The Bell Curve: Intelligence and Class Structure in American Life (52 page)

There is a further question to answer: Does a 15-point IQ difference between grandparents and their grandchildren mean that the grandchildren are 15 points
smarter?
Some experts do not believe that the rise is wholly, perhaps not even partly, a rise in intelligence but in the narrower skills involved in intelligence test taking per se;
¹¹⁵
others believe that at least some of rise is in genuine intelligence, perhaps owing to the improvements in public education (by the schools and the media), health care, and nutrition. There is evidence that the rise in scores may be due to a contraction in the distribution of test scores in the population at large, with most of the shrinkage in the bottom half of the distribution.
¹¹⁶
In large-scale studies of the Danish population, virtually all of the upward drift in intelligence test scores is accounted for by the rising performances of the lower half of the distribution.
¹¹⁷
The data we presented earlier on the rise in SAT scores by American blacks are consistent with this story. In general, egalitarian modern societies draw the lower tail of the distribution closer to the mean and thereby raise the average.
¹¹⁸
These findings accord with everyday experience as well. Whether one looks at the worlds of science, literature, politics, or the arts, one does not get the impression that the top of the IQ distribution is filled with more subtle, insightful, or powerful intellects than it was in our grandparents’ day.

Whatever we discover about the reasons for the upward drift in the mean of the distribution of test scores, two points are clear. First, a rapid rise in intelligence does not plausibly stretch far into either the past or the future. No one is suggesting, for example, that the IQ of the average American in 1776 was 30 or that it will be 150 a century from now.
¹¹⁹
The rising trend in test scores may already be leveling off in some countries.
¹²⁰
Second, at any point in time, it is one’s position in the distribution that has the most significant implications for social and economic life as we know it and also for the position of one’s children.
¹²¹

Flynn suggests that the intergenerational change in IQ has more to do with a shifting link between IQ scores and the underlying trait of intelligence than with a change in intelligence per se.
¹²²
Even so, the instability of test scores across generations should caution against taking the current ethnic differences as etched in stone. There are things we do not yet understand about the relation between IQ and intelligence, which may be relevant for comparisons not just across times but also across cultures and races.

R
ACIAL
A
NCESTRY.
Just over 100 families with adopted children of white, black, and mixed racial ancestry are being studied in an ongoing analysis of the effects of being raised by white adopting parents of middle or higher social status.
¹²³
This famous transracial adoption study by psychologists Sandra Scarr and Richard Weinberg is the most comprehensive attempt yet to separate the effects of genes and of family environment on the cognitive development of American blacks and whites. The first reports (when the children were about 7 years old) indicated that the black and interracial children had IQs of about 106, well above the national black average or the black average in Minnesota, where the samples were drawn. This result pointed to a considerable impact of the home setting on intelligence. However, a racial and adoptive ordering on IQ existed even in the first follow-up: The mean IQs were 117 for the biological children of white parents, 112 for the white adoptive children, 109 for the adopted children with one black and one white or Asian parent, and 97 for the adopted children with two black parents.
¹²⁴
Altogether, the data were important and interesting but not decisive regarding the source of the B/W difference. They could most easily have been squared with a theory that the B/W difference has both genetic and environmental elements in it, but, with considerable straining, could perhaps have been stretched to argue for no genetic influence at all.

A follow-up a decade later, with the children in adolescence, does not favor the no-genetics case.
¹²⁵
The new ordering of IQ means was 109 for the biological children of white parents, 106 for the white adoptive children, 99 for the adopted children with one black parent, and 89 for the adopted children with two black parents.
¹²⁶
The mean of 89 for adopted children with two black parents was slightly above the national black mean but not above the black mean for the North Central United States. The bottom line is that the gap between the adopted children with two black parents and the adopted children with two white parents was seventeen points, in line with the B/W difference customarily observed. Whatever the environmental impact may have been, it cannot have been large.

Scarr and Weinberg continue to argue that the results are consistent with some form of mixed gene and environmental source of the B/W difference, which seems to us the most plausible conclusion.
¹²⁷
But whatever the final consensus about the data may be, the debate over the Minnesota transracial adoption study has shifted from an argument about whether the environment explains all or just some of the B/W difference to an argument about whether it explains more than a trivial part of the difference.

Several smaller studies bearing on racial ancestry and IQ were well summarized almost two decades ago by Loehlin, Lindzey, and Spuhler.
¹²⁹
They found the balance of evidence tipped toward some sort of mixed gene-environment explanation of the B/W difference without saying how much of the difference is genetic and how much environmental.
¹³⁰
This also echoes the results of Snyderman and Rothman’s survey of contemporary specialists.

The German Story

One of the intriguing studies arguing against a large genetic component to IQ differences came about thanks to the Allied occupation of Germany following World War II, when about 4,000 illegitimate children of mixed racial origin were born to German women. A German researcher tracked down 264 children of black servicemen and constructed a comparison group of 83 illegitimate offspring of white occupation troops. The results showed no overall difference in average IQ.
¹²⁸
The actual IQs of the fathers were unknown, and therefore a variety of selection factors cannot be ruled out. The study is inconclusive but certainly consistent with the suggestion that the B/W difference is largely environmental.

