New book sorts nature and nurture from nutty science, says Jim Holt

Intelligence is measured by IQ tests. Intelligence is mostly amatter of heredity, as we know from studies of identical twins rearedapart.

Since IQ differences between individuals are mainlygenetic, the same must be true for IQ differences between groups. Sothe IQ ranking of racial or ethnic groups — Ashkenazi Jews on top,followed by East Asians, whites in general, and then blacks — is fixedby nature, not culture.

This summary, with only a hint of caricature, is thehereditarian view of intelligence — widely denounced as racism wrappedin pseudoscience.

But critics of this view have often found it easier to impugn the authors’ motives than to refute their conclusions.

Richard E Nisbett, a prominent cognitive psychologist whoteaches at the University of Michigan in the US, doesn’t shirk the hardwork. He offers a meticulous and eye-opening critique ofhereditarianism in Intelligence and How to Get It — Why schools andculture count , published by WW Norton & Company.

The book contains a few tips on how to boost yourchild’s IQ, b ut its real value lies in Nisbett’s forceful marshallingof evidence — drawn from neuroscience and genetics, as well as fromstudies of educational interventions and parenting styles — whichstresses the importance of nonhereditary factors in determining IQ.

He grants that IQ tests — which gauge both “fluid”intelligence (abstract reasoning skills) and “crystallised”intelligence (knowledge) — measure something real.

However, Nisbett bridles at the hereditarian claim thatIQ is 75% to 85% heritable; the real figure, he thinks, is less than50%.

Estimates come from comparing the IQs of blood relatives— identical twins, fraternal twins, siblings — growing up in differentadoptive families. But there is a snare here. As Nisbett observes,“adoptive families. .. are all alike.” Not only are they more affluentthan average, they also tend to give children lots of cognitivestimulation.

This underscores an important point: there is no fixed value for heritability.

The notion makes sense only relative to a population.

Even if genes play some role in determining IQdifferences within a population, which Nisbett grants, that impliesnothing about average differences between populations.

The classic example is maize 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 plants are completely genetic.

Yet the average difference between the two plots is entirely environmental.

Could the same logic explain the disparity in average IQbetween Americans of European and of African descent? Nisbett thinksso. The racial IQ gap, he argues, is “purely environmental”.

For one thing, it’s been shrinking: over the past 30years, the measured IQ difference between black and white 12-year-oldshas dropped from 15 points to 9.5 points.

Among his more direct evidence, Nisbett cites impressivestudies in population genetics. African-Americans have on average about20% European genes, largely as a legacy of slavery. But the proportionof European genes ranges widely among individuals, from near zero tomore than 80%.

If the racial gap is mostly genetic, then blacks withmore European genes ought to have higher IQs on average. In fact, theydo not.

Nisbett is similarly sceptical that genetics couldaccount for the intellectual prowess of Ashkenazi Jews, whose averageIQ measures somewhere between 110 and 115.

As for the alleged IQ superiority of East Asians over USwhites, that turns out to be an artifact of sloppy comparisons; when IQtests are properly normed, Americans actually score slightly higherthan East Asians.

If IQ differences are indeed 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, they show 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 in the US, for example, childrenare rarely asked “known-answer questions” — that is, questions wherethe parents already know the right answer. (‘What colour is theelephant, Billy?’) Consequently, as Nisbett observes, the children arenonplussed by such questions at school. (‘If the teacher doesn’t knowthis, then I sure don’t.’)

The challenge is to find educational programmes that are as effective as adoption in raising IQ.

So far, Nisbett writes, almost all school-age interventions have yielded disappointing results.

But some intensive early-childhood interventions have produced enduring IQ gains.

By the author’s reckoning, it would cost less than100-billion a year to extend such programmes to the neediest third ofUS preschoolers.

The gain would be incalculable. (…)

Source: The Times