The Evolved Nurturing Initiative
Seeking the nearly constant physical presence of a caregiver is an instinct with which babies are born and it only diminishes partially and gradually throughout childhood. When cultural messages urge parents to violate this natural need, with ideologies that emphasize "toughening-up," for example, it causes developmental problems. Physiologically, the responsive presence of a loving parent helps the child build properly functioning physiology (e.g., breathing, heart rate, endocrine system development) and learn to self-regulate, little by little. The brain develops rapidly during the first 5 years of life so any extensive or intense distress is harmful and undermines growth.
For example, cortisol is toxic at high levels, which can occur with high stress, dissolving synapses (brain cell connections) and redirecting energy toward self-preservation instead of growth. The stress response system is one of many systems that is setting its parameters and thresholds in early life. When a child is made deeply distressed regularly, as is required by many popular parenting methods, it will set this and other systems to be highly sensitive, leading to a disposition to be easily distressed (or emotionally detached) for life.