darwin and modern science-第149章

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s　Darwin　admitted　this　doctrine　as　supplementary　to　that　which　was　more　distinctively　his　ownfor　example　in　the　case　of　the　instincts　of　domesticated　animals。　　Still；　even　in　such　cases；　〃it　may　be　doubted；〃　he　says　（Ibid。　pages　210；　211。）；　〃whether　any　one　would　have　thought　of　training　a　dog　to　point；　had　not　some　one　dog　naturally　shown　a　tendency　in　this　line。。。so　that　habit　and　some　degree　of　selection　have　probably　concurred　in　civilising　by　inheritance　our　dogs。〃　　But　in　the　interpretation　of　the　instincts　of　domesticated　animals；　a　more　recently　suggested　hypothesis；　that　of　organic　selection　（Independently　suggested；　on　somewhat　different　lines；　by　Profs。　J。　Mark　Baldwin；　Henry　F。　Osborn　and　the　writer。）；　may　be　helpful。　　According　to　this　hypothesis　any　intelligent　modification　of　behaviour　which　is　subject　to　selection　is　probably　coincident　in　direction　with　an　inherited　tendency　to　behave　in　this　fashion。　　Hence　in　such　behaviour　there　are　two　factors：　　（1）　an　incipient　variation　in　the　line　of　such　behaviour；　and　（2）　an　acquired　modification　by　which　the　behaviour　is　carried　further　along　the　same　line。　　Under　natural　selection　those　organisms　in　which　the　two　factors　cooperate　are　likely　to　survive。　　Under　artificial　selection　they　are　deliberately　chosen　out　from　among　the　rest。

Organic　selection　has　been　termed　a　compromise　between　the　more　strictly　Darwinian　and　the　Lamarckian　principles　of　interpretation。　　But　it　is　not　in　any　sense　a　compromise。　　The　principle　of　interpretation　of　that　which　is　instinctive　and　hereditary　is　wholly　Darwinian。　　It　is　true　that　some　of　the　facts　of　observation　relied　upon　by　Lamarckians　are　introduced。　　For　Lamarckians　however　the　modifications　which　are　admittedly　factors　in　survival；　are　regarded　as　the　parents　of　inherited　variations；　for　believers　in　organic　selection　they　are　only　the　foster　parents　or　nurses。　It　is　because　organic　selection　is　the　direct　outcome　of　and　a　natural　extension　of　Darwin's　cardinal　thesis　that　some　reference　to　it　here　is　justifiable。　　The　matter　may　be　put　with　the　utmost　brevity　as　follows。　　（1）　Variations　（V）　occur；　some　of　which　are　in　the　direction　of　increased　adaptation　（＋）；　others　in　the　direction　of　decreased　adaptation　（…）。　　（2）　Acquired　modifications　（M）　also　occur。　　Some　of　these　are　in　the　direction　of　increased　accommodation　to　circumstances　（＋）；　while　others　are　in　the　direction　of　diminished　accommodation　（…）。　　Four　major　combinations　are　

（a）　　＋　V　with　＋　M；　（b）　　＋　V　with　…　M；　（c）　　…　V　with　＋　M；　（d）　　…　V　with　…　M。

Of　these　（d）　must　inevitably　be　eliminated　while　（a）　are　selected。　　The　predominant　survival　of　（a）　entails　the　survival　of　the　adaptive　variations　which　are　inherited。　　The　contributory　acquisitions　（＋M）　are　not　inherited；　but　they　are　none　the　less　factors　in　determining　the　survival　of　the　coincident　variations。　　It　is　surely　abundantly　clear　that　this　is　Darwinism　and　has　no　tincture　of　Lamarck's　essential　principle；　the　inheritance　of　acquired　characters。

Whether　Darwin　himself　would　have　accepted　this　interpretation　of　some　at　least　of　the　evidence　put　forward　by　Lamarckians　is　unfortunately　a　matter　of　conjecture。　　The　fact　remains　that　in　his　interpretation　of　instinct　and　in　allied　questions　he　accepted　the　inheritance　of　individually　acquired　modifications　of　behaviour　and　structure。

