ISOLATION 361 



evolution. So much, indeed, both Darwin and Romanes have 

 already contended, though Wallace, on the other hand, opposes 

 this view. 



The following examples well illustrate the peculiar fixity 

 of type which some species display when isolated. One of the 

 Pied Kingfishers {Ceryle guttata) is met with both in Japan and 

 the Himalayas. Though divided by thousands of miles no 

 apparent change in the coloration of the individuals of the two 

 areas is to be traced. The same is true of one of the crested 

 Eagles {SpiscBtus orientalis), except that this bird is met with 

 also in Formosa. Two other species, it may be remarked, are 

 also peculiar to the Himalayas and Formosa — a Pigeon (Palum- 

 bus pulchricollis) and a red-breasted Flycatcher {Sipkia super- 

 ciliaris). In both species, individuals from these widely 

 separated areas are indistinguishable. 



Birds whose range may be described as cosmopolitan afford 

 no less striking lessons on this head. The Osprey, for ex- 

 ample, which is met with over the whole world, Arctic and 

 Antarctic regions excepted, retains throughout its range the 

 same superficial characters. The Barn Owl, on the other 

 hand, which enjoys a similar range, has given rise to numerous 

 geographical races which some choose to regard as distinct 

 species, others as sub-species. Be that as it may, the one has 

 changed, the other has not. 



The inference that certain species have been evolved within 

 the small areas where they are now found, by isolation, seems 

 irresistible ; the following cases of species with a yet more 

 circumscribed habitat may be regarded as affording very strik- 

 ing additional evidence in favour of this hypothesis. Thus, the 

 only known flightless Grebe {Podidpes micropterus) is confined 

 to Lake Titicaca, Bolivia, which has an elevation of 12,644 

 feet The only known flightless Cormorant {Pkalacrocorax 

 harrissi) is found on one of the Galapagos Islands off" the west 

 coast of South America. The little Humming-bird {Oreotro- 

 chilus chimborazd) is found only around the volcano of Chim- 

 borazo" at an altitude of 14,000 feet, and the nearly related O. 

 ptchincha from the neighbouring volcanoes of Pichincha and 

 Cotopaxi at an elevation of 16,000 feet — living, by the way, 

 in a world of almost continual hail, sleet and rain! — while 

 the isolated rocks of Juan Fernandez boast two species of the 



