Theconditionsfavourabletoselectionbymanare，——theclosestattentiontoeverycharacter，——long—continuedperseverance，——facilityinmatchingorseparatinganimals，——andespeciallyalargenumberbeingkept，sothattheinferiorindividualsmaybefreelyrejectedordestroyed，andthebetteronespreserved。Whenmanyarekepttherewillalsobeagreaterchanceoftheoccurrenceofwell—markeddeviationsofstructure。Lengthoftimeisall—
important;foraseachcharacter，inordertobecomestronglypronounced，hastobeaugmentedbytheselectionofsuccessivevariationsofthesamekind，thiscanbeeffectedonlyduringalongseriesofgenerations。Lengthoftimewill，also，allowanynewfeaturetobecomefixedbythecontinuedrejectionofthoseindividualswhichrevertorvary，andbythepreservationofthosewhichstillinheritthenewcharacter。Hence，althoughsomefewanimalshavevariedrapidlyincertainrespectsundernewconditionsoflife，asdogsinIndiaandsheepintheWestIndies，yetalltheanimalsandplantswhichhaveproducedstronglymarkedracesweredomesticatedatanextremelyremoteepoch，oftenbeforethedawnofhistory。Asaconsequenceofthis，norecordhasbeenpreservedoftheoriginofourchiefdomesticbreeds。Evenatthepresentdaynewstrainsorsub—breedsareformedsoslowlythattheirfirstappearancepassesunnoticed。Amanattendstosomeparticularcharacter，ormerelymatcheshisanimalswithunusualcare，andafteratimeaslightdifferenceisperceivedbyhisneighbours;——thedifferencegoesonbeingaugmentedbyunconsciousandmethodicalselection，untilatlastanewsub—breedisformed，receivesalocalname，andspreads;butbythistimeitshistoryisalmostforgotten。Whenthenewbreedhasspreadwidely，itgivesrisetonewstrainsandsub—breeds，andthebestofthesesucceedandspread，supplantingotherandolderbreeds;andsoalwaysonwardsinthemarchofimprovement。
Whenawell—markedbreedhasoncebeenestablished，ifnotsupplantedbystillfurtherimprovedsub—breeds，andifnotexposedtogreatlychangedconditionsoflifeinducingfurthervariabilityorreversiontolong—lostcharacters，itmayapparentlylastforanenormousperiod。Wemayinferthatthisisthecasefromthehighantiquityofcertainraces;butsomecautionisnecessaryonthishead，forthesamevariationmayappearindependentlyafterlongintervalsoftime，orindistantplaces。Wemaysafelyassumethatthishasoccurredwiththeturnspit—dog，ofwhichoneisfiguredontheancientEgyptianmonuments——withthesolid—hoofedswine（28/11。Godron’Del’Espece’
tome11859page368。）mentionedbyAristotle——withfive—toedfowlsdescribedbyColumella——andcertainlywiththenectarine。ThedogsrepresentedontheEgyptianmonuments，about2000B。C。，showusthatsomeofthechiefbreedsthenexisted，butitisextremelydoubtfulwhetheranyareidenticallythesamewithourpresentbreeds。AgreatmastiffsculpturedonanAssyriantomb，640B。C。，issaidtobethesamewiththedogstillimportedfromThibetintothesameregion。ThetruegreyhoundexistedduringtheRomanclassicalperiod。
Comingdowntoalaterperiod，wehaveseenthat，thoughmostofthechiefbreedsofthepigeonexistedbetweentwoandthreecenturiesago，theyhavenotallretainedexactlythesamecharactertothepresentday;butthishasoccurredincertaincasesinwhichnoimprovementwasdesired，forinstance，inthecaseoftheSpotandIndianground—tumbler。
