122 OTHER FACTORS OF EVOLUTION 



as Spencer says elsewhere,' " Should it be said that such a process 

 is too marvellous to be reasonably assumed, the reply is that it is 

 not more marvellous than heredity itself, which, were it not 

 familiar to us, would be thought incredible." In regard to the 

 general question he had previously said ^ : "At last then we are 

 obliged to admit that the actual organising process transcends con- 

 ception. It is not enough to say that we cannot know it ; we must 

 say that we cannot even conceive it : can only conceive the possi- 

 bility of a suggested interpretation." 



Setting aside all prejudice, therefore, and with only a warrantable 

 leaning towards the doctrine which so far has been found to be 

 most congruous with the facts, it only remains to look at some of 

 the actual evidence tending to support the view that the Effects 

 of Use and Disuse, and also the direct Effects produced by altered 

 External Conditions can be, and are frequently, transmitted to 

 offspring. 



The effects of Use and Disuse are effects that would be met 

 with in animals rather than in plants, and apart from secondary 

 sexual characters to which reference has already been made, the 

 discussion in recent years has largely been confined to questions 

 touching the effects of use-inheritance on the frame of man 

 himself. 



It is well known that Darwin 3 collected a number of facts 

 implying that functionally altered structures are transmitted by 

 heredity. Among the facts that he adduced, he showed especially 

 that there is a changed ratio between the wing-bones and the leg- 

 bones in the domesticated as compared with the wild duck, and 

 that alterations in the bones of fowls and rabbits had also taken 

 place. Concerning such changes he said : — " From the foregoing 

 facts there can be no doubt that certain parts of the skeleton in 

 our anciently domesticated animals have been modified in length 

 and weight by the effects of decreased or increased use." He also 

 attached much importance to the increased or diminished length of 

 the intestines, resulting apparently from changed diet. It has been 

 found, for instance, that the intestines of the domestic cat are one- 

 third longer than those of the wild cat of Europe, and Darwin 

 adds : — " The increased length appears to be due to the domestic 



" " Principles of Biology," II, Appendix G. 



= Loc. cit, II, p. 621. 



3 "Animals and Plants," 1868, II, pp. 295-303. 



