darwin and modern science-第13节

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IBILITY　OF　FUNCTIONAL　MODIFICATIONS　（so…　called　〃acquired〃　characters）；　and　this　is　not　only　undemonstrable；　but　is　scarcely　theoretically　conceivable；　for　the　secondary　variations　which　accompany　or　follow　the　first　as　correlative　variations；　occur　also　in　cases　in　which　the　animals　concerned　are　sterile　and　THEREFORE　CANNOT　TRANSMIT　ANYTHING　TO　THEIR　DESCENDANTS。　　This　is　true　of　WORKER　BEES；　and　particularly　of　ANTS；　and　I　shall　here　give　a　brief　survey　of　the　present　state　of　the　problem　as　it　appears　to　me。

Much　has　been　written　on　both　sides　of　this　question　since　the　published　controversy　on　the　subject　in　the　nineties　between　Herbert　Spencer　and　myself。　　I　should　like　to　return　to　the　matter　in　detail；　if　the　space　at　my　disposal　permitted；　because　it　seems　to　me　that　the　arguments　I　advanced　at　that　time　are　equally　cogent　to…day；　notwithstanding　all　the　objections　that　have　since　been　urged　against　them。　　Moreover；　the　matter　is　by　no　means　one　of　subordinate　interest；　it　is　the　very　kernel　of　the　whole　question　of　the　reality　and　value　of　the　principle　of　selection。　　For　if　selection　alone　does　not　suffice　to　explain　〃HARMONIOUS　ADAPTATION〃　as　I　have　called　Spencer's　COADAPTATION；　and　if　we　require　to　call　in　the　aid　of　the　Lamarckian　factor　it　would　be　questionable　whether　selection　could　explain　any　adaptations　whatever。　　In　this　particular　caseof　worker　bees　the　Lamarckian　factor　may　be　excluded　altogether；　for　it　can　be　demonstrated　that　here　at　any　rate　the　effects　of　use　and　disuse　cannot　be　transmitted。

But　if　it　be　asked　why　we　are　unwilling　to　admit　the　cooperation　of　the　Darwinian　factor　of　selection　and　the　Lamarckian　factor；　since　this　would　afford　us　an　easy　and　satisfactory　explanation　of　the　phenomena；　I　answer：　　BECAUSE　THE　LAMARCKIAN　PRINCIPLE　IS　FALLACIOUS；　AND　BECAUSE　BY　ACCEPTING　IT　WE　CLOSE　THE　WAY　TOWARDS　DEEPER　INSIGHT。　　It　is　not　a　spirit　of　combativeness　or　a　desire　for　self…vindication　that　induces　me　to　take　the　field　once　more　against　the　Lamarckian　principle；　it　is　the　conviction　that　the　progress　of　our　knowledge　is　being　obstructed　by　the　acceptance　of　this　fallacious　principle；　since　the　facile　explanation　it　apparently　affords　prevents　our　seeking　after　a　truer　explanation　and　a　deeper　analysis。

The　workers　in　the　various　species　of　ants　are　sterile；　that　is　to　say；　they　take　no　regular　part　in　the　reproduction　of　the　species；　although　individuals　among　them　may　occasionally　lay　eggs。　　In　addition　to　this　they　have　lost　the　wings；　and　the　receptaculum　seminis；　and　their　compound　eyes　have　degenerated　to　a　few　facets。　　How　could　this　last　change　have　come　about　through　disuse；　since　the　eyes　of　workers　are　exposed　to　light　in　the　same　way　as　are　those　of　the　sexual　insects　and　thus　in　this　particular　case　are　not　liable　to　〃disuse〃　at　all？　　The　same　is　true　of　the　receptaculum　seminis；　which　can　only　have　been　disused　as　far　as　its　glandular　portion　and　its　stalk　are　concerned；　and　also　of　the　wings；　the　nerves　tracheae　and　epidermal　cells　of　which　could　not　cease　to　function　until　the　whole　wing　had　degenerated；　for　the　chitinous　skeleton　of　the　wing　does　not　function　at　all　in　the　active　sense。

But；　on　the　other　hand；　the　workers　in　all　species　have　undergone　modifications　in　a　positive　direction；　as；　for　instance；　the　greater　development　of　brain。　　In　many　species　large　workers　have　evolved；the　so…　called　SOLDIERS；　with　enormous　jaws　and　teeth；　which　defend　the　colony；　and　in　others　there　are　SMALL　workers　which　have　taken　over　other　special　functions；　such　as　the　rearing　of　the　young　Aphides。　　This　kind　of　division　of　the　workers　into　two　castes　occurs　among　several　tropical　species　of　ants；　but　it　is　also　present　in　the　Italian　species；　Colobopsis　truncata。　　Beautifully　as　the　size　of　the　jaws　could　be　explained　as　due　to　the　increased　use　made　of　them　by　the　〃soldiers；〃　or　the　enlarged　brain　as　due　to　the　mental　activities　of　the　workers；　the　fact　of　the　infertility　of　these　forms　is　an　insurmountable　obstacle　to　accepting　such　an　explanation。　Neither　jaws　nor　brain　can　have　been　evolved　on　the　Lamarckian　principle。

The　problem　of　coadaptation　is　no　easier　in　the　case　of　the　ant　than　in　the　case　of　the　Giant　Stag。　　Darwin　himself　gave　a　pretty　illustration　to　show　how　imposing　the　difference　between　the　two　kinds　of　workers　in　one　species　would　seem　if　we　translated　it　into　human　terms。　　In　regard　to　the　Driver　ants　（Anomma）　we　must　picture　to　ourselves　a　piece　of　work；　〃for　instance　the　building　of　a　house；　being　carried　on　by　two　kinds　of　workers；　of　which　one　group　was　five　feet　four　inches　high；　the　other　sixteen　feet　high。〃　　（〃Origin　of　Species〃　（6th　edition）；　page　232。）

