The Bell Curve: Intelligence and Class Structure in American Life
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The United States is still very far from this state of affairs at the extremes. If one thinks of babies growing up in slums with crack-addicted mothers, at one extreme, compared to children growing up in affluent, culturally rich homes with parents dedicated to squeezing every last IQ point out of them, then even a heritability of .6 leaves room for considerable change if the changes in environment are commensurably large. We take up the evidence on that issue in detail in Chapter 17, when we consider the many educational and social interventions that have attempted to raise IQ. But those are, by definition, the extremes, the two tails of the distribution of environments. Moving a child from an environment that is the very worst to the very best may make a big difference. In reality, what most interventions accomplish is to move children from awful environments to ones that are merely below average, and such changes are limited in their potential consequences when heritability so constrains the limits of environmental effects.41
So while we can look forward to a future in which science discovers how to foster intelligence environmentally and how to use the science humanely, inherited cognitive ability is now extremely important. In this sense, luck continues to matter in life’s outcomes, but now it is more a matter of the IQ handed out in life’s lottery than anything else about circumstances. High cognitive ability as of the 1990s means, more than even before, that the chances of success in life are good and getting better all the time, and these are decreasingly affected by , the social environment, which by extension indicates that they must be increasingly affected by genes. Holding these thoughts in mind, now consider the phenomenon known as assortative mating.
Love, Marriage, and IQ
The old saw notwithstanding, opposites do not really attract when it comes to love and marriage. Likes attract. In one of the classic papers, originally published in 1943, two sociologists studied 1,000 engaged couples in Chicago, expecting to find at least some traits in which opposites did indeed attract. But out of fifty-one social characteristics studied, the sign of the correlation was positive for every single one. For all but six of the fifty-one traits, the correlations were statistically significant.42 Modest but consistently positive correlations have been found for a wide variety of physical traits as well, ranging from stature (the correlations from many studies average about +.25) to eye color (also averaging about +.25, even within national populations).43
Of the many correlations involving husbands and wives, one of the highest is for IQ. In most of the major studies, the correlation of husband and wife IQ has been in the region of .4, though estimates as low as .2 and as high as .6 have been observed. Jensen’s review of the literature in the late 1970s found that the average correlation of forty-three spouse correlations for various tests of cognitive ability was +.45, almost as high as the typical correlation of IQs among siblings.44
If the Propensity to Mate by Cognitive Ability Has Remained the Same:
When the propensity to mate by cognitive ability is combined with the educational and occupational stratification we have described, the impact on the next generation will be larger than on the previous one, even if the underlying propensity to mate by cognitive ability remains the same.
Consider 100 Harvard/Radcliffe marriages from the class of 1930 versus another 100 from the class of 1964. We stipulate that the propensity to marry people of similar intelligence has not changed in the intervening thirty-four years. Nonetheless, the ones who marry in 1964 will produce a set of children with considerably higher mean IQ than the ones who married in 1930, because the level of intelligence at Harvard and Radcliffe had risen so dramatically.
How much difference can it make? If the average Harvard man in the class of 1930 married the average Radcliffe woman in the same graduating class—as far as we can tell, both would have had IQs of about 117—then the expected mean IQ of their children, after taking regression to the mean into account, will be about 114, or at the 82d percentile.45 But average Harvard and Radcliffe newlyweds in the class of 1964 were likely to have children with a mean IQ of about 124, at the 95th percentile. In terms of distributions rather than averages, about a third of the children of the Harvard newlyweds of 1930 could be expected to have IQs of less than 110—not even college material by some definitions.46 In contrast, only 6 percent of the children of the Harvard newlyweds of 1965 could be expected to fall below this cutoff. Meanwhile, only about 22 percent of the children of the 1930 newlyweds could be expected to match or exceed the average of the children of the 1965 newlyweds. In such numbers lurk large social effects.
If the Propensity to Mate by Cognitive Ability Has Increased:
We have been assuming that the propensity to mate by IQ has remained the same. In reality, it has almost certainly increased and will continue to increase.
We hedge with “almost” because no quantitative studies tell whether assortative mating by intelligence has been increasing recently. But we do know from sociologist Robert Mare of the University of Wisconsin that assortative mating by educational level increased over the period from 1940 to 1987—an increase in “homogamy,” in the sociologists’ language. The increase in homogamy was most pronounced among college-educated persons. Specifically, the odds of a college graduate’s marrying someone who was not a college graduate declined from 44 percent in 1940 to 35 percent in Mare’s most recent data (for 1985 to 1987). The proportion hit a low of 33 percent in the 1980 data.47 Because educational attainment and IQ are so closely linked and became more closely linked in the postwar period, Mare’s results suggest a substantial increase in assortative mating by IQ, with the greatest change occurring at the upper levels of IQ.
