As just explained, superficial changes in appearance need not be devastating, diseases usually are not fatal until old age, and sex can be satisfying throughout adulthood. However, decline in brain functioning cannot be so easily dismissed. Descartes famously said, “I think, therefore I am.” Loss of brain power is equated with loss of self. Is that what adulthood brings?

Like every other part of the body, the brain slows down with age. Neurons take longer to fire, and messages sent from the axon of one neuron are not picked up as quickly by the dendrites of other neurons. Reaction time lengthens.

However, major neurocognitive disorder (formerly called dementia), when thinking is so erratic or memory so impaired that normal life is impossible, rarely occurs until after age 70 or so—if then (Neurocognitive disorders (NCDs) are described in detail in Chapter 14).

For most adults under age 65, brain changes do not correlate with intellectual depth (Greenwood & Parasuraman, 2012). To use a metaphor, adult brains cannot sprint but they can run a marathon—judges, bishops, and world leaders in politics, religion, and industry are usually at least 50, often much older than that. Their thinking has benefited from experience.

A leading researcher on adult intellect wrote, “Decline prior to 60 years of age is almost inevitably a symptom or precursor of pathological age changes” (Schaie, 2005/2013, p. 497). Pathological means disease-connected, not the result of normal aging. If severe brain loss occurs before late adulthood, the cause is one of the following:

Brains and intelligence vary as much as humans do. Intellectual abilities can rise, fall, zigzag, or stay the same, depending on genes and on the specifics of each life. This again illustrates the life-span perspective: Intelligence is multi-directional, multi-cultural, multi-contextual, and plastic. Generally, brain functioning is maintained: If you think deeply and clearly at age 20, you will probably do so at age 60.

You read in Chapter 7 that IQ correlates with school achievement in childhood. But what about achievement over the years of adulthood?

One leading theoretician, Charles Spearman (1927), proposed that there is a single entity that he called general intelligence (g), which each adult has to some degree. Although g cannot be measured directly, it can be inferred from various abilities, such as vocabulary, memory, and reasoning. Measuring those abilities produces an IQ score. That score correlates with health and wealth in adulthood.

Once a person reaches adulthood, an IQ score indicates whether that adult is a genius, average, or slow, no matter what the person’s age. As you remember, in childhood, a person’s score depends not only on items correct, with different items for preschoolers and older children, but also on the child’s age. That it not true for adults. The same IQ tests are usually given to people aged 18 to 88, and they are scored the same way.

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The belief that g exists still influences thinking and testing on intelligence. Many neuroscientists seek genetic underpinnings for the intellect. Efforts to find specific genes or abilities that comprise g have not succeeded (Deary et al., 2010; Haier et al., 2009), but some aspects of brain function, particularly in the prefrontal cortex, hold promise (Barbey et al., 2013; Roca et al., 2010). Other scientists believe that g may arise from prenatal brain development, experiences in infancy, or physical health.

Still others question whether a single entity, g, exists. They emphasize the role of experience, noting that national and ethnic differences in average IQ scores suggest that context is crucial. Some aspects of this controversy were explored by a famous researcher, K. Warner Schaie, as the following explains.

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Developmentalists study patterns of cognitive gain and loss. They contend that, because virtually every pattern is possible, it is misleading to ask whether adult intelligence either increases or decreases; it does not move in lockstep. “Vast domains of cognitive performance . . . may not follow a common, age-linked trajectory of decrement” (Dannefer & Patterson, 2008, p. 116).

Consequently, many researchers focus on specific intellectual abilities, finding that each component has its own pattern. One proposal, Howard Gardner’s multiple intelligences, was described in Chapter 7. Here we consider two more: One that posits two distinct abilities and another that posits three.

TWO CLUSTERS OF INTELLIGENCE Broadly speaking, tests of intellectual abilities can be sorted into two clusters, those that measure raw learning potential and those that measure accumulated knowledge. The first group is called fluid and the second, crystallized.

As its name implies, fluid intelligence is like water, flowing to its own level no matter where it happens to be. Fluid intelligence is quick and flexible, enabling people to learn anything, even abstractions that are neither familiar nor connected to what they already know. Curiosity, learning for the joy of it, solving puzzles, and the thrill at discovering something new are marks of fluid intelligence (Silvia & Sanders, 2010).

The kinds of questions that test fluid intelligence among Western adults might be:

Question 12.24

Puzzles are often used to measure fluid intelligence, with speedy solutions given bonus points (as on many IQ tests). Immediate recall—of nonsense words, of numbers, of a sentence just read—is one indicator of fluid intelligence because working memory is crucial (Chuderski, 2013; Nisbett et al., 2012).

Since fluid intelligence appears to be disconnected from past learning, it may seem impractical. Not so. A study of adults aged 34 to 83 found that people high in fluid intelligence were more exposed to stress but were less likely to suffer from it. They used their intellect to turn stresses into positive experiences (Stawski et al., 2010).

The ability to detoxify stress may be one reason that high fluid intelligence in emerging adulthood leads to longer life and higher IQ later on. Fluid intelligence is associated with openness to new experiences and overall brain health (Batterham et al., 2009; Silvia & Sanders, 2010).

By contrast, facts, information, and knowledge as a result of education and experience comprise crystallized intelligence. The size of a person’s vocabulary, the knowledge of chemical formulas, and the long-term memory for dates in history might all indicate crystallized intelligence. Tests to measure this intelligence might include questions like these:

Question 12.25

Question 12.26

Question 12.27

Question 12.28

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Although such questions seem to measure achievement more than aptitude, these two are connected, especially in adulthood. Intelligent adults read widely, think deeply, and remember what they learn, so achievement reflects aptitude. Thus, crystallized intelligence is an outgrowth of fluid intelligence (Nisbett et al., 2012).

Vocabulary, for example, improves with reading. Using the words joy, ecstasy, bliss, and delight—each appropriately, with distinct nuances (quite apart from the drugs, perfumes, or yogurts that use these names)—is a sign of intelligence. Remember the knowledge base (Chapter 7): As people know more, they learn more. That explains why a person’s years of education are considered a rough indicator of adult IQ (Nisbett et al., 2012).

To know the whole of a person’s intelligence, both fluid and crystallized intelligence must be measured. Age complicates the IQ calculation because scores on items measuring fluid intelligence decrease with age, whereas scores on crystallized intelligence increase.

Thus total IQ is often fairly steady from ages 30 to 70. Although brain slowdown begins early in adulthood, it is rarely apparent until massive declines in fluid intelligence affect crystallized intelligence. Only then do overall IQ scores fall.

This suggests that it is foolish to try to find g, a single omnibus intelligence, because components need to be measured separately. In testing for g, real developmental changes will be masked because fluid and crystallized abilities cancel each other out.

THREE FORMS OF INTELLIGENCE: STERNBERG Robert Sternberg (1988, 2003, 2011, 2015) agrees that a single intelligence score is misleading. He believes that successful intelligence is not simply the ability to do well in school (the focus of early IQ tests) but the ability to adapt to various cultural contexts, learning from experience (Sternberg, 2015).

Obviously, the years of adulthood bring many experiences, which provide opportunities for intelligence to grow. Sternberg proposed three fundamental intelligences: analytic, creative, and practical, each of which can be tested (see Table 12.1).

Analytic intelligence includes all the mental processes that foster academic proficiency by making efficient learning, remembering, and thinking possible. Analytic strengths are valuable in emerging adulthood, particularly in college, in graduate school, and in job training. Multiple-choice tests and brief essays that call forth remembered information, with one and only one right answer, indicate analytic intelligence.

Creative intelligence involves intellectual flexibility and innovation. Creative thinking is divergent rather than convergent, valuing the unexpected, imaginative, and unusual rather than standard and conventional answers. Sternberg developed tests of creative intelligence that include writing a short story titled “The Octopus’s Sneakers” or planning an advertising campaign for a new doorknob. Those with many unusual ideas earn high scores.

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Practical intelligence involves adapting to the demands of a given situation, including understanding the expectations and needs of other people. This form of intelligence is particularly needed in adulthood.

Sternberg emphasizes that everyone should deploy the strengths and guard against the limitations of each type of intelligence. Choosing which intelligence to use takes wisdom, which Sternberg considers a fourth ingredient of successful intelligence:

One needs creativity to generate novel ideas, analytical intelligence to ascertain whether they are good ideas, practical intelligence to implement the ideas and persuade others of their value, and wisdom to ensure that the ideas help reach a common good.

[Sternberg, 2012, p. 21]

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INTELLIGENCE IN DAILY LIFE Practical intelligence is sometimes called tacit intelligence because it is not obvious on tests. Instead it comes from “the school of hard knocks” and may be “street smarts,” not “book smarts.” Experience advances practical intelligence, and thus adults who are able to learn from their past may gain in practical intelligence every year.

The benefits of practical intelligence in adult life are obvious. Few adults need to define obscure words or deduce the next element in a number sequence (analytic intelligence); and few need to compose new music, restructure local government, or invent a useful gadget (creative intelligence). Ideally, those few have already found a niche for themselves and rely on people with practical intelligence to implement their analytic or creative ideas.

Almost every adult, however, must solve real-world challenges: maintaining a home; advancing a career; managing family finances; sifting information from media, mail, and the Internet; addressing the emotional needs of family members, neighbors, and colleagues (Blanchard-Fields, 2007). Scores on tests of practical intelligence hold steady from age 20 to 70, because these skills are needed throughout life (Schaie, 2005/2013).

Without practical intelligence, analytic intelligence in adulthood is ineffective because people resist academic brilliance as unrealistic and elite, as the term ivory tower implies. Similarly, a stunningly creative idea may be rejected as ridiculous and weird rather than seriously considered—if it is not accompanied by practical intelligence.

For example, imagine a business manager, or a school principal, or a political leader, or a parent without practical intelligence trying to change routine practices. Some routines should be changed, of course, but that does not mean that they will be.

Perhaps that manager, principal, leader, or parent used analytic intelligence to determine that the old way was destructive and then used creative intelligence to find a better way. But practical intelligence is essential. If innovation does not take into account human views and needs, then the workers, teachers, voters, or family members may resist, misinterpret, and predict failure. The innovator would be frustrated; the people stuck to their old ways.

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No abstract test can assess practical intelligence because context is crucial. Instead, adults need to be observed coping with daily life. In hiring a new employee, the interviewer might describe an actual situation and ask how the applicant would handle it. Many companies use such situational tests to hire managers. The prospective employee may be asked:

You assign a new project to one of your subordinates, who protests, saying it cannot be done without more resources and time. Rank your possible responses, from best to worst. Explain your reasoning.

Situational tests are used so often in the medical professions that review books have been made available for those preparing for such exams (e.g., Varian & Cartwright, 2013). Because practical intelligence is crucial on the job, probationary periods, internships, apprentices, and so on are common.

LEARNING IN NATIONS Difficult as it is to determine which adults are truly intelligent, it is even more difficult to judge nations, in part because each culture has its own concept of intelligence based partly on tradition and partly on current needs. Earl Hunt, a psychologist who studies intelligence, contends that the nations with the most advanced economies and greatest national wealth are those that make the best use of cognitive artifacts—that is, ways to amplify and extend general cognitive ability (Hunt, 2012).

Historically, written language, the number system, universities, and the scientific method were cognitive artifacts. Each of these artifacts extended human intellectual abilities by helping people interact to learn more.

Sheer survival (in earlier centuries, more newborns died than lived) and longer life (few people survived past age 65) resulted from cognitive artifacts. One example is the germ theory of disease, a cognitive artifact developed from other artifacts such as the scientific method that enabled doctors to do research and learn from each other (Hunt, 2011).

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In more recent times, universal education, immunization, clean water, electricity, global travel, and the Internet have resulted in advanced societies. According to this idea, smart people are better able to use the cognitive artifacts of their society to advance their own intelligence. Then they develop more cognitive artifacts, and the whole community benefits.

For instance, most developed nations provide free preschool and kindergarten to all children. That increases learning in the young, eventually advancing the nation. By contrast, other nations value fertility more than health, choose profit instead of education, educate one gender more than the other, and forbid some expressions of knowledge. That undercuts intellectual development (Hunt, 2011).

A recent meta-analysis of 167 nations found that disaster deaths decreased when education increased (measured by the proportion of women, aged 20 to 39, with at least an eighth-grade education) (Lutz et al., 2014). The hypothesis was that educated people are better able to support prevention measures and to use various cognitive artifacts (such as safer housing construction, stockpiling supplies, physical and mental health care). Elaborate statistical testing found “female education is indeed strongly associated with a reduction in disaster fatalities” but national wealth was not (Lutz et al., 2014, p. 1061).