CHAPTER XV 



ENDEMISM AND DISTRIBUTION: SPECIES 



1 HE term endemic has long been used to connote a species, 

 genus, or other group confined to a small area, such especially as 

 a single island, a group of islands, a mountain chain, or a com- 

 paratively small country like South Africa or ^Vest Australia, 

 largely bounded by the sea or by a marked alteration of climate. 

 In recent years species of larger areas have been spoken of as 

 endemic, but the term is used in an arbitrary way, for one 

 speaks of species as endemic to Australia, though not to Brazil, 

 which really has far more of them (533 endemic genera, perhaps 

 12,000 endemic species). 



There is almost never any real and demonstrable difference 

 between species and genera of small and of large area, other 

 than in the territory occupied, but since the rise of natural 

 selection it has been generally assumed that such a difference 

 really occurs. On that theory one will expect to find many 

 species "going under" in the struggle for existence, and the fact 

 that so many are actually localised to small areas of territory, 

 particularly in somewhat isolated regions of the globe, provides 

 the necessary material for this explanation to rest upon. Botanists 

 have long been accustomed to look upon endemic forms as the 

 oldest, and very often as in some way expressly suited to the 

 very local conditions in which they occur. This latter must of 

 course be true for any species, anywhere, or it would be exter- 

 minated in a short time; but the study of detail which has re- 

 sulted in the putting forward of the hypothesis of Age and Area 

 gives reason to believe that in general the supposition of greater 

 age of endemics is incorrect. 



As endemics usually occur in somewhat isolated places or 

 countries, the question at once arises whether endemism is corre- 

 lated with isolation as such, for if so, the fact will have an im- 

 portant bearing on the question of evolution generally. There is 

 also some ground, however, for supposing that the soil in isolated 

 regions may be less completely taken up b}^ its associations of 

 plants, so that a newcomer would have a better chance of sur- 

 vival; and this may be the explanation. 



From about 48° N., to the southwards, all important islands. 