Mare identifies some of the reasons for increased homogamy in the trends involving educational attainment, age at leaving school, and age at marriage. But there are a variety of other potential explanations (some of which he notes) that involve cognitive ability specifically. For example, a smart wife in the 1990s has a much greater dollar payoff for a man than she did fifty years ago.48 The feminist movement has also increased the likelihood of marrying by cognitive ability.
First, the feminist revolution in practice (which began in the 1950s, antedating the revolution in rhetoric) drastically increased the odds that bright young women will be thrown in contact with bright young men during the years when people choose spouses. This is most obvious in college, where the proportion of women continuing to college surged from about half the proportion of men in 1950 to equality in 1975.49 It was not just the numbers, however. All of the elite men’s colleges became coeducational, as did many of elite women’s colleges. Strict parietal rules gave way to coeducational dorms. Intelligence has always been an important factor for sorting among prospective mates, but comparison shopping at single-sex colleges like Vassar or Yale was a struggle; the feminist revolution in the universities led to an explosion of information, as it were, that made it easier for the brightest to pair up.
The same phenomenon extended to the workplace. Large proportions of the cognitive elite delay marriage until the later twenties or even thirties. Only a few decades ago, delay tended to dilute the chances of assortative mating by IQ. In a world where the brightest women were usually not in the work force or were in a few restricted occupations, the pool from which a man in his late twenties found a bride were moderated primarily by socioeconomic status; he found his mate among the women he encountered in his neighborhood, church, social organizations, and other settings that were matched mostly by socioeconomic status. But today background status is less important than intelligence. The young man newly graduated from his elite law school joins his elite New York firm, thereupon encountering young women, just as highly selected for cognitive ability as he was, in the adjacent offices at his own firm, at business lunches, across the table in negotiations, on a daily basis. The opportunities for propinquity to work its magic were increased in the workplace too, and will continue to increase in the years to come.
The second effect of feminism is less ponderable but ma
y be important anyway. Not so many years ago, the cliché was true: brains were not considered sexy in a woman, and many men undervalued brains as an asset in a prospective spouse or even felt threatened by smart women. Such attitudes may linger in some men, but feminism has surely weakened them and, to some degree, freed relationships among men and women so that a woman’s potential for occupational success can take as dominant a place in the man’s marriage calculus as it has traditionally taken in the woman’s.50 We speculate that the effect has been most liberating among the brightest. If we are right, then the trends in educational homogamy that Mare has demonstrated are an understated reflection of what is really going on. Intermarriage among people in the top few percentiles of intelligence may be increasing far more rapidly than suspected.
THE LIMITS OF CHURNING
American society has historically been full of churning, as new groups came to this country, worked their way up, and joined the ranks of the rich and powerful. Meanwhile, some of the children of the rich and powerful, or their grandchildren, were descending the ladder. This process has made for a vibrant, self-renewing society. In depressing contrast, we have been envisioning a society that becomes increasingly quiescent at the top, as a cognitive elite moves toward the upper income brackets and runs most of the institutions of society, taking on some of the characteristics of a caste.
Is the situation really so extreme? To some extent, not yet. For example, national surveys still indicate that fewer than 60 percent in the top quartile of intelligence actually complete a bachelor’s degree.51 This would seem to leave a lot of room for churning. But when we focus instead on the students in the top few centiles of cognitive ability (from which the nation’s elite colleges pick almost exclusively), an extremely high proportion are already being swept into the comfortable precincts of the cognitive elite.52 In the NLSY, for example, 81 percent of those in the top 5 percent of IQ had obtained at least a bachelor’s degree by 1990, when the youngest members of the sample were 25 years old.53
When we examine the remaining 19 percent who had not obtained college degrees, the efficiency of American society in pushing the most talented to the top looks even more impressive. For example, only a small portion of that 19 percent were smart students who had been raised in a low-income family and did not get to college for lack of opportunity. Only 6 percent of persons in the top five IQ centiles did not have a college degree and came from families in the lower half of socioeconomic status.54
If this 19 percent of high-IQ persons-without-B.A.s does not fit the stereotype of the deprived student, who were they? Some were becoming members of the cognitive elite even though they do not have a college degree. Bill Gates, college dropout and founder of Microsoft, is the larger-than-life prototype. Five percentage points of the 19 percent were working in one of the high-IQ occupations, indicating that they were probably of the minor-league Bill Gates variety (corroborated by their incomes, which were high). Of the remaining 14 percent who were not working in high-IQ occupations, a quarter had family incomes in excess of $50,000 while they were still only in their late twenties and early thirties, putting them in the top 20 percent of family incomes for their age group.55 In total, roughly half of these smart non-college graduates are already taking their place among the smart college graduates, by virtue of their incomes, their occupations, or both. It seems a safe bet that the neighborhoods where they live and the way they socialize their children are going to be indistinguishable from those of most of their counterparts in the top five centiles who completed college.
