Development Of The Smile And Fear Of Strangers In The First Year Of Life (1963)

for in this film we will try to do two things one we will attempt to show the normal sequences in development of the smile and the fear of strangers in infants second we will attempt to document the findings that these two Behavior behaviors are under partial hereditary control the film is largely based on footage taken in the course of a study of infant identical and fraternal twins the first report of this study appeared in science entitled inheritance of behavior in infants we quote from the abstract of that article mental and motor abilities and personality development were studied in 20 pairs of infant twins of the same sex on a monthly basis in their first year that is before Mutual imitation becomes a factor blood group determinations made after the study was completed revealed 11 fraternal and nine identical pairs within pair differences were significantly greater within fraternal pairs on all tests and rating scales from science April 12th 1963 once again this film concentrates on two aspects of our findings the development of the smile and the subsequent development of a fear of strangers in the film we will see examples of concordant development in identical twins discordant development in fraternal twins and finally an exception discordant development in an identical pair in addition in order to clarify certain developmental issues examples of nun Twins and a blind infant will be seen we start with an example of pre-social smiling in a nun twin this is Tony the author's son at 11 days of age he has just been fed and is falling off to sleep his smile is typical of the first month in that no specific external stimulation is required and it occurs when the baby is sated comfortable and sleepy thus this is not a social smile this type of smiling drops out most infants after the first month in the second month it usually takes some external stimulation to elicit the smile Arturo a fraternal twin was our best example of an eyes closed Smiler he would also smile with eyes closed to a voice or to the tinkle of a bell he was as sleepy head and was rarely Wide Awake his fraternal brother Felix was a remarkable contrast he was very alert but rarely smiled in fact father was somewhat worried about the few smiles here he tries his best to make Felix smile Felix not only illustrates contrasting development so typical in our fraternal pairs but also his visual fixation of mother's face illustrates behavior that normally precedes the true social smile visual fixation of the adult's face is further illustrated by Chucky and Marty an identical pair here we see complete concordance for this Behavior usually about 10 days after this intense visual fixation of the adult's face begins the first social smile occurs concordant development of visual fixation of the adult face is further illustrated by another identical pair Lori and Lisa Lori and Lisa were neck and neck in all phases of of development throughout the study we shall see more of them later we digress from our twins for a while it is of great interest that infants in the first three months will not only fixate a human face but a model of a human face as well Mark's mother alternately presents him with the face and its reversed blank side Dr Robert fance working under highly controlled conditions presented infants of various ages with a number of figures including one similar to this model he found that as soon as infants could visually fix upon a stimulus they preferred one resembling the human face in some infants this occurred earlier than 2 4 hours of age would suggest an innate Readiness to fixate a faik pattern since visual fixation of a face and smiling are intimately connected we may well ask what happens in blind infants David can only perceive light due to cataracts caused by German Measles and Fetal life in a study now underway limited because fortunately blinded infants are now rare we find that the early social Smiles of blind infants are extremely fleeting many unsmiling feet of film were taken of David at this age but he did occasionally smile when talked to or played with it appears that vision is prerequisite to a prolonged social smile in these early months however it is also clear that although vision is of great importance in the normal smile it is not necessary for smiling our data shows that by 6 months of age blind infants can engage in prolonged social smiling David has had an operation but can still only perceive light it is of interest to us also that deaf infants are usually indistinguishable from normals in the development of the smile since seeing infants blind infants and deaf infants all smile we may conclude that the sensory channels are probably secondary although important it would seem that smiling is primarily the instinctive response of an infant to another while infants under 5 months of age will usually smile at any person after this age they become increasingly discriminating and smiles are increasingly reserved for familiar persons discrimination turns to weariness sometime in the third or fourth trimester of the first year and most infants begin to react with fear when with a stranger this process is very similar to the development of the flight response in lower mammals and in Birds there too fear of strangers often follows a period in which indiscriminate attachments are possible back to to our twins Lori with her mother looking about her body and hands are relaxed now a stranger holds her note the drawn neck and the clenched hands her identical twin Lisa reacts identically first we see her with Mother then with the stranger again note the drawn neck and the clenched hands the same same Girls 2 months later here is Lori alone with mother and with a stranger here is Lisa alone with mother and with a stranger by 8 months both girls were relatively unafraid of strangers Lori is here with mother and with a female stranger this time the award position is primarily due to the male strangers discomfort with babies rather than Lor's discomfort Lisa with mother now with the female stranger again our awkward male stranger thus we have seen an identical pair whose reactions to strangers are highly similar in timing and intensity Richard and Robert are fraternal twins and are highly dissimilar in their reactions Richard has been something of a scaredy cat for several months although Mrs Keller the investigator has made a visit each month of his life he still cries after a while he relaxes but he cries again when Mrs Keller Don a Halloween mask fraternal brother Robert provides a clear contrast he gives no indication of fright at any point in the procedure 2 months later Richard still tends to frighten easily the Jack in the Box makes a noise when it pops out fraternal twin Robert is still a happy go-lucky fellow our last example is an exception a pair of identical twins who are decidedly unalike in their reactions to to fear inducing situations Susie who was easily startled by noises in the first two months is here confronted by a whistling Jack in the Box Annie while similar to Susie in many aspects of Behavior reacts differently in this type of situation at present we have no explanation for this nonconcordance careful investigation led us to rule out differential treatment by parents birth order traumatic delivery and a number of other possible causes at one year of age Susie is exceedingly frightened by strangers and has been since 7 months of age mother is at the camera filming this scene Annie who showed relatively mild fear at 8 months now is over it to summarize heredity probably plays a role in the development of the smile and the fear of strangers our evidence for this is that identical twins show greater concordance than fraternal twins although there are some exceptions the phenomena themselves are of the greatest importance for they seem to be prototypes for much of later Behavior the smile is probably the first expression in human life of pleasure with another whereas fear of strangers is normally the first expression of fear of another these two phenomena are probably Universal in mankind and it is our belief that both are intimately related to human evolution and to human viability