darwin and modern science-第51章

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y…four　years　in　a　number　of　able　volumes；　and　is　regarded　by　many　biologists；　such　as　Mr　Francis　Galton；　Sir　E。　Ray　Lankester；　and　Professor　J。　Arthur　Thomson　（who　has　recently　made　a　thoroughgoing　defence　of　it　in　his　important　work　〃Heredity〃　（London；　1908。））；　as　the　most　striking　advance　in　evolutionary　science。　　On　the　other　hand；　the　theory　has　been　rejected　by　Herbert　Spencer；　Sir　W。　Turner；　Gegenbaur；　Kolliker；　Hertwig；　and　many　others。　　For　my　part　I　have；　with　all　respect　for　the　distinguished　Darwinian；　contested　the　theory　from　the　first；　because　its　whole　foundation　seems　to　me　erroneous；　and　its　deductions　do　not　seem　to　be　in　accord　with　the　main　facts　of　comparative　morphology　and　physiology。　　Weismann's　theory　in　its　entirety　is　a　finely　conceived　molecular　hypothesis；　but　it　is　devoid　of　empirical　basis。　　The　notion　of　the　absolute　and　permanent　independence　of　the　germ…plasm；　as　distinguished　from　the　soma…plasm；　is　purely　speculative；　as　is　also　the　theory　of　germinal　selection。　　The　determinants；　ids；　and　idants；　are　purely　hypothetical　elements。　　The　experiments　that　have　been　devised　to　demonstrate　their　existence　really　prove　nothing。

It　seems　to　me　quite　improper　to　describe　this　hypothetical　structure　as　〃Neodarwinism。〃　　Darwin　was　just　as　convinced　as　Lamarck　of　the　transmission　of　acquired　characters　and　its　great　importance　in　the　scheme　of　evolution。　　I　had　the　good　fortune　to　visit　Darwin　at　Down　three　times　and　discuss　with　him　the　main　principles　of　his　system；　and　on　each　occasion　we　were　fully　agreed　as　to　the　incalculable　importance　of　what　I　call　transformative　inheritance。　　It　is　only　proper　to　point　out　that　Weismann's　theory　of　the　germ…plasm　is　in　express　contradiction　to　the　fundamental　principles　of　Darwin　and　Lamarck。　　Nor　is　it　more　acceptable　in　what　one　may　call　its　〃ultradarwinism〃the　idea　that　the　theory　of　selection　explains　everything　in　the　evolution　of　the　organic　world。　　This　belief　in　the　〃omnipotence　of　natural　selection〃　was　not　shared　by　Darwin　himself。　　Assuredly；　I　regard　it　as　of　the　utmost　value；　as　the　process　of　natural　selection　through　the　struggle　for　life　affords　an　explanation　of　the　mechanical　origin　of　the　adapted　organisation。　　It　solves　the　great　problem：　　how　could　the　finely　adapted　structure　of　the　animal　or　plant　body　be　formed　unless　it　was　built　on　a　preconceived　plan？　　It　thus　enables　us　to　dispense　with　the　teleology　of　the　metaphysician　and　the　dualist；　and　to　set　aside　the　old　mythological　and　poetic　legends　of　creation。　　The　idea　had　occurred　in　vague　form　to　the　great　Empedocles　2000　years　before　the　time　of　Darwin；　but　it　was　reserved　for　modern　research　to　give　it　ample　expression。　　Nevertheless；　natural　selection　does　not　of　itself　give　the　solution　of　all　our　evolutionary　problems。　　It　has　to　be　taken　in　conjunction　with　the　transformism　of　Lamarck；　with　which　it　is　in　complete　harmony。

The　monumental　greatness　of　Charles　Darwin；　who　surpasses　every　other　student　of　science　in　the　nineteenth　century　by　the　loftiness　of　his　monistic　conception　of　nature　and　the　progressive　influence　of　his　ideas；　is　perhaps　best　seen　in　the　fact　that　not　one　of　his　many　successors　has　succeeded　in　modifying　his　theory　of　descent　in　any　essential　point　or　in　discovering　an　entirely　new　standpoint　in　the　interpretation　of　the　organic　world。　　Neither　Nageli　nor　Weismann；　neither　De　Vries　nor　Roux；　has　done　this。　　Nageli；　in　his　〃Mechanisch…Physiologische　Theorie　der　Abstammungslehre〃　（Munich；　1884。）；　which　is　to　a　great　extent　in　agreement　with　Weismann；　constructed　a　theory　of　the　idioplasm；　that　represents　it　（like　the　germ…plasm）　as　developing　continuously　in　a　definite　direction　from　internal　causes。　　But　his　internal　〃principle　of　progress〃　is　at　the　bottom　just　as　teleological　as　the　vital　force　of　the　Vitalists；　and　the　micellar　structure　of　the　idioplasm　is　just　as　hypothetical　as　the　〃dominant〃　structure　of　the　germ…plasm。　　In　1889　Moritz　Wagner　sought　to　explain　the　origin　of　species　by　migration　and　isolation；　and　on　that　basis　constructed　a　special　〃migration…theory。〃　　This；　however；　is　not　out　of　harmony　with　the　theory　of　selection。　　It　merely　elevates　one　single　factor　in　the　theory　to　a　predominant　position。　　Isolation　is　only　a　special　case　of　selection；　as　I　had　pointed　out　in　the　fifteenth　chapter　of　my　〃Natural　history　of　creation〃。　　The　〃mutation…theory〃　of　De　Vries　（〃Die　Mutationstheorie〃；　Leipzig；　1903。）；　that　would　explain　the　origin　of　species　by　sudden　and　saltatory　variations　rather　than　by　gradual　modification；　is　regarded　by　many　botanists　as　a　great　step　in　advance；　but　it　is　generally　rejected　by　zoologists。　　It　affords　no　explanation　of　the　facts　of　adaptation；　and　has　no　causal　value。

