HUMBOLDT, DARWIN, AND WALLACE. 35 1 



phenomena of which may be explained with remarkable 

 simplicity and clearness by the theory of selection. I 

 mean Chorology, or the theory of the local distribution of 

 organisms over the surface of the earth. By this I do 

 not only mean the geographical distribution of animal 

 and vegetable species over the different parts and provinces 

 of the earth, over continents and islands, seas, and rivers ; 

 but also their topographical distribution in a vertical 

 direction, their ascending to the heights of mountains, and 

 their descending into the depths of the ocean. (Gen. 

 Morph. ii. 286.) 



The strange chorological series of phenomena which 

 show the horizontal distribution of organisms over parts of 

 the earth, and their vertical distribution in heights and 

 depths, have long since excited general interest. In recent 

 times Alexander Humboldt ^^ and Frederick Schouw have 

 especially discussed the geography of plants, and Berghaus 

 and Schmarda the geography of animals, on a large scale. 

 But although these and several other naturalists have in 

 many ways increased our knowledge of the distribution of 

 animal and vegetable forms, and laid open to us a new 

 domain of science, full of wonderful and interesting 

 phenomena, yet Chorology as a whole remained, as 

 far as their labours were concerned, only a desultory 

 knowledge of a mass of individual facts. It could not be 

 called a science as long as the causes for the explanation of 

 these facts were wanting. These causes were first disclosed 

 by the theory of selection and its doctrine of the migrations 

 of animal and vegetable species, and it is only since the 

 works of Darwin and Wallace that we have been able to 

 speak of an independent science of Chorology. 



