darwin and modern science-第90节

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TING　value；　and　I　cordially　congratulate　you　on　your　first　great　work。　　You　will　find；　I　should　think；　that　Wallace　will　fully　appreciate　it。〃　　（〃Life　and　Letters〃；　II。　pages　391…393。）　　Four　days　later；　Nov。　24；　Darwin　wrote　to　Hooker　on　the　same　subject：　　〃I　have　now　finished　his　paper。。。'　it　seems　to　me　admirable。　　To　my　mind　the　act　of　segregation　of　varieties　into　species　was　never　so　plainly　brought　forward；　and　there　are　heaps　of　capital　miscellaneous　observations。〃　　（〃More　Letters〃；　I。　page　214。）

Darwin　was　here　referring　to　the　tendency　of　similar　varieties　of　the　same　species　to　pair　together；　and　on　Nov。　25　he　wrote　to　Bates　asking　for　fuller　information　on　this　subject。　　（〃More　Letters〃；　I。　page　215。　　See　also　parts　of　Darwin's　letter　to　Bates　in　〃Life　and　Letters〃；　II。　page　392。）　　If　Bates's　opinion　were　well　founded；　sexual　selection　would　bear　a　most　important　part　in　the　establishment　of　such　species。　　（See　Poulton；　〃Essays　on　Evolution〃；　1908；　pages　65；　85…88。）　　It　must　be　admitted；　however；　that　the　evidence　is　as　yet　quite　insufficient　to　establish　this　conclusion。　　It　is　interesting　to　observe　how　Darwin　at　once　fixed　on　the　part　of　Bates's　memoir　which　seemed　to　bear　upon　sexual　selection。　　A　review　of　Bates's　theory　of　Mimicry　was　contributed　by　Darwin　to　the　〃Natural　History　Review〃　（New　Ser。　Vol。　III。　1863；　page　219。）　and　an　account　of　it　is　to　be　found　in　the　〃Origin〃　（Edition　1872；　pages　375…378。）　and　in　〃The　Descent　of　Man〃。　　（Edition　1874；　pages　323…325。）

Darwin　continually　writes　of　the　value　of　hypothesis　as　the　inspiration　of　inquiry。　　We　find　an　example　in　his　letter　to　Bates；　Nov。　22；　1860：　　〃I　have　an　old　belief　that　a　good　observer　really　means　a　good　theorist；　and　I　fully　expect　to　find　your　observations　most　valuable。〃　　（〃More　Letters〃；　I。　page　176。）　　Darwin's　letter　refers　to　many　problems　upon　which　Bates　had　theorised　and　observed；　but　as　regards　Mimicry　itself　the　hypothesis　was　thought　out　after　the　return　of　the　letter　from　the　Amazons；　when　he　no　longer　had　the　opportunity　of　testing　it　by　the　observation　of　living　Nature。　　It　is　by　no　means　improbable　that；　had　he　been　able　to　apply　this　test；　Bates　would　have　recognised　that　his　division　of　butterfly　resemblances　into　two　classes；one　due　to　the　theory　of　mimicry；　the　other　to　the　influence　of　local　conditions；could　not　be　sustained。

Fritz　Muller's　contributions　to　the　problem　of　Mimicry　were　all　made　in　S。E。　Brazil；　and　numbers　of　them　were　communicated；　with　other　observations　on　natural　history；　to　Darwin；　and　by　him　sent　to　Professor　R。　Meldola　who　published　many　of　the　facts。　　Darwin's　letters　to　Meldola　（Poulton；　〃Charles　Darwin　and　the　theory　of　Natural　Selection〃；　London；　1896；　pages　199…218。）　contain　abundant　proofs　of　his　interest　in　Muller's　work　upon　Mimicry。　　One　deeply　interesting　letter　（Loc。　cit。　pages　201；　202。）　dated　Jan。　23；　1872；　proves　that　Fritz　Muller　before　he　originated　the　theory　of　Common　Warning　Colours　（Synaposematic　Resemblance　or　Mullerian　Mimicry）；　which　will　ever　be　associated　with　his　name；　had　conceived　the　idea　of　the　production　of　mimetic　likeness　by　sexual　selection。

