darwin and modern science-第8节

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　to　be　the　case　some　day。　　Anyhow；　one　may　be　excused　in　not　having　discovered　the　fact　in　a　work　on　Naval　Timber。〃　　（〃Life　and　Letters〃　II。　page　301。）

De　Quatrefages　and　De　Varigny　have　maintained　that　the　botanist　Naudin　stated　the　theory　of　evolution　by　natural　selection　in　1852。　　He　explains　very　clearly　the　process　of　artificial　selection；　and　says　that　in　the　garden　we　are　following　Nature's　method。　　〃We　do　not　think　that　Nature　has　made　her　species　in　a　different　fashion　from　that　in　which　we　proceed　ourselves　in　order　to　make　our　variations。〃　　But；　as　Darwin　said；　〃he　does　not　show　how　selection　acts　under　nature。〃　　Similarly　it　must　be　noted　in　regard　to　several　pre…Darwinian　pictures　of　the　struggle　for　existence　（such　as　Herder's；　who　wrote　in　1790　〃All　is　in　struggle。。。each　one　for　himself〃　and　so　on）；　that　a　recognition　of　this　is　only　the　first　step　in　Darwinism。

Profs。　E。　Perrier　and　H。F。　Osborn　have　called　attention　to　a　remarkable　anticipation　of　the　selection…idea　which　is　to　be　found　in　the　speculations　of　Etienne　Geoffroy　St　Hilaire　（1825…1828）　on　the　evolution　of　modern　Crocodilians　from　the　ancient　Teleosaurs。　　Changing　environment　induced　changes　in　the　respiratory　system　and　far…reaching　consequences　followed。　　The　atmosphere；　acting　upon　the　pulmonary　cells；　brings　about　〃modifications　which　are　favourable　or　destructive　（'funestes'）；　these　are　inherited；　and　they　influence　all　the　rest　of　the　organisation　of　the　animal　because　if　these　modifications　lead　to　injurious　effects；　the　animals　which　exhibit　them　perish　and　are　replaced　by　others　of　a　somewhat　different　form；　a　form　changed　so　as　to　be　adapted　to　（a　la　convenance）　the　new　environment。〃

Prof。　E。B。　Poulton　（〃Science　Progress〃；　New　Series；　Vol。　I。　1897。　　〃A　Remarkable　Anticipation　of　Modern　Views　on　Evolution〃。　　See　also　Chap。　VI。　in　〃Essays　on　Evolution〃；　Oxford；　1908。）　has　shown　that　the　anthropologist　James　Cowles　Prichard　（1786…1848）　must　be　included；　even　in　spite　of　himself；　among　the　precursors　of　Darwin。　　In　some　passages　of　the　second　edition　of　his　〃Researches　into　the　Physical　History　of　Mankind〃　（1826）；　he　certainly　talks　evolution　and　anticipates　Prof。　Weismann　in　denying　the　transmission　of　acquired　characters。　　He　is；　however；　sadly　self…　contradictory　and　his　evolutionism　weakens　in　subsequent　editionsthe　only　ones　that　Darwin　saw。　　Prof。　Poulton　finds　in　Prichard's　work　a　recognition　of　the　operation　of　Natural　Selection。　　〃After　enquiring　how　it　is　that　'these　varieties　are　developed　and　preserved　in　connection　with　particular　climates　and　differences　of　local　situation；'　he　gives　the　following　very　significant　answer：　　'One　cause　which　tends　to　maintain　this　relation　is　obvious。　　Individuals　and　families；　and　even　whole　colonies；　perish　and　disappear　in　climates　for　which　they　are；　by　peculiarity　of　constitution；　not　adapted。　　Of　this　fact　proofs　have　been　already　mentioned。'〃　　Mr　Francis　Darwin　and　Prof。　A。C。　Seward　discuss　Prichard's　〃anticipations〃　in　〃More　Letters　of　Charles　Darwin〃；　Vol。　I。　page　43；　and　come　to　the　conclusion　that　the　evolutionary　passages　are　entirely　neutralised　by　others　of　an　opposite　trend。　　There　is　the　same　difficulty　with　Buffon。

Hints　of　the　idea　of　Natural　Selection　have　been　detected　elsewhere。　　James　Watt　（See　Prof。　Patrick　Geddes's　article　〃Variation　and　Selection〃；　〃Encyclopaedia　Britannica　（9th　edition）　1888。）；　for　instance；　has　been　reported　as　one　of　the　anticipators　（1851）。　　But　we　need　not　prolong　the　inquiry　further；　since　Darwin　did　not　know　of　any　anticipations　until　after　he　had　published　the　immortal　work　of　1859；　and　since　none　of　those　who　got　hold　of　the　idea　made　any　use　of　it。　　What　Darwin　did　was　to　follow　the　clue　which　Malthus　gave　him；　to　realise；　first　by　genius　and　afterwards　by　patience；　how　the　complex　and　subtle　struggle　for　existence　works　out　a　natural　selection　of　those　organisms　which　vary　in　the　direction　of　fitter　adaptation　to　the　conditions　of　their　life。　　So　much　success　attended　his　application　of　the　Selection…formula　that　for　a　time　he　regarded　Natural　Selection　as　almost　the　sole　factor　in　evolution；　variations　being　pre…　supposed；　gradually；　however；　he　came　to　recognise　that　there　was　some　validity　in　the　factors　which　had　been　emphasized　by　Lamarck　and　by　Buffon；　and　in　his　well…known　summing　up　in　the　sixth　edition　of　the　〃Origin〃　he　says　of　the　transformation　of　species：　　〃This　has　been　effected　chiefly　through　the　natural　selection　of　numerous　successive；　slight；　favourable　variations；　aided　in　an　important　manner　by　the　inherited　effects　of　the　use　and　disuse　of　parts；　and　in　an　unimportant　manner；　that　is；　in　relation　to　adaptive　structures；　whether　past　or　present；　by　the　direct　action　of　external　conditions；　and　by　variations　which　seem　to　us　in　our　ignorance　to　arise　spontaneously。〃

