446 ANNALS NEW YORK ACADEMY OF SCIENCES 



But though Mr. Darwin could be stirred by attack to a vigorous defense, 

 and sometimes even to an o-y^r-defense, of natural selection, he contended, at 

 other times, with equal vigor, that his main interest was with variation, 

 however produced, which was the necessary basis of the whole evolutionary 

 process. He admitted, however, that the cause of variation was to him 

 inexplicable and, like all beginnings, it remains to this day a deep mystery. 

 Darwin said of it: 



"Our ignorance of the laws of variation is profound. Not in one case out of a 

 hundred can we pretend to assign any reason why this or that part has varied." * 



In another place he remarks : 



"When we reflect on the millions of buds which many trees have produced 

 before some one bud has varied, we are lost in wonder as to what the precise cause 

 of each variation can be." * 



He never definitely undertook to solve this mystery, though he reflected 

 and reasoned on it much. The nearest he came to formulating a law con- 

 cerning it was the expression of his conviction that variability was more a 

 matter of organic constitution than a result of external agencies. Thus 

 he declares: 



"If we look to such cases as that of a peach tree which, after having been culti- 

 vated by tens of thousands during many years in many countries, and after having 

 annually produced millions of buds, all of which have apparently been exposed to 

 precisely the same conditions, yet at last suddenly produces a single bud with its 

 whole character greatly transformed, we are driven to the conclusion that the trans- 

 formation stands in no direct relation to the conditions of life." ^ 



From examples like this Mr. Darwin deduced a "general rule that 

 conspicuous variations occur rarely, and in one indi\ddual alone out of 

 millions, though all may have been exposed, as far as we can judge, to nearly 

 the same conditions" ^ and while this is, in a general way, in accordance 

 with the admission of de Vries that although mutations are "not so very 

 rare in nature," ^ the numbers "under observation are as yet very rare," ' 

 we shall see a little later that Mr. Darwin's deduction is not strictly accurate, 

 since it excludes the idea of a whole genus or species or variety mutating 

 at once. 



Wliile on this subject, I may mention that Mr. Darwin anticipated the 



1 " Origin of Species," 6th ed., p. 131. 



2 " Animals and Plants Under Domestication," 2d ed.. Vol. II, p. 281. 



3 Ibid., 2d ed., Vol. I, p. 441. See also, ibid., Vol. II, pp. 277, 279, 282. 



4 Ibid., Vol. II, p. 276. 



fi " Species and Varieties, their Origin by Mutation," 2d ed., p. 597. 

 « Ibid., p. 8. 



