Introduction

Societies have long been concerned about the problem of mental retardation. In the United States, this concern led to a serious government-funded effort to identify preventable causes of mental subnormality in the Collaborative Perinatal Project. Only in recent history has etiology been a major focus of investigations or theories of mental retardation. Attitudes toward the mentally subnormal have changed from avoidance to acceptance, from institutions for isolation to schools for teaching, and finally, from considering the affliction inexplicable and unchangeable to changeable, at least trainable, and perhaps even preventable. Historically, intelligence has been widely recognized as a dimension with a presumed continuity between high and low, or more and less, some mystical pecking order in which we all place ourselves—smarter than some, duller than others.