Key Concepts

• Vv'hy do biologists organize living things into groups)

• V\11,lt do the levels of classification indicate about the relationships bet\lleen org.uusms?

• VV1:1,1 t characteristics .ire used to cl.issitv org.uusms into domains and kingdoms?

Classification is the process of grouping things based on their similarities. Biologists use classification to organize living things into groups so that the organisms are easier to study. The scientific study of how living things are classified is called taxonomy. Taxonomv and evolution Me closelv related. ,. .

CWOhlS Linn.ieus created ,I 11,11ni11g system for organisms called binomial nomenclature, in which each org.inism is gi\'E'n ,1 two-part name. The first part of an organism's scientific name is its genus. A genus is ,1 classification grouping that contains similar. closelv reL) ted organisms. TIlt" second word often describes ,1

distinct feature of the organism. Together. the tw o words indicate a unique species

Modern biologists classitv organisms into eight lenols: domain. kingdom, phylum, class. order, f.unil y. genus, and species, Org,misms are groul:>ed bv their shared characteristics, The more classification levels that two organisms share, the more characteristics they have in common,

Today. a three-domain svstem of classitic.i tion Ie, conunonlv used. The.. . three domains ,1re Bacteria. Archae.i. .uid Fuk.irva. VV'ithIll the domains are kingdoms. Organisms are placed into domains and kingdoms based on their cell type, their ability to make food. and the number of cells in their bodies.

Members of the domain Bacteria are prokarvotes. Prokaryotes ,11'e org.uiisms whose cells lack ,) nucleus. A nucleus is ,1 dense area in ,) cell tha t contains nucleic acids. Inprokarvores. nucleic ,Kids are SC<1 ttered throughout the ceIL

like bacteria, members of the domain Archaen ,1fe unicellutar prok.irvotes. Archaen and bacteria ,1fe pl.iced in different domains because there are important differences in the structure .uid chemical makeup of their cells.

Members of the domain Eukarva are eukaryotes-c-org.uusms with cells that contain nuclei. Scientists classify eukarvotes into one of four kingdoms: protists, fungi, plants. 01 animals.

Protists (\1I1 be .iurotrophs or heterotrophs. unicelhtl.tr or multicellular. Most fungi .ire multicellular eukaryotes.All fungi ,He heterotrophs

Plants ,we ,111 multicellular eukarvotes. III general, plants are autotrophs and feed almost i111 of the heterotrophs on land. All .inimnls Me multicellular eukarvotes. AJl animals are hetorotrophs

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Classifying OrganismsUnderstanding Main IdeasAnswer the following questions in the space provided.

1. List the major levels of classification, starting with the highest level.________________________________________________________________________

________________________________________________________________________

______________________________________________________________________

2. What three characteristics are used to place organisms into domians and kingdoms?________________________________________________________________________

________________________________________________________________________

______________________________________________________________________

Building VocabularyMatch each term with its definition by writing the letter of the correct definition in the right column on the line beside the term in the left column.

____ 3. classification

____ 4. binomial nomenclature

____ 5. eukaryote

____ 6. genus

____ 7. taxonomy

____ 8. prokaryote

a. naming system developed by Carolus Linnaeus

b. process of grouping things based on their similarities

c. first word in an organism’s scientific name

d. organism whose cell lacks a nucleus

e. the scientific study of how things are classified

f. organism whose cell(s) contain a nucleus




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How Many Species of Animals Are There?There are more species of insects than any other type of animal on Earth. The majority of animals, including insects, live in the tropics. If you can estimate how many species of insects there are in the tropics, you can get a pretty good estimate of the number of species of animals on Earth.

Over the years, entomologists (scientists who study insects) have been discovering and naming new kinds (species) of insects, and now over a million kinds of insects are known. Dr. Terry Erwin, an entomologist at the Smithsonian Institution, studies beetles. Beetles make up a large percentage of insects and related animals. By estimating the number of species of beetles in the tropics, Dr. Erwin was able to estimate the total number of species of animals in the world. Dr. Erwin used the following information to arrive at his estimate:

■ Dr. Erwin found 1,200 species of beetles living in Luehea seemannii trees.

■ Of those 1,200 species of beetles, he estimated that 163 are found only in the Luehea seemannii tree, and not in other species of trees.

■ There are about 50,000 species of trees in the tropics.

■ Beetles make up about 40% of insects and related animals.

■ Dr. Erwin estimated that there are about twice as many species of insects and related animals in tropical trees as there are on the ground of the forest.

Answer the following questions on a separate sheet of paper. Use a calculator to make the calculations.

1. If each kind of tree has 163 species of beetles that are found only on that type of tree but no others, how many kinds of beetles are there in tropical trees?

2. Using your answer from question 1, estimate how many species of insects and related animals there are in tropical trees.

3. Using your answer from question 2, estimate how many species of insects and related animals are on the forest floor in the tropics.

4. Using your answer from questions 2 and 3, estimate how many species of insects and related animals there might be in the trees and the forest floor together in the tropics.

5. Why did Dr. Erwin focus on tropical forests to estimate the total number of animal species in the world?

6. What are some likely sources of error in Dr. Erwin’s estimation method?



Da te

Chapter 7 Changes Over Time Section 5 Summary

Branching Trees

Key Concept

Groups of organisms with similar characteristics m.iv be desl'ended from ,1

common ancestor. The more similar two groups are, the more recent their common ancestor probublv is. A branching tree diagram shows probable evolutionarv relationships ,111LOn8 org.inisms, It .ilso shows the order in which specific characteristics may have evolved. 81\111Ching tree di.igr.uns begin .it the b.ise with common ancestors of ,111 the org.misms in the diagram.

