SELECTION 169 



organism will be determined by the resultant 

 of all these selection processes, and though 

 the exact manner of it be extremely complex, 

 it will be the most generally efficient organism 

 which will on the average survive. Its 

 characters will be such as have remained 

 4 useful ' throughout its life, such as have 

 adapted the organism to the generality of 

 life-conditions under which it has lived." 



DIFFERENT KINDS OF SELECTION. There 

 are two main modes of natural selection. 

 There is the ordinary " lethal selection," 

 which works by the discriminate elimination 

 of the relatively less fit; and there is " repro- 

 ductive selection," which works through the 

 increased and more effective reproductivity 

 incident on the success of the more fit. When 

 Darwin says " natural selection acts by life 

 and death ... by the survival of the fittest 

 and by the destruction of the less well-fitted 

 individuals," he describes lethal selection, 

 and many use the term natural selection in 

 this sense only. But when Weismann says : 

 " Those that are best adapted in colour 

 will secure the most abundant food and will 

 reproduce most prolifically, and they will 

 thus have a better prospect of transmitting 

 their usual colouring to their offspring," he is 

 obviously describing reproductive selection. 



