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The way to get smart
By Jim Holt |
April 12, 2009, Sunday
|
Print Edition
Print Edition
SUCCESS in life depends on intelligence, which is measured by IQ tests. Intelligence is mostly a matter of heredity, as we know from studies of identical twins reared apart.
Social programs that seek to raise IQ are bound to be futile. Cognitive inequalities, being written in the genes, are here to stay, and so are the social inequalities that arise from them.
What I have just summarized, with only a hint of caricature, is the hereditarian view of intelligence. This is the view endorsed, for instance, by Richard J. Herrnstein and Charles Murray in "The Bell Curve" (1994), and by Arthur R. Jensen in "The g Factor" (1998). Although hereditarianism has been widely denounced as racism wrapped in pseudoscience, these books drew on a large body of research and were carefully reasoned. Critics often found it easier to impugn the authors' motives than to refute their conclusions.
Richard E. Nisbett, a prominent cognitive psychologist who teaches at the University of Michigan, doesn't shirk the hard work. In "Intelligence and How to Get It," he offers a meticulous and eye-opening critique of hereditarianism.
True to its self-help like title, the book does contain a few tips on how to boost your child's IQ - like exercising during pregnancy. But its real value lies in Nisbett's forceful marshaling of the evidence, much of it recent, favoring what he calls "the new environmentalism," which stresses the importance of non-hereditary factors in determining IQ.
So fascinating is this evidence - drawn from neuroscience and genetics, as well as from studies of educational interventions and parenting styles - that the author's slightly academic prose style can be forgiven.
Intellectually, the IQ debate is a treacherous one. Concepts like heritability are so tricky that even experts stumble into fallacy. Moreover, the relevant data mostly come from "natural experiments," which can harbor subtle biases. When the evidence is ambiguous, it is all the easier for ideology to influence one's scientific judgment. Liberals hope that social policy can redress life's unfairness. Conservatives hold that natural inequality must be accepted as inevitable. When each side wants to believe certain scientific conclusions for extra-scientific reasons, skepticism is the better part of rigor.
Nisbett himself proceeds with due caution. He grants that IQ tests - which gauge both "fluid" intelligence (abstract reasoning skills) and "crystallized" intelligence (knowledge) - measure something real. They also measure something important: even within the same family, higher-IQ children go on to make more money than their less-bright siblings.
However, Nisbett bridles at the hereditarian claim that IQ is 75 to 85 percent heritable; the real figure, he thinks, is less than 50 percent. Estimates come from comparing the IQ of blood relatives - identical twins, fraternal twins, siblings - growing up in different adoptive families. But there is a snare here. As Nisbett observes, "adoptive families, like Tolstoy's happy families, are all alike." Not only are they more affluent than average, they also tend to give children lots of cognitive stimulation. Thus data from them yield erroneously high estimates of IQ heritability.
This underscores an important point: there is no fixed value for heritability. The notion makes sense only relative to a population. Heritability of IQ is higher for upper-class families than for lower-class families, because lower-class families provide a wider range of cognitive environments, from terrible to pretty good.
Even if genes play some role in determining IQ differences within a population, which Nisbett grants, that implies nothing about average differences between populations. The classic example is corn seed planted on two plots of land, one with rich soil and the other with poor soil. Within each plot, differences in the height of the corn plants are completely genetic. Yet the average difference between the two plots is entirely environmental.
Could the same logic explain the disparity in average IQ between Americans of European and of African descent? Nisbett thinks so. The racial IQ gap, he argues, is "purely environmental." For one thing, it's been shrinking: over the last 30 years, the measured IQ difference between black and white 12-year-olds has dropped from 15 points to 9.5 points.
If IQ differences are largely environmental, what might help eliminate group disparities? The most dramatic results come from adoption. When poor children are adopted by upper-middle-class families, there's an IQ gain of 12 to 16 points. Upper-class parents talk to their children more than working-class parents do.
And there are subtler differences. In poorer black families, for example, children are rarely asked "known-answer questions" - that is, questions where the parents already know the right answer. ("What color is the elephant, Billy?")
