entifically obsolete. Scientists have shifted their focus to take account of the fact that genetic and environmental influences work together in dynamic ways over the course of development. At any time, both are sources of human potential and growth as well as risk and dysfunction. Both genetically determined characteristics and those that are highly affected by experience are open to intervention. The most important questions now concern how environments influence the expression of genes and how genetic makeup, combined with children 's previous experiences, affects their ongoing interactions with their environments during the early years and beyond.

The range of human possibilities is exceedingly broad. At the moment of birth, each baby is neither a preformed individual whose destiny is set, nor a blank slate whose individuality can be shaped entirely by external forces. Children clearly differ in their genetic endowment from the time of conception. Some actively seek out experiences and some are more inhibited. Some cry frequently and others are better able to soothe themselves. Some are more predictable and easy to read while others are less easily understood. Biology, however, is modified by life experience. Depending on the caregiving they receive and the environments they encounter, shy children can become sociable, fearful children can become secure explorers of their surroundings, and highly exuberant children can develop considerable self-control. Each child's individual capacities are both limited and broadened by his or her genetic makeup and life circumstances. Both operate together in influencing the probability of any given outcome.

• Parents and other regular caregivers in children's lives are “active ingredients” of environmental influence during the early childhood period. Children grow and thrive in the context of close and dependable relationships that provide love and nurturance, security, responsive interaction, and encouragement for exploration. Without at least one such relationship, development is disrupted and the consequences can be severe and long-lasting. If provided or restored, however, a sensitive caregiving relationship can foster remarkable recovery.

  Young children establish and can benefit greatly from a variety of close relationships. Yet those adults who are most consistently available and committed to the child's well-being play a special role in promoting competence and adaptation that cannot be replaced by individuals who are present less consistently or whose emotional commitment is not unconditional. Young children who do not have a relationship with at least one emotionally invested, predictably available caregiver —even in the presence of adequate physical care and cognitive stimulation —display an array of developmental deficits that may endure over time. Some children develop intense emotional ties to parents and other caregivers who are unresponsive, rejecting, highly erratic, or frankly abusive. These relationships can also be a