CHAPTER XVIII 



THE ORIGIN OF THE LIVING MACHINE; ADAPTATION; 

 THE FORCES OF ORGANIC EVOLUTION 



ADAPTATION 



Meaning of Adaptation. One of the most striking facts of 

 the organic world, resulting from heredity and variation, is the 

 adaptation of animals and plants to their environment. By 

 this term is meant that the parts of each animal and plant are 

 so particularly fitted to the conditions of its life that it seems as 

 if they were intelligently fashioned with this end in view. 



A few illustrations will make the matter a little clearer. The 

 tree, with its roots extending under ground, with its branches 

 growing into the air and bearing the broadly expanded leaf 

 surface for the purpose of absorbing air, is 

 evidently exactly adapted for its life in the 

 soil and in the air. The roots are mechani- 

 cally built so that they can push their way 

 through the soil; the stems are rigid enough 

 to support the heavy branches, and the 

 leaves are broad and thin and of exactly the 

 proper shape to absorb the largest amount of 

 air. The wing of a bird is an example of 

 adaptation; for its structure, its shape, the 

 lightness of its bones, its ability to expand its 

 feathers, the delicate manner in which the 

 parts of the feathers are attached to each 

 other, are all admirably adapted to an organ whose function 

 is to support the bird in the air. The bird's feet are a beauti- 

 ful instance of adaptation, since wading birds, swimming birds, 

 and scratching birds have feet plainly adapted to their peculiar 



342 



FIG. 140. THE 



PENGUIN, A BIRD 

 ADAPTED FOR LIFE 

 IN THE WATER 



