Indomitablepatience，thefinestpowersofdiscrimination，andsoundjudgmentmustbeexercisedduringmanyyears。Aclearlypredeterminedobjectmustbekeptsteadilyinview。Fewmenareendowedwithallthesequalities，especiallywiththatofdiscriminatingveryslightdifferences;judgmentcanbeacquiredonlybylongexperience;butifanyofthesequalitiesbewanting，thelabourofalifemaybethrownaway。Ihavebeenastonishedwhencelebratedbreeders，whoseskillandjudgmenthavebeenprovedbytheirsuccessatexhibitions，haveshownmetheiranimals，whichappearedallalike，andhaveassignedtheirreasonsformatchingthisandthatindividual。TheimportanceofthegreatprincipleofSelectionmainlyliesinthispowerofselectingscarcelyappreciabledifferences，whichneverthelessarefoundtobetransmissible，andwhichcanbeaccumulateduntiltheresultismademanifesttotheeyesofeverybeholder。
Theprincipleofselectionmaybeconvenientlydividedintothreekinds。
METHODICALSELECTIONisthatwhichguidesamanwhosystematicallyendeavourstomodifyabreedaccordingtosomepredeterminedstandard。UNCONSCIOUS
SELECTIONisthatwhichfollowsfrommennaturallypreservingthemostvaluedanddestroyingthelessvaluedindividuals，withoutanythoughtofalteringthebreed;andundoubtedlythisprocessslowlyworksgreatchanges。
Unconsciousselectiongraduatesintomethodical，andonlyextremecasescanbedistinctlyseparated;forhewhopreservesausefulorperfectanimalwillgenerallybreedfromitwiththehopeofgettingoffspringofthesamecharacter;butaslongashehasnotapredeterminedpurposetoimprovethebreed，hemaybesaidtobeselectingunconsciously。（20/1。Theterm\"unconsciousselection\"hasbeenobjectedtoasacontradiction;butseesomeexcellentobservationsonthisheadbyProf。Huxley（’Nat。Hist。Review’