EARLY CRITICISM. 57 



disuse, etc. — an independent origin, even from quite 

 distinct lines, would be probable ; and we find, 

 accordingly, that those who would advance such 

 theories believe in what is called the " polyphyletic " 

 origin of species {e.g. the horse), and in the principle 

 of " convergence " carried far enough to produce the 

 same complex character {e.g. vertebrate teeth) twice 

 over without any genetic connection between the 

 forms in which the character appears. 



Under natural selection, however, such a result 

 would be infinitely improbable, and hence this theory 

 strongly supports, and indeed explains, the theory 

 of " specific centres," viz. that each species has arisen 

 in one area only, and has spread from that into the 

 other areas over which it now occurs. This view was 

 strongly held by Lyell and Hooker after an ex- 

 haustive study of the facts then known as to the 

 geographical distribution of plants and animals ; and 

 yet both of these distinguished naturalists seem to 

 have feared that Darwin, in advancing a theory 

 which was entirely consistent with their convictions 

 and utterly inconsistent with any other views upon 

 the same subject, was in some way undermining 

 the conclusions at which they had arrived. 



Thus Lyell wrote (July 25th, 1856) to Hooker :— 



" I fear much that if Darwin argues that species are 

 phantoms, he will also have to admit that single centres of 

 dispersion are phantoms also, and that would deprive me of 

 much of the value which I ascribe to the present provinces 

 of animals and plants, as illustrating modern and tertiary 

 changes in physical geography." 



