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THE AMERICAN NATURALIST [Vol. XLIII 



sciously biased in this matter is shown by an extract from 

 a letter written to Asa Gray, in 1860, in which he says: 



I reflected much on the chance of favorable monstrosities (i. e., great 

 and sudden variation) arising. I have, of course, no objection to this, 

 indeed it would be a great aid, but I did not allude to the subject [i. e., 

 in « the Origin »] for, after much labor, I could find nothing which 

 satisfied me of the probability of such occurrences. There seems to me 

 in almost every case too much, too complex, and too beautiful adapta- 



The idea involved in this passage is that adaptation is 

 produced— rather than preserved— by natural selection 

 and that, as natural selection must, according to Mr. 

 Darwin's curious prepossession, act only upon slow and 

 small changes of character, adaptation itself must neces- 

 sarily be in every case a matter of gradual growth. This 

 sort of argument appears to justify the fear shared by 

 both Lyell and Hooker that Darwin was at times disposed 

 to stake his whole case on the maintenance of an unneces- 

 sary assumption. Hooker wrote him as early as 1859 or 

 1860 that he was making a hobby of natural selection and 

 overriding it, since he undertook to make it account for 

 too much. 39 Darwin mildly protested that he did not see 

 how he could do more than he had done to disclaim any 

 intention of accounting for everything by natural selec- 

 tion. 40 In this discussion, however, it is apparent that 

 while Darwin was overloading the theory of natural selec- 

 tion with a responsibility for the origin of the adapted 

 or fit, he was at the same time unduly limiting it to only 

 one class of the fit, namely those which had arisen by slow 

 degrees. If he had taken the position that natural selec- 

 tion could and would operate upon any kind or any de- 

 gree of variability, he need not to have imagined' that 

 his mam doctrine was in jeopardy. 



But though Mr. Darwin could be stirred by attack to 

 a vigorous defense, and sometimes even to an over- 

 defense, of natural selection, he contended, at other times, 

 *ith equal vigor, that his main interest was with varia- 



