The Bell Curve: Intelligence and Class Structure in American Life

by Richard J. Herrnstein

  This change, apparently reflecting some bedrock shifts in attitudes toward marriage in postindustrial societies, may have profound significance. And yet marriage is still alive and well in the sense that it remains a hugely popular institution. Over 90 percent of Americans of both sexes have married by the time they reach their 40s.2

  In the early 1970s, the marriage rate began a prolonged decline for no immediately apparent reason

  Sources: U.S. Bureau of the Census, 1975, Table B214-215; SAUS, 1992, Table 127, and comparable tables in various editions.

  Marriage and IQ

  What does cognitive ability have to do with marriage, and is there any reason to think that it could be interacting with society’s declining propensity to marry?

  We know from work by Robert Retherford that in premodern societies the wealthy and successful married at younger ages than the poor and underprivileged.3 Retherford further notes that intelligence and social status are correlated wherever they have been examined; hence, we can assume that intelligence—via social status—facilitated’marriage in premodern societies.

  With the advent of modernity, however, this relationship flips over. Throughout the West since the nineteenth century, people in the more privileged sector of society have married later and at lower rates than the less privileged. We examine the demographic implications of this phenomenon in Chapter 15. For now, the implication is that in late-twentieth-century America, we should expect to find lower marriage rates among the highly intelligent in the NLSY.

  Everyday experience bears out this finding for people who live in academic communities or professional circles, where they see many smart men and women in their 30s and 40s who are still single and look as if they might stay that way forever. The intelligent professional woman is the most visible of this new tribe, rising in her career, too busy for, or not interested in, marriage and children. Among men, other images have recently become part of the culture: the intelligent, successful, and unmarried heterosexual male who cannot make a commitment and the intelligent, successful, and unmarried homosexual male who no longer needs to go through the motions of a marriage.

  At the other end of the scale, there are similar reasons in research and common sense to suggest that marriage rates will tend to be low among people at the very bottom of the IQ distribution.4 For a number of reasons, having to do with everything from initiative to romance to economics, people with very low IQs are likely to be at a disadvantage in competing for marriage partners.

  Our first look at the NLSY data conforms to these expectations, though not dramatically. The next table shows the situation for the NLSY sample among whites who had reached the age of 30. There were surprises in these results for us, and perhaps for some of our readers. We would not have guessed that the average age of marriage for people in the top 5 percent of the intelligence distribution was only 25, for example.5 A main point of the table is to introduce the theme threaded throughout the chapter: Our, your, and the media’s impressions of the state of the American family are not necessarily accurate.

  The Role of Socioeconomic Background

  Note in the table below that marriage percentages are highest for people in the middle of the intelligence distribution and taper off on both ends. The same is true, though less dramatically, if the table is constructed by socioeconomic class: The percentage of whites who had married before the age of 30 declines at both extremes. Furthermore, we have good reasons for thinking that this pattern is not a sampling fluke but reflects underlying dynamics of marriage. This pattern makes interpreting regression results tricky, because the regression techniques we are using compute the lines in the graphs based on the assumption that the lines are not trying to make U-turns. For the record: When we run the standard initial analysis incorporating IQ, age, and socioeconomic status as predictors of marriage, IQ has no significant independent role; there is a slight, statistically insignificant downward probability of marriage as IQ goes up. Socioeconomic background has a much larger suppressive role on marriage: The richer and better educated your parents, the less likely you are to marry, according to these results, which, again, must be interpreted cautiously.

  Which Whites Get Married When?

  Percentage Who Had Ever Married Before Age 30 Cognitive Class Average Age at First Marriage

  67 I Very bright 25.4

  72 II Bright 24.3

  81 III Normal 22.9

  81 IV Dull 21.5

  72 V Very Dull 21.3

  78 Overall averages 22.1

  The Role of Education

  The real culprit in explaining marriage rates in a young population is education. In the rest of the chapters of Part II, we point out many instances in which taking education into account does not much affect IQ’s independent role. Not so with marriage. When we take education into account, the apparent relationship reverses: The probability of marrying goes up, not down, for people with high IQs—a result found in other databases as well.6 Our standard analysis with the two educational samples, high school graduates (no more and no less) and college graduates (no more and no less) elucidates this finding.

  The next figure shows that neither IQ nor socioeconomic background was important in determining marriage for the college sample. In sharp contrast, IQ made a significant difference in the high school sample. A high school graduate from an average socioeconomic background who was at the bottom of the IQ distribution (2 standard deviations below the mean) had a 60 percent chance of having married. A high school graduate at the top of the IQ distribution had an 89 percent chance of having married. Meanwhile, the independent role of socioeconomic status in the high school sample was either slightly negative or nil (the downward slope is not statistically significant).