Darwin's　letter　to　Meldola　shows　that　he　was　by　no　means　inclined　to　dismiss　the　suggestion　as　worthless；　although　he　considered　it　daring。　　〃You　will　also　see　in　this　letter　a　strange　speculation；　which　I　should　not　dare　to　publish；　about　the　appreciation　of　certain　colours　being　developed　in　those　species　which　frequently　behold　other　forms　similarly　ornamented。　　I　do　not　feel　at　all　sure　that　this　view　is　as　incredible　as　it　may　at　first　appear。　　Similar　ideas　have　passed　through　my　mind　when　considering　the　dull　colours　of　all　the　organisms　which　inhabit　dull…coloured　regions；　such　as　Patagonia　and　the　Galapagos　Is。〃　　A　little　later；　on　April　5；　he　wrote　to　Professor　August　Weismann　on　the　same　subject：　　〃It　may　be　suspected　that　even　the　habit　of　viewing　differently　coloured　surrounding　objects　would　influence　their　taste；　and　Fritz　Muller　even　goes　so　far　as　to　believe　that　the　sight　of　gaudy　butterflies　might　influence　the　taste　of　distinct　species。〃　　（〃Life　and　Letters〃；　III。　page　157。）

This　remarkable　suggestion　affords　interesting　evidence　that　F。　Muller　was　not　satisfied　with　the　sufficiency　of　Bates's　theory。　　Nor　is　this　surprising　when　we　think　of　the　numbers　of　abundant　conspicuous　butterflies　which　he　saw　exhibiting　mimetic　likenesses。　　The　common　instances　in　his　locality；　and　indeed　everywhere　in　tropical　America；　were　anything　but　the　hard…pressed　struggling　forms　assumed　by　the　theory　of　Bates。　　They　belonged　to　the　groups　which　were　themselves　mimicked　by　other　butterflies。　Fritz　Muller's　suggestion　also　shows　that　he　did　not　accept　Bates's　alternative　explanation　of　a　superficial　likeness　between　models　themselves；　based　on　some　unknown　influence　of　local　physico…chemical　forces。　　At　the　same　time　Muller's　own　suggestion　was　subject　to　this　apparently　fatal　objection；　that　the　sexual　selection　he　invoked　would　tend　to　produce　resemblances　in　the　males　rather　than　the　females；　while　it　is　well　known　that　when　the　sexes　differ　the　females　are　almost　invariably　more　perfectly　mimetic　than　the　males　and　in　a　high　proportion　of　cases　are　mimetic　while　the　males　are　non…mimetic。

