218 THE ORIGIN OF SPECIES [pt. ii 



the whole those are the best limited which consist of plants of 

 complex floral structure." "Those classes and orders which are 

 the least complex in organisation are the most widely distributed, 

 that is to say they contain a larger proportion of widely diffused 

 species. ...This tendency of the least complex species to be most 

 widely diffused is most marked in Acotyledons (Cryptogams), 

 and least so in Dicotyledons." "The most widely distributed 

 and commonest species are the least modified." 



It is clear, after reading these axioms, that another explana- 

 tion of the greater commonness of new (endemic) species upon 

 islands, southern land masses, and mountains is thus opened, 

 and one which may prove to be of great importance. Age and 

 Area shows that these widely distributed forms, which are the 

 most variable, are the oldest, and probably the parents of the 

 forms of lesser distribution. But at the edge of the dispersal of 

 any genus or other group, one will get, most markedly, the 

 oldest types; these being the most variable, will be the most 

 likely to give rise to new forms, and this, with the probable 

 comparative openness of the associations, may be the simplest 

 explanation of the frequency of endemics in the regions we have 

 indicated. A cursory examination of a number of genera shows 

 that this is very probably a general rule, but it would lead too 

 far to go into it in more detail at present; this must be left for 

 later work. 



There is as yet practically no evidence that several mutations 

 are required to form a Linnean species. We have no reason to 

 say that a new and strictly local species is appreciably better 

 adapted, in the great majority of cases, than the older one, 

 unless for the conditions in which it first finds itself upon its 

 evolution. If species A give rise to species B at a certain point 



AAAAAAAAAAAAAAAAAAAAAAA X 



B 



then, unless B is suited to the conditions that obtain at that 

 point in the year in which it was evolved, it is going to die out 

 again. For the immediate conditions at B, then, it may be 

 better adapted than A (as for example, perhaps, the endemics 

 of the Bahamas, p. 64), but when both species arrive at .Y, there 

 is no reason why B should be better adapted than A to the con- 

 ditions there. It will be mainly a matter of chance. 



This being so, there seems no reason why intermediate muta- 

 tions, if they were formed, should die out, especially as the 



