Ifanimalsandplantshadneverbeendomesticated，andwildonesalonehadbeenobserved，weshouldprobablyneverhaveheardthesaying，that"likebegetslike。"Thepropositionwouldhavebeenasself—evidentasthatallthebudsonthesametreearealike，thoughneitherpropositionisstrictlytrue。For，ashasoftenbeenremarked，probablynotwoindividualsareidenticallythesame。Allwildanimalsrecogniseeachother，whichshowsthatthereissomedifferencebetweenthem;andwhentheeyeiswellpractised，theshepherdknowseachsheep，andmancandistinguishafellow—
manoutofmillionsonmillionsofothermen。Someauthorshavegonesofarastomaintainthattheproductionofslightdifferencesisasmuchanecessaryfunctionofthepowersofgeneration，astheproductionofoffspringliketheirparents。Thisview，asweshallseeinafuturechapter，isnottheoreticallyprobable，thoughpracticallyitholdsgood。
Thesayingthat"likebegetslike"has，infact，arisenfromtheperfectconfidencefeltbybreeders，thatasuperiororinferioranimalwillgenerallyreproduceitskind;butthisverysuperiorityorinferiorityshowsthattheindividualinquestionhasdepartedslightlyfromitstype。
Thewholesubjectofinheritanceiswonderful。Whenanewcharacterarises，whateveritsnaturemaybe，itgenerallytendstobeinherited，atleastinatemporaryandsometimesinamostpersistentmanner。Whatcanbemorewonderfulthanthatsometriflingpeculiarity，notprimordiallyattachedtothespecies，shouldbetransmittedthroughthemaleorfemalesexualcells，whicharesominuteasnottobevisibletothenakedeye，andafterwardsthroughtheincessantchangesofalongcourseofdevelopment，undergoneeitherinthewomborintheegg，andultimatelyappearintheoffspringwhenmature，orevenwhenquiteold，asinthecaseofcertaindiseases？Oragain，whatcanbemorewonderfulthanthewell—ascertainedfactthattheminuteovuleofagoodmilkingcowwillproduceamale，fromwhomacell，inunionwithanovule，willproduceafemale，andshe，whenmature，willhavelargemammaryglands，yieldinganabundantsupplyofmilk，andevenmilkofaparticularquality？Nevertheless，therealsubjectofsurpriseis，asSirH。Hollandhaswellremarked（12/1。’MedicalNotesandReflections’3rdedition1855page267。）notthatacharactershouldbeinherited，butthatanyshouldeverfailtobeinherited。Inafuturechapter，devotedtoanhypothesiswhichIhavetermedpangenesis，anattemptwillbemadetoshowthemeansbywhichcharactersofallkindsaretransmittedfromgenerationtogeneration。
Somewriters（12/2。Mr。Buckleinhis’HistoryofCivilisation’expressesdoubtsonthesubject，owingtothewantofstatistics。SeealsoMr。Bowen，ProfessorofMoralPhilosophy，in’Proc。AmericanAcad。ofSciences’volume5page102。），whohavenotattendedtonaturalhistory，haveattemptedtoshowthattheforceofinheritancehasbeenmuchexaggerated。Thebreedersofanimalswouldsmileatsuchsimplicity;andiftheycondescendedtomakeanyanswer，mightaskwhatwouldbethechanceofwinningaprizeiftwoinferioranimalswerepairedtogether？Theymightaskwhetherthehalf—wildArabswereledbytheoreticalnotionstokeeppedigreesoftheirhorses？
WhyhavepedigreesbeenscrupulouslykeptandpublishedoftheShorthorncattle，andmorerecentlyoftheHerefordbreed？Isitanillusionthattheserecentlyimprovedanimalssafelytransmittheirexcellentqualitiesevenwhencrossedwithotherbreeds？havetheShorthorns，withoutgoodreason，beenpurchasedatimmensepricesandexportedtoalmosteveryquarteroftheglobe，athousandguineashavingbeengivenforabull？Withgreyhoundspedigreeshavelikewisebeenkept，andthenamesofsuchdogs，asSnowball，Major，etc。，areaswellknowntocoursersasthoseofEclipseandHerodontheturf。EvenwiththeGamecock，pedigreesoffamousstrainswereformerlykept，andextendedbackforacentury。Withpigs，theYorkshireandCumberlandbreeders"preserveandprintpedigrees;"andtoshowhowsuchhighly—bredanimalsarevalued，ImaymentionthatMr。