When infants show distress through crying and apparent attempts to withdraw, adults usually conclude that the children are afraid. When the baby is old enough to cling and to seek proximity to his mother, these behaviors, along with crying and withdrawing, are probably universal indications to adults that young children are afraid. Fear behavior is neither rigid nor automatic.
 
The physiological basis for fear reactions is inherited, but its expression is an interaction with the environment. Possible reactions are those that facilitate withdrawal from dangers the young are likely to encounter: strangers, heights, excessive stimulation. As the section o attachment behavior has shown, attachment and fear are articulated in ways that promote survival of the infant and that permit exploration and growth. When strange person, object, or situation causes distress and withdrawal, contact through clinging, touching, or even looking at a loved person restores the baby?s equilibrium in such a way that he can approach and explore. Loss of support, pain, loud noises, and other intense stimuli also cause distress reactions which look like fear and which can usually be alleviated by holding the baby close. Individual differences in temperament make for more intense reactions in some infants and less in others. Some can be comforted more easily than others.
 
A group of infants between 2 and 23 months were examined in a series of fear- provoking situations and other tests, and their mothers were interviewed. Fears of loud noises, masks, a Jack-in-the-box, and a mechanical dog were correlated and showed more intensity in younger and older infants than in those in the middle of the age range. The babies who indicated most fear in these situations of intense stimulation and strange objects tended to be the ?cuddliest? babies, or to show highest need for physical contact. This result is consistent with the observation that clinging seems to allay fear.
 
Fear of falling was tested on a visual cliff a platform of strong glass with a textured pattern under it. Half of the patterned surface is directly under the glass and the other half far below it, giving the visual illusion of a drop-off, halfway across the platform. The fear of crossing the visual cliff increased with age, from 6 months onward. Non-creepers showed different reactions to the two sides of the cliff when placed on its edge, but no fear reactions. Even when pulled across the cliff, they had no fear reactions. Creepers showed some fear, and walkers more fear. Below 10 months of age, the babies did more tactile than visual exploration but after that age, visual exploration increased and tactile decreased.
 
By 5 or 6 months most of the infants could distinguish between the two sides of the cliff, but not between what would support them and what would not. It looked as though experience with space through locomotion was necessary for being able to tell by looking what would offer support for the body. Fear of the cliff was correlated with previous falls, cuddliness, and protest at separation from the mother.Fear of strangers ordinarily occurs in the second half of the first year and rarely before then. The babies in the study described above showed no fear of strangers until 7 months, moderate fear between 7 and 12, and more fear after 12 months.
 
A certain amount of maturity is necessary before unfamiliar images and expectations must be built up first, in order to have a basis for comparison.Sex differences in fear of strangers were found in another study. The age of onset of fear of strangers was taken as the first month in which the baby showed a clear-cut avoidance response to an unfamiliar adult. For girls, the mean age for this measure was 6.7 months and for boys, 9.1 months. Fear of strangers is also related to the number of social contacts an infant has, both within and outside his family. First-born children showed fear of strangers at younger ages than did later-horns.
 
Fear of strangers becomes meaningful when viewed in the sequence of attachment behavior described on page 216. Positive attachments to the mother and other important human beings are built up, and then discrimination against others is developed. In the previously mentioned study of attachment in infancy, 77 percent of babies were found to show their first fear of strangers about one month after they showed the beginnings of specific attachments. At 8 to ½ months, the amount of looking at a stranger has been found negatively related to the infant?s rear of strangers. Ainsworth, from her observations of infants in Uganda, describes a developmental sequence in response to strangers during the first year of life: (1) No observable discrimination between strange and familiar people. (2) Different responses to mother and strangers, but accepts strangers. (3) The baby stares at strangers but does not show fear reactions. (4) The baby does not approach strangers but allows them to hold him, showing some uneasiness. (5) Fear reactions, ranging from slight apprehension to panic.
 
Fear of strangers decreases during the second and third years of life, as shown by increasing willingness to accept comfort from a stranger. Fear of being left alone and fear of the dark probably have a large hereditary, maturational basis. It could be very dangerous for a young, wild primate to be left alone, especially in the dark. His fears and protestations would have real survival value. What meaning does this have for human parents? If they think of such fears as natural outcomes of development in infancy, then they will expect to provide comfort and reassurance if 5uch fears are aroused and to be patient until children grow beyond them.