byThomasHenryHuxley
Theinquirywhichweundertook，atourlastmeeting，intothestateofourknowledgeofthecausesofthephenomenaoforganicnature，——ofthepastandofthepresent，——resolveditselfintotwosubsidiaryinquiries：thefirstwas，whetherweknowanything，eitherhistoricallyorexperimentally，ofthemodeoforiginoflivingbeings；thesecondsubsidiaryinquirywas，whether，grantingtheorigin，weknowanythingabouttheperpetuationandmodificationsoftheformsoforganicbeings。ThereplywhichIhadtogivetothefirstquestionwasaltogethernegative，andthechiefresultofmylastlecturewas，that，neitherhistoricallynorexperimentally，doweatpresentknowanythingwhatsoeverabouttheoriginoflivingforms。Wesawthat，historically，wearenotlikelytoknowanythingaboutit，althoughwemayperhapslearnsomethingexperimentally；butthatatpresentweareanenormousdistancefromthegoalIindicated。
Inow，then，takeupthenextquestion，Whatdoweknowofthereproduction，theperpetuation，andthemodificationsoftheformsoflivingbeings，supposingthatwehaveputthequestionastotheiroriginationononeside，andhaveassumedthatatpresentthecausesoftheiroriginationarebeyondus，andthatweknownothingaboutthem？
Uponthisquestionthestateofourknowledgeisextremelydifferent；
itisexceedinglylarge，and，ifnotcomplete，ourexperienceiscertainlymostextensive。Itwouldbeimpossibletolayitallbeforeyou，andthemostIcando，orneeddoto—night，istotakeuptheprincipalpointsandputthembeforeyouwithsuchprominenceasmaysubservethepurposesofourpresentargument。
Themethodoftheperpetuationoforganicbeingsisoftwokinds，——theasexualandthesexual。Inthefirsttheperpetuationtakesplacefromandbyaparticularactofanindividualorganism，whichsometimesmaynotbeclassedasbelongingtoanysexatall。Inthesecondcase，itisinconsequenceofthemutualactionandinteractionofcertainportionsoftheorganismsofusuallytwodistinctindividuals，——themaleandthefemale。Thecasesofasexualperpetuationarebynomeanssocommonasthecasesofsexualperpetuation；andtheyarebynomeanssocommonintheanimalasinthevegetableworld。Youareallprobablyfamiliarwiththefact，asamatterofexperience，thatyoucanpropagateplantsbymeansofwhatarecalled\"cuttings；\"forexample，thatbytakingacuttingfromageraniumplant，andrearingitproperly，bysupplyingitwithlightandwarmthandnourishmentfromtheearth，itgrowsupandtakestheformofitsparent，havingallthepropertiesandpeculiaritiesoftheoriginalplant。
Sometimesthisprocess，whichthegardenerperformsartificially，takesplacenaturally；thatistosay，alittlebulb，orportionoftheplant，detachesitself，dropsoff，andbecomescapableofgrowingasaseparatething。Thatisthecasewithmanybulbousplants，whichthrowoffinthiswaysecondarybulbs，whicharelodgedinthegroundandbecomedevelopedintoplants。Thisisanasexualprocess，andfromitresultstherepetitionorreproductionoftheformoftheoriginalbeingfromwhichthebulbproceeds。
Amonganimalsthesamethingtakesplace。Amongthelowerformsofanimallife，theinfusorialanimalculaewehavealreadyspokenofthrowoffcertainportions，orbreakthemselvesupinvariousdirections，sometimestransverselyorsometimeslongitudinally；ortheymaygiveoffbuds，whichdetachthemselvesanddevelopintotheirproperforms。
Thereisthecommonfresh—waterPolype，forinstance，whichmultipliesitselfinthisway。Justinthesamewayasthegardenerisabletomultiplyandreproducethepeculiaritiesandcharactersofparticularplantsbymeansofcuttings，socanthephysiologicalexperimentalist——aswasshownbytheAbbeTrembleymanyyearsago——socanhedothesamethingwithmanyofthelowerformsofanimallife。