DeCandolle（28/12。’GeographieBotan。’1855page989。）hasfullydiscussedtheantiquityofvariousracesofplants;hestatesthattheblackseededpoppywasknowninthetimeofHomer，thewhite—seededsesamumbytheancientEgyptians，andalmondswithsweetandbitterkernelsbytheHebrews;butitdoesnotseemimprobablethatsomeofthesevarietiesmayhavebeenlostandreappeared。Onevarietyofbarleyandapparentlyoneofwheat，bothofwhichwerecultivatedatanimmenselyremoteperiodbytheLake—inhabitantsofSwitzerland，stillexist。Itissaid（28/13。Pickering’RacesofMan’1850
page318。）that"specimensofasmallvarietyofgourdwhichisstillcommoninthemarketofLimawereexhumedfromanancientcemeteryinPeru。"DeCandolleremarksthat，inthebooksanddrawingsofthesixteenthcentury，theprincipalracesofthecabbage，turnip，andgourdcanberecognised:thismighthavebeenexpectedatsolateaperiod，butwhetheranyoftheseplantsareabsolutelyidenticalwithourpresentsub—varietiesisnotcertain。Itis，however，saidthattheBrusselssprout，avarietywhichinsomeplacesisliabletodegeneration，hasremainedgenuineformorethanfourcenturiesinthedistrictwhereitisbelievedtohaveoriginated。（28/14。’JournalofaHorticulturalTour’byaDeputationoftheCaledonianHist。Soc。1823page293。）
Inaccordancewiththeviewsmaintainedbymeinthisworkandelsewhere，notonlythevariousdomesticraces，butthemostdistinctgeneraandorderswithinthesamegreatclass——forinstance，mammals，birds，reptiles，andfishes——areallthedescendantsofonecommonprogenitor，andwemustadmitthatthewholevastamountofdifferencebetweentheseformshasprimarilyarisenfromsimplevariability。Toconsiderthesubjectunderthispointofviewisenoughtostrikeonedumbwithamazement。Butouramazementoughttobelessenedwhenwereflectthatbeingsalmostinfiniteinnumber，duringanalmostinfinitelapseoftime，haveoftenhadtheirwholeorganisationrenderedinsomedegreeplastic，andthateachslightmodificationofstructurewhichwasinanywaybeneficialunderexcessivelycomplexconditionsoflifehasbeenpreserved，whilsteachwhichwasinanywayinjurioushasbeenrigorouslydestroyed。Andthelong—continuedaccumulationofbeneficialvariationswillinfalliblyhaveledtostructuresasdiversified，asbeautifullyadaptedforvariouspurposesandasexcellentlyco—ordinated，asweseeintheanimalsandplantsaroundus。HenceIhavespokenofselectionastheparamountpower，whetherappliedbymantotheformationofdomesticbreeds，orbynaturetotheproductionofspecies。Imayrecurtothemetaphorgiveninaformerchapter:ifanarchitectweretorearanobleandcommodiousedifice，withouttheuseofcutstone，byselectingfromthefragmentsatthebaseofaprecipicewedge—formedstonesforhisarches，elongatedstonesforhislintels，andflatstonesforhisroof，weshouldadmirehisskillandregardhimastheparamountpower。Now，thefragmentsofstone，thoughindispensabletothearchitect，beartotheedificebuiltbyhimthesamerelationwhichthefluctuatingvariationsoforganicbeingsbeartothevariedandadmirablestructuresultimatelyacquiredbytheirmodifieddescendants。
Someauthorshavedeclaredthatnaturalselectionexplainsnothing，unlesstheprecisecauseofeachslightindividualdifferencebemadeclear。Ifitwereexplainedtoasavageutterlyignorantoftheartofbuilding，howtheedificehadbeenraisedstoneuponstone，andwhywedge—formedfragmentswereusedforthearches，flatstonesfortheroof，etc。;andiftheuseofeachpartandofthewholebuildingwerepointedout，itwouldbeunreasonableifhedeclaredthatnothinghadbeenmadecleartohim，becausetheprecisecauseoftheshapeofeachfragmentcouldnotbetold。Butthisisanearlyparallelcasewiththeobjectionthatselectionexplainsnothing，becauseweknownotthecauseofeachindividualdifferenceinthestructureofeachbeing。
