a history of science-4-第22章

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　Buffon　had　put　forward　the　idea　of　transmutation　of　species；　and　he　reiterated　it　from　time　to　time　from　then　on　till　his　death　in　1788。　But　the　time　was　not　yet　ripe　for　the　idea　of　transmutation　of　species　to　burst　its　bonds。

And　yet　this　idea；　in　a　modified　or　undeveloped　form；　had　taken　strange　hold　upon　the　generation　that　was　upon　the　scene　at　the　close　of　the　eighteenth　century。　Vast　numbers　of　hitherto　unknown　species　of　animals　had　been　recently　discovered　in　previously　unexplored　regions　of　the　globe；　and　the　wise　men　were　sorely　puzzled　to　account　for　the　disposal　of　all　of　these　at　the　time　of　the　deluge。　　It　simplified　matters　greatly　to　suppose　that　many　existing　species　had　been　developed　since　the　episode　of　the　ark　by　modification　of　the　original　pairs。　The　remoter　bearings　of　such　a　theory　were　overlooked　for　the　time；　and　the　idea　that　American　animals　and　birds；　for　example；　were　modified　descendants　of　Old…World　formsthe　jaguar　of　the　leopard；　the　puma　of　the　lion；　and　so　onbecame　a　current　belief　with　that　class　of　humanity　who　accept　almost　any　statement　as　true　that　harmonizes　with　their　prejudices　without　realizing　its　implications。

Thus　it　is　recorded　with　eclat　that　the　discovery　of　the　close　proximity　of　America　at　the　northwest　with　Asia　removes　all　difficulties　as　to　the　origin　of　the　Occidental　faunas　and　floras；　since　Oriental　species　might　easily　have　found　their　way　to　America　on　the　ice；　and　have　been　modified　as　we　find　them　by　〃the　well…known　influence　of　climate。〃　And　the　persons　who　gave　expression　to　this　idea　never　dreamed　of　its　real　significance。　　In　truth；　here　was　the　doctrine　of　evolution　in　a　nutshell；　and；　because　its　ultimate　bearings　were　not　clear；　it　seemed　the　most　natural　of　doctrines。　　But　most　of　the　persons　who　advanced　it　would　have　turned　from　it　aghast　could　they　have　realized　its　import。　As　it　was；　however；　only　here　and　there　a　man　like　Buffon　reasoned　far　enough　to　inquire　what　might　be　the　limits　of　such　assumed　transmutation；　and　only　here　and　there　a　Darwin　or　a　Goethe　reached　the　conviction　that　there　are　no　limits。


LAMARCK　VERSUS　CUVIER

And　even　Goethe　and　Darwin　had　scarcely　passed　beyond　that　tentative　stage　of　conviction　in　which　they　held　the　thought　of　transmutation　of　species　as　an　ancillary　belief　not　ready　for　full　exposition。　There　was　one　of　their　contemporaries；　however；　who；　holding　the　same　conception；　was　moved　to　give　it　full　explication。　This　was　the　friend　and　disciple　of　Buffon；　Jean　Baptiste　de　Lamarck。　　Possessed　of　the　spirit　of　a　poet　and　philosopher；　this　great　Frenchman　had　also　the　widest　range　of　technical　knowledge；　covering　the　entire　field　of　animate　nature。　　The　first　half　of　his　long　life　was　devoted　chiefly　to　botany；　in　which　he　attained　high　distinction。　　Then；　just　at　the　beginning　of　the　nineteenth　century；　he　turned　to　zoology；　in　particular　to　the　lower　forms　of　animal　life。　Studying　these　lowly　organisms；　existing　and　fossil；　he　was　more　and　more　impressed　with　the　gradations　of　form　everywhere　to　be　seen；　the　linking　of　diverse　families　through　intermediate　ones；　and　in　particular　with　the　predominance　of　low　types　of　life　in　the　earlier　geological　strata。　　Called　upon　constantly　to　classify　the　various　forms　of　life　in　the　course　of　his　systematic　writings；　he　found　it　more　and　more　difficult　to　draw　sharp　lines　of　demarcation；　and　at　last　the　suspicion　long　harbored　grew　into　a　settled　conviction　that　there　is　really　no　such　thing　as　a　species　of　organism　in　nature；　that　〃species〃　is　a　figment　of　the　human　imagination；　whereas　in　nature　there　are　only　individuals。

