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 
Reeve 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 1 
Insects furnish a countless number of analogous examples— 
the Goliathi of Africa, the Ornithopteree of the Indian 
Islands, the Heliconide of South America, the Danaidz 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 
