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Abilities, Personality, and Success
Proposition #9: Class structure is importantly based on differences in abilities that have a substantial genetic component.
It is time to confront the question directly: To what extent is professional and economic success in life a function of characteristics that have a substantial genetic component? Proposition #9 extrapolates from a famous syllogism that Richard Herrnstein published in 1973:
1. If differences in mental abilities are inherited, and
2. If success requires those abilities, and
3. If earnings and prestige depend upon success,
4. Then social standing (which reflects earnings and prestige) will be based to some extent on inherited differences among people.1
The goal of this chapter is to present the case that Herrnstein’s syllogism is borne out by the evidence and warrants a somewhat stronger statement when it comes to the role of genes in shaping class structure. If individual success is based even modestly on heritable traits, the aggregate effect on a society’s class structure will be important, as I cautiously characterize it in Proposition #9. “Profound” is probably more accurate.
This goal should not obscure a larger truth. I’ll say it briefly but italicize it: The bulk of the variance in success in life is unexplained by either nature or nurture. Researchers are lucky if they explain half of the variance in educational attainment with measures of abilities and socioeconomic background. They’re lucky if they can explain even a quarter of the variance in earned income with such measures. The takeaway for thinking about our futures as individuals is that we do not live in a deterministic world ruled by either genes or social background, let alone by race or gender. But Proposition #9 is about social classes, not individuals. The takeaway for thinking about the future of modern Western societies is that the role of genes is important for shaping class structure.
Heritable Traits and Success: The Primacy of g
The most important single heritable trait that explains socioeconomic success is the general mental ability known as g, which in turn is best measured by a good IQ test.[2] It is not only the most important, but typically far more important than any other single heritable trait. On the other side of the picture, I will be showing you some evidence that all other heritable traits have combined effects that are quite substantial—in some circumstances and for some measures of success as important in combination as IQ.
Preliminaries
Many of the things that may concern you about IQ tests are not true. For a recent accessible and accurate summary of the state of knowledge about IQ, I recommend Stuart Ritchie’s Intelligence: All That Matters, a sprightly book that’s only 160 pages long.3 But here are some of the main points that you need to know, along with additional documentation.
IQ tests are not biased against minorities.4 Education does raise IQ, but within a narrow range (you can’t become a genius by staying in school long enough).5 IQ scores are usually stable, though not perfectly so, after around age six, when the first reliable measures become available, until decline in old age.[6] IQ meets higher standards of reliability and validity in measuring the construct it is intended to measure than any psychological measure of personality or temperament.7
All of these statements have abundant, replicated evidence behind them and are not subjects of controversy among specialists. This still leaves a list of “But what about…” questions that people raise about IQ. This is not the place to deal with all of them, but two misapprehensions are so widespread that I must at least briefly deal with them here.
“IQ tests just measure how well you perform on IQ tests.” The proper description of what g means for daily life goes far beyond performing well on tests. Sociologist Linda Gottfredson’s description is the best I’ve found:
Intelligence is a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—“catching on,” “making sense” of things, or “figuring out” what to do.8
To put it another way, life is an IQ test.9 Compared to people with low IQs, people who have high IQs are more likely to see that the tempting short-term payoff will be costly in the long term. They are more likely to eat healthy foods, refrain from smoking, and exercise regularly.10 They have fewer accidents.11 More broadly, think of everyday life as a multitude of decisions. For some of those decisions, there’s no objectively right or wrong choice; everything depends on personal priorities. That’s why some people take up wingsuit gliding despite the mortality statistics—for them, the reward is worth the risk. But many everyday decisions have an option that has an objectively higher probability of producing an outcome that the individual does not want. For those thousands of decisions over the course of a year, g is useful in reducing the number of mistakes.12 The general mental factor g helps people navigate the caprices and complications of everyday life.13
g HAS NOTHING TO DO WITH MERIT
I deliberately avoid the word meritocracy to describe a society in which able people rise to the top, because the most important single ingredient, g, is a matter of luck. I’m willing to believe that people have some control over their industriousness, perseverance, resilience, and other personal qualities that have brought them success, even though those qualities are partly heritable. g is different. People can make a little or a lot of what they were given; maybe they can even tweak their IQs by a couple of points; but no one gets an IQ score of 130 by trying hard. Merit had nothing to do with it.
“The most successful people I know aren’t the ones with the highest IQs.” Two separate issues are commonly confused.
First, the image of the intellectual genius who is a social klutz is overblown. It happens—some people who have extremely high IQs have poor social skills and can be successful only in certain occupations (some genius programmers come to mind). Some people with high IQs seem to have oddly little common sense. They are exceptions, however. The qualities besides IQ that contribute to success tend to be correlated with IQ, and those correlations apply across the full range of IQ.
Second, there’s a good reason why people say, “The most successful people I know aren’t the ones with the highest IQs.” They’re probably right. The reason they’re right is what statisticians call restriction of range or truncation of range. Few people these days live their lives in close daily contact with people who have a wide range of IQs. Instead, people mostly hang out with others who are in their own IQ ballpark and are thereby victimized by the illusion created by restriction of range.
More than 30 years ago, sociologist Steven Goldberg told me an analogy for explaining it that I have been borrowing ever since: IQ has the same role for explaining success in many professions as weight has in explaining the success of offensive linemen in the NFL. The best offensive linemen in the NFL are not necessarily the heaviest. The correlation between weight and productivity for all the offensive linemen on the rosters of NFL teams is probably near zero. But you can’t get the job unless you weigh at least 300 pounds.14 Similarly, CEOs of Fortune 500 companies, senior partners in Park Avenue law firms, and tenured professors at Harvard may not be the ones with the highest IQs among the potential occupants for such jobs. They distinguished themselves from the others just as smart or smarter through other personal assets. But restriction of range means that you are seeing what role those other personal assets play when everyone figuratively weighs 300 pounds to begin with.
The First Order Effects of g in Producing Success
Having a high level of g is a general resource for getting an advanced education and being productive on the job—two of the most elemental building blocks of success.
Educational attainment. Over the last century, the gateway to econom
ic success has increasingly been defined by education, and the ability to take advantage of education is g’s most obvious asset. In 2007, sociologist Tarmo Strenze published a meta-analysis of 65 samples with information on IQ and educational attainment. IQ’s correlation with eventual educational attainment for persons who had been tested at ages 16–18, before the end of compulsory education, was +.58.15
The relationship between IQ and academic success is about as strong for graduate school as for college. A 2010 meta-analysis of the literature on such tests found a correlation between the SAT and first-year college GPA of +.51 and a correlation with cumulative GPAs for the entire college career of +.53. The correlations between scores on various graduate school admissions tests and subsequent graduate school GPAs ranged between +.35 and +.46. The correlation between the Law School Admission Test and scores on bar exams was +.46. The mean correlation of the Medical College Admission Test and scores on medical licensing exams was +.64.16
Job productivity. One of the most common assertions about IQ is that it doesn’t predict performance in the real world of work. The truth is the opposite. It’s not just that IQ predicts job performance for people with cognitively demanding jobs; IQ predicts job performance to some degree for people across the entire range of jobs. People who are responsible for new hires at a workplace should know that an IQ score is a better predictor of job performance than a résumé, evaluation through a job interview, assessment centers, or work samples. The note has details.[17] How important are the effects of IQ? Taking all jobs together, the predictive validity of IQ scores for overall job performance is about +.50 (it’s higher than that for high-complexity jobs). You can square that figure and point out that IQ explains only 25 percent of the variance in job performance. If you’re an employer, however, and are told that a standard deviation increase in IQ is associated with half a standard deviation increase in overall job performance, a predictive validity of +.50 is a big deal.18
Since we live in an age when the social sciences are suffering from a replication crisis, I emphasize again that the generalizations I have made about the relationships of g to educational attainment and job productivity are drawn from hundreds of studies.
Psychometric g Versus Other Personal Traits
The popular suspicion of IQ’s relationship to success has been tenacious, but for an understandable reason. Anyone who has reached adulthood is aware of all the things besides intelligence that matter in achieving success. The most obvious is simple hard work. In any job setting with more than a few employees, we observe that some people work long hours and others do as little as possible. But other traits also matter. Some people are resilient while others give up when things go badly. Some people have a knack for leading people and others do not. Some people are a pleasure to work with and others are abrasive and off-putting. Industriousness, resilience, charisma, cooperativeness, and many other traits are objectively valuable for productivity in most kinds of jobs and rightly affect supervisors’ decisions about who gets ahead.
Since we know these other qualities are so important in everyday life, it seems that good measures of them should explain at least as much about success as an IQ score. People have in fact invested a great deal of effort in coming up with such measures. The ones that have gotten the most public attention are Howard Gardner’s “multiple intelligences” and two constellations of qualities that have been labeled “emotional intelligence” and “grit.” All three talk about qualities other than g that are important to success. I recommend Howard Gardner’s Frames of Mind: The Theory of Multiple Intelligences (1983), Daniel Goleman’s Emotional Intelligence: Why It Can Matter More Than IQ (1995), and Angela Duckworth’s more recent Grit: The Power of Passion and Perseverance (2016) for nontechnical accounts of qualities that aren’t directly measured by IQ tests and that are unequivocally important.
The technical validation of these three approaches is another matter. There’s a big difference between persuasively arguing that something is important to success and providing a measure of that “something” that is reliable, valid, and not already captured by other measures. Tests of emotional intelligence or grit need to explain variance that measures of IQ and personality traits don’t explain. That task has proved to be daunting. Multiple intelligences, emotional intelligence, grit, and other ideas about the causes of success were introduced into a world that already had measures of g and personality traits that have passed repeated tests of reliability and construct validity. The new kids on the block have had a hard time demonstrating that they could explain additional variance.[19]
Progress has been made in understanding the role of traits other than IQ, however.20 A technical literature documents the importance of self-control for success in life independently of IQ.21 A related concept, locus of control (how much people believe they are in control of what happens to them), has an independent role in explaining both financial success and financial hardship.22 When it comes to academic performance, simple self-confidence in one’s own ability was found to explain variance in academic achievement in mathematics and English (but not in science) even after controlling for IQ.23 Others have documented an independent role for the importance of intellectual interest and curiosity.24
But the most extensive technical literature involves the Big Five personality factors—emotional stability, extraversion, conscientiousness, openness, and agreeableness—so much that a 2014 meta-analysis of the relationship of personality to academic performance by psychologist Arthur Poropat had two dozen samples to work with. Conscientiousness consistently played the most important role, with openness in second place. Poropat reported effect sizes for them of +1.14 and +0.96 respectively, far larger than those for agreeableness (+0.19), emotional stability (+0.36), or extraversion (+0.23).25 In addition to its value for academic performance, conscientiousness has also been found to predict job performance, salary, promotion,26 and occupational prestige.27 These findings make sense. The facets for measuring conscientiousness—competence, orderliness, dutifulness, industriousness, self-discipline, and deliberateness—come close to describing the ideal candidate for many kinds of jobs that require solid day-by-day performance rather than flights of creativity.28 Other studies have found that emotional stability, openness, and agreeableness have independent associations with similar outcomes that contribute to success. But while such effects have been found, they are quite small compared to the role of g.
The effect sizes in the Poropat meta-analysis do not control for IQ—an important omission. I have found three major studies that have analyzed the role of personality in the presence of a good measure of childhood IQ.[29] One (first author was Rodica Damian) is based on 81,075 persons from Project Talent, a subsample of a nationally representative American sample tested in high school in 1961 who were followed up at ages 28–30. Another (first author was Roger Staff) is based on a subset of 443 persons drawn from the Aberdeen Birth Cohort of 1936 who were followed up at age 64. The third study, by Helen Cheng and Adrian Furnham, is based on 4,808 persons from the British National Child Development Study of 1958 who were followed up at age 50. The following table shows what happened when IQ, parental SES, and the Big Five personality traits were entered together in analyses of adult educational attainment and occupational prestige.
COMPARATIVE ROLES OF IQ AND PERSONALITY TRAITS IN MEASURES OF ADULT OUTCOMES
Childhood IQ
Project Talent
Educational attainment: +0.41
Occupational prestige: +0.39
Aberdeen Birth Cohort
Adult reading: +0.65
Adult SES: +0.52
British NCDP
Educational attainment: +0.35
Occupational prestige: +0.14
Extraversion
Project Talent
Educational attainment: +0.08
Occupational prestige: +0.09
Aberdeen Birth Cohort
Adult reading: –0.05
Adult SES: +0.07
British NCDP
Educational attainment: –0.02
Occupational prestige: +0.07
Agreeableness
Project Talent
Educational attainment: +0.07
Occupational prestige: +0.08
Aberdeen Birth Cohort
Adult reading: +0.02
Adult SES: +0.05
British NCDP
Educational attainment: 0.00
Occupational prestige: 0.00
Conscientiousness
Project Talent
Educational attainment: +0.09
Occupational prestige: +0.09
Aberdeen Birth Cohort
Adult reading: +0.01
Adult SES: +0.07
British NCDP
Educational attainment: 0.00
Occupational prestige: +0.05
Emotional stability
Project Talent
Educational attainment: +0.05
Occupational prestige: +0.05
Aberdeen Birth Cohort
Adult reading: +0.04
Adult SES: +0.14
British NCDP
Educational attainment: +0.03
Occupational prestige: +0.01
Openness
Project Talent
Educational attainment: +0.09
Occupational prestige: +0.09
Aberdeen Birth Cohort
Adult reading: +0.15
Adult SES: +0.18
British NCDP
Educational attainment: +0.16
Occupational prestige: +0.05
Sources: Damian, Su, Shanahan et al. (2014): Tables 3, 6; Staff, Hogan, and Whalley (2017): Table 2; Cheng and Furnham (2012): Fig. 2.
You can’t compare the size of the effects across the rows in the table. The metrics are all related to standard deviations, but they are too different to make the numbers comparable.[30] Rather, you should scan down the columns. None of the Big Five personality factors has nearly the independent role that childhood IQ has. In fact, even these modest effects are exaggerated, because the results for any one factor control only for childhood IQ, not for the other four personality factors (that is, the multivariate model was run five times, once for each model, not once with all five factors entered as independent variables). The message of the information in the table is not that other personal traits besides g are irrelevant after all. But each individual trait plays a subordinate role.
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