M。deTrembleyshowedthatyoucouldtakeapolypeandcutitintotwo，orfour，ormanypieces，mutilatingitinalldirections，andthepieceswouldstillgrowupandreproducecompletelytheoriginalformoftheanimal。Theseareallcasesofasexualmultiplication，andthereareotherinstances，andstillmoreextraordinaryones，inwhichthisprocesstakesplacenaturally，inamorehidden，amorereconditekindofway。Youareallofyoufamiliarwiththoselittlegreeninsects，the’Aphis’orblight，asitiscalled。Theselittleanimals，duringaveryconsiderablepartoftheirexistence，multiplythemselvesbymeansofakindofinternalbudding，thebudsbeingdevelopedintoessentiallyasexualanimals，whichareneithermalenorfemale；theybecomeconvertedintoyoung’Aphides’，whichrepeattheprocess，andtheiroffspringafterthem，andsoonagain；youmaygoonfornineorten，oreventwentyormoresuccessions；andthereisnoverygoodreasontosayhowsoonitmightterminate，orhowlongitmightnotgooniftheproperconditionsofwarmthandnourishmentwerekeptup。
Sexualreproductionisquiteadistinctmatter。Here，inallthesecases，whatisrequiredisthedetachmentoftwoportionsoftheparentalorganisms，whichportionsweknowastheeggandthespermatozoon。Inplantsitistheovuleandthepollen—grain，asinthefloweringplants，ortheovuleandtheantherozooid，asintheflowerless。Amongallformsofanimallife，thespermatozoaproceedfromthemalesex，andtheeggistheproductofthefemale。Now，whatisremarkableaboutthismodeofreproductionisthis，thattheeggbyitself，orthespermatozoabythemselves，areunabletoassumetheparentalform；butiftheybebroughtintocontactwithoneanother，theeffectofthemixtureoforganicsubstancesproceedingfromtwosourcesappearstoconferanaltogethernewvigourtothemixedproduct。
Thisprocessisbroughtabout，asweallknow，bythesexualintercourseofthetwosexes，andiscalledtheactofimpregnation。
Theresultofthisactonthepartofthemaleandfemaleis，thattheformationofanewbeingissetupintheovuleoregg；thisovuleoreggsoonbeginstobedividedandsubdivided，andtobefashionedintovariouscomplexorganisms，andeventuallytodevelopintotheformofoneofitsparents，asIexplainedinthefirstlecture。Thesearetheprocessesbywhichtheperpetuationoforganicbeingsissecured。Whythereshouldbethetwomodes——whythisre—invigorationshouldberequiredonthepartofthefemaleelementwedonotknow；butitismostassuredlythefact，anditispresumable，that，howeverlongtheprocessofasexualmultiplicationcouldbecontinued，Isaythereisgoodreasontobelievethatitwouldcometoanendifanewcommencementwerenotobtainedbyaconjunctionofthetwosexualelements。
Thatcharacterwhichiscommontothesetwodistinctprocessesisthis，that，whetherweconsiderthereproduction，orperpetuation，ormodificationoforganicbeingsastheytakeplaceasexually，orastheymaytakeplacesexually，——ineithercase，Isay，theoffspringhasaconstanttendencytoassume，speakinggenerally，thecharacteroftheparent。AsIsaidjustnow，ifyoutakeaslipofaplant，andtenditwithcare，itwilleventuallygrowupanddevelopintoaplantlikethatfromwhichithadsprung；andthistendencyissostrongthat，asgardenersknow，thismodeofmultiplyingbymeansofcuttingsistheonlysecuremodeofpropagatingverymanyvarietiesofplants；thepeculiarityoftheprimitivestockseemstobebetterpreservedifyoupropagateitbymeansofaslipthanifyouresorttothesexualmode。
