The Wallace-Darwin Correspondence 



tion in harmony with such changed conditions; especially 

 when we consider that, to have produced the almost in- 

 finite modifications of organic beings, this coincidence 

 must have taken place an almost infinite number of 

 times. 



Now it seems to me that you have yourself led to this 

 objection being made by so often stating the case too 

 strongly against yourself. For example, at the commence- 

 ment of Chapter IV. you ask if it is '^ improbable that 

 useful variations should sometimes occur in the course of 

 thousands of generations " ; and a little further on you 

 say, *^ unless profitable variations do occur, natural selec- 

 tion can do nothing." Now, such expressions have given 

 your opponents the advantage of assuming that favourable 

 variations are rare accidents^ or may even for long periods 

 never occur at all, and thus Janet's argument would appear 

 to many to have great force. I think it would be better to 

 do away with all such qualifying expressions, and con- 

 stantly maintain (what I certainly believe to be the fact) 

 that variations of every kind are always occurring in every 

 part of every species^ and therefore that favourable varia- 

 tions are always ready when wanted. You have, I am 

 sure, abundant materials to prove this, and it is, I believe, 

 the grand fact that renders modification and adaptation 

 to conditions almost always possible. I would put the 

 burthen of proof on my opponents to show that any one 

 organ, structure, or faculty does not vary, even during one 

 generation, among all the individuals of a species ; and also 

 to show any mode or way in which any such organ, etc., 

 does not vary. I would ask them to give any reason for 

 supposing that any organ, etc., is ever absolutely identical 

 at any one time in all the individuals of a species, and if 

 not, then it is always varying, and there are always materials 

 which, from the simple fact that the " fittest survive," will 



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