Amongtheenormousvariety，——Ibelievetherearesomewhereaboutahundredandfiftykindsofpigeons，——therearefourkindswhichmaybeselectedasrepresentingtheextremestdivergencesofonekindfromanother。TheirnamesaretheCarrier，thePouter，theFantail，andtheTumbler。Inthelargediagramstheyareeachrepresentedintheirrelativesizestoeachother。ThisfirstoneistheCarrier。youwillnoticethislargeexcrescenceonitsbeak。ithasacomparativelysmallhead。thereisabarespaceroundtheeyes。ithasalongneck，averylongbeak，verystronglegs，largefeet，longwings，andsoon。ThesecondoneisthePouter，averylargebird，withverylonglegsandbeak。ItiscalledthePouterbecauseitisinthehabitofcausingitsgullettoswellupbyinflatingitwithair。Ishouldtellyouthatallpigeonshaveatendencytodothisattimes，butinthePouteritiscarriedtoanenormousextent。Thebirdsappeartobequiteproudoftheirpowerofswellingandpuffingthemselvesoutinthisway。andIthinkitisaboutasdrollasightasyoucanwellseetolookatacagefullofthesepigeonspuffingandblowingthemselvesoutinthisridiculousmanner。
ThethirdkindImentioned——theFantail——isasmallbird，withexceedinglysmalllegsandaverysmallbeak。Itismostcuriouslydistinguishedbythesizeandextentofitstail，which，insteadofcontainingtwelvefeathers，mayhavemanymore，——saythirty，orevenmore——Ibelievetherearesomewithasmanyasforty-two。Thisbirdhasacurioushabitofspreadingoutthefeathersofitstailinsuchawaythattheyreachforward，andtouchitshead。andifthiscanbeaccomplished，Ibelieveitislookeduponasapointofgreatbeauty。
Buthereisthelastgreatvariety，——theTumbler。andofthatgreatvariety，oneoftheprincipalkinds，andonemostprized，isthespecimenrepresentedhere——theshort-facedTumbler。Itsbeakisreducedtoamerenothing。Justcomparethebeakofthisoneandthatofthefirstone，theCarrier——Ibelievetheorthodoxcomparisonoftheheadandbeakofathoroughlywell-bredTumbleristostickanoatintoacherry，andthatwillgiveyoutheproperrelativeproportionsoftheheadandbeak。Thefeetandlegsareexceedinglysmall，andthebirdappearstobequiteadwarfwhenplacedsidebysidewiththisgreatCarrier。
Thesearedifferencesenoughinregardtotheirexternalappearance。butthesedifferencesarebynomeansthewholeoreventhemostimportantofthedifferenceswhichobtainbetweenthesebirds。Thereishardlyasinglepointoftheirstructurewhichhasnotbecomemoreorlessaltered。andtogiveyouanideaofhowextensivethesealterationsare，Ihaveheresomeverygoodskeletons，forwhichIamindebtedtomyfriend，Mr。Tegetmeier，agreatauthorityinthesematters。bymeansofwhich，ifyouexaminethemby-and-by，youwillbeabletoseetheenormousdifferenceintheirbonystructures。
Ihadtheprivilege，sometimeago，ofaccesstosomeimportantMSS。ofMr。Darwin，who，Imaytellyou，hastakenverygreatpainsandspentmuchvaluabletimeandattentionontheinvestigationofthesevariations，andgettingtogetherallthefactsthatbearuponthem。I
obtainedfromtheseMSS。thefollowingsummaryofthedifferencesbetweenthedomesticbreedsofpigeons。thatistosay，anotificationofthevariouspointsinwhichtheirorganizationdiffers。Inthefirstplace，thebackoftheskullmaydifferagooddeal，andthedevelopmentofthebonesofthefacemayvaryagreatdeal。thebackvariesagooddeal。theshapeofthelowerjawvaries。thetonguevariesverygreatly，notonlyincorrelationtothelengthandsizeofthebeak，butitseemsalsotohaveakindofindependentvariationofitsown。Thentheamountofnakedskinroundtheeyes，andatthebaseofthebeak，mayvaryenormously。somaythelengthoftheeyelids，theshapeofthenostrils，andthelengthoftheneck。Ihavealreadynoticedthehabitofblowingoutthegullet，soremarkableinthePouter，andcomparativelysointheothers。Therearegreatdifferences，too，inthesizeofthefemaleandthemale，theshapeofthebody，thenumberandwidthoftheprocessesoftheribs，thedevelopmentoftheribs，andthesize，shape，anddevelopmentofthebreastbone。Wemaynotice，too，——andImentionthefactbecauseithasbeendisputedbywhatisassumedtobehighauthority，——thevariationinthenumberofthesacralvertebrae。Thenumberofthesevariesfromeleventofourteen，andthatwithoutanydiminutioninthenumberofthevertebraeofthebackorofthetail。Thenthenumberandpositionofthetail-feathersmayvaryenormously，andsomaythenumberoftheprimaryandsecondaryfeathersofthewings。Again，thelengthofthefeetandofthebeak，——althoughtheyhavenorelationtoeachother，yetappeartogotogether，——thatis，youhavealongbeakwhereveryouhavelongfeet。Therearedifferencesalsointheperiodsoftheacquirementoftheperfectplumage，——thesizeandshapeoftheeggs，——thenatureofflight，andthepowersofflight，——so-calledhomingbirdshavingenormousflyingpowers。*while，ontheotherhand，thelittleTumblerissocalledbecauseofitsextraordinaryfacultyofturningheadoverheelsintheair，insteadofpursuingadirectcourse。And，lastly，thedispositionsandvoicesofthebirdsmayvary。Thusthecaseofthepigeonsshowsyouthatthereishardlyasingleparticular，——whetherofinstinct，orhabit，orbonystructure，orofplumage，——ofeithertheinternaleconomyortheexternalshape，inwhichsomevariationorchangemaynottakeplace，which，byselectivebreeding，maybecomeperpetuated，andformthefoundationof，andgiveriseto，anewrace。
[footnote：TheCarrier，IlearnfromMr。Tegetmeier，doesnot’carry’。ahigh-bredbirdofthisbreedbeingbutapoorflier。Thebirdswhichflylongdistances，andcomehome，——homingbirds，——andareconsequentlyusedascarriers，arenotcarriersinthefancysense。]
Ifyoucarryinyourmind’seyethesefourvarietiesofpigeons，youwillbearwithyouasgoodanotionasyoucanhave，perhaps，oftheenormousextenttowhichadeviationfromaprimitivetypemaybecarriedbymeansofthisprocessofselectivebreeding。
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THECONDITIONSOFEXISTENCEASAFFECTINGTHEPERPETUATIONOF
LIVINGBEINGS
INthelastLectureIendeavouredtoprovetoyouthat，while，asageneralrule，organicbeingstendtoreproducetheirkind，thereisinthem，also，aconstantlyrecurringtendencytovary——tovarytoagreaterortoalessextent。Suchavariety，Ipointedouttoyou，mightarisefromcauseswhichwedonotunderstand。wethereforecalleditspontaneous。anditmightcomeintoexistenceasadefiniteandmarkedthing，withoutanygradationsbetweenitselfandtheformwhichprecededit。Ifurtherpointedout，thatsuchavarietyhavingoncearisen，mightbeperpetuatedtosomeextent，andindeedtoaverymarkedextent，withoutanydirectinterference，orwithoutanyexerciseofthatprocesswhichwecalledselection。AndthenIstatedfurther，thatbysuchselection，whenexercisedartificially——ifyoutookcaretobreedonlyfromthoseformswhichpresentedthesamepeculiaritiesofanyvarietywhichhadariseninthismanner——thevariationmightbeperpetuated，asfaraswecansee，indefinitely。
Thenextquestion，anditisanimportantoneforus，isthis：Isthereanylimittotheamountofvariationfromtheprimitivestockwhichcanbeproducedbythisprocessofselectivebreeding？Inconsideringthisquestion，itwillbeusefultoclassthecharacteristics，inrespectofwhichorganicbeingsvary，undertwoheads：wemayconsiderstructuralcharacteristics，andwemayconsiderphysiologicalcharacteristics。
Inthefirstplace，asregardsstructuralcharacteristics，Iendeavouredtoshowyou，bytheskeletonswhichIhaduponthetable，andbyreferencetoagreatmanywell-ascertainedfacts，thatthedifferentbreedsofPigeons，theCarriers，Pouters，andTumblers，mightvaryinanyoftheirinternalandimportantstructuralcharacterstoaverygreatdegree。notonlymighttherebechangesintheproportionsoftheskull，andthecharactersofthefeetandbeaks，andsoon。butthattheremightbeanabsolutedifferenceinthenumberofthevertebraeoftheback，asinthesacralvertebraeofthePouter。andsogreatistheextentofthevariationintheseandsimilarcharactersthatIpointedouttoyou，byreferencetotheskeletonsandthediagrams，thattheseextremevarietiesmayabsolutelydiffermorefromoneanotherintheirstructuralcharactersthandowhatnaturalistscalldistinctSPECIESofpigeons。thatistosay，thattheydiffersomuchinstructurethatthereisagreaterdifferencebetweenthePouterandtheTumblerthanthereisbetweensuchwildanddistinctformsastheRockPigeonortheRingPigeon，ortheRingPigeonandtheStockDove。andindeedthedifferencesareofgreatervaluethanthis，forthestructuraldifferencesbetweenthesedomesticatedpigeonsaresuchaswouldbeadmittedbyanaturalist，supposingheknewnothingatallabouttheirorigin，toentitlethemtoconstituteevendistinctgenera。
AsIhaveusedthistermSPECIES，andshallprobablyuseitagooddeal，IhadbetterperhapsdevoteawordortwotoexplainingwhatImeanbyit。
Animalsandplantsaredividedintogroups，whichbecomegraduallysmaller，beginningwithaKINGDOM，whichisdividedintoSUB-KINGDOMS。
thencomethesmallerdivisionscalledPROVINCES。andsoonfromaPROVINCEtoaCLASSfromaCLASStoanORDER，fromORDERStoFAMILIES，andfromthesetoGENERA，untilwecomeatlengthtothesmallestgroupsofanimalswhichcanbedefinedonefromtheotherbyconstantcharacters，whicharenotsexual。andthesearewhatnaturalistscallSPECIESinpractice，whatevertheymaydointheory。
If，inastateofnature，youfindanytwogroupsoflivingbeings，whichareseparatedonefromtheotherbysomeconstantly-recurringcharacteristic，Idon’tcarehowslightandtrivial，solongasitisdefinedandconstant，anddoesnotdependonsexualpeculiarities，thenallnaturalistsagreeincallingthemtwospecies。thatiswhatismeantbytheuseofthewordspecies——thatistosay，itis，forthepracticalnaturalist，amerequestionofstructuraldifferences。*
[footnote]*Ilaystresshereonthe’practical’
significationofSpecies。Whetheraphysiologicaltestbetweenspeciesexistornot，itishardlyeverapplicablebythepracticalnaturalist。
Wehaveseennow——torepeatthispointoncemore，anditisveryessentialthatweshouldrightlyunderstandit——wehaveseenthatbreeds，knowntohavebeenderivedfromacommonstockbyselection，maybeasdifferentintheirstructurefromtheoriginalstockasspeciesmaybedistinctfromeachother。
Butistheliketrueofthephysiologicalcharacteristicsofanimals？
Dothephysiologicaldifferencesofvarietiesamountindegreetothoseobservedbetweenformswhichnaturalistscalldistinctspecies？Thisisamostimportantpointforustoconsider。
Asregardsthegreatmajorityofphysiologicalcharacteristics，thereisnodoubtthattheyarecapableofbeingdeveloped，increased，andmodifiedbyselection。
Thereisnodoubtthatbreedsmaybemadeasdifferentasspeciesinmanyphysiologicalcharacters。IhavealreadypointedouttoyouverybrieflythedifferenthabitsofthebreedsofPigeons，allofwhichdependupontheirphysiologicalpeculiarities，——asthepeculiarhabitoftumbling，intheTumbler——thepeculiaritiesofflight，inthehomingbirds，——thestrangehabitofspreadingoutthetail，andwalkinginapeculiarfashion，intheFantail，——and，lastly，thehabitofblowingoutthegullet，socharacteristicofthePouter。Theseareallduetophysiologicalmodifications，andinalltheserespectsthesebirdsdifferasmuchfromeachotherasanytwoordinaryspeciesdo。
SowithDogsintheirhabitsandinstincts。ItisaphysiologicalpeculiaritywhichleadstheGreyhoundtochaseitspreybysight，——thatenablestheBeagletotrackitbythescent，——thatimpelstheTerriertoitsrat-huntingpropensity，——andthatleadstheRetrievertoitshabitofretrieving。Thesehabitsandinstinctsarealltheresultsofphysiologicaldifferencesandpeculiarities，whichhavebeendevelopedfromacommonstock，atleastthereiseveryreasontobelieveso。Butitisamostsingularcircumstance，thatwhileyoumayrunthroughalmostthewholeseriesofphysiologicalprocesses，withoutfindingachecktoyourargument，youcomeatlasttoapointwhereyoudofindacheck，andthatisinthereproductiveprocesses。Forthereisamostsingularcircumstanceinrespecttonaturalspecies——atleastaboutsomeofthem——anditwouldbesufficientforthepurposesofthisargumentifitweretrueofonlyoneofthem，butthereis，infact，agreatnumberofsuchcases——andthatis，that，similarastheymayappeartobetomereracesorbreeds，theypresentamarkedpeculiarityinthereproductiveprocess。Ifyoubreedfromthemaleandfemaleofthesamerace，youofcoursehaveoffspringofthelikekind，andifyoumaketheoffspringbreedtogether，youobtainthesameresult，andifyoubreedfromtheseagain，youwillstillhavethesamekindofoffspring。
thereisnocheck。Butifyoutakemembersoftwodistinctspecies，howeversimilartheymaybetoeachotherandmakethembreedtogether，youwillfindacheck，withsomemodificationsandexceptions，however，whichIshallspeakofpresently。Ifyoucrosstwosuchspecieswitheachother，then，——althoughyoumaygetoffspringinthecaseofthefirstcross，yet，ifyouattempttobreedfromtheproductsofthatcrossing，whicharewhatarecalledHYBRIDS——thatis，ifyoucoupleamaleandafemalehybrid——thentheresultisthatinninety-ninecasesoutofahundredyouwillgetnooffspringatall。therewillbenoresultwhatsoever。
Thereasonofthisisquiteobviousinsomecases。themalehybrids，althoughpossessingalltheexternalappearancesandcharacteristicsofperfectanimals，arephysiologicallyimperfectanddeficientinthestructuralpartsofthereproductiveelementsnecessarytogeneration。
Itissaidtobeinvariablythecasewiththemalemule，thecrossbetweentheAssandtheMare。andhenceitis，that，althoughcrossingtheHorsewiththeAssiseasyenough，andisconstantlydone，asfarasIamaware，ifyoutaketwomules，amaleandafemale，andendeavourtobreedfromthem，yougetnooffspringwhatever。nogenerationwilltakeplace。Thisiswhatiscalledthesterilityofthehybridsbetweentwodistinctspecies。
Youseethatthisisaveryextraordinarycircumstance。onedoesnotseewhyitshouldbe。Thecommonteleologicalexplanationis，thatitistopreventtheimpurityofthebloodresultingfromthecrossingofonespecieswithanother，butyouseeitdoesnotinrealitydoanythingofthekind。Thereisnothinginthisfactthathybridscannotbreedwitheachother，toestablishsuchatheory。thereisnothingtopreventtheHorsebreedingwiththeAss，ortheAsswiththeHorse。Sothatthisexplanationbreaksdown，asagreatmanyexplanationsofthiskinddo，thatareonlyfoundedonmereassumptions。
Thusyouseethatthereisagreatdifferencebetweenmongrels，whicharecrossesbetweendistinctraces，andhybrids，whicharecrossesbetweendistinctspecies。Themongrelsare，sofarasweknow，fertilewithoneanother。Butbetweenspecies，inmanycases，youcannotsucceedinobtainingeventhefirstcross：atanyrateitisquitecertainthatthehybridsareoftenabsolutelyinfertileonewithanother。
Hereisafeature，then，greatorsmallasitmaybe，whichdistinguishesnaturalspeciesofanimals。Canwefindanyapproximationtothisinthedifferentracesknowntobeproducedbyselectivebreedingfromacommonstock？Uptothepresenttimetheanswertothatquestionisabsolutelyanegativeone。Asfarasweknowatpresent，thereisnothingapproximatingtothischeck。IncrossingthebreedsbetweentheFantailandthePouter，theCarrierandtheTumbler，oranyothervarietyorraceyoumayname——sofarasweknowatpresent——thereisnodifficultyinbreedingtogetherthemongrels。TaketheCarrierandtheFantail，forinstance，andletthemrepresenttheHorseandtheAssinthecaseofdistinctspecies。thenyouhave，astheresultoftheirbreeding，theCarrier-Fantailmongrel，——wewillsaythemaleandfemalemongrel，——and，asfarasweknow，thesetwowhencrossedwouldnotbelessfertilethantheoriginalcross，orthanCarrierwithCarrier。Here，yousee，isaphysiologicalcontrastbetweentheracesproducedbyselectivemodificationandnaturalspecies。Ishallinquireintothevalueofthisfact，andofsomemodifyingcircumstancesbyandby。forthepresentImerelyputitbroadlybeforeyou。
Butwhileconsideringthisquestionofthelimitationsofspecies，awordmustbesaidaboutwhatiscalledRECURRENCE——thetendencyofraceswhichhavebeendevelopedbyselectivebreedingfromvarietiestoreturntotheirprimitivetype。Thisissupposedbymanytoputanabsolutelimittotheextentofselectiveandallothervariations。
Peoplesay，Itisallverywelltotalkaboutproducingthesedifferentraces，butyouknowverywellthatifyouturnedallthesebirdswild，thesePouters，andCarriers，andsoon，theywouldallreturntotheirprimitivestock。Thisisverycommonlyassumedtobeafact，anditisanargumentthatiscommonlybroughtforwardasconclusive。butifyouwilltakethetroubletoinquireintoitratherclosely，Ithinkyouwillfindthatitisnotworthverymuch。Thefirstquestionofcourseis，Dotheythusreturntotheprimitivestock？Andcommonlyasthethingisassumedandaccepted，itisextremelydifficulttogetanythinglikegoodevidenceofit。Itisconstantlysaid，forexample，thatifdomesticatedHorsesareturnedwild，astheyhavebeeninsomepartsofAsiaMinorandSouthAmerica，thattheyreturnatoncetotheprimitivestockfromwhichtheywerebred。Butthefirstanswerthatyoumaketothisassumptionis，toaskwhoknowswhattheprimitivestockwas。andthesecondansweris，thatinthatcasethewildHorsesofAsiaMinoroughttobeexactlylikethewildHorsesofSouthAmerica。Iftheyarebothlikethesamething，theyoughtmanifestlytobelikeeachother！Thebestauthorities，however，tellyouthatitisquitedifferent。ThewildHorseofAsiaissaidtobeofaduncolour，withalargishhead，andagreatmanyotherpeculiarities。whilethebestauthoritiesonthewildHorsesofSouthAmericatellyouthatthereisnosimilaritybetweentheirwildHorsesandthoseofAsiaMinor。thecutoftheirheadsisverydifferent，andtheyarecommonlychestnutorbay-coloured。Itisquiteclear，therefore，thatasbythesefactsthereoughttohavebeentwoprimitivestocks，theygofornothinginsupportoftheassumptionthatracesrecurtooneprimitivestock，andsofarasthisevidenceisconcerned，itfallstotheground。
Supposeforamomentthatitwereso，andthatdomesticatedraces，whenturnedwild，didreturntosomecommoncondition，Icannotseethatthiswouldprovemuchmorethanthatsimilarconditionsarelikelytoproducesimilarresults。andthatwhenyoutakebackdomesticatedanimalsintowhatwecallnaturalconditions，youdoexactlythesamethingasifyoucarefullyundidalltheworkyouhadgonethrough，forthepurposeofbringingtheanimalfromitswildtoitsdomesticatedstate。Idonotseeanythingverywonderfulinthefact，ifittookallthattroubletogetitfromawildstate，thatitshouldgobackintoitsoriginalstateassoonasyouremovedtheconditionswhichproducedthevariationtothedomesticatedform。Thereisanimportantfact，however，forciblybroughtforwardbyMr。Darwin，whichhasbeennoticedinconnectionwiththebreedingofdomesticatedpigeons。anditis，thathoweverdifferentthesebreedsofpigeonsmaybefromeachother，andwehavealreadynoticedthegreatdifferencesinthesebreeds，thatif，amonganyofthosevariations，youchancetohaveabluepigeonturnup，itwillbesuretohavetheblackbarsacrossthewings，whicharecharacteristicoftheoriginalwildstock，theRockPigeon。
Now，thisiscertainlyaveryremarkablecircumstance。butIdonotseemyselfhowittellsverystronglyeitheronewayortheother。I
think，infact，thatthisargumentinfavourofrecurrencetotheprimitivetypemightproveagreatdealtoomuchforthosewhosoconstantlybringitforward。Forexample，Mr。Darwinhasveryforciblyurged，thatnothingiscommonerthanifyouexamineadunhorse——andI
hadanopportunityofverifyingthisillustrationlately，whileintheislandsoftheWestHighlands，wherethereareagreatmanydunhorses——tofindthathorseexhibitalongblackstripedownhisback，veryoftenstripesonhisshoulder，andveryoftenstripesonhislegs。I，myself，sawaponyofthisdescriptionashorttimeago，inabaker’scart，nearRothesay，inBute：ithadthelongstripedowntheback，andstripesontheshouldersandlegs，justlikethoseoftheAss，theQuagga，andtheZebra。Now，ifweinterpretthetheoryofrecurrenceasappliedtothiscase，mightitnotbesaidthatherewasacaseofavariationexhibitingthecharactersandconditionsofananimaloccupyingsomethinglikeanintermediatepositionbetweentheHorse，theAss，theQuagga，andtheZebra，andfromwhichthesehadbeendeveloped？InthesamewaywithregardeventoMan。Everyanatomistwilltellyouthatthereisnothingcommoner，indissectingthehumanbody，thantomeetwithwhatarecalledmuscularvariations——thatis，ifyoudissecttwobodiesverycarefully，youwillprobablyfindthatthemodesofattachmentandinsertionofthemusclesarenotexactlythesameinboth，therebeinggreatpeculiaritiesinthemodeinwhichthemusclesarearranged。anditisverysingular，thatinsomedissectionsofthehumanbodyyouwillcomeuponarrangementsofthemusclesverysimilarindeedtothesamepartsintheApes。Istheconclusioninthatcasetobe，thatthisisliketheblackbarsinthecaseofthePigeon，andthatitindicatesarecurrencetotheprimitivetypefromwhichtheanimalshavebeenprobablydeveloped？Truly，Ithinkthattheopponentsofmodificationandvariationhadbetterleavetheargumentofrecurrencealone，oritmayprovealtogethertoostrongforthem。
Tosumup，——theevidenceasfaraswehavegoneisagainsttheargumentastoanylimittodivergences，sofarasstructureisconcerned。andinfavourofaphysiologicallimitation。Byselectivebreedingwecanproducestructuraldivergencesasgreatasthoseofspecies，butwecannotproduceequalphysiologicaldivergences。ForthepresentIleavethequestionthere。
Now，thenextproblemthatliesbeforeus——anditisanextremelyimportantone——isthis：Doesthisselectivebreedingoccurinnature？
Because，ifthereisnoproofofit，allthatIhavebeentellingyougoesfornothinginaccountingfortheoriginofspecies。Arenaturalcausescompetenttoplaythepartofselectioninperpetuatingvarieties？Herewelabourunderverygreatdifficulties。InthelastlectureIhadoccasiontopointouttoyoutheextremedifficultyofobtainingevidenceevenofthefirstoriginofthosevarietieswhichweknowtohaveoccurredindomesticatedanimals。Itoldyou，thatalmostalwaystheoriginofthesevarietiesisoverlooked，sothatIcouldonlyproducetwoofthreecases，asthatofGratioKelleiaandoftheAnconsheep。Peopleforget，ordonottakenoticeofthemuntiltheycometohaveaprominence。andifthatistrueofartificialcases，underourowneyes，andinanimalsinourowncare，howmuchmoredifficultitmustbetohaveatfirsthandgoodevidenceoftheoriginofvarietiesinnature！Indeed，Idonotknowthatitispossiblebydirectevidencetoprovetheoriginofavarietyinnature，ortoproveselectivebreeding。butIwilltellyouwhatwecanprove——andthiscomestothesamething——thatvarietiesexistinnaturewithinthelimitsofspecies，and，whatismore，thatwhenavarietyhascomeintoexistenceinnature，therearenaturalcausesandconditions，whichareamplycompetenttoplaythepartofaselectivebreeder。andalthoughthatisnotquitetheevidencethatonewouldliketohave——thoughitisnotdirecttestimony——yetitisexceedinggoodandexceedinglypowerfulevidenceinitsway。
Astothefirstpoint，ofvarietiesexistingamongnaturalspecies，I
mightappealtotheuniversalexperienceofeverynaturalist，andofanypersonwhohaseverturnedanyattentionatalltothecharacteristicsofplantsandanimalsinastateofnature。butImayaswelltakeafewdefinitecases，andIwillbeginwithManhimself。
Iamoneofthosewhobelievethat，atpresent，thereisnoevidencewhateverforsaying，thatmankindsprangoriginallyfromanymorethanasinglepair。Imustsay，thatIcannotseeanygoodgroundwhatever，orevenanytenablesortofevidence，forbelievingthatthereismorethanonespeciesofMan。Nevertheless，asyouknow，justastherearenumbersofvarietiesinanimals，sothereareremarkablevarietiesofmen。Ispeaknotmerelyofthosebroadanddistinctvariationswhichyouseeataglance。Everybody，ofcourse，knowsthedifferencebetweenaNegroandawhiteman，andcantellaChinamanfromanEnglishman。Theyeachhavepeculiarcharacteristicsofcolourandphysiognomy。butyoumustrecollectthatthecharactersoftheseracesgoveryfardeeper——theyextendtothebonystructure，andtothecharactersofthatmostimportantofallorganstous——thebrain。sothat，amongmenbelongingtodifferentraces，orevenwithinthesamerace，onemanshallhaveabrainathird，orhalf，orevenseventypercent。biggerthananother。andifyoutakethewholerangeofhumanbrains，youwillfindavariationinsomecasesofahundredpercent。
Apartfromthesevariationsinthesizeofthebrain，thecharactersoftheskullvary。ThusifIdrawthefiguresofaMongulandofaNegroheadontheblackboard，inthecaseofthelastthebreadthwouldbeaboutseven-tenths，andintheotheritwouldbenine-tenthsofthetotallength。Sothatyouseethereisabundantevidenceofvariationamongmenintheirnaturalcondition。Andifyouturntootheranimalsthereisjustthesamething。Thefox，forexample，whichhasaverylargegeographicaldistributionalloverEurope，andpartsofAsia，andontheAmericanContinent，variesgreatly。TherearemostlylargefoxesintheNorth，andsmalleronesintheSouth。InGermanyalone，theforestersreckonsomeeightdifferentsorts。
Ofthetiger，noonesupposesthatthereismorethanonespecies。theyextendfromthehottestpartsofBengal，intothedry，cold，bittersteppesofSiberia，intoalatitudeof50degrees，——sothattheymayevenpreyuponthereindeer。Thesetigershaveexceedinglydifferentcharacteristics，butstilltheyallkeeptheirgeneralfeatures，sothatthereisnodoubtastotheirbeingtigers。TheSiberiantigerhasathickfur，asmallmane，andalongitudinalstripedowntheback，whilethetigersofJavaandSumatradifferinmanyimportantrespectsfromthetigersofNorthernAsia。Solionsvary。sobirdsvary。andso，ifyougofurtherbackandlowerdownincreation，youfindthatfishesvary。Indifferentstreams，inthesamecountryeven，youwillfindthetrouttobequitedifferenttoeachotherandeasilyrecognisablebythosewhofishintheparticularstreams。Thereisthesamedifferencesinleeches。leechcollectorscaneasilypointouttoyouthedifferencesandthepeculiaritieswhichyouyourselfwouldprobablypassby。sowithfresh-watermussels。so，infact，witheveryanimalyoucanmention。
Inplantsthereisthesamekindofvariation。Takesuchacaseevenasthecommonbramble。Thebotanistsareallatwaraboutit。someofthemwantingtomakeoutthattherearemanyspeciesofit，andothersmaintainingthattheyarebutmanyvarietiesofonespecies。andtheycannotsettletothisdaywhichisaspeciesandwhichisavariety！
Sothattherecanbenodoubtwhatsoeverthatanyplantandanyanimalmayvaryinnature。thatvarietiesmayariseinthewayIhavedescribed，——asspontaneousvarieties，——andthatthosevarietiesmaybeperpetuatedinthesamewaythatIhaveshownyouspontaneousvarietiesareperpetuated。Isay，therefore，thattherecanbenodoubtastotheoriginandperpetuationofvarietiesinnature。
Butthequestionnowis：——Doesselectiontakeplaceinnature？isthereanythingliketheoperationofmaninexercisingselectivebreeding，takingplaceinnature？Youwillobservethat，atpresent，Isaynothingaboutspecies。Iwishtoconfinemyselftotheconsiderationoftheproductionofthosenaturalraceswhicheverybodyadmitstoexist。
Thequestionis，whetherinnaturetherearecausescompetenttoproduceraces，justinthesamewayasmanisabletoproducebyselection，suchracesofanimalsaswehavealreadynoticed。
Whenavarietyhasarisen，theCONDITIONSOFEXISTENCEaresuchastoexerciseaninfluencewhichisexactlycomparabletothatofartificialselection。ByConditionsofExistenceImeantwothings，——thereareconditionswhicharefurnishedbythephysical，theinorganicworld，andthereareconditionsofexistencewhicharefurnishedbytheorganicworld。Thereis，inthefirstplace，CLIMATE。underthatheadIincludeonlytemperatureandthevariedamountofmoistureofparticularplaces。InthenextplacethereiswhatistechnicallycalledSTATION，whichmeans——giventheclimate，theparticularkindofplaceinwhichananimaloraplantlivesorgrows。forexample，thestationofafishisinthewater，ofafresh-waterfishinfreshwater。thestationofamarinefishisinthesea，andamarineanimalmayhaveastationhigherordeeper。Soagainwithlandanimals：thedifferencesintheirstationsarethoseofdifferentsoilsandneighbourhoods。somebeingbestadaptedtoacalcareous，andotherstoanarenaceoussoil。ThethirdconditionofexistenceisFOOD，bywhichImeanfoodinthebroadestsense，thesupplyofthematerialsnecessarytotheexistenceofanorganicbeing。inthecaseofaplanttheinorganicmatters，suchascarbonicacid，water，ammonia，andtheearthysaltsorsalines。inthecaseoftheanimaltheinorganicandorganicmatters，whichwehaveseentheyrequire。thentheseareall，atleastthetwofirst，whatwemaycalltheinorganicorphysicalconditionsofexistence。Foodtakesamid-place，andthencometheorganicconditions。bywhichImeantheconditionswhichdependuponthestateoftherestoftheorganiccreation，uponthenumberandkindoflivingbeings，withwhichananimalissurrounded。Youmayclasstheseundertwoheads：thereareorganicbeings，whichoperateas’opponents’，andthereareorganicbeingswhichoperateas’helpers’toanygivenorganiccreature。Theopponentsmaybeoftwokinds：therearethe’indirectopponents’，whicharewhatwemaycall’rivals’。andtherearethe’directopponents’，thosewhichstrivetodestroythecreature。andthesewecall’enemies’。ByrivalsImean，ofcourse，inthecaseofplants，thosewhichrequirefortheirsupportthesamekindofsoilandstation，and，amonganimals，thosewhichrequirethesamekindofstation，orfood，orclimate。thosearetheindirectopponents。
thedirectopponentsare，ofcourse，thosewhichpreyuponananimalorvegetable。The’helpers’mayalsoberegardedasdirectandindirect：
inthecaseofacarnivorousanimal，forexample，aparticularherbaceousplantmayinmultiplyingbeanindirecthelper，byenablingtheherbivoraonwhichthecarnivorepreystogetmorefood，andthustonourishthecarnivoremoreabundantly。thedirecthelpermaybebestillustratedbyreferencetosomeparasiticcreature，suchasthetape-worm。Thetape-wormexistsinthehumanintestines，sothatthefewerthereareofmenthefewertherewillbeoftape-worms，otherthingsbeingalike。Itisahumiliatingreflection，perhaps，thatwemaybeclassedasdirecthelperstothetape-worm，butthefactisso：
wecanallseethatiftherewerenomentherewouldbenotape-worms。
Itisextremelydifficulttoestimate，inaproperway，theimportanceandtheworkingoftheConditionsofExistence。IdonotthinktherewereanyofuswhohadtheremotestnotionofproperlyestimatingthemuntilthepublicationofMr。Darwin’swork，whichhasplacedthembeforeuswithremarkableclearness。andImustendeavour，asfarasI
caninmyownfashion，togiveyousomenotionofhowtheywork。Weshallfinditeasiesttotakeasimplecase，andoneasfreeaspossiblefromeverykindofcomplication。
Iwillsuppose，therefore，thatallthehabitablepartofthisglobe——thedryland，amountingtoabout51，000，000squaremiles，——I
willsupposethatthewholeofthatdrylandhasthesameclimate，andthatitiscomposedofthesamekindofrockorsoil，sothattherewillbethesamestationeverywhere。wethusgetridofthepeculiarinfluenceofdifferentclimatesandstations。Iwillthenimaginethatthereshallbebutoneorganicbeingintheworld，andthatshallbeaplant。Inthiswestartfair。Itsfoodistobecarbonicacid，waterandammonia，andthesalinemattersinthesoil，whichare，bythesupposition，everywherealike。Wetakeonesingleplant，withnoopponents，nohelpers，andnorivals。itistobeafairfield，andnofavour。Now，Iwillaskyoutoimaginefurtherthatitshallbeaplantwhichshallproduceeveryyearfiftyseeds，whichisaverymoderatenumberforaplanttoproduce。andthat，bytheactionofthewindsandcurrents，theseseedsshallbeequallyandgraduallydistributedoverthewholesurfaceoftheland。Iwantyounowtotraceoutwhatwilloccur，andyouwillobservethatIamnottalkingfallaciouslyanymorethanamathematiciandoeswhenheexpoundshisproblem。Ifyoushowthattheconditionsofyourproblemaresuchasmayactuallyoccurinnatureanddonottransgressanyoftheknownlawsofnatureinworkingoutyourproposition，thenyouareassafeintheconclusionyouarriveatasisthemathematicianinarrivingatthesolutionofhisproblem。Inscience，theonlywayofgettingridofthecomplicationswithwhichasubjectofthiskindisenvironed，istoworkinthisdeductivemethod。Whatwillbetheresult，then？Iwillsupposethateveryplantrequiresonesquarefootofgroundtoliveupon。andtheresultwillbethat，inthecourseofnineyears，theplantwillhaveoccupiedeverysingleavailablespotinthewholeglobe！IhavechalkedupontheblackboardthefiguresbywhichI
arriveattheresult：-
Plants。Plants1x50in1styear=50
50x502nd=2，500
2，500x503rd=125，000
125，000x504th=6，250，000
6，250，000x505th=312，500，000
312，500，000x506th=15，625，000，000
15，625，000，000x507th=781，250，000，000
781，250，000，000x508th=39，062，500，000，000
39，062，500，000，000x50&9th=1，953，125，000，000，000
51，000，000sq。miles——thedrysurfaceoftheearthx27，878，400——thenumberofsq。ft。in1sq。mile=sq。ft。1，421，798，400，000，000being531，326，600，000，000squarefeetlessthanwouldberequiredattheendoftheninthyear。
Youwillseefromthisthat，attheendofthefirstyearthesingleplantwillhaveproducedfiftymoreofitskind。bytheendofthesecondyearthesewillhaveincreasedto2，500。andsoon，insucceedingyears，yougetbeyondeventrillions。andIamnotatallsurethatIcouldtellyouwhattheproperarithmeticaldenominationofthetotalnumberreallyis。but，atanyrate，youwillunderstandthemeaningofallthosenoughts。Thenyouseethat，atthebottom，Ihavetakenthe51，000，000ofsquaremiles，constitutingthesurfaceofthedryland。andasthenumberofsquarefeetareplacedunderandsubtractedfromthenumberofseedsthatwouldbeproducedintheninthyear，youcanseeatoncethattherewouldbeanimmensenumbermoreofplantsthantherewouldbesquarefeetofgroundfortheiraccommodation。Thisiscertainlyquiteenoughtoprovemypoint。thatbetweentheeighthandninthyearafterbeingplantedthesingleplantwouldhavestockedthewholeavailablesurfaceoftheearth。
Thisisathingwhichishardlyconceivable——itseemshardlyimaginable——yetitisso。ItisindeedsimplythelawofMalthusexemplified。Mr。Malthuswasaclergyman，whoworkedoutthissubjectmostminutelyandtruthfullysomeyearsago。heshowedquiteclearly，——andalthoughhewasmuchabusedforhisconclusionsatthetime，theyhaveneveryetbeendisprovedandneverwillbe——heshowedthatinconsequenceoftheincreaseinthenumberoforganicbeingsinageometricalratio，whilethemeansofexistencecannotbemadetoincreaseinthesameratio，thattheremustcomeatimewhenthenumberoforganicbeingswillbeinexcessofthepowerofproductionofnutriment，andthatthussomecheckmustarisetothefurtherincreaseofthoseorganicbeings。Attheendoftheninthyearwehaveseenthateachplantwouldnotbeabletogetitsfullsquarefootofground，andattheendofanotheryearitwouldhavetosharethatspacewithfiftyotherstheproduceoftheseedswhichitwouldgiveoff。
What，then，takesplace？Everyplantgrowsup，flourishes，occupiesitssquarefootofground，andgivesoffitsfiftyseeds。butnoticethis，thatoutofthisnumberonlyonecancometoanything。thereisthus，asitwere，forty-ninechancestooneagainstitsgrowingup。itdependsuponthemostfortuitouscircumstanceswhetheranyoneofthesefiftyseedsshallgrowupandflourish，orwhetheritshalldieandperish。ThisiswhatMr。Darwinhasdrawnattentionto，andcalledtheSTRUGGLEFOREXISTENCE。andIhavetakenthissimplecaseofaplantbecausesomepeopleimaginethatthephraseseemstoimplyasortoffight。
Ihavetakenthisplantandshownyouthatthisistheresultoftheratiooftheincrease，thenecessaryresultofthearrivalofatimecomingforeveryspecieswhenexactlyasmanymembersmustbedestroyedasareborn。thatistheinevitableultimateresultoftherateofproduction。Now，whatistheresultofallthis？Ihavesaidthatthereareforty-ninestrugglingagainsteveryone。anditamountstothis，thatthesmallestpossiblestartgiventoanyoneseedmaygiveitanadvantagewhichwillenableittogetaheadofalltheothers。
anythingthatwillenableanyoneoftheseseedstogerminatesixhoursbeforeanyoftheotherswill，otherthingsbeingalike，enableittochokethemoutaltogether。Ihaveshownyouthatthereisnoparticularinwhichplantswillnotvaryfromeachother。itisquitepossiblethatoneofourimaginaryplantsmayvaryinsuchacharacterasthethicknessoftheintegumentofitsseeds。itmighthappenthatoneoftheplantsmightproduceseedshavingathinnerintegument，andthatwouldenabletheseedsofthatplanttogerminatealittlequickerthanthoseofanyoftheothers，andthoseseedswouldmostinevitablyextinguishtheforty-ninetimesasmanythatwerestrugglingwiththem。
Ihaveputitinthisway，butyouseethepracticalresultoftheprocessisthesameasifsomepersonhadnurturedtheoneanddestroyedtheotherseeds。Itdoesnotmatterhowthevariationisproduced，solongasitisonceallowedtooccur。Thevariationintheplantoncefairlystartedtendstobecomehereditaryandreproduceitself。theseedswouldspreadthemselvesinthesamewayandtakepartinthestrugglewiththeforty-ninehundred，orforty-ninethousand，withwhichtheymightbeexposed。Thus，bydegrees，thisvariety，withsomeslightorganicchangeormodification，mustspreaditselfoverthewholesurfaceofthehabitableglobe，andextirpateorreplacetheotherkinds。ThatiswhatismeantbyNATURALSELECTION。thatisthekindofargumentbywhichitisperfectlydemonstrablethattheconditionsofexistencemayplayexactlythesamepartfornaturalvarietiesasmandoesfordomesticatedvarieties。Noonedoubtsatallthatparticularcircumstancesmaybemorefavourableforoneplantandlesssoforanother，andthemomentyouadmitthat，youadmittheselectivepowerofnature。Now，althoughIhavebeenputtingahypotheticalcase，youmustnotsupposethatIhavebeenreasoninghypothetically。Thereareplentyofdirectexperimentswhichbearoutwhatwemaycallthetheoryofnaturalselection。thereisextremelygoodauthorityforthestatementthatifyoutaketheseedofmixedvarietiesofwheatandsowit，collectingtheseednextyearandsowingitagain，atlengthyouwillfindthatoutofallyourvarietiesonlytwoorthreehavelived，orperhapsevenonlyone。Therewereoneortwovarietieswhichwerebestfittedtogeton，andtheyhavekilledouttheotherkindsinjustthesamewayandwithjustthesamecertaintyasifyouhadtakenthetroubletoremovethem。AsIhavealreadysaid，theoperationofnatureisexactlythesameastheartificialoperationofman。
Butifthisbetrueofthatsimplecase，whichIputbeforeyou，wherethereisnothingbuttherivalryofonememberofaspecieswithothers，whatmustbetheoperationofselectiveconditions，whenyourecollectasamatteroffact，thatforeveryspeciesofanimalorplanttherearefiftyorahundredspecieswhichmightall，moreorless，becomprehendedinthesameclimate，food，andstation——thateveryplanthasmultitudinousanimalswhichpreyuponit，andwhichareitsdirectopponents。andthatthesehaveotheranimalspreyinguponthem，——thateveryplanthasitsindirecthelpersinthebirdsthatscatterabroaditsseed，andtheanimalsthatmanureitwiththeirdung——Isay，whenthesethingsareconsidered，itseemsimpossiblethatanyvariationwhichmayariseinaspeciesinnatureshouldnottendinsomewayorothereithertobealittlebetterorworsethanthepreviousstock。ifitisalittlebetteritwillhaveanadvantageoverandtendtoextirpatethelatterinthiscrushandstruggle。andifitisalittleworseitwillitselfbeextirpated。
Iknownothingthatmoreappropriatelyexpressesthis，thanthephrase，thestruggleforexistence。becauseitbringsbeforeyourminds，inavividsortofway，someofthesimplestpossiblecircumstancesconnectedwithit。Whenastruggleisintensetheremustbesomewhoaresuretobetroddendown，crushed，andoverpoweredbyothers。andtherewillbesomewhojustmanagetogetthroughonlybythehelpoftheslightestaccident。IrecollectreadinganaccountofthefamousretreatoftheFrenchtroops，underNapoleon，fromMoscow。Wornout，tired，anddejected，theyatlengthcametoagreatriveroverwhichtherewasbutonebridgeforthepassageofthevastarmy。Disorganisedanddemoralisedasthatarmywas，thestrugglemustcertainlyhavebeenaterribleone——everyoneheedingonlyhimself，andcrushingthroughtheranksandtreadingdownhisfellows。Thewriterofthenarrative，whowashimselfoneofthosewhowerefortunateenoughtosucceedingettingover，andnotamongthethousandswhowereleftbehindorforcedintotheriver，ascribedhisescapetothefactthathesawstridingonwardthroughthemassagreatstrongfellow，——oneoftheFrenchCuirassiers，whohadonalargebluecloak——andhehadenoughpresenceofmindtocatchandretainaholdofthisstrongman’scloak。Hesays，Icaughtholdofhiscloak，andalthoughhesworeatmeandcutatandstruckmebyturns，andatlast，whenhefoundhecouldnotshakemeoff，felltoentreatingmetoleavegoorIshouldpreventhimfromescaping，besidesnotassistingmyself，Istillkepttightholdofhim，andwouldnotquitmygraspuntilhehadatlastdraggedmethrough。Hereyouseewasacaseofselectivesaving——ifwemaysotermit——dependingforitssuccessonthestrengthoftheclothoftheCuirassier’scloak。Itisthesameinnature。everyspecieshasitsbridgeofBeresina。ithastofightitswaythroughandstrugglewithotherspecies。andwhenwellnighoverpowered，itmaybethatthesmallestchance，somethinginitscolour，perhaps——theminutestcircumstance——willturnthescaleonewayortheother。
Supposethatbyavariationoftheblackraceithadproducedthewhitemanatanytime——youknowthattheNegroesaresaidtobelievethistohavebeenthecase，andtoimaginethatCainwasthefirstwhiteman，andthatwearehisdescendants——supposethatthishadeverhappened，andthatthefirstresidenceofthishumanbeingwasontheWestCoastofAfrica。ThereisnogreatstructuraldifferencebetweenthewhitemanandtheNegro，andyetthereissomethingsosingularlydifferentintheconstitutionofthetwo，thatthemalariasofthatcountry，whichdonothurttheblackatall，cutoffanddestroythewhite。Thenyouseetherewouldhavebeenaselectiveoperationperformed。ifthewhitemanhadriseninthatway，hewouldhavebeenselectedoutandremovedbymeansofthemalaria。Nowtherereallyisaverycuriouscaseofselectionofthissortamongpigs，anditisacaseofselectionofcolourtoo。InthewoodsofFloridathereareagreatmanypigs，anditisaverycuriousthingthattheyareallblack，everyoneofthem。
ProfessorWymanwastheresomeyearsago，andonnoticingnopigsbuttheseblackones，heaskedsomeofthepeoplehowitwasthattheyhadnowhitepigs，andthereplywasthatinthewoodsofFloridatherewasarootwhichtheycalledthePaintRoot，andthatifthewhitepigsweretoeatanyofit，ithadtheeffectofmakingtheirhoofscrack，andtheydied，butiftheblackpigseatanyofit，itdidnothurtthematall。Herewasaverysimplecaseofnaturalselection。A
skilfulbreedercouldnotmorecarefullydevelopetheblackbreedofpigs，andweedoutallthewhitepigs，thanthePaintRootdoes。
ToshowyouhowremarkablyindirectmaybesuchnaturalselectiveagenciesasIhavereferredto，IwillconcludebynoticingacasementionedbyMr。Darwin，andwhichiscertainlyoneofthemostcuriousofitskind。ItisthatoftheHumbleBee。Ithasbeennoticedthatthereareagreatmanymorehumblebeesintheneighbourhoodoftowns，thanoutintheopencountry。andtheexplanationofthematteristhis：thehumblebeesbuildnests，inwhichtheystoretheirhoneyanddepositthelarvaeandeggs。Thefieldmiceareamazinglyfondofthehoneyandlarvae。therefore，whereverthereareplentyoffieldmice，asinthecountry，thehumblebeesarekeptdown。butintheneighbourhoodoftowns，thenumberofcatswhichprowlaboutthefieldseatupthefieldmice，andofcoursethemoremicetheyeatupthelesstherearetopreyuponthelarvaeofthebees——thecatsarethereforetheINDIRECT
HELPERSofthebees！*Comingbackastepfartherwemaysaythattheoldmaidsarealsoindirectfriendsofthehumblebees，andindirectenemiesofthefieldmice，astheykeepthecatswhicheatupthelatter！Thisisanillustrationsomewhatbeneaththedignityofthesubject，perhaps，butitoccurstomeinpassing，andwithitIwillconcludethislecture。
[footnote]*Thehumblebees，ontheotherhand，aredirecthelpersofsomeplants，suchastheheartseaseandredclover，whicharefertilizedbythevisitsofthebees。andtheyareindirecthelpersofthenumerousinsectswhicharemoreorlesscompletelysupportedbytheheartseaseandredclover。
***
ACRITICALEXAMINATIONOFTHEPOSITIONOFMR。DARWIN’SWORK，ON
THEORIGINOFSPECIES，INRELATIONTOTHECOMPLETETHEORYOFTHE
CAUSESOFTHEPHENOMENAOFORGANICNATURE
INtheprecedingfivelecturesIhaveendeavouredtogiveyouanaccountofthosefacts，andofthosereasoningsfromfacts，whichformthedatauponwhichalltheoriesregardingthecausesofthephenomenaoforganicnaturemustbebased。And，althoughIhavehadfrequentoccasiontoquoteMr。Darwin——asallpersonshereafter，inspeakinguponthesesubjects，willhaveoccasiontoquotehisfamousbookontheOriginofSpecies，——youmustyetrememberthat，whereverIhavequotedhim，ithasnotbeenupontheoreticalpoints，orforstatementsinanywayconnectedwithhisparticularspeculations，butonmattersoffact，broughtforwardbyhimself，orcollectedbyhimself，andwhichappearincidentallyinhisbook。Ifaman’will’makeabook，professingtodiscussasinglequestion，anencyclopaedia，Icannothelpit。
Now，havinghadanopportunityofconsideringinthissortofwaythedifferentstatementsbearinguponalltheorieswhatsoever，Ihavetolaybeforeyou，asfairlyasIcan，whatisMr。Darwin’sviewofthematterandwhatpositionhistheorieshold，whenjudgedbytheprincipleswhichIhavepreviouslylaiddown，asdecidingourjudgmentsuponalltheoriesandhypotheses。
Ihavealreadystatedtoyouthattheinquiryrespectingthecausesofthephenomenaoforganicnatureresolvesitselfintotwoproblems——thefirstbeingthequestionoftheoriginationoflivingororganicbeings。andthesecondbeingthetotallydistinctproblemofthemodificationandperpetuationoforganicbeingswhentheyhavealreadycomeintoexistence。ThefirstquestionMr。Darwindoesnottouch。hedoesnotdealwithitatall。buthesays——giventheoriginoforganicmatter——supposingitscreationtohavealreadytakenplace，myobjectistoshowinconsequenceofwhatlawsandwhatdemonstrablepropertiesoforganicmatter，andofitsenvironments，suchstatesoforganicnatureasthosewithwhichweareacquaintedmusthavecomeabout。This，youwillobserve，isaperfectlylegitimateproposition。everypersonhasarighttodefinethelimitsoftheinquirywhichhesetsbeforehimself。
andyetitisamostsingularthingthatinallthemultifarious，and，notunfrequently，ignorantattackswhichhavebeenmadeuponthe’OriginofSpecies’，thereisnothingwhichhasbeenmorespeciouslycriticisedthanthisparticularlimitation。Ifpeoplehavenothingelsetourgeagainstthebook，theysay——Well，afterall，yousee，Mr。
Darwin’sexplanationofthe’OriginofSpecies’isnotgoodformuch，because，inthelongrun，headmitsthathedoesnotknowhoworganicmatterbegantoexist。Butifyouadmitanyspecialcreationforthefirstparticleoforganicmatteryoumayjustaswelladmititforalltherest。fivehundredorfivethousanddistinctcreationsarejustasintelligible，andjustaslittledifficulttounderstand，asone。Theanswertothesecavilsistwo-fold。Inthefirstplace，allhumaninquirymuststopsomewhere。allourknowledgeandallourinvestigationcannottakeusbeyondthelimitssetbythefiniteandrestrictedcharacterofourfaculties，ordestroytheendlessunknown，whichaccompanies，likeitsshadow，theendlessprocessionofphenomena。SofarasIcanventuretoofferanopiniononsuchamatter，thepurposeofourbeinginexistence，thehighestobjectthathumanbeingscansetbeforethemselves，isnotthepursuitofanysuchchimeraastheannihilationoftheunknown。butitissimplytheunweariedendeavourtoremoveitsboundariesalittlefurtherfromourlittlesphereofaction。
Iwonderifanyhistorianwouldforamomentadmittheobjection，thatitispreposteroustotroubleourselvesaboutthehistoryoftheRomanEmpire，becausewedonotknowanythingpositiveabouttheoriginandfirstbuildingofthecityofRome！Woulditbeafairobjectiontourge，respectingthesublimediscoveriesofaNewton，oraKepler，thosegreatphilosophers，whosediscoverieshavebeenoftheprofoundestbenefitandservicetoallmen，——tosaytothem——Afterallthatyouhavetoldusastohowtheplanetsrevolve，andhowtheyaremaintainedintheirorbits，youcannottelluswhatisthecauseoftheoriginofthesun，moon，andstars。Sowhatistheuseofwhatyouhavedone？
Yettheseobjectionswouldnotbeonewhitmorepreposterousthantheobjectionswhichhavebeenmadetothe’OriginofSpecies。’Mr。Darwin，then，hadaperfectrighttolimithisinquiryashepleased，andtheonlyquestionforus——theinquirybeingsolimited——istoascertainwhetherthemethodofhisinquiryissoundorunsound。whetherhehasobeyedthecanonswhichmustguideandgovernallinvestigation，orwhetherhehasbrokenthem。anditwasbecauseourinquirythiseveningisessentiallylimitedtothatquestion，thatIspentagooddealoftimeinaformerlecture(which，perhaps，someofyouthoughtmighthavebeenbetteremployed)，inendeavouringtoillustratethemethodandnatureofscientificinquiryingeneral。WeshallnowhavetoputinpracticetheprinciplesthatIthenlaiddown。
Istatedtoyouinsubstance，ifnotinwords，thatwherevertherearecomplexmassesofphenomenatobeinquiredinto，whethertheybephenomenaoftheaffairsofdailylife，orwhethertheybelongtothemoreabstruseanddifficultproblemslaidbeforethephilosopher，ourcourseofproceedinginunravellingthatcomplexchainofphenomenawithaviewtogetatitscause，isalwaysthesame。inallcaseswemustinventanhypothesis。wemustplacebeforeourselvessomemoreorlesslikelysuppositionrespectingthatcause。andthen，havingassumedanhypothesis，havingsupposedcauseforthephenomenainquestion，wemustendeavour，ontheonehand，todemonstrateourhypothesis，or，ontheother，toupsetandrejectitaltogether，bytestingitinthreeways。
Wemust，inthefirstplace，bepreparedtoprovethatthesupposedcausesofthephenomenaexistinnature。thattheyarewhatthelogicianscall’veracausae’——truecauses——inthenextplace，weshouldbepreparedtoshowthattheassumedcausesofthephenomenaarecompetenttoproducesuchphenomenaasthosewhichwewishtoexplainbythem。andinthelastplace，weoughttobeabletoshowthatnootherknowncausesarecompetenttoproducethosephenomena。Ifwecansucceedinsatisfyingthesethreeconditionsweshallhavedemonstratedourhypothesis。orratherIoughttosayweshallhaveproveditasfarascertaintyispossibleforus。for，afterall，thereisnooneofoursurestconvictionswhichmaynotbeupset，oratanyratemodifiedbyafurtheraccessionofknowledge。Itwasbecauseitsatisfiedtheseconditionsthatweacceptedthehypothesisastothedisappearanceofthetea-potandspoonsinthecaseIsupposedinapreviouslecture。wefoundthatourhypothesisonthatsubjectwastenableandvalid，becausethesupposedcauseexistedinnature，becauseitwascompetenttoaccountforthephenomena，andbecausenootherknowncausewascompetenttoaccountforthem。anditisuponsimilargroundsthatanyhypothesisyouchoosetonameisacceptedinscienceastenableandvalid。
WhatisMr。Darwin’shypothesis？AsIapprehendit——forIhaveputitintoashapemoreconvenientforcommonpurposesthanIcouldfind’verbatim’inhisbook——asIapprehendit，Isay，itis，thatallthephenomenaoforganicnature，pastandpresent，resultfrom，orarecausedby，theinter-actionofthosepropertiesoforganicmatter，whichwehavecalledATAVISMandVARIABILITY，withtheCONDITIONSOF
EXISTENCE。or，inotherwords，——giventheexistenceoforganicmatter，itstendencytotransmititsproperties，anditstendencyoccasionallytovary。and，lastly，giventheconditionsofexistencebywhichorganicmatterissurrounded——thattheseputtogetherarethecausesofthePresentandofthePastconditionsofORGANICNATURE。
SuchisthehypothesisasIunderstandit。NowletusseehowitwillstandthevarioustestswhichIlaiddownjustnow。Inthefirstplace，dothesesupposedcausesofthephenomenaexistinnature？Isitthefactthatinnaturethesepropertiesoforganicmatter——atavismandvariability——andthosephenomenawhichwehavecalledtheconditionsofexistence，——isittruethattheyexist？Well，ofcourse，iftheydonotexist，allthatIhavetoldyouinthelastthreeorfourlecturesmustbeincorrect，becauseIhavebeenattemptingtoprovethattheydoexist，andItakeitthatthereisabundantevidencethattheydoexist。sofar，therefore，thehypothesisdoesnotbreakdown。
Butinthenextplacecomesamuchmoredifficultinquiry：——Arethecausesindicatedcompetenttogiverisetothephenomenaoforganicnature？Isuspectthatthisisindubitabletoacertainextent。Itisdemonstrable，Ithink，asIhaveendeavouredtoshowyou，thattheyareperfectlycompetenttogiverisetoallthephenomenawhichareexhibitedbyRACESinnature。Furthermore，IbelievethattheyarequitecompetenttoaccountforallthatwemaycallpurelystructuralphenomenawhichareexhibitedbySPECIESinnature。OnthatpointalsoIhavealreadyenlargedsomewhat。Again，Ithinkthatthecausesassumedarecompetenttoaccountformostofthephysiologicalcharacteristicsofspecies，andInotonlythinkthattheyarecompetenttoaccountforthem，butIthinkthattheyaccountformanythingswhichotherwiseremainwhollyunaccountableandinexplicable，andImaysayincomprehensible。Forafullexpositionofthegroundsonwhichthisconvictionisbased，ImustreferyoutoMr。Darwin’swork。allthatIcandonowistoillustratewhatIhavesaidbytwoorthreecasestakenalmostatrandom。
Idrewyourattention，onapreviousevening，tothefactswhichareembodiedinoursystemsofClassification，whicharetheresultsoftheexaminationandcomparisonofthedifferentmembersoftheanimalkingdomonewithanother。Imentionedthatthewholeoftheanimalkingdomisdivisibleintofivesub-kingdoms。thateachofthesesub-kingdomsisagaindivisibleintoprovinces。thateachprovincemaybedividedintoclasses，andtheclassesintothesuccessivelysmallergroups，orders，families，genera，andspecies。
Now，ineachofthesegroups，theresemblanceinstructureamongthemembersofthegroupiscloserinproportionasthegroupissmaller。
Thus，amanandawormaremembersoftheanimalkingdominvirtueofcertainapparentlyslightthoughreallyfundamentalresemblanceswhichtheypresent。Butamanandafisharemembersofthesamesub-kingdom’Vertebrata’，becausetheyaremuchmorelikeoneanotherthaneitherofthemistoaworm，orasnail，oranymemberoftheothersub-kingdoms。ForsimilarreasonsmenandhorsesarearrangedasmembersofthesameClass，’Mammalia’。menandapesasmembersofthesameOrder，’Primates’。andiftherewereanyanimalsmorelikementhantheywerelikeanyoftheapes，andyetdifferentfrommeninimportantandconstantparticularsoftheirorganization，weshouldrankthemasmembersofthesameFamily，orofthesameGenus，butasofdistinctSpecies。
Thatitispossibletoarrangeallthevariedformsofanimalsintogroups，havingthissortofsingularsubordinationonetotheother，isaveryremarkablecircumstance。but，asMr。Darwinremarks，thisisaresultwhichisquitetobeexpected，iftheprincipleswhichhelaysdownbecorrect。Takethecaseoftheraceswhichareknowntobeproducedbytheoperationofatavismandvariability，andtheconditionsofexistencewhichcheckandmodifythesetendencies。TakethecaseofthepigeonsthatIbroughtbeforeyou。thereitwasshownthattheymightbeallclassedasbelongingtosomeoneoffiveprincipaldivisions，andthatwithinthesedivisionsothersubordinategroupsmightbeformed。Themembersofthesegroupsarerelatedtooneanotherinjustthesamewayasthegeneraofafamily，andthegroupsthemselvesasthefamiliesofanorder，ortheordersofaclass。whileallhavethesamesortofstructuralrelationswiththewildrock-pigeon，asthemembersofanygreatnaturalgrouphavewitharealorimaginarytypicalform。Now，weknowthatallvarietiesofpigeonsofeverykindhavearisenbyaprocessofselectivebreedingfromacommonstock，therock-pigeon。hence，yousee，thatifallspeciesofanimalshaveproceededfromsomecommonstock，thegeneralcharacteroftheirstructuralrelations，andofoursystemsofclassification，whichexpressthoserelations，wouldbejustwhatwefindthemtobe。Inotherwords，thehypotheticalcauseis，sofar，competenttoproduceeffectssimilartothoseoftherealcause。
Take，again，anothersetofveryremarkablefacts，——theexistenceofwhatarecalledrudimentaryorgans，organsforwhichwecanfindnoobvioususe，intheparticularanimaleconomyinwhichtheyarefound，andyetwhicharethere。
Sucharethesplint-likebonesinthelegofthehorse，whichIhereshowyou，andwhichcorrespondwithboneswhichbelongtocertaintoesandfingersinthehumanhandandfoot。Inthehorseyouseetheyarequiterudimentary，andbearneithertoesnorfingers。sothatthehorsehasonlyonefingerinhisfore-footandonetoeinhishindfoot。
Butitisaverycuriousthingthattheanimalscloselyalliedtothehorseshowmoretoesthanhe。astherhinoceros，forinstance：hehastheseextratoeswellformed，andanatomicalfactsshowveryclearlythatheisverycloselyrelatedtothehorseindeed。Sowemaysaythatanimals，inananatomicalsensenearlyrelatedtothehorse，havethosepartswhicharerudimentaryinhim，fullydeveloped。
Again，thesheepandthecowhavenocutting-teeth，butonlyahardpadintheupperjaw。Thatisthecommoncharacteristicofruminantsingeneral。Butthecalfhasinitsupperjawsomerudimentsofteethwhichneveraredeveloped，andneverplaythepartofteethatall。
Well，ifyougobackintime，youfindsomeoftheolder，nowextinct，alliesoftheruminantshavewell-developedteethintheirupperjaws。
andatthepresentdaythepig(whichisinstructurecloselyconnectedwithruminants)haswell-developedteethinitsupperjaw。sothathereisanotherinstanceoforganswell-developedandveryuseful，inoneanimal，representedbyrudimentaryorgans，forwhichwecandiscovernopurposewhatsoever，inanothercloselyalliedanimal。Thewhalebonewhale，again，hashornywhaleboneplatesinitsmouth，andnoteeth。
buttheyoungfoetalwhale，beforeitisborn，hasteethinitsjaws。
they，however，areneverused，andtheynevercometoanything。Butothermembersofthegrouptowhichthewhalebelongshavewell-developedteethinbothjaws。
Uponanyhypothesisofspecialcreation，factsofthiskindappeartometobeentirelyunaccountableandinexplicable，buttheyceasetobesoifyouacceptMr。Darwin’shypothesis，andseereasonforbelievingthatthewhalebonewhaleandthewhalewithteethinitsmouthbothsprangfromawhalethathadteeth，andthattheteethofthefoetalwhalearemerelyremnants——recollections，ifwemaysosay——oftheextinctwhale。Sointhecaseofthehorseandtherhinoceros：supposethatbothhavedescendedbymodificationfromsomeearlierformwhichhadthenormalnumberoftoes，andthepersistenceoftherudimentaryboneswhichnolongersupporttoesinthehorsebecomescomprehensible。
InthelanguagethatwespeakinEngland，andinthelanguageoftheGreeks，thereareidenticalverbalroots，orelementsenteringintothecompositionofwords。ThatfactremainsunintelligiblesolongaswesupposeEnglishandGreektobeindependentlycreatedtongues。butwhenitisshownthatbothlanguagesaredescendedfromoneoriginal，theSanscrit，wegiveanexplanationofthatresemblance。Inthesamewaytheexistenceofidenticalstructuralroots，ifImaysotermthem，enteringintothecompositionofwidelydifferentanimals，isstrikingevidenceinfavourofthedescentofthoseanimalsfromacommonoriginal。
Toturntoanotherkindofillustration：——Ifyouregardthewholeseriesofstratifiedrocks——thatenormousthicknessofsixtyorseventythousandfeetthatIhavementionedbefore，constitutingtheonlyrecordwehaveofamostprodigiouslapseoftime，thattimebeing，inallprobability，butafractionofthatofwhichwehavenorecord——ifyouobserveinthesesuccessivestrataofrockssuccessivegroupsofanimalsarisinganddyingout，aconstantsuccession，givingyouthesamekindofimpression，asyoutravelfromonegroupofstratatoanother，asyouwouldhaveintravellingfromonecountrytoanother——whenyoufindthisconstantsuccessionofforms，theirtracesobliteratedexcepttothemanofscience，——whenyoulookatthiswonderfulhistory，andaskwhatitmeans，itisonlyapalteringwithwordsifyouareofferedthereply，——’Theyweresocreated。’
Butif，ontheotherhand，youlookonallformsoforganizedbeingsastheresultsofthegradualmodificationofaprimitivetype，thefactsreceiveameaning，andyouseethattheseolderconditionsarethenecessarypredecessorsofthepresent。Viewedinthislightthefactsofpalaeontologyreceiveameaning——uponanyotherhypothesis，Iamunabletosee，intheslightestdegree，whatknowledgeorsignificationwearetodrawoutofthem。Again，noteasbearinguponthesamepoint，thesingularlikenesswhichobtainsbetweenthesuccessiveFaunaeandFlorae，whoseremainsarepreservedontherocks：youneverfindanygreatandenormousdifferencebetweentheimmediatelysuccessiveFaunaeandFlorae，unlessyouhavereasontobelievetherehasalsobeenagreatlapseoftimeoragreatchangeofconditions。
Theanimals，forinstance，ofthenewesttertiaryrocks，inanypartoftheworld，arealways，andwithoutexception，foundtobecloselyalliedwiththosewhichnowliveinthatpartoftheworld。Forexample，inEurope，Asia，andAfrica，thelargemammalsareatpresentrhinoceroses，hippopotamuses，elephants，lions，tigers，oxen，horses，etc……andifyouexaminethenewesttertiarydeposits，whichcontaintheanimalsandplantswhichimmediatelyprecededthosewhichnowexistinthesamecountry，youdonotfindgiganticspecimensofant-eatersandkangaroos，butyoufindrhinoceroses，elephants，lions，tigers，etc。，——ofdifferentspeciestothosenowliving，——butstilltheircloseallies。IfyouturntoSouthAmerica，where，atthepresentday，wehavegreatslothsandarmadilloesandcreaturesofthatkind，whatdoyoufindinthenewesttertiaries？Youfindthegreatsloth-likecreature，the’Megatherium’，andthegreatarmadillo，the’Glyptodon’，andsoon。AndifyougotoAustraliayoufindthesamelawholdsgood，namely，thatthatconditionoforganicnaturewhichhasprecededtheonewhichnowexists，presentsdifferencesperhapsofspecies，andofgenera，butthatthegreattypesoforganicstructurearethesameasthosewhichnowflourish。
Whatmeaninghasthisfactuponanyotherhypothesisorsuppositionthanoneofsuccessivemodification？Butifthepopulationoftheworld，inanyage，istheresultofthegradualmodificationoftheformswhichpeopleditintheprecedingage，——ifthathasbeenthecase，itisintelligibleenough。becausewemayexpectthatthecreaturethatresultsfromthemodificationofanelephantinemammalshallbesomethinglikeanelephant，andthecreaturewhichisproducedbythemodificationofanarmadillo-likemammalshallbelikeanarmadillo。
Uponthatsupposition，Isay，thefactsareintelligible。uponanyother，thatIamawareof，theyarenot。
Sofar，thefactsofpalaeontologyareconsistentwithalmostanyformofthedoctrineofprogressivemodification。theywouldnotbeabsolutelyinconsistentwiththewildspeculationsofDeMaillet，orwiththelessobjectionablehypothesisofLamarck。ButMr。Darwin’sviewshaveonepeculiarmerit。andthatis，thattheyareperfectlyconsistentwithanarrayoffactswhichareutterlyinconsistentwithandfatalto，anyotherhypothesisofprogressivemodificationwhichhasyetbeenadvanced。ItisoneremarkablepeculiarityofMr。
Darwin’shypothesisthatitinvolvesnonecessaryprogressionorincessantmodification，andthatitisperfectlyconsistentwiththepersistenceforanylengthoftimeofagivenprimitivestock，contemporaneouslywithitsmodifications。Toreturntothecaseofthedomesticbreedsofpigeons，forexample。youhavetheDove-cotpigeon，whichcloselyresemblestheRockpigeon，fromwhichtheyallstarted，existingatthesametimewiththeothers。Andifspeciesaredevelopedinthesamewayinnature，aprimitivestockanditsmodificationsmay，occasionally，allfindtheconditionsfittedfortheirexistence。andthoughtheycomeintocompetition，toacertainextent，withoneanother，thederivativespeciesmaynotnecessarilyextirpatetheprimitiveone，or’viceversa’。
NowpalaeontologyshowsusmanyfactswhichareperfectlyharmoniouswiththeseobservedeffectsoftheprocessbywhichMr。Darwinsupposesspeciestohaveoriginated，butwhichappeartometobetotallyinconsistentwithanyotherhypothesiswhichhasbeenproposed。Therearesomegroupsofanimalsandplants，inthefossilworld，whichhavebeensaidtobelongtopersistenttypes，becausetheyhavepersisted，withverylittlechangeindeed，throughaverygreatrangeoftime，whileeverythingaboutthemhaschangedlargely。Therearefamiliesoffisheswhosetypeofconstructionhaspersistedallthewayfromthecarboniferousrockrightuptothecretaceous。andotherswhichhavelastedthroughalmostthewholerangeofthesecondaryrocks，andfromtheliastotheoldertertiaries。Itissomethingstupendousthis——toconsideragenuslastingwithoutessentialmodificationsthroughallthisenormouslapseoftimewhilealmosteverythingelsewaschangedandmodified。
ThusIhavenodoubtthatMr。Darwin’shypothesiswillbefoundcompetenttoexplainthemajorityofthephenomenaexhibitedbyspeciesinnature。butinanearlierlectureIspokecautiouslywithrespecttoitspowerofexplainingallthephysiologicalpeculiaritiesofspecies。
Thereis，infact，onesetofthesepeculiaritieswhichthetheoryofselectivemodification，asitstandsatpresent，isnotwhollycompetenttoexplain，andthatisthegroupofphenomenawhichI
mentionedtoyouunderthenameofHybridism，andwhichIexplainedtoconsistinthesterilityoftheoffspringofcertainspecieswhencrossedonewithanother。Itmattersnotonewhitwhetherthissterilityisuniversal，orwhetheritexistsonlyinasinglecase。
Everyhypothesisisboundtoexplain，or，atanyrate，notbeinconsistentwith，thewholeofthefactswhichitprofessestoaccountfor。andifthereisasingleoneofthesefactswhichcanbeshowntobeinconsistentwith(Idonotmerelymeaninexplicableby，butcontraryto)thehypothesis，thehypothesisfallstotheground，——itisworthnothing。Onefactwithwhichitispositivelyinconsistentisworthasmuch，andaspowerfulinnegativingthehypothesis，asfivehundred。IfIamrightinthusdefiningtheobligationsofanhypothesis，Mr。
Darwin，inordertoplacehisviewsbeyondthereachofallpossibleassault，oughttobeabletodemonstratethepossibilityofdevelopingfromaparticularstockbyselectivebreeding，twoforms，whichshouldeitherbeunabletocrossonewithanother，orwhosecross-bredoffspringshouldbeinfertilewithoneanother。
For，yousee，ifyouhavenotdonethatyouhavenotstrictlyfulfilledalltheconditionsoftheproblem。youhavenotshownthatyoucanproduce，bythecauseassumed，allthephenomenawhichyouhaveinnature。HerearethephenomenaofHybridismstaringyouintheface，andyoucannotsay，’Ican，byselectivemodification，producethesesameresults。’Now，itisadmittedonallhandsthat，atpresent，sofarasexperimentshavegone，ithasnotbeenfoundpossibletoproducethiscompletephysiologicaldivergencebyselectivebreeding。Istatedthisveryclearlybefore，andInowrefertothepoint，because，ifitcouldbeproved，notonlythatthis’has’notbeendone，butthatit’cannot’bedone。ifitcouldbedemonstratedthatitisimpossibletobreedselectively，fromanystock，aformwhichshallnotbreedwithanother，producedfromthesamestock。andifwewereshownthatthismustbethenecessaryandinevitableresultsofallexperiments，IholdthatMr。Darwin’shypothesiswouldbeutterlyshattered。
Buthasthisbeendone？orwhatisreallythestateofthecase？Itissimplythat，sofaraswehavegoneyetwithourbreeding，wehavenotproducedfromacommonstocktwobreedswhicharenotmoreorlessfertilewithoneanother。
Idonotknowthatthereisasinglefactwhichwouldjustifyanyoneinsayingthatanydegreeofsterilityhasbeenobservedbetweenbreedsabsolutelyknowntohavebeenproducedbyselectivebreedingfromacommonstock。Ontheotherhand，Idonotknowthatthereisasinglefactwhichcanjustifyanyoneinassertingthatsuchsterilitycannotbeproducedbyproperexperimentation。Formyownpart，Iseeeveryreasontobelievethatitmay，andwillbesoproduced。For，asMr。
Darwinhasveryproperlyurged，whenweconsiderthephenomenaofsterility，wefindtheyaremostcapricious。wedonotknowwhatitisthatthesterilitydependson。Therearesomeanimalswhichwillnotbreedincaptivity。whetheritarisesfromthesimplefactoftheirbeingshutupanddeprivedoftheirliberty，ornot，wedonotknow，buttheycertainlywillnotbreed。Whatanastoundingthingthisis，tofindoneofthemostimportantofallfunctionsannihilatedbymereimprisonment！
So，again，therearecasesknownofanimalswhichhavebeenthoughtbynaturaliststobeundoubtedspecies，whichhaveyieldedperfectlyfertilehybrids。whilethereareotherspecieswhichpresentwhateverybodybelievestobevarieties*whicharemoreorlessinfertilewithoneanother。Thereareothercaseswhicharetrulyextraordinary。
thereisone，forexample，whichhasbeencarefullyexamined，——oftwokindsofsea-weed，ofwhichthemaleelementoftheone，whichwemaycallA，fertilizesthefemaleelementoftheother，B。whilethemaleelementofBwillnotfertilizethefemaleelementofA。sothat，whiletheformerexperimentseemstoshowusthattheyare’varieties’，thelatterleadstotheconvictionthattheyare’species’。
*[footnote]AndasIconceivewithverygoodreason。butifanyobjectorurgesthatwecannotprovethattheyhavebeenproducedbyartificialornaturalselection，theobjectionmustbeadmitted——ultrascepticalasitis。Butinscience，scepticismisaduty。
Whenweseehowcapriciousanduncertainthissterilityis，howunknowntheconditionsonwhichitdepends，Isaythatwehavenorighttoaffirmthatthoseconditionswillnotbebetterunderstoodbyandby，andwehavenogroundforsupposingthatwemaynotbeabletoexperimentsoastoobtainthatcrucialresultwhichImentionedjustnow。SothatthoughMr。Darwin’shypothesisdoesnotcompletelyextricateusfromthisdifficultyatpresent，wehavenottheleastrighttosayitwillnotdoso。
Thereisawidegulfbetweenthethingyoucannotexplainandthethingthatupsetsyoualtogether。Thereishardlyanyhypothesisinthisworldwhichhasnotsomefactinconnectionwithitwhichhasnotbeenexplained，butthatisaverydifferentaffairtoafactthatentirelyopposesyourhypothesis。inthiscaseallyoucansayis，thatyourhypothesisisinthesamepositionasagoodmanyothers。
Now，astothethirdtest，thattherearenoothercausescompetenttoexplainthephenomena，Iexplainedtoyouthatoneshouldbeabletosayofanhypothesis，thatnootherknowncausesthanthosesupposedbyitarecompetenttogiverisetothephenomena。Here，Ithink，Mr。
Darwin’sviewisprettystrong。IreallybelievethatthealternativeiseitherDarwinismornothing，forIdonotknowofanyrationalconceptionortheoryoftheorganicuniversewhichhasanyscientificpositionatallbesideMr。Darwin’s。Idonotknowofanypropositionthathasbeenputbeforeuswiththeintentionofexplainingthephenomenaoforganicnature，whichhasinitsfavourathousandthpartoftheevidencewhichmaybeadducedinfavourofMr。Darwin’sviews。
Whatevermaybetheobjectionstohisviews，certainlyallothersareabsolutelyoutofcourt。
TaketheLamarckianhypothesis，forexample。Lamarckwasagreatnaturalist，andtoacertainextentwenttherightwaytowork。hearguedfromwhatwasundoubtedlyatruecauseofsomeofthephenomenaoforganicnature。Hesaiditisamatterofexperiencethatananimalmaybemodifiedmoreorlessinconsequenceofitsdesiresandconsequentactions。Thus，ifamanexercisehimselfasablacksmith，hisarmswillbecomestrongandmuscular。suchorganicmodificationisaresultofthisparticularactionandexercise。Lamarckthoughtthatbyaverysimplesuppositionbasedonthistruthhecouldexplaintheoriginofthevariousanimalspecies：hesaid，forexample，thattheshort-leggedbirdswhichliveonfishhadbeenconvertedintothelong-leggedwadersbydesiringtogetthefishwithoutwettingtheirbodies，andsostretchingtheirlegsmoreandmorethroughsuccessivegenerations。IfLamarckcouldhaveshownexperimentally，thatevenracesofanimalscouldbeproducedinthisway，theremighthavebeensomegroundforhisspeculations。Buthecouldshownothingofthekind，andhishypothesishasprettywelldroppedintooblivion，asitdeservedtodo。Isaidinanearlierlecturethattherearehypothesesandhypotheses，andwhenpeopletellyouthatMr。Darwin’sstrongly-basedhypothesisisnothingbutameremodificationofLamarck’s，youwillknowwhattothinkoftheircapacityforformingajudgmentonthissubject。
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