ABSTRACT
The identification of sources of variation in intelligence test scores has been the subject of many studies and theoretical discussions. These efforts have received a new impetus as a consequence of the revival of the venerable nature-nurture controversy. In this investigation, the relationship between IQ at age four and a variety of factors related to prenatal course, delivery, physical and mental development, and social environment was examined. The correlations between physical growth variables and IQ were consistently greater when examined within each sex than when the sexes were combined. Within the race, sex, and socioeconomic subgroups, IQs were significantly higher among children who had higher scores on the Bayley Scales of Mental and Motor Development at eight months. Maternal characteristics had smaller and more inconsistent relationships with IQ than did family characteristics. IQs were significantly lower among children whose mothers had lighter placentas, vertex deliveries not assisted by forceps, and a shorter second stage of labor.
