The Bell Curve: Intelligence and Class Structure in American Life (12 page)

When one combines the people known to be in high-IQ professions with estimates of the numbers of business executives who are drawn from the top tenth in cognitive ability, the results do not leave much room for maneuver. The specific proportions are open to argument, but the main point seems beyond dispute: Even as recently as midcentury, America was still a society in which most bright people were scattered throughout the wide range of jobs. As the century draws to a close, a very high proportion of that same group is now concentrated within a few occupations that are highly screened for IQ.

J
obs sort people by their IQs, just as college does. But there is a difference between educational and occupational sorting. People spend only one to two decades in school. School may seem like forever when we are there, but we spend most of our lives with the sorting that centers on work and carries over into circles of friends and colleagues, and into communities—if not physically the same workplaces, communities, and friends throughout the life span, then generically similar ones. In this chapter, we continue our discussion of the contours of the intellectual landscape. An examination of occupational sorting will carry us through to the end of Part I.

No one decreed that occupations should sort us out by our cognitive abilities, and no one enforces the process. It goes on beneath the surface, guided by its own invisible hand. Testers observe that job status and intelligence test scores have gone together since there were intelligence tests to give.
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As tests evolved and as the measurement of status was formalized, studying the relation between the jobs and intelligence became a cottage industry for social scientists. By now, the relation has been confirmed many times, in many countries, and in many approaches to the data.
²

This is not to say that the experts find nothing to quarrel about. The technical literature is replete with disagreement. Aside from the purely technical bones of contention, the experts argue about whether the IQ-job status connection is a by-product of a more fundamental link between
educational level and job status. For example, it takes a law degree to be a lawyer, and it takes intelligence to get into and through law school, but aside from that, is there any good reason why lawyers need to have higher IQs on average than, say, bus drivers? At the height of egalitarianism in the 1970s, the received wisdom in many academic circles was “no,” with Christopher Jencks’s
Inequality
the accepted text.
³
A related argument, stated forcefully by James Fallows, arises over whether an IQ score is a credential for certain jobs, like a union card for a musician, or whether there is a necessary link between job status and intelligence, like a good ear.
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By the time we get to the end of Part I, our answers to such questions should be clear. Here we review a few of the more illuminating findings, to push the discussion beyond the fact that occupational status is correlated with IQ.

One notable finding is that the correlation between IQ and job status is just about as high if the IQ test is given in childhood, decades before people enter the job market, as it is among young adults who are taking an intelligence test after years of education. For example, in a small but elegant longitudinal study of childhood intelligence and adult outcomes, the boys and girls in the sample were given IQ tests in childhood and then their job statuses and levels of schooling were measured on standard scales after they were at least 26 years old.
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The IQ scores they got when they were 7 or 8 years old were about as correlated with the status level of their adult jobs as their adult IQs would have been.
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Inasmuch as childhood IQ is more correlated with status than completed education, as it is in some studies, the thesis that IQ scores really just measure educational level is weakened.

Family members typically resemble each other in their occupational status.
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We are talking here not about a son or a niece or a brother-in-law going into the family business but about job status, however measured. On rating scales that categorize jobs from those with the highest status to those with the lowest, family members tend to land at similar levels. There are many exceptions; we all hear occasionally about families with several members who are doctors and lawyers plus another who is a blue-collar worker, or vice versa. But such stories call attention to themselves because they describe rarities. Mostly, relatives occupy neighboring, if not the same, rungs on the job status ladder, and the closer the relationship is, the nearer they are. Such commonplace findings have many possible explanations, but an obvious one that is not mentioned or tested often by social scientists is that since intelligence
runs in families and intelligence predicts status, status
must
run in families. In fact, this explanation somehow manages to be both obvious and controversial.
⁸

One useful study of family resemblance in status comes from Denmark and is based on several hundred men and women adopted in or around Copenhagen between 1924 and 1947.
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Four out of five of these adopted people had been placed with their adopting families in their first year of life; the average age of placement overall was 3 months. To all intents and purposes, then, the adoptees shared little common environment with their biological siblings, but they shared a home environment with their adoptive siblings. In adulthood, they were compared with both their biological siblings and their adoptive siblings, the idea being to see whether common genes or common home life determined where they landed on the occupational ladder. The biologically related siblings resembled each other in job status, even though they grew up in different homes. And among them, the full siblings had more similar job status than the half siblings. Meanwhile, adoptive siblings were
not
significantly correlated with each other in job status.
¹⁰

The above comments apply to all sorts of occupations, from low status to high. But the relationship of IQ to occupations changes as the job becomes more cognitively demanding. Almost anyone can become a ditch digger (if he has a strong enough back); many can become cabinetmakers (if they have good enough small-motor skills), but only people from a fairly narrow range of cognitive ability can become lawyers. If lawyering pays more than cabinetmaking, what happens as the number of lawyering jobs increases, as it has in America? More people with high IQs are diverted to lawyering, which means that they are not going to become cabinetmakers or ditch diggers.

