168 The Origin of Species by Mutation. 



common origin of all species but in bringing the origin 

 of species within the range of direct observation and 

 even in placing in our hands a certain amount of control 

 over these natural processes. 



But we are to-day just as far from this goal as we 

 were in Darwin's time. The opponents of the theory of 

 Descent have from the very beginning argued that we 

 ought at least to be able to observe the origin of species 

 and, perhaps, even to effect it experimentally. This crit- 

 icism must even now be recognized as fully justified, 

 although it is of course no longer one on the answer to 

 which the validity of the doctrine of Descent depends. 



It is just at this point that the prevalent confusion 

 over species becomes most evident. What shall we make 

 the object of observation and experiment? Our oppo- 

 nents answer : ''The origin of the ordinary Linnean spe- 

 cies of the systematist." But these are artificial groups 

 whose limits can be altered by the personal taste of any 

 systematist and are indeed as a matter of fact much too 

 often so altered. The origin of such a species, like that 

 of a genus, is a historical occurrence and it can neither 

 be repeated experimentally, nor can the whole process 

 be observed. 



A plant-form can only attain the rank of a systematic 

 species by producing a series of new forms and by the 

 subsequent elimination of those which formerly related 

 it to its parent form. It is obviously as impossible to 

 observe the origin of an artificially circumscribed group 

 like this as it would be to observe that of a genus or 

 familv- 



The object of an experimental treatment of these 

 phenomena must assuredly be to make the origin of the 

 units which really exist in nature the subject of experi- 