  High IQ raises the probability of marriage for the white high school sample, while high socioeconomic background lowers it

  Note: For computing the plot, age, and either SES (for the black curves) or IQ (for the gray curves) were set at their mean values.

  DIVORCE

  People marry, but do they stay married? Here is where the change has been not only dramatic but, some would say, cataclysmic, as shown below. In 1920, only death parted husbands and wives in about 82 percent of marriages and, in any given year (the datum shown in the next figure below), only about 8 out of 1,000 married females experienced a divorce. As late as 1964, despite the sweeping changes in technology, wealth, and social life that had occurred in the intervening forty-four years, the number was very little changed: 10 of every 1,000. The peak divorce rates just following World War II had fully subsided, and the divorce rate still lay upon a trendline established between 1920 and 1940.

  The divorce revolution

  Sources: U.S. Bureau of the Census, 1975, Table B214-215; SAUS, 1992, Table 127, and comparable table in various editions.

  Then came the revolution. The steep upward sweep of the divorce rate from the mid-1960s through the end of the 1970s represents one of the most rapid, compressed changes in a basic social behavior that the twentieth century has witnessed. When the divorce rate hit its peak at the end of the 1970s, a marriage had more than a fifty-fifty chance of ending in divorce.7 Despite a downward trend since 1980, divorce remains at twice the annual rate of the mid-1960s.

  Divorce and IQ

  We do not attempt to explain this profound change in our lives, which no doubt has roots in changing mores, changing laws, changing roles of women, changing labor markets, and who knows what else. Instead, we address the narrow question: How does divorce currently correlate with intelligence?

  There are plausible reasons for expecting that cognitive ability will have an impact on divorce. For example, one may hypothesize that bright people less often marry on a whim, hence they have fewer disastrous short marriages. Bright people are perhaps less likely to act on impulse when the marriage has problems, hence are less likely to divorce precipitously during the first years of marriage. More generally, it may be argued that brighter people are better able to work
out differences that might otherwise eventually destroy a marriage. We are, of course, referring to statistical tendencies for which individual exceptions abound.

  Within the confines of the NLSY experience, these expectations are borne out to some degree, as shown in the table. The results are based on the first five years of marriage. Those in Class I were ten times as likely to stay married for at least five years as to get divorced; for those in Classes III, IV, and V—the bottom three-quarters of the population—the ratio of marital survival to divorce for at least five years was only 3.5 to 1.8 Virtually all of the effect of IQ seems to have been concentrated at the top of the distribution. The divorce rates across the bottom three-quarters of the cognitive ability distribution were essentially identical.

  Which Whites Get Divorced When?

  Cognitive Class Percentage Divorced in First Five Years of Marriage

  I Very bright 9

  II Bright 15

  III Normal 23

  IV Dull 22

  V Very dull 21

  Overall averages 20

  The Role of Socioeconomic Background

  Do these findings hold up when we begin to add in other considerations? The figure below shows the results for the white sample who had been married at least five years.9 The consistent finding, represented fairly by the figure, was that higher IQ was still associated with a lower probability of divorce after extracting the effects of other variables, and parental SES had a significant positiverelationship to divorce—that is, IQ being equal, children of higher-status families were more likely to get divorced than children of lower-status families.10

  IQ and socioeconomic background have opposite effects on the likelihood of an early divorce among young whites

  Note: In addition to IQ, age, and parental SES, the independent variables included date of first marriage. For computing the plot, age, date of first marriage, and either SES (for the black curve) or IQ (for the gray curve) were set at their mean values.

  The Role of Education

  It is clear to all researchers who examine the data that higher education is associated with lower levels of divorce. This was certainly true of the NLSY, where the college sample (persons with a bachelor’s degree, no more and no less) had a divorce rate in the first five years of marriage that was less than half that of the high school sample: 7 percent compared to 19 percent. But this raw outcome is deceptive.11 Holding some critical other things equal—IQ, socioeconomic status, age, and date of marriage—the divorce rate for the high school graduates in the first five years of marriage was lowerthan for college graduates.

  For whom did IQ make more difference: the high school sample or the college sample? The answer is the college sample, by far. For them, the probability of divorce in the first five years plunged from 28 percent for someone with an IQ of 100 to 9 percent for someone with an IQ of 130. The much more minor effect of IQ among high school graduates was not statistically significant.12

  Do Broken Families Beget Broken Families?

