4.88 THE POPULAR SCIENCE MONTHLY. 



importance to tliem. As late as Marcli, 1877, lie wrote to Neu- 

 mayr, of Vienna, that " there can not be any doubt that species 

 can be modified through the direct action of the environment. I 

 have some cause for not having more strongly insisted on this 

 head in my ' Origin of Species,' as most of the best facts have 

 been observed since its publication." He was led to this modifica- 

 tion of his views by Neumayr's essay on " Die Congerien," and by 

 Hyatt's work in showing that similar forms may be derived from 

 distinct lines of descent. In his correspondence with Huxley, 

 Darwin remarks that one point has greatly troubled him. If, as 

 he believed, accidental conditions produced little direct efi'ect, 

 " What the devil determined each yjarticular variation ? What 

 makes the tuft of feathers come on the cock's head, or moss on 

 the moss-rose ? " 



It is quite plain, indeed, that subsequent to the publication of 

 the " Origin," and especially in 1862, in his correspondence with 

 Lyell, Darwin was inclined to give more power to physical con- 

 ditions, and, in fact, was wavering in his mind as to the force of 

 the different influences at work. In his letters to Hooker, in 1862, 

 the same tendency may be noted, and the preparation of the " Va- 

 riation of Animals and Plants under Domestication " led him to 

 believe rather more in the direct action of physical conditions, 

 though he seemed to regret it because it lessened the glory of nat- 

 ural selection, and, to use his own language, " is so confoundedly 

 doubtful." One can plainly trace from the correspondence how, 

 prior to the publication of the " Origin," he more and more, as his 

 facts accumulated, and as the theory of natural selection grew 

 upon him, relegated to an inferior place the influence of environ- 

 ment ; while, subsequent to the publication of that work, and up 

 to the time of his death, the tendency seemed to be in the opposite 

 direction. 



Many eminent workers have differed greatly from Darwin in 

 the influence allowed to these external conditions, and this is par- 

 ticularly the case with our American writers. Indeed, no one can 

 well study organic life, especially in its lower manifestations, 

 without being impressed with the great power of the environ- 

 ment. Joseph Le Conte speaks of the organic kingdom lying, as it 

 were, " passive and plastic in the molding hands of the environ- 

 ment." Leidy, W^yman, Clark, Packard, etc., have insisted on the 

 influence of physical conditions. Baird and Ridgway on geo- 

 graphical distribution. Whitman on concrescence, Hyatt on gravi- 

 tation, Cope and Ryder on mechanical stress, have all published 

 valuable corroborative evidence ; while many other writers have 

 added their views and testimony, which have been admirably con- 

 densed by Prof. Morse in two addresses before this association. 

 Allen demonstrates plainly the influence of climate and temper- 



