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Is Intelligence Nature or Nurture?

24 September, 2015 - 10:26

Intelligence has both genetic a nd environmental causes, and these have been systematically studied through a large number of twin and adoption studies (Neisser et al., 1996; Plomin, DeFries, Craig, & McGuffin, 2003). 1 These studies have found that between 40% and 80% of the variability in IQ is due to genetics, meaning that overall genetics plays a bigger role than does environment in creating IQ differences among individuals (Plomin & Spinath, 2004). 2 The IQs of identical twins correlate very highly (r = .86), much higher than do the scores of fraternal twins who are less genetically similar (r = .60). And the correlations between the IQs of parents and their biological children (r= .42) is significantly greater than the correlation between parents and adopted children (r = .19). The role of genetics gets stronger a s children get older. The intelligence of very young children (less than 3 years old) does not predict adult intelligence, but by age 7 it does, and IQ scores remain very stable in adulthood (Deary, Whiteman, Starr, Whalley, & Fox, 2004). 3

But there is also evidence for the role of nurture, indicating that individuals are not born with fixed, unchangeable levels of intelligence. Twins raised together in the same home have more similar IQs than do twins who are raised in different homes, and fraternal twins have more similar IQs than do nontwin siblings, which is likely due to the fact that they are treated more similarly than are siblings.

The fact that intelligence becomes more stable as we get older provides evidence that early environmental experiences matter more than later ones. Environmental factors also explain a greater proportion of the variance in intelligence for children from lower-class households than they do for children from upper-class households (Turkheimer, Haley, Waldron, D’Onofrio, & Gottesman, 2003). 4 This is because most upper-class households tend to provide a safe, nutritious, and supporting environment for children, whereas these factors are more variable in lower-class households.

Social and economic deprivation can adversely affect IQ. Children from households in poverty have lower IQs than do children from households with more resources even when other factors such as education, race, and parenting are controlled (Brooks-Gunn & Duncan, 1997). 5 Poverty may lead to diets that are undernourishing or lacking in appropriate vitamins, and poor children may also be more likely to be exposed to toxins such as lead in drinking water, dust, or paint chips (Bellinger & Needleman, 2003). 6 Both of these factors can slow brain development and reduce intelligence.

If impoverished environments can harm intelligence, we might wonder whether enriched environments can improve it. Government-funded after-school programs such as Head Start are designed to help children learn. Research has found that attending such programs may increase intelligence for a short time, but these increases rarely last after the programs end (McLoyd, 1998; Perkins & Grotzer, 1997). 7 But other studies suggest that Head Start and similar programs may improve emotional intelligence and reduce the likelihood that children will drop out of school or be held back a grade (Reynolds, Temple, Robertson, & Mann 2001). 8

Intelligence is improved by education; the number of years a person has spent in school correlates at about r = .6 with IQ (Ceci, 1991). 9 In part this correlation may be due to the fact that people with higher IQ scores enjoy taking classes more than people with low IQ scores, and they thus are more likely to stay in school. But education also has a causal effect on IQ. Comparisons between children who are a lmost exactly the same age but who just do or just do not make a deadline for entering school in a given school year show that those who enter school a year earlier have higher IQ than those who have to wait until the next year to begin school (Baltes & Reinert, 1969; Ceci & Williams, 1997). 10 Children’s IQs tend to drop significantly during summer vacations (Huttenlocher, Levine, & Vevea, 1998), 11 a finding that suggests that a longer school year, as is used in Europe a nd East Asia, is beneficial.

It is important to remember that the relative roles of nature and nurture can never be completely separated. A child who has higher than average intelligence will be treated differently than a child who has lower than average intelligence, and these differences in behaviors will likely amplify initial differences. This means that modest genetic differences can be multiplied into big differences over time.

