HEREDITY 569 



fittest" but others have suggested that the expression "rejection 

 of the unfit" is probably more appropriate. 



Such a theory accounts for the various adaptations of animals 

 and plants to their various situations. The polar bear is adapted 

 to arctic regions; elephants, to tropical regions; the Cacti and 

 Mesquite, to deserts; water plants, to water; Orchids with their 

 peculiarly shaped flowers, to pollination by only certain kinds of 

 insects, and so on. 



Heredity. Darwin assumed that variations are, in part at 

 least, hereditary and thus the variations of the parents tend to 

 reappear in the offspring. The individuals which survive in the 

 struggle impart to their offspring the variations that made it 

 possible for them to survive. Thus variations that fit individuals 

 to win in the struggle for existence are perpetuated through suc- 

 cessive generations. The advantageous variations are more per- 

 fectly developed in some individuals than in others and the 

 individuals with the useful variations most perfectly developed 

 are most likely to survive. They are most likely to be the 

 parents of the next generation where again the individuals with 

 the useful variat ons most perfectly developed have the advan- 

 tage in the struggle, and therefore the best chance to be the par- 

 ents of the following generation. In each generation, therefore, 

 the useful variations most perfectly developed are more likely to 

 be perpetuated in the next generation than those useful varia- 

 tions less perfectly developed. In other words, the most fit 

 individuals, that is, the individuals having the most perfectly 

 developed useful variations have the best chance to survive and 

 have their fitness perpetuated in offspring, while the unfit 

 individuals perish and leave no offspring. Thus the individuals 

 of each generation are, in most part at least, the offspring of the 

 most fit individuals of the previous generation. In each suc- 

 ceeding generation the proportion of individuals having the 

 advantageous variations to the degree best adapting them to 

 their surrounding increases. Obviously, according to this 

 assumption, useful variations become more intensified and more 

 universal in succeeding generations. Eventually they become so 

 prominent and general as to characterize an entire group which 

 may be regarded as a new type or species of individuals. Thus 

 according to Darwin's theory, heredity preserves not only the 

 fitness individuals inherit from their ancestors, but also the 



