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petently advocated by Sir Peter Mitchell; but in no direction has 

 there been more striking endeavor than in the testing of old and once 

 widely accepted theories by the touchstone of detailed analysis and 

 experiment. That is a distinctive feature of post-war zoology, and 

 its milestone was erected by Alfred J. Lotka in 1925. It has had a 

 salutary effect upon theorizing, for "Experience is the greatest baffler 

 of speculation," but if speculation gains in precision through running 

 this new gauntlet, it must not be forgotten that experiment also gains 

 from the association: "Knowledge directeth practice and practice 

 increaseth knowledge." 



So, since I think that truth may lie between analysis of long-range 

 views and synthesis of detailed discoveries, I take this opportunity of 

 laying before you some ideas concerning life and evolution. 



THE SECRET OF LIFE 



There was a Scottish politician and philosopher, a former Duke of 

 Arg}dl, who, among many sayings that are forgotten, took pleasure 

 in reminding the world that "Science has cast no light on the ultimate 

 nature of life." He stood for the rather facile vitalism which loves 

 a mystery and regards the probings of science as bringing knowledge 

 only with the accompaniment of disillusionment. In the opposite 

 camp is the mechanist, in whose view the processes of life are to be 

 explained solely and completely by the concepts of chemistry and 

 physics. The two aspects, the mechanistic and the vitalistic views, 

 have been canvassed so thoroughly that it would be profitless to trace 

 the controversy again, if indeed the controversy has any real antithesis 

 and does not represent simply two facets of one common truth. But it 

 is legitimate to ask what recent years have contributed toward the 

 solving of the secret of life. 



The outstanding fact which strikes the observer is that the extreme 

 positions, physical and biological, have become untenable, and that 

 concessions are being made by both sides. The vitalist's vitality is 

 being whittled down, animation is being put into the mechanist's 

 machine. Sir James Jeans (1933) from the physicist's point of view 

 has stated that living things in some way possess the power of evading 

 the established physical order of disorganization, and in so doing he 

 has conceded more than most biologists demand. When, in his plea 

 at the Cambridge meeting of this Association, in 1938, for the inclu- 

 sion of probability in the scheme of physical conceptions, Dr. C. G. 

 Darwin stated that the trouble about forecasting the future from our 

 knowledge of the present was the impossibility of knowing the present, 

 he was formulating precisely that difficulty of knowing the conditions 

 of life activity which besets the biological experimenter in endeavor- 



