darwin and modern science-第94部分

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　which　has　not　served　as　a　basis　for　the　reconstruction　of　bridges；　and　it　must　be　a　group　which　we　feel　justified　in　assuming　to　be　old　enough　to　have　availed　itself　of　ancient　land…connections。

The　occurrence　of　one　species　of　Peripatus　in　the　whole　of　Australia；　Tasmania　and　New　Zealand　（the　latter　being　joined　to　Australia　by　way　of　New　Britain　in　Cretaceous　times　but　not　later）　puts　the　genus　back　into　this　epoch；　no　unsatisfactory　assumption　to　the　morphologist。　　The　apparent　absence　of　Peripatus　in　Madagascar　indicates　that　it　did　not　come　from　the　east　into　Africa；　that　it　was　neither　Afro…Indian；　nor　Afro…Australian；　nor　can　it　have　started　in　South　America。　　We　therefore　assume　as　its　creative　centre　Australia　or　Malaya　in　the　Cretaceous　epoch；　whence　its　occurrence　in　Sumatra；　Malay　Peninsula；　New　Britain；　New　Zealand　and　Australia　is　easily　explained。　　Then　extension　across　Antarctica　to　Patagonia　and　Chile；　whence　it　could　spread　into　the　rest　of　South　America　as　this　became　consolidated　in　early　Tertiary　times。　　For　getting　to　the　Antilles　and　into　Mexico　it　would　have　to　wait　until　the　Miocene；　but　long　before　that　time　it　could　arrive　in　Africa；　there　surviving　as　a　Congolese　and　a　Cape　species。　　This　story　is　unsupported　by　a　single　fossil。　　Peripatus　may　have　been　〃sub…universal〃　all　over　greater　Gondwana　land　in　Carboniferous　times；　and　then　its　absence　from　Madagascar　would　be　difficult　to　explain；　but　the　migrations　suggested　above　amount　to　little　considering　that　the　distance　from　Tasmania　to　South　America　could　be　covered　in　far　less　time　than　that　represented　by　the　whole　of　the　Eocene　epoch　alone。

There　is　yet　another　field；　essentially　the　domain　of　geographical　distribution；　the　cultivation　of　which　promises　fair　to　throw　much　light　upon　Nature's　way　of　making　species。　　This　is　the　study　of　the　organisms　with　regard　to　their　environment。　　Instead　of　revealing　pedigrees　or　of　showing　how　and　when　the　creatures　got　to　a　certain　locality；　it　investigates　how　they　behaved　to　meet　the　ever　changing　conditions　of　their　habitats。　　There　is　a　facies；　characteristic　of；　and　often　peculiar　to；　the　fauna　of　tropical　moist　forests；　another　of　deserts；　of　high　mountains；　of　underground　life　and　so　forth；　these　same　facies　are　stamped　upon　whole　associations　of　animals　and　plants；　although　these　may　beand　in　widely　separated　countries　generally　aredrawn　from　totally　different　families　of　their　respective　orders。　　It　does　not　go　to　the　root　of　the　matter　to　say　that　these　facies　have　been　brought　about　by　the　extermination　of　all　the　others　which　did　not　happen　to　fit　into　their　particular　environment。　　One　might　almost　say　that　tropical　moist　forests　must　have　arboreal　frogs　and　that　these　are　made　out　of　whatever　suitable　material　happened　to　be　available；　in　Australia　and　South　America　Hylidae；　in　Africa　Ranidae；　since　there　Hylas　are　absent。　　The　deserts　must　have　lizards　capable　of　standing　the　glare；　the　great　changes　of　temperature；　of　running　over　or　burrowing　into　the　loose　sand。　　When　as　in　America　Iguanids　are　available；　some　of　these　are　thus　modified；　while　in　Africa　and　Asia　the　Agamids　are　drawn　upon。　　Both　in　the　Damara　and　in　the　Transcaspian　deserts；　a　Gecko　has　been　turned　into　a　runner　upon　sand！

