Nature versus nurture on IQ

Meta studies show both important, environment can lower IQ.

After the Bell Curve - New York Times

“It doesn’t really matter whether the heritability of I.Q. is this particular figure or that one,” says Sir Michael Rutter of the University of London. “Changing the environment can still make an enormous difference.” If heredity defines the limits of intelligence, the research shows, experience largely determines whether those limits will be reached.

The average I.Q. of children from well-to-do parents who were placed with families from the same social stratum was 119.6. But when such infants were adopted by poor families, their average I.Q. was 107.5 — 12 points lower. The same holds true for children born into impoverished families: youngsters adopted by parents of similarly modest means had average I.Q.’s of 92.4, while the I.Q.’s of those placed with well-off parents averaged 103.6. These studies confirm that environment matters — the only, and crucial, difference between these children is the lives they have led.

A later study of French youngsters adopted between the ages of 4 and 6 shows the continuing interplay of nature and nurture. Those children had little going for them. Their I.Q.’s averaged 77, putting them near retardation. Most were abused or neglected as infants, then shunted from one foster home or institution to the next.

Nine years later, they retook the I.Q. tests, and contrary to the conventional belief that I.Q. is essentially stable, all of them did better. The amount they improved was directly related to the adopting family’s status. Children adopted by farmers and laborers had average I.Q. scores of 85.5; those placed with middle-class families had average scores of 92. The average I.Q. scores of youngsters placed in well-to-do homes climbed more than 20 points, to 98 — a jump from borderline retardation to a whisker below average. That is a huge difference — a person with an I.Q. of 77 couldn’t explain the rules of baseball, while an individual with a 98 I.Q. could actually manage a baseball team — and it can only be explained by pointing to variations in family circumstances.

In recent years, the case for investing in early-childhood education has become stronger and stronger. The federal Early Head Start program for infants and toddlers is effective when it is well implemented — in part because it succeeds in getting parents more involved with their children. Recent research also shows that one year of high-quality state prekindergarten can give children as much as a seven-month advantage in vocabulary; this, in turn, is a good predictor of how well they will read when they are in primary school. As you would expect, poor children benefit the most, especially when they are in classes with middle-class youngsters.

Tags: IQ, heredity, environment, genetics