darwin and modern science-第99节

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！



Guppy's　heart　failed　him　when　he　had　to　deal　with　the　isolated　case　of　Agathis　which　alone　seemed　inexplicable　by　known　means　of　transport。　　But　when　we　remember　that　it　is　a　relic　of　the　pre…Angiospermous　flora；　and　is　of　Araucarian　ancestry；　it　cannot　be　said　that　the　impossibility；　in　so　prolonged　a　history；　of　the　bodily　transference　of　cone…bearing　branches　or　even　of　trees；　compels　us　as　a　last　resort　to　fall　back　on　continental　extension　to　account　for　its　existing　distribution。

When　Darwin　was　in　the　Galapagos　Archipelago；　he　tells　us　that　he　fancied　himself　〃brought　near　to　the　very　act　of　creation。〃　　He　saw　how　new　species　might　arise　from　a　common　stock。　　Krakatau　shows　us　an　earlier　stage　and　how　by　simple　agencies；　continually　at　work；　that　stock　might　be　supplied。　It　also　shows　us　how　the　mixed　and　casual　elements　of　a　new　colony　enter　into　competition　for　the　ground　and　become　mutually　adjusted。　　The　study　of　Plant　Distribution　from　a　Darwinian　standpoint　has　opened　up　a　new　field　of　research　in　Ecology。　　The　means　of　transport　supply　the　materials　for　a　flora；　but　their　ultimate　fate　depends　on　their　equipment　for　the　〃struggle　for　existence。〃　　The　whole　subject　can　no　longer　be　regarded　as　a　mere　statistical　inquiry　which　has　seemed　doubtless　to　many　of　somewhat　arid　interest。　　The　fate　of　every　element　of　the　earth's　vegetation　has　sooner　or　later　depended　on　its　ability　to　travel　and　to　hold　its　own　under　new　conditions。　　And　the　means　by　which　it　has　secured　success　is　an　each　case　a　biological　problem　which　demands　and　will　reward　the　most　attentive　study。　　This　is　the　lesson　which　Darwin　has　bequeathed　to　us。　　It　is　summed　up　in　the　concluding　paragraph　of　the　〃Origin〃　（〃Origin　of　Species〃　（6th　edition）；　page　429。）：〃It　is　interesting　to　contemplate　a　tangled　bank；　clothed　with　many　plants　of　many　kinds；　with　birds　singing　on　the　bushes；　with　various　insects　flitting　about；　and　with　worms　crawling　through　the　damp　earth；　and　to　reflect　that　these　elaborately　constructed　forms；　so　different　from　each　other；　and　dependent　upon　each　other　in　so　complex　a　manner；　have　all　been　produced　by　laws　acting　around　us。〃


XVII。　　GEOGRAPHICAL　DISTRIBUTION　OF　ANIMALS。

By　HANS　GADOW；　M。A。；　Ph。D。；　F。R。S。　Strickland　Curator　and　Lecturer　on　Zoology　in　the　University　of　Cambridge。

The　first　general　ideas　about　geographical　distribution　may　be　found　in　some　of　the　brilliant　speculations　contained　in　Buffon's　〃Histoire　Naturelle〃。　　The　first　special　treatise　on　the　subject　was　however　written　in　1777　by　E。A。W。　Zimmermann；　Professor　of　Natural　Science　at　Brunswick；　whose　large　volume；　〃Specimen　Zoologiae　Geographicae　Quadrupedum〃。。。；　deals　in　a　statistical　way　with　the　mammals；　important　features　of　the　large　accompanying　map　of　the　world　are　the　ranges　of　mountains　and　the　names　of　hundreds　of　genera　indicating　their　geographical　range。　　In　a　second　work　he　laid　special　stress　on　domesticated　animals　with　reference　to　the　spreading　of　the　various　races　of　Mankind。

In　the　following　year　appeared　the　〃Philosophia　Entomologica〃　by　J。C。　Fabricius；　who　was　the　first　to　divide　the　world　into　eight　regions。　　In　1803　G。R。　Treviranus　（〃Biologie　oder　Philosophie　der　lebenden　Natur〃；　Vol。　II。　Gottingen；　1803。）　devoted　a　long　chapter　of　his　great　work　on　〃Biologie〃　to　a　philosophical　and　coherent　treatment　of　the　distribution　of　the　whole　animal　kingdom。　　Remarkable　progress　was　made　in　1810　by　F。　Tiedemann　（〃Anatomie　und　Naturgeschichte　der　Vogel〃。　　Heidelberg；　1810。）　of　Heidelberg。　　Few；　if　any；　of　the　many　subsequent　Ornithologists　seem　to　have　appreciated；　or　known　of；　the　ingenious　way　in　which　Tiedemann　marshalled　his　statistics　in　order　to　arrive　at　general　conclusions。　　There　are；　for　instance；　long　lists　of　birds　arranged　in　accordance　with　their　occurrence　in　one　or　more　continents：　　by　correlating　the　distribution　of　the　birds　with　their　food　he　concludes　〃that　the　countries　of　the　East　Indian　flora　have　no　vegetable　feeders　in　common　with　America；〃　and　〃that　it　is　probably　due　to　the　great　peculiarity　of　the　African　flora　that　Africa　has　few　phytophagous　kinds　in　common　with　other　countries；　whilst　zoophagous　birds　have　a　far　more　independent；　often　cosmopolitan；　distribution。〃　　There　are　also　remarkable　chapters　on　the　influence　of　environment；　distribution；　and　migration；　upon　the　structure　of　the　Birds！　　In　short；　this　anatomist　dealt　with　some　of　the　fundamental　causes　of　distribution。