Theshapeofthefragmentsofstoneatthebaseofourprecipicemaybecalledaccidental，butthisisnotstrictlycorrect;fortheshapeofeachdependsonalongsequenceofevents，allobeyingnaturallaws;onthenatureoftherock，onthelinesofdepositionorcleavage，ontheformofthemountain，whichdependsonitsupheavalandsubsequentdenudation，andlastlyonthestormorearthquakewhichthrowsdownthefragments。Butinregardtotheusetowhichthefragmentsmaybeput，theirshapemaybestrictlysaidtobeaccidental。Andhereweareledtofaceagreatdifficulty，inalludingtowhichIamawarethatIamtravellingbeyondmyproperprovince。AnomniscientCreatormusthaveforeseeneveryconsequencewhichresultsfromthelawsimposedbyHim。ButcanitbereasonablymaintainedthattheCreatorintentionallyordered，ifweusethewordsinanyordinarysense，thatcertainfragmentsofrockshouldassumecertainshapessothatthebuildermighterecthisedifice？Ifthevariouslawswhichhavedeterminedtheshapeofeachfragmentwerenotpredeterminedforthebuilder’ssake，canitbemaintainedwithanygreaterprobabilitythatHespeciallyordainedforthesakeofthebreedereachoftheinnumerablevariationsinourdomesticanimalsandplants;——manyofthesevariationsbeingofnoservicetoman，andnotbeneficial，farmoreofteninjurious，tothecreaturesthemselves？DidHeordainthatthecropandtail—feathersofthepigeonshouldvaryinorderthatthefanciermightmakehisgrotesquepouterandfantailbreeds？DidHecausetheframeandmentalqualitiesofthedogtovaryinorderthatabreedmightbeformedofindomitableferocity，withjawsfittedtopindownthebullforman’sbrutalsport？Butifwegiveuptheprincipleinonecase，——ifwedonotadmitthatthevariationsoftheprimevaldogwereintentionallyguidedinorderthatthegreyhound，forinstance，thatperfectimageofsymmetryandvigour，mightbeformed，——noshadowofreasoncanbeassignedforthebeliefthatvariations，alikeinnatureandtheresultofthesamegenerallaws，whichhavebeenthegroundworkthroughnaturalselectionoftheformationofthemostperfectlyadaptedanimalsintheworld，manincluded，wereintentionallyandspeciallyguided。Howevermuchwemaywishit，wecanhardlyfollowProfessorAsaGrayinhisbelief"thatvariationhasbeenledalongcertainbeneficiallines，"likeastream"alongdefiniteandusefullinesofirrigation。"Ifweassumethateachparticularvariationwasfromthebeginningofalltimepreordained，thenthatplasticityoforganisation，whichleadstomanyinjuriousdeviationsofstructure，aswellastheredundantpowerofreproductionwhichinevitablyleadstoastruggleforexistence，and，asaconsequence，tothenaturalselectionorsurvivalofthefittest，mustappeartoussuperfluouslawsofnature。Ontheotherhand，anomnipotentandomniscientCreatorordainseverythingandforeseeseverything。Thuswearebroughtfacetofacewithadifficultyasinsolubleasisthatoffreewillandpredestination。
INDEX。
ABBASPACHA，afancieroffantailedpigeons。
ABBEY，Mr。，ongrafting。
—onmignonette。
ABBOTT，Mr。Keith，onthePersiantumblerpigeon。
ABBREVIATIONofthefacialbones。
ABORTIONoforgans。
ABSORPTIONofminorityincrossedraces。
ABUTILON，grafthybridisationof。
ACCLIMATISATION，ofmaize。
ACERBI，onthefertilityofdomesticanimalsinLapland。
Achatinella。
Achilleamillefolium，budvariationin。
Aconitumnapellus，rootsof，innocuousincoldclimates。
Acoruscalamus，sterilityof。
ACOSTA，onfowlsinSouthAmericaatitsdiscovery。