Again，inexperimentsupontheloweranimals，suchasthepolype，towhichIhavereferred，itismostextraordinarythat，althoughcutupintovariouspieces，eachparticularpiecewillgrowupintotheformoftheprimitivestock；thehead，ifseparated，willreproducethebodyandthetail；andifyoucutoffthetail，youwillfindthatthatwillreproducethebodyandalltherestofthemembers，withoutinanywaydeviatingfromtheplanoftheorganismfromwhichtheseportionshavebeendetached。Andsofardoesthisgo，thatsomeexperimentalistshavecarefullyexaminedthelowerordersofanimals，——amongthemtheAbbeSpallanzani，whomadeanumberofexperimentsuponsnailsandsalamanders，——andhavefoundthattheymightmutilatethemtoanincredibleextent；thatyoumightcutoffthejaworthegreaterpartofthehead，orthelegorthetail，andrepeattheexperimentseveraltimes，perhaps，cuttingoffthesamememberagainandagain；andyeteachofthosetypeswouldbereproducedaccordingtotheprimitivetype：naturemakingnomistake，neverputtingonafreshkindofleg，orhead，ortail，butalwaystendingtorepeatandtoreturntotheprimitivetype。
Itisthesameinsexualreproduction：itisamatterofperfectlycommonexperience，thatthetendencyonthepartoftheoffspringalwaysis，speakingbroadly，toreproducetheformoftheparents。Theproverbhasitthatthethistledoesnotbringforthgrapes；so，amongourselves，thereisalwaysalikeness，moreorlessmarkedanddistinct，betweenchildrenandtheirparents。Thatisamatteroffamiliarandordinaryobservation。Wenoticethesamethingoccurringinthecasesofthedomesticanimals——dogs，forinstance，andtheiroffspring。Inallthesecasesofpropagationandperpetuation，thereseemstobeatendencyintheoffspringtotakethecharactersoftheparentalorganisms。Tothattendencyaspecialnameisgiven——itiscalled’Atavism’，itexpressesthistendencytoreverttotheancestraltype，andcomesfromtheLatinword’atavus’，ancestor。
Well，this’Atavism’whichIshallspeakof，is，asIsaidbefore，oneofthemostmarkedandstrikingtendenciesoforganicbeings；but，sidebysidewiththishereditarytendencythereisanequallydistinctandremarkabletendencytovariation。Thetendencytoreproducetheoriginalstockhas，asitwere，itslimits，andsidebysidewithitthereisatendencytovaryincertaindirections，asifthereweretwoopposingpowersworkingupontheorganicbeing，onetendingtotakeitinastraightline，andtheothertendingtomakeitdivergefromthatstraightline，firsttoonesideandthentotheother。
Sothatyouseethesetwotendenciesneednotpreciselycontradictoneanother，astheultimateresultmaynotalwaysbeveryremotefromwhatwouldhavebeenthecaseifthelinehadbeenquitestraight。
Thistendencytovariationislessmarkedinthatmodeofpropagationwhichtakesplaceasexually；itisinthatmodethattheminorcharactersofanimalandvegetablestructuresaremostcompletelypreserved。Still，itwillhappensometimes，thatthegardener，whenhehasplantedacuttingofsomefavouriteplant，willfind，contrarytohisexpectation，thattheslipgrowsupalittledifferentfromtheprimitivestock——thatitproducesflowersofadifferentcolourormake，orsomedeviationinonewayoranother。Thisiswhatiscalledthe’sporting’ofplants。
Inanimalsthephenomenaofasexualpropagationaresoobscure，thatatpresentwecannotbesaidtoknowmuchaboutthem；butifweturntothatmodeofperpetuationwhichresultsfromthesexualprocess，thenwefindvariationaperfectlyconstantoccurrence，toacertainextent；
