338 Evolution and Adaptation 



conceivable that two such principles as these control the evo- 

 lution of organisms, it still requires a good deal of imagination 

 to conceive how the two go on working together. Moreover, 

 it is highly probable that whole groups have evolved in the 

 direction of greater simplification, as seen especially in the 

 case of those groups that have become degenerate. To 

 what principle can we refer processes of this sort ? 



It is certainly a strange conclusion this, at which Nageli 

 finally arrives, for, after strenuously combating the idea that 

 the external factors of climate and of food have influence in 

 producing new species, he does not hesitate to ascribe all 

 sorts of imaginary influences to other external causes. The 

 apparent contradiction is due, perhaps, to the fact that his 

 experience with actual species led him to deny that the direct 

 action of the environment produces permanent changes, while 

 in theory he saw the necessity of adding to his perfecting 

 principle some other factor to explain the adaptations of the 

 new forms produced by inner causes. Nageli seems to have 

 felt strongly the impossibility of explaining the process of 

 evolution and of adaptation as the outcome of the selection 

 of chance variations, now in this direction, now in that. He 

 seems to have felt that there must be something within the 

 organism that is driving it ever upward, and he attempts to 

 avoid the ideological element, which such a conception is 

 almost certain to introduce, by postulating the inheritance of 

 the effects of long-continued action of the environment, in so 

 far as certain factors in the environment produce a response 

 in the organism. Nevertheless, this combination is not one 

 that is likely to commend itself, aside from the fact that the 

 assumptions have no evidence to support them. Despite 

 Nageli's protest that his principles are purely physical, and 

 that there is nothing mystical in his point of view, it must be 

 admitted that his conception, as a whole, is so vague and 

 difficult in its application that it probably deserves the neglect 

 which it generally receives. 