The　difficulty　was　met　several　years　later　by　Fritz　Muller's　well…known　theory；　published　in　1879　（〃Kosmos〃；　May　1879；　page　100。）；　and　immediately　translated　by　Meldola　and　brought　before　the　Entomological　Society。　　（〃Proc。　Ent。　Soc。　Lond。〃　1879；　page　xx。）　　Darwin's　letter　to　Meldola　dated　June　6；　1879；　shows　〃that　the　first　introduction　of　this　new　and　most　suggestive　hypothesis　into　this　country　was　due　to　the　direct　influence　of　Darwin　himself；　who　brought　it　before　the　notice　of　the　one　man　who　was　likely　to　appreciate　it　at　its　true　value　and　to　find　the　means　for　its　presentation　to　English　naturalists。〃　　（〃Charles　Darwin　and　the　Theory　of　Natural　Selection〃；　page　214。）　　Of　the　hypothesis　itself　Darwin　wrote　〃F。　Muller's　view　of　the　mutual　protection　was　quite　new　to　me。〃　　（Ibid。　page　213。）　　The　hypothesis　of　Mullerian　mimicry　was　at　first　strongly　opposed。　　Bates　himself　could　never　make　up　his　mind　to　accept　it。　　As　the　Fellows　were　walking　out　of　the　meeting　at　which　Professor　Meldola　explained　the　hypothesis；　an　eminent　entomologist；　now　deceased；　was　heard　to　say　to　Bates：　　〃It's　a　case　of　save　me　from　my　friends！〃　　The　new　ideas　encountered　and　still　encounter　to　a　great　extent　the　difficulty　that　the　theory　of　Bates　had　so　completely　penetrated　the　literature　of　natural　history。　　The　present　writer　has　observed　that　naturalists　who　have　not　thoroughly　absorbed　the　older　hypothesis　are　usually　far　more　impressed　by　the　newer　one　than　are　those　whose　allegiance　has　already　been　rendered。　　The　acceptance　of　Natural　Selection　itself　was　at　first　hindered　by　similar　causes；　as　Darwin　clearly　recognised：　　〃If　you　argue　about　the　non…　acceptance　of　Natural　Selection；　it　seems　to　me　a　very　striking　fact　that　the　Newtonian　theory　of　gravitation；　which　seems　to　every　one　now　so　certain　and　plain；　was　rejected　by　a　man　so　extraordinarily　able　as　Leibnitz。　　The　truth　will　not　penetrate　a　preoccupied　mind。〃　　（To　Sir　J。　Hooker；　July　28；　1868；　〃More　Letters〃；　I。　page　305。　　See　also　the　letter　to　A。R。　Wallace；　April　30；　1868；　in　〃More　Letters〃　II。　page　77；　lines　6…8　from　top。）

There　are　many　naturalists；　especially　students　of　insects；　who　appear　to　entertain　an　inveterate　hostility　to　any　theory　of　mimicry。　　Some　of　them　are　eager　investigators　in　the　fascinating　field　of　geographical　distribution；　so　essential　for　the　study　of　Mimicry　itself。　　The　changes　of　pattern　undergone　by　a　species　of　Erebia　as　we　follow　it　over　different　parts　of　the　mountain　ranges　of　Europe　is　indeed　a　most　interesting　inquiry；　but　not　more　so　than　the　differences　between　e。g。　the　Acraea　johnstoni　of　S。E。　Rhodesia　and　of　Kilimanjaro。　　A　naturalist　who　is　interested　by　the　Erebia　should　be　equally　interested　by　the　Acraea；　and　so　he　would　be　if　the　student　of　mimicry　did　not　also　record　that　the　characteristics　which　distinguish　the　northern　from　the　southern　individuals　of　the　African　species　correspond　with　the　presence；　in　the　north　but　not　in　the　south；　of　certain　entirely　different　butterflies。　　That　this　additional　information　should　so　greatly　weaken；　in　certain　minds；　the　appeal　of　a　favourite　study；　is　a　psychological　problem　of　no　little　interest。　　This　curious　antagonism　is　I　believe　confined　to　a　few　students　of　insects。　　Those　naturalists　who；　standing　rather　farther　off；　are　able　to　see　the　bearings　of　the　subject　more　clearly；　will　usually　admit　the　general　support　yielded　by　an　ever…growing　mass　of　observations　to　the　theories　of　Mimicry　propounded　by　H。W。　Bates　and　Fritz　Muller。　　In　like　manner　natural　selection　itself　was　in　the　early　days　often　best　understood　and　most　readily　accepted　by　those　who　were　not　naturalists。　　Thus　Darwin　wrote　to　D。T。　Ansted；　Oct。　27；　1860：　　〃I　am　often　in　despair　in　making　the　generality　of　NATURALISTS　even　comprehend　me。　　Intelligent　men　who　are　not　naturalists　and　have　not　a　bigoted　idea　of　the　term　species；　show　more　clearness　of　mind。〃　　（〃More　Letters〃；　I。　page　175。）

Even　before　the　〃Origin〃　appeared　Darw