26 THE STORY OF ANIMAL LIFE 



shades. It is all a question of the survival of 

 the fittest the unfit being represented by colours 

 too easily seen, and therefore quickly snapped 

 up. As for the spire, it has already been shown 

 how that is adapted to circumstances. It is 

 worthy of remark that in the kindred Edible 

 Periwinkle, Littorina littorea, which has a sharp 

 spire, elderly specimens may be seen with the 

 end of the spire damaged. 



Turn again for a moment to our first in- 

 stance the adaptation of men to a sedentary 

 or an outdoor occupation. Here we dwelt upon 

 the change produced by their mode of life; we 

 left out of sight the " survival of the fittest." 

 Yet here it is equally surely at work. How 

 often does the young mountaineer, less agile 

 than his fellows, come by a violent death ? Only 

 those who are equal to the necessities of the life 

 survive many are lost. How often does the 

 clerk, tied to his desk, fail in health and die ? 

 How often, hating a sedentary life for which he 

 is unfitted, does he throw his energies into 

 athletics, lose interest in his office work, and get 

 dismissed? Here again comes in "the survival 

 of the fittest" for a desk: alas! perhaps the 

 only means of livelihood. 



But why do variations occur ? This is the 

 question first asked by a child, when you try 

 to explain the working of " natural selection." 

 It is also the last question asked by scientists, 

 who are still industriously engaged upon study- 

 ing the problem. 



In the above instances from human life, we 

 have considered the occurrence of changes 

 brought about in the organism by the circum- 

 stances of life ; or as scientists say, by the " en- 



