E. B. Poulton 351 



the various forces to which it is likely to be exposed by produc- 

 ing the appropriate modification, and this, it is claimed, is in 

 many instances more valuable than the more perfect, but 

 more rigid, adjustment of inherent variations to a fixed set of 

 conditions. 



" A good example of the eminent advantages of adaptability 

 in many directions over accurate adjustment in fewer directions 

 is to be found in a comparison between the higher parts of the 

 nervous system in insects and birds. The insect performs its 

 various actions instinctively and perfectly from the first. It is 

 almost incapable of education and of modifying its actions as 

 the result of the observation of the effects of some new danger. 

 It would appear that the introduction of the electric light can 

 only affect the insects which are most attracted to it, by the 

 gradual operation of natural selection. In the clothes-moths 

 which infest our houses, we may see an example of this ; for 

 these insects seem to be comparatively indifferent to light. 

 Birds, on the other hand, have the power of learning from 

 experience, of reasoning from the results of observation. At 

 first terrified by railway trains, they learn that they are not 

 dangerous, and cease to be alarmed ; while the effect of fire- 

 arms results in their increased wariness. 



"If this view of individual adaptability as due to natural selec- 

 tion be not accepted, it may be supposed that the individual 

 modifications are due either to the direct action of the external 

 forces or to the tendencies of the organism. But it is impossible 

 to understand how the mechanical operation of such forces as 

 pressure, friction, stress, etc., continued through a lifetime, 

 could evoke useful responses, or why the response should just 

 attain and then be arrested at a level of maximum efficiency. 

 The other supposition, that organisms are so constituted that 

 they must react under external stimuli by the production of 

 new, useful characters, or the useful modification of old ones, 

 seems to me to be essentially the same as the old ' innate 

 tendency toward perfection ' as the motive cause of evolution 

 a conception which is not much more satisfactory than special 

 creation itself. The inadequacy of these views is clearly shown 



