322 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



But in this rearing in captivity a new element enters almost 

 at once. That is the choosing or selection of certain of these 

 young to be allowed to grow up, and again the choosing among 

 these when grown up of those to be the parents of more young. 

 This selection may be almost unconsciously done, or it may be 

 made intentionally and carefully, so as to preserve the most 

 desirable individuals and have them give birth to others like 

 themselves. 



Then there comes the crossing of special individuals or the 

 hybridizing with other races in the hope of adding or combin- 

 ing in the offspring the desirable qualities of both kinds of 

 parents. It is this careful selecting and crossing that are 

 usually meant when animal breeding is spoken of. And our 

 modern hosts of kinds or races of domesticated animals, the 

 scores of sorts of dogs and cats and cattle and pigeons and 

 ducks, have all been produced by "breeding." The acts of 

 choosing and hybridizing and choosing again and rearing from 

 these chosen offspring and again from each following genera- 

 tion until a form is arrived at very different in appearance or 

 habit from the original ancestor are called also artificial selec- 

 tion. It was largely on a basis of his observations of the 

 methods and results of artificial selection that Charles Darwin 

 founded his great theory of natural selection, which is, simply, 

 that nature unconsciously chooses or selects among animal or 

 plant individuals and kinds through the survival and producing 

 of young by those types born with traits advantageous in the 

 struggle for existence, this struggle being inevitable on account 

 of the geometrical ratio by which animals multiply. 



The art of the animal breeder has reached in these later days, 

 the days since Darwin particularly, a very high stage of devel- 

 opment. It is becoming a science, because the breeders are 

 studying the laws of variation and heredity and making their 

 hybridizations and selections on a basis of the scientific knowl- 

 edge of these laws (see next chapter). 



An important thing to note in connection with animal 

 breeding and artificial selection is that the selecting and modi- 

 fying are all made to change the animals along lines wholly 

 determined by man; lines that make the animals more useful 