Darwin　was　chiefly　concerned　with　instinct　from　the　biological　rather　than　from　the　psychological　point　of　view。　　Indeed　it　must　be　confessed　that；　from　the　latter　standpoint；　his　conception　of　instinct　as　a　〃mental　faculty〃　which　〃impels〃　an　animal　to　the　performance　of　certain　actions；　scarcely　affords　a　satisfactory　basis　for　genetic　treatment。　　To　carry　out　the　spirit　of　Darwin's　teaching　it　is　necessary　to　link　more　closely　biological　and　psychological　evolution。　　The　first　step　towards　this　is　to　interpret　the　phenomena　of　instinctive　behaviour　in　terms　of　stimulation　and　response。　　It　may　be　well　to　take　a　particular　case。　　Swimming　on　the　part　of　a　duckling　is；　from　the　biological　point　of　view；　a　typical　example　of　instinctive　behaviour。　　Gently　lower　a　recently　hatched　bird　into　water：　　coordinated　movements　of　the　limbs　follow　in　rhythmical　sequence。　　The　behaviour　is　new　to　the　individual　though　it　is　no　doubt　closely　related　to　that　of　walking；　which　is　no　less　instinctive。　　There　is　a　group　of　stimuli　afforded　by　the　〃presentation〃　which　results　from　partial　immersion：　　upon　this　there　follows　as　a　complex　response　an　application　of　the　functional　activities　in　swimming；　the　sequence　of　adaptive　application　on　the　appropriate　presentation　is　determined　by　racial　preparation。　　We　know；　it　is　true；　but　little　of　the　physiological　details　of　what　takes　place　in　the　central　nervous　system；　but　in　broad　outline　the　nature　of　the　organic　mechanism　and　the　manner　of　its　functioning　may　at　least　be　provisionally　conjectured　in　the　present　state　of　physiological　knowledge。　　Similarly　in　the　case　of　the　pecking　of　newly…hatched　chicks；　there　is　a　visual　presentation；　there　is　probably　a　cooperating　group　of　stimuli　from　the　alimentary　tract　in　need　of　food；　there　is　an　adaptive　application　of　the　activities　in　a　definite　mode　of　behaviour。　　Like　data　are　afforded　in　a　great　number　of　cases　of　instinctive　procedure；　sometimes　occurring　very　early　in　life；　not　infrequently　deferred　until　the　organism　is　more　fully　developed；　but　all　of　them　dependent　upon　racial　preparation。　　No　doubt　there　is　some　range　of　variation　in　the　behaviour；　just　such　variation　as　the　theory　of　natural　selection　demands。　　But　there　can　be　no　question　that　the　higher　animals　inherit　a　bodily　organisation　and　a　nervous　system；　the　functional　working　of　which　gives　rise　to　those　inherited　modes　of　behaviour　which　are　termed　instinctive。

It　is　to　be　noted　that　the　term　〃instinctive〃　is　here　employed　in　the　adjectival　form　as　a　descriptive　heading　under　which　may　be　grouped　many　and　various　modes　of　behaviour　due　to　racial　preparation。　　We　speak　of　these　as　inherited；　but　in　strictness　what　is　transmitted　through　heredity　is　the　complex　of　anatomical　and　physiological　conditions　under　which；　in　appropriate　circumstances；　the　organism　so　behaves。　　So　far　the　term　〃instinctive〃　has　a　restricted　biological　connotation　in　terms　of　behaviour。　　But　the　connecting　link　between　biological　evolution　and　psychological　evolution　is　to　be　sought；as　Darwin　fully　realised；in　the　phenomena　of　instinct；　broadly　considered。　　The　term　〃instinctive〃　has　also　a　psychological　connotation。　　What　is　that　connotation？

Let　us　take　the　case　of　the　swimming　duckling　or　the　pecking　chick；　and　fix　our　attention　on　the　first　instinctive　performance。　　Grant　that　just　as　there　is；　strictly　speaking；　no　inherited　behaviour；　but　only　the　conditions　which　render　such　behaviour　under　appropriate　circumstances　possible；　so　too　there　is　no　inherited　experience；　but　only　the　conditions　which　render　such　experience　possible；　then　the　cerebral　conditions　in　both　cases　are　the　same。　　The　biological　behaviour…complex；　including　the　total　stimulation　and　the　total　response　with　the　intervening　or　resultant　processes　in　the　sensorium；　is　accompanied　by　an　experience…complex　including　the　initial　stimulation…consciousness　and　resulting　response…　consciousness。　　In　the　experience…complex　are　comprised　data　which　in　psychological　analysis　are　grouped　under　the　headings　of　cognition；　affective　tone　and　conation。　　But　the　complex　is　probably　experienced　as　an　unanalysed　whole。　　If　then　we　use　the　term　〃instinctive〃　so　as　to　comprise　all　congenital　modes　of　behaviour　which　contribute　to　experience；　we　are　in　a　position　to　grasp　the　view　that　the　net　result　in　consciousness　constitutes　what　we　may　term　the　primary　tissue　of　experience。　　To　the　development　of　this　experience　each　instinctive　act　contributes。　　The　nature　and　manner　of　organisation　of　this　primary　tissue　of　experience　are　dependent　on　inherited　biological　aptitudes；　but　they　are　from　the　outset　onwards　subject　to　secondary　development　dependent　on　acquired　aptitudes。　　Biological　values　are　supplemented　by　psychological　values　in　terms　of　satisfaction　or　the　reverse。

In　our　study　of　instinct　we　have　to　select　some　particular　ph