DETERMINATION OF WHAT THE DARWINIAN THEORY IS. 227 



knew so well, must have been obvious to him. There- 

 fore it is that I bring both considerations together in 

 connection with the Origin. 



But however that may be, it is the momenta of the 

 resultant theory which are specially our quest at pre- 

 sent. For these, directing attention to the whole of 

 each of the passages named, we select, as sufficiently 

 explicit and decisive, the following expressions : Certain 

 resemblances having suggested to him "that species 

 gradually become modified," the subject " haunted " him. 

 " Adaptations " as, " for instance, of a woodpecker or a 

 tree-frog to climb trees, or of a seed for dispersal by 

 hooks or plumes " had always " much struck " him ; and 

 their explanation he saw must be a necessary element in 

 any theory that had modification for its principle. Man, by 

 breeding, artificially produced adaptations ; and the secret 

 of his success was " selection." But natural selection 

 could only naturally take place, and that was by " the 

 struggle for existence." It could be only so that " favour- 

 able variations would tend to be preserved, and unfavour- 

 able ones to be destroyed." " Here, then," says Mr. 

 Darwin, " I had at last got a theory by which to work." 

 In the struggle for existence, the unfavourable variation 

 would die out ; but the favourable one would survive : " the 

 result would be the formation of a new species." This is 

 eminently simple ; and one cannot help thinking at once, 

 There can be no difficulty in submitting each sub-idea of 

 the common idea to the test of proof. Nor did the addi- 

 tional sub-idea of " divergence," subsequently suggested, 

 really lead to a complication of any consequence. Diver- 

 gence meant that variations, or the subjects modified by 

 them, naturally betook themselves to " places " that were 

 naturally adapted to them. The same stock might, as 

 modified, yield horses for the plough, horses for the road, 

 and horses for the race-course, etc. 