To　sum　up：　　the　idea　of　organic　evolution；　older　than　Aristotle；　slowly　developed　from　the　stage　of　suggestion　to　the　stage　of　verification；　and　the　first　convincing　verification　was　Darwin's；　from　being　an　a　priori　anticipation　it　has　become　an　interpretation　of　nature；　and　Darwin　is　still　the　chief　interpreter；　from　being　a　modal　interpretation　it　has　advanced　to　the　rank　of　a　causal　theory；　the　most　convincing　part　of　which　men　will　never　cease　to　call　Darwinism。


III。　　THE　SELECTION　THEORY

By　August　Weismann。　Professor　of　Zoology　in　the　University　of　Freiburg　（Baden）。

I。　　THE　IDEA　OF　SELECTION。

Many　and　diverse　were　the　discoveries　made　by　Charles　Darwin　in　the　course　of　a　long　and　strenuous　life；　but　none　of　them　has　had　so　far…reaching　an　influence　on　the　science　and　thought　of　his　time　as　the　theory　of　selection。　　I　do　not　believe　that　the　theory　of　evolution　would　have　made　its　way　so　easily　and　so　quickly　after　Darwin　took　up　the　cudgels　in　favour　of　it；　if　he　had　not　been　able　to　support　it　by　a　principle　which　was　capable　of　solving；　in　a　simple　manner；　the　greatest　riddle　that　living　nature　presents　to　us；I　mean　the　purposiveness　of　every　living　form　relative　to　the　conditions　of　its　life　and　its　marvellously　exact　adaptation　to　these。

Everyone　knows　that　Darwin　was　not　alone　in　discovering　the　principle　of　selection；　and　that　the　same　idea　occurred　simultaneously　and　independently　to　Alfred　Russel　Wallace。　　At　the　memorable　meeting　of　the　Linnean　Society　on　1st　July；　1858；　two　papers　were　read　（communicated　by　Lyell　and　Hooker）　both　setting　forth　the　same　idea　of　selection。　　One　was　written　by　Charles　Darwin　in　Kent；　the　other　by　Alfred　Wallace　in　Ternate；　in　the　Malay　Archipelago。　　It　was　a　splendid　proof　of　the　magnanimity　of　these　two　investigators；　that　they　thus；　in　all　friendliness　and　without　envy；　united　in　laying　their　ideas　before　a　scientific　tribunal：　　their　names　will　always　shine　side　by　side　as　two　of　the　brightest　stars　in　the　scientific　sky。

But　it　is　with　Charles　Darwin　that　I　am　here　chiefly　concerned；　since　this　paper　is　intended　to　aid　in　the　commemoration　of　the　hundredth　anniversary　of　his　birth。

The　idea　of　selection　set　forth　by　the　two　naturalists　was　at　the　time　absolutely　new；　but　it　was　also　so　simple　that　Huxley　could　say　of　it　later；　〃How　extremely　stupid　not　to　have　thought　of　that。〃　　As　Darwin　was　led　to　the　general　doctrine　of　descent；　not　through　the　labours　of　his　predecessors　in　the　early　years　of　the　century；　but　by　his　own　observations；　so　it　was　in　regard　to　the　principle　of　selection。　　He　was　struck　by　the　innumerable　cases　of　adaptation；　as；　for　instance；　that　of　the　woodpeckers　and　tree…frogs　to　climbing；　or　the　hooks　and　feather…like　appendages　of　seeds；　which　aid　in　the　distribution　of　plants；　and　he　said　to　himself　that　an　explanation　of　adaptations　was　the　first　thing　to　be　sought　for　in　attempting　to　formulate　a　theory　of　evolution。

But　since　adaptations　point　to　CHANGES　which　have　been　undergone　by　the　ancestral　forms　of　existing　species；　it　is　necessary；　first　of　all；　to　inquire　how　far　species　in　general　are　VARIABLE。　　Thus　Darwin's　attention　was　directed　in　the　first　place　to　the　phenomenon　of　variability；　and　the　use　man　has　made　of　this；　from　very　early　times；　in　the　breeding　of　his　domesticated　animals　and　cultivated　plants。　　He　inquired　carefully　how　breeders　set　to　work；　when　they　wished　to　modify　the　structure　and　appearance　of　a　species　to　their　own　ends；　and　it　was　soon　clear　to　him　that　SELECTION　FOR　BREEDING　PURPOSES　played　the　chief　part。

But　how　was　it　possible　that　such　processes　should　occur　in　free　nature？　　Who　is　here　the　breeder；　making　the　selection；　choosing　out　one　individual　to　bring　forth　offspring　and　rejecting　others？　　That　was　the　problem　that　for　a　long　time　remained　a　riddle　to　him。

Darwin　himself　relates　how　illumination　suddenly　came　to　him。　　He　had　been　reading；　for　his　own　pleasure；　Malthus'　book　on　Population；　and；　as　he　had　long　known　from　numerous　observations；　that　every　species　gives　rise　to　many　more　descendants　than　ever　attain　to　maturity；　and　that；　therefore；　the　greater　number　of　the　descendants　of　a　species　perish　without　reproducing；　the　idea　came　to　him　that　the　decision　as　to　which　member　of　a　species　was　to　perish；　and　which　was　to　attain　to　maturity　and　reproduction　might　not　be　a　matter　of　chance；　but　might　be　determined