Untilmanselectsbirdsdifferingintherelativelengthofthewing—
feathersortoes，etc。，nosensiblechangeinthesepartsshouldbeexpected。Norcouldmandoanythingunlessthesepartshappenedtovaryunderdomestication:Idonotpositivelyassertthatthisisthecase，althoughIhaveseentracesofsuchvariabilityinthewing—feathers，andcertainlyinthetail—feathers。Itwouldbeastrangefactiftherelativelengthofthehindtoeshouldnevervary，seeinghowvariablethefootisbothinsizeandinthenumberofthescutellae。Withrespecttothedomesticracesnotroostingorbuildingintrees，itisobviousthatfancierswouldneverattendtoorselectsuchchangesinhabits;butwehaveseenthatthepigeonsinEgypt，whichdonotforsomereasonlikesettlingonthelowmudhovelsofthenatives，areled，apparentlybycompulsion，toperchincrowdsonthetrees。Wemayevenaffirmthat，ifourdomesticraceshadbecomegreatlymodifiedinanyoftheabovespecifiedrespects，anditcouldbeshownthatfanciershadneverattendedtosuchpoints，orthattheydidnotstandincorrelationwithotherselectedcharacters，thefact，ontheprinciplesadvocatedinthischapter，wouldhaveofferedaseriousdifficulty。
Letusbrieflysumupthelasttwochaptersonthepigeon。Wemayconcludewithconfidencethatallthedomesticraces，notwithstandingtheirgreatamountofdifference，aredescendedfromtheColumbalivia，includingunderthisnamecertainwildraces。Butthedifferencesbetweenthelatterthrownolightwhateveronthecharacterswhichdistinguishthedomesticraces。
Ineachbreedorsub—breedtheindividualbirdsaremorevariablethanbirdsinastateofnature;andoccasionallytheyvaryinasuddenandstrongly—markedmanner。Thisplasticityoforganisationapparentlyresultsfromchangedconditionsoflife。Disusehasreducedcertainpartsofthebody。Correlationofgrowthsotiestheorganisationtogether，thatwhenonepartvariesotherpartsvaryatthesametime。Whenseveralbreedshaveoncebeenformed，theirintercrossingaidstheprogressofmodification，andhasevenproducednewsub—breeds。Butas，intheconstructionofabuilding，merestonesorbricksareoflittleavailwithoutthebuilder’sart，so，intheproductionofnewraces，selectionhasbeenthepresidingpower。Fancierscanactbyselectiononexcessivelyslightindividualdifferences，aswellasonthosegreaterdifferenceswhicharecalledsports。Selectionisfollowedmethodicallywhenthefanciertriestoimproveandmodifyabreedaccordingtoaprefixedstandardofexcellence;
orheactsunmethodicallyandunconsciously，bymerelytryingtorearasgoodbirdsashecan，withoutanywishorintentiontoalterthebreed。Theprogressofselectionalmostinevitablyleadstotheneglectandultimateextinctionoftheearlierandlessimprovedforms，aswellasofmanyintermediatelinksineachlonglineofdescent。Thusithascometopassthatmostofourpresentracesaresomarvellouslydistinctfromeachother，andfromtheaboriginalrock—pigeon。