Much　more　important　than　these　theories　is　that　of　Wilhelm　Roux　（〃Der　Kampf　der　Theile　im　Organismus〃；　Leipzig；　1881。）　of　〃the　struggle　of　parts　within　the　organism；　a　supplementation　of　the　theory　of　mechanical　adaptation。〃　　He　explains　the　functional　autoformation　of　the　purposive　structure　by　a　combination　of　Darwin's　principle　of　selection　with　Lamarck's　idea　of　transformative　heredity；　and　applies　the　two　in　conjunction　to　the　facts　of　histology。　　He　lays　stress　on　the　significance　of　functional　adaptation；　which　I　had　described　in　1866；　under　the　head　of　cumulative　adaptation；　as　the　most　important　factor　in　evolution。　　Pointing　out　its　influence　in　the　cell…life　of　the　tissues；　he　puts　〃cellular　selection〃　above　〃personal　selection；〃　and　shows　how　the　finest　conceivable　adaptations　in　the　structure　of　the　tissue　may　be　brought　about　quite　mechanically；　without　preconceived　plan。　　This　〃mechanical　teleology〃　is　a　valuable　extension　of　Darwin's　monistic　principle　of　selection　to　the　whole　field　of　cellular　physiology　and　histology；　and　is　wholly　destructive　of　dualistic　vitalism。

The　most　important　advance　that　evolution　has　made　since　Darwin　and　the　most　valuable　amplification　of　his　theory　of　selection　is；　in　my　opinion；　the　work　of　Richard　Semon：　　〃Die　Mneme　als　erhaltendes　Prinzip　im　Wechsel　des　organischen　Geschehens〃　（Leipzig；　1904。）。　　He　offers　a　psychological　explanation　of　the　facts　of　heredity　by　reducing　them　to　a　process　of　（unconscious）　memory。　　The　physiologist　Ewald　Hering　had　shown　in　1870　that　memory　must　be　regarded　as　a　general　function　of　organic　matter；　and　that　we　are　quite　unable　to　explain　the　chief　vital　phenomena；　especially　those　of　reproduction　and　inheritance；　unless　we　admit　this　unconscious　memory。　In　my　essay　〃Die　Perigenesis　der　Plastidule〃　（Berlin；　1876。）　I　elaborated　this　far…reaching　idea；　and　applied　the　physical　principle　of　transmitted　motion　to　the　plastidules；　or　active　molecules　of　plasm。　　I　concluded　that　〃heredity　is　the　memory　of　the　plastidules；　and　variability　their　power　of　comprehension。〃　　This　〃provisional　attempt　to　give　a　mechanical　explanation　of　the　elementary　processes　of　evolution〃　I　afterwards　extended　by　showing　that　sensitiveness　is　（as　Carl　Nageli；　Ernst　Mach；　and　Albrecht　Rau　express　it）　a　general　quality　of　matter。　　This　form　of　panpsychism　finds　its　simplest　expression　in　the　〃trinity　of　substance。〃

To　the　two　fundamental　attributes　that　Spinoza　ascribed　to　substance　Extension　（matter　as　occupying　space）　and　Cogitation　（energy；　force）we　now　add　the　third　fundamental　quality　of　Psychoma　（sensitiveness；　soul）。　　I　further　elaborated　this　trinitarian　conception　of　substance　in　the　nineteenth　chapter　of　my　〃Die　Lebenswunder〃　（1904）　（〃Wonders　of　Life〃；　London；　1904。）；　and　it　seems　to　me　well　calculated　to　afford　a　monistic　solution　of　many　of　the　antitheses　of　philosophy。

This　important　Mneme…theory　of　Semon　and　the　luminous　physiological　experiments　and　observations　associated　with　it　not　only　throw　considerable　light　on　transformative　inheritance；　but　provide　a　sound　physiological　foundation　for　the　biogenetic　law。　　I　had　endeavoured　to　show　in　1874；　in　the　first　chapter　of　my　〃Anthropogenie〃　（English　translation；　〃The　Evolution　of　Man〃；　2　volumes；　London；　1879　and　1905。）；　that　this　fundamental　law　of　organic　evolution　holds　good　generally；　and　that　there　is　everywhere　a　direct　causal　connection　between　ontogeny　and　phylogeny。　　〃Phylogenesis　is　the　mechanical　cause　of　ontogen