Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use Reading Essentials Evidence forEvolution common ancestor.common a from descended each because another one torelated are They time. same the at alive sometimes werespecies horse Different line. straight a than bush a like more looks It evolution.horse versionof realistic more a showsway.below this diagram The occur not Evolutionorderlysteps.does of series a in another replaced species one is, That line. straight a evolvedhorsesin Biological EvidenceofEvolution Change OverTime The Environmentand changed yourmind. you’ve readthislesson,rereadthestatementstoseeifyouhave column ifyouagreewiththestatementoraDdisagree. After whether youagreeordisagreewiththem.PlaceanAintheBefore What doyouthink? Before The pictures of horse fossils in Lesson 1 seem to show that that show to seem 1 Lesson in fossils horse of pictures The Plants andanimalssharesimilargenes. are relatedtoeachother. Living speciescontainnoevidencethatthey FL7_C11_017A_904406 Millions of Years Ago (mya) 55–34 33–23 23–5 5–present day Propalaeotherium Pachynolophus

Paleotherium Anchitherium Hyracotherium Read thetwostatementsbelowanddecide Statement Mesohippus Megahippus Hypohippus Orohippus Miohippus Hipparion Equus Nannippus Merychippus Parahippus Pliohippus Hippidion Epihippus Callippus The EnvironmentandChangeOverTime After • • Essential Questions organisms related? How areEarth’s species overtime? descended fromother theory thatspecies species supportsthe What evidencefromliving CHAPTER 11 LESSON 3

233 Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use Bird are body parts

Reading Essentials Reading structures Bat comparative anatomy. comparative Humans, cats, frogs, bats, and birds Homologous structures, such as the Frog (huh MAH luh gus) The study of similarities and differences among and differences among The study of similarities Homologous It is easy to see that some species from a evolved common Studying the structural and functional similarities and Living Living species that are closely related share a close common Cat forelimbs forelimbs of humans, cats, frogs, bats, and birds, suggest that these species are related. The more alike two structures are, the more likely it is that the from species a evolved have recent common ancestor. ancestor. For example, robins, finches,ancestor. and hawks similar have body parts. They all feathers, have wings, and beaks. The same is true for tigers, leopards, and house cats. But how are hawks related to cats? differences in species that do not look alike can show the relationships. ancestor. How closely they ancestor. are related depends on how closely in time they or diverged, split, from Evidence thatof ancestor. common ancestors can be found in the fossil record and in living organisms. Homologous Structures Homologous Comparative Anatomy Comparative structures of living species is called structures of living species is called look different and in move different Humans ways. use their arms for balance and their hands to grasp objects. Cats use their forelimbs to walk, run, and jump. Frogs use their forelimbs to jump. The forelimbs of bats and birds are wings and are used for the flying. forelimb bones of However, all these species show similar patterns, as shown in the The figureforelimbs of below. the species in the figure are different sizes, but their placement and structure suggest common ancestry. of organisms that are similar in structure and position but of organisms that are similar in structure different in function. Human The Environment and Change Over Time Summarize

How do homologous FL7_C11_018A_904406 Humerus Ulna Radius FL7_C11_019A_904406 structures provide evidence for evolution? 234 1. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use lost theiroriginalfunctionthroughevolution. structure for a specific purpose. specific a for structure the used that species ancestral an torelated is vestigialstructure a with species the that is vestigialstructures for explanation NAH luh gus) structures. structures. gus) luh NAH ancestry.common close suggest to structure in different too are insects and birds of wings function—flight—the same the for used Though tinyhairs. coveredwith are wings Fly feathers. coveredwith are wings bird But flight. for used are species both in wings The flies? and birds of wings the about How structure? in differs but job same the does that species Reading Essentials Vestigial fly. Vestigial Structures Analogous Structures that performasimilarfunctionbutdifferinstructure. closely related. closely not are flies and birds that show structure wing in differences

Bird wings and fly wings, shown below,shown(uh wings, analogous are fly and wings Bird An ostrich’s wings are an example of vestigial structures. vestigialstructures. of example an are ostrich’swings An (veh STIH jee ul) jee STIH(veh

FL7_C11_020A_904406 Ostriches have wings. Yethavecannot wings. Ostriches they Can you think of a body part in two in part body a of think you Can Analogous structures structures