Whilst　Tiedemann　restricted　himself　to　Birds；　A。　Desmoulins　in　1822　wrote　a　short　but　most　suggestive　paper　on　the　Vertebrata；　omitting　the　birds；　he　combated　the　view　recently　proposed　by　the　entomologist　Latreille　that　temperature　was　the　main　factor　in　distribution。　　Some　of　his　ten　main　conclusions　show　a　peculiar　mixture　of　evolutionary　ideas　coupled　with　the　conception　of　the　stability　of　species：　　whilst　each　species　must　have　started　from　but　one　creative　centre；　there　may　be　several　〃analogous　centres　of　creation〃　so　far　as　genera　and　families　are　concerned。　　Countries　with　different　faunas；　but　lying　within　the　same　climatic　zones；　are　proof　of　the　effective　and　permanent　existence　of　barriers　preventing　an　exchange　between　the　original　creative　centres。

The　first　book　dealing　with　the　〃geography　and　classification〃　of　the　whole　animal　kingdom　was　written　by　W。　Swainson　（〃A　Treatise　on　the　Geography　and　Classification　of　Animals〃；　Lardner's　〃Cabinet　Cyclopaedia〃　London；　1835。）　in　1835。　　He　saw　in　the　five　races　of　Man　the　clue　to　the　mapping　of　the　world　into　as　many　〃true　zoological　divisions；〃　and　he　reconciled　the　five　continents　with　his　mystical　quinary　circles。

Lyell's　〃Principles　of　Geology〃　should　have　marked　a　new　epoch；　since　in　his　〃Elements〃　he　treats　of　the　past　history　of　the　globe　and　the　distribution　of　animals　in　time；　and　in　his　〃Principles〃　of　their　distribution　in　space　in　connection　with　the　actual　changes　undergone　by　the　surface　of　the　world。　　But　as　the　sub…title　of　his　great　work　〃Modern　changes　of　the　Earth　and　its　inhabitants〃　indicates；　he　restricted　himself　to　comparatively　minor　changes；　and；　emphatically　believing　in　the　permanency　of　the　great　oceans；　his　numerous　and　careful　interpretations　of　the　effect　of　the　geological　changes　upon　the　dispersal　of　animals　did　after　all　advance　the　problem　but　little。

Hitherto　the　marine　faunas　had　been　neglected。　　This　was　remedied　by　E。　Forbes；　who　established　nine　homozoic　zones；　based　mainly　on　the　study　of　the　mollusca；　the　determining　factors　being　to　a　great　extent　the　isotherms　of　the　sea；　whilst　the　25　provinces　were　given　by　the　configuration　of　the　land。　　He　was　followed　by　J。D。　Dana；　who；　taking　principally　the　Crustacea　as　a　basis；　and　as　leading　factors　the　mean　temperatures　of　the　coldest　and　of　the　warmest　months；　established　five　latitudinal　zones。　　By　using　these　as　divisors　into　an　American；　Afro…European；　Oriental；　Arctic　and　Antarctic　realm；　most　of　which　were　limited　by　an　eastern　and　western　land…boundary；　he　arrived　at　about　threescore　provinces。

In　1853　appeared　L。K。　Schmarda's　（〃Die　geographische　Verbreitung　der　Thiere〃；　Wien；　1853。）　two　volumes；　embracing　the　whole　subject。　　Various　centres　of　creation　being；　according　to　him；　still　traceable；　he　formed　the　hypothesis　that　these　centres　were　originally　islands；　which　later　became　enlarged　and　joined　together　to　form　the　great　continents；　so　that　the　original　faunas　could　overlap　and　mix　whilst　still　remaining　pure　at　their　respective　centres。　　After　devoting　many　chapters　to　the　possible　physical　causes　and　modes　of　dispersal；　he　divided　the　land　into　21　realms　which　he　shortly　characterises；　e。g。　Australia　as　the　only　country　inhabited　by　marsupials；　monotremes　and　meliphagous　birds。　　Ten　main　marine　divisions　were　diagnosed　in　a　similar　way。　　Although　some　of　these　realms　were　not　badly　selected　from　the　point　of　view　of　being　applicable　to　more　than　one　class　of　animals；　they　were　obviously　too　numerous　for　general　purposes；　and　this　drawback　was　overcome；　in　1857；　by　P。L。　Sclater。　　（〃On　the　general　Geographical　Distribution　of　the　members　of　the　class　Aves〃；　〃Proc。　Linn。　Soc。〃　（Zoology　II。　1858；　pages　130…145。）　　Starting　with　the　idea；　that　〃each　species　must　have　been　created　within　and　over　the　geographical　area；　which　it　now　occupies；〃　he　concluded　〃that　the　most　natural　primary　ontological　divisions　of　the　Earth's　surface〃　were　those　six　regions；　which　since　their　adoption　by　Wallace　in　his　epoch…making　work；　have　become　classical。　　Broadly　speaking；　these　six　regions　are　equivalent　to　the　great　masses　of　land；　they　are　convenient　terms　for　geographical　facts；　especially　since　the　Palaearctic　region　expresses　the　unity　of　Europe　with　the　bulk　of　Asia。　　Sclater　further　brigaded　the　regions　of　the　Old　World　as　Palaeogaea　and　the　two　Americas　as　Neogaea；　a　fundamental　mistake；　justifiable　to　a　certain　extent　only　since　he　based　his　regions　mainly　upon　the　present　distribution　of　the　Passerine　birds。

Unfortunately　these　six　regions　are　not　of　equal　value。　　The　Indian　countries　and　the　Ethiopian　region　（Africa　south　of　the　Sahara）　are　obviously　nothing　but　the　tropical；　southern　continuations　or　appendages　of　one　greater　complex。　　Further；　the　great　eastern　mas