and，indeed，Ithinkthatacertainamountofvariationfromtheprimitivestockisthenecessaryresultofthemethodofsexualpropagationitself；for，inasmuchasthethingpropagatedproceedsfromtwoorganismsofdifferentsexesanddifferentmakesandtemperaments，andastheoffspringistobeeitherofonesexortheother，itisquiteclearthatitcannotbeanexactdiagonalofthetwo，oritwouldbeofnosexatall；itcannotbeanexactintermediateformbetweenthatofeachofitsparents——itmustdeviatetoonesideortheother。
Youdonotfindthatthemalefollowstheprecisetypeofthemaleparent，nordoesthefemalealwaysinherittheprecisecharacteristicsofthemother，——thereisalwaysaproportionofthefemalecharacterinthemaleoffspring，andofthemalecharacterinthefemaleoffspring。
Thatmustbequiteplaintoallofyouwhohavelookedatallattentivelyonyourownchildrenorthoseofyourneighbours；youwillhavenoticedhowveryoftenitmayhappenthatthesonshallexhibitthematernaltypeofcharacter，orthedaughterpossessthecharacteristicsofthefather’sfamily。Thereareallsortsofintermixturesandintermediateconditionsbetweenthetwo，wherecomplexion，orbeauty，orfiftyotherdifferentpeculiaritiesbelongingtoeithersideofthehouse，arereproducedinothermembersofthesamefamily。Indeed，itissometimestoberemarkedinthiskindofvariation，thatthevarietybelongs，strictlyspeaking，toneitheroftheimmediateparents；youwillseeachildinafamilywhoisnotlikeeitheritsfatheroritsmother；butsomeoldpersonwhoknewitsgrandfatherorgrandmother，or，itmaybe，anuncle，or，perhaps，evenamoredistantrelative，willseeagreatsimilaritybetweenthechildandoneofthese。Inthiswayitconstantlyhappensthatthecharacteristicofsomepreviousmemberofthefamilycomesoutandisreproducedandrecognisedinthemostunexpectedmanner。
Butapartfromthatmatterofgeneralexperience，therearesomecaseswhichputthatcuriousmixtureinaveryclearlight。YouareawarethattheoffspringoftheAssandtheHorse，orratherofthehe—AssandtheMare，iswhatiscalledaMule；and，ontheotherhand，theoffspringoftheStallionandtheshe—Assiswhatiscalleda’Hinny’。
Ineversawonemyself；buttheyhavebeenverycarefullystudied。Now，thecuriousthingisthis，thatalthoughyouhavethesameelementsintheexperimentineachcase，theoffspringisentirelydifferentincharacter，accordingasthemaleinfluencecomesfromtheAssortheHorse。WheretheAssisthemale，asinthecaseoftheMule，youfindthattheheadislikethatoftheAss，thattheearsarelong，thetailistuftedattheend，thefeetaresmall，andthevoiceisanunmistakablebray；theseareallpointsofsimilaritytotheAss；but，ontheotherhand，thebarrelofthebodyandthecutoftheneckaremuchmorelikethoseoftheMare。Then，ifyoulookattheHinny，——theresultoftheunionoftheStallionandtheshe—Ass，thenyoufinditistheHorsethathasthepredominance；thattheheadismorelikethatoftheHorse，theearsareshorter，thelegscoarser，andthetypeisaltogetheraltered；whilethevoice，insteadofbeingabray，istheordinaryneighoftheHorse。Here，yousee，isamostcuriousthing：
youtakeexactlythesameelements，AssandHorse，butyoucombinethesexesinadifferentmanner，andtheresultismodifiedaccordingly。
Youhaveinthiscase，however，aresultwhichisnotgeneralanduniversal——thereisusuallyanimportantpreponderance，butnotalwaysonthesameside。
Here，then，isoneintelligible，and，perhaps，necessarycauseofvariation：thefact，thattherearetwosexessharingintheproductionoftheoffspring，andthatthesharetakenbyeachisdifferentandvariable，notonlyforeachcombination，butalsofordifferentmembersofthesamefamily。
