第2章

If，however，theconditionoftheworld，whichhasobtainedthroughoutgeologictime，isbutthesequeltoavastseriesofchangeswhichtookplaceinpre-geologictime，thenitseemsnotunlikelythatthedurationofthislatteristothatoftheformerasthevastextentofgeologictimeistothelengthofthebriefepochwecallthehistoricalperiod；andthateventheoldestrocksarerecordsofanepochalmostinfinitelyremotefromthatwhichcouldhavewitnessedthefirstshapingofourglobe。

Itisprobablethatnomoderngeologistwouldhesitatetoadmitthegeneralvalidityofthesereasoningswhenappliedtothephysicsofhissubject，whenceitisthemoreremarkablethatthemomentthequestionchangesfromoneofphysicsandchemistrytooneofnaturalhistory，scientificopinionsandthepopularprejudices，whichreflecttheminadistortedform，undergoasuddenmetamorphosis。Geologistsandpalaeontologistswriteaboutthe"beginningoflife"andthe"first-createdformsoflivingbeings，"asiftheywerethemostfamiliarthingsintheworld；andevencautiouswritersseemtobeonquitefriendlytermswiththe"archetype"wherebytheCreatorwasguided"amidstthecrashoffallingworlds。"Justasitusedtobeimaginedthattheancientworldwasphysicallyopposedtothepresent，soitisstillwidelyassumedthatthelivingpopulationofourglobe，whetheranimalorvegetable，intheolderepochs，exhibitedformssostrikinglycontrastedwiththosewhichweseearoundus，thatthereishardlyanythingincommonbetweenthetwo。Itisconstantlytacitlyassumedthatwehavebeforeusalltheformsoflifewhichhaveeverexisted；andthoughtheprogressofknowledge，yearlyandalmostmonthly，drivesthedefendersofthatpositionfromtheirground，theyentrenchthemselvesinthenewlineofdefencesasifnothinghadhappened，andproclaimthatthe"new"beginningisthe"real"

beginning。

Withoutforaninstantdenyingorendeavouringtosoftendowntheconsiderablepositivedifferences（thenegativeonesaremetbyanotherlineofargument）whichundoubtedlyobtainbetweentheancientandthemodernworldsoflife，webelievetheyhavebeenvastlyoverstatedandexaggerated，andthisbeliefisbaseduponcertainfactswhosevaluedoesnotseemtohavebeenfullyappreciated，thoughtheyhavelongbeenmoreorlesscompletelyknown。

Themultitudinouskindsofanimalsandplants，bothrecentandfossil，are，asiswellknown，arrangedbyzoologistsandbotanists，inaccordancewiththeirnaturalrelations，intogroupswhichreceivethenamesofsub-kingdoms，classes，orders，families，generaandspecies。

Nowitisamostremarkablecircumstancethat，viewedonthegreatscale，livingbeingshavedifferedsolittlethroughoutallgeologictimethatthereisnosub-kingdomandnoclasswhollyextinctorwithoutlivingrepresentatives。

Ifwedescendtothesmallergroups，wefindthatthenumberofordersofplantsisabouttwohundred；andIhaveitonthebestauthoritythatnotoneoftheseisexclusivelyfossil；sothatthereisabsolutelynotasingleextinctordinaltypeofvegetablelife；anditisnotuntilwedescendtothenextgroup，orthefamilies，thatwefindtypeswhicharewhollyextinct。Thenumberofordersofanimals，ontheotherhand，maybereckonedatahundredandtwenty，orthereabouts，andofthese，eightorninehavenolivingrepresentatives。

Theproportionofextinctordinaltypesofanimalstotheexistingtypes，therefore，doesnotexceedsevenpercent——amarvellouslysmallproportionwhenweconsiderthevastnessofgeologictime。

Anotherclassofconsiderations——ofadifferentkind，itistrue，buttendinginthesamedirection——seemstohavebeenoverlooked。Notonlyisittruethatthegeneralplanofconstructionofanimalsandplantshasbeenthesameinallrecordedtimeasatpresent，butthereareparticularkindsofanimalsandplantswhichhaveexistedthroughoutvastepochs，sometimesthroughthewholerangeofrecordedtime，withverylittlechange。Byreasonofthispersistency，thetypicalformofsuchakindmightbecalleda"persistenttype，"incontradistinctiontothosetypeswhichhaveappearedforbutashorttimeinthecourseoftheworld"shistory。Examplesofthesepersistenttypesareabundantenoughinboththevegetableandtheanimalkingdoms。Theoldestgroupofplantswithwhichwearewellacquaintedisthatofwhoseremainscoalisconstituted；andasfarastheycanbeidentified，thecarboniferousplantsareferns，orclub-mosses，orConiferae，inmanycasesgenericallyidenticalwiththosenowliving！

Amonganimals，instancesofthesamekindmaybefoundineverysub-kingdom。The"Globigerina"oftheAtlanticsoundingsisidenticalwiththatwhichoccursinthechalk；andthecastsoflowersilurian"Foraminifera"，whichEhrenberghasrecentlydescribed，seemtoindicatetheexistenceatthatremoteperiodofformssingularlylikethosewhichnowexist。Amongthecorals，thepalaeozoic"Tabulata"areconstructedonpreciselythesametypeasthemodernmillepores；andifweturntomolluscs，themostcompetentmalacologistsfailtodiscoveranygenericdistinctionbetweenthe"Craniae"，"Lingulae"and"Discinae"ofthesilurianrocksandthosewhichnowlive。Ourexisting"Nautilus"hasitsrepresentativespeciesineverygreatformation，fromtheoldesttothenewest；and"Loligo"，thesquidofmodernseas，appearsinthelias，oratthebottomofthemesozoicseries，inaform，atmost，specificallydifferentfromitslivingcongeners。Inthegreatassemblageofannuloseanimals，thetwohighestclasses，theinsectsandspidertribe，exhibitawonderfulpersistencyoftype。Thecockroachesofthecarboniferousepochareexceedinglysimilartothosewhichnowrunaboutourcoal-cellars；anditslocusts，termitesanddragon-fliesarecloselyalliedtothemembersofthesamegroupswhichnowchirrupaboutourfields，undermineourhouses，orsailwithswiftgraceaboutthebanksofoursedgypools。And，inlikemanner，thepalaeozoicscorpionscanonlybedistinguishedbytheeyeofanaturalistfromthemodernones。

Finally，withrespecttothe"Vertebrata"，thesamelawholdsgood:

certaintypes，suchasthoseoftheganoidandplacoidfishes，havingpersistedfromthepalaeozoicepochtothepresenttimewithoutagreateramountofdeviationfromthenormalstandardthanthatwhichisseenwithinthelimitsofthegroupasitnowexists。Evenamongthe"Reptilia"——theclasswhichexhibitsthelargestproportionofentirelyextinctformsofanyonetype，——thatofthe"Crocodilia"，haspersistedfromatleastthecommencementoftheMesozoicepochuptothepresenttimewithsomuchconstancy，thattheamountofchangewhichitexhibitsmayfairly，inrelationtothetimewhichhaselapsed，becalledinsignificant。Andtheimperfectknowledgewehaveoftheancientmammalianpopulationofourearthleadstothebeliefthatcertainofitstypes，suchasthatofthe"Marsupialia"，havepersistedwithcorrespondinglylittlechangethroughasimilarrangeoftime。