PARENT AND OFFSPRING 387 



398. Natural and artificial selection. Whenever variations 

 occur we may in a measure determine which variants shall 

 have a chance to reproduce their kind. In the next genera- 

 tion variations will again appear, and selection will again be 

 necessary if we desire to perpetuate the type we began with. 

 It is possible to make a race of plants or animals less variable 



Fio. 179. A bull of the Brahman, or zebu, breed from India 



The hump over the shoulders and the backward pointed horns are characteristic 

 features of this animal. Photograph by Robert K. Nabours 



by selecting constantly for a certain type and by eliminating 

 the variations which do not conform to that type. 



Man decides which of all the variations he desires for his 

 own use and then tries to maintain these particular types 

 and eliminate the others. This constitutes artificial selection. 

 In open nature, through natural selection, those things that 

 can live are the ones that do live. The animals of the ex- 

 tremely cold countries vary in the thickness and heat-retain- 

 ing qualities of their coats of fur. They vary also in their 

 fleetness in pursuit of food, in their ability to escape enemies, 



