TRIAL AND ERROR 277 



hitherto been regarded as an almost machine-like response to external 

 stimulation is not made with the definiteness that has been supposed. 

 On the contrary, what seems to take place is a feeling about for a 

 favorable condition. When this is found there is either continued 

 motion in this most favored direction or quiescence in the most favor- 

 able position. Here again we should have to do with trial and error, 

 but with less complicated possibility of movement and, in all proba- 

 bility, with a different basis for the selection of the favorable condition. 



Still a fourth expansion of the category of trial and error is possible 

 in a metaphorical sense. This is to explain the general course of 

 evolution. If we accept in all strictness the conclusions of Weismann, 

 there is no possibility of foreseeing with very great accuracy any change 

 in a race. Changes of one kind appear here, changes of another kind 

 appear there. Aside from the conditions of mating, however, there is 

 no way of tracing to any known causes the changes observed. We are 

 left then with what, at the present stage of knowledge, seem entirely 

 unforeseen and undetermined chance changes in the animal structure, 

 with an accompanying set of instincts and general activities. The real 

 determining factor is, of course, natural selection. In brief the en- 

 vironment determines which of the many forms and functions that 

 originate by chance shall survive. By personification, and even more 

 literally, we can think of the chance variations as the analogue of the 

 trials of the individual animal, and survival as corresponding to the 

 movement that is successful and so retained. 



If we should then be permitted to generalize, we should have chance 

 at the basis of all learning, all advancement, all adaptation. The 

 primary facts would be the variation in structure, which would form 

 the basis for all other adaptation. Within the organism at the lowest 

 stage would be found adaptation from moment to moment on the basis 

 of successful chance adjustment. At this stage, however, there is no 

 learning. One adjustment is of no value for later activities, as the 

 animal is at the same level, in the same condition, after the adaptive 

 movement has been made as it was before. At the next stage, in addi- 

 tion to the increased complexity of the organism which makes possible 

 more numerous movements, there is retention of the successful trials. 

 A movement once made is accompanied by a change in the organism 

 which makes that movement more likely to occur in the future. From 

 this point upward there is variation in degree of complexity of possible 

 movements, in the readiness with which movements once attained are 

 retained and repeated, but there is no great change in the mechanics 

 of the problem. 



What does change throughout, and what is, after all, on this theory 

 the essential factor in all development, is the selecting agent and the 

 rewards which serve to make one thing permanent rather than another. 