That　certain　sets　of　individuals　are　more　like　one　another　than　like　other　sets　is　of　course　patent；　but　this　only　means；　said　Lamarck；　that　these　similar　groups　have　had　comparatively　recent　common　ancestors；　while　dissimilar　sets　of　beings　are　more　remotely　related　in　consanguinity。　　But　trace　back　the　lines　of　descent　far　enough；　and　all　will　culminate　in　one　original　stock。　　All　forms　of　life　whatsoever　are　modified　descendants　of　an　original　organism。　From　lowest　to　highest；　then；　there　is　but　one　race；　one　species；　just　as　all　the　multitudinous　branches　and　twigs　from　one　root　are　but　one　tree。　For　purposes　of　convenience　of　description；　we　may　divide　organisms　into　orders；　families；　genera；　species；　just　as　we　divide　a　tree　into　root；　trunk；　branches；　twigs；　leaves；　but　in　the　one　case；　as　in　the　other；　the　division　is　arbitrary　and　artificial。

In　Philosophie　Zoologique　（1809）；　Lamarck　first　explicitly　formulated　his　ideas　as　to　the　transmutation　of　species；　though　he　had　outlined　them　as　early　as　1801。　　In　this　memorable　publication　not　only　did　he　state　his　belief　more　explicitly　and　in　fuller　detail　than　the　idea　had　been　expressed　by　any　predecessor；　but　he　took　another　long　forward　step；　carrying　him　far　beyond　all　his　forerunners　except　Darwin；　in　that　he　made　an　attempt　to　explain　the　way　in　which　the　transmutation　of　species　had　been　brought　about。　The　changes　have　been　wrought；　he　said；　through　the　unceasing　efforts　of　each　organism　to　meet　the　needs　imposed　upon　it　by　its　environment。　Constant　striving　means　the　constant　use　of　certain　organs。　Thus　a　bird　running　by　the　seashore　is　constantly　tempted　to　wade　deeper　and　deeper　in　pursuit　of　food；　its　incessant　efforts　tend　to　develop　its　legs；　in　accordance　with　the　observed　principle　that　the　use　of　any　organ　tends　to　strengthen　and　develop　it。　But　such　slightly　increased　development　of　the　legs　is　transmitted　to　the　off　spring　of　the　bird；　which　in　turn　develops　its　already　improved　legs　by　its　individual　efforts；　and　transmits　the　improved　tendency。　Generation　after　generation　this　is　repeated；　until　the　sum　of　the　infinitesimal　variations；　all　in　the　same　direction；　results　in　the　production　of　the　long…legged　wading…bird。　In　a　similar　way；　through　individual　effort　and　transmitted　tendency；　all　the　diversified　organs　of　all　creatures　have　been　developedthe　fin　of　the　fish；　the　wing　of　the　bird；　the　hand　of　man；　nay；　more；　the　fish　itself；　the　bird；　the　man；　even。　　Collectively　the　organs　make　up　the　entire　organism；　and　what　is　true　of　the　individual　organs　must　be　true　also　of　their　ensemble；　the　living　being。

Whatever　might　be　thought　of　Lamarck's　explanation　of　the　cause　of　transmutationwhich　really　was　that　already　suggested　by　Erasmus　Darwinthe　idea　of　the　evolution　for　which　he　contended　was　but　the　logical　extension　of　the　conception　that　American　animals　are　the　modified　and　degenerated　descendants　of　European　animals。　But　people　as　a　rule　are　little　prone　to　follow　ideas　to　their　logical　conclusions；　and　in　this　case　the　conclusions　were　so　utterly　opposed　to　the　proximal　bearings　of　the　idea　that　the　whole　thinking　world　repudiated　them　with　acclaim。　The　very　persons　who　had　most　eagerly　accepted　the　idea　of　transmutation　of　European　species　into　American　species；　and　similar　limited　variations　through　changed　environment；　because　of　the　relief　thus　given　the　otherwise　overcrowded　ark；　were　now　foremost　in　denouncing　such　an　extension　of　the　doctrine　of　transmutation　as　Lamarck　proposed。