A branching tree diagram shows evolutionary relationships by grouping organisms according to shared derived characteristics. A shared derived characteristic is usuallv ,1 homologous structure. such as 'I backbone. th.it is shared In' .ill org.uusins in ,I group On ,I branching tree dingr.un. all the organisms abono' the label have the trait.

A branching tree diagram 11,lS groups within grl)ufYs. Species within an\ group are more closelv rebted to one another them to species not in the grollp.

Characteristics that 'lppeM lower on" branching tree probablv developed before characteristics higher on the tree. For example. ,1 branching tree di,lgr,11n shows that during evolution.iry history, animals with backbones <11,n)e,ued e.irlier than animals with both ,I backbone ,U1C'

four limbs.

To dLIW a branching tree diagram. vou begin with the common ancestor or all members in the group. Just above the common ancestor, put tne grour with none of the shared derived char.icteristirs. On the branch above that, put the grtXtp with two of the characteristics. This process continues until vou get to the org,lnism or group with the grente",t number of sh.u-sd derjn:"d characteristics. Branching tree diagr.ims can show fossils ,1S well ,1S living org.uusms

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Branching TreesUnderstanding Main IdeasAnswer the questions in the space provided.

1. What indicates how recent a common ancestor probably is?______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

2. Explain what a branching tree diagram shows.______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

3. How are the organisms on a branching tree diagram grouped?_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Use the letters a–e to order the groups in a branching tree diagram from lowest to highest.

____ 4. organisms with two shared derivative characteristics

____ 5. “Common Ancestor”

____ 6. organisms with the most shared derivative characteristics

____ 7. organisms with no shared derivative characteristics

____ 8. organisms with one shared derivative characteristic

Building VocabularyDefine the term in the space provided.

9. shared derivative characteristic______________________________________________________________________

______________________________________________________________________




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A Branching Tree for MammalsVertebrate groups include fishes, amphibians, reptiles, birds, and mammals. Of these groups, only mammals produce milk to feed their young.

Mammals are divided into three groups: monotremes, marsupials, and placental mammals. Female monotremes release milk through pores in their skin; marsupials and monotremes both release milk through structures called nipples. Before birth, the young of placental mammals receive needed materials through an organ called the placenta.

Placental mammals are further divided into groups. The members of one of the groups, called primates, have opposable thumbs. An opposable thumb is a thumb that can touch all four of the other fingers.Read the table below, which lists the characteristics of some vertebrates. Then answer the questions on a separate sheet of paper.

1. Use the characteristics in the table to draw a branching tree diagram that classifies these vertebrates.

2. Which animal in the table is not a mammal? How do you know?3. Is a koala a monotreme, marsupial, or placental mammal? How do you

know? 4. Does an elephant have an opposable thumb?5. Which animal has all the characteristics in the table? What is its position

on the branching tree?

Characteristics of Some Vertebrates

Vertebrate Feed Young With Milk

Milk Released Through Nipples

Have a True Placenta

Have an Opposable Thumb

Chimpanzee yes yes yes yes

Duckbill platypus

yes no no no

Elephant yes yes yes no

Koala yes yes no no

Rattlesnake no no no no




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Key TermsAnswer the clues to solve this crossword puzzle.

Clues down Clues across

8

7

9

11

6

2

1

5

3 4

10

1. The gradual change in a species over time

4. A trait that helps an organism survive and reproduce

6. The process by which individuals that are better adapted to their environment are more likely to survive is called natural ________________________.

8. A fossil formed when an organism buried in sediment dissolves, leaving a hollow area

2. Any difference between individuals of the same species

3. The theory that evolution occurs slowly but steadily

5. Similar structures that related species inherited from a common ancestor are ________________________ structures.

7. The theory that evolution occurs during short periods of rapid change is punctuated _______________________.

9. The preserved remains of an organism

10. A group of similar organisms that can mate and produce fertile offspring

11. No members of a species are still alive

Changes Over Time ■ Chapter 7 Key Terms

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Changes Over Time ■ Chapter 7 Vocabulary Skill

Identify Multiple MeaningsSome words, such as theory and cast, have different meanings in science and in everyday use. Look at the different meanings of theory and cast in the graphic below.

Apply It!In the sentences below, identify which meaning of theory was used—the everyday meaning or the scientific meaning.

1. The theory of evolution explains how organisms have changed over time.2. Do you have a theory about why Sarah is a vegetarian?

Complete each sentence with the correct word from the list above and state whether the use is everyday or science.

3. The details of the ancient creature’s body were captured in the ________________________.

4. All my friends signed the ________________________ on my broken leg.

Word Everyday Meaning Scientific Meaning

theory n. A guess; an idea of how or why something might happenExample: Emily has a theory that basketball is harder to play than baseball.

n. A well-tested concept that explains a wide range of observationsExample: The cell theory says that all organisms are made of cells.

cast n. A device that protects a broken bone by preventing it from moving.Example: Tim’s broken elbow has healed so the cast can be removed.

n. A type of fossil that forms when a mold becomes filled with mineralsExample: The cast of the footprint shows that the extinct animal had five toes.

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Section Surnmary Darwin's Theory

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