Active Causes of Organic Evolution 193 



of these and especially the manner in which they radiate out 

 in definite lines and threads over the surface of water and on 

 to firmer lighted substrata indicate probable resultant, even 

 though sluggish, correlations of two or more responses. But 

 a wide field for experunental study remains open here. 



The exact and predicable proenvironal courses taken how- 

 ever by practically every unicellular and multicellular member 

 of the Caryota, at least during some stage in its history, form 

 a factor of vast importance in organic evolution. Further- 

 more, when we reach the higher fields of mind and memory, 

 it conducts us along pathways that liitherto have been closed, 

 or nearly so, to continuous practical investigation. 



The proenvironal response acts usually — perhaps always — 

 vdth extreme accuracy, so as to plot out a course or pathway 

 that may ultimately guide the organism along the same path 

 as that already pursued by it, or by its ancestors for genera- 

 tions. Tliis occurs if environal agents or stimuli remain con- 

 tinuously uniform in strength, direction of application, and 

 otherwise. But the environal stimuli may become changed, 

 and cooperate to carry the organism along an ascending and 

 evolving line that conduces to betterment of the individual 

 and in time of the species. Or again one or more of the sep- 

 arate stimuli may give rise to a resultant response that con- 

 duces to an analytic, descending, or devolving condition, and 

 this will surely, though it may be slowly, lead to extinction 

 of the individual and in time of the species, if such analytic 

 stimuli exceed the catalytic. 



We would now define this factor as "the resultant response 

 of an organism to the sum-total of all the environal agents that 

 act on it or on any part of it, and which causes the organism 

 to proenviron a course or pathway that is temporarily satis- 

 fying to it, and that can alone be taken in virtue of the action 

 of the several environal agents, and the reaction to each of 

 these by appropriate organismal molecules," or in more con- 

 densed language we may define the law as "the correlated 

 resultant response by any body to the summated correlation of 

 stimulatory action, that leads to a temporarily satisfied state." 



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