Introduction

In a child's world, the family is of paramount importance. Throughout human evolutionary history, parents and close relatives provided calories, protection, and information necessary for survival, growth, health, social success, and eventual reproduction. The human brain is therefore likely to have evolved special sensitivity to interactions among family caretakers, particularly during infancy and early childhood. This special sensitivity for negotiating the psychosocial dynamic of the family environment has important consequences for child development.

Changing, unpredictable environments require adjustment of priorities. Growth, immunity, digestion, and sex are irrelevant when being chased by a predator (Sapolsky, 1994), or when coping with a traumatic social event. Emergencies, large and small, good and bad, perceived by the brain stimulate a variety of neuroendocrine systems. Hundreds of different endogenous chemicals, hormones, neurotransmitters, cytokines, and so forth, are released from secretory glands and cells in response to information received and processed by the central nervous system (CNS). The movement of these chemicals in plasma and other intercellular fluids communicates information among the different cells and tissues, helping the body to respond appropriately to varying environmental demands.

Physiological stress responses affect the allocation of energetic and other somatic resources to different bodily functions via a complex assortment of neuroendocrine mechanisms.