142 MENDELISM chap. 



sudden step, not by a process of gradual and almost 

 imperceptible augmentation. It is not continuous but 

 discontinuous, because it is based upon the presence or 

 absence of some definite factor or factors — upon discon- 

 tinuity in the gametes from which it sprang. Once 

 formed, its continued existence is subject to the arbitra- 

 ment of natural selection. If of value in the struggle for 

 existence natural selection will decide that those who 

 possess it shall have a better chance of survival and of 

 leaving offspring than those who do not possess it. If it 

 is harmful to the individual natural selection will soon 

 bring about its elimination. But if the new variation is 

 neither harmful nor useful there seems no reason why it 

 should not persist. 



In this way we avoid a difficulty that beset the older 

 view. For on that view no new character could be de- 

 veloped except by the piling up of minute variations 

 through the action of natural selection. Consequently 

 any character found in animals and plants must be sup- 

 posed to be of some definite use to the individual. Other- 

 wise it could not have developed through the action of 

 natural selection. But there are plenty of characters 

 to which it is exceedingly difficult to ascribe any utility, 

 and the ingenuity of the supporters of this view has often 

 been severely taxed to account for their existence. On 

 the more modern view this difficulty is avoided. The 

 origin of a new variation is independent of natural selec- 