Secondly，thereisavariation，toacertainextent——though，inallprobability，theinfluenceofthiscausehasbeenverymuchexaggerated——butthereisnodoubtthatvariationisproduced，toacertainextent，bywhatarecommonlyknownasexternalconditions，——suchastemperature，food，warmth，andmoisture。Inthelongrun，everyvariationdepends，insomesense，uponexternalconditions，seeingthateverythinghasacauseofitsown。Iusetheterm\"externalconditions\"nowinthesenseinwhichitisordinarilyemployed：certainitis，thatexternalconditionshaveadefiniteeffect。Youmaytakeaplantwhichhassingleflowers，andbydealingwiththesoil，andnourishment，andsoon，youmayby—and—byconvertsingleflowersintodoubleflowers，andmakethornsshootoutintobranches。Youmaythickenormakevariousmodificationsintheshapeofthefruit。Inanimals，too，youmayproduceanalogouschangesinthisway，asinthecaseofthatdeepbronzecolourwhichpersonsrarelyloseafterhavingpassedanylengthoftimeintropicalcountries。Youmayalsoalterthedevelopmentofthemusclesverymuch，bydintoftraining；alltheworldknowsthatexercisehasagreateffectinthisway；wealwaysexpecttofindthearmofablacksmithhardandwiry，andpossessingalargedevelopmentofthebrachialmuscles。Nodoubttraining，whichisoneoftheformsofexternalconditions，convertswhatareoriginallyonlyinstructions，teachings，intohabits，or，inotherwords，intoorganizations，toagreatextent；butthissecondcauseofvariationcannotbeconsideredtobebyanymeansalargeone。ThethirdcausethatIhavetomention，however，isaveryextensiveone。Itisonethat，forwantofabettername，hasbeencalled\"spontaneousvariation；\"whichmeansthatwhenwedonotknowanythingaboutthecauseofphenomena，wecallitspontaneous。Intheorderlychainofcausesandeffectsinthisworld，thereareveryfewthingsofwhichitcanbesaidwithtruththattheyarespontaneous。Certainlynotinthesephysicalmatters，——inthesethereisnothingofthekind，——everythingdependsonpreviousconditions。Butwhenwecannottracethecauseofphenomena，wecallthemspontaneous。
Ofthesevariations，multitudinousastheyare，butlittleisknownwithperfectaccuracy。Iwillmentiontoyousometwoorthreecases，becausetheyareveryremarkableinthemselves，andalsobecauseI
shallwanttousethemafterwards。Reaumur，afamousFrenchnaturalist，agreatmanyyearsago，inanessaywhichhewroteupontheartofhatchingchickens，——whichwasindeedaverycuriousessay，——hadoccasiontospeakofvariationsandmonstrosities。Oneveryremarkablecasehadcomeunderhisnoticeofavariationintheformofahumanmember，inthepersonofaMaltese，ofthenameofGratioKelleia，whowasbornwithsixfingersuponeachhand，andthelikenumberoftoestoeachofhisfeet。Thatwasacaseofspontaneousvariation。Nobodyknowswhyhewasbornwiththatnumberoffingersandtoes，andaswedon’tknow，wecallitacaseof\"spontaneous\"variation。Thereisanotherremarkablecasealso。Iselectthese，becausetheyhappentohavebeenobservedandnotedverycarefullyatthetime。Itfrequentlyhappensthatavariationoccurs，butthepersonswhonoticeitdonottakeanycareinnotingdowntheparticulars，untilatlength，wheninquiriescometobemade，theexactcircumstancesareforgotten；andhence，multitudinousasmaybesuch\"spontaneous\"variations，itisexceedinglydifficulttogetattheoriginofthem。
Thesecondcaseisoneofwhichyoumayfindthewholedetailsinthe\"PhilosophicalTransactions\"fortheyear1813，inapapercommunicatedbyColonelHumphreytothePresidentoftheRoyalSociety，——\"OnanewVarietyintheBreedofSheep，\"givinganaccountofaveryremarkablebreedofsheep，whichatonetimewaswellknowninthenorthernstatesofAmerica，andwhichwentbythenameoftheAnconortheOtterbreedofsheep。Intheyear1791，therewasafarmerofthenameofSethWrightinMassachusetts，whohadaflockofsheep，consistingofaramand，Ithink，ofsometwelveorthirteenewes。Ofthisflockofewes，oneatthebreeding—timeborealambwhichwasverysingularlyformed；
