1 84 Animal Life and Intelligence, 



It is scarcely possible to over-estimate what Darwin's 

 labour and genius have done for the study of animal life. 

 Through Darwin's informing spirit, biology has become a 

 science. But now we must be on our guard. So long as 

 natural selection was winning its way to acceptance, every 

 application of the theory had to be made with caution, and 

 was subjected to keen, if sometimes ignorant, criticism. 

 Now there is, perhaps, some danger lest it should suffer 

 the Nemesis of triumphant creeds, and be used blindly as 

 a magic formula. 



First, we should be careful not to use the phrase, " of 

 advantage to the species," vaguely and indefinitely, but 

 should in all cases endeavour clearly to indicate wherein 

 lies the particular advantage, and how its possession 

 enables the organism to escape elimination ; next, we must 

 remember that the advantage must be immediate and 

 present, prospective advantage being, of course, inoperative ; 

 then we must endeavour to show that the advantage is 

 really sufficient to decide the question of elimination or 

 non-elimination ; lastly, we must distinguish between 

 indiscriminate and differential destruction, between mere 

 numerical reduction by death or otherwise and selective 

 elimination. 



(1) In illustration of the first point, we may select a 

 passage from the writings of even so great a biologist as 

 Professor Weismann. As is well known. Professor Weis- 

 mann believes that senility and death are no part of the 

 natural heritage of animal life, but have been introduced 

 among the metazoa on utilitarian grounds. In his earlier 

 papers, he attributed the introduction of death, and the 

 tissue-degeneration that precedes it, to the direct action of 

 natural selection.* More lately, he attributes it to the 

 cessation of selection.! Concerning this later view, we 

 shall have somewhat to say presently ; we may now con- 

 sider the former as an example of too indefinite a use of 

 such phrases as "of advantage to the species." " Worn- 

 out individuals," says Professor Weismann, ''are not only 



* Weismann. " Essaj^s on Heredity," p. 24. f Ibid. p. 140. 



