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 teleological 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. 
