1404 



HORMONAL REGULATION OF BEHAVIOR 



stages in ontogeny ("critical periods") cer- 

 tain types of behavior are indelibly shaped 

 and molded for the life of the animal. 



B. THE CRITICAL PERIOD HYPOTHESIS 



Research advances in psychology during 

 the past decade have added so much infor- 

 mation relevant to the establishment of the 

 modalities of social behavior that it may be 

 anachronistic to discuss the "critical pe- 

 riod" for learning as merely an hypothesis. 

 Stated briefly, it is now well established that 

 there are limited and often highly specific 

 periods during the early life of an animal 

 during which important social learning 

 takes place, more or less permanently affect- 

 ing the subsequent social behavior of the 

 individual. There is known to be consider- 

 able species variation in the occurrence and 

 duration of these critical learning periods. 

 In the graylag goose, for example, one criti- 

 cal period can be identified as beginning 

 immediately after hatching (Lorenz, 1935, 

 1950, 1952) . Scott and his co-workers (Scott, 

 Fredericson and Fuller, 1951 ; Scott and 

 Marston, 1950; Scott, 1958) in a meticu- 

 lously detailed series of observations have 

 identified five distinct periods in the life 

 history of the dog. In this species, the pe- 

 riod from 3 to 7 weeks (Period III, Primary 

 Socialization I is the time when primary 

 social modalities become established. Phys- 

 iologically this period is characterized by 

 advancing but incomplete myelinization 

 and development of the central nervous 

 system and associated sense organs ; for the 

 first time conditioning becomes possible. 

 Critical periods have also been identified 

 and studied in the mouse (Williams and 

 Scott, 1953), sheep (Scott, 1945), howling 

 monkey (Carpenter, 1934), and red deer 

 (Darling, 1937). 



The finding that a critical period for pri- 

 mary socialization is such a widespread phe- 

 nomenon in animals gives us reason to ex- 

 pect a continuity of this situation in the 

 human species. Scott (1958) speculates, on 

 the basis of his findings in dogs, that one 

 might expect the earliest critical period in 

 humans to begin between the 6th to 24th 

 week of life and to last two years or possibly 

 longer. Needless to say, much has already 

 been written in the psychiatric and psycho- 

 analytic literature to support a contention 



that these earliest years of life are crucial 

 ones in personality development. The find- 

 ings in regard to the establishment of psy- 

 chologic sex reported in detail on the pages 

 to follow are in substantial agreement with 

 the view that critical learning periods in the 

 human are indeed an established reality. 



C. IMPRINTING 



There is a particular phenomenon well 

 described by the ethologists which deserves 

 special mention, namely, the phenomenon of 

 imprinting. Our work (Ilampson and 

 Money, 1955; Money, 1955; Money and 

 Hampson, 1955; Money, Hampson and 

 Hampson, 1955a, b, 1957; Hampson, 1955; 

 Hampson, Hampson and Money, 1955; 

 Hampson, Money and Hampson, 1956) 

 with hermaphroditic children has led us to 

 see an analogy between establishment of 

 gender role in early childhood and the phe- 

 nomenology of imprinting as described in 

 lower animals.- 



The following are two examples which il- 

 lustrate the basic similarities involved. 



L In >e;us past the sight of a string of day-old 

 goslings following their parent would have been 

 cited as an example of innate, unlearned in,stinctive 

 behavior. Heinroth (1910), Lorenz (1935), and oth- 

 ers have shown how, in birds, species recognition 

 as well as appropriate behavior in response to an- 

 other member of its species, is not pre-established 

 but is subject to modification through early life 

 experience. A greylag gosling, for example, that has 

 lived a few days with its parents will never re- 

 spond to a human as if the human were its parent. 

 On the other hand, to quote Lorenz (in Schiller, 

 1953), "if a greylag gosling is taken into human 

 care immediately after hatching, all the behavior 

 patterns which are slanted to the parents respond 

 at once to the human being. In fact, only very 

 careful treatment can induce incubator-hatched 



"Lorenz (in Schiller, 1957) specified two fea- 

 tures characteristic of the phenomenon of imprint- 

 ing which differentiate it from other types of learn- 

 ing. (1) Imprinting is limited to a very definite 

 and often extremely short phase of ontogeny, the 

 "critical period." (2) The result of this process of 

 determination is irreversible. In this context the 

 term learning is used in the broad sense referring 

 to a family of processes inferred from the observa- 

 tion that animals learn. To quote Verplanrk 

 (1957): "When we say that an animal learns, we 

 are stating that, other things being equal, some 

 behavior now occurs in a situation in which it had 

 not occurred previously, or that the behavior now- 

 occurring in a given situation is different from the 

 behavior that occurred on the last occasion the 

 animal was in that situation." 



