The Making of Species 



is the result of a congenital variation or a somatic 

 one. This will be rendered clear by a hypotheti- 

 cal example. Let us suppose that a certain 

 mammal is forced, owing to the intensity of the 

 struggle for existence, to migrate into the Arctic 

 regions. Let us further suppose that this organ- 

 ism is preyed upon by some creature that hunts 

 by sight rather than by scent. Let us yet 

 further imagine that this predacious species is 

 swifter than our animal, on which it preys. It 

 is obvious that, other things being equal, the 

 more closely the creature preyed upon assimilates 

 to its surroundings the more likely is it to escape 

 the observation of its foes, and so to survive and 

 give birth to offspring. Now suppose that the 

 glare from the snow-covered ground bleaches its 

 coat. This whitening of the fur is a somatic 

 variation, one which is induced by the environ- 

 ment. Such an animal will be as difficult to see, 

 if the bleaching is such as to render it snow- 

 white, as if its whiteness were due to a germinal 

 variation. Thus, as regards its chances of sur- 

 vival, it matters not whether its whiteness be the 

 result of germinal or somatic variation. But if 

 the whiteness is due to a somatic variation, its 

 offspring will show no tendency to inherit the 

 variation ; they will have in turn to undergo the 

 bleaching process. If, on the other hand, the 

 whiteness is due to a germinal variation, the 

 offspring will tend to inherit this peculiarity and 



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