THE STRUGGLE FOR EXISTENCE. 63 



The intensity of the struggle may be judged by the 

 death -rate. In a region where the population has 

 reached a stationary state, the number of each species 

 remains approximately the same. On the average, then, 

 only one out of the whole progeny can survive to repre- 

 sent each parent individual of the previous generation. 

 All except these fortunate individuals are destroyed 

 sooner or later before they have succeeded in leaving 

 offspring to perpetuate their kind, or in securing the 

 success in life of any of their progeny. The greatest 

 amount of destruction takes place when the organisms 

 are still quite young. 



The struggle for existence, natural selection, and adap- 

 tation, are so intimately connected, that it is scarcely 

 possible to treat of one of the^e without at the same time 

 dealing with the other two. While the struggle may be 

 considered as the primary factor, to the action of which 

 the selection is due, it is also the very means whereby 

 adaptation is brought about. The transmission of heredi- 

 tary factors is, of course, necessary for the selection to 

 be effective. Obviously natural selection acts merely as 

 a sieve, separating individuals so formed as to survive 

 in the struggle for existence, from others which are not. 

 It may be represented equally well as a survival of the 

 fit, or as an elimination of the unfit. This point is worth 

 insisting on, because, strangely enough, it has been often 

 brought forward as a serious criticism that natural selec- 

 tion is, after all, merely a process of elimination. 



In the long-run those organisms less well adapted to 

 survive will have less chance of leaving successful off- 

 spring behind them, will be crushed out in the struggle, 

 will be eliminated. The only difference between the 

 well adapted and the badly adapted in a given environ- 

 ment is that in the first case the total inheritance, the 

 hereditary mechanism or factors, react to stimuli in such 

 a way as to lead to success, while in the second case they 

 do not. Selection, therefore, is between that kind of 



