Oil the Origin of Species, lit 



His next step is to establish analogies between variation and 

 specific difference, as observed in nature. Many species are 

 doubtful ; that is, naturalists are not quite decided that they may 

 not be varieties. This is true ; but such species are the excep- 

 tions, and the differences of view have arisen as much from defec- 

 tive observation or reasoning as from any real difficulty. Again, 

 in large genera the species approach each other very nearly. 

 This is inevitable^from the nature of the case, and though it may 

 cause difficulties in distinguishing them, it proves nothing as to 

 their not being true species. Species which range "widely also are 

 prone to vary, and this also follows from the nature of the case, 

 great range and much variability being really cause and effect, 

 and reacting on each other. Farther, it is stated that species 

 belonging to large genera are more prone to vary than species 

 belonging to small genera. This has not been established as a 

 general principle, nor, if it should be, would it necessarily bear 

 the interpretation put upon it. To reach the facts we must be 

 certain that we are comparing natural genera consisting of species 

 having true affinities of structure, and that all our generic dis- 

 tinctions are based on the same grades of difference. Further, we 

 must make separate lists of the genera small now but large if we 

 take all geological time, as for instance the genus Lingular of 

 genera small in any particular country, but large if the whole 

 world be taken ; and lastly, of genera large in some particular 

 region or country. This last is the only case which can fairly 

 test Mr. Darwin's principle, and we must say that in our limited 

 experience there appear to be quite as many exceptions as agree- 

 ments with the rule. Take, for instance, the genera SoUdago and 

 Aster among American plants, which, thoi^gh growing together 

 in numerous species, are not remarkably variable. Further, when 

 a generic type has proved suitable to occupy many places in a 

 particular country, it may well be that many of its species will 

 be capable of a wide range, and so variable. For such reasons 

 we hold that the attempt made on the ground of analogies be- 

 tween the species and the variety to break down the distinction 

 between them signally fails. 



But if the reader is willing to take this for granted, Mr. Darwin 

 will carry him a step further. He next proceeds to maintain that in 

 nature there is a power of selection similar to that which the breeder 

 exercises — a power of " Natural Selection " not heretofore recog- 

 nised, and by virtue of which varieties are produced and developed 



