ORGANIC EVOLUTION 65 



domestic animals have come from wild animals ; 

 they have been derived by a process of selective 

 evolution conducted by man himself. By con- 

 tinually choosing as the progenitors of each 

 generation those with qualities best suited to his 

 whims and purposes, man has evolved races as 

 different from each other in appearance and struc- 

 ture, and as different from the original species, as 

 many groups which, in the wild state, constitute 

 distinct species ; indeed, man has in some cases 

 created entirely new species, both of plants and 

 animals — species that breed- true and are what 

 biologists call ' good ' — by his own selections. 



There are something over 150 different varieties 

 of the domestic pigeon. Some of these varieties — 

 as many as a dozen, Mr. Darwin thinks — differ 

 from each other sufficiently to be reckoned, if 

 they are considered solely with reference to their 

 structures, as entirely distinct species. The 

 carrier, for instance, the giant of the pigeons, 

 measures 17 inches from bill-tip to the end of its 

 tail, and has a beak ij inches long. Around each 

 eye is a large dahlia-iike wattle, and another large 

 wattle is on the beak, giving the beak the appear- 

 ance of having been thrust through the kernel of 

 a walnut. The tumbler is small, squatty, and 

 almost beakless. It has the preposterous habit 

 of rising high in the air and then tumbling heels 

 over head. The roller, one of the many varieties 

 of the tumbler, descends to the ground in a series 

 of back somersaults, executed so rapidly that it 

 looks like a falling ball. The runt is large, weigli- 



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