54 A STUDY IN HEREDITY 



tion ? How is it effected ? On what lines does 

 it work ? 



It is difficult to answer this question by a study 

 of wild nature. The same difficulties which prevent 

 proof of selection ^ face us also when we attempt 

 to prove absence of selection. Moreover, the 

 degeneration, like the evolution, of wild animals 

 is always more or less complex. So many dangers 

 environ them, so many characters, eyes, ears, nose, 

 muscles, etc., fend off the dangers, that the 

 stringency of selection is seldom very great as 

 regards any one character. No character there- 

 fore undergoes very rapid evolution ; for the effects 

 of the elimination of the unfit are too much dis- 

 tributed among the many useful characters. As 

 we have seen, rapid evolution is not possible except 

 when the effects of the elimination of the unfit are 

 concentrated on only one or two characters. This 

 can occur among wild creatures only when a great 

 and rapid change in the environment happens — a 

 thing which rarely occurs ; for, as a rule, the 

 environment changes very slowly. Seldom, there- 

 fore, can any man observe evolution in wild nature 

 during the short course of his own life. For 

 similar, but even stronger reasons, no man can 

 observe degeneration at work in wild nature; his 

 life is not long enough to cover periods during 



* Vide Ante, p. 25. 