Although　the　ant　is　a　small　animal　as　compared　with　man　or　with　the　Irish　Elk；　the　〃soldier〃　with　its　relatively　enormous　jaws　is　hardly　less　heavily　burdened　than　the　Elk　with　its　antlers；　and　in　the　ant's　case；　too；　a　strengthening　of　the　skeleton；　of　the　muscles；　the　nerves　of　the　head；　and　of　the　legs　must　have　taken　place　parallel　with　the　enlargement　of　the　jaws。　　HARMONIOUS　ADAPTATION　（coadaptation）　has　here　been　active　in　a　high　degree；　and　yet　these　〃soldiers〃　are　sterile！　　There　thus　remains　nothing　for　it　but　to　refer　all　their　adaptations；　positive　and　negative　alike；　to　processes　of　selection　which　have　taken　place　in　the　rudiments　of　the　workers　within　the　egg　and　sperm…cells　of　their　parents。　　There　is　no　way　out　of　the　difficulty　except　the　one　Darwin　pointed　out。　　He　himself　did　not　find　the　solution　of　the　riddle　at　once。　　At　first　he　believed　that　the　case　of　the　workers　among　social　insects　presented　〃the　most　serious　special　difficulty〃　in　the　way　of　his　theory　of　natural　selection；　and　it　was　only　after　it　had　become　clear　to　him；　that　it　was　not　the　sterile　insects　themselves　but　their　parents　that　were　selected；　according　as　they　produced　more　or　less　well　adapted　workers；　that　he　was　able　to　refer　to　this　very　case　of　the　conditions　among　ants　〃IN　ORDER　TO　SHOW　THE　POWER　OF　NATURAL　SELECTION〃　（〃Origin　of　Species〃；　page　233；　see　also　edition　1；　page　242。）。　　He　explains　his　view　by　a　simple　but　interesting　illustration。　　Gardeners　have　produced；　by　means　of　long　continued　artificial　selection；　a　variety　of　Stock；　which　bears　entirely　double；　and　therefore　infertile　flowers　（Ibid。　page　230。）。　　Nevertheless　the　variety　continues　to　be　reproduced　from　seed；　because　in　addition　to　the　double　and　infertile　flowers；　the　seeds　always　produce　a　certain　number　of　single；　fertile　blossoms；　and　these　are　used　to　reproduce　the　double　variety。　　These　single　and　fertile　plants　correspond　〃to　the　males　and　females　of　an　ant…colony；　the　infertile　plants；　which　are　regularly　produced　in　large　numbers；　to　the　neuter　workers　of　the　colony。〃

This　illustration　is　entirely　apt；　the　only　difference　between　the　two　cases　consisting　in　the　fact　that　the　variation　in　the　flower　is　not　a　useful；　but　a　disadvantageous　one；　which　can　only　be　preserved　by　artificial　selection　on　the　part　of　the　gardener；　while　the　transformations　that　have　taken　place　parallel　with　the　sterility　of　the　ants　are　useful；　since　they　procure　for　the　colony　an　advantage　in　the　struggle　for　existence；　and　they　are　therefore　preserved　by　natural　selection。　　Even　the　sterility　itself　in　this　case　is　not　disadvantageous；　since　the　fertility　of　the　true　females　has　at　the　same　time　considerably　increased。　　We　may　therefore　regard　the　sterile　forms　of　ants；　which　have　gradually　been　adapted　in　several　directions　to　varying　functions；　AS　A　CERTAIN　PROOF　that　selection　really　takes　place　in　the　germ…cells　of　the　fathers　and　mothers　of　the　workers；　and　that　SPECIAL　COMPLEXES　OF　PRIMORDIA　（IDS）　are　present　in　the　workers　and　in　the　males　and　females；　and　these　complexes　contain　the　primordia　of　the　individual　parts　（DETERMINANTS）。　　But　since　all　living　entities　vary；　the　determinants　must　also　vary；　now　in　a　favourable；　now　in　an　unfavourable　direction。　　If　a　female　produces　eggs；　which　contain　favourably　varying　determinants　in　the　worker…ids；　then　these　eggs　will　give　rise　to　workers　modified　in　the　favourable　direction；　and　if　this　happens　with　many　females；　the　colony　concerned　will　contain　a　better　kind　of　worker　than　other　colonies。

I　digress　here　in　order　to　give　an　account　of　the　intimate　processes；　which；　according　to　my　view；　take　place　within　the　germ…plasm；　and　which　I　have　called　〃GERMINAL　SELECTION。〃　　These　processes　are　of　importance　since　they　form　the　roots　of　variation；　which　in　its　turn　is　the　root　of　natural　selection。　　I　cannot　here　do　more　than　give　a　brief　outline　of　the　theory　in　order　to　show　how　the　Darwin…Wallace　theory　of　selection　has　gained　support　from　it。

With　others；　I　regard　the　minimal　amount　of　substance　which　is　contained　within　the　nucleus　of　the　germ…cells；　in　the　form　of　rods；　bands；　or　granules；　as　the　GERM…SUBSTANCE　or　GERM…PLASM；　and　I　call　the　individual　granules　IDS。　　There　is　always　a　multiplicity　of　such　ids　present　in　the　nucleus；　either　occurring　individually；　or　united　in　the　form　of　rods　or　bands　（chromosomes）。　　Each　id　contains　the　primary　constituents　of　a　WHOLE　individual；　so　that　several　ids　are　concerned　in　the　development　of　a　new　individual。

In　every　being　of　complex　str