21 LIFE GOES ON
ITISobeeafossil.Thefateofnearlyalllivinganisms—over99.9pertofthem—istopostdowntonothingness.Whenyoursparkisgone,everymoleculeyouownwillbenibbledoffyouorsluicedawaytobeputtouseihersystem.That’sjustthewayitis.Evenifyoumakeitintothesmallpoolanisms,thelessthan0.1pert,thatdodevoured,thecesofbeingfossilizedareverysmall.
Iobeeafossil,severalthingsmusthappen.First,youmustdieintherightplalyabout15pertofrockspreservefossils,soit’snogoodkeelingoveronafuturesiteofgranite.Inpracticaltermsthedeceasedmustbeeburiedinsediment,whereitleaveanimpression,likealeafimud,ordeposewithoutexposuretooxygetingthemoleculesinitsbonesandhardparts(andveryoccasionallysofterparts)tobereplacedbydissolvedminerals,creatirifiedcopyoftheinal.ThenasthesedimentsinwhichthefossilliesarecarelesslypressedandfoldedandpushedaboutbyEarth’sprocesses,thefossilmustsomehowmaintainaifiableshape.Finally,butaboveall,aftertensofmillionsorperhapshundredsofmillionsofyearshiddenaway,itmustbefoundandreizedassomethingworthkeeping.
Onlyaboutoneboneinabillion,itisthought,everbeesfossilized.Ifthatisso,itmeansthatthepletefossillegacyofalltheAmerisalivetoday—that’s270millionpeoplewith206boneseach—willonlybeaboutfiftybones,onequarterofapleteskeleton.That’snottosayofcoursethatanyoftheseboneswillactuallybefound.Bearinginmindthattheybeburiedanywherewithinanareaofslightlyover3.6millionsquaremiles,littleofwhichwilleverbeturnedover,muchlessexamiwouldbesomethingofamiracleiftheywere.Fossilsareineverysensevanishinglyrare.Mostofwhathaslivedohhasleftbehindnorecordatall.Ithasbeeimatedthatlessthanonespeciesihousandhasmadeitintothefossilrecord.Thatinitselfisastunninglyinfinitesimalproportion.However,ifyouaccepttheoimatethattheEarthhasproduced30billionspeciesofcreatureinitstimeandRichardLeakeyandRogerLewin’sstatement(ihExtin)thatthereare250,000speciesofcreatureinthefossilrecord,thatreducestheproportiontojustonein120,000.EitherepossessisthemerestsamplingofallthelifethatEarthhasspawned.
Moreover,therecordwedohaveishopelesslyskewed.Mostlandanimals,ofcourse,don’tdieinsediments.Theydropintheopenaeorotorweatherdowntonothing.Thefossilrecordsequentlyisalmostabsurdlybiasedinfavorofmariures.
About95pertofallthefossilswepossessareofanimalsthatonceliveduer,mostlyinshallowseas.
ImentionallthistoexplainwhyonagraydayinFebruaryIwenttotheNaturalHistoryMuseuminLondoacheerful,vaguelyrumpled,verylikeablepaleontologistnamedRichardFortey.
Forteyknowsanawfullotaboutanawfullot.Heistheauthorofawry,splendidbookcalledLife:AnUnauthorisedBiography,whichcoversthewholepageantofanimatecreation.
ButhisfirstloveisatypeofmariurecalledtrilobitesthatoeemedinOrdoviseasbuthaveedforalongtimeexceptinfossilizedform.Allsharedabasicbodyplanofthreeparts,orlobes—head,tail,thorax—fromwhiesthename.ForteyfoundhisfirstwhenhewasaboyclamberingoverrocksatSt.David’sBayinWales.Hewashookedforlife.
Hetookmetoagalleryoftallmetalcupboards.Eachcupboardwasfilledwithshallowdrawers,andeachdrawerwasfilledwithstonytrilobites—twentythousandspesinall.
“Itseemslikeabignumber,”heagreed,“butyouhavetorememberthatmillionsuponmillionsoftrilobiteslivedformillionsuponmillionsofyearsinaseas,sotwentythousandisn’tahugenumber.Andmostoftheseareonlypartialspes.Findingapletetrilobitefossilisstillabigmomentforapaleontologist.”
Trilobitesfirstappeared—fullyformed,seeminglyfromnowhere—about540millionyearsago,hestartofthegreatoutburstofplexlifepopularlyknownastheCambrianexplosion,andthenvanished,alongwithagreatdealelse,inthegreatandstillmysteriousPermiain300,000orsoturieslater.Aswithallextinctcreatures,thereisanaturaltemptatiardthemasfailures,butinfacttheywereamosuccessfulanimalsevertolive.Theirreignranfor300millionyears—twicethespanofdinosaurs,whichwerethemselvesoneofhistreatsurvivors.Humans,Forteypointsout,havesurvivedsofarforone-halfof1pertaslong.
Withsomuchtimeattheirdisposal,thetrilobitesproliferatedprodigiously.Mostremainedsmall,aboutthesizeofmoderles,butsomegrewtobeasbigasplatters.Altogethertheyformedatleastfivethousandgeneraandsixtythousandspecies—thoughmoreturnupallthetime.ForteyhadretlybeenataferenSouthAmericawhereheroachedbyanacademiallprovincialuyiina.“Shehadaboxthatwasfullofiingthings—trilobitesthathadneverbeenseenbeforeinSouthAmerica,orindeedanywhere,andagreatdealelse.Shehadnoresearchfacilitiestostudythemandnofundstolookformore.Hugepartsoftheworldarestillunexplored.”
“Intermsoftrilobites?”
“No,intermsofeverything.”
Throughouttheeeury,trilobiteswerealmosttheonlyknownformsofearlyplexlife,andforthatreasonwereassiduouslycollectedandstudied.Thebigmysteryaboutthemwastheirsuddenappearance.Evennow,asForteysays,itbestartlingtogothtformationofrodtoworkyourwardthroughtheeonsfindingnovisiblelifeatall,andthensuddenly“awholeProfallotaspisorElenellusasbigasacrabwillpopintoyourwaitinghands.”Thesewerecreatureswithlimbs,gills,nervoussystems,probingantennae,“abrainofsorts,”inFortey’swords,araeyeseverseen.Madeofcalciterods,thesamestuffthatformslimestoheystitutedtheearliestvisualsystemsknown.Morethanthis,theearliesttrilobitesdidn’tsistofjustouresomespeciesbutdozens,anddidn’tappeariwolocationsbutallover.ManythinkingpeopleintheeeurysawthisasproofofGod’shandiworkaationofDarwin’sevolutionaryideals.Ifevolutionproceededslowly,theyasked,thenhowdidheatforthissuddenappearanplex,fullyformedcreatures?Thefactis,hecouldn’t.
Andsomattersseemeddestioremainforeveruntilonedayin1909,threemonthsshyofthefiftiethanniversaryofthepublicationofDarwin’sOntheinofSpecies,aleontologistnamedCharlesDoolittleWaladearaordinaryfindintheadianRockies.
Walcottwasbornin1850andgrewupiewYork,inafamilyofmodestmeans,whichbecamemoremodeststillwiththesuddehofhisfatherwhenWalcottwasaninfant.AsaboyWalcottdiscoveredthathehadaknackforfindingfossils,particularlytrilobites,andbuiltupacolleofsuffitdistinthatitwasboughtbyLouisAgassizforhismuseumatHarvardforasmallfortune—about</strong>70,000intoday’smoney.
Althoughhehadbarelyahighschooleducationandwasselftaughtinthesces,Walcottbecamealeadingauthorityontrilobitesandwasthefirstpersoablishthattrilobiteswerearthropods,thegroupthatincludesmodersandcrustas.
In1879hetookajobasafieldresearcherwiththenewlyformedUatesGeologicalSurveyandservedwithsuchdistinthatwithinfifteenyearshehadriseshead.In1907heointedsecretaryoftheSmithsonianInstitution,whereheremaiilhisdeathin1927.Despitehisadministrativeobligatioiodofieldworkandtowriteprolifically.“Hisbooksfillalibraryshelf,”acctoFortey.Notially,hewasalsoafoundingdirectoroftheNationalAdvisoryitteeforAeronautics,whicheventuallybecametheNationalAeronautidSpaceAgency,orNASA,andthusrightlybesideredthegrandfatherofthespaceage.
ButwhatheisrememberedfornowisanastutebutluckyfindinBritishbia,highabovethelittletownofField,iesummerof1909.ThearyversionofthestoryisthatWalcott,apaniedbyhiswife,wasridingonhorsebaountaintrailbehespotcalledtheBurgessRidgewhenhiswife’shorseslippedonloosestones.Dismountingtoassisther,Walcottdiscoveredthatthehorsehadturnedaslabofshalethattainedfossilcrustasofanespeciallyaandunusualtype.Snowwasfalling—winteresearlytotheadianRockies—sotheydidn’tlinger,buttheyearatthefirstopportunityWalcottreturhespot.Tragthepresumedrouteoftherocks’slide,heclimbed750feettohemountain’ssummit.There,8,000feetabovesealevel,hefoundashaleoutcrop,aboutthelengthofacityblock,taininganunrivaledarrayoffossilsfromsoohemomentwhenplexlifeburstforthindazzlingprofusion—thefamousCambrianexplosion.Walcotthadfound,iheholygrailofpaleontology.TheoutcropbecameknownastheBurgessShale,andforalongtimeitprovided“oursolevistaupontheiionofmodernlifeinallitsfullness,”asthelateStephenJayGouldrecordedinhispopularbookWonderfulLife.
Gould,everscrupulous,discoveredfromreadingWalcott’sdiariesthatthestoryoftheBurgessShale’sdiscoveryappearstohavebeeembroidered—Walakesionofaslippinghorseorfallingsnow—butthereisnodisputingthatitwasaraordinaryfind.
ItisalmostimpossibleforuswhosetimeohislimitedtoabreezyfewdecadestoappreciatehowremoteintimefromustheCambrianoutburstwas.Ifyoucouldflybackwardsintothepastattherateofoneyearpersed,itwouldtakeyouabouthalfanhourtoreachthetimeofChrist,andalittleoverthreeweekstogetbacktothebeginningsofhumanlife.
ButitwouldtakeyoutweoreachthedawnoftheCambrianperiod.Itwas,inotherwords,aremelylongtimeago,andtheworldwasaverydifferentplace.
Forohing,500-million-plusyearsagowhentheBurgessShalewasformeditwasn’tatthetopofamountainbutatthefootofone.Specificallyitwasashallowobasinatthebottomofasteepcliff.Theseasofthattimeteemedwithlife,butnormallytheanimalsleftnorecordbecausetheyweresoft-bodiedanddecayedupondying.ButatBurgessthecliffcollapsed,andthecreaturesbelow,entombedinamudslide,werepressedlikeflowersinabook,theirfeaturespreservedinwondrousdetail.
Inannualsummertripsfrom1910to1925(bywhichtimehewasseventy-fiveyearsold),Walcottexcavatedtensofthousandsofspes(Gouldsays80,000;thenormallyunimpeachablefactcheckersofNationalGeraphicsay60,000),whichhebroughtbacktoWashingtonforfurtherstudy.Inbothsheernumbersanddiversitythecollearalleled.SomeoftheBurgessfossilshadshells;manyothersdidnot.Someweresighted,othersblind.Thevarietywasenormous,sistingof140speciesbyonet.“TheBurgessShaleincludedarangeofdisparityinanatomicaldesignsneveragainequaled,andnotmatchedtodaybyallthecreaturesintheworld’sos,”Gouldwrote.
Unfortunately,acctoGould,Walcottfailedtodisthesignificeofwhathehadfound.“Snatgdefeatfromthejawsofvictouldwroteinanotherwork,EightLittlePiggies,“Walcottthenproceededtomisinterpretthesemagnifitfossilsinthedeepestpossibleway.”Heplacedthemintomroups,makingthemaraltotoday’sworms,jellyfish,andothercreatures,andthusfailedtoappreciatetheirdistiness.“Undersuinterpretation,”Gouldsighed,“lifebeganinprimordialsimplicityandmovedinexorably,predictablyonwardtomoreaer.”
Walcottdiedin1927andtheBurgessfossilswerelargelyfotten.FornearlyhalfaturytheystayedshutawayindrawersintheAmeriMuseumofNaturalHistoryinWashington,seldomsultedandneverquestiohenin1973agraduatestudentfromCambridgeUynamedSimonwayMorrispaidavisittothecolle.Hewasastonishedbywhathefound.ThefossilswerefarmorevariedandmagnifitthanWalcotthadindicatedinhiswritings.Intaxonomythecategorythatdescribesthebasicbodyplansofallanismsisthephylum,andhere,wayMorriscluded,weredrawerafterdrawerofsuatomicalsingularities—allamazinglyandunatablyunreizedbythemanwhohadfoundthem.
Withhissupervisor,HarryWhittington,andfellowgraduatestudentDerekBriggs,wayMorrisspeseveralyearsmakingasystematicrevisionoftheentirecolle,andkingoutoingmonographafteranotherasdiscoverypiledupondiscovery.Manyofthecreaturesemployedbodyplansthatwerenotsimplyuhingseenbeforeorsiwerebizarrelydifferent.One,Opabinia,hadfiveeyesandanozzle-likesnoutwithclawsontheend.Another,adisc-shapedbeingcalledPeytoia,lookedalmosticallylikeapineappleslice.Athirdhadevidentlytotteredaboutonrowsofstilt-likelegs,andwassooddthattheyHalluia.TherewassomureizedyinthecollethatatonepointuponopeninganewdrawerwayMorrisfamouslywasheardtomutter,“Ohfuotanotherphylum.”
TheEnglishteam’srevisionsshowedthattheCambrianhadbeenatimeofunparalleledinnovationandexperimentationinbodydesigns.Foralmostfourbillionyearslifehaddawdledalongwithoutaableambitionsinthedireofplexity,andthensuddenly,inthespaceofjustfiveortenmillionyears,ithadcreatedallthebasicbodydesignsstillioday.Nameacreature,fromaodewormtoCameronDiaz,andtheyallusearchitecturefirstcreatedintheCambrianparty.
Whatwasmostsurprising,however,wasthatthereweresomanybodydesignsthathadfailedtomakethecut,sotospeak,anodesdants.Altogether,acctoGould,atleastfifteenandperhapsasmanyastwentyoftheBurgessanimalsbelonizedphylum.(Thenumbersoongrewinsomepopularatstoasmanyasonehundred—farmorethantheCambridgestistseveractuallyclaimed.)“Thehistoryoflife,”wroteGould,“isastoryofmassiveremovalfollowedbydifferentiationwithinafewsurvivingstoottheventionaltaleofsteadilyincreasingexcellenplexity,anddiversity.”
Evolutionarysuccess,itappeared,wasalottery.
Ourethatdidmaoslipthrough,asmallwormlikebeingcalledPikaiagras,wasfoundtohaveaprimitivespinaln,makingittheearliestknoworofalllatervertebrates,includingus.PikaiawerebynomeansabundantamongtheBurgessfossils,sogoodnessknowshowclosetheymayhaveetoextin.Gould,inafamousquotation,leavesnodoubtthatheseesourlinealsuccessasafortunatefluke:“WindbackthetapeoflifetotheearlydaysoftheBurgessShale;letitplayagainfromaicalstartingpoint,andthecebeesvanishinglysmallthatanythinglikehumanintelligencewouldgracethereplay.”
Gould’sbookublishedin1989togeneralcriticalacclaimandwasagreatercialsuccess.Whatwasn’tgenerallyknownwasthatmanystistsdidn’tagreewithGould’sclusionsatall,andthatitwasallsooveryugly.IextoftheCambrian,“explosion”wouldsoonhavemoretodowithmoderntempersthanaphysiologicalfacts.
Infact,,plexanismsexistedatleastahundredmillionyearsbeforetheCambrian.Weshouldhaveknownawholelotsooner.NearlyfortyyearsafterWaladehisdiscoveryinada,ohersideoftheplainAustralia,ayounggeologistnamedReginaldSpriggfoundsomethingevenolderandinitswayjustasremarkable.
In1946SpriggwasayoungassistantgovergeologistforthestateofSouthAustraliawhenhewassenttomakeasurveyofabandonedmiheEdiaHillsoftheFlindersRange,anexpanseofbakingoutbaethreehundredmilesnorthofAdelaide.Theideawastoseeiftherewereanyoldmihatmightbeprofitablyreworkedusieologies,sohewasn’tstudyingsurfacerocksatall,stilllessfossils.Butonedaywhileeatinghislunch,Spriggidlyoverturnedahunkofsandstoneandwassurprised—toputitmildly—toseethattherock’ssurfacewascoveredindelicatefossils,ratherliketheimpressionsleavesmakeinmud.TheserockspredatedtheCambrianexplosion.Hewaslookingatthedawnofvisiblelife.
SpriggsubmittedapapertoNature,butitwasturneddown.HereadititheannualmeetingoftheAustralianandNewZealandAssociationfortheAdvaofSce,butitfailedtofindfavorwiththeassociation’shead,whosaidtheEdiaimprintsweremerely“fortuitousinanicmarkings”—patternsmadebywindorrainortides,butnotlivingbeings.Hishopesirelycrushed,SpriggtraveledtoLondonaedhisfindingstothe1948IionalGeologicalgress,butfailedtoexciteeitheriorbelief.Finally,forwantofabetteroutlet,hepublishedhisfindingsiransasoftheRoyalSocietyofSouthAustralia.Thehisgoverjobandtookupoilexploration.
Nineyearslater,in1957,aschoolboynamedJohnMason,whilewalkingthroughwoodForestintheEnglishMidlands,foundarockwithastrangefossilinit,similartoamodernseapelylikesomeofthespesSprigghadfoundaryingtotelleveryoneabouteversiheschoolboyturintoapaleontologistattheUyofLeicester,whoidentifieditatonceasPrecambrian.YoungMasongothispictureinthepapersandwastreatedasaprecocioushero;hestillisinmanybooks.ThespewasnamedinhishonorChamiamasoni.
Todaysome’sinalEdiaspes,alongwithmanyoftheotherfifteenhundredspesthathavebeenfoundthroughouttheFlindersRangesitime,beseeninaglasscaseinanupstairsroomofthestoutandlovelySouthAustralianMuseuminAdelaide,buttheydon’tattractagreatdealofattention.Thedelicatelyetchedpatterherfaintandnotterriblyarrestingtotheuntraiheyaremostlysmallanddisc-shaped,withoccasional,vaguetrailingribbons.Forteyhasdescribedthemas“soft-bodiedoddities.”
Thereisstillverylittleagreementaboutwhatthesethingswereorhowtheylived.Theyhad,asfarasbetold,nomouthoranuswithwhichtotakeinanddischargedigestivematerials,andnointernalanswithwhichtoprocessthemalongtheway.“Inlife,”Forteysays,“mostofthemprobablysimplylayuponthesurfaceofthesandysediment,likesoft,structurelessandinanimateflatfish.”Attheirliveliest,theywerenomoreplexthanjellyfish.AlltheEdiacreatureswerediploblastic,meaningtheywerebuiltfromtwolayersoftissue.Withtheexceptionofjellyfish,allanimalstodayaretriploblastic.
Someexpertsthinktheyweren’tanimalsatall,butmorelikeplantsi.Thedistinsbetweenplantandanimalarenotalwaysclearevennow.Themodernspongespendsitslifefixedtoasiandhasnoeyesorbraii,aisananimal.“WhenwegobacktothePrecambrianthediffereweenplantsandanimalswereprobablyevenlessclear,”saysFortey.“Thereisn’tanyrulethatsaysyouhavetobedemonstrablyoheother.”
NorisitagreedthattheEdiaanismsareinanywayaraltoanythingalivetoday(exceptpossiblysomejellyfish).Manyauthoritiesseethemasakindoffailedexperiment,astabatplexitythatdidn’ttake,possiblybecausethesluggishEdiaanismsweredevouredoroutpetedbythelitherandmoresophisticatedanimalsoftheCambrianperiod.
“Thereisnothingcloselysimilaralivetoday,”Forteyhaswritten.“Theyaredifficulttointerpretasanykindofaorsofwhatwastofollow.”
Thefeelingwasthatultimatelytheyweren’tterriblyimportanttothedevelopmentoflifeoh.ManyauthoritiesbelievethattherewasamassexterminationatthePrecambrian–CambrianboundaryandthatalltheEdiacreatures(excepttheuainjellyfish)failedtomoveontothephase.Therealbusinessofplexlife,inotherwords,startedwiththeCambrianexplosion.That’showGouldsawitinanycase.
AsfortherevisionsoftheBurgessShalefossils,almostatoncepeoplebegantoquestioerpretationsand,inparticular,Gould’sinterpretationoftheinterpretations.“FromthefirsttherewereanumberofstistswhodoubtedtheatthatSteveGouldhadpresented,howevermuchtheyadmiredthemannerofitsdelivery,”Forteywroteihatisputtingitmildly.
“IfonlyStephenGouldcouldthinkasclearlyashewrites!”barkedtheOxfordacademicRichardDawkinsintheopeninglineofareview(intheLondonSundayTelegraph)ofWonderfulLife.Dawkinsaowledgedthatthebookwas“unputdownable”anda“literarytour-de-force,”butaccusedGouldofengagingina“grandiloquentandnear-disingenuous”
misrepresentationofthefactsbysuggestingthattheBurgessrevisionshadstuhepaleontologiunity.“Theviewthatheisattag—thatevolutionmarchesinexorablytoinnaclesuchasman—hasnotbeenbelievedfor50years,”Dawkinsfumed.
Ahatwasexactlytheclusiontowhiygeneralreviewersweredrawn.
One,writingintheNewYorkTimesBookReview,cheerfullysuggestedthatasaresultofGould’sbookstists“havebeenthrowingoutsomepreceptionsthattheyhadnotexaminedfeions.Theyare,relutlyorenthusiastically,acceptingtheideathathumansareasmuactofnatureasaproductoforderlydevelopment.”
ButtherealheatdirectedatGouldarosefromthebeliefthatmanyofhisclusionsweresimplymistakenorcarelesslyinflated.WritinginthejournalEvolution,DawkinsattackedGould’sassertionsthat“evolutionintheCambrianwasadifferentkindofprocessfromtoday”andexpressedexasperationatGould’srepeatedsuggestionsthat“theCambrianeriodofevolutionary‘experiment,’evolutionary‘trialanderror,’evolutionary‘falsestarts.’.
..Itwasthefertiletimewhenallthegreat‘fualbodyplans’wereied.
Nowadays,evolutionjusttinkerswitholdbodyplans.BatheCambrian,newphylaandnewclassesarose.Nowadaysweonewspecies!”
Notinghowoftenthisidea—thattherearenonewbodyplans—ispickedup,Dawkinssays:
“Itisasthoughagardenerlookedatanoaktreeandremarked,wly:‘Isn’titstranomajornewboughshaveappearedonthistreeformanyyears?Thesedays,allthenewgroearstobeatthetwiglevel.’”
“Itwasastraime,”Forteysaysnow,“especiallywhenyoureflectedthatthiswasallaboutsomethingthathappenedfivehundredmillionyearsago,butfeelingsreallydidrunquitehigh.IjokedinoneofmybooksthatIfeltasifIoughttoputasafetyhelmetonbeforewritingabouttheCambrianperiod,butitdidactuallyfeelabitlikethat.”
StraofallwastheresponseofoheheroesofWonderfulLife,SimonwayMorris,whostartledmanyinthepaleontologiunitybyroundingabruptlyonGouldinabookofhisown,TheCrucibleofCreation.ThebooktreatedGould“withpt,evenloathing,”inFortey’swords.“Ihaveneverenteredsuchspleeninabookbyaprofessional,”Forteywrotelater.“ThecasualreaderofTheCrucibleofCreation,unawareofthehistory,wouldherthattheauthor’sviewshadoncebeencloseto(ifnotactuallysharedwith)Gould’s.”
WhenIaskedForteyaboutit,hesaid:“Well,itwasverystrange,quiteshogreally,becauseGould’sportrayalofhimhadbeensoflattering.IcouldonlyassumethatSimonwasembarrassed.Youknow,scegesbutbooksareperma,andIsupposeheregrettedbeingsoirremediablyassociatedwithviewsthathenoloogetherheld.Therewasallthatstuffabout‘ohfuotherphylum’andIexpectheregrettedbeingfamousforthat.”
penedwasthattheearlyCambrianfossilsbegantoundergoaperiodofcriticalreappraisal.ForteyandDerekBriggs—oheotherprincipalsinGould’sbook—usedamethodknownascladistiparethevariousBurgessfossils.Insimpleterms,cladistisistsanizinganismsonthebasisofsharedfeatures.Fivesasanexampletheideaofparingashrewandanelephant.Ifyousideredtheelephant’slargesizeandstrikingtrunkyoumightcludethatitcouldhavelittleinonwithatiny,sniffingshrew.Butifyouparedbothofthemwithalizard,youwouldseethattheelephantandshrewwereinfactbuilttomuchthesameplan.Inessence,whatForteyissayingisthatGouldsawelephantsandshrewswheretheysawmammals.TheBurgesscreatures,theybelieved,weren’tasstrangeandvariousastheyappearedatfirstsight.“Theywereoftennerthantrilobites,”Forteysaysnow.“Itisjustthatwehavehadaturyorsotogetusedtotrilobites.Familiarity,youknow,breedsfamiliarity.”
Thiswasn’t,Ishouldnote,becauseofsloppinessoriion.Interpretingtheformsaionshipsofaanimalsonthebasisofoftendistortedandfragmentaryevidenceisclearlyatrickybusiness.EdwardO.WilsonhashatifyoutookselectedspeodersaedthemasBurgess-stylefossilsnobodywouldeverguessthattheywereallfromthesamephylum,sodiffereheirbodyplans.AlsoinstrumentalinhelpingrevisiohediscoveriesoftwofurtherearlyCambriansites,oneinGreenlandandoneina,plusmorescatteredfinds,whichbetweenthemyieldedmanyadditionalandofteerspes.
TheupshotisthattheBurgessfossilswerefoundtobenotsodifferentafterall.
Halluia,ittur,hadbeenrestructedupsidedown.Itsstilt-likelegswereactuallyspikesalongitsback.Peytoia,theweirdcreaturethatlookedlikeapineappleslice,wasfoundtobenotadistinctcreaturebutmerelypartofalargeranimalcalledAnomalocaris.
ManyoftheBurgessspeshavenowbeenassigolivingphyla—justwhereWalcottputtheminthefirstplace.HalluiaandsomeothersarethoughttoberelatedtoOnychroupofcaterpillar-likeanimals.Othershavebeenreclassifiedasprecursorsofthemodernannelids.Infact,saysFortey,“therearerelativelyfewCambriandesignsthatarewhollynovel.Moreofteurnouttobejustiingelaborationsofwell-establisheddesigns.”AshewroteinhisbookLife:“Nonewasasstrangeasapresentdaybarnarotesqueasaqueee.”
SotheBurgessShalespesweren’tsospectacularafterall.Thismadethem,asForteyhaswritten,“nolessiing,orodd,justmoreexplicable.”Theirweirdbodyplanswerejustakindofyouthfulexuberaheevolutionaryequivalent,asitwere,ofspikedhairandtouds.Eve松语文学www.16sy.coM免费小说阅读
Iobeeafossil,severalthingsmusthappen.First,youmustdieintherightplalyabout15pertofrockspreservefossils,soit’snogoodkeelingoveronafuturesiteofgranite.Inpracticaltermsthedeceasedmustbeeburiedinsediment,whereitleaveanimpression,likealeafimud,ordeposewithoutexposuretooxygetingthemoleculesinitsbonesandhardparts(andveryoccasionallysofterparts)tobereplacedbydissolvedminerals,creatirifiedcopyoftheinal.ThenasthesedimentsinwhichthefossilliesarecarelesslypressedandfoldedandpushedaboutbyEarth’sprocesses,thefossilmustsomehowmaintainaifiableshape.Finally,butaboveall,aftertensofmillionsorperhapshundredsofmillionsofyearshiddenaway,itmustbefoundandreizedassomethingworthkeeping.
Onlyaboutoneboneinabillion,itisthought,everbeesfossilized.Ifthatisso,itmeansthatthepletefossillegacyofalltheAmerisalivetoday—that’s270millionpeoplewith206boneseach—willonlybeaboutfiftybones,onequarterofapleteskeleton.That’snottosayofcoursethatanyoftheseboneswillactuallybefound.Bearinginmindthattheybeburiedanywherewithinanareaofslightlyover3.6millionsquaremiles,littleofwhichwilleverbeturnedover,muchlessexamiwouldbesomethingofamiracleiftheywere.Fossilsareineverysensevanishinglyrare.Mostofwhathaslivedohhasleftbehindnorecordatall.Ithasbeeimatedthatlessthanonespeciesihousandhasmadeitintothefossilrecord.Thatinitselfisastunninglyinfinitesimalproportion.However,ifyouaccepttheoimatethattheEarthhasproduced30billionspeciesofcreatureinitstimeandRichardLeakeyandRogerLewin’sstatement(ihExtin)thatthereare250,000speciesofcreatureinthefossilrecord,thatreducestheproportiontojustonein120,000.EitherepossessisthemerestsamplingofallthelifethatEarthhasspawned.
Moreover,therecordwedohaveishopelesslyskewed.Mostlandanimals,ofcourse,don’tdieinsediments.Theydropintheopenaeorotorweatherdowntonothing.Thefossilrecordsequentlyisalmostabsurdlybiasedinfavorofmariures.
About95pertofallthefossilswepossessareofanimalsthatonceliveduer,mostlyinshallowseas.
ImentionallthistoexplainwhyonagraydayinFebruaryIwenttotheNaturalHistoryMuseuminLondoacheerful,vaguelyrumpled,verylikeablepaleontologistnamedRichardFortey.
Forteyknowsanawfullotaboutanawfullot.Heistheauthorofawry,splendidbookcalledLife:AnUnauthorisedBiography,whichcoversthewholepageantofanimatecreation.
ButhisfirstloveisatypeofmariurecalledtrilobitesthatoeemedinOrdoviseasbuthaveedforalongtimeexceptinfossilizedform.Allsharedabasicbodyplanofthreeparts,orlobes—head,tail,thorax—fromwhiesthename.ForteyfoundhisfirstwhenhewasaboyclamberingoverrocksatSt.David’sBayinWales.Hewashookedforlife.
Hetookmetoagalleryoftallmetalcupboards.Eachcupboardwasfilledwithshallowdrawers,andeachdrawerwasfilledwithstonytrilobites—twentythousandspesinall.
“Itseemslikeabignumber,”heagreed,“butyouhavetorememberthatmillionsuponmillionsoftrilobiteslivedformillionsuponmillionsofyearsinaseas,sotwentythousandisn’tahugenumber.Andmostoftheseareonlypartialspes.Findingapletetrilobitefossilisstillabigmomentforapaleontologist.”
Trilobitesfirstappeared—fullyformed,seeminglyfromnowhere—about540millionyearsago,hestartofthegreatoutburstofplexlifepopularlyknownastheCambrianexplosion,andthenvanished,alongwithagreatdealelse,inthegreatandstillmysteriousPermiain300,000orsoturieslater.Aswithallextinctcreatures,thereisanaturaltemptatiardthemasfailures,butinfacttheywereamosuccessfulanimalsevertolive.Theirreignranfor300millionyears—twicethespanofdinosaurs,whichwerethemselvesoneofhistreatsurvivors.Humans,Forteypointsout,havesurvivedsofarforone-halfof1pertaslong.
Withsomuchtimeattheirdisposal,thetrilobitesproliferatedprodigiously.Mostremainedsmall,aboutthesizeofmoderles,butsomegrewtobeasbigasplatters.Altogethertheyformedatleastfivethousandgeneraandsixtythousandspecies—thoughmoreturnupallthetime.ForteyhadretlybeenataferenSouthAmericawhereheroachedbyanacademiallprovincialuyiina.“Shehadaboxthatwasfullofiingthings—trilobitesthathadneverbeenseenbeforeinSouthAmerica,orindeedanywhere,andagreatdealelse.Shehadnoresearchfacilitiestostudythemandnofundstolookformore.Hugepartsoftheworldarestillunexplored.”
“Intermsoftrilobites?”
“No,intermsofeverything.”
Throughouttheeeury,trilobiteswerealmosttheonlyknownformsofearlyplexlife,andforthatreasonwereassiduouslycollectedandstudied.Thebigmysteryaboutthemwastheirsuddenappearance.Evennow,asForteysays,itbestartlingtogothtformationofrodtoworkyourwardthroughtheeonsfindingnovisiblelifeatall,andthensuddenly“awholeProfallotaspisorElenellusasbigasacrabwillpopintoyourwaitinghands.”Thesewerecreatureswithlimbs,gills,nervoussystems,probingantennae,“abrainofsorts,”inFortey’swords,araeyeseverseen.Madeofcalciterods,thesamestuffthatformslimestoheystitutedtheearliestvisualsystemsknown.Morethanthis,theearliesttrilobitesdidn’tsistofjustouresomespeciesbutdozens,anddidn’tappeariwolocationsbutallover.ManythinkingpeopleintheeeurysawthisasproofofGod’shandiworkaationofDarwin’sevolutionaryideals.Ifevolutionproceededslowly,theyasked,thenhowdidheatforthissuddenappearanplex,fullyformedcreatures?Thefactis,hecouldn’t.
Andsomattersseemeddestioremainforeveruntilonedayin1909,threemonthsshyofthefiftiethanniversaryofthepublicationofDarwin’sOntheinofSpecies,aleontologistnamedCharlesDoolittleWaladearaordinaryfindintheadianRockies.
Walcottwasbornin1850andgrewupiewYork,inafamilyofmodestmeans,whichbecamemoremodeststillwiththesuddehofhisfatherwhenWalcottwasaninfant.AsaboyWalcottdiscoveredthathehadaknackforfindingfossils,particularlytrilobites,andbuiltupacolleofsuffitdistinthatitwasboughtbyLouisAgassizforhismuseumatHarvardforasmallfortune—about</strong>70,000intoday’smoney.
Althoughhehadbarelyahighschooleducationandwasselftaughtinthesces,Walcottbecamealeadingauthorityontrilobitesandwasthefirstpersoablishthattrilobiteswerearthropods,thegroupthatincludesmodersandcrustas.
In1879hetookajobasafieldresearcherwiththenewlyformedUatesGeologicalSurveyandservedwithsuchdistinthatwithinfifteenyearshehadriseshead.In1907heointedsecretaryoftheSmithsonianInstitution,whereheremaiilhisdeathin1927.Despitehisadministrativeobligatioiodofieldworkandtowriteprolifically.“Hisbooksfillalibraryshelf,”acctoFortey.Notially,hewasalsoafoundingdirectoroftheNationalAdvisoryitteeforAeronautics,whicheventuallybecametheNationalAeronautidSpaceAgency,orNASA,andthusrightlybesideredthegrandfatherofthespaceage.
ButwhatheisrememberedfornowisanastutebutluckyfindinBritishbia,highabovethelittletownofField,iesummerof1909.ThearyversionofthestoryisthatWalcott,apaniedbyhiswife,wasridingonhorsebaountaintrailbehespotcalledtheBurgessRidgewhenhiswife’shorseslippedonloosestones.Dismountingtoassisther,Walcottdiscoveredthatthehorsehadturnedaslabofshalethattainedfossilcrustasofanespeciallyaandunusualtype.Snowwasfalling—winteresearlytotheadianRockies—sotheydidn’tlinger,buttheyearatthefirstopportunityWalcottreturhespot.Tragthepresumedrouteoftherocks’slide,heclimbed750feettohemountain’ssummit.There,8,000feetabovesealevel,hefoundashaleoutcrop,aboutthelengthofacityblock,taininganunrivaledarrayoffossilsfromsoohemomentwhenplexlifeburstforthindazzlingprofusion—thefamousCambrianexplosion.Walcotthadfound,iheholygrailofpaleontology.TheoutcropbecameknownastheBurgessShale,andforalongtimeitprovided“oursolevistaupontheiionofmodernlifeinallitsfullness,”asthelateStephenJayGouldrecordedinhispopularbookWonderfulLife.
Gould,everscrupulous,discoveredfromreadingWalcott’sdiariesthatthestoryoftheBurgessShale’sdiscoveryappearstohavebeeembroidered—Walakesionofaslippinghorseorfallingsnow—butthereisnodisputingthatitwasaraordinaryfind.
ItisalmostimpossibleforuswhosetimeohislimitedtoabreezyfewdecadestoappreciatehowremoteintimefromustheCambrianoutburstwas.Ifyoucouldflybackwardsintothepastattherateofoneyearpersed,itwouldtakeyouabouthalfanhourtoreachthetimeofChrist,andalittleoverthreeweekstogetbacktothebeginningsofhumanlife.
ButitwouldtakeyoutweoreachthedawnoftheCambrianperiod.Itwas,inotherwords,aremelylongtimeago,andtheworldwasaverydifferentplace.
Forohing,500-million-plusyearsagowhentheBurgessShalewasformeditwasn’tatthetopofamountainbutatthefootofone.Specificallyitwasashallowobasinatthebottomofasteepcliff.Theseasofthattimeteemedwithlife,butnormallytheanimalsleftnorecordbecausetheyweresoft-bodiedanddecayedupondying.ButatBurgessthecliffcollapsed,andthecreaturesbelow,entombedinamudslide,werepressedlikeflowersinabook,theirfeaturespreservedinwondrousdetail.
Inannualsummertripsfrom1910to1925(bywhichtimehewasseventy-fiveyearsold),Walcottexcavatedtensofthousandsofspes(Gouldsays80,000;thenormallyunimpeachablefactcheckersofNationalGeraphicsay60,000),whichhebroughtbacktoWashingtonforfurtherstudy.Inbothsheernumbersanddiversitythecollearalleled.SomeoftheBurgessfossilshadshells;manyothersdidnot.Someweresighted,othersblind.Thevarietywasenormous,sistingof140speciesbyonet.“TheBurgessShaleincludedarangeofdisparityinanatomicaldesignsneveragainequaled,andnotmatchedtodaybyallthecreaturesintheworld’sos,”Gouldwrote.
Unfortunately,acctoGould,Walcottfailedtodisthesignificeofwhathehadfound.“Snatgdefeatfromthejawsofvictouldwroteinanotherwork,EightLittlePiggies,“Walcottthenproceededtomisinterpretthesemagnifitfossilsinthedeepestpossibleway.”Heplacedthemintomroups,makingthemaraltotoday’sworms,jellyfish,andothercreatures,andthusfailedtoappreciatetheirdistiness.“Undersuinterpretation,”Gouldsighed,“lifebeganinprimordialsimplicityandmovedinexorably,predictablyonwardtomoreaer.”
Walcottdiedin1927andtheBurgessfossilswerelargelyfotten.FornearlyhalfaturytheystayedshutawayindrawersintheAmeriMuseumofNaturalHistoryinWashington,seldomsultedandneverquestiohenin1973agraduatestudentfromCambridgeUynamedSimonwayMorrispaidavisittothecolle.Hewasastonishedbywhathefound.ThefossilswerefarmorevariedandmagnifitthanWalcotthadindicatedinhiswritings.Intaxonomythecategorythatdescribesthebasicbodyplansofallanismsisthephylum,andhere,wayMorriscluded,weredrawerafterdrawerofsuatomicalsingularities—allamazinglyandunatablyunreizedbythemanwhohadfoundthem.
Withhissupervisor,HarryWhittington,andfellowgraduatestudentDerekBriggs,wayMorrisspeseveralyearsmakingasystematicrevisionoftheentirecolle,andkingoutoingmonographafteranotherasdiscoverypiledupondiscovery.Manyofthecreaturesemployedbodyplansthatwerenotsimplyuhingseenbeforeorsiwerebizarrelydifferent.One,Opabinia,hadfiveeyesandanozzle-likesnoutwithclawsontheend.Another,adisc-shapedbeingcalledPeytoia,lookedalmosticallylikeapineappleslice.Athirdhadevidentlytotteredaboutonrowsofstilt-likelegs,andwassooddthattheyHalluia.TherewassomureizedyinthecollethatatonepointuponopeninganewdrawerwayMorrisfamouslywasheardtomutter,“Ohfuotanotherphylum.”
TheEnglishteam’srevisionsshowedthattheCambrianhadbeenatimeofunparalleledinnovationandexperimentationinbodydesigns.Foralmostfourbillionyearslifehaddawdledalongwithoutaableambitionsinthedireofplexity,andthensuddenly,inthespaceofjustfiveortenmillionyears,ithadcreatedallthebasicbodydesignsstillioday.Nameacreature,fromaodewormtoCameronDiaz,andtheyallusearchitecturefirstcreatedintheCambrianparty.
Whatwasmostsurprising,however,wasthatthereweresomanybodydesignsthathadfailedtomakethecut,sotospeak,anodesdants.Altogether,acctoGould,atleastfifteenandperhapsasmanyastwentyoftheBurgessanimalsbelonizedphylum.(Thenumbersoongrewinsomepopularatstoasmanyasonehundred—farmorethantheCambridgestistseveractuallyclaimed.)“Thehistoryoflife,”wroteGould,“isastoryofmassiveremovalfollowedbydifferentiationwithinafewsurvivingstoottheventionaltaleofsteadilyincreasingexcellenplexity,anddiversity.”
Evolutionarysuccess,itappeared,wasalottery.
Ourethatdidmaoslipthrough,asmallwormlikebeingcalledPikaiagras,wasfoundtohaveaprimitivespinaln,makingittheearliestknoworofalllatervertebrates,includingus.PikaiawerebynomeansabundantamongtheBurgessfossils,sogoodnessknowshowclosetheymayhaveetoextin.Gould,inafamousquotation,leavesnodoubtthatheseesourlinealsuccessasafortunatefluke:“WindbackthetapeoflifetotheearlydaysoftheBurgessShale;letitplayagainfromaicalstartingpoint,andthecebeesvanishinglysmallthatanythinglikehumanintelligencewouldgracethereplay.”
Gould’sbookublishedin1989togeneralcriticalacclaimandwasagreatercialsuccess.Whatwasn’tgenerallyknownwasthatmanystistsdidn’tagreewithGould’sclusionsatall,andthatitwasallsooveryugly.IextoftheCambrian,“explosion”wouldsoonhavemoretodowithmoderntempersthanaphysiologicalfacts.
Infact,,plexanismsexistedatleastahundredmillionyearsbeforetheCambrian.Weshouldhaveknownawholelotsooner.NearlyfortyyearsafterWaladehisdiscoveryinada,ohersideoftheplainAustralia,ayounggeologistnamedReginaldSpriggfoundsomethingevenolderandinitswayjustasremarkable.
In1946SpriggwasayoungassistantgovergeologistforthestateofSouthAustraliawhenhewassenttomakeasurveyofabandonedmiheEdiaHillsoftheFlindersRange,anexpanseofbakingoutbaethreehundredmilesnorthofAdelaide.Theideawastoseeiftherewereanyoldmihatmightbeprofitablyreworkedusieologies,sohewasn’tstudyingsurfacerocksatall,stilllessfossils.Butonedaywhileeatinghislunch,Spriggidlyoverturnedahunkofsandstoneandwassurprised—toputitmildly—toseethattherock’ssurfacewascoveredindelicatefossils,ratherliketheimpressionsleavesmakeinmud.TheserockspredatedtheCambrianexplosion.Hewaslookingatthedawnofvisiblelife.
SpriggsubmittedapapertoNature,butitwasturneddown.HereadititheannualmeetingoftheAustralianandNewZealandAssociationfortheAdvaofSce,butitfailedtofindfavorwiththeassociation’shead,whosaidtheEdiaimprintsweremerely“fortuitousinanicmarkings”—patternsmadebywindorrainortides,butnotlivingbeings.Hishopesirelycrushed,SpriggtraveledtoLondonaedhisfindingstothe1948IionalGeologicalgress,butfailedtoexciteeitheriorbelief.Finally,forwantofabetteroutlet,hepublishedhisfindingsiransasoftheRoyalSocietyofSouthAustralia.Thehisgoverjobandtookupoilexploration.
Nineyearslater,in1957,aschoolboynamedJohnMason,whilewalkingthroughwoodForestintheEnglishMidlands,foundarockwithastrangefossilinit,similartoamodernseapelylikesomeofthespesSprigghadfoundaryingtotelleveryoneabouteversiheschoolboyturintoapaleontologistattheUyofLeicester,whoidentifieditatonceasPrecambrian.YoungMasongothispictureinthepapersandwastreatedasaprecocioushero;hestillisinmanybooks.ThespewasnamedinhishonorChamiamasoni.
Todaysome’sinalEdiaspes,alongwithmanyoftheotherfifteenhundredspesthathavebeenfoundthroughouttheFlindersRangesitime,beseeninaglasscaseinanupstairsroomofthestoutandlovelySouthAustralianMuseuminAdelaide,buttheydon’tattractagreatdealofattention.Thedelicatelyetchedpatterherfaintandnotterriblyarrestingtotheuntraiheyaremostlysmallanddisc-shaped,withoccasional,vaguetrailingribbons.Forteyhasdescribedthemas“soft-bodiedoddities.”
Thereisstillverylittleagreementaboutwhatthesethingswereorhowtheylived.Theyhad,asfarasbetold,nomouthoranuswithwhichtotakeinanddischargedigestivematerials,andnointernalanswithwhichtoprocessthemalongtheway.“Inlife,”Forteysays,“mostofthemprobablysimplylayuponthesurfaceofthesandysediment,likesoft,structurelessandinanimateflatfish.”Attheirliveliest,theywerenomoreplexthanjellyfish.AlltheEdiacreatureswerediploblastic,meaningtheywerebuiltfromtwolayersoftissue.Withtheexceptionofjellyfish,allanimalstodayaretriploblastic.
Someexpertsthinktheyweren’tanimalsatall,butmorelikeplantsi.Thedistinsbetweenplantandanimalarenotalwaysclearevennow.Themodernspongespendsitslifefixedtoasiandhasnoeyesorbraii,aisananimal.“WhenwegobacktothePrecambrianthediffereweenplantsandanimalswereprobablyevenlessclear,”saysFortey.“Thereisn’tanyrulethatsaysyouhavetobedemonstrablyoheother.”
NorisitagreedthattheEdiaanismsareinanywayaraltoanythingalivetoday(exceptpossiblysomejellyfish).Manyauthoritiesseethemasakindoffailedexperiment,astabatplexitythatdidn’ttake,possiblybecausethesluggishEdiaanismsweredevouredoroutpetedbythelitherandmoresophisticatedanimalsoftheCambrianperiod.
“Thereisnothingcloselysimilaralivetoday,”Forteyhaswritten.“Theyaredifficulttointerpretasanykindofaorsofwhatwastofollow.”
Thefeelingwasthatultimatelytheyweren’tterriblyimportanttothedevelopmentoflifeoh.ManyauthoritiesbelievethattherewasamassexterminationatthePrecambrian–CambrianboundaryandthatalltheEdiacreatures(excepttheuainjellyfish)failedtomoveontothephase.Therealbusinessofplexlife,inotherwords,startedwiththeCambrianexplosion.That’showGouldsawitinanycase.
AsfortherevisionsoftheBurgessShalefossils,almostatoncepeoplebegantoquestioerpretationsand,inparticular,Gould’sinterpretationoftheinterpretations.“FromthefirsttherewereanumberofstistswhodoubtedtheatthatSteveGouldhadpresented,howevermuchtheyadmiredthemannerofitsdelivery,”Forteywroteihatisputtingitmildly.
“IfonlyStephenGouldcouldthinkasclearlyashewrites!”barkedtheOxfordacademicRichardDawkinsintheopeninglineofareview(intheLondonSundayTelegraph)ofWonderfulLife.Dawkinsaowledgedthatthebookwas“unputdownable”anda“literarytour-de-force,”butaccusedGouldofengagingina“grandiloquentandnear-disingenuous”
misrepresentationofthefactsbysuggestingthattheBurgessrevisionshadstuhepaleontologiunity.“Theviewthatheisattag—thatevolutionmarchesinexorablytoinnaclesuchasman—hasnotbeenbelievedfor50years,”Dawkinsfumed.
Ahatwasexactlytheclusiontowhiygeneralreviewersweredrawn.
One,writingintheNewYorkTimesBookReview,cheerfullysuggestedthatasaresultofGould’sbookstists“havebeenthrowingoutsomepreceptionsthattheyhadnotexaminedfeions.Theyare,relutlyorenthusiastically,acceptingtheideathathumansareasmuactofnatureasaproductoforderlydevelopment.”
ButtherealheatdirectedatGouldarosefromthebeliefthatmanyofhisclusionsweresimplymistakenorcarelesslyinflated.WritinginthejournalEvolution,DawkinsattackedGould’sassertionsthat“evolutionintheCambrianwasadifferentkindofprocessfromtoday”andexpressedexasperationatGould’srepeatedsuggestionsthat“theCambrianeriodofevolutionary‘experiment,’evolutionary‘trialanderror,’evolutionary‘falsestarts.’.
..Itwasthefertiletimewhenallthegreat‘fualbodyplans’wereied.
Nowadays,evolutionjusttinkerswitholdbodyplans.BatheCambrian,newphylaandnewclassesarose.Nowadaysweonewspecies!”
Notinghowoftenthisidea—thattherearenonewbodyplans—ispickedup,Dawkinssays:
“Itisasthoughagardenerlookedatanoaktreeandremarked,wly:‘Isn’titstranomajornewboughshaveappearedonthistreeformanyyears?Thesedays,allthenewgroearstobeatthetwiglevel.’”
“Itwasastraime,”Forteysaysnow,“especiallywhenyoureflectedthatthiswasallaboutsomethingthathappenedfivehundredmillionyearsago,butfeelingsreallydidrunquitehigh.IjokedinoneofmybooksthatIfeltasifIoughttoputasafetyhelmetonbeforewritingabouttheCambrianperiod,butitdidactuallyfeelabitlikethat.”
StraofallwastheresponseofoheheroesofWonderfulLife,SimonwayMorris,whostartledmanyinthepaleontologiunitybyroundingabruptlyonGouldinabookofhisown,TheCrucibleofCreation.ThebooktreatedGould“withpt,evenloathing,”inFortey’swords.“Ihaveneverenteredsuchspleeninabookbyaprofessional,”Forteywrotelater.“ThecasualreaderofTheCrucibleofCreation,unawareofthehistory,wouldherthattheauthor’sviewshadoncebeencloseto(ifnotactuallysharedwith)Gould’s.”
WhenIaskedForteyaboutit,hesaid:“Well,itwasverystrange,quiteshogreally,becauseGould’sportrayalofhimhadbeensoflattering.IcouldonlyassumethatSimonwasembarrassed.Youknow,scegesbutbooksareperma,andIsupposeheregrettedbeingsoirremediablyassociatedwithviewsthathenoloogetherheld.Therewasallthatstuffabout‘ohfuotherphylum’andIexpectheregrettedbeingfamousforthat.”
penedwasthattheearlyCambrianfossilsbegantoundergoaperiodofcriticalreappraisal.ForteyandDerekBriggs—oheotherprincipalsinGould’sbook—usedamethodknownascladistiparethevariousBurgessfossils.Insimpleterms,cladistisistsanizinganismsonthebasisofsharedfeatures.Fivesasanexampletheideaofparingashrewandanelephant.Ifyousideredtheelephant’slargesizeandstrikingtrunkyoumightcludethatitcouldhavelittleinonwithatiny,sniffingshrew.Butifyouparedbothofthemwithalizard,youwouldseethattheelephantandshrewwereinfactbuilttomuchthesameplan.Inessence,whatForteyissayingisthatGouldsawelephantsandshrewswheretheysawmammals.TheBurgesscreatures,theybelieved,weren’tasstrangeandvariousastheyappearedatfirstsight.“Theywereoftennerthantrilobites,”Forteysaysnow.“Itisjustthatwehavehadaturyorsotogetusedtotrilobites.Familiarity,youknow,breedsfamiliarity.”
Thiswasn’t,Ishouldnote,becauseofsloppinessoriion.Interpretingtheformsaionshipsofaanimalsonthebasisofoftendistortedandfragmentaryevidenceisclearlyatrickybusiness.EdwardO.WilsonhashatifyoutookselectedspeodersaedthemasBurgess-stylefossilsnobodywouldeverguessthattheywereallfromthesamephylum,sodiffereheirbodyplans.AlsoinstrumentalinhelpingrevisiohediscoveriesoftwofurtherearlyCambriansites,oneinGreenlandandoneina,plusmorescatteredfinds,whichbetweenthemyieldedmanyadditionalandofteerspes.
TheupshotisthattheBurgessfossilswerefoundtobenotsodifferentafterall.
Halluia,ittur,hadbeenrestructedupsidedown.Itsstilt-likelegswereactuallyspikesalongitsback.Peytoia,theweirdcreaturethatlookedlikeapineappleslice,wasfoundtobenotadistinctcreaturebutmerelypartofalargeranimalcalledAnomalocaris.
ManyoftheBurgessspeshavenowbeenassigolivingphyla—justwhereWalcottputtheminthefirstplace.HalluiaandsomeothersarethoughttoberelatedtoOnychroupofcaterpillar-likeanimals.Othershavebeenreclassifiedasprecursorsofthemodernannelids.Infact,saysFortey,“therearerelativelyfewCambriandesignsthatarewhollynovel.Moreofteurnouttobejustiingelaborationsofwell-establisheddesigns.”AshewroteinhisbookLife:“Nonewasasstrangeasapresentdaybarnarotesqueasaqueee.”
SotheBurgessShalespesweren’tsospectacularafterall.Thismadethem,asForteyhaswritten,“nolessiing,orodd,justmoreexplicable.”Theirweirdbodyplanswerejustakindofyouthfulexuberaheevolutionaryequivalent,asitwere,ofspikedhairandtouds.Eve松语文学www.16sy.coM免费小说阅读
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