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sLivingLegacy

Whenthe26-year-oldCharlesDarwinsailedintotheGalá

pagosIslandsin1835onboardtheHMSBeagle,hetooklittlenoticeofacollectionofbirdsthatarenowintimatelyassociatedwithhisname.Thenaturalist,infact,misclassifiedasgrosbeakssomeofthebirdsthatarenowknownasDarwin’sfinches.AfterDarwinreturnedtoEngland,ornithologistandartistJohnGouldbegantomakeillustrationsofagroupofpreservedbirdspecimensbroughtbackintheBeagle’shold,andtheartistrecognizedthemalltobedifferentspeciesoffinches.FromGould’swork,Darwin,theself-taughtnaturalist,cametounderstandhowthefinches’beaksizemusthavechangedoverthegenerationstoaccommodatedifferencesinthesizeofseedsorinsectsconsumedonthevariousislands.“Seeingthisgradationanddiversityofstructureinonesmall,intimatelyrelatedgroupofbirds,onemightreallyfancythatfromanoriginalpaucityofbirdsinthisarchipelago,onespecieshadbeentakenandmodifiedfordifferentends,”henotedinTheVoyageofTheBeagle,publishedafterhisreturnin1839.TwentyyearslaterDarwinwouldtranslatehisunderstandingoffinchadaptationtoconditionsondifferentislandsintoafullyformedtheoryofevolution,oneemphasizingthepowerofnaturalselectiontoensurethatmorefavorabletraitsendureinsuccessivegenerations.Darwin’stheory,corefeaturesofwhichhavewithstoodcriticalscrutinyfromscientificandreligiouscritics,constitutedonlythestartingpointforanendlesslyrichsetofresearchquestionsthatcontinuetoinspirepresent-dayscientists.Biologistsarestillseekingexperimentalresultsthataddresshownaturalselectionproceedsatthemolecularlevel—andhowitaffectsthedevelopmentofnewspecies.Darwin’sfamedfinchesplayacontinuingroleinprovidinganswers.Thescientisthadassumedthatevolutionproceededslowly,over“thelapseofages,”apaceimperceptibletotheshortlifetimeofhumanobservers.Insteadthefincheshaveturnedintoidealresearchsubjectsforstudyingevolutioninrealtimebecausetheybreedrelativelyrapidly,areisolatedondifferentislandsandrarelymigrate.

Sincethe1970sevolutionarybiologistsPeterR.GrantandB.RosemaryGrantofPrincetonUniversityhaveusedtheGalá

pagosasagiantlaboratorytoobservemorethan20,000finchesandhaveshownconclusivelyhowaveragebeakandbodysizechangesinanewgenerationasElNiñ

oscomeandgo,shiftingclimatefromwettoarid.Theyhavealsobeenabletochroniclepossibleexamplesofnewspeciesthatarestartingtoemerge.

TheGrantsarejustoneamongmanygroupsthathaveembarkedonmissionstowitnessevo-lutioninaction,exemplarsofhowevolutioncanattimesmoveinfrenziedburstsmeasuredinyears,noteons,contradictingDarwin¡

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scharacterizationofaslowand-steadyprogression.ThesestudiesfocusonthecichlidfishoftheAfricanGreatLakes,Alaskansticklebacks,andtheEleutherodactylusfrogsofCentralandSouthAmericaandtheCaribbean,amongothers.Ruminationsonevolution¡

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oftenmusingsonhowonlythefittestprevail¡

carryanancientpedigree,predatingevenSocrates.The18thand19thcenturiesproducedfertilespeculationsabouthowlifehadevolved,includingideasforwardedbyDarwin¡

sgrandfather,ErasmusDarwin,wholivedbetween1731and1802.

Darwinianevolutionwasthefirstcapableofwithstandingrigoroustestsofscientificscrutinyinboththe19thcenturyandbeyond.Todayinvestigators,equippedwithsophisticatedcameras,computersandDNA-samplingtoolsthoroughlyalientothecargoholdoftheBeagle,demonstratethecontinuedvitalityofDarwin¡

swork.Thenaturalist¡

srelevancetobasicscienceandpracticalpursuits¡

frombiotechnologytoforensicscience¡

isthereasonforthisyear¡

sworldwidecelebrationofthebicentennialofhisbirthandthesesquicentennialofthepublicationofhismasterwork,OntheOriginofSpeciesby

MeansofNaturalSelection,orthePreservationofFavoredRacesintheStruggleforLife.

Darwin’stheoryrepresentsafoundationalpillarofmodernsciencethatstandsalongsiderelativity,quantummechanicsandothervitalsupportstructures.JustasCopernicuscasttheearthoutfromthecenteroftheuniverse,theDarwinianuniversedisplacedhumansastheepicenterofthenaturalworld.NaturalselectionaccountsforwhatevolutionarybiologistFranciscoJ. 