There is doubtless some relatively small fraction of those in the top 5 percent intellectually who will never rise to successful positions, whether because of lack of motivation or objective barriers. But what a small percentage of the highly talented they are. And we may add a reminder that we are watching an ongoing process. Think back to Chapter 1 and imagine the trend line from 1900 to 1990 stretched out to, say, 2020. Whatever the number of the cognitive elite who slip between the cracks now, it is a much smaller figure than it was in the 1950s, radically smaller than it was in the 1900s, and presumably it will get smaller still in the future.
These observations have several implications. At a practical policy level, the most obvious is that programs to expand opportunity for the disadvantaged are not going to make much difference in getting the most talented youths to college. An extremely high proportion of those who want to go are already going. The broader implication is that the funneling system is already functioning at a high level of efficiency, thereby promoting three interlocking phenomena:
The cognitive elite is getting richer, in an era when everybody else is having to struggle to stay even.
The cognitive elite is increasingly segregated physically from everyone else, in both the workplace and the neighborhood.
The cognitive elite is increasingly likely to intermarry.
These phenomena are driven by forces that do not lend themselves to easy reconfiguration by politicians. As we leave Part I, here is a topic to keep in the back of your mind: What if the cognitive elite were to become not only richer than everyone else, increasingly segregated, and more genetically distinct as time goes on but were also to acquire common political interests? What might those interests be, and how congruent might they be with a free society? How decisively could the cognitive elite affect policy if it were to acquire such a common political interest?
These issues will return in the last chapters in the book. They are postponed for now, because we must first explore the social problems that might help create such a new political coalition.
PART II
Cognitive Classes and Social Behavior
Whereas Part I dealt with positive outcomes—attainment of high educational levels, prestigious occupations, high incomes—Part II presents our best estimate of how much intelligence has to do with America’s most pressing social problems. The short answer is “quite a lot,” and the reason is that different levels of cognitive ability are associated with different patterns of social behavior. High cognitive ability is generally associated with socially desirable behaviors, low cognitive ability with socially undesirable ones.
“Generally associated with” does not mean “coincident with.” For virtually all of the topics we will be discussing, cognitive ability accounts for only small to middling proportions of the variation among people. It almost always explains less than 20 percent of the variance, to use the statistician’s term, usually less than 10 percent and often less than 5 percent. What this means in English is that you cannot predict what a given person will do from his IQ score—a point that we have made in Part I and will make again, for it needs repeating. On the other hand, despite the low association at the individual level, large differences in social behavior separate groups of people when the groups differ intellectually on the average.
We will argue that intelligence itself, not just its correlation with socioeconomic status, is responsible for these group differences. Our thesis appears to be radical, judging from its neglect by other social scientists. Could low intelligence possibly be a cause of irresponsible childbearing and parenting behaviors, for example? Scholars of childbearing and parenting do not seem to think so. The 850 double-column pages of the authoritative Handbook of Marriage and the Family, for example, allude to intelligence about half a dozen times, always in passing.1 Could low intelligence possibly be a cause of unemployment or poverty? Only a scattering of economists have broached the possibility.2
This neglect points to a gaping hole in the state of knowledge about social behavior. It is not that cognitive ability has been considered and found inconsequential but that it has barely been considered at all The chapters in Part II add cognitive ability to the mix of variables that social scientists have traditionally used, clearing away some of the mystery that has surrounded the nation’s most serious social problems.
We will also argue that cognitive ability is an important factor in thinking about the nature of the present
problems, whether or not cognitive ability is a cause. For example, if many of the single women who have babies also have low IQ, it makes no difference (in one sense) whether the low IQ caused them to have the babies or whether the path of causation takes a more winding route. The reality that less intelligent women have most of the out-of-wedlock babies affects and constrains public policy, whatever the path of causation. The simple correlation, unadjusted for other factors—what social scientists called the zero-order correlation—between cognitive ability and social behaviors is socially important.
The chapters of Part II cover a wide range of topics, each requiring extensive documentation. Many statistics, many tables and graphs, many citations to technical journals crowd the pages. But the chapters generally follow a similar pattern, and many of the complexities will be less daunting if you understand three basics: the NLSY, our use of cognitive classes, and our standard operating procedure for statistical analysis.