PROBLEM D What Have We Learned about Producing 



New Types of Animals and Plants? 



A chapter in man's history. Long before 

 history was written men had learned to 

 domesticate animals and to cultivate 

 plants. Then many centuries ago they 

 became interested in improving these 

 animals and plants. They wanted wheat 

 that would grow in the cold, oat plants 

 that were tall and strong, sheep with 

 more wool, cows that gave better milk, 

 horses that could pull heavier loads or 

 run faster. Through the centuries their 

 progress in producing better types of 

 animals and plants ^^'as slow but steady. 

 Examine Figure 440. From ancestors, no 

 doubt like this wild horse, the race horse 

 and the work horse have been developed. 

 From the wild sheep has come the merino 

 sheep with wool that is thick and of good 

 quality. Men did all this before they un- 

 derstood heredity. Within recent years 

 there has been great improvement in cat- 

 tle, hogs, chickens, such animals as the 

 mink and fox, and many others. The 

 plant breeders, too, by applying their 

 knowledge of chromosomes and genes 

 are now taking far more rapid strides 

 than in the early days. 



How does the breeder work? You will 

 see that there are three methods of pro- 

 ducing new and better types of plants 

 and animals. 



The first method — selecting the best 

 gene combination. Producing better 

 plants and animals by selection is a 

 method that has been used by men as far 



Fig. 440 How does the ■wild Lwrse Iroiii Asia 

 (top) differ from the thoroughbred? What 

 other breeds of horses have been developed? 



(v. S. BUREAU OF ANIMAL INDUSTRY) 



