PDF - Wallace Online

10 NATURAL SELECTION iIn all those cases in which an island has been separatedfrom a continent, or raised by volcanic or coralline actionfrom the sea, or in which a mountain-chain has been elevatedin a recent geological epoch, the phenomena of peculiargroups or even of single representative species will not exist.Our own island is an example of this, its separation from thecontinent being geologically very recent, and we have consequentlyscarcely a species which is peculiar to it while the;Alpine range, one of the most recent mountain elevations,separates faunas and floras which scarcely differ more thanmay be due to climate and latitude alone.The series of facts alluded to in Proposition (3), of closelyallied species in rich groups being found geographically neareach other, is most striking and important. Mr. LovellEeeve has well exemplified it in his able and interestingpaper on the Distribution of the Bulimi. It is also seen inthe Humming-birds and Toucans, little groups of two or threeclosely allied species being often found in the same or closelyadjoining districts, as we have had the good fortune of personallyverifying. Fishes give evidence of a similar kind :each great river has its peculiar genera, and in more extensivegenera its groups of closely allied species. But it is the samethroughout Nature ; every class and order of animals willcontribute similar facts. Hitherto no attempt has beenmade to explain these singular phenomena, or to show howthey have arisen. Why are the genera of Palms and ofOrchids in almost every case confined to one hemisphere?Why are the closely allied species of brown-backed Trogonsall found in the East, and the green-backed in the West ?Why are the Macaws and the Cockatoos similarly restricted ?Insects furnish a countless number of analogous examplesthe Goliathi of Africa, the Ornithopteras of the IndianIslands, the Heliconidse of South America, the Danaidae ofthe East, and in all the most closely allied species found ingeographical proximity. The question forces itselfuponevery thinking mind, Why are these things so ? Theycould not be as' they are had no law regulated their creationand dispersion. The law here enunciated not merely ex-while theplains but necessitates the facts we see to exist,vast and -long continued geological changes of the earth