Reading Essentials for Biology Glencoe (794133), страница 40
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Themodern theory of evolution, in fact, is the main concept in biology. What you learn about evolution will make it easier for you tounderstand the subject of biology. A place to start is by learningabout the ideas of Charles Darwin, an English naturalist wholived from 1809 to 1882. Darwin’s ideas about evolution havebeen supported by fossil evidence.How did fossils shape ideas about evolution?A fossil is evidence that an organism lived long ago. Scientistswondered how fossils formed.
They wondered why many fossilspecies had died out or become extinct. They also wanted toknow more about how extinct species and modern species mightbe related. There were many ideas about how species evolved.But the ideas of Charles Darwin became the basis of modernevolutionary theory.LocateInformation Underline everyheading in the reading thatasks a question. Then, use adifferent color to highlightthe answers to those questions as you find them.1.
What forms the basis ofmodern evolutionarytheory?________________________What did Darwin study?Darwin spent five years on a research voyage around the world.He became interested in how species might be related to oneanother. While in the Galápagos (guh LAH puh gus) Islands offthe west coast of South America, Darwin saw many species ofplants and animals. He noted that these species looked similar tospecies he had seen in other places. He wondered if a speciesmight be able to change over time. But at the time, he could notexplain how such changes might happen.READING ESSENTIALS________________________________________________Chapter 15163NameDateClassSection15.1Natural Selection and the Evidence for Evolution, continuedAfter returning to England, Darwin spent twenty years doingresearch. He studied, experimented, read, and collected samples.He tried to figure out why some animals survive and others donot.
Darwin bred pigeons and saw that there were small differences, or variations, in traits of individual pigeons. He also noticedthat these traits could be inherited by offspring. Eventually, heconducted an experiment where he bred pigeons that had certaindesirable traits. He observed that their offspring were born withthe same desirable traits. Breeding organisms with a certaintrait to produce offspring with identical traits is called artificialselection.
Darwin decided that there must be a process in thenatural world that works like artificial selection. Using evidencefrom his research, Darwin decided that that process in nature wasnatural selection.________________________________________________In natural selection, organisms with favorable traits are ableto reproduce and pass their traits on to their offspring, who thenreproduce. Those without such favorable traits are more likely todie out before reproducing. For example, suppose fish that areslow get eaten before they can reproduce, while fish that are fastsurvive and reproduce. These offspring inherit the trait of speedfrom their parents. This way, they too are more likely to surviveand pass on that trait to their offspring.________________________What have we learned since Darwin?Much evidence supports Darwin’s theories.
However, it ishard to directly observe evolutionary processes that take placeover millions of years. Despite this, much data has been gatheredfor many years from many sources. Most of today’s biologistsagree that evolution by natural selection best explains this data.The study of genetics adds even more to our understanding ofevolution. We now know that traits are controlled by genes. Allthe genes that are available in a population are its gene pool.Changes in a population’s gene pool over time play an importantrole in evolution.Adaptations: Evidence for EvolutionAn adaptation is anything that gives an organism a better chanceof survival.
The two main types of adaptations are structuraladaptations and physiological (fih zee uh LAH jih kul) adaptations.164Chapter 15READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is natural selection?2. What is the process inwhich organisms withfavorable traits tend tosurvive and pass on thesetraits to their offspring?NameDateClassSection15.1Natural Selection and the Evidence for Evolution, continuedWhat are structural adaptations?Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Structural adaptations take many different forms.
Thorns, teeth,hair, beaks, and color are examples of structural adaptations thatare inherited. Some adaptations take millions of years to becomewidespread in a population. Mole rats developed large teeth andclaws. This structural adaptation helps them dig holes and protectthemselves. Adaptations that keep predators from approaching anorganism include a rose’s thorns and a porcupine’s quills.Some animals develop coloring that helps them blend with theirsurroundings.
This is an example of a subtle structural adaptationcalled camouflage (KA muh flahj). Camouflaged organisms surviveand reproduce because they cannot be easily found by predators.Mimicry (MIHM ih kree) is another type of structural adaptation. It occurs when one species looks like another species. In oneform of mimicry, a harmless species takes on the look of a dangerous species.
Predators that avoid the harmful species have a hardtime telling the two species apart, and so they avoid both. In thisway, the harmless species benefits. Another type of mimicry happens when two or more harmful species grow to resemble eachother. For example, bees, wasps, and yellow jacket hornets all lookalike and can sting. For this reason, some predators stay awayfrom anything that has a bee-like appearance.3. Analyze Which of thefollowing is an exampleof mimicry? (Circle yourchoice.)a. A harmless fly lookslike a wasp.b. A frog’s color matchesthe tree it lives in.c. A pesticide stopsworking on certaintypes of weeds.What are physiological adaptations?Some changes in gene pools can happen fairly quickly.
A fewmedicines that have been developed within the last 50 years havebegun to lose their effectiveness. The bacteria that the medicinesused to treat have undergone physiological adaptations. Theseadaptations keep the bacteria from being killed off by various medications.
Physiological adaptations are changes in an organism’smetabolic processes. Some insects and weeds also have evolved tothe point where they are not affected by chemical sprays.Other Evidence for EvolutionStructural and physiological adaptations are considered directevidence of evolution. But most of the evidence to support evolution is indirect. It comes from fossils and sciences such as anatomy,embryology (em bree AHL uh jee), and biochemistry.
Scientistsdo not have fossils for all the changes that have taken place. However, fossils provide a big picture of how groups have changed.READING ESSENTIALSChapter 15165NameDateClassSection15.1Natural Selection and the Evidence for Evolution, continuedAgePaleocene65 millionyears agoEocene54 millionyears agoOligocene33 millionyears agoMiocene23 millionyears agoPresentOrganismSkull andteethFossils are important to the study of evolution because theyprovide a record of early life. When you compare an organism asit looks today with a fossil of that organism, you can see how ithas changed over time.
For example, scientists have learned fromfossils that the ancestors of camels were as small as rabbits aretoday. This is illustrated on the table above.4. What is the term forstructural features thathave a common evolutionary origin?________________________________________________________________________What can anatomy teach us about evolution?Homologous Structures The anatomy of different organismsalso shows evolutionary patterns. For example, some organismshave homologous structures. These are structural featureswith a common evolutionary origin. Such structures can be similar in arrangement, function, or both.The figure on page 167 shows how the forelimbs of three verydifferent animals can be homologous. Biologists think that suchsimilarities are evidence that these organisms evolved from acommon ancestor.Analogous Structures However, being structurally similar doesnot always mean that two species are closely related. For instance,birds and butterflies both have wings.
But insects and birdsevolved separately. When body parts of organisms do not have acommon evolutionary origin but are similar in function, they areknown as analogous structures.166Chapter 15READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Limb bonesNameDateClassSection15.1Natural Selection and the Evidence for Evolution, continuedCrocodileforelimbWhaleforelimbBirdwingCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Although analogous structures do not have the same origin,they do provide evidence of evolution.
For example, the ancestorsof birds and insects both probably evolved wings separately whileadapting to similar ways of life.Vestigial Structures Another type of body feature that shows evolutionary relationship is a vestigial (veh STIH jee ul) structure.This is a body structure in a present-day organism that no longerserves its original purpose. The eyes of mole rats are an example.Mole rats still have eyes, but they are no longer used for sight.Vestigial structures are evidence of evolution because they showstructural change over time.Embryology An embryo is the earliest stage of growth anddevelopment of a plant or animal.
Young embryos of fishes, birds,reptiles, and mammals have structures that suggest they all had acommon ancestor.5. Compare What is thedifference betweenanalogous and vestigialstructures?________________________________________________________________________________________________________________________What evidence does biochemistry provide forevolution?Biochemistry also provides strong evidence for evolution. Nearlyall organisms share DNA, ATP, and many enzymes in their chemical makeup. Groups that share more similarities in their biochemistry are considered to be more closely related. In the 1970s,biologists began to use RNA and DNA nucleotide sequences toconstruct evolutionary diagrams that show the levels of relationship among species.
Today, scientists combine data from fossilsand studies of anatomy, embryology, and biochemistry to interpret relationships among species.READING ESSENTIALSChapter 15167NameDateClassSection15.1Natural Selection and the Evidence for Evolution, continued◗ After You ReadMini Glossaryanalogous structures: structures that do nothave a common evolutionary origin but aresimilar in functionartificial selection: process of breeding organisms with specific traits to produce offspringwith the same traitscamouflage (KA muh flahj): structural adaptation that enables species to blend with theirsurroundings; allows a species to avoiddetection by predatorsembryo: the earliest stage of growth and development of a plant or an animalhomologous structures: structures with commonevolutionary origin; can be similar inarrangement, function, or bothmimicry: structural adaptation that enables onespecies to resemble another species; mayprovide protection from predators or otheradvantagesnatural selection: mechanism for change inpopulations; occurs in nature when organisms with favorable variations survive,reproduce, and pass their variations to thenext generationvestigial (veh STIH jee ul) structure: a structurein a present-day organism that no longerserves its original purpose, but was probablyuseful to its ancestor1.
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