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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