darwin and modern science-第135节

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ally　led　on　to　the　consideration　of　many　of　the　phenomena　which　are　discussed　under　the　head　of　sexual　selection。　　The　subject　is　difficult　and　complex；　and　it　was　treated　by　Darwin　with　all　the　strength　he　could　summon　to　the　task。　　It　can　only　be　dealt　with　here　from　a　special　point　of　viewthat　which　may　serve　to　illustrate　the　influence　of　certain　mental　factors　on　the　course　of　evolution。　　From　this　point　of　view　too　much　stress　can　scarcely　be　laid　on　the　dominance　of　emotion　during　the　period　of　courtship　and　pairing　in　the　more　highly　organised　animals。　　It　is　a　period　of　maximum　vigour；　maximum　activity；　and；　correlated　with　special　modes　of　behaviour　and　special　organic　and　visceral　accompaniments；　a　period　also　of　maximum　emotional　excitement。　　The　combats　of　males；　their　dances　and　aerial　evolutions；　their　elaborate　behaviour　and　display；　or　the　flood　of　song　in　birds；　are　emotional　expressions　which　are　at　any　rate　coincident　in　time　with　sexual　periodicity。　　From　the　combat　of　the　males　there　follows　on　Darwin's　principles　the　elimination　of　those　which　are　deficient　in　bodily　vigour；　deficient　in　special　structures；　offensive　or　protective；　which　contribute　to　success；　deficient　in　the　emotional　supplement　of　which　persistent　and　whole…hearted　fighting　is　the　expression；　and　deficient　in　alertness　and　skill　which　are　the　outcome　of　the　psychological　development　of　the　powers　of　perception。　　Few　biologists　question　that　we　have　here　a　mode　of　selection　of　much　importance；　though　its　influence　on　psychological　evolution　often　fails　to　receive　its　due　emphasis。　　Mr　Wallace　（〃Darwinism〃；　pages　282；　283；　London；　1889。）　regards　it　as　〃a　form　of　natural　selection〃；　〃to　it；〃　he　says；　〃we　must　impute　the　development　of　the　exceptional　strength；　size；　and　activity　of　the　male；　together　with　the　possession　of　special　offensive　and　defensive　weapons；　and　of　all　other　characters　which　arise　from　the　development　of　these　or　are　correlated　with　them。〃　　So　far　there　is　little　disagreement　among　the　followers　of　Darwin　for　Mr　Wallace；　with　fine　magnanimity；　has　always　preferred　to　be　ranked　as　such；　notwithstanding　his　right；　on　which　a　smaller　man　would　have　constantly　insisted；　to　the　claim　of　independent　originator　of　the　doctrine　of　natural　selection。　　So　far　with　regard　to　sexual　selection　Darwin　and　Mr　Wallace　are　agreed；　so　far　and　no　farther。　　For　Darwin；　says　Mr　Wallace　（Ibid。　page　283。）；　〃has　extended　the　principle　into　a　totally　different　field　of　action；　which　has　none　of　that　character　of　constancy　and　of　inevitable　result　that　attaches　to　natural　selection；　including　male　rivalry；　for　by　far　the　larger　portion　of　the　phenomena；　which　he　endeavours　to　explain　by　the　direct　action　of　sexual　selection；　can　only　be　so　explained　on　the　hypothesis　that　the　immediate　agency　is　female　choice　or　preference。　　It　is　to　this　that　he　imputes　the　origin　of　all　secondary　sexual　characters　other　than　weapons　of　offence　and　defence。。。In　this　extension　of　sexual　selection　to　include　the　action　of　female　choice　or　preference；　and　in　the　attempt　to　give　to　that　choice　such　wide…reaching　effects；　I　am　unable　to　follow　him　more　than　a　very　little　way。〃

Into　the　details　of　Mr　Wallace's　criticisms　it　is　impossible　to　enter　here。　We　cannot　discuss　either　the　mode　of　origin　of　the　variations　in　structure　which　have　rendered　secondary　sexual　characters　possible　or　the　modes　of　selection　other　than　sexual　which　have　rendered　them；　within　narrow　limits；　specifically　constant。　　Mendelism　and　mutation　theories　may　have　something　to　say　on　the　subject　when　these　theories　have　been　more　fully　correlated　with　the　basal　principles　of　selection。　　It　is　noteworthy　that　Mr　Wallace　says　（〃Darwinism〃；　pages　283；　284。）：　　〃Besides　the　acquisition　of　weapons　by　the　male　for　the　purpose　of　fighting　with　other　males；　there　are　some　other　sexual　characters　which　may　have　been　produced　by　natural　selection。　Such　are　the　various　sounds　and　odours　which　are　peculiar　to　the　male；　and　which　serve　as　a　call　to　the　female　or　as　an　indication　of　his　presence。　　These　are　evidently　a　valuable　addition　to　the　means　of　recognition　of　the　two　sexes；　and　are　a　further　indication　that　the　pairing　season　has　arrived；　and　the　production；　intensification；　and　differentiation　of　these　sounds　and　odours　are　clearly　within　the　power　of　natural　selection。　　The　same　remark　will　apply　to　the　peculiar　calls　of　birds；　and　even　to　the　singing　of　the　males。〃　　Why　the　same　remark　should　not　apply　to　their　colours　and　adornments　is　not　obvious。　　What　is　obvious　is　that　〃means　of　recognition〃　and　〃indication　that　the　pairing　season　has　arrived〃　are　dependent　on　the　perceptive　powers　of　the　female　who　recognises　and　for　whom　the　indication　has　meaning。　　The　hypothesis　of　female　preference；　stripped　of　the　aesthetic　surplusage　which　is　psychologically　both　unnecessary　and　unproven；　is　really　only　different　in　degree　from　that　which　Mr　Wallace　admits　in　principle　when　he　says　that　it　is　probable　that　the　female　is　pleased　or　excited　by　the　display。

Let　us　for　our　present　purpose　leave　on　one　side　and　regard　as　sub　judice　the　question　whether　the　specific　details　of　secondary　sexual　characters　are　the　outcome　of　female　choice。　　For　us　the　question　is　whether　certain　psychological　accompaniments　of　the　pairing　situation　have　influenced　the　course　of　evolution　and　whether　these　psychological　accompaniments　are　themselves　the　outcome　of　evolution。　　As　a　matter　of　observation；　specially　differentiated　modes　of　behaviour；　often　very　elaborate；　frequently　requiring　highly　developed　skill；　and　apparently　highly　charged　with　emotional　tone；　are　the　precursors　of　pairing。　　They　are　generally　confined　to　the　males；　whose　fierce　combats　during　the　period　of　sexual　activity　are　part　of　the　emotional　manifestation。　　It　is　inconceivable　that　they　have　no　biological　meaning；　and　it　is　difficult　to　conceive　that　they　have　any　other　biological　end　than　to　evoke　in　the　generally　more　passive　female　the　pairing　impulse。　　They　are　based　on　instinctive　foundations　ingrained　in　the　nervous　constitution　through　natural　（or　may　we　not　say　sexual？）　selection　in　virtue　of　their　profound　utility。　　They　are　called　into　play　by　a　specialised　presentation　such　as　the　sight　or　the　scent　of　the　female　at；　or　a　little　in　advance　of；　a　critical　period　of　the　physiological　rhythm。　　There　is　no　necessity　that　the　male　should　have　any　knowledge　of　the　end　to　which　his　strenuous　activity　leads　up。　　In　presence　of　the　female　there　is　an　elaborate　application　of　all　the　energies　of　behaviour；　just　because　ages　of　racial　preparation　have　made　him　biologically　and　emotionally　what　he　isa　functionally　sexual　male　that　must　dance　or　sing　or　go　through　hereditary　movements　of　display；　when　the　appropriate　stimulation　comes。　　Of　course　after　the　first　successful　courtship　his　future　behaviour　will　be　in　some　degree　modified　by　his　previous　experience。　　No　doubt　during　his　first　courtship　he　is　gaining　the　primary　data　of　a　peculiarly　rich　experience；　instinctive　and　emotional。　　But　the　biological　foundations　of　the　behaviour　of　courtship　are　laid　in　the　hereditary　coordinations。　　It　would　seem　that　in　some　cases；　not　indeed　in　all；　but　perhaps　especially　in　those　cases　in　which　secondary　sexual　behaviour　is　most　highly　evolved；correlative　with　the　ardour　of　the　male　is　a　certain　amount　of　reluctance　in　the　female。　　The　pairing　act　on　her　part　only　takes　place　after　prolonged　stimulation；　for　affording　which　the　behaviour　of　male　courtship　is　the　requisite　presentation。　　The　most　vigorous；　defiant　and　mettlesome　male　is　preferred　just　because　he　alone　affords　a　contributory　stimulation　adequate　to　evoke　the　pairing　impulse　with　its　attendant　emotional　tone。

It　is　true　that　this　places　female　preference　or　choice　on　a　much　lower　psychological　plane　than　Darwin　in　some　passages　seems　to　contemplate　where；　for　example；　he　says　that　the　female　appreciates　the　display　of　the　male　and　places　to　her　credit　a　taste　for　the　beautiful。　　But　Darwin　himself　distinctly　states　（〃Descent　of　Man〃　（2nd　edition）；　Vol。　II。　pages　136；　137；　（Popular　edition）；　pages　642；　643。）　that　〃it　is　not　probable　that　she　consciously　deliberates；　but　she　is　most　excited　or　attracted　by　the　most　beautiful；　or　melodious；　or　gallant　males。〃　　The　view　here　put　forward；　which　has　been　developed　by　Prof。　Groos　（〃The　Play　of　Animals〃；　page　244；　London；　1898。）；　therefore　seems　to　have　Darwin's　own　sanction。　　The　phenomena　are　not　only　biological；　there　are　psychological　elements　as　well。　　One　can　hardly　suppose　that　the　female　is　unconscious　of　the　male's　presence；　the　final　yielding　must　surely　be　accompanied　by　heightened　emotional　tone。　　Whether　we　call　it　choice　or　not　is　merely　a　matter　of　definition　of　terms。　　The　behaviour　is　in　part　determined　by　supplementary　psychological　values。　　Prof。　Groos　regards　the　coyness　of　females　as　〃a　most　efficient　means　of　preventing　the　too　early　and　too　frequent　yielding　to　the　sexual　impulse。〃　　（Ibid。　page　283。）　　Be　that　as　it　may；　it　is；　in　any　case；　if　we　grant　the　facts；　a　means　through　which　male　sexual　behaviour　with　all　its　biological　and　psychological　implications；　is　raised　to　a　level　otherwise　perhaps　unattainable　by　natural　means；　wh