276 POPULAR SCIENCE MONTHLY 



TRIAL AXD ERROR AS A FACTOR IN EVOLUTION 



By Professor W. B. PILLSBUKY, 



UNIVERSITY OF MICHIGAN 



SINCE Darwin wrote there have been many general formulae ad- 

 vanced under which all forms of development might be brought, 

 and while each has sufficed for a time, each has been seen to fail and 

 each has been replaced with greater or less completeness when tested 

 by a new set of facts. While no one of the formulae can be regarded 

 as final, each has been valuable in so far as it has summarized the facts 

 and points of view of the age under which it has developed. 



Within the last decade there seem to be facts developing in varying 

 fields that support a new formula, which, while perhaps not so definite 

 in its explanation as many that have preceded it, can at least lay claim 

 to very wide application. This generally stated is that all progress 

 is the result of chance trials and a selection from the trials of those 

 that are successful in attaining some end. The first formulation of 

 the process in so many words seems to have been to describe the method 

 by which animals learn. As Professor Thorndike and many later 

 investigators have shown, an animal learns simply as the result of a 

 selection from his chance movements — those which serve for some 

 definite end. When a horse learns to open a gate or a dog to bring a 

 stick through a fence, learning is accomplished by trying all possibili- 

 ties until the end desirable at the moment is attained, and after it is 

 once attained there is usually a smaller number of false movements 

 and a shorter time of accomplishment at each succeeding trial, until 

 finally all movements but the right one have been eliminated. These 

 observations make a sufficient number of possible movements and a 

 selecting agent the only essentials in the learning process. 



From this comparatively modest starting point the doctrine has 

 extended in both directions. It seems fairly evident from experiments 

 that man must learn new movements in exactly the same way as the 

 animal. He, too, can not be helped to learn by being put through the 

 movement from outside. Knowledge of anatomical relations and 

 rational external knowledge is valueless except as it serves as a point 

 of departure. The only method by which the child or man can acquire 

 new movements is by painfully trying and selecting the movements 

 that most nearly accomplish the end in view. 



Recently Professors Jennings and Holmes, in studies of the reac- 

 tions of relatively low forms of life, seem to show that much that has 