ithadaverylongbody，veryshortlegs，andthoselegswerebowed！I
willtellyouby—and—byhowthissingularvariationinthebreedofsheepcametobenoted，andtohavetheprominencethatitnowhas。Forthepresent，Imentiononlythesetwocases；buttheextentofvariationinthebreedofanimalsisperfectlyobvioustoanyonewhohasstudiednaturalhistorywithordinaryattention，ortoanypersonwhocomparesanimalswithothersofthesamekind。Itisstrictlytruethatthereareneveranytwospecimenswhichareexactlyalike；howeversimilar，theywillalwaysdifferinsomecertainparticular。
NowletusgobacktoAtavism，——tothehereditarytendencyIspokeof。
Whatwillcomeofavariationwhenyoubreedfromit，whenAtavismcomes，ifImaysayso，tointersectvariation？ThetwocasesofwhichIhavementionedthehistory，giveamostexcellentillustrationofwhatoccurs。GratioKelleia，theMaltese，marriedwhenhewastwenty—twoyearsofage，and，asIsupposetherewerenosix—fingeredladiesinMalta，hemarriedanordinaryfive—fingeredperson。Theresultofthatmarriagewasfourchildren；thefirst，whowaschristenedSalvator，hadsixfingersandsixtoes，likehisfather；thesecondwasGeorge，whohadfivefingersandtoes，butoneofthemwasdeformed，showingatendencytovariation；thethirdwasAndre；hehadfivefingersandfivetoes，quiteperfect；thefourthwasagirl，Marie；shehadfivefingersandfivetoes，butherthumbsweredeformed，showingatendencytowardthesixth。
Thesechildrengrewup，andwhentheycametoadultyears，theyallmarried，andofcourseithappenedthattheyallmarriedfive—fingeredandfive—toedpersons。Nowletusseewhatweretheresults。Salvatorhadfourchildren；theyweretwoboys，agirl，andanotherboy；thefirsttwoboysandthegirlweresix—fingeredandsix—toedliketheirgrandfather；thefourthboyhadonlyfivefingersandfivetoes。Georgehadonlyfourchildren；thereweretwogirlswithsixfingersandsixtoes；therewasonegirlwithsixfingersandfivetoesontherightside，andfivefingersandfivetoesontheleftside，sothatshewashalfandhalf。Thelast，aboy，hadfivefingersandfivetoes。Thethird，Andre，youwillrecollect，wasperfectlywell—formed，andhehadmanychildrenwhosehandsandfeetwereallregularlydeveloped。Marie，thelast，who，ofcourse，marriedamanwhohadonlyfivefingers，hadfourchildren；thefirst，aboy，wasbornwithsixtoes，buttheotherthreewerenormal。
Nowobservewhatveryextraordinaryphenomenaarepresentedhere。Youhaveanaccidentalvariationarisingfromwhatyoumaycallamonstrosity；youhavethatmonstrositytendencyorvariationdilutedinthefirstinstancebyanadmixturewithafemaleofnormalconstruction，andyouwouldnaturallyexpectthat，intheresultsofsuchanunion，themonstrosity，ifrepeated，wouldbeinequalproportionwiththenormaltype；thatistosay，thatthechildrenwouldbehalfandhalf，sometakingthepeculiarityofthefather，andtheothersbeingofthepurelynormaltypeofthemother；butyouseewehaveagreatpreponderanceoftheabnormaltype。Well，thiscomestobemixedoncemorewiththepure，thenormaltype，andtheabnormalisagainproducedinlargeproportion，notwithstandingtheseconddilution。Nowwhatwouldhavehappenediftheseabnormaltypeshadintermarriedwitheachother；thatistosay，supposethetwoboysofSalvatorhadtakenitintotheirheadstomarrytheirfirstcousins，thetwofirstgirlsofGeorge，theiruncle？Youwillrememberthatthesearealloftheabnormaltypeoftheirgrandfather。Theresultwouldprobablyhavebeen，thattheiroffspringwouldhavebeenineverycaseafurtherdevelopmentofthatabnormaltype。Youseeitisonlyinthefourth，inthepersonofMarie，thatthetendency，whenitappearsbutslightlyinthesecondgeneration，iswashedoutinthethird，whiletheprogenyofAndre，whoescapedinthefirstinstance，escapealtogether。
