the origin of species(物种起源)-第39节

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een　species。　I　might　have　adduced　for　this　same　purpose　the　differences　between　the　races　of　man；　which　are　so　strongly　marked；　I　may　add　that　some　little　light　can　apparently　be　thrown　on　the　origin　of　these　differences；　chiefly　through　sexual　selection　of　a　particular　kind；　but　without　here　entering　on　copious　details　my　reasoning　would　appear　frivolous。　
The　foregoing　remarks　lead　me　to　say　a　few　words　on　the　protest　lately　made　by　some　naturalists；　against　the　utilitarian　doctrine　that　every　detail　of　structure　has　been　produced　for　the　good　of　its　possessor。　They　believe　that　very　many　structures　have　been　created　for　beauty　in　the　eyes　of　man；　or　for　mere　variety。　This　doctrine；　if　true；　would　be　absolutely　fatal　to　my　theory。　Yet　I　fully　admit　that　many　structures　are　of　no　direct　use　to　their　possessors。　Physical　conditions　probably　have　had　some　little　effect　on　structure；　quite　independently　of　any　good　thus　gained。　Correlation　of　growth　has　no　doubt　played　a　most　important　part；　and　a　useful　modification　of　one　part　will　often　have　entailed　on　other　parts　diversified　changes　of　no　direct　use。　So　again　characters　which　formerly　were　useful；　or　which　formerly　had　arisen　from　correlation　of　growth；　or　from　other　unknown　cause；　may　reappear　from　the　law　of　reversion；　though　now　of　no　direct　use。　The　effects　of　sexual　selection；　when　displayed　in　beauty　to　charm　the　females；　can　be　called　useful　only　in　rather　a　forced　sense。　But　by　far　the　most　important　consideration　is　that　the　chief　part　of　the　organisation　of　every　being　is　simply　due　to　inheritance；　and　consequently；　though　each　being　assuredly　is　well　fitted　for　its　place　in　nature；　many　structures　now　have　no　direct　relation　to　the　habits　of　life　of　each　species。　Thus；　we　can　hardly　believe　that　the　webbed　feet　of　the　upland　goose　or　of　the　frigate…bird　are　of　special　use　to　these　birds；　we　cannot　believe　that　the　same　bones　in　the　arm　of　the　monkey；　in　the　fore　leg　of　the　horse；　in　the　wing　of　the　bat；　and　in　the　flipper　of　the　seal；　are　of　special　use　to　these　animals。　We　may　safely　attribute　these　structures　to　inheritance。　But　to　the　progenitor　of　the　upland　goose　and　of　the　frigate…bird；　webbed　feet　no　doubt　were　as　useful　as　they　now　are　to　the　most　aquatic　of　existing　birds。　So　we　may　believe　that　the　progenitor　of　the　seal　had　not　a　flipper；　but　a　foot　with　five　toes　fitted　for　walking　or　grasping；　and　we　may　further　venture　to　believe　that　the　several　bones　in　the　limbs　of　the　monkey；　horse；　and　bat；　which　have　been　inherited　from　a　common　progenitor；　were　formerly　of　more　special　use　to　that　progenitor；　or　its　progenitors；　than　they　now　are　to　these　animals　having　such　widely　diversified　habits。　Therefore　we　may　infer　that　these　several　bones　might　have　been　acquired　through　natural　selection；　subjected　formerly；　as　now；　to　the　several　laws　of　inheritance；　reversion；　correlation　of　growth；　&c。　Hence　every　detail　of　structure　in　every　living　creature　（making　some　little　allowance　for　the　direct　action　of　physical　conditions）　may　be　viewed；　either　as　having　been　of　special　use　to　some　ancestral　form；　or　as　being　now　of　special　use　to　the　descendants　of　this　form　either　directly；　or　indirectly　through　the　complex　laws　of　growth。　
Natural　selection　cannot　possibly　produce　any　modification　in　any　one　species　exclusively　for　the　good　of　another　species；　though　throughout　nature　one　species　incessantly　takes　advantage　of；　and　profits　by；　the　structure　of　another。　But　natural　selection　can　and　does　often　produce　structures　for　the　direct　injury　of　other　species；　as　we　see　in　the　fang　of　the　adder；　and　in　the　ovipositor　of　the　ichneumon；　by　which　its　eggs　are　deposited　in　the　living　bodies　of　other　insects。　If　it　could　be　proved　that　any　part　of　the　structure　of　any　one　species　had　been　formed　for　the　exclusive　good　of　another　species；　it　would　annihilate　my　theory；　for　such　could　not　have　been　produced　through　natural　selection。　Although　many　statements　may　be　found　in　works　on　natural　history　to　this　effect；　I　cannot　find　even　one　which　seems　to　me　of　any　weight。　It　is　admitted　that　the　rattlesnake　has　a　poison…fang　for　its　own　defence　and　for　the　destruction　of　its　prey；　but　some　authors　suppose　that　at　the　same　time　this　snake　is　furnished　with　a　rattle　for　its　own　injury；　namely；　to　warn　its　prey　to　escape。　I　would　almost　as　soon　believe　that　the　cat　curls　the　end　of　its　tail　when　preparing　to　spring；　in　order　to　warn　the　doomed　mouse。　But　I　have　not　space　here　to　enter　on　this　and　other　such　cases。　
