THE KINSHIP OF LIFE. 25 



Nature, of "natural selection," has saved the whiter 

 rabbits and condemned the darker ones to destruction. 

 In the summer these conditions are changed ; those in- 

 dividuals who retain the ancestral gray are then the 

 ones best fitted to live. And so after many centuries, 

 as we may conceive, there has come about a gradual 

 change in the fur of our hares, until now in the northern 

 species the fur is white in winter, while all are alike 

 gray or brown in the summer. 



Precisely similar is the change in the plumage of the 

 arctic partridge, or ptarmigan, as well as in the various 

 other northern birds. But this is not all. A change in 

 colour such as enables the hare or the ptarmigan to evade 

 its pursuers would also aid these pursuers to steal un- 

 aware on their prey. Nature has no preferences, and 

 helps alike victim and victor. And so it comes about 

 that predatory weasels and owls in winter assume a 

 snow-white garb, and that this is laid aside in the sum- 

 mer. It is doubtless true that other influences co-oper- 

 ate in producing these changes in colour. White fur is 

 warmest in cold weather, for it radiates less heat. We 

 may say that all these animals are dressed in white in 

 winter to keep them warm. But this again would be sim- 

 ply a phase of " natural selection." If the animals suffer 

 from cold, the dark ones will be chilled first. Thus in 

 more ways than one the white animal has the advantage 

 of the other in the winter. This advantage enables it 

 to outlive the other. It causes its descendants to outlive 

 and eventually to displace those of its darker rival. 



To such causes as these we must ascribe the nice 

 adjustment of each species to its surroundings. If a 

 species or a group of individuals can not adapt them- 

 selves to their environment, they will be crowded out by 

 others who can do so. The former will disappear en- 

 tirely from the earth, or else they will be limited to 



