Children develop in an environment of relationships. They also develop in an environment of chemicals. Many of these chemicals, such as the nutrients in a well-balanced diet, are essential for good health. Others, such as lead in drinking water, are poisonous and can cause illness or death. Some chemicals that disrupt brain architecture are produced in our own bodies as a result of severe and prolonged stress. Others enter through contaminants in the air we breathe, the water we drink, and the food we eat. Brain development begins well before birth and continues through the early adult years. The biology of that process is influenced by the genes that are passed on from the parents to the child; by the environment of the mother's womb; and by the world the child experiences during infancy and childhood, which can either weaken or strengthen the initial blueprint. Thus, brains are built over time, and the circumstances in which they are built are every bit as important as the initial architectural framework handed down by genetics.