Working with James Robertson, Bowlby observed that children experienced separation anxiety, an intense distress, when separated from their mothers. The child's distress and anxiety did not disappear even when they were being fed by another carer. Bowlby suggested that attachment could be understood as evolving from the caregiver providing safety and security for the infant. According to Bowlby, infants have a universal need to seek close proximity with their caregiver when under stress or feeling threatened.