Consequently, as Nisbett observes, the children are nonplussed by such questions at school. ("If the teacher doesn't know this, then I sure don't.") The challenge is to find educational programs that are as effective as adoption in raising IQ.
Social programs that seek to raise IQ are bound to be futile. Cognitive inequalities, being written in the genes, are here to stay, and so are the social inequalities that arise from them.
What I have just summarized, with only a hint of caricature, is the hereditarian view of intelligence. This is the view endorsed, for instance, by Richard J. Herrnstein and Charles Murray in "The Bell Curve" (1994), and by Arthur R. Jensen in "The g Factor" (1998). Although hereditarianism has been widely denounced as racism wrapped in pseudoscience, these books drew on a large body of research and were carefully reasoned. Critics often found it easier to impugn the authors' motives than to refute their conclusions.
Richard E. Nisbett, a prominent cognitive psychologist who teaches at the University of Michigan, doesn't shirk the hard work. In "Intelligence and How to Get It," he offers a meticulous and eye-opening critique of hereditarianism.
True to its self-help like title, the book does contain a few tips on how to boost your child's IQ - like exercising during pregnancy. But its real value lies in Nisbett's forceful marshaling of the evidence, much of it recent, favoring what he calls "the new environmentalism," which stresses the importance of non-hereditary factors in determining IQ.
So fascinating is this evidence - drawn from neuroscience and genetics, as well as from studies of educational interventions and parenting styles - that the author's slightly academic prose style can be forgiven.
Intellectually, the IQ debate is a treacherous one. Concepts like heritability are so tricky that even experts stumble into fallacy. Moreover, the relevant data mostly come from "natural experiments," which can harbor subtle biases. When the evidence is ambiguous, it is all the easier for ideology to influence one's scientific judgment. Liberals hope that social policy can redress life's unfairness. Conservatives hold that natural inequality must be accepted as inevitable. When each side wants to believe certain scientific conclusions for extra-scientific reasons, skepticism is the better part of rigor.
Nisbett himself proceeds with due caution. He grants that IQ tests - which gauge both "fluid" intelligence (abstract reasoning skills) and "crystallized" intelligence (knowledge) - measure something real. They also measure something important: even within the same family, higher-IQ children go on to make more money than their less-bright siblings.
However, Nisbett bridles at the hereditarian claim that IQ is 75 to 85 percent heritable; the real figure, he thinks, is less than 50 percent. Estimates come from comparing the IQ of blood relatives - identical twins, fraternal twins, siblings - growing up in different adoptive families. But there is a snare here. As Nisbett observes, "adoptive families, like Tolstoy's happy families, are all alike." Not only are they more affluent than average, they also tend to give children lots of cognitive stimulation. Thus data from them yield erroneously high estimates of IQ heritability.
This underscores an important point: there is no fixed value for heritability. The notion makes sense only relative to a population. Heritability of IQ is higher for upper-class families than for lower-class families, because lower-class families provide a wider range of cognitive environments, from terrible to pretty good.
Even if genes play some role in determining IQ differences within a population, which Nisbett grants, that implies nothing about average differences between populations. The classic example is corn seed planted on two plots of land, one with rich soil and the other with poor soil. Within each plot, differences in the height of the corn plants are completely genetic. Yet the average difference between the two plots is entirely environmental.
Could the same logic explain the disparity in average IQ between Americans of European and of African descent? Nisbett thinks so. The racial IQ gap, he argues, is "purely environmental." For one thing, it's been shrinking: over the last 30 years, the measured IQ difference between black and white 12-year-olds has dropped from 15 points to 9.5 points.
If IQ differences are largely environmental, what might help eliminate group disparities? The most dramatic results come from adoption. When poor children are adopted by upper-middle-class families, there's an IQ gain of 12 to 16 points. Upper-class parents talk to their children more than working-class parents do.
And there are subtler differences. In poorer black families, for example, children are rarely asked "known-answer questions" - that is, questions where the parents already know the right answer. ("What color is the elephant, Billy?")
Consequently, as Nisbett observes, the children are nonplussed by such questions at school. ("If the teacher doesn't know this, then I sure don't.") The challenge is to find educational programs that are as effective as adoption in raising IQ.
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