Now imagine that process writ large, and consider what has happened Within the handful of occupations that are most highly screened for IQ. We will concentrate here on a dozen such occupations, which we will refer to as “high-IQ professions.” Some of them have existed as long as IQ tests and are included in the list of occupations for the 1900 census: accountants, architects, chemists, college teachers, dentists, engineers, lawyers, and physicians. Others have emerged more recently or are relabeled
in more recent occupational breakdowns: computer scientists, mathematicians, natural scientists, and social scientists.

The mean IQ of people entering those fields is about 120, give or take a few points.
¹¹
The state of knowledge is not perfect, and the sorting process is not precise. Different studies find slightly different means for these occupations, with some suggesting that physicians have a mean closer to 125, for example.
¹²
Theoretical physicists probably average higher than natural scientists in general. Within each profession, the range of scores may be large. Even an occupation with a high mean may include individuals with modest scores; it will certainly include a sizable proportion below its mean—50 percent of them, if the distribution is symmetrical above and below its mean.
¹³

Nonetheless, 120 is a good ballpark figure for estimating the mean person in these high-IQ professions, and it also has the advantage of marking the cutoff point for approximately the top tenth of the entire population in IQ.
¹⁴
Armed with this information plus a few conjectures, we may explore how cognitive stratification at the top of the American labor market has changed over the years. The figure below shows the answer for the twentieth century to date.

Once again, the portrait of American society depends on vantage point. Let us begin with the bottom line, showing the percentage of the entire labor force that is engaged in high-IQ professions. There has been a proportional increase during the twentieth century, but these people still constituted only about one out of fifteen Americans in the labor force as of 1990.

Now consider Americans in the top 10 percent (the top decile, in other words) in cognitive ability—everyone over the age of 25, including housewives, the retired, and others who are not counted as being part of the labor force. These people are represented by the middle line in the graph. In 1900, the number of jobs in the high-IQ professions soaked up only about one out of twenty of these talented people. By 1990, they soaked up almost five times as many, or one out of four.

Finally, consider the top line in the graph, which is limited to Americans who are in both the top decile of IQ and the labor force. In 1900, about one out of eleven was in one of the high-IQ professions; by 1990, more than one out of three. This still leaves almost two out of three of them unaccounted for, but we will get to them in the next section of the chapter.

The top IQ decile becomes rapidly more concentrated in high-IQ professions from 1940 onward

Source:
U.S. Bureau of the Census 1975, Table D233—682; SAVS 1981, Table 675; U.S. Department of Labor, 1991, Table 22.

The specific proportions should be taken with a grain of salt, based, as they are, on estimates of IQs within the occupations. But we have a way of checking the 1990 estimate against actual experience, using the National Longitudinal Survey of Youth (described fully in the introduction to Part II), and our estimate fits quite closely.
¹⁵
In any case, the basic trends are unmistakable. Unlike the steep slopes we saw for educational changes in the first half of the century, the high-IQ professions gained proportionally little of the working force through 1940. But after 1940, the trickle swelled to a flood, shown by the nonlinear upward sweep of the proportion in the top IQ decile who have more recently gone to work in this limited number of jobs.

The High-IQ Professions and the Cognitive Elite

We have been discussing the top decile: everyone with an IQ of 120 or higher. What about people in the even more rarefied cognitive elite, the top fraction of a centile who are so concentrated in a handful of universities during their college years? We have little to tell us exactly what is happening now, but we know what the situation was fifty years ago, through Lewis Terman’s famous study of 1,500 highly gifted children who were born in the early 1900s and followed throughout their lives. Their average IQs were over three standard deviations above the mean, meaning that the Terman sample represented about l/300th of the population. As of 1940, the members of the Terman sample who had finished their schooling were engaged in high-IQ professions at three times the rate of people in the top 10 percent—24 percent for the Terman sample against 8 percent for the top decile in 1940, as the preceding figure shows.
¹⁶
If that was the case in 1940, when fewer than one in twelve people in the top decile were working in high-IQ professions, what might be the proportion for a comparable sample today? Presumably much higher, though how much higher is impossible to estimate with the available data.
¹⁷

The changes in our twelve high-IQ professions understate how much occupational cognitive segregation there has been in this century. We lack data about other professions and occupations in which mean IQ may be comparably high (e.g., military officers, writers, journalists). But the biggest omission involves business executives. For while the mean IQ of all people who go into business cannot be near 120,
¹⁸
both common sense and circumstantial evidence suggest that people who rise to the upper echelons of large businesses tend to have high IQs and that this tendency has increased during the course of the century.