XIV THE ORIGIN OF SPECIES AND GENERA 287 



from some pre-existing species, and therefore the origin 

 of all existing species from some one or more ancestral 

 forms. It is maintained that there are other laws at work 

 besides natural selection, and Mr. Darwin has himself 

 admitted that there probably are such. Most of the 

 opponents of Darwinism argue in favour of some guiding 

 or organising power, either internal or external, as abso- 

 lutely necessary to the production of the kind and amount 

 of variation necessary for the development of the various 

 complex organs and special adaptations which characterise 

 each important class of animals. Others go still further 

 and maintain that " natural selection " is powerless to 

 produce new species in any case, its function being to 

 keep those which are produced in a state of health and 

 perfection by weeding out all that are imperfect ; or, they 

 argue that, so long as the " cause of variation " is unknown 

 the power that preserves those variations when they have 

 arisen plays a very subordinate part. These last writers 

 maintain that the causes, whatever they are, which pro- 

 duce certain variations in certain species at certain times, 

 are the true and only causes of the origin of species. 



Now all these objections, in so far as they refer to the 

 origin of the different species of one genus from a common 

 ancestral species, or even of all the species and genera of 

 one family from some still more remote ancestor, may, I 

 think, be shown to be invalid ; because we have direct 

 evidence, almost amounting to demonstration, that changes 

 to this extent are producible by the known laws of vari- 

 ation and the admitted action of natural selection. But 

 when we go further back, and propose to account for the 

 origin of distinct families, orders, and classes of animals 

 by the same process, the evidence becomes far less clear and 

 decisive. We find groups possessing organs no rudiment 

 of which exists in other groups ; we find classes differing 

 radically in structure from other classes ; and we have no 

 direct evidence that changes of this nature are now in 

 progress, as we have that the lesser changes resulting in 

 new species and new genera are in progress. 



Yet the evidence that these deeper and more important 

 changes in the structure of organised beings have taken 



