THE STRUGGLE FOR EXISTENCE 83 



ings, as hand to glove ; but when the surroundings 

 change the adaptation is gone. In some cases, 

 indeed, the living creature is adapted to change 

 with the changes of its surroundings : turning white 

 in winter, for instance, like the mountain-hare and 

 the ptarmigan. But when the outer world changes 

 irregularly, then the shoe pinches. The living 

 creature must accept defeat or struggle, and its 

 struggle may bring it success until a constitutional 

 variation in the right direction has time to establish 

 itself. 



{d) Another reason for struggle is often over- 

 looked — namely, the seH-assertiveness of the 

 vigorous animal. The lusty creature tends to be 

 a hustler. It elbows its way through the crowd, 

 jostling its neighbours. Even the plant pushes 

 and obstructs, ensnares and strangles, stings and 

 kills. 



Results op the Struggle for Existence. — 

 There are three chief results of the ubiquitous 

 struggle for existence. 



(a) In the first place, there may be a reduction 

 in numbers which relieves the pressure of popula- 

 tion without directly making for progress. Out 

 of 533 larvae of the large garden white butterfly 

 collected by Prof. Poulton, 422 died from ichneu- 

 mon grubs: four out of every five — a great 

 mortality. But since there was no evidence that 

 the survivors were saved by being the possessors of 

 some peculiarity which those eUminated lacked, the 

 thinning had no evolutionary importance. It was 

 merely fortuitous or indiscriminate elimination. 



(b) In the second place, it may be that the 

 organism is driven, by the pressure of the struggle, 

 to seek out a new habitat, to choose a more appro- 



