THEORETICAL BIOLOGY 



463 



the fate of a flower garden if 

 the weeds are allowed to have 

 full play is a good example ; 

 animals war against oneanother 

 from the highest to the lowest. 

 Thus it eomes about in the 

 long run that those organisms 

 which reach maturity and re- 

 produce themselves are such 

 as have some special advantage 

 over their less fortunate asso- 

 ciates, it may be greater 

 muscular strength, greater 

 fleetness of foot, greater cun- 

 ning, or they may even prevail 

 through being less conspicu- 

 ous. Hence this struggle for 

 existence results in the survival 

 of the fittest, and the elimi- 

 nation of the unfit. Thus 

 nature is exercising a continual 

 selective power, preserving 

 those organisms whose 

 variations best adapt 

 them to life amidst their 

 surroundings ; this is 

 natural selection, the 

 fundamental proposition 

 in Da r w i n ' s 

 theory ; he offer- 

 no explanation 

 to the origin of 

 the variations 

 w h i c h natu r e 

 chooses, they are 

 fortuitous. 



Fig. 421. Enchenopa. Tree hoppers on a locust twig, showing their resemblance to the 

 thorns; when at rest the body is depressed into contact with the twig as here represci 

 — when walking it is raised as in Fig. 207 and the legs become more conspicu 

 (Drawn from life by the author.) 



