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94 THE THEORIES OF EVOLUTION 



ficient in the majority of cases to assure decisive 

 advantages in the struggle. This can only be done 

 by more general variations observable in a large num- 

 ber of individuals and responsible for new adapta- 

 tions. Natural selection exists beyond doubt; only, 

 when it takes place within one given species, it rather 

 tends to eliminate whatever is below the average level 

 than to foster the upward evolution of whatever is 

 above it. Its role appears to be regulative rather 

 than creative. 



Darwin's theory of selection was, so to speak, an 

 attitude of mind made necessary by the state of sci- 

 entific knowledge at his time. Later research work 

 has reduced to more reasonable proportions his orig- 

 inal hypothesis which was too absolute. The services, 

 however, which this hypothesis has rendered to sci- 

 ence are of inestimable value. 



