10 NATURAL SELECTION i 



In all those cases in which an island has been separated 

 from a continent, or raised by volcanic or coralline action 

 from the sea, or in which a mountain-chain has been elevated 

 in a recent geological epoch, the phenomena of peculiar 

 groups or even of single representative species will not exist. 

 Our own island is an example of this, its separation from the 

 continent being geologically very recent, and we have con- 

 sequently scarcely 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 than 

 may be due to climate and latitude alone. 



The series of facts alluded to in Proposition (3), of closely 

 allied species in rich groups being found geographically near 

 each other, is most striking and important. Mr. Lovell 

 Eeeve has well exemplified it in his able and interesting 

 paper on the Distribution of the Bulimi. It is also seen in 

 the Humming-birds and Toucans, little groups of two or three 

 closely allied species being often found in the same or closely 

 adjoining districts, as we have had the good fortune of per- 

 sonally verifying. Fishes give evidence of a similar kind : 

 each great river has its peculiar genera, and in more extensive 

 genera its groups of closely allied species. But it is the same 

 throughout Nature ; every class and order of animals will 

 contribute similar facts. Hitherto no attempt has been 

 made to explain these singular phenomena, or to show how 

 they have arisen. Why are the genera of Palms and of 

 Orchids in almost every case confined to one hemisphere? 

 Why are the closely allied species of brown-backed Trogons 

 all 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 examples 

 the Goliathi of Africa, the Ornithopteras of the Indian 

 Islands, the Heliconidse of South America, the Danaidae of 

 the East, and in all the most closely allied species found in 

 geographical proximity. The question forces itself upon 

 every thinking mind, Why are these things so ? They 

 could not be as' they are had no law regulated their creation 

 and dispersion. The law here enunciated not merely ex- 

 plains but necessitates the facts we see to exist, while the 

 vast and long - continued geological changes of the earth 



