byThomasH。HuxleyINtheprecedingfivelecturesIhaveendeavouredtogiveyouanaccountofthosefacts，andofthosereasoningsfromfacts，whichformthedatauponwhichalltheoriesregardingthecausesofthephenomenaoforganicnaturemustbebased。And，althoughIhavehadfrequentoccasiontoquoteMr。Darwin——asallpersonshereafter，inspeakinguponthesesubjects，willhaveoccasiontoquotehisfamousbookonthe\"OriginofSpecies，\"——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；sothatthehorsehasonlyone\"finger\"inhisfore—footandone\"toe\"inhishindfoot。
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，hashorny\"whalebone\"platesinitsmouth，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，whichhavebeensaidtobelongto\"persistenttypes，\"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。
ButyoumustrecollectthatwhenIsayIthinkitiseitherMr。Darwin’shypothesisornothing；thateitherwemusttakehisview，orlookuponthewholeoforganicnatureasanenigma，themeaningofwhichiswhollyhiddenfromus；youmustunderstandthatImeanthatIacceptitprovisionally，inexactlythesamewayasIacceptanyotherhypothesis。
Menofsciencedonotpledgethemselvestocreeds；theyareboundbyarticlesofnosort；thereisnotasinglebeliefthatitisnotaboundendutywiththemtoholdwithalighthandandtopartwithitcheerfully，themomentitisreallyprovedtobecontrarytoanyfact，greatorsmall。Andif，incourseoftimeIseegoodreasonsforsuchaproceeding，Ishallhavenohesitationincomingbeforeyou，andpointingoutanychangeinmyopinionwithoutfindingtheslightestoccasiontoblushforsodoing。SoIsaythatweacceptthisviewasweacceptanyother，solongasitwillhelpus，andwefeelboundtoretainitonlysolongasitwillserveourgreatpurpose——theimprovementofMan’sestateandthewideningofhisknowledge。Themomentthis，oranyotherconception，ceasestobeusefulforthesepurposes，awaywithittothefourwinds；wecarenotwhatbecomesofit！
Buttosaytruth，althoughithasbeenmybusinesstoattendcloselytothecontroversiesrousedbythepublicationofMr。Darwin’sbook，I
thinkthatnotoneoftheenormousmassofobjectionsandobstacleswhichhavebeenraisedisofanyverygreatvalue，exceptthatsterilitycasewhichIbroughtbeforeyoujustnow。Alltherestaremisunderstandingsofsomesort，arisingeitherfromprejudice，orwantofknowledge，orstillmorefromwantofpatienceandcareinreadingthework。
Foryoumustrecollectthatitisnotabooktobereadwithasmucheaseasitspleasantstylemayleadyoutoimagine。Youspinthroughitasifitwereanovelthefirsttimeyoureadit，andthinkyouknowallaboutit；thesecondtimeyoureadityouthinkyouknowratherlessaboutit；andthethirdtime，youareamazedtofindhowlittleyouhavereallyapprehendeditsvastscopeandobjects。IcanpositivelysaythatInevertakeitupwithoutfindinginitsomenewview，orlight，orsuggestionthatIhavenotnoticedbefore。Thatisthebestcharacteristicofathoroughandprofoundbook；andIbelievethisfeatureofthe’OriginofSpecies’explainswhysomanypersonshaveventuredtopassjudgmentandcriticismsuponitwhicharebynomeansworththepapertheyarewrittenon。
BeforeconcludingtheselecturesthereisonepointtowhichImustadvert，——though，asMr。Darwinhassaidnothingaboutmaninhisbook，itconcernsmyselfratherthanhim；——forIhavestronglymaintainedonsundryoccasionsthatifMr。Darwin’sviewsaresound，theyapplyasmuchtomanastothelowermammals，seeingthatitisperfectlydemonstrablethatthestructuraldifferenceswhichseparatemanfromtheapesarenotgreaterthanthosewhichseparatesomeapesfromothers。Therecannotbetheslightestdoubtintheworldthattheargumentwhichappliestotheimprovementofthehorsefromanearlierstock，orofapefromape，appliestotheimprovementofmanfromsomesimplerandlowerstockthanman。Thereisnotasinglefaculty——functionalorstructural，moral，intellectual，orinstinctive，——thereisnofacultywhateverthatisnotcapableofimprovement；thereisnofacultywhatsoeverwhichdoesnotdependuponstructure，andasstructuretendstovary，itiscapableofbeingimproved。
Well，Ihavetakenagooddealofpainsatvarioustimestoprovethis，andIhaveendeavouredtomeettheobjectionsofthosewhomaintain，thatthestructuraldifferencesbetweenmanandtheloweranimalsareofsovastacharacterandenormousextent，thatevenifMr。Darwin’sviewsarecorrect，youcannotimaginethisparticularmodificationtotakeplace。Itis，infact，easymattertoprovethat，sofarasstructureisconcerned，mandifferstonogreaterextentfromtheanimalswhichareimmediatelybelowhimthanthesedofromothermembersofthesameorder。Upontheotherhand，thereisnoonewhoestimatesmorehighlythanIdothedignityofhumannature，andthewidthofthegulfinintellectualandmoralmatters，whichliesbetweenmanandthewholeofthelowercreation。
ButIfindthisveryargumentbroughtforwardvehementlybysome。\"Yousaythatmanhasproceededfromamodificationofsomeloweranimal，andyoutakepainstoprovethatthestructuraldifferenceswhicharesaidtoexistinhisbraindonotexistatall，andyouteachthatallfunctions，intellectual，moral，andothers，aretheexpressionortheresult，inthelongrun，ofstructures，andofthemolecularforceswhichtheyexert。\"ItisquitetruethatIdoso。
\"Well，but，\"Iamtoldatonce，somewhattriumphantly，\"yousayinthesamebreaththatthereisagreatmoralandintellectualchasmbetweenmanandtheloweranimals。Howisthispossiblewhenyoudeclarethatmoralandintellectualcharacteristicsdependonstructure，andyettellusthatthereisnosuchgulfbetweenthestructureofmanandthatoftheloweranimals？\"
Ithinkthatobjectionisbaseduponamisconceptionoftherealrelationswhichexistbetweenstructureandfunction，betweenmechanismandwork。Functionistheexpressionofmolecularforcesandarrangementsnodoubt；but，doesitfollowfromthis，thatvariationinfunctionsodependsuponvariationinstructurethattheformerisalwaysexactlyproportionedtothelatter？Ifthereisnosuchrelation，ifthevariationinfunctionwhichfollowsonavariationinstructure，maybeenormouslygreaterthanthevariationofthestructure，then，yousee，theobjectionfallstotheground。
Takeacoupleofwatches——madebythesamemaker，andascompletelyalikeaspossible；setthemuponthetable，andthefunctionofeach——whichisitsrateofgoing——willbeperformedinthesamemanner，andyoushallbeabletodistinguishnodifferencebetweenthem；butletmetakeapairofpincers，andifmyhandissteadyenoughtodoit，letmejustlightlycrushtogetherthebearingsofthebalance—wheel，orforcetoaslightlydifferentangletheteethoftheescapementofoneofthem，andofcourseyouknowtheimmediateresultwillbethatthewatch，sotreated，fromthatmomentwillceasetogo。Butwhatproportionistherebetweenthestructuralalterationandthefunctionalresult？Isitnotperfectlyobviousthatthealterationisoftheminutestkind，yetthatslightasitis，ithasproducedaninfinitedifferenceintheperformanceofthefunctionsofthesetwoinstruments？
Well，now，applythattothepresentquestion。Whatisitthatconstitutesandmakesmanwhatheis？Whatisitbuthispoweroflanguage——thatlanguagegivinghimthemeansofrecordinghisexperience——makingeverygenerationsomewhatwiserthanitspredecessor，——moreinaccordancewiththeestablishedorderoftheuniverse？
Whatisitbutthispowerofspeech，ofrecordingexperience，whichenablesmentobemen——lookingbeforeandafterand，insomedimsense，understandingtheworkingofthiswondrousuniverse——andwhichdistinguishesmanfromthewholeofthebruteworld？Isaythatthisfunctionaldifferenceisvast，unfathomable，andtrulyinfiniteinitsconsequences；andIsayatthesametime，thatitmaydependuponstructuraldifferenceswhichshallbeabsolutelyinappreciabletouswithourpresentmeansofinvestigation。Whatisthisveryspeechthatwearetalkingabout？Iamspeakingtoyouatthismoment，butifyouweretoalter，intheminutestdegree，theproportionofthenervousforcesnowactiveinthetwonerveswhichsupplythemusclesofmyglottis，Ishouldbecomesuddenlydumb。Thevoiceisproducedonlysolongasthevocalchordsareparallel；andtheseareparallelonlysolongascertainmusclescontractwithexactequality；andthatagaindependsontheequalityofactionofthosetwonervesIspokeof。Sothatachangeoftheminutestkindinthestructureofoneofthesenerves，orinthestructureofthepartinwhichitoriginates，orofthesupplyofbloodtothatpart，orofoneofthemusclestowhichitisdistributed，mightrenderallofusdumb。Butaraceofdumbmen，deprivedofallcommunicationwiththosewhocouldspeak，wouldbelittleindeedremovedfromthebrutes。Andthemoralandintellectualdifferencebetweenthemandourselveswouldbepracticallyinfinite，thoughthenaturalistshouldnotbeabletofindasingleshadowofevenspecificstructuraldifference。
Butletmedismissthisquestionnow，and，inconclusion，letmesaythatyoumaygoawaywithitasmymatureconviction，thatMr。Darwin’sworkisthegreatestcontributionwhichhasbeenmadetobiologicalsciencesincethepublicationofthe’RegneAnimal’ofCuvier，andsincethatofthe’HistoryofDevelopment’ofVonBaer。Ibelievethatifyoustripitofitstheoreticalpartitstillremainsoneofthegreatestencyclopaediasofbiologicaldoctrinethatanyonemaneverbroughtforth；andIbelievethat，ifyoutakeitastheembodimentofanhypothesis，itisdestinedtobetheguideofbiologicalandpsychologicalspeculationforthenextthreeorfourgenerations。