Seven percent of newborns in the United States weigh in at less than five and one half pounds. These "low birth weight" babies face challenges that others will never knowchallenges that begin with a greater risk of infant mortality and extend well into adulthood in the form of health and developmental problems. Because low birth weight is often accompanied by social risk factors such as minority racial status, low education, young maternal age, and low income, the question of causes and consequencesof precisely how biological and social factors figure into this equationbecomes especially...