32 GEOGRAPHICAL DISTRIBUTION 



Now according to analogy of domesticated 

 animals let us see what would result. Let us 

 take case of farmer on Pampas, where everything 

 approaches nearer to state of nature. He works on 

 organisms having strong tendency to vary : and he 

 knows (that the) only way to make a distinct breed 

 is to select and separate. It would be useless to 

 separate the best bulls and pair with best cows 

 if their offspring run loose and bred with the other 

 herds, and tendency to reversion not counteracted ; 

 he would endeavour therefore to get his cows on 

 islands and then commence his work of selection. 

 If several farmers in different rincons 1 were to set 

 to work, especially if with different objects, several 

 breeds would soon be produced. So would it be 

 with horticulturist and so history of every plant 

 shows; the number of varieties 2 increase in propor- 

 tion to care bestowed on their selection and, with 

 crossing plants, separation. Now, according to this 

 analogy, change of external conditions, and isolation 

 either by chance landing (of) a form on an island, or 

 subsidence dividing a continent, or great chain of 

 mountains, and the number of individuals not being 

 numerous will best favour variation and selection 3 . 

 No doubt change could be effected in same country 

 without any barrier by long continued selection on 

 one species : even in case of a plant not capable of 

 crossing would easier get possession and solely 



1 Rincon in Spanish means a nook or corner, it is here probably used to 

 mean a small farm. 



2 The following is written across the page : " No one would expect a set 

 of similar varieties to be produced in the different countries, so species 

 different." 



3 (The following passage seems to have been meant to follow here.) The 

 parent of an organism, we may generally suppose to be in less favourable 

 condition than the selected offspring and therefore generally in fewer 

 numbers. (This is not borne out by horticulture, mere hypothesis ; as an 

 organism in favourable conditions might by selection be adapted to still 

 more favourable conditions.) 



Barrier would further act in preventing species formed in one part 

 migrating to another part. 