Wehaveinthiscaseagoodexampleofnature’stendencytotheperpetuationofavariation。Hereitiscertainlyavariationwhichcarriedwithitnouseorbenefit；andyetyouseethetendencytoperpetuationmaybesostrong，that，notwithstandingagreatadmixtureofpureblood，thevarietycontinuesitselfuptothethirdgeneration，whichislargelymarkedwithit。Inthiscase，asIhavesaid，therewasnomeansofthesecondgenerationintermarryingwithanybutfive—fingeredpersons，andthequestionnaturallysuggestsitself，Whatwouldhavebeentheresultofsuchmarriage？Reaumurnarratesthiscaseonlyasfarasthethirdgeneration。Certainlyitwouldhavebeenanexceedinglycuriousthingifwecouldhavetracedthismatteranyfurther；hadthecousinsintermarried，asix—fingeredvarietyofthehumanracemighthavebeensetup。
Toshowyouthatthissuppositionisbynomeansanunreasonableone，letmenowpointoutwhattookplaceinthecaseofSethWright’ssheep，whereithappenedtobeamatterofmomenttohimtoobtainabreedorraiseaflockofsheeplikethataccidentalvarietythatI
havedescribed——andIwilltellyouwhy。InthatpartofMassachusettswhereSethWrightwasliving，thefieldswereseparatedbyfences，andthesheep，whichwereveryactiveandrobust，wouldroamabroad，andwithoutmuchdifficultyjumpoverthesefencesintootherpeople’sfarms。Asamatterofcourse，thisexuberantactivityonthepartofthesheepconstantlygaverisetoallsortsofquarrels，bickerings，andcontentionsamongthefarmersoftheneighbourhood；soitoccurredtoSethWright，whowas，likehissuccessors，moreorless’cute，thatifhecouldgetastockofsheeplikethosewiththebandylegs，theywouldnotbeabletojumpoverthefencessoreadily，andheacteduponthatidea。Hekilledhisoldram，andassoonastheyoungonearrivedatmaturity，hebredaltogetherfromit。TheresultwasevenmorestrikingthaninthehumanexperimentwhichImentionedjustnow。
ColonelHumphreystestifiesthatitalwayshappenedthattheoffspringwereeitherpureAnconsorpureordinarysheep；thatinnocasewasthereanymixingoftheAnconswiththeothers。Inconsequenceofthis，inthecourseofaveryfewyears，thefarmerwasabletogetaveryconsiderableflockofthisvariety，andalargenumberofthemwerespreadthroughoutMassachusetts。Mostunfortunately，however——I
supposeitwasbecausetheyweresocommon——nobodytookenoughnoticeofthemtopreservetheirskeletons；andalthoughColonelHumphreysstatesthathesentaskeletontothePresidentoftheRoyalSocietyatthesametimethatheforwardedhispaper，Iamafraidthatthevarietyhasentirelydisappeared；forashorttimeafterthesesheephadbecomeprevalentinthatdistrict，theMerinosheepwereintroduced；andastheirwoolwasmuchmorevaluable，andastheywereaquietraceofsheep，andshowednotendencytotrespassorjumpoverfences，theOtterbreedofsheep，thewoolofwhichwasinferiortothatoftheMerino，wasgraduallyallowedtodieout。
Youseethatthesefactsillustrateperfectlywellwhatmaybedoneifyoutakecaretobreedfromstocksthataresimilartoeachother。
Afterhavinggotavariation，if，bycrossingavariationwiththeoriginalstock，youmultiplythatvariation，andthentakecaretokeepthatvariationdistinctfromtheoriginalstock，andmakethembreedtogether，——thenyoumayalmostcertainlyproducearacewhosetendencytocontinuethevariationisexceedinglystrong。
