Human intelligence: one or many?

Intelligence is most widely studied in humans. Animals and plants also are endowed with intelligence. Yes, plants do have intelligence. A botanist may vouchsafe that plant intelligence is the ability of plants to sense the environment and adjust their morphology, physiology, and phenotype accordingly. “Ability” is the phenomenal aspect of the intelligence. Artificial intelligence is the simulation of human intelligence in machines. 

What really is intelligence?

The definition of intelligence is controversial. In 1994 the Harvard psychologist Richard J. Herrnstein and political scientist Charles Murray published a book The Bell Curve which soon became controversial and best-selling. The book's title comes from the bell-shaped normal distribution of intelligence quotient (IQ) scores in a population. The central argument in the book is that intelligence is influenced by both inherited and environmental factors. The book also argues that those with high intelligence, the “cognitive elite”, are becoming separated from those of average and below-average intelligence, and that this is a dangerous social trend with the United States moving toward a more divided society similar to that in Latin America.

Much of the controversy concerned the parts of the book in which the authors wrote about racial differences in intelligence and discuss the implications of those differences. The authors were reported throughout the popular press as arguing that these IQ differences are genetic; however, they wrote in chapter 13: "It seems highly likely to us that both genes and the environment have something to do with racial differences."  The introduction to the chapter more cautiously states, "The debate about whether and how much genes and environment have to do with ethnic differences remains unresolved."  Shortly after publication, many people rallied both in criticism and defense of the book.

“Mainstream Science on Intelligence”  was a public statement issued by a group of 52 academic researchers in the fields allied to intelligence testing. It was originally published in the Wall Street Journal in December 13, 1994. The statement says: “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.”

Intelligence tests

Intelligence tests are widely used in educational, business, and military settings due to their efficacy in predicting behavior. Intelligence quotient (IQ) is the number arrived at by dividing the mental age with chronological age and then multiplying with 100. The mental age is assessed through intelligence tests. Average IQ is 100. The IQ is correlated with many important social outcomes—individuals with low IQs are more likely to be divorced, have a child out of marriage, be incarcerated, and need long-term welfare support, while individuals with high IQs are associated with more years of education, higher status jobs and higher income. Intelligence is significantly correlated with successful training and performance outcomes, and IQ is the single best predictor of successful job performance.

Core of human intelligence or g

Charles Edward Spearman 

Specific abilities and G factor

There are many different kinds of IQ tests using a wide variety of test tasks. Some tests consist of a single type of task, others rely on a broad collection of tasks with different contents including visual-spatial, verbal, numerical tasks and asking for different cognitive processes such as reasoning, memory, rapid decisions, visual comparisons, spatial imagery, reading, and retrieval of general knowledge. The British psychologist Charles Edward Spearman found that a single common factor explained the positive correlations among different tasks of an intelligence test. Spearman named it g or "general intelligence factor". He interpreted it as the core of human intelligence that, to a larger or smaller degree, influences success in all cognitive tasks and thereby creates the positive manifold. This interpretation of g as a common cause of test performance is still dominant in intelligence tests.

Multiple intelligences

The American developmental psychologist Howard Earl Gardner proposed the theory of multiple intelligences based on studies not only of normal children and adults but also of gifted individuals called savants and prodigies and of persons who have suffered brain damage. This led Gardner to break intelligence down into at least eight different components: logical, linguistic, spatial, musical, kinesthetic pertaining to body-movements, interpersonal, naturalist pertaining to environment, and existential. 

Howard Earl Gardner 

1. Logical/Mathematical intelligence: This area has to do with logic, abstractions, reasoning and numbers and critical thinking. While it is often assumed that those with this intelligence naturally excel in mathematics, chess, computer programming and other logical or numerical activities. Logical reasoning is closely linked to fluid intelligence and to general ability.

2. Spatial intelligence: This area deals with spatial judgment and the ability to visualize with the mind's eye. Careers which suit those with this type of intelligence include artists, designers and architects. A spatial person is also good with puzzles.

3. Verbal/Linguistic intelligence: This area has to do with words, spoken or written. People with high verbal-linguistic intelligence display a facility with words and languages. They are typically good at reading, writing, telling stories and memorizing words along with dates. They tend to learn best by reading, taking notes, listening to lectures, and by discussing and debating about what they have learned. Those with verbal-linguistic intelligence learn foreign languages very easily as they have high verbal memory and recall, and an ability to understand and manipulate syntax and structure. Verbal ability is one of the most g-loaded abilities.

4. Kinesthetic/Bodily intelligence: The core elements of the bodily-kinesthetic intelligence are control of one's bodily motions and the capacity to handle objects skillfully. Gardner elaborates to say that this intelligence also includes a sense of timing, a clear sense of the goal of a physical action, along with the ability to train responses so they become like reflexes. In theory, people who have bodily-kinesthetic intelligence should learn better by involving muscular movement. They are generally good at physical activities such as sports or dance. They may enjoy acting or performing, and in general they are good at building and making things.

5. Musical intelligence: This area has to do with sensitivity to sounds, rhythms, tones, and music. People with a high musical intelligence normally have good pitch and are able to sing, play musical instruments, and compose music. Since there is a strong auditory component to this intelligence, those who are strongest in it may learn best via lecture. Language skills are typically highly developed in those whose base intelligence is musical. In addition, they will sometimes use songs or rhythms to learn. They have sensitivity to rhythm, pitch, meter, tone, melody or timbre.

6. a. Interpersonal intelligence:  Interpersonal intelligence is the ability to understand others. In theory, individuals who have high interpersonal intelligence are characterized by their sensitivity to others' moods, feelings, temperaments and motivations, and their ability to cooperate in order to work as part of a group.

6. b. Intrapersonal intelligence: This area has to do with introspective and self-reflective capacities. This refers to having a deep understanding of the self; what your strengths/ weaknesses are, what makes you unique, being able to predict your own reactions/emotions. Philosophical and critical thinking is common with this intelligence. Many people with this intelligence are authors, philosophers, and members of clergy.

7. Naturalistic intelligence: This area to do with nurturing and relating information to one’s natural surroundings. They become naturalists, farmers and gardeners.

8. Existential intelligence: Some proponents of multiple intelligence theory proposed spiritual or religious intelligence as a possible additional type. Gardner did not want to commit to a spiritual intelligence, but suggested that an “existential” intelligence may be a useful construct.

It seems that Gardner crystallized and categorized different facets of human intelligence into distinct types of intelligence. In individual with high general intelligence different abilities may develop in appropriate circumstances if properly motivated, supported and persevered.