throughout childhood, and found they scored substantially lower. Fetal alcohol syndrome, due to prenatal exposure to excessive amounts of alcohol, may lead to mental retardation. Even smaller amounts of alcohol may harm: mothers who reported drinking 1.5 oz of alcohol daily during pregnancy had children who scored an average of 5 points lower on IQ tests by age four (Neisser et al., 1996). Perinatal factors such as complications during delivery may also influence intelligence. The correlation between very low birth weight (less than 2,500 gm.) and later intelligence is fairly large (Breslau et al., 1994, Baumeister & Bacharach, 1996, as cited in Mackintosh, 1998).Social and cultural aspects of environment may influence intelligence: Werner and Smith (1992) found that temperament affected developmental outcomes for children, beginning at birth. Infants who smiled often and were affectionate attracted more care and emotional support from their parents and others. Schools promote the development of intellectual skills such as systematic problem-solving, abstract thinking, and categorization; children who attend regularly may be expected to benefit more than those who attend sporadically. Plomin (1991) suggests other factors such as parental affection, birth order, gender differences, experiences outside the family, accidents, and illnesses may account for differences in IQ between siblings. In their study of adoptive and biologically related families with children between 16 and 22 years of age, Scarr and Weinberg (1983) found environment more powerful in influencing IQ level in the young child than the young adult. They argue that "by providing better schooling, nutrition, health care, psychological services and the like, we can raise the level of intellectual development." In the short run, a number of interventions have been shown to raise test scores. The Venezuelan Intelligence Project involved exposing hundreds of seventh-grade chil...