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235 Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use Reading Essentials Reading Modern toothed whale Vestigial pelvis Vestigial After 10–15 million more years of evolution, the ancestors of 10–15 million more years After not walk on land. They were adapted modern whales could Modern whales have two small to an aquatic environment. legs. vestigial pelvic bones that no longer support The whale shown in the figure has above pelvic tiny bones inside its body. Pelvic bones inside Pelvic are its hip body. bones, which in many species attach the leg bones to Modernthe whales body. do not legs. have The pelvic bones in whales suggest that whales came from ancestors that used legs for walking on land. The fossil evidence supports this conclusion. fossils Many of whale ancestors show a slow loss of legs millions over of They years. at thealso show, same time, that whale ancestors became better adapted to their watery environments. Ambulocetus natans SC.7.L.15.1,

Between 50–40 million years ago, this mammal breathed air and walked clumsily and walked breathed air mammal this ago, million years 50–40 Between of its rear because was dicult but swimming in water, a lot of time It spent on land. legs smaller lived longer that made their rear born with variations legs. Individuals of modern whales. This mammal is an ancestor more. and reproduced Pelvis The Environment and Change Over Time NGSSSCheck

Explain why scientists FL7_C11_021A_904406 conclude that whales evolved from ancestors that SC.7.L.15.2 236 2. on land. walked Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use Reading Essentials Diversity How New Species Form The Study ofEvolutionToday extinct species. extinct and living among relationshipshave shown biology molecular anatomy,fossils, of studies Their embryology,species. and living of hundreds in selection natural have work.observed They his extended and refined, havetheory,confirmed, scientists his published biology.Darwin modern Since of cornerstone basic ideas that Darwin came up with over150yearsago. with up came Darwin that ideas basic same the Yet,use stillmolecules. at they looking byevolution study now Scientists organisms. in changes dramatic to rise giveways simpleand in reorganized be can genes that finding biology. areevolutionary Scientists in study of area active an is This genes. called blocks building basic same the using species. new of origin the about details more study scientists help will discoveriesfossil Further time. the discoveredall are holes the in fill Yet,that fossils new scales. time human on study to difficult is about came first species worksquickly,different Howit saybursts. in Others gradually.and worksslowly it say Some species. new produces selection natural which at rate the about ideas different havescientists how shows below figure The details. the of some day.discovered debateevery nearly scientistsis But selection Time The theory of evolution by natural selection is the the is selection natural byevolution of theory The Evolution has produced Earth’s wide diversity of living things things living of diversity wide Earth’s produced Evolutionhas natural byevolution of theory the supporting evidence New It is also difficult to study with the incomplete fossil record. incompletefossil the with study to difficult also is It Gradual change

in apopulation. gradually selected variations are slowly assmall Changes occur Rapid change variation No Bursts ofchange variation No Rapid change variations. pass withno periods oftime quickly. Long Change occurs The EnvironmentandChangeOverTime variation No 3. diversity oflife. how building blockstoexplain Use theanalogyof genes relatetothe Analyze

237 Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use a

END OF LESSON a body part part body a

Reading Essentials Reading similar similar similar (circle one) (circle structure or function structure or function structure or function Similar Structure or Function or Structure Similar that has lost its original function through evolution through function original its lost has that body part that is similar in structure and position position and structure in similar is that part body it though organism, another of part body the to function different a has vestigial (veh STIH jee ul) structure: jee vestigial (veh STIH homologous (huh MAH luh gus) structure: (huh MAH luh homologous

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The Environment and Change Over Time

part that performs a similar function to the body body the to function similar a performs that part in differs it though organism, another of part structure and differences among structures of living species living of structures among differences and Vestigial Homologous Analogous Structures if you agree with the statement or a D if you if you agree with the statement or a D if you Did you change your mind? Did you change your mind? disagree. disagree. Reread the statements at the beginning of at the beginning of the statements the statements Reread Reread column with an A column with an A the lesson. Fill in the After the lesson. Fill in the After What What do do you you thinkthink Use what learnedyou have about analogous, homologous, and structuresvestigial to thecomplete table. The last row has been for completed you. Review Review the terms and their definitions in the Mini Use Glossary. one of the terms to write your own sentence. 238 2. comparative anatomy: 1. Mini Glossary structure: (uh NAH luh gus) analogous