THE FACTORS OF ORGANIC EVOLUTION. 33 



of functionally-produced modifications, which, judging by 

 the passage quoted above concerning the views of these 

 earlier enquirers, would seem to have been at one time 

 denied, but which as we have seen was always to some ! 

 extent recognized, came to be recognized more and more, ) 

 and deliberately included as a factor of importance. 



Of this reaction displayed in the later writings of Mr. 

 Darwin, let us now ask Has it not to be carried further ? 

 Was the share in organic evolution which Mr. Darwin 

 latterly assigned to the transmission of modifications caused 

 by use and disuse, its due share ? Consideration of the 

 groups of evidences given above, will, I think, lead us 

 to believe that its share has been much larger than he 

 supposed even in his later days. 



There is first the implication yielded by extensive 

 classes of phenomena which remain inexplicable in tho 

 absence of this factor. If, as we see, co-operative parts do 

 not vary together, even when few and close together, and 

 may not therefore be assumed to do so when many and 

 remote, we cannot account for those innumerable changes 

 in organization which are implied when, for advantageous 

 use of some modified part, many other parts which join it 

 in action have to be modified. 



Further, as increasing complexity of structure, accom 

 panying increasing complexity of life, implies increasing 

 number of faculties, of which each one conduces to preserva 

 tion of self or descendants ; and as the various individuals 

 of a species, severally requiring something like the normal 

 amounts of all these, may individually profit, here by an 

 unusual amount of one_,_and jthere by an unusual amount of 

 another^ it f ollows~ikat as the number of faculties becomes 

 greater, it becomes more difficult for any one to be further 

 developed by natural selection. Only where increase of 

 some one is predominantly advantageous does the means 

 seem adequate to the end. Especially in the case of 



