Mimicry Among Animals 



other hand, if an animal spreads from a tem- 

 perate into an aretic district, the conditions 

 are changed. During a large portion of the 

 year, and just when the struggle for exist' nee 

 is most severe, white is the prevailing tint of 

 nature, and dark colours will be the most con- 

 spicuous. The white varieties will now have 

 an advantage; they will escape from their ene- 

 mies or will secure food, while their brown com- 

 panions will be devoured or will starve; and 

 "as like produces like" is the established rule 

 in nature, the white race will become permanently 

 established, and dark varieties, when they 

 occasionally appear, will soon die out from their 

 want of adaptation to their environment. In 

 each case the fittest will survive, and a race 

 will be eventually produced adapted to the 

 conditions in which it lives. 



AVe have here an illustration of the simple 

 and effectual means by which animals arc 

 brought into harmony with the rest of nature. 

 That slight amount of variability in every 

 species, which we often look upon as something 

 accidental or abnormal, or so insignificant as 

 to be hardly worthy of notice, is yet the foun- 

 dation of all those wonderful and harmonious 

 resemblances which play such an important 

 part in the economy of nature. Variation is 

 generally very small in amount, but it is all 

 that is required, because the change in the 

 external conditions to which an animal is sub- 

 ject is generally very slow and intermittent. 

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