WHAT EVOLUTION IS 105 



are endowed with such powers of in- 

 crease that even the slowest would in 

 time overrun the earth. 



Darwin further recognized the 

 fact that the offspring of all animals 

 and plants are more or less diverse, 

 and that no two are ever exactly 

 alike. This is apparent to everyone. 

 In a litter of puppies the individuals 

 are quickly and easily distinguished 

 by size, markings, vigor, disposition, 

 and the like, and we name them and 

 treat them as we do separate persons. 



These slight individual differences 

 are, according to Darwin, either fa- 

 vorable or unfavorable for the con- 

 tinued life of the given organism and, 

 since more individuals come into the 

 world than can possibly survive, those 

 with unfavorable traits are less likely 

 to reach maturity and leave offspring 

 than those with favorable traits. In 

 this way there is a continual elimi- 



