Intelligence (also called intellect) is an umbrella term used to describe a property of the mind that encompasses many related abilities, such as the capacities to reason, to plan, to solve problems, to think abstractly, to comprehend ideas, to use language, and to learn. There are several ways to define intelligence. In some cases, intelligence may include traits such as creativity, personality, character, knowledge, or wisdom. However, most psychologists prefer not to include these traits in the definition of intelligence.
Theories of intelligence can be divided into those based on a unilinear construct of general intelligence and those based on multiple intelligences. Francis Galton, influenced by Charles Darwin, was first to advance a theory of general intelligence. For Galton, intelligence was a real faculty with a biological basis that could be studied by measuring reaction times to certain cognitive tasks.[1]
Alfred Binet and the French school of intelligence believed that intelligence quotient (IQ) was an average of numerous dissimilar abilities, rather than a real thing with specific identifiable properties. The Stanford-Binet intelligence test has been used by both theorists of general intelligence and multiple intelligence. It is, however, the basis for the development of various theories of multiple intelligence.[1]
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Intelligence comes from the Latin verb "intellegere", which means "to understand". By this rationale, intelligence (as understanding) is arguably different from being "smart" (able to adapt to one's environment), or being "clever" (able to creatively adapt).
At least two major "consensus" definitions of intelligence have been proposed. First, from Intelligence: Knowns and Unknowns, a report of a task force convened by the American Psychological Association in 1995:
Individuals differ from one another in their ability to understand complex ideas, to adapt effectively to the environment, to learn from experience, to engage in various forms of reasoning, to overcome obstacles by taking thought. Although these individual differences can be substantial, they are never entirely consistent: a given person’s intellectual performance will vary on different occasions, in different domains, as judged by different criteria. Concepts of "intelligence" are attempts to clarify and organize this complex set of phenomena. Although considerable clarity has been achieved in some areas, no such conceptualization has yet answered all the important questions and none commands universal assent. Indeed, when two dozen prominent theorists were recently asked to define intelligence, they gave two dozen somewhat different definitions.[2][3]
A second definition of intelligence comes from "Mainstream Science on Intelligence", which was signed by 52 intelligence researchers in 1994:
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.[4]
Another simple and efficient definition is : the ability to apply knowledge in order to perform better in an environment
Researchers in the fields of psychology and learning have also defined human intelligence:
| Researcher | Quotation |
|---|---|
| Alfred Binet | [J]udgment, otherwise called good sense, practical sense, initiative, the faculty of adapting one's self to circumstances...auto-critique.[5] |
| David Wechsler | [T]he aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with his environment.[6] |
| Cyril Burt | [I]nnate general cognitive ability[7] |
| Howard Gardner | To my mind, a human intellectual competence must entail a set of skills of problem solving—enabling the individual to resolve genuine problems or difficulties that he or she encounters and, when appropriate, to create an effective product—and must also entail the potential for finding or creating problems—and thereby laying the groundwork for the acquisition of new knowledge.[8] |
| Linda Gottfredson | [T]he ability to deal with cognitive complexity[9] |
| Sternberg & Salter | [G]oal-directed adaptive behavior[10] |
The most widely accepted theory of intelligence is based on psychometrics testing or intelligence quotient (IQ) tests. However, dissatisfaction with traditional IQ tests has led to the development of a number of alