206 Causes and Course of Organic Evolution 



There has been no more attractive side to it, also, than that 

 which attempted to explain why an evidently steady upward 

 advance was made. Was there a great unseen guiding hand — 

 a Paley's inspiring mechanician? Or did the whole result 

 from natural forces or agencies common to all plants and ani- 

 mals? We shall not attempt here and now to review tht^ 

 many suggestions that have been propounded as sufficient 

 explanations. Synopses of these can be found in Thomson's 

 "Heredity" (79). 



The author believes that in the Law of Proenvironment 

 the agency is secured that would fully furnish an explanation. 

 As already defined and shortly explained, it is that capacity 

 which all caryotic or nucleate organisms and undoubtedly 

 many of the acaryotic or non-nucleate show, of being stimu- 

 lated by and then positively growing or moving, in part or 

 in whole, toward an environment that represents the satisfying 

 resultant or mean between all of the environal stimuli by which 

 they are surrounded. 



Proenvironment and Struggle for existence though often con- 

 ducing toward the same biological result, viz., selective sur- 

 vival, are totally distinct- factors. Thus the former is an 

 inherent physiological capacity of the organism, that manifests 

 itself when one or more new stimuli, or differing strengths 

 of stimuli, are applied. The latter may be and often is con- 

 nected with stimulation response, but may equally secure its 

 results by rapidity of growth, or of motion unconnected with 

 the stimuli; or by formation of localized defensive products 

 that primarily are waste products. Proenvironment again is 

 an expression of what the chemico-physical organization of 

 each organism responds to, as conducting to the most satis- 

 fying environment for it or some part of it that such an organi- 

 zation can secure; struggle for existence is most often the 

 chemico-physical effort to survive amid an environment that 

 the organism is already exposed to. The former is an exactly 

 predicable relation of the organism to environal stimuli, so 

 that, if the molecular sensitivity of the cells and the direction 

 as well as the strength and kind of each stimulus were measured, 



