By contrast, only 10 percent of the low reactives were both subdued with the examiner and shy with unfamiliar children. The temperament of the high reactive infants constrained their development of an extremely extroverted personality rather than causing a fearful, anxious personality in most of these children. The children who showed high fear at all ages were most likely to develop anxious symptoms by the time they were seven. The high reactive infants who became inhibited children also displayed extreme sensitivity to criticism over violation of standards they believed were appropriate. That is, they seemed as prone to guilt as to fear and anxiety.
Humans are unique among species in the capacity for guilt.
With phylogeny, the central nucleus of the amygdala, critical to the acquisition of conditioned fear reactions in animals, became progressively smaller, while the basolateral nucleus and its connections with the prefrontal cortex were enhanced. This fact, together with an appreciation that humans, but not primates, show signs of distress when they violate their moral standards, implies that guilt and shame may be as important as fear in everyday human functioning, as well as in psychopathology. The human moral sense, which generally keeps us from harming others of our species, is a unique product of evolution maintained through selection because it ensures our survival. This symptom appears more frequently in soldiers who have participated in an atrocity or feel guilty for surviving than in those who came close to death but did not participate in or witness an atrocity or lose a friend. Feelings of guilt and depression are as salient in PTSD as is fear.