356 ANIMAL BIOLOGY 



their parents whose qualities they inherit. But occasion- 

 ally organisms have been observed to depart considerably 

 from the parental type, producing what are called varia- 

 tions. It is often remarked that no two individuals 

 are exactly alike, and this applies as much to plants and 

 animals as to human beings. Many of the differences 

 between organisms of the same ancestry are due to food, 

 climate and other environmental causes, and are probably 

 not inherited; but other variations which occur less fre- 

 quently are undoubtedly transmitted. Thus there was 

 born in Massachusetts a peculiar ram having an unusually 

 long body and short, crooked legs. Its enterprising 

 owner conceived that it would be desirable to produce a 

 breed of sheep like this ram, and he found that it was 

 capable of transmitting its peculiar qualities to its off- 

 spring. There was thus produced the Ancon, or otter 

 variety of sheep. The Merino sheep likewise originated 

 from a sudden variation. Breeds of hornless cattle 

 have been produced in a similar manner, and a great 

 many of our cultivated varieties of plants and animals 

 have also originated from a sudden variation. These 

 sudden transmissible variations are commonly spoken of 

 as sports or mutations. 



It is owing to the occurrence of variations of a trans- 

 missible kind that breeders of plants and animals are able 

 to effect such striking changes in their stock. The breeder 

 selects those variations which are best fitted for his purpose 

 and breeds from them. Other variations in the same direc- 

 tion are selected, until a race is finally produced which is 

 often very different from the original one. Horses have 

 been bred for speed, for strength and other qualities for 

 generations, producing the slender high-spirited race horse 

 on the one hand, and our heavy draft horses on the other. 

 Cows have been bred for increased yield of milk with the 



