DARWIN'S NATURAL SELECTION 51 



That four-footed beast which we now call a 



whale, 

 Held his hind-legs so close that they grew to 



a tail, 

 Which he uses for threshing the sea, like a 



flail, 

 Which nobody can deny." 



But Darwin's theory is altogether inde- 

 pendent of the ''stretching" idea. The causes 

 and origin of heredity and variation are up to 

 this moment, alike wrapped in mystery. But 

 when science succeeds in penetrating those 

 secrets, it is extremely unlikely that Darwin's 

 theory will be seriously weakened, no matter 

 what the causes may prove to be. 



Now about the giraffe. We will suppose, 

 for the sake of illustration, two giraffes, a 

 male and a female, whose necks are precisely 

 five feet long. We will confine our illustration 

 to the question of the neck alone. We will 

 suppose this particular pair to give birth to a 

 family of three. First comes heredity. All we 

 ask of heredity is that the young shall be 

 giraffes, not camels or any other species ; and 

 this heredity guarantees. Now comes varia- 

 tion. As this is an ideal case for the purpose 

 of illustrating the theory, we will have one of 

 the three shorter-necked than the parents, 



