390 



Special Vertebrate Organogenesis 



DEVELOPMENT OF BEHAVIOR 



No account of neurogenesis can be com- 

 plete without relating itself to the prob- 

 lems of behavior. After all, behavior is not 

 only another overt sign of the molecular, 

 cytological, morphological and functional or- 

 ganization of the nervous system, but is its 

 dominant manifestation to the accomplish- 

 ment of which all other features have been 

 made subservient by phylogenetic and onto- 

 genetic adaptation. Unfortunately, space re- 

 strictions do not permit me to give the topic 

 its due treatment. However, in order to indi- 

 cate at least some major aspects, I repeat here, 

 with slight modifications, a summary pub- 

 lished on an earlier occasion (Weiss, '50c). 



It is a healthy sign that the sharp separa- 

 tion once advocated between a purely phe- 

 nomenological study of behavior, on the 

 one hand, and the physiological study of its 

 possible neurological foundations, on the 

 other, has not been generally adopted. The 

 pursuit of any one scientific field under an 

 injunction against trespassing into another 

 is neither rational nor productive, especially 

 if both have common objects. It simply is 

 not true that nothing can be learned about 

 the "organism as a whole" by studying its 

 constituent parts and their interrelations. 

 On the other hand, it would, of course, be 

 equally erroneous to assume that mere pre- 

 occupation with the elements will tell the 

 full story of their collective behavior. In 

 the light of developments, it would seem 

 unwarranted to subscribe to either a purely 

 holistic or a purely elementarian theory of 

 neural functions and behavior to the exclu- 

 sion of the other, or to pursue studies on 

 behavior alone or on its neurological foun- 

 dations alone without the benefits that each 

 field can derive from the advances of the 

 other. Regardless of the pertinence of his 

 detailed propositions, it certainly has been 

 the historical merit of Coghill to have built 

 a strong case for the conjoint attack on the 

 problems of behavior and against the sepa- 

 ratist trends of technical disciplines. 



The realization that much can be learned 

 about behavior by the study of its develop- 

 ment is of relatively recent date. But, as 

 frequently happens in the history of science, 

 the formation of theory outraced the acqui- 

 sition of factual knowledge, and soon stu- 

 dents of the development of behavior were 

 found to be rallied around two opposite 

 doctrines, one stressing the primacy of the 

 holistic, the other the elementarian, view- 

 point. Each centered its argxmients on cer- 



tain objects, observations, and techniques 

 different from those of the other, and evi- 

 dently each party felt justified in consid- 

 ering its particular niche as a fair sample 

 of the behavioral universe. Thus what in 

 sober evaluation would have become a 

 fruitful stimulus to further clarification of 

 the issues assumed the dogmatic aspect of 

 an irreconcilable antithesis. Again, as often 

 happens in the course of scientific history, 

 the conflict is turning out to be a matter 

 of one-sided viewpoints and imdue generali- 

 zations rather than of facts. Contrasting 

 views on whether neural functions emerge 

 as mass actions (Coghill, '29; Hooker, '52) 

 or in localized fragments (Windle, '50) can 

 be reconciled if the diversity of sample 

 species and techniques is duly considered 

 and if one refrains from raising observations 

 gathered from a limited field to the dignity 

 of doctrines of universal and unqualified 

 validity. 



PHENOMENOLOGY OF THE DEVELOP- 

 MENT OF BEHAVIOR 



The phenomenology of behavioral devel- 

 opment is actually an old discipline. It 

 started with the recognition of the fact that 

 behavior does have a stepwise ontogenetic 

 history, and it went on to describe the steps 

 involved. Only in the second instance did 

 it proceed to test the significance of the steps 

 as instruments or causal links in the develop- 

 ment of the whole sequence. However, ever 

 since the demonstration that embryos raised 

 in narcosis would develop behavioral pat- 

 terns of normal organization (Carmichael, 

 '26; Matthews and Detwiler, '26), even 

 though the overt expression of the whole 

 series of precursor steps had been suppressed, 

 it has been clear that the behavioral steps 

 are merely external manifestations of under- 

 lying intrinsic developments rather than 

 practice steps. The complex performances 

 of later stages cannot possibly be founded 

 upon the tested success of their simpler 

 precursors, since they seem none the worse 

 for the omission of the intermediate func- 

 tional tests due to narcosis. Again, undue 

 generalizations must be avoided, and what 

 is said here for the early and fundamental 

 steps of behavioral development does not 

 apply equally to the terminal phases, in 

 which the inherent developmental patterns 

 are polished and perfected by actual prac- 

 tice and adjustment. 



The phenomenological study of the de- 

 velopment of behavior has revealed that. 