Brown，whowonallthefirstprizesforsmallbreedsatBirminghamin1850，soldayoungsowandboarofhisbreedtoLordDuciefor43guineas;thesowalonewasafterwardssoldtotheRev。F。Thursbyfor65guineas;whowrites，"Shepaidmeverywell，havingsoldherproducefor300pounds，andhavingnowfourbreedingsowsfromher。"（12/3。ForgreyhoundsseeLow’DomesticAnimalsoftheBritishIslands’1845page721。Forgame—fowlssee’ThePoultryBook’byMr。Tegetmeier1866page123。ForpigsseeMr。Sidney’seditionof’YouattonthePig’1860pages11，22。）Hardcashpaiddown，overandoveragain，isanexcellenttestofinheritedsuperiority。Infact，thewholeartofbreeding，fromwhichsuchgreatresultshavebeenattainedduringthepresentcentury，dependsontheinheritanceofeachsmalldetailofstructure。Butinheritanceisnotcertain;forifitwere，thebreeder’sart（12/4。’TheStudFarm’byCecilpage39。）wouldbereducedtoacertainty，andtherewouldbelittlescopeleftforthatwonderfulskillandperseveranceshownbythemenwhohaveleftanenduringmonumentoftheirsuccessinthepresentstateofourdomesticatedanimals。
Itishardlypossible，withinamoderatecompass，toimpressonthemindofthosewhohavenotattendedtothesubject，thefullconvictionoftheforceofinheritancewhichisslowlyacquiredbyrearinganimals，bystudyingthemanytreatiseswhichhavebeenpublishedonthevariousdomesticanimals，andbyconversingwithbreeders。Iwillselectafewfactsofthekind，which，asfarasIcanjudge，havemostinfluencedmyownmind。Withmanandthedomesticanimals，certainpeculiaritieshaveappearedinanindividual，atrareintervals，oronlyonceortwiceinthehistoryoftheworld，buthavereappearedinseveralofthechildrenandgrandchildren。ThusLambert，"theporcupine—man，"whoseskinwasthicklycoveredwithwartyprojections，whichwereperiodicallymoulted，hadallhissixchildrenandtwograndsonssimilarlyaffected。（12/5。
’PhilosophicalTransactions’1755page23。Ihaveseenonlysecond—handaccountsofthetwograndsons。Mr。Sedgwick，inapapertowhichIshallhereafteroftenrefer，statesthatFOURgenerationswereaffected，andineachthemalesalone。）Thefaceandbodybeingcoveredwithlonghair，accompaniedbydeficientteeth（towhichIshallhereafterrefer），occurredinthreesuccessivegenerationsinaSiamesefamily;butthiscaseisnotunique，asawoman（12/6。BarbaraVanBeck，figured，asIaminformedbytheRev。W。D。Fox，inWoodburn’s’GalleryofRarePortraits’1816volume2）
withacompletelyhairyfacewhowasexhibitedinLondonin1663，andanotherinstancehasrecentlyoccurred。ColonelHallam（12/7。’Proc。
Zoolog。Soc。’1833page16。）hasdescribedaraceoftwo—leggedpigs，"thehinderextremitiesbeingentirelywanting;"andthisdeficiencywastransmittedthroughthreegenerations。Infact，allracespresentinganyremarkablepeculiarity，suchassolid—hoofedswine，Mauchampsheep，niatacattle，etc。，areinstancesofthelong—continuedinheritanceofraredeviationsofstructure。
Whenwereflectthatcertainextraordinarypeculiaritieshavethusappearedinasingleindividualoutofmanymillions，allexposedinthesamecountrytothesamegeneralconditionsoflife，and，again，thatthesameextraordinarypeculiarityhassometimesappearedinindividualslivingunderwidelydifferentconditionsoflife，wearedriventoconcludethatsuchpeculiaritiesarenotdirectlyduetotheactionofthesurroundingconditions，buttounknownlawsactingontheorganisationorconstitutionoftheindividual;——thattheirproductionstandsinhardlycloserrelationtotheconditionsoflifethandoeslifeitself。Ifthisbeso，andtheoccurrenceofthesameunusualcharacterinthechildandparentcannotbeattributedtobothhavingbeenexposedtothesameunusualconditions，thenthefollowingproblemisworthconsideration，asshowingthattheresultcannotbedue，assomeauthorshavesupposed，tomerecoincidence，butmustbeconsequentonthemembersofthesamefamilyinheritingsomethingincommonintheirconstitution。