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THE CHANGING WORLD OF LIFE 



Artificial Selection 



What nature does through natural and sexual selection, man can do 

 through artificial selection of animals in which he can control their 

 breeding. The results may not be for the best welfare of the animal, 

 but may make the animal more like man would like for it to be. 



Compare a slim, vigorous, aggressive, razorback hog, which is some- 

 what like the ancestral hog, with one of the modern breeds, such as a 

 Poland China. It is easy to see the effects of artificial selection. By 

 selecting for breeding those hogs that were the best pork producers, 

 man has developed an ideal pork producing breed, but this has not been 



Photos by Winchester 



Fig. 34.6. Results of artificial selection. Through many generations of selection, dogs 

 of great variation in size, appearance, and temperament have been produced. This 

 little girl has to kneel to pet her cocker spaniel ; but the great dane is almost big 



enough for her to ride. 



for the best interest of the hogs. Through such selection the Poland 

 China is now almost completely dependent on man for its existence and 

 probably could not survive if turned loose in the woods to shift for 

 itself. 



Normally, mammals only produce milk during the suckling period 

 and then only enough to supply the needs of their offspring, but through 

 selection man has developed breeds of cows and goats that produce milk 

 in large quantities most of their lives so that we can use it. The same 

 principle applies to egg laying in chickens. 



A study of the many breeds of dogs shows us to what extremes arti- 

 ficial selection may go. A great dane and a cocker spaniel are different 

 in size, body build, length of hair, disposition, and many other charac- 



