LastweekmyyoungestsonandIvisitedmyfatherathisnewhomeinTucson，Arizona.Hemovedthereafewyearsago，andIwaseagertoseehisnewplaceandmeethisfriends.
Myearliestmemoriesofmyfatherareofatall，handsome，successfulmandevotedtohisworkandfamily，butuncomfortablewithhischildren.AsachildIlovedhim；asaschoolgirlandyoungadult(成年人)Ifearedhimandfeltbitterabouthim.HeseemedunhappywithmeunlessIgotstraightA’sandunhappywithmyboyfriendsiftheirfatherswerenotas“successful”ashewas.WheneverIwentoutwithhimonweekends，Iusedtostruggletothinkupthingstosay，feelingonguard.
Onthefirstdayofmyvisit，wewentoutwithoneofmyfather’sfriendsforlunchatanoutdoorcafe.Wewalkedalongthatafternoon，didsomeshopping，ateonthestreettable，andlaughedovermyson’sfunnyfacialexpressions.Gonewasmyfather’scritical(挑剔的)airandstrictrules.WhowasthispersonIknewasmyfather，whoseemedsofriendlyandinterestingtobearound？Whathadheldhimbackbefore
Domestic(驯养的)horsesnowpullploughs，raceintheKentuckyDerby，andcarrypolice.Butearlyhorsesweren’ttame(驯服的)enoughtoperformthesekindsoftasks.Scientiststhinkthefirstinteractionshumanshadwithhorseswerefardifferentfromthosetoday.
Thousandsofyearsago，peoplekilledthewildhorsesthatlivedaroundthemforfood.Overtime，peoplebegantocatchtheanimalsandraisethem.Thiswasthefirststepindomestication.
Aspeoplebegantotameandridehorses，theychosetokeepthoseanimalsthathadmoredesirablecharacteristics.Forexample，peoplemayhavechosentokeephorsesthathadagentlepersonalitysotheycouldberiddenmoreeasily.Peoplewhousedhorsestopullheavyloadswouldhavechosentokeepstrongeranimals.Characteristicslikestrengtharepartlycontrolledbytheanimals’genes.Soasthedomesticatedhorsesreproduced，theypassedthecharacteristicsontotheiryoung.Eachnewgenerationofhorseswouldshowmoreofthesechosencharacteristics.
Modern-dayhorsebreedscomeinawidevarietyofshapesandsizes.Thisvarietydidn’texistinthehorsepopulationbeforedomestication.TheShetlandhorseisoneofthesmallestbreeds－typicallyreachingonlyonemetertall.Withshort，stronglegs，theanimalswerebredtopullcoaloutofmineshafts(矿井)withlowceilings.HugehorsesliketheClydesdalecameonthescenearound1700.Peoplebredtheseheavy，tallhorsestopulllargevehiclesusedforcarryingheavyloads.
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