Letitbeassumedthat，inalargepopulation，aparticularaffectionoccursonanaverageinoneoutofamillion，sothattheapriorichancethatanindividualtakenatrandomwillbesoaffectedisonlyoneinamillion。Letthepopulationconsistofsixtymillions，composed，wewillassume，oftenmillionfamilies，eachcontainingsixmembers。Onthesedata，ProfessorStokeshascalculatedformethattheoddswillbenolessthan8333millionsto1thatinthetenmillionfamiliestherewillnotbeevenasinglefamilyinwhichoneparentandtwochildrenwillbeaffectedbythepeculiarityinquestion。Butnumerousinstancescouldbegiven，inwhichseveralchildrenhavebeenaffectedbythesamerarepeculiaritywithoneoftheirparents;andinthiscase，moreespeciallyifthegrandchildrenbeincludedinthecalculation，theoddsagainstmerecoincidencebecomesomethingprodigious，almostbeyondenumeration。
Insomerespectstheevidenceofinheritanceismorestrikingwhenweconsiderthereappearanceoftriflingpeculiarities。Dr。HodgkinformerlytoldmeofanEnglishfamilyinwhich，formanygenerations，somemembershadasinglelockdifferentlycolouredfromtherestofthehair。IknewanIrishgentleman，who，ontherightsideofhishead，hadasmallwhitelockinthemidstofhisdarkhair:heassuredmethathisgrandmotherhadasimilarlockonthesameside，andhismotherontheoppositeside。Butitissuperfluoustogiveinstances;everyshadeofexpression，whichmayoftenbeseenalikeinparentsandchildren，tellsthesamestory。Onwhatacuriouscombinationofcorporealstructure，mentalcharacter，andtraining，handwritingdepends！yeteveryonemusthavenotedtheoccasionalclosesimilarityofthehandwritinginfatherandson，althoughthefatherhadnottaughthisson。Agreatcollectorofautographsassuredmethatinhiscollectiontherewereseveralsignaturesoffatherandsonhardlydistinguishableexceptbytheirdates。Hofacker，inGermany，remarksontheinheritanceofhandwriting;andithasevenbeenassertedthatEnglishboyswhentaughttowriteinFrancenaturallyclingtotheirEnglishmannerofwriting;butforsoextraordinaryastatementmoreevidenceisrequisite。
（12/8。Hofacker’UeberdieEigenschaften’etc。1828s。34。WithrespecttoFrance，ReportbyParisetin’ComptesRendus’1847page592。）Gait，gestures，voice，andgeneralbearingareallinherited，astheillustriousHunterandSirA。Carlislehaveinsisted。（12/9。HunterasquotedinHarlan’s’Med。Researches’page530。SirA。Carlisle’Phil。Transact。’1814
page94。）Myfathercommunicatedtomesomestrikinginstances，inoneofwhichamandiedduringtheearlyinfancyofhisson，andmyfather，whodidnotseethissonuntilgrownupandoutofhealth，declaredthatitseemedtohimasifhisoldfriendhadrisenfromthegrave，withallhishighlypeculiarhabitsandmanners。Peculiarmannerspassintotricks，andseveralinstancescouldbegivenoftheirinheritance;asinthecase，oftenquoted，ofthefatherwhogenerallysleptonhisback，withhisrightlegcrossedovertheleft，andwhosedaughter，whilstaninfantinthecradle，followedexactlythesamehabit，thoughanattemptwasmadetocureher。（12/10。GiroudeBuzareingues’DelaGeneration’page282。Ihavegivenananalogouscaseinmybookon’TheExpressionoftheEmotions。’）I
willgiveoneinstancewhichhasfallenundermyownobservation，andwhichiscuriousfrombeingatrickassociatedwithapeculiarstateofmind，namely，pleasureableemotion。Aboyhadthesingularhabit，whenpleased，ofrapidlymovinghisfingersparalleltoeachother，and，whenmuchexcited，ofraisingbothhands，withthefingersstillmoving，tothesidesofhisfaceonalevelwiththeeyes;whenthisboywasalmostanoldman，hecouldstillhardlyresistthistrickwhenmuchpleased，butfromitsabsurdityconcealedit。Hehadeightchildren。Ofthese，agirl，whenpleased，attheageoffourandahalfyears，movedherfingersinexactlythesameway，andwhatisstillodder，whenmuchexcited，sheraisedbothherhands，withherfingersstillmoving，tothesidesofherface，inexactlythesamemannerasherfatherhaddone，andsometimesevenstillcontinuedtodosowhenalone。Ineverheardofanyone，exceptingthisonemanandhislittledaughter，whohadthisstrangehabit;andcertainlyimitationwasinthisinstanceoutofthequestion。
