EVOLUTION AND ADAPTATION 

 CHAPTER I 



THE PROBLEM OF ADAPTATION 



Between an organism and its environment there takes 

 place a constant interchange of energy and of material. This 

 is, in general, also true for all bodies whether living or lifeless ; 

 but in the living organism this relation is a peculiar one ; first, 

 because the plant or the animal is so constructed that it is 

 suited to a particular set of physical conditions, and, second, 

 because it may so respond to a change in the outer world 

 that it further adjusts itself to changing conditions, ie. the 

 response may be of such a kind that it better insures the 

 existence of the individual, or of the race. The two ideas 

 contained in the foregoing statement cover, in a general way, 

 what we mean by the adaptation of living things. The fol- 

 lowing examples will serve to illustrate some of the very 

 diverse phenomena that are generally included under this 

 head. 



Structural Adaptations 



The most striking cases of adaptations are those in which 

 a special, in the sense of an unusual, relation exists between 

 the individual and its surroundings. For example, the fore- 

 leg of the mole is admirably suited for digging underground. 

 A similar modification is found in an entirely different group 

 of the animal kingdom, namely, in the mole-cricket, in which 

 the first legs are also well suited for digging. By their use the 

 mole-cricket makes a burrow near the surface of the ground, 