Psychology in Everyday Life: Emotional Intelligence

Although most psychologists have considered intelligence a cognitive ability, people also use their emotions to help them solve problems and relate effectively to others. Emotional intelligence refers to theability toaccurately identify,assess,andunderstand emotions,as wellastoeffectively control ones own emotions(Feldman-Barrett & Salovey, 2002; Mayer, Salovey, & Caruso, 2000). 12

The idea of emotional intelligence is seen in Howard Gardner’sinterpersonal intelligence(the capacity to understand the emotions, intentions, motivations, and desires of other people) and intrapersonalintelligence(the capacity to understand oneself, including one’s emotions). Public interest in, and research on, emotional intellgence became widely prevalent following the publication of Daniel Goleman’s best-selling book,EmotionalIntelligence: Why It CanMatter More Than IQ (Goleman, 1998). 13

There are a variety of measures of emotional intelligence (Mayer, Salovey, & Caruso, 2008; Petrides & Furnham, 2000). 14 One popular measure, the Mayer-Salovey-Caruso Emotional Intelligence Test (, includes items about the ability to understand, experience, and manage emotions, such as these:

  • What mood(s) might be helpful to feel when meeting in-laws for the very first time?
  • Tom felt anxious and became a bit stressed when he thought about all the work he needed to do. When his supervisor brought him an additional project, he felt   (fill in the blank).
  • Contempt most closely combines which two emotions?
  1. anger and fear
  2. fear and surprise
  3. disgust and anger
  4. surprise and disgust
  • Debbie just came back from vacation. She was feeling peaceful and content. How well would each of the following actions help her preserve her good mood?
  • Action 1: She started to make a list of things at home that she needed to do.
  • Action 2: She began thinking about where and when she would go on her next vacation.
  • Action 3: She decided it was best to ignore the feeling since it wouldn't last anyway.

One problem with emotional intelligence tests is that they often do not show a great deal of reliability or construct validity (Føllesdal & Hagtvet, 2009). 15 Although it has been found that people with higher emotional intelligence are also healthier (Martins, Ramalho, & Morin, 2010), 16findings are mixed about whether emotional intelligence predicts life success—for instance, job performance (Harms & Credé, 2010). 17Furthermore, other researchers have questioned the construct validity of the measures, arguing that emotional intelligence really measures knowledge about what emotions are, but not necessarily how to use those emotions (Brody, 2004), 18 and that emotional intelligence is actually a personality trait, a part of g, o r a skill that can be applied in some specific work situations— for instance, academic and work situations (Landy, 2005). 19

Although measures of the ability to understand, experience, and manage emotions may not predict effective behaviors, another important aspect of emotional intelligence—emotionregulation—does. Emotion regulation refers to the ability to control and productively use one’s emotions. Research has found that people who are better able to override their impulses to seek immediate gratification and who are less impulsive also have higher cognitive and social intelligence. They have better SAT scores, are rated by their friends as more socially adept, and cope with frustration and stress better than those with less skill at emotion regulation (Ayduk e t al., 2000; Eigsti et al., 2006; Mischel & Ayduk, 2004). 20

Because emotional intelligence seems so important, many school systems have designed programs to teach it to their students. However, the effectiveness of these programs has not been rigorously tested, and we do not yet know whether emotional intelligence can be taught, or if learning it would improve the quality of people’s lives (Mayer & Cobb, 2000). 21


  • Intelligence is the ability to think, to learn from experience, to solve problems, and to adapt to new situations. Intelligence is important because it has an impact on many human behaviors.
  • Psychologists believe that there is a construct that accounts for the overall differences in intelligence among people, known as general intelligence (g).
  • There is also evidence for specific intelligences (s), measures of specific skills in narrow domains, including creativity and practical intelligence.
  • The intelligence quotient (IQ) is a measure of intelligence that is adjusted for age. The Wechsler Adult lntelligence Scale (WAIS) is the most widely used IQ test for adults.
  • Brain volume, speed of neural transmission, and working memory capacity are related to IQ.
  • Between 40% and 80% of the variability in IQ is due to genetics, meaning that overall genetics plays a bigger role than does environment in creating IQ differences among individuals.
  • Intelligence is improved by education and may be hindered by environmental factors such as poverty.
  • Emotional intelligence refers to the ability to identify, assess, manage, and control one’s emotions. People who are better able to regulate their behaviors and emotions are also more successful in their personal and social encounters.


  1. Consider your own IQ. Are you smarter than the average person? What specific intelligences do you think you excel in?
  2. Did your parents try to improve your intelligence? Do you think their efforts were successful?
  3. Consider the meaning of the Flynn effect. Do you think people are really getting smarter?
  4. Give some examples of how emotional intelligence (or the lack of it) influences your everyday life and the lives of other people you know.