We　cannot　assume　that　at　various　epochs　deserts；　and　at　others　moist　forests　were　continuous　all　over　the　world。　　The　different　facies　and　associations　were　developed　at　various　times　and　places。　　Are　we　to　suppose　that；　wherever　tropical　forests　came　into　existence；　amongst　the　stock　of　humivagous　lizards　were　always　some　which　presented　those　nascent　variations　which　made　them　keep　step　with　the　similarly　nascent　forests；　the　overwhelming　rest　being　eliminated？　　This　principle　would　imply　that　the　same　stratum　of　lizards　always　had　variations　ready　to　fit　any　changed　environment；　forests　and　deserts；　rocks　and　swamps。　　The　study　of　Ecology　indicates　a　different　procedure；　a　great；　almost　boundless　plasticity　of　the　organism；　not　in　the　sense　of　an　exuberant　moulding　force；　but　of　a　readiness　to　be　moulded；　and　of　this　the　〃variations〃　are　the　visible　outcome。　　In　most　cases　identical　facies　are　produced　by　heterogeneous　convergences　and　these　may　seem　to　be　but　superficial；　affecting　only　what　some　authors　are　pleased　to　call　the　physiological　characters；　but　environment　presumably　affects　first　those　parts　by　which　the　organism　comes　into　contact　with　it　most　directly；　and　if　the　internal　structures　remain　unchanged；　it　is　not　because　these　are　less　easily　modified　but　because　they　are　not　directly　affected。　　When　they　are　affected；　they　too　change　deeply　enough。

That　the　plasticity　should　react　so　quicklyindeed　this　very　quickness　seems　to　have　initiated　our　mistaking　the　variations　called　forth　for　something　performedand　to　the　point；　is　itself　the　outcome　of　the　long　training　which　protoplasm　has　undergone　since　its　creation。

In　Nature's　workshop　he　does　not　succeed　who　has　ready　an　arsenal　of　tools　for　every　conceivable　emergency；　but　he　who　can　make　a　tool　at　the　spur　of　the　moment。　　The　ordeal　of　the　practical　test　is　Charles　Darwin's　glorious　conception　of　Natural　Selection。


XVIII。　　DARWIN　AND　GEOLOGY。

By　J。W。　JUDD；　C。B。；　LL。D。；　F。R。S。

（Mr　Francis　Darwin　has　related　how　his　father　occasionally　came　up　from　Down　to　spend　a　few　days　with　his　brother　Erasmus　in　London；　and；　after　his　brother's　death；　with　his　daughter；　Mrs　Litchfield。　　On　these　occasions；　it　was　his　habit　to　arrange　meetings　with　Huxley；　to　talk　over　zoological　questions；　with　Hooker；　to　discuss　botanical　problems；　and　with　Lyell　to　hold　conversations　on　geology。　　After　the　death　of　Lyell；　Darwin；　knowing　my　close　intimacy　with　his　friend　during　his　later　years；　used　to　ask　me　to　meet　him　when　he　came　to　town；　and　〃talk　geology。〃　　The　〃talks〃　took　place　sometimes　at　Jermyn　Street　Museum；　at　other　times　in　the　Royal　College　of　Science；　South　Kensington；　but　more　frequently；　after　having　lunch　with　him；　at　his　brother's　or　his　daughter's　house。　　On　several　occasions；　however；　I　had　the　pleasure　of　visiting　him　at　Down。　　In　the　postscript　of　a　letter　（of　April　15；　1880）　arranging　one　of　these　visits；　he　writes：　　〃Since　poor；　dear　Lyell's　death；　I　rarely　have　the　pleasure　of　geological　talk　with　anyone。〃）

In　one　of　the　very　interesting　conversations　which　I　had　with　Charles　Darwin　during　the　last　seven　years　of　his　life；　he　asked　me　in　a　very　pointed　manner　if　I　were　able　to　recall　the　circumstances；　accidental　or　otherwise；　which　had　led　me　to　devote　myself　to　geological　studies。　　He　informed　me　that　he　was　making　similar　inquiries　of　other　friends；　and　I　gathered　from　what　he　said　that　he　contemplated　at　that　time　a　study　of　the　causes　producing　SCIENTIFIC　BIAS　in　individual　minds。　　I　have　no　means　of　knowing　how　far　this　project　ever　assumed　anything　like　concrete　form；　but　certain　it　is　that　Darwin　himself　often　indulged　in　the　processes　of　mental　introspection　and　analysis；　and　he　has　thus　fortunately　left　usin　his　fragments　of　autobiography　and　in　his　correspondencethe　materials　from　which　may　be　reconstructed　a　fairly　complete　history　of　his　own　mental　development。

