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Intelligence can be defined as the ability to learn from experience, solve problems, and use knowledge to adapt to new situations. Simply Psychology states that intelligence “has been defined in many ways: higher level abilities (such as abstract reasoning, mental representation, problem solving, and decision making), the ability to learn, emotional knowledge, creativity, and adaptation to meet the demands of the environment effectively.” Specifically, psychologist Robert Sternberg defined intelligence as “the mental abilities necessary for adaptation to, as well as shaping and selection of, any environmental context.” With its many definitions, intelligence is a fascinating and multifaceted topic with a rich history and diverse explanations. 

History of Studying Intelligence 

To begin with Charles Spearman, an English psychologist, established the two-factor theory of intelligence in 1904, using factor analysis. By identifying custers of closely related test items, factor analysis revealed that people who did well in one skill area also tended to do well in others. Spearman called this “g,” or general intelligence across multiple abilities. 

Later, Louis Leon Thurstone, a psychologist and pioneer in psychometrics and psychophysics, challenged Spearman’s idea of one general measure and trait for overall intelligence. Thurstone found that the results of fifty-six skill tests fell into seven clusters, including spatial ability, memory, perceptual speed, numerical ability, verbal comprehension, inductive reasoning, word fluency. Thurstone’s theories that intelligence is made up of both general ability and specific abilities, he set the foundation for future examination of the different forms of intelligence.  

Building on Thurstone, in the early 1980’s, American psychologist Howard Garnder proposed eight intelligences: lin­guistic, logical-mathematical, musical, spatial, bodily-kinesthetic, intrapersonal, interpersonal, and naturalist. He believes that most tasks require a blend of these intelligences, which can also contribute to other traits, such as creativity. 

In 1985, Robert Sternberg introduced his intelligence triarchy theory, made up of analytical (academic problem solving), practical (everyday tasks), and creative (adapting to novel situations). In addition to these types of intelligences, Sternberg also proposed five components of creativity, or the ability to produce novel and valuable ideas. These include a creative environment, a venturesome personality, expertise, intrinsic motivation, and imaginative thinking.

Apart from these intelligences, emotional inetlligence plays a crucial role in socializing and succeeding in our everyday lifes. Emotional intelligence is made up of the ability to perceive, understand and manage/use emotions. Those who have high emotional intelligence- that is, can recognize emotion in faces, predict how emotions can change, and know how to express their own emotions- tend to have greater success in career and social situations. 

Intelligence and Brain Anatomy 

Brain anatomy does have a relationship with intelligence. There is a +.33 correlation with brain size, adjusted for body size, and intelligence scores. The size of the brain and activity in specific areas, particularly the frontal parietal lobes, is associated with intelligence. Most importantly, having enough gray matter (brain cell bodies) and white matter (axons) increases the efficiency of communication between brain centers, thus increasing processing speed. Those who perceive quickly are especially likely to get higher scores on verbal tests, and score somewhat higher on intelligence tests. 

Intelligence Tests

Intelligence tests assess people’s mental abilities and compare them with those of others, using numerical scores. Working with Théodore Simon, French psychologist Alfred Binet developed an intelligence test to predict children’s success in the Paris school system. To do so, he determined the child’s mental age, or the chronological age that most typically corresponds to a given level of performance. Later, Stanford Lewis Terman adapted the test to extend to adulthood, forming the Stanford-Binet IQ test. One’s intelligence quotient (IQ) is calculated by dividing one’s mental age by their chronological age and multiplying that quotient by 100. 

Currently, the Wechsler Adult Intelligence Scale (WAIS) is the most widely used intelligence test by measuring IQ and sub-scores for verbal, speed, spatial, and memory intelligence. There are two types of tests used when discussing intelligence, including aptitude tests, which are designed to predict an individual’s future performance, and achievement tests, which assess what a person has learned. 

When creating tests, standardization is crucial as it bases scores on a comparison with the pperformacne of others who have taken the test. This results in a normal curve in which less and less people are part of the group toward the edges. According to the Wechsler intelligence score, about 68% of people score within fifteen points above or below 100, while about 95% of people fall within thirty points of 100. The Flynn Effect forces the re-standardization (updates) of tests since IQ has improved over the years worldwide. Some reasons for this increase are nutrition, education, and parental involvement. 

To determine whether tests are reliable, researchers establish split-half reliability, in which each half of a test yields similar results. To determine test-retest reliability, researchers make sure that if an individual takes the tests multiple times, the results would be the same. Also, content validity is important so that the test measures what it is meant to through correlations in results. Lastly, predictive validity means that the test accurately predicts future performance. One test used to predict future performance is the SAT, which is used to gauge a student’s readiness for college. Some argue that the SAT unfairly judges students because of other factors affecting students’ performance, including access to resources for studying and other educational opportunities.

Criticism of Intelligence Tests 

Critics of intelligence tests argue that they only test a narrow range of intelligence by minimizing the importance of creativity and the conditional influences of motivation, emotion, and attitudes. In addition, a racial gap in intelligence scores demonstrates the effect of environmental factors and test bias. 

The average IQ score for African American was 85, while the average for white people is 100. According to genetics research, races are remarkably similar under the skin and when different races received similar knowledge, they showed the same information-processing skills. Environmental effects prove to be crucial in the influence of the resources provided by school and culture. In addition, the stereotype threat plays a role in explaining these differences as it is the feeling that one will be evaluated based on negative stereotypes. When someone is worried about how they think they will do, they will likely perform worse, showing how anxiety over racial stereotypes can lower scores. 

Intelligence tests can also negatively influence education for children at schools with gifted programs. Under the extremes of intelligence, having intellectual disability is a score below 70 IQ, causing difficulty with adaptive abilities including conceptual skills, social skills, and executive function. On the other hand, those who are gifted and talented have an IQ of 130 or above. “Gifted” children are often tested and placed in separated, tracked programs. Critics argue that these programs unfairly widens the achievement gap between children, preventing students from interacting and learning from each other. 

Influences on Intelligence 

Heritability refers to the proportion of variation among individuals that can be attributed to genes; the heritability of intelligence is estimated to be between 50% and 80%. Intelligence is polygenetic, meaning that many genes contribute to this trait. Twin and adoption studies demonstrate the impact of genes. For instance, identical twins have similar specific talents, such as music, and the intelligence of adoptees is more similar to their birth parents than adoptive parents.  

Environment influences also greatly impact intelligence. For instance, under extremely harsh conditions, intelligence can decrease, such as abuse, neglect, and poverty. A child’s home environment, including their parents’ parenting style, as well as the availability of learning resources and nutrition contribute to intelligence. Schooling can affect intelligence with the quality of preschool and grade school, as well as additional education through college. College can increase IQ scores if students are willing to truly learn and practice skills. Furthermore, the intelligence scores of identical twins raised together are more similar than identical twins raised apart, showing that the environment works alongside genetics to influence intelligence. 


Overall, intelligence helps us make sense of the world by giving us the capacity for logical thinking, self-awareness, emotional development, creativity, and problem solving. Despite their drawbacks, intelligence tests give us insight into how intelligence differs over time and among groups. Nevertheless, intelligence is a blend of our genetics passed through generations, and our environments. 


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