darwin and modern science-第136节

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psychological　implications；　is　raised　to　a　level　otherwise　perhaps　unattainable　by　natural　means；　while　in　the　female　it　affords　opportunities　for　the　development　in　the　individual　and　evolution　in　the　race　of　what　we　may　follow　Darwin　in　calling　appreciation；　if　we　empty　this　word　of　the　aesthetic　implications　which　have　gathered　round　it　in　the　mental　life　of　man。

Regarded　from　this　standpoint　sexual　selection；　broadly　considered；　has　probably　been　of　great　importance。　　The　psychological　accompaniments　of　the　pairing　situation　have　profoundly　influenced　the　course　of　biological　evolution　and　are　themselves　the　outcome　of　that　evolution。

Darwin　makes　only　passing　reference　to　those　modes　of　behaviour　in　animals　which　go　by　the　name　of　play。　　〃Nothing；〃　he　says　（〃Descent　of　Man〃；　Vol。　II。　page　60；　（Popular　edition）；　page　566。）；　〃is　more　common　than　for　animals　to　take　pleasure　in　practising　whatever　instinct　they　follow　at　other　times　for　some　real　good。〃　　This　is　one　of　the　very　numerous　cases　in　which　a　hint　of　the　master　has　served　to　stimulate　research　in　his　disciples。　　It　was　left　to　Prof。　Groos　to　develop　this　subject　on　evolutionary　lines　and　to　elaborate　in　a　masterly　manner　Darwin's　suggestion。　　〃The　utility　of　play；〃　he　says　（〃The　Play　of　Animals〃；　page　76。）；　〃is　incalculable。　　This　utility　consists　in　the　practice　and　exercise　it　affords　for　some　of　the　more　important　duties　of　life；〃that　is　to　say；　for　the　performance　of　activities　which　will　in　adult　life　be　essential　to　survival。　　He　urges　（Ibid。　page　75。）　that　〃the　play　of　young　animals　has　its　origin　in　the　fact　that　certain　very　important　instincts　appear　at　a　time　when　the　animal　does　not　seriously　need　them。〃　　It　is；　however；　questionable　whether　any　instincts　appear　at　a　time　when　they　are　not　needed。　　And　it　is　questionable　whether　the　instinctive　and　emotional　attitude　of　the　play…fight；　to　take　one　example；　can　be　identified　with　those　which　accompany　fighting　in　earnest；　though　no　doubt　they　are　closely　related　and　have　some　common　factors。　　It　is　probable　that　play；　as　preparatory　behaviour；　differs　in　biological　detail　（as　it　almost　certainly　does　in　emotional　attributes）　from　the　earnest　of　after…life　and　that　it　has　been　evolved　through　differentiation　and　integration　of　the　primary　tissue　of　experience；　as　a　preparation　through　which　certain　essential　modes　of　skill　may　be　acquiredthose　animals　in　which　the　preparatory　play…propensity　was　not　inherited　in　due　force　and　requisite　amount　being　subsequently　eliminated　in　the　struggle　for　existence。　　In　any　case　there　is　little　question　that　Prof。　Groos　is　right　in　basing　the　play…propensity　on　instinctive　foundations。　　（〃The　Play　of　Animals〃　page　24。）　　None　the　less；　as　he　contends；　the　essential　biological　value　of　play　is　that　it　is　a　means　of　training　the　educable　nerve…tissue；　of　developing　that　part　of　the　brain　which　is　modified　by　experience　and　which　thus　acquires　new　characters；　of　elaborating　the　secondary　tissue　of　experience　on　the　predetermined　lines　of　instinctive　differentiation　and　thus　furthering　the　psychological　activities　which　are　included　under　the　comprehensive　term　〃intelligent。〃

In　〃The　Descent　of　Man〃　Darwin　dealt　at　some　length　with　intelligence　and　the　higher　mental　faculties。　　（〃Descent　of　Man〃　（1st　edition）；　Chapters　II；　III；　V；　（2nd　edition）；　Chapters　III；　IV；　V。）　　His　object；　he　says；　is　to　show　that　there　is　no　fundamental　difference　between　man　and　the　higher　mammals　in　their　mental　faculties；　that　these　faculties　are　variable　and　the　variations　tend　to　be　inherited；　and　that　under　natural　selection　beneficial　variations　of　all　kinds　will　have　been　preserved　and　injurious　ones　eliminated。

Darwin　was　too　good　an　observer　and　too　honest　a　man　to　minimise　the　〃enormous　difference〃　between　the　level　of　mental　attainment　of　civilised　man　and　that　reached　by　any　animal。　　His　contention　was　that　the　difference；　great　as　it　is；　is　one　of　degree　and　not　of　kind。　　He　realised　that；　in　the　development　of　the　mental　faculties　of　man；　new　factors　in　evolution　have　supervenedfactors　which　play　but　a　subordinate　and　subsidiary　part　in　animal　intelligence。　　Intercommunication　by　means　of　language；　approbation　and　blame；　and　all　that　arises　out　of　reflective　thought；　are　but　foreshadowed　in　the　mental　life　of　animals。　　Still　he　contends　that　these　may　be　explained　on　the　doctrine　of　evolution。　　He　urges　（Ibid。　Vol。　I。　pages　70；　71；　（Popular　edition）；　pages　70；　71。）〃　that　man　is　variable　in　body　and　mind；　and　that　the　variations　are　induced；　either　directly　or　indirectly；　by　the　same　general　causes；　and　obey　the　same　general　laws；　as　with　the　lower　animals。〃　　He　correlates　mental　development　with　the　evolution　of　the　brain。　　（Ibid。　page　81。）　　〃As　the　various　mental　faculties　gradually　developed　themselves；　the　brain　would　almost　certainly　become　larger。　　No　one；　I　presume；　doubts　that　the　large　proportion　which　the　size　of　man's　brain　bears　to　his　body；　compared　to　the　same　proportion　in　the　gorilla　or　orang；　is　closely　connected　with　his　higher　mental　powers。〃　　〃With　respect　to　the　lower　animals；〃　he　says　（〃Descent　of　Man〃　（Popular　edition）；　page　82。）；　〃M。E。　Lartet　（〃Comptes　Rendus　des　Sciences〃；　June　1；　1868。）；　by　comparing　the　crania　of　tertiary　and　recent　mammals　belonging　to　the　same　groups；　has　come　to　the　remarkable　conclusion　that　the　brain　is　generally　larger　and　the　convolutions　are　more　complex　in　the　more　recent　form。〃

