Final answer:
At about 1 year of age, babies typically experience separation anxiety, which is a developmental behavior stemming from their understanding of object permanence, leading to distress when separated from caregivers or faced with strangers.
Step-by-step explanation:
Most babies at about 1 year of age experience separation anxiety when their parent is out of sight or when they are with a nonparent caregiver. This developmental behavior is closely linked to the concept of object permanence, which babies typically develop between 5 and 8 months of age. Object permanence is the understanding that objects continue to exist even when they cannot be observed. Once babies develop this understanding, they also start to show anxiety when separated from caregivers because they are aware that their caregivers continue to exist even though they are not currently visible.
Separation anxiety may manifest as crying, clinging, or reaching out for familiar caregivers. This is reflective of an attachment and understanding of their environment wherein they might exhibit fear or apprehension towards strangers or in unfamiliar settings. Jean Piaget, a Swiss psychologist known for his work on child development, theorized that infants are unable to assimilate the stranger into an existing schema, which results in stranger anxiety.