METHODS OF EXHIBITING REACTIVE TENDENCIES 



CHARACTERISTIC OF ONTOGENETIC AND 



PHYLOGENETIC STAGES 



ROBERT M. YERKES 



From the Harvard Psychological Laboratory 



Methods which have contributed importantly to our knowl- 

 edge of the ontogeny and phylogeny of reactive tendencies, and 

 more especially to those types of adaptive behavior which we 

 call ideational, are few and unsatisfactory. Only recently have 

 experimental devices and procedures been suggested which are 

 alike suited to reveal the reactive tendencies of ontogenesis and 

 phylogenesis and to stimulate interest in genetic description of 

 behavior. 



Following a brief historical sketch, I shall describe an appa- 

 ratus by means of which three of the most recent and promising 

 of our behavioristic methods may be used. 



From the birth of interest in the problems of psychogenesis, 

 about the middle of the last century, until the end of the cen- 

 tury, no scientific means of approaching the problems of idea- 

 tional behavior 1 were developed. Romanes, Brehm, Morgan, 

 and their psychological contemporaries who happened to be 

 interested in evolutionary or genetic problems worked either 

 from anecdotal materials or from observations gathered by the 

 use of crude and unstandardized methods which may fairly be 

 characterized as wholly unsuited to scientific inquiry. We re- 

 gard their contributions to genetic psychology as suggestive of 

 possibilities of research or as defining problems rather than as 

 important additions to our knowledge of fact. 



With the appearance of Thorndike's mental initiative, the 



situation radically changed, for the puzzle-box or problem method 



came into existence and began to be used systematically as a 



1 1 shall designate as ideational behavior those forms of adaptive response which 

 in objective characteristics are identical with, or strikingly resemble, what we ap- 

 propriately and with common consent call ideational behavior in man. 