Thisiswhatiscalled\"selection\"；anditisbyexactlythesameprocessasthatbywhichSethWrightbredhisAnconsheep，thatourbreedsofcattle，dogs，andfowls，areobtained。Therearesomepossibilitiesofexception，butstill，speakingbroadly，Imaysaythatthisisthewayinwhichallourvariedracesofdomesticanimalshavearisen；andyoumustunderstandthatitisnotonepeculiarityoronecharacteristicaloneinwhichanimalsmayvary。Thereisnotasinglepeculiarityorcharacteristicofanykind，bodilyormental，inwhichoffspringmaynotvarytoacertainextentfromtheparentandotheranimals。
Amongourselvesthisiswellknown。Thesimplestphysicalpeculiarityismostlyreproduced。Iknowacaseofamanwhosewifehasthelobeofoneofherearsalittleflattened。Anordinaryobservermightscarcelynoticeit，andyeteveryoneofherchildrenhasanapproximationtothesamepeculiaritytosomeextent。Ifyoulookattheotherextreme，too，thegravestdiseases，suchasgout，scrofula，andconsumption，maybehandeddownwithjustthesamecertaintyandpersistenceaswenoticedintheperpetuationofthebandylegsoftheAnconsheep。
However，thesefactsarebestillustratedinanimals，andtheextentofthevariation，asiswellknown，isveryremarkableindogs。Forexample，therearesomedogsverymuchsmallerthanothers；indeed，thevariationissoenormousthatprobablythesmallestdogwouldbeaboutthesizeoftheheadofthelargest；thereareverygreatvariationsinthestructuralformsnotonlyoftheskeletonbutalsointheshapeoftheskull，andintheproportionsofthefaceandthedispositionoftheteeth。
ThePointer，theRetriever，Bulldog，andtheTerrier，differverygreatly，andyetthereiseveryreasontobelievethateveryoneoftheseraceshasarisenfromthesamesource，——thatallthemostimportantraceshavearisenbythisselectivebreedingfromaccidentalvariation。
Astillmorestrikingcaseofwhatmaybedonebyselectivebreeding，anditisabettercase，becausethereisnochanceofthatpartialinfusionoferrortowhichIalluded，hasbeenstudiedverycarefullybyMr。Darwin，——thecaseofthedomesticpigeons。Idaresaytheremaybesomeamongyouwhomaybepigeon’fanciers’，andIwishyoutounderstandthatinapproachingthesubject，Iwouldspeakwithallhumilityandhesitation，asIregrettosaythatIamnotapigeonfancier。Iknowitisagreatartandmystery，andathinguponwhichamanmustnotspeaklightly；butIshallendeavour，asfarasmyunderstandinggoes，togiveyouasummaryofthepublishedandunpublishedinformationwhichIhavegainedfromMr。Darwin。
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—called\"homing\"birdshavingenormousflyingpowers；*while，ontheotherhand，thelittleTumblerissocalledbecauseofitsextraordinaryfacultyofturningheadoverheelsintheair，insteadofpursuingadirectcourse。And，lastly，thedispositionsandvoicesofthebirdsmayvary。Thusthecaseofthepigeonsshowsyouthatthereishardlyasingleparticular，——whetherofinstinct，orhabit，orbonystructure，orofplumage，——ofeithertheinternaleconomyortheexternalshape，inwhichsomevariationorchangemaynottakeplace，which，byselectivebreeding，maybecomeperpetuated，andformthefoundationof，andgiveriseto，anewrace。
[footnote：The\"Carrier，\"IlearnfromMr。Tegetmeier，doesnot’carry’；ahigh—bredbirdofthisbreedbeingbutapoorflier。Thebirdswhichflylongdistances，andcomehome，——\"homing\"birds，——andareconsequentlyusedascarriers，arenot\"carriers\"inthefancysense。]
Ifyoucarryinyourmind’seyethesefourvarietiesofpigeons，youwillbearwithyouasgoodanotionasyoucanhave，perhaps，oftheenormousextenttowhichadeviationfromaprimitivetypemaybecarriedbymeansofthisprocessofselectivebreeding。