Can Artificial Breeds Maintain Themselves? 185 



(2) they give rise under favorable conditions to strains 

 presenting new characters. 



We cannot here discuss further the meaning of the 

 sporadic appearance of unusual characters in plants and ani- 

 mals without first considering the facts of heredity (see page 

 311), since the significance of mutations, the existence of 

 which can no longer be doubted, lies not in the extent to 

 which they depart from the ancestral type, but in the fact 

 that the deviation whether large or small is transmitted to 

 subsequent generations. It is the discontinuity of the muta- 

 tion that distinguishes it from the fluctuations, which result 

 apparently from the action of a multitude of factors upon 

 the developing individual and which are not transmitted to 

 offspring. 



Can Artificial Breeds Maintain Themselves? 



It is impossible to say whether artificial species, or those 

 that emerge through artificial breeding, protection and selec- 

 tion, can maintain themselves in a state of nature. Some 

 certainly cannot. They depend upon special care and pro- 

 tection against extremes of temperature, against insects and 

 other enemies. Many cultivated plants would be quickly 

 exterminated by their natural enemies, and by their com- 

 petition with " weeds," if left to themselves. On the other 

 hand, cultivated varieties of wheat will resist the rust as 

 none of the " natural " varieties seem to have done in the 

 past. Whether these particular varieties can maintain them- 

 selves under wild conditions, however, is important for our 

 purpose only in relation to the question of adaptation. Are 

 such strains fit to live? Here we must again remember that 

 fitness is a matter of reciprocal relationship. It is always 

 relative. The tiger is fit to live in a tropical jungle; the polar 

 bear is fit to live in a different environment. With external 

 conditions constantly changing, the plant or animal that is 

 fit or prosperous today may tomorrow be on the way toward 

 extermination. 



