高中英语现代文背诵篇章46Vision素材

46 VisionHuman vision like that of other primates has evolved in an arboreal environment. In the den

46Vision Humanvisionlikethatofotherprimateshasevolvedinanarboreal environment.Inthedensecomplexworldofatropicalforest,itismore importanttoseewellthattodevelopanacutesenseofsmell.Inthecourseof evolutionmembersoftheprimatelinehaveacquiredlargeeyeswhilethesnout hasshrunktogivetheeyeanunimpededview.Ofmammalsonlyhumansandsome primatesenjoycolorvision.Theredflagisblacktothebull.Horseslivein amonochromeworld.lightvisibletohumaneyeshoweveroccupiesonlyavery narrowbandinthewholeelectromagneticspectrum.Ultravioletraysare invisibletohumansthoughantsandhoneybeesaresensitivetothem.Humans thoughantsandhoneybeesaresensitivetothem.Humanshavenodirect perceptionofinfraredraysunliketherattlesnakewhichhasreceptorstuned intowavelengthslongerthan0.7micron.Theworldwouldlookeerilydifferent ifhumaneyesweresensitivetoinfraredradiation.Theninsteadofthe darknessofnight,wewouldbeabletomoveeasilyinastrangeshadowless worldwhereobjectsglowedwithvaryingdegreesofintensity.Buthumaneyes excelinotherways.Theyareinfactremarkablydiscerningincolorgradation. Thecolorsensitivityofnormalhumanvisionisrarelysurpassedevenby sophisticatedtechnicaldevices.