Editorial. 135 



such trial and error reactions as are common among more 

 complex animals. It would appear rather that all animals 

 more or less thoroughly prove or test their environment by 

 the method of trial and error. Sometimes we find a wide 

 range of reactions, as in the cat, dog and monkey ; and 

 again we find a narrow range, as in the unicellular organisms. 

 Organisms differ, then, not in the essential method of reacting, 

 but, first, in the scope or variety of reactions exhibited in the 

 proving of things, that is, in the thoroughness with which they 

 are capable of testing a situation ; second, in the influence 

 which the tests have upon subsequent reactions. According to 

 Jennings and other students of simple forms of animal behavior, 

 the unicellular organisms go through much the same series of 

 trial and error reactions each successive time a situation is pre- 

 sented to them ; they do not in any marked degree profit by 

 their experience. Higher organisms, on the contrary, give un- 

 mistakable evidence of profiting by their proving of things, for 

 from the chance stumbling upon the right act which is charac- 

 teristic of the trial and error method at first, they progress to the 

 point at which the right reaction is given as soon as the situa- 

 tion is presented : they learn, by experience, the appropriate 

 form of reaction. Some animals quickly lay hold upon that 

 which is good and tenaciously hold to it, others profit scarcely 

 at all by the repetition of a reaction. Certain animals continue 

 to stumble upon the right reaction from the beginning to the 

 end of life, others become able to select the profitable reaction. 

 In general the statement is true that those organisms which 

 mosc nearly prove all things are also best able to hold fast that 

 which is good, but as will be shown later there are certain strik- 

 ing and significant exceptions to this rule. 



If, now, we seek for the developmental relations of the two 

 aspects of activity which have been selected as primarily signi- 

 ficant — scope of the reaction series and ability to learn, with its 

 resultant mechanization of action — we note that the scope of re- 

 action is primarily a phylogenetic aspect, ability to learn an 

 ontogenetic aspect. For in the race, generally speaking, activ- 

 ity developes from the simple uniform series of trial reactions to 



