APPLICATIONS AND THEORIES OF EVOLUTION 473 



497. Mutation theory. Charles Darwin had collected many 

 examples of sports that occurred in various crops or herds, 

 but he supposed these to be so exceptional that he did not 

 consider them seriously as the material upon which selection 

 operates in the formation of new species. But Hugo de Vries 

 has emphasized just this class of facts. We saw (p. 462) that 

 he had made direct observations as to the appearance of muta- 

 tions among plants kept in his gardens and greenhouses, and 

 we saw also that mutations are capable of transmitting their 

 peculiarities to their offspring. 



The mutation theory of evolution declares that selection can 

 establish new species only if there first appear individuals with 

 heritable qualities that are distinctive. It is not claimed that 

 the mutants have advantages over their parental type, although 

 they may have ; it is sufficient for the theory if the new types 

 are capable of living' and of establishing themselves. This 

 theory of evolution, and all the other newer theories, are 

 closely connected with the study of heredity and are supported 

 by the results of experiments. 



498. Applications. It should certainly make a practical dif- 

 ference to us which of the many theories of evolution is proved 

 to be true. Suppose we were convinced as many people are 



that the gains and losses of the individual organism affect 

 the constitution of the offspring. Would that not make a dif- 

 ference in our handling of our crops and our domestic animals ? 

 Would it not make a difference in the way we conduct human 

 affairs ? We might then believe that the son of a criminal must 

 be a criminal, or that the son of a judge must be righteous. 

 We might make our laws much more rigorous for the chil- 

 dren of evildoers, and much more lenient for the offspring 

 of good citizens. 



Or, suppose we were certain as many people are that 

 the selection theory is true. Then we should follow the recom- 

 mendations of those who tell us not to build hospitals for the 

 sick, but to let them die or survive. This recommendation is 



