ACQUIRED CHARACTERS xlv 



which use-inheritance might be the factor concerned, for we 

 are prepared to admit all along that it may be a factor. 

 What we want is one indubitable instance that it is a factor — 

 one case in which the process takes place under our eyes, 

 in which use-inheritance is not claimed merely as the most 

 probable of several rival explanations, but in which it is 

 obviously the only real and true explanation. Nothing 

 short of this is of the slightest use for throwing light on the 

 problem before us. 



Use-inheritance is so plausible a theory, that if a single 

 case were brought forward to prove that it is actually a 

 process occurring in nature, it might well be accepted thence- 

 forward as an important factor in evolution. At present, 

 the inductive philosopher must not only refuse to accept it ; 

 he must regard it as being in contradiction to the probabilities 

 of the case. For the search for supporting facts has now 

 been long in progress. The theory was suggested by Lamarck 

 more than a century ago ; and in the last half-century it 

 has been discussed with the greatest detail and publicity. 

 The fact that no instances have been discovered cannot but 

 suggest, as a reason, that there are none to discover. 



The third factor which I named, that of natural selec- 

 tion, differs profoundly in this respect from the other two. 

 A priori, it is quite satisfactory : it unquestionably might 

 explain organic evolution. But we can go much farther : 

 we know that new races actually do arise by selection ; 

 we are able to witness the actual process. Hence, selection 

 is proved to be a vera causa. Like use-inheritance it is 

 competent theoretically to account for a great part of the 

 evolutionary process ; unHke use-inheritance it is not invented 

 for the occasion, but is a process which may actually be 

 observed to take place. 



Lamarck committed the error, eminently excusable in 

 the age in which he lived, of assuming that when he has 

 formed a theory which will fit the facts, and when he can 

 think of no other theory which will also fit the facts, then 

 that theory must be true. I shall adduce an even more 