  One other cause of divorce is mentioned so commonly that it requires exploration: a broken home in the preceding generation. The children of divorced parents have an elevated risk themselves of getting divorced.13 It is not hard to think of reasons why: They have not witnessed how a successful marriage works, they are more likely to see divorce as an acceptable alternative, the turbulence of a failing marriage leaves psychological scars, and so forth.14

  None of these reasons has an obvious connection with cognitive ability. They could be valid without necessarily affecting the independent prophylactic role that being smart plays in preventing (or perhaps simply delaying) divorce. And so indeed it worked out in the NLSY. Given a young person of average IQ and socioeconomic background, the probability of divorce within the first five years of marriage was lowest for those who at age 14 had been living with both parents (20 percent), a bit higher for those who had been living with a remarried parent (22 percent), and higher still for those living with an un-remarried or never-married mother (25 percent)15 These are not large effects, however, and are not significant in a statistical sense. We can say only that the results supported the general proposition that, when it comes to raising children who will themselves stay married, two adults as parents are generally better than one and that two biological parents in the household are better than one or none. But it is worth noting that the introduction of these variables did nothing to change the importance of the rest of the variables. Higher cognitive ability conferred just about as much protection from, and higher status just as much risk for, divorce as in the preceding analyses.

  The NLSY gives us a window on the early years of marriage, though not necessarily about marriage as a whole. Based on national divorce rates, we know that most of the divorces that the members of the NLSY will experience have yet to occur. We will have to wait and see what happens to the NLSY sample in later years.

  One final point about the divorce results is worth noting, however. These findings may help explain the common observation that divorce is less likely when the husband has high education, income, or socioeconomic status or that marriages are more likely to fall apart if they start when the couple is afflicted with unemployment.16 If we had showed a breakdown of divorce rates in the NLSY by social and economic measures alone, we too would have shown such effects. But each of those variables is correlated with cognitive ability, and the studies that examine them almost never include an independent measure of intelligence per se. Some portion of what has so often been observed about the risk factors for divorce turns out to be more narrowly the result of low cognitive ability.

  ILLEGITIMACY

  Childbearing touches on one of the most sensitive topics in the study of intelligence and its social consequences: fertility patterns among the smart and the dumb, and their possible long-term effects on the intellectual capital of a nation’s population. We devote a full chapter to this topic (Chapter 15) in the portion of the book dealing with the national, multiracial perspective. In this chapter, the focus is on family problems, and one of the leading current problems is the failure of two-parent families to form in the first place, as denoted by births to single women—illegitimacy.

  We use the older term “illegitimacy” in favor of the phrases currently in favor, “out-of-wedlock births” or “births to single women,” because we think that, in the long run, the word illegitimacy will prove to be the right one. We are instructed in this by the anthropologist Bronis-law Malinowski. In his research early in the century, Malinowski observed a constant running throughout the rich diversity of human cultures and indeed throughout history. He decided that this amounted to “a universal sociological law” and called it the “principle of legitimacy.” No matter what the culture might be, “there runs the rule that the father is indispensable for the full sociological status of the child as well as of the mother, that the group consisting of a woman and her offspring is sociologically incomplete and illegitimate.”17 The rule applied alike to East or West, primitive cultures or advanced ones, cultures where premarital sex was accepted or banned, where children were considered an asset or a burden, where fathers could have one wife or many. Despite our faith that Malinowski was observing something that will once again be considered true about human societies, the contemporary Western democracies, including the United States, seem intent on proving Malinowski wrong, as shown in the next figure.

  The illegitimacy revolution

  Sources: Various editions of the Natality volume of Vital Statistics, compiled annually by the Public Health Service.

  In the seventy-one years from 1920 to 1990, the proportion of children born to single women in the United States went from less than 3 percent, roughly where it had been throughout American history, to 30 percent.18 It would have been about 6 percent had the trendline established from 1920 to 1952 remained unchanged. The trendline shifted upward during the 1950s, but not dramatically. If we had maintained the trendline established from 1952 to 1963, the United States
would have had about 11 percent of births out of wedlock in 1991. Instead, the figure was 30 percent, the result of a steep, sustained increase that gatlered steam in the mid-1960s and continued into the early 1990s. The increase for the most recent available year, 1991, was one of the largest in history. There are no signs as we write that illegitimacy is reaching an asymptote.

  Anyone who is trying to understand social trends must also realize that the magic of compound interest has created an even more explosive rise in the population of unmarried mothers and children. In 1960, for example, there were just 73,000 never-married mothers between the ages of 18 and 34. In 1980, there were 1.0 million.19 In 1990, there were approximately 2.9 million.20 Thus the illegitimacy ratio increased by sixfold from 1960 to 1990—bad enough—but the number of never-married mothers increased fortyfold. From just 1980 to 1990, while the illegitimacy ratio was increasing by half, the number of unmarried mothers almost tripled.