Applications of Organic Selection 175 



accumulating certain variations in producing well-marked 

 types is seen in artificial selection, where certain creatures 

 are set apart for breeding. But any influence, such as the 

 individual's own accommodation to his environment, which 

 is important enough to keep him and his like alive, while 

 others go under in the struggle for existence, may be con- 

 sidered with reason a real cause in producing just such 

 effects. Thus by the processes of accommodation, a 

 weapon analogous to artificial selection is put into the 

 hands of the organism itself, and the species profits by it. 

 Headley characterizes this aspect of the case as follows : 

 ' The creatures pilot themselves. . . . Selection ceases to 

 be purely natural; it is in part artificial' (see below. 

 Appendix B, I., and above, p. 171). 



For example, suppose that cats catch more long-tailed 

 rats than short-tailed rats. Natural selection would then 

 work to reduce the length of the rats' tails. But the breeder 

 can secure longer-tailed rats by removing the longest-tailed, 

 in successive generations, to an environment where there 

 are no cats. Now suppose we find that the long-tailed 

 rats have also more intelligence than the short-tailed ones, 

 and use it effectively in escaping from the cats, then the 

 effects of natural selection may be reversed : the short- 

 tailed rats will now suffer more from the cats, and tJie result 

 will be exactly tJie same as that produced by the breeder — 

 a race of longer-tailed rats. But it is due to the screening 

 utility of the intelligent accommodations made by the rats 

 with long tails. 



§ 2. Applications of Organic Selection 



This point of view has had especial application and 

 development in connection with determinate evolution, 