Acropera，numberofseedsin。
ADAM，M。，originofCytisusadami。
ADAM，W。，onconsanguineousmarriages。
ADAMS，onhereditarydiseases。
ADVANCEMENTinscaleoforganisation。
Aegilopstriticoides，observationsofFabreandGodronon。
—increasingfertilityofhybridsof，withwheat。
Aesculuspavia，tendencyof，tobecomedouble。
Aethusacynapium。
AFFINITY，sexualelective。
AFRICA，whitebullfrom。
—feralcattlein。
—food—plantsofsavagesof。
—South，diversityofbreedsofcattlein。
—West，changeinfleeceofsheepin。
Agavevivipara，seedingof，inpoorsoil。
AGE，changesintrees，dependenton。
—asbearingonpangenesis。
AGOUTI，fertilityof，incaptivity。
AGRICULTURE，antiquityof。
Agrostis，seedsof，usedasfood。
AGUARA。
AINSWORTH，Mr。，onthechangeinthehairofanimalsatAngora。
AKBARKHAN，hisfondnessforpigeons，Alaudaarvensis。
ALBIN，on"GoldenHamburgh"fowls。
—figureofthehook—billedduck。
ALBINISM。
ALBINO，negro，attackedbyinsects。
ALBINOES，heredityof。
ALBINUS，thicknessoftheepidermisonthepalmsofthehandsinman。
ALCO。
ALDROVANDI，onrabbits。
—descriptionofthenunpigeon。
—onthefondnessoftheDutchforpigeonsintheseventeenthcentury。
—noticeofseveralvarietiesofpigeons。
—onthebreedsoffowls。
—ontheoriginofthedomesticduck。
ALEFIELD，Dr。，onthevarietiesofpeasandtheirspecificunity。
—onthevarietiesofbeans。
ALEXANDERtheGreat，hisselectionofIndiancattle。
ALGAE，retrogressivemetamorphosisin。
—divisionofzoosporesof，ALLEN，J。，birdsinUnitedStates。
ALLEN，W。，onferalfowls。
ALLMAN，Professor，onamonstrousSaxifragageum。
—ontheHydroida。
ALMOND，antiquityof。
—bitter，noteatenbymice。
Alnusglutinosa，andincana，hybridsof。
ALPACA，selectionof。
Althaearosea。
Amaryllis。
Amaryllisvittata，effectofforeignpollenon。
AMAUROSIS，hereditary。
Amblystomalurida。
AMERICA，limitswithinwhichnousefulplantshavebeenfurnishedby。
—coloursofferalhorsesin。
—North，nativecultivatedplantsof。
—skinofferalpigfrom。
—South，variationsincattleof。
AMMON，onthepersistencyofcolourinhorses。
Amygdaluspersica。
Anagallisarvensis。
ANALOGOUSvariation。
—inhorses，—inthehorseandass。
—infowls。
Anasboschas。
—skullof，figured。
"ANCON"sheepofMassachusetts。
ANDALUSIANfowls。
ANDALUSIANrabbits。
ANDERSON，J。，ontheoriginofBritishsheep。
—ontheselectionofqualitiesincattle。
—onaone—earedbreedofrabbits。
—ontheinheritanceofcharactersfromaone—earedrabbit，andthree—leggedbitch。
—onthepersistencyofvarietiesofpeas。
—ontheproductionofearlypeasbyselection。
—onthevarietiesofthepotato。
—oncrossingvarietiesofthemelon。
—onreversioninthebarberry。
ANDERSON，Mr。，onthereproductionoftheweepingashbyseed。
—onthecultivationofthetreepaeonyinChina。
ANDERSSON，Mr。，ontheDamara，Bechuana，andNamaquacattle。
—onthecowsoftheDamaras。
—selectionpractisedbytheDamarasandNamaquas。
—ontheuseofgrass—seedsandtherootsofreedsasfoodinSouthAfrica。
Anemonecoronaria，doubledbyselection。
ANGINApectoris，hereditary，occurringatacertainage。
ANGLESEA，cattleof。
ANGOLAsheep。
ANGORA，changeinhairofanimalsat。
—catsof。
—rabbitsof，ANIMALS，domesticationof，facilitatedbyfearlessnessofman。
—refusalofwild，tobreedincaptivity。
—compound，individualpeculiaritiesof，reproducedbybudding。
—variationbyselectioninusefulqualitiesof。
ANNUALplants，rarityofbud—variationin。
ANOMALIESintheosteologyofthehorse。
ANOMALOUSbreedsofpigs。
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