But dissenting voices can be heard in the academic world. For example, a well-known book,
Not in Our Genes,
by geneticist Richard Lewontin and psychologists Steven Rose and Leon Kamin, criticizes anyone who even suggests that there may be a genetic component to the B/W difference or who reads the data as we do, as tipping toward a mixture of genetic and environmental influences.
¹³¹
How can they do this? Mostly by emphasizing those aspects of the data that suggest environmental influences, such as the correlations between the adopting parents’ IQs or educational levels and the IQs of their black adopted children in the Minnesota study from the first follow-up (the book was published before the second follow-up). But they have nothing to say about the aspects that are consistent with genetic influence, such as the even larger correlations between the educational level of either the biological mothers or fathers and the IQs of their adopted-away black children.
¹³²
Although Lewontin, Rose, and Kamin do not say it in so many words, their argument makes sense if it is directed at the claim that the B/W difference is
entirely
genetic. It does little to elucidate the ongoing scientific inquiry into whether the difference has a genetic component.

We have touched on only the highlights of the arguments on both sides of the genetic issue. One main topic we have left untouched involves the malleability of intelligence, with two extremes of thought: that intelligence is remarkably unmalleable, which undercuts environmental arguments in general and cultural ones in particular, and that intelligence is highly malleable, supporting those same arguments. Because the malleability of intelligence is so critical a policy issue, it deserves a chapter of its own (Chapter 17).

If the reader is now convinced that either the genetic or environmental explanation has won out to the exclusion of the other, we have not done a sufficiently good job of presenting one side or the other. It seems highly likely to us that both genes and the environment have something to do with racial differences. What might the mix be? We are resolutely agnostic on that issue; as far as we can determine, the evidence does not yet justify an estimate.

We are not so naive to think that making such statements will do much good. People find it next to impossible to treat ethnic differences
with detachment. That there are understandable reasons for this only increases the need for thinking clearly and with precision about what is and is not important. In particular, we have found that the genetic aspect of ethnic differences has assumed an overwhelming importance. One symptom of this is that while this book was in preparation and regardless of how we described it to anyone who asked, it was assumed that the book’s real subject had to be not only ethnic differences in cognitive ability but the genetic source of those differences. It is as if people assumed that we are faced with two alternatives: either (1) the cognitive difference between blacks and whites is genetic, which entails unspoken but dreadful consequences, or (2) the cognitive difference between blacks and whites is environmental, fuzzily equated with some sort of cultural bias in IQ tests, and the difference is therefore temporary and unimportant.

But those are not the only alternatives. They are not even alternatives at all. The major ethnic differences in the United States are not the result of biased tests in the ordinary sense of the term. They may well include some (as yet unknown) genetic component, but nothing suggests that they are entirely genetic. And, most important, it matters little whether the genes are involved at all.

We have already explained why the bias argument does not readily explain the ethnic differences and also why we say that genes may be part of the story. To show why we believe that it makes next to no difference whether genes are part of the reason for the observed differences, a thought experiment may help. Imagine that tomorrow it is discovered that the B/W difference in measured intelligence is entirely genetic in origin. The worst case has come to pass. What difference would this news make in the way that you approach the question of ethnic differences in intelligence? Not someone else but
you.
What has changed for the worse in knowing that the difference is genetic? Here are some hypothetical possibilities.

If it were known that the B/W difference is genetic, would I treat individual blacks differently from the way I would treat them if the differences were environmental?
Probably, human nature being what it is, some people would interpret the news as a license for treating all whites as intellectually superior to all blacks. But we hope that putting this possibility down in words makes it obvious how illogical—besides utterly unfounded—such reactions would be. Many blacks would continue to be smarter than many whites. Ethnic differences would continue to be differences
in means and distributions; they would continue to be useless, for all practical purposes, when assessing individuals. If you were an employer looking for intellectual talent, an IQ of 120 is an IQ of 120, whether the face is black or white, let alone whether the mean difference in ethnic groups were genetic or environmental. If you were a teacher looking at a classroom of black and white faces, you would have exactly the same information you have now about the probabilities that they would do well or poorly.

If you were a government official in charge of educational expenditures and programs, you would continue to try to improve the education of inner-city blacks, partly out of a belief that everyone should be educated to the limits of his ability, partly out of fairness to the individuals of every degree of ability within that population—but also, let it be emphasized, out of a hardheaded calculation that the net social and economic return of a dollar spent on the elementary and secondary education of a student does not depend on the heritability of a group difference in IQ. More generally:
We cannot think of a legitimate argument why any encounter between individual whites and blacks need be affected by the knowledge that an aggregate ethnic difference in measured intelligence is genetic instead of environmental.

It is true that employers might under some circumstances find it economically advantageous to use ethnicity as a crude but inexpensive screen to cut down hiring costs (assuming it were not illegal to do so). But this incentive exists already, by virtue of the existence of a difference in observed intelligence regardless of whether the difference is genetic. The
existence
of the difference has many intersections with policy issues. The
source
of the difference has none that we can think of, at least in the short term. Whether it does or not in the long term, we discuss below.

If the differences are genetic, aren’t they harder to change than if they are environmental?
Another common reaction, this one relies on false assumptions about intelligence. The underlying error is to assume that an environmentally caused deficit is somehow less hard-wired, that it has less impact on “real” capabilities, than does a genetically caused deficit. We have made this point before, but it bears repeating. Some kinds of environmentally induced conditions can be changed (lack of familiarity with television shows for a person without a television set will probably be reduced by purchasing him a television set), but there is no reason to think that intelligence is one of them. To preview a conclusion
we will document at length in Chapter 17, an individual’s realized intelligence, no matter whether realized through genes or the environment, is not very malleable.