Natural　selection　will　never　produce　in　a　being　anything　injurious　to　itself；　for　natural　selection　acts　solely　by　and　for　the　good　of　each。　No　organ　will　be　formed；　as　Paley　has　remarked；　for　the　purpose　of　causing　pain　or　for　doing　an　injury　to　its　possessor。　If　a　fair　balance　be　struck　between　the　good　and　evil　caused　by　each　part；　each　will　be　found　on　the　whole　advantageous。　After　the　lapse　of　time；　under　changing　conditions　of　life；　if　any　part　comes　to　be　injurious；　it　will　be　modified；　or　if　it　be　not　so；　the　being　will　become　extinct；　as　myriads　have　become　extinct。　
Natural　selection　tends　only　to　make　each　organic　being　as　perfect　as；　or　slightly　more　perfect　than；　the　other　inhabitants　of　the　same　country　with　which　it　has　to　struggle　for　existence。　And　we　see　that　this　is　the　degree　of　perfection　attained　under　nature。　The　endemic　productions　of　New　Zealand；　for　instance；　are　perfect　one　compared　with　another；　but　they　are　now　rapidly　yielding　before　the　advancing　legions　of　plants　and　animals　introduced　from　Europe。　Natural　selection　will　not　produce　absolute　perfection；　nor　do　we　always　meet；　as　far　as　we　can　judge；　with　this　high　standard　under　nature。　The　correction　for　the　aberration　of　light　is　said；　on　high　authority；　not　to　be　perfect　even　in　that　most　perfect　organ；　the　eye。　If　our　reason　leads　us　to　admire　with　enthusiasm　a　multitude　of　inimitable　contrivances　in　nature；　this　same　reason　tells　us；　though　we　may　easily　err　on　both　sides；　that　some　other　contrivances　are　less　perfect。　Can　we　consider　the　sting　of　the　wasp　or　of　the　bee　as　perfect；　which；　when　used　against　many　attacking　animals；　cannot　be　withdrawn；　owing　to　the　backward　serratures；　and　so　inevitably　causes　the　death　of　the　insect　by　tearing　out　its　viscera？　
If　we　look　at　the　sting　of　the　bee；　as　having　originally　existed　in　a　remote　progenitor　as　a　boring　and　serrated　instrument；　like　that　in　so　many　members　of　the　same　great　order；　and　which　has　been　modified　but　not　perfected　for　its　present　purpose；　with　the　poison　originally　adapted　to　cause　galls　subsequently　intensified；　we　can　perhaps　understand　how　it　is　that　the　use　of　the　sting　should　so　often　cause　the　insect's　own　death：　for　if　on　the　whole　the　power　of　stinging　be　useful　to　the　community；　it　will　fulfil　all　the　requirements　of　natural　selection；　though　it　may　cause　the　death　of　some　few　members。　If　we　admire　the　truly　wonderful　power　of　scent　by　which　the　males　of　many　insects　find　their　females；　can　we　admire　the　production　for　this　single　purpose　of　thousands　of　drones；　which　are　utterly　useless　to　the　community　for　any　other　end；　and　which　are　ultimately　slaughtered　by　their　industrious　and　sterile　sisters？　It　may　be　difficult；　but　we　ought　to　admire　the　savage　instinctive　hatred　of　the　queen…bee；　which　urges　her　instantly　to　destroy　the　young　queens　her　daughters　as　soon　as　born；　or　to　perish　herself　in　the　combat；　for　undoubtedly　this　is　for　the　good　of　the　community；　and　maternal　love　or　maternal　hatred；　though　the　latter　fortunately　is　most　rare；　is　all　the　same　to　the　inexorable　principle　of　natural　selection。　If　we　admire　the　several　ingenious　contrivances；　by　which　the　flowers　of　the　orchis　and　of　many　other　plants　are　fertilised　through　insect　agency；　can　we　consider　as　equally　perfect　the　elaboration　by　our　fir…trees　of　dense　clouds　of　pollen；　in　order　that　a　few　granules　may　be　wafted　by　a　chance　breeze　on　to　the　ovules？　
Summary　of　Chapter。　We　have　in　this　chapter　discussed　some　of　the　difficulties　and　objections　which　may　be　urged　against　my　theory。　Many　of　them　are　very　grave；　but　I　think　that　in　the　discussion　light　has　been　thrown　on　several　facts；　which　on　the　theory　of　independent　acts　of　creation　are　utterly　obscure。　We　have　seen　that　species　at　any　one　period　are　not　indefinitely　variable；　and　are　not　linked　together　by　a　multitude　of　intermediate　gradations；　partly　because　the　process　of　natural　selection　will　always　be　very　slow；　and　will　act；　at　any　one　time；　only　on　a　very　few　forms；　and　partly　because　the　very　process　of　natural　selection　almost　implies　the　continual　supplanting　and　extinction　of　preceding　and　intermediate　gradations。　Closely　allied　species；　now　living　on　a　continuous　area；　must　often　have　been　formed　when　the　area　was　not　continuous；　and　when　the　conditions　of　life　did　not　insensibly　graduate　away　from　one　part　to　another。　When　two　varieties　are　formed　in　two　districts　of　a　continuous　area；　an　intermediate　variety　will　often　be　formed；　fitted　for　an　intermediate　zone；　but　from　reasons　assigned；　the　intermediate　variety　will　usually　exist　in　lesser　numbers　than　the　two　forms　which　it　connects；　consequently　the　two　latter；　during　the　course　of　further　modification；　from　ex