And；　for　that　matter；　the　leaders　of　the　scientific　world　were　equally　antagonistic　to　the　Lamarckian　hypothesis。　　Cuvier　in　particular；　once　the　pupil　of　Lamarck；　but　now　his　colleague；　and　in　authority　more　than　his　peer；　stood　out　against　the　transmutation　doctrine　with　all　his　force。　He　argued　for　the　absolute　fixity　of　species；　bringing　to　bear　the　resources　of　a　mind　which；　as　a　mere　repository　of　facts；　perhaps　never　was　excelled。　As　a　final　and　tangible　proof　of　his　position；　he　brought　forward　the　bodies　of　ibises　that　had　been　embalmed　by　the　ancient　Egyptians；　and　showed　by　comparison　that　these　do　not　differ　in　the　slightest　particular　from　the　ibises　that　visit　the　Nile　to…day。

Cuvier's　reasoning　has　such　great　historical　interestbeing　the　argument　of　the　greatest　opponent　of　evolution　of　that　daythat　we　quote　it　at　some　length。

〃The　following　objections；〃　he　says；　〃have　already　been　started　against　my　conclusions。　　Why　may　not　the　presently　existing　races　of　mammiferous　land　quadrupeds　be　mere　modifications　or　varieties　of　those　ancient　races　which　we　now　find　in　the　fossil　state；　which　modifications　may　have　been　produced　by　change　of　climate　and　other　local　circumstances；　and　since　raised　to　the　present　excessive　difference　by　the　operations　of　similar　causes　during　a　long　period　of　ages？

〃This　objection　may　appear　strong　to　those　who　believe　in　the　indefinite　possibility　of　change　of　form　in　organized　bodies；　and　think　that；　during　a　succession　of　ages　and　by　alterations　of　habitudes；　all　the　species　may　change　into　one　another；　or　one　of　them　give　birth　to　all　the　rest。　Yet　to　these　persons　the　following　answer　may　be　given　from　their　own　system：　If　the　species　have　changed　by　degrees；　as　they　assume；　we　ought　to　find　traces　of　this　gradual　modification。　　Thus；　between　the　palaeotherium　and　the　species　of　our　own　day；　we　should　be　able　to　discover　some　intermediate　forms；　and　yet　no　such　discovery　has　ever　been　made。　Since　the　bowels　of　the　earth　have　not　preserved　monuments　of　this　strange　genealogy；　we　have　no　right　to　conclude　that　the　ancient　and　now　extinct　species　were　as　permanent　in　their　forms　and　characters　as　those　which　exist　at　present；　or；　at　least；　that　the　catastrophe　which　destroyed　them　did　not　leave　sufficient　time　for　the　productions　of　the　changes　that　are　alleged　to　have　taken　place。

〃In　order　to　reply　to　those　naturalists　who　acknowledge　that　the　varieties　of　animals　are　restrained　by　nature　within　certain　limits；　it　would　be　necessary　to　examine　how　far　these　limits　extend。　This　is　a　very　curious　inquiry；　and　in　itself　exceedingly　interesting　under　a　variety　of　relations；　but　has　been　hitherto　very　little　attended　to。　。　。　。　。　。　。　。　。

Wild　animals　which　subsist　upon　herbage　feel　the　influence　of　climate　a　little　more　extensively；　because　there　is　added　to　it　the　influence　of　food；　both　in　regard　to　its　abundance　and　its　quality。　Thus　the　elephants　of　one　forest　are　larger　than　those　of　another；　their　tusks　also　grow　somewhat　longer　in　places　where　their　food　may　happen　to　be　more　favorable　for　the　production　of　the　substance　of　ivory。　The　same　may　take　place　in　regard　to　the　horns　of　stags　and　reindeer。　But　let　us　examine　two　elephants；　the　most　dissimilar　that　can　be　conceived；　we　shall　not　discover　the　smallest　difference　in　the　number　and　articulations　of　the　bones；　the　structure　of　the　teeth；　etc。　。　。　。　。　。　。　。　。

〃Nature　appears　also　to　have　guarded　against　the　alterations　of　species　which　might　proceed　from　mixture　of　breeds　by　influencing　the　various　species　of　animals　with　mutual　aversion　from　one　another。　Hence　all　the　cunning　and　all　the　force　that　man　is　able　to　exert　is　necessary　to　accomplish　such　unions；　even　between　species　that　have　the　nearest　resemblances。　　And　when　the　mule　breeds　that　are　thus　produced　by　these　forced　conjunctions　happen　to　be　fruitful；　which　is　seldom　the　case；　this　fecundity　never　continues　beyond　a　few　generations；　and　would　not　probably　proceed　so　far　without　a　continuance　of　the　same　cares　which　excited　it　at　first。　Thus　we　never　see　in　a　wild　state　intermediate　productions　between　the　hare