There　are　two　perfectly　distinct　inquiries　which　we　have　to　undertake　in　connection　with　the　development　of　Darwin's　ideas　on　the　subject　of　evolution：

FIRST。　　How；　when；　and　under　what　conditions　was　Darwin　led　to　a　conviction　that　species　were　not　immutable；　but　were　derived　from　pre…existing　forms？

SECONDLY。　　By　what　lines　of　reasoning　and　research　was　he　brought　to　regard　〃natural　selection〃　as　a　vera　causa　in　the　process　of　evolution？

It　is　the　first　of　these　inquiries　which　specially　interests　the　geologist；　though　geology　undoubtedly　played　a　partand　by　no　means　an　insignificant　partin　respect　to　the　second　inquiry。

When；　indeed；　the　history　comes　to　be　written　of　that　great　revolution　of　thought　in　the　nineteenth　century；　by　which　the　doctrine　of　evolution；　from　being　the　dream　of　poets　and　visionaries；　gradually　grew　to　be　the　accepted　creed　of　naturalists；　the　paramount　influence　exerted　by　the　infant　science　of　geologyand　especially　that　resulting　from　the　publication　of　Lyell's　epoch…making　work；　the　〃Principles　of　Geology〃cannot　fail　to　be　regarded　as　one　of　the　leading　factors。　　Herbert　Spencer　in　his　〃Autobiography〃　bears　testimony　to　the　effect　produced　on　his　mind　by　the　recently　published　〃Principles〃；　when；　at　the　age　of　twenty；　he　had　already　begun　to　speculate　on　the　subject　of　evolution　（Herbert　Spencer's　〃Autobiography〃；　London；　1904；　Vol。　I。　pages　175…177。）；　and　Alfred　Russel　Wallace　is　scarcely　less　emphatic　concerning　the　part　played　by　Lyell's　teaching　in　his　scientific　education。　　（See　〃My　Life；　a　record　of　Events　and　Opinions〃；　London；　1905；　Vol。　I。　page　355；　etc。　　Also　his　review　of　Lyell's　〃Principles〃　in　〃Quarterly　Review〃　（Vol。　126）；　1869；　pages　359…394。　　See　also　〃The　Darwin…Wallace　Celebration　by　the　Linnean　Society〃　（1909）；　page　118。）　　Huxley　wrote　in　1887　〃I　owe　more　than　I　can　tell　to　the　careful　study　of　the　〃Principles　of　Geology〃　in　my　young　days。〃　　（〃Science　and　Pseudo　Science〃；　〃Collected　Essays〃；　London；　1902；　Vol。　V。　page　101。）　　As　for　Charles　Darwin；　he　never　tiredeither　in　his　published　writings；　his　private　correspondence　or　his　most　intimate　conversationsof　ascribing　the　awakening　of　his　enthusiasm　and　the　direction　of　his　energies　towards　the　elucidation　of　the　problem　of　development　to　the　〃Principles　of　Geology〃　and　the　personal　influence　of　its　author。　　Huxley　has　well　expressed　what　the　author　of　the　〃Origin　of　Species〃　so　constantly　insisted　upon；　in　the　statements　〃Darwin's　greatest　work　is　the　outcome　of　the　unflinching　application　to　Biology　of　the　leading　idea　and　the　method　applied　in　the　〃Principles〃　to　Geology　（〃Proc。　Roy。　Soc。〃　Vol。　XLIV。　（1888）；　page　viii。；　〃Collected　Essays〃　II。　page　268；　1902。）；　and　〃Lyell；　for　others；　as　for　myself；　was　the　chief　agent　in　smoothing　the　road　for　Darwin。〃　　（〃Life　and　Letters　of　Charles　Darwin〃　II。　page　190。）

We　propose　therefore　to　consider；　first；　what　Darwin　owed　to　geology　and　its　cultivators；　and　in　the　second　place　how　he　was　able　in　the　end　so　fully　to　pay　a　great　debt　which　he　never　failed　to　acknowledge。　　Thanks　to　the　invaluable