The Environment and Intelligence

What kinds of experiences hinder intellectual development and what kinds of environmental “nutrients” promote it?

Here are some of the factors associated with reduced mental ability:

• Poor prenatal care. If a pregnant woman is malnourished, contracts infections, smokes, is exposed to secondhand smoke, or drinks alcohol regularly, her child is at risk of having learning disabilities and a lower IQ.
• Malnutrition. The average IQ gap between severely malnourished and well-nourished children can be as high as 20 points (Stoch&Smythe, 1963; Winick, Meyer, & Harris, 1975).
• Exposure to toxins. Lead, especially, can damage the brain and nervous system, even at fairly low levels, producing attention problems, lower IQ scores, and poorer school achievement (Hornung, Lanphear, & Dietrich, 2009; Needleman et al., 1996).
  Many children in the United States are exposed to dangerous levels of lead from dust, contaminated soil, lead paint, and old lead pipes, and the concentration of lead in black children’s blood is 50 percent higher than in white children’s (Lanphear et al., 2002).
• Stressful family experiences. Factors that predict reduced intellectual competence include, among others, having a father who does not live with the family, a mother with a history of mental illness, parents with limited work skills, and a history of stressful events, such as domestic violence, early in life (Sameroff et al., 1987). On average, each risk factor reduces a child’s IQ score by 4 points. And when children live in severely disadvantaged neighborhoods, their IQs decline over time, even after they have moved to better areas; the drop is comparable to that seen when a child misses a year of school (Sampson, 2008).

In contrast, a healthy and stimulating environment can raise IQ scores, as several intervention studies with at-risk children have shown. In one longitudinal study called the Abecedarian Project, inner-city children who got lots of mental enrichment at home and in child care or school, starting in infancy, showed signficant IQ gains and had much better school achievement than did children in a control group (Campbell & Ramey, 1995).

In another important study, of abandoned children living in Romanian orphanages, researchers randomly assigned some children to remain in the orphanages and others to move to good foster homes.

By age 4, the fostered children scored dramatically higher on IQ tests that did those left behind. Children who moved before age 2 showed the largest gains, almost 15 points on average. A comparison group of children reared in their biological homes did even better, with average test scores 10 to 20 points higher than those of the foster children (Nelson et al., 2007).
(Since this study was done, Romania has stopped institutionalizing abandoned children younger than 2 years unless the infants are seriously disabled.)

Perhaps the best evidence for the importance of environmental influences on intelligence is the fact that around the world, IQ scores have been climbing steadily for at least three generations (Flynn, 1987, 1999).

The fastest increase in a group’s average IQ scores ever reported has occurred in Kenya, where IQ scores of rural 6- to 8-year-old children jumped about 11 points between 1984 and 1998 (Daley et al., 2003). Genes cannot possibly have changed enough to account for these findings, and most scientists attribute the increases to improvements in education, the growth in jobs requiring abstract thought, and better health.

We see, then, that although heredity may provide the range of a child’s intellectual potential—a Homer Simpson can never become an Einstein—many other factors affect where in that range the child will fall.

from: Invitation to Psychology by Carole Wade, Carol Tavris