148 PROBLEMS OF EVOLUTION 



themselves to it (l) by developing great power of flight, or (2) an 

 offensive taste ; (3) they may " mimic" another nauseous species, 

 or (4) come to resemble some such thing as a dead leaf, and so 

 be protectively coloured. The higher animals have to find some 

 means of keeping down their temperature when the thermometer 

 stands very high, or when they are taking hard exercise, and they 

 may manage this either by rapid breathing, as all birds do, or by 

 means of perspiration. 



The en- In the light of such facts, ought we to speak of the environ- 

 Vir pro n perly ment as P^ ast i c - ? The answer depends on the definition of the 

 defined, is word environment ; rightly defined the environment of an organ- 

 ngl ism includes everything external to itself 'with 'which it is in any 

 'way en rapport. The limitation which I have emphasized by italics 

 is important. Other things are no more part of its environment 

 than ghosts are part of ours, if, however near at hand, they are 

 imperceptible by any of our senses. If we define the environ- 

 ment thus, it is by no means plastic, it is rigid. 1 An adaptation 

 having once been effected, there must be no non-conformity. The 

 camel, having made the desert his habitat, must eat such food as 

 the desert supplies, or else remove to other regions where the 

 conditions are different. Beasts of prey being part of their en- 

 vironment, antelopes must somehow, by speed or wariness, escape 

 from them. Plants that trust to sheep or cattle to carry their 

 seeds must grow burs that will stick. The environment is a 

 despot to all that have once become its subjects. 



But though absolute conformity is required, yet there are 

 various ways of conforming : the hop, the briony and the ivy 

 prove this. Moreover there are often alternative environ- 

 ments, with any of which a satisfactory rapport may be brought 

 about. The species is, in fact, in the position of an Oriental 

 people : its liberty is the liberty of occasionally choosing a new 

 despot. Moreover it has a privilege which Orientals have not 

 always : it may carry out orders in one of several ways, adopting 

 what for it may be the one way possible. 



1 I was certainly wrong in using the term "plastic" of the environment in 

 Natural Science, May i 899. But my contention now is the same as then. I have 

 only expressed it more correctly. 