AyalaoftheUniversityofCalifornia,Irvine,hascalled“designwithoutadesigner”,atermthatparriesthestillvigorouseffortsbysometheologianstoslightthetheoryofevolution.DarwincompletedtheCopernicanRevolutionbydrawingoutforbiologythenotionofnatureasalawfulsystemofmatterinmotionthathumanreasoncanexplainwithoutrecoursetosupernaturalagencies。

Ayalawrotein2007.Inthisanniversaryyear,Darwin‘sgreatestbequestcanbefoundintheenormousbodyofresearchandtheorizingthatextendsdirectlyfromhiswritings.Italsoservestounderlinehowevolutionitselfhasundergoneradicalalterationinthepast150years,amergeroftheoriginaltheorywiththescienceofthegene,whichDarwinhadaslittleunderstandingofastheancientsdid.ThisspecialissueofScientificAmericanhighlightsmajorquestionsthatarestillbeingaddressed:

Howcommonisnaturalselection?

Towhatextentdoesnaturalselectionactuallyoccuratthemolecularlevelofthegene?

Whatistheoriginofthegeneticvariationonwhichnaturalselectionoperates?

Doesitworkbyadministeringafitnesstesttoindividualgenes,wholeorganisms,orevenentiregroupsofanimals,plantsormicrobes?

Doesitapplytohumansiftheyareabletoexercisearigidcontrolovertheirenvironmentandeventheirbiology?

ANaturalistbyNatureLikeAlbertEinsteinandothersgiftedwithgenius,Darwinmarchedtohisowndrumbeat.Heshowednosignsofacademicprecociousness.Bornintoawell-to-dofamilyintheEnglishcountryside,theyoungDarwinwasadecidedlymediocrestudentwhohatedtheregimentationofacurriculumcenteredontheclassics.（Einsteinwasarebelliousyouthandanerraticuniversitystudent.）Followinghisfather’sdesire,Darwinenteredmedicalschoolbutwasrepulsedbycuttingopenahumancadaverandneverfinishedhisstudies.Paradoxically,hehadlittleproblemkillingbirdsandsmallanimalswhenhunting,justoneofthetaskshesetforhimselfonforaystowatchwildlifeandcollectspecimens.DespairingthatCharleswouldeveramounttoanything,RobertDarwinorderedhissecondsontoapplytotheUniversityofCambridgetoobtainadegreethatwouldallowhimtojointheclergy.Themanwhoseideasareviewedbysomeclericsasafundamentalinsulttoreligiousfaithgraduated（barely）withadegreeintheology.

Althoughhisfathertriedtodissuadehim,DarwinjumpedattheoffertobecomeanaturalistonboardasurveyshipnamedtheBeagle,anexperiencehewouldlatercharacterizeas“thefirstrealtrainingoreducationofmymind.”Thefive-year,around-the-globejourneyprovidedexposuretothenaturalworldandampletimeforContemplationthatshapedhislaterthinking.MilestonesalongthewayincludedexperiencingthegreatdiversityofspeciesintropicalBrazilanddiscoveryoffossils,includingagiantsloth400milessouthofBuenosAires,whichcausedhimtoponderhowthesecreaturesbecameextinct.AccountsbygauchosontheArgentinepampasoftheirkillingofindigenouspeoplestaughthimabouttheprimal,territorialimpulsesofthehumananimal.Andofcourse,therewastherelativelybrief,five-weekstayinthefryingHotGalapagos,wherehewasabletocontemplatehowcloselyrelatedspeciesofturtlesandmockingbirdsinhabitedneighboringislands,implyingacommonancestryforbothgroups.

Atsea,DarwinalsoreadavidlytwovolumesofCharlesLyell’sPrinciplesofGeologythatembracedtheideaofuniformitarianisminwhichtheprocessesoferosion,sedimentationandvolcanicactivityoccurredinthepastataboutthesameratesastheydonow.Lyellrejectedthethenprevailingcatastrophism,whichholdsthatsudden,violenteventsdrivenbysupernaturalforceshaddriventheshapingofthelandscape.AtrekinlandintheAndes,wheretheexplorersfoundanancientmarinedepositupliftedto7,000feet,helpedtobringLyell’sideasvividlytolife.Darwinhadnoawarenessthathehadembarkedonatripthatwouldforevertransformthebiologicalsciences.The57-monthjourneyproducednomomentofsuddenrealization,nothingequivalenttoEinsteinis’sannusmirabilisof1905inwhichhepublishedpapersaboutspecialrelativity,Brownianmotionandotherthemes.Thetreasuretroveofthejourneywaswhattodaycouldbecalledanimmensedatabase:

acollectionof368pagesofzoologynotes,1,383pagesofgeologynotes,a770-pagediary,inadditionto1,529speciesinbottlesofalcoholand3,907driedspecimens,nottomentionlivetortoisescaughtintheGalpagos.BythetimetheBeaglereturnedtoEnglandinOctoberof1836,Darwin¡

sletters,alongwithsomespecimens,hadcirculatedamongBritishscientists,cementinghisreputationasapeer.Thisrecognitionassuredthathisfather¡

saspirationsforhisson’splaceintheclergywerecastaside.WithinafewyearsDarwinmarriedafirstcousin,EmmaWedgwood,andthenmovedtoacountryestatewhosegardensandgreenhouseswouldprovidealivinglaboratoryforhisworkuntilhisdeath,anexistencemadepossiblebythefamily’ssubstantialwealth.Unexplainedillness,withsymptomsrangingfromheadachestoheartflutterstomusclespasms,plaguedDarwinaftertheexpeditionuntilhediedin1882,quashinganythoughtsoffurtherexpeditions.

OriginsofaTheory

Darwinhadbeguntoformulatehistheoriesbyt