Sir　E。　Ray　Lankester　has　sought　to　express　in　the　simplest　terms　the　implications　of　the　increase　in　size　of　the　cerebrum。　　〃In　what；〃　he　asks；　〃does　the　advantage　of　a　larger　cerebral　mass　consist？〃　　〃Man；〃　he　replies　〃is　born　with　fewer　ready…made　tricks　of　the　nerve…centresthese　performances　of　an　inherited　nervous　mechanism　so　often　called　by　the　ill…　defined　term　'instincts'than　are　the　monkeys　or　any　other　animal。　　Correlated　with　the　absence　of　inherited　ready…made　mechanism；　man　has　a　greater　capacity　of　developing　in　the　course　of　his　individual　growth　similar　nervous　mechanisms　（similar　to　but　not　identical　with　those　of　'instinct'）　than　any　other　animal。。。The　power　of　being　educated　'educability'　as　we　may　term　itis　what　man　possesses　in　excess　as　compared　with　the　apes。　　I　think　we　are　justified　in　forming　the　hypothesis　that　it　is　this　'educability'　which　is　the　correlative　of　the　increased　size　of　the　cerebrum。〃　　There　has　been　natural　selection　of　the　more　educable　animals；　for　〃the　character　which　we　describe　as　'educability'　can　be　transmitted；　it　is　a　congenital　character。　　But　the　RESULTS　of　education　can　NOT　be　transmitted。　　In　each　generation　they　have　to　be　acquired　afresh；　and　with　increased　'educability'　they　are　more　readily　acquired　and　a　larger　variety　of　them。。。The　fact　is　that　there　is　no　community　between　the　mechanisms　of　instinct　and　the　mechanisms　of　intelligence；　and　that　the　latter　are　later　in　the　history　of　the　evolution　of　the　brain　than　the　former　and　can　only　develop　in　proportion　as　the　former　become　feeble　and　defective。〃　　（〃Nature〃；　Vol。　LXI。　pages　624；　625　（1900）。）

In　this　statement　we　have　a　good　example　of　the　further　development　of　views　which　Darwin　foreshadowed　but　did　not　thoroughly　work　out。　　It　states　the　biological　case　clearly　and　tersely。　　Plasticity　of　behaviour　in　special　accommodation　to　special　circumstances　is　of　survival　value；　it　depends　upon　acquired　characters；　it　is　correlated　with　increase　in　size　and　complexity　of　the　cerebrum；　under　natural　selection　therefore　the　larger　and　more　complex　cerebrum　as　the　organ　of　plastic　behaviour　has　been　the　outcome　of　natural　selection。　　We　have　thus　the　biological　foundations　for　a　further　development　of　genetic　psychology。

There　are　diversities　of　opinion；　as　Darwin　showed；　with　regard　to　the　range　of　instinct　in　man　and　the　higher　animals　as　contrasted　with　lower　types。　　Darwin　himself　said　（〃Descent　of　Man〃；　Vol。　I。　page　100。）　that　〃Man；　perhaps；　has　somewhat　fewer　instincts　than　those　possessed　by　the　animals　which　come　next　to　him　in　the　series。〃　　On　the　other　hand；　Prof。　Wm。　James　says　（〃Principles　of　Psychology；〃　Vol。　II。　page　289。）　that　man　is　probably　the　animal　with　most　instincts。　　The　true　position　is　that　man　and　the　higher　animals　have　fewer　complete　and　self…sufficing　instincts　than　those　which　stand　lower　in　the　scale　of　mental　evolution；　but　that　they　have　an　equally　large　or　perhaps　larger　mass　of　instinctive　raw　material　which　may　furnish　the　stuff　to　be　elaborated　by　intelligent　processes。　　There　is；　perhaps；　a　greater　abundance　of　the　primary　tissue　of　experience　to　be　refashioned　and　integrated　by　secondary　modification；　there　is　probably　the　same　differentiation　in　relation　to　the　determining　biological　ends；　but　there　is　at　the　outset　less　differentiation　of　the　particular　and　specific　modes　of　behaviour。　　The　specialised　instinctive　performances　and　their　concomitant　experience…complexes　are　at　the　outset　more　indefinite。　　Only　through　acquired　connections；　correlated　with　experience；　do　they　become　definitely　organised。

The　full　working…out　of　the　delicate　and　subtle　relationship　of　instinct　and　educabilitythat　is；　of　the　hereditary　and　the　acquired　factors　in　the　mental　lifeis　the　task　which　lies　before　genetic　and　c