776 THE POPULAR SCIENCE MONTHLY. 



sequent works, had he insisted on this factor. The change thus indi- 

 cated is especially significant as having occurred at a time of life when 

 the natural tendency is toward fixity of opinion. 



During that earlier period when he was discovering the multitudi- 

 nous cases in which his own hypothesis afforded solutions, and simul- 

 taneously observing how utterly futile in these multitudinous cases 

 was the hypothesis propounded by his grandfather and Lamarck, Mr. 

 Darwin was, not unnaturally, almost betrayed into the belief that the 

 one is all-suflicient and the other inoperative. But in the mind of one 

 so candid and ever open to more evidence, there naturally came a re- 

 action. The inheritance of functionally-produced modifications, which, 

 judging by the passage quoted above concerning the views of these 

 earlier inquirers, 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 or- 

 ganic evolution which Mr. Darwin latterly assigned to the transmission 

 of modifications caused by use and disuse, its due share ? Considera- 

 tion 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 phe- 

 nomena which remain inexplicable in the 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 or- 

 ganization 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, accompanying in- 

 creasing complexity of life, implies increasing number of faculties, of 

 which each one conduces to preservation 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 there by an imusual amount of another ; 

 it follows that 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 lyredominayxtly advantageous does 

 the means seem adequate to the end. Especially in the case of powers 

 which do not subserve self-preservation in appreciable degrees, does 

 development by natural selection appear impracticable. 



It is a fact recognized by Mr. Darwin, that where, by selection 

 through successive generations, a part has been increased or decreased, 