Somewritershavedoubtedwhetherthosecomplexmentalattributes，onwhichgeniusandtalentdepend，areinherited，evenwhenbothparentsarethusendowed。ButhewhowillstudyMr。Galton’sableworkon’HereditaryGenius’willhaveitsdoubtsallayed。
Unfortunatelyitmattersnot，asfarasinheritanceisconcerned，howinjuriousaqualityorstructuremaybeifcompatiblewithlife。Noonecanreadthemanytreatises（12/11。TheworkswhichIhavereadandfoundmostusefulareDr。ProsperLucas’sgreatwork’Traitedel’HerediteNaturelle’
1847;Mr。W。Sedgwickin’BritishandForeignMedico—Chirurg。Review’AprilandJuly1861andAprilandJuly1863:Dr。GarrodonGoutisquotedinthesearticles。SirHenryHolland’MedicalNotesandReflections’3rdedition1855。Piorry’Del’HereditedanslesMaladies’1840。Adams’A
PhilosophicalTreatiseonHereditaryPeculiarities’2ndedition1815。Essayon’HereditaryDiseases’byDr。J。Steinan1843。SeePagetin’MedicalTimes’1857page192ontheInheritanceofCancer;Dr。Gouldin’Proc。ofAmericanAcad。ofSciences’November8，1853givesacuriouscaseofhereditarybleedinginfourgenerations。Harlan’MedicalResearches’page593。）onhereditarydiseaseanddoubtthis。Theancientswerestronglyofthisopinion，or，asRanchinexpressesit，OmnesGraeci，Arabes，etLatiniineoconsentiunt。Alongcataloguecouldbegivenofallsortsofinheritedmalformationsandofpredispositiontovariousdiseases。Withgout，fiftypercentofthecasesobservedinhospitalpracticeare，accordingtoDr。Garrod，inherited，andagreaterpercentageinprivatepractice。Everyoneknowshowofteninsanityrunsinfamilies，andsomeofthecasesgivenbyMr。Sedgwickareawful，——asofasurgeon，whosebrother，father，andfourpaternaluncleswereallinsane，thelatterdyingbysuicide;ofaJew，whosefather，mother，andsixbrothersandsisterswereallmad;andinsomeothercasesseveralmembersofthesamefamily，duringthreeorfoursuccessivegenerations，havecommittedsuicide。Strikinginstanceshavebeenrecordedofepilepsy，consumption，asthma，stoneinthebladder，cancer，profusebleedingfromtheslightestinjuries，ofthemothernotgivingmilk，andofbadparturitionbeinginherited。InthislatterrespectImaymentionanoddcasegivenbyagoodobserver（12/12。
MarshallquotedbyYouattinhisworkon’Cattle’page284。），inwhichthefaultlayintheoffspring，andnotinthemother:inapartofYorkshirethefarmerscontinuedtoselectcattlewithlargehind—quarters，untiltheymadeastraincalled"Dutch—buttocked，"and"themonstroussizeofthebuttocksofthecalfwasfrequentlyfataltothecow，andnumbersofcowswereannuallylostincalving。"
[Insteadofgivingnumerousdetailsonvariousinheritedmalformationsanddiseases，Iwillconfinemyselftooneorgan，thatwhichisthemostcomplex，delicate，andprobablybest—knowninthehumanframe，namely，theeye，withitsaccessoryparts。（12/13。Almostanyotherorganmighthavebeenselected。ForinstanceMr。J。Tomes’SystemofDentalSurgery’2ndedition1873page114givesmanyinstanceswithteeth，andothershavebeencommunicatedtome。）Tobeginwiththelatter:Ihavereceivedanaccountofafamilyinwhichoneparentandthechildrenareaffectedbydroopingeyelids，insopeculiaramanner，thattheycannotseewithoutthrowingtheirheadsbackwards。Mr。Wade，ofWakefield，hasgivenmeananalogouscaseofamanwhohadnothiseyelidsthusaffectedatbirth，norowedtheirstate，asfaraswasknown，toinheritance，buttheybegantodroopwhilsthewasaninfantaftersufferingfromfits，andhehastransmittedtheaffectiontotwooutofhisthreechildren，aswasevident...完整阅读请扫描二维码下载丁香书院APP免费看：