Origins of Intelligence

Where does intelligence come from? Some researchers believe that intelligence is a trait inherited from a person’s parents. Scientists who research this topic typically use twin studies to determine the heritability of intelligence. The Minnesota Study of Twins Reared Apart is one of the most well-known twin studies. In this investigation, researchers found that identical twins raised together and identical twins raised apart exhibit a higher correlation between their IQ scores than siblings or fraternal twins raised together (Bouchard et al., 1990). The findings from this study reveal a genetic component to intelligence, also known as nature.

At the same time, other psychologists believe that intelligence is shaped by a child’s developmental environment, or the nurture that they receive. If parents were to provide their children with intellectual stimuli from before they are born, it is likely that they would absorb the benefits of that stimulation, and it would be reflected in intelligence levels.

The reality is that aspects of both nature and nurture affect intelligence. One study suggests that although genetics seem to be in control of the level of intelligence, the environment influences the manifestation of cognitive abilities (Bartels et al., 2002).

Range of Reaction

Range of reaction is the theory that each person responds to the environment in a unique way based on their genetic makeup. According to this idea, genetic potential is a fixed quantity, but whether full intellectual potential is reached depends on the environmental stimulation experienced, especially in childhood. Socioeconomic status, family life, nutrition, and quality of education are all environmental factors that can impact intelligence.

Think about this scenario: A couple adopts a child who has average genetic intellectual potential. They raise her in an extremely stimulating environment. What will happen to the couple’s new daughter? It is likely that the stimulating environment will improve her intellectual outcomes over the course of her life. But what happens if this experiment is reversed? If a child with an extremely strong genetic background is placed in an environment that does not stimulate them, it is likely that their intelligence will remain around an average level. The intelligence levels of all individuals seem to benefit from rich stimulation in their early environments.

Theories of Intelligence

The American Psychological Association defines intelligence as “the ability to derive information, learn from experience, adapt to the environment, understand, and correctly utilize thought and reason” (2018b). However, cognitive processes are complex, and describing them in a measurable way is challenging. Researchers have taken different approaches to define intelligence in an attempt to comprehensively describe and measure it.

Charles Spearman (1863–1945) was one of the first psychologists to attempt to define, measure, and test intelligence. He observed school children and noticed that their performance in unrelated classes was positively correlated; children who did well in one class were more likely to do well in others and children who struggled in one class tended to struggle in others (Spearman, 1904). He hypothesized that there must be a single underlying construct that affects cognitive abilities called the general intelligence factor ("g") (Spearman, 1904). Many psychologists now believe that “g” relates to abstract thinking and includes the abilities to acquire knowledge, to adapt to novel situations, and to benefit from instruction and experience (Gottfredson, 1997; Sternberg, 2003). 

However, Spearman acknowledged in his work that there are other attributes, or specific intelligence factors ("s"), that contribute to intelligence (Beaujean, 2019). These can be thought of as specific skills a person has that relate to certain intelligence tasks. For example, people working in a music-related field may have “s” that improves their performance on rhythm tasks.

Cattell’s Crystallized and Fluid Intelligence

In the 1940s, Raymond Cattell proposed a theory of intelligence that divided general intelligence into two components: crystallized intelligence and fluid intelligence (Cattell, 1963). Crystallized intelligence is characterized as acquired knowledge and the ability to retrieve it. When you learn, remember, and recall information, you are using crystallized intelligence. A student often uses crystallized intelligence by demonstrating mastery of course information on an exam. Fluid intelligence encompasses the ability to see complex relationships and solve problems. Navigating your way home after being detoured onto an unfamiliar route by road construction would draw upon your fluid intelligence. Fluid intelligence helps you tackle complex, abstract challenges in your daily life, whereas crystallized intelligence helps you overcome concrete, straightforward problems (Cattell, 1963).

Sternberg’s Triarchic Theory of Intelligence

Robert Sternberg is another advocate for the idea of multiple intelligences. Sternberg’s Triarchic Theory of Intelligence suggests that intelligence has three components: analytical intelligence, practical intelligence, and creative intelligence (Sternberg, 1997). People may display varying levels of each of these types of intelligence and they are not necessarily correlated with each other.

Analytical intelligence is closely aligned with academic problem solving, which includes the ability to analyze, evaluate, judge, compare, and contrast. When students analyze a short story or solve math problems, they are using analytical intelligence. Practical intelligence can be compared to common sense learned from life experiences, not from books or formal education. Think about the choice between going down a dark alley at night or walking along a lit sidewalk: practical intelligence would encourage the route that seems more likely to ensure a safe journey home. Creative intelligenceis the ability to adapt to new situations and create new ideas. Someone who can create a tower out of raw spaghetti and marshmallows likely has high creative intelligence.

Creativity

Creativity is often assessed as a function of one’s ability to engage in divergent thinking. Divergent thinking can be described as thinking “outside the box;” it allows an individual to arrive at multiple, unique solutions to a given problem even if they are wrong or unrealistic. In contrast, convergent thinking describes the ability to provide a correct and well-established solution to a problem (Cropley, 2006; Gilford, 1967). The brain areas associated with convergent and divergent thinking are different from each other, meaning that creativity and logical thinking are often separate processes within the brain (Tarasova et al., 2010). This may explain why creative intelligence is not highly correlated with analytical intelligence; exceptionally creative scientists, artists, mathematicians, and engineers do not score higher on intelligence tests than their less creative peers (Furnham & Bakhtiar, 2008; Simonton, 2000).

Gardner’s Theory of Multiple Intelligences

Howard Gardner argued that it is evolutionarily beneficial for people to have different talents, skills, and intelligences. Gardner’s Theory of Multiple Intelligences states that there are eight specific types of intelligence and people possess all of them in varying degrees (1983, 1999). See table 6.6.2 for a list of Gardner’s eight specific intelligences.

Table 6.6.2 Howard Gardner’s eight specific intelligences

Some have argued that these “intelligences” seem more like “abilities” or “talents” rather than real intelligence. There is no clear conclusion about how many intelligences there are. Are sense of humor, artistic skills, dramatic skills, and so forth also separate intelligences? Furthermore, the cognitive-based intelligences (linguistic, logical-mathematical, and spatial) are highly correlated, which shows continued evidence for the singular intelligence factor “g” (Visser et al., 2006).

The idea of multiple intelligences changed the field of education by encouraging personalized learning (Cuevas, 2015). While the Multiple Intelligences Theory is not explicitly about “learning styles,” or how students may best learn information, Gardner encouraged teachers to make learning as specific as possible to each student (Allcock & Hulme, 2010; Cuevas, 2015; Gardner, 1993). For instance, to teach math problems to students who have particularly good kinesthetic intelligence, a teacher might encourage them to move their bodies or hands according to the numbers.

Despite their popularity in educational settings, though, there is little evidence that teaching to a specific learning style improves understanding of material (Allcock & Hulme, 2010; Pashler et al., 2009; Yale, n.d.). In fact, learning styles may harm students who think they can only learn or study in one particular way (Zwaagstra, 2022). While it’s likely that students have a preference of how they would like to learn, catering to those preferences doesn’t ensure that they will learn better (Rogowsky et al., 2020).

Video 8.4 Theories of Intelligence reviews a few of the different theoretical views of intelligence.

Measuring Intelligence

The goal of most intelligence tests is to measure “g,” the general intelligence factor. Good intelligence tests are reliable (consistent over time) and valid (they actually measure intelligence rather than something else). Because intelligence is highly individualized, psychologists have invested substantial effort in creating and improving these measures.

The First Intelligence Test

From 1904-1905, French psychologists Alfred Binet (1857–1914) and Théodore Simon (1872–1961) worked for the French government to develop a measure to identify children who would be unsuccessful in the regular school curriculum so they could receive specialized education (Aiken, 1994). Binet and Simon developed what most psychologists today regard as the first intelligence test, the Binet-Simon test. It consisted of a wide variety of questions that included the ability to name objects, define words, draw pictures, complete sentences, compare items, and construct sentences.

Binet and Simon believed that the questions they asked the children assessed the basic abilities to understand, reason, and make judgments (Binet & Simon, 1915; Siegler, 1992). The correlations among these different types of measures were all positive; students who got one item correct were more likely to get other items correct as well, even though the questions themselves were very different from each other.

Soon after Binet and Simon introduced their test, the American psychologist Lewis Terman at Stanford University (1877–1956) developed an American version of Binet’s test known as the Stanford-Binet intelligence test. The Stanford-Binet measures general intelligence through a variety of tasks, including vocabulary, memory for pictures, naming of familiar objects, repeating sentences, and following commands.

The Wechsler Adult lntelligence Scale (WAIS) is the most widely used intelligence test for adults, but there are also versions for children and adolescents (Watkins et al., 1995). The WAIS consists of different tasks to assess intelligence, including working memory, arithmetic ability, spatial ability, and general knowledge about the world. The WAIS-IV, the current version of the test, yields scores on four domains: verbal, perceptual, working memory, and processing speed. It is correlated highly with other IQ tests, criteria for academic and life success, and measures of everyday function for people with intellectual disabilities.

Measuring Infant Intelligence

Intelligence tests for infants originally measured the development of motor, sensory, and language skills (Levine & Munsch, 2018). While these tests can help determine if a child is neurologically impaired or developmentally delayed, they are not highly correlated with cognitive abilities later in life (Levine & Munsch, 2018). However, information processing tests that measure how well a person can acquire, remember, and retrieve information are correlated with intellect (Fagan et al., 2007).

One common information processing test measures visual recognition memory, or if an infant can distinguish between what is new or familiar to them (Fagan et al., 2007; Levine & Munsch, 2018). This is often done through habituation tasks that measure attention and looking time. A researcher may show an infant an image of a car for 30 seconds, put it away, and then show 2 images: the original picture of the car and a new one of a tree. The researcher then records how long the infant looked at each image. Infants will usually spend about 60% of their time looking at the new image (Fagan et al., 2007).

Other techniques for measuring information processing test object permanence and cross-modal transfer. For object permanence, does the child recognize that an object still exists even if they can no longer see it? If a researcher shows them their favorite stuffed animal and then puts it under a towel in front of them, will they reach towards it? Cross-modal transfer tests measure if an infant recognizes an object using a different sense than they originally did (American Psychological Association, 2018a). For example, the infant might be handed a textured ball to play with, but a screen prevents them from seeing it. The textured ball is taken away and the infant is shown images of both a smooth and textured ball. Which one will they spend more time looking at? Studies show that infants will look longer at the unfamiliar object, like the smooth ball, than they will at the familiar object, such as the textured ball (Gottfried et al., 1977; Rose et al., 2009).

Performance on information processing tasks as an infant can predict an adolescent’s general intelligence, academic achievement, and specific cognitive abilities like perceptual reasoning and reading ability (Bornstein, 2013; Fagan et al., 2007; Rose et al., 1992).