evolution of life read - somma science...evolution of life the diversity of life on earth today is...

Evolution of Life Name:___________________________________Class:__________Date:____________

Vocabulary

Term Definition Adaptation Characteristicthathelpslivingthingssurviveandreproduceinagivenenvironment.Evolution Changeinthecharacteristicsoflivingthingsovertime;thechangeinspeciesovertime.Are dinosaurs evidence of past life forms? Evolutioncanbedescribedasachangeinspeciesovertime.DinosaurfossilsaresignificantevidenceofevolutionandofpastlifeonEarth.Evolution of Life ThediversityoflifeonEarthtodayistheresultofevolution.LifebeganonEarthatleast3.5to4billionyearsago,andithasbeenevolvingeversince.Atfirst,alllivingthingsonEarthweresimple,single-celledorganisms.Muchlater,thefirstmulticellularorganismsevolved,andafterthat,Earth’sbiodiversitygreatlyincreased.FigurebelowshowsatimelineofthehistoryoflifeonEarth.ThistimelineshowsthehistoryoflifeonEarth.Intheentirespanofthetime,humansarearelativelynewaddition.

Today,themostacceptedtheoryoflifeonEarthisevolution,andthereisavastamountofevidencesupportingthistheory.However,thiswasn’talwaysthecase.

Darwin and the Theory of Evolution Theideaofevolutionhasbeenaroundforcenturies.Infact,itgoesallthewaybacktotheancientGreekphilosopherAristotle.However,evolutionismostoftenassociatedwithCharlesDarwin.Darwinpublishedabookonevolutionin1859titledOntheOriginofSpecies.Inthebook,Darwinstatedthetheoryofevolutionbynaturalselection.Healsopresentedagreatdealofevidencethatevolutionoccurs.Evolutionisachangeinthecharacteristicsoflivingthingsovertime.AsdescribedbyDarwin,evolutionoccursbyaprocesscallednaturalselection.Innaturalselection,somemembersofaspecies,beingbetteradaptedorsuitedtotheirenvironment,producemoreoffspringthanothers,sotheypass"advantageoustraits"totheiroffspring.Overmanygenerations,thiscanleadtomajorchangesinthecharacteristicsofthespecies.EvolutionexplainshowlivingthingsarechangingtodayandhowmodernlivingthingshavedescendedfromancientlifeformsthatnolongerexistonEarth.Aslivingthingsevolve,theygenerallybecomebettersuitedfortheirenvironment.Thisisbecausetheyevolveadaptations.Anadaptationisatraitthathelpsanorganismsurviveandreproduceinagivenenvironment.DespitealltheevidenceDarwinpresented,histheorywasnotwell-receivedatfirst.Manypeoplefoundithardtoaccepttheideathathumanshadevolvedfromanape-likeancestor,andtheysawevolutionasachallengetotheirreligiousbeliefs.LookatthecartooninFigurebelow.Drawnin1871,itdepictsDarwinhimselfasanape.ThecartoonreflectshowmanypeoplefeltaboutDarwinandhistheoryduringhisowntime.Darwinhadactuallyexpectedthistypeofreactiontohistheoryandhadwaitedalongtimebeforepublishinghisbookforthisreason.Itwasonlywhenanotherscientist,namedAlfredRusselWallace,developedessentiallythesametheoryofevolutionthatDarwinputhisbookintoprint.CharlesDarwin’snameislinkedwiththetheoryofevolution.Thiscartoonfromthe1870smakesfunofbothDarwinandhistheory.AlthoughDarwinpresentedagreatdealofevidenceforevolutioninhisbook,hewasunabletoexplainhowevolutionoccurs.That’sbecauseheknewnothingaboutgenes.Asaresult,hedidn’tknowhowcharacteristicsarepassedfromparentstooffspring,letalonehowtheycouldchangeovertime.Evolutionary Theory After Darwin SinceDarwin’stime,scientistshavegatheredevenmoreevidencetosupportthetheoryofevolution.Someoftheevidencecomesfromfossils,andsomecomesfromstudiesthatshowhowsimilarlivingthingsaretooneanother.Bythe1930s,scientistshadalsolearnedaboutgenes.Asaresult,theycouldfinallyexplainhowcharacteristicsoforganismscouldpassfromonegenerationtothenextandchangeovertime.Usingmoderntechnology,scientistscannowdirectlycomparethegenesoflivingspecies.Themoregenesdifferentspeciesshareincommon,themorecloselyrelatedthespeciesarepresumedtobe.Considerhumansandchimpanzees.Theyshareabout98%oftheirgenes.Thismeansthattheysharedacommonancestorinthenot-too-distantpast.ThisisjustoneofmanypiecesofevidencethatshowwearepartoftheevolutionoflifeonEarth.Misconceptions About Evolution Today,evolutionisstillquestionedbysomepeople.Often,peoplewhodisagreewiththetheoryofevolutiondonotreallyunderstandit.Forexample,somepeoplethinkthatthetheoryofevolutionexplainshowlifeonEarthfirstbegan.Infact,thetheoryexplainsonlyhowlifechangedafteritfirstappeared.Somepeoplethinkthetheoryofevolutionmeansthathumansevolvedfrommodernapes.Infact,thetheorysuggestshumans

andmodernapeshaveacommonancestorthatlivedseveralmillionyearsago.Theseandothermisconceptionsaboutevolutioncontributetothecontroversythatstillsurroundsthisfundamentalprincipleofbiology.Summary

• LifebeganonEarthatleast3.5to4billionyearsago,andithasbeenevolvingeversince.• Darwinstatedthetheoryofevolutionbynaturalselection,presentingagreatdealofevidence

tosupporthistheory.• Evolutionisachangeinthecharacteristicsoflivingthingsovertime.Evolutionoccursbynatural

selection.• Characteristicsoforganismsarepassedfromonegenerationtothenextthroughtheirgenes.

Review

1. Whatisevolution?2. Whatisnaturalselection?3. Briefly,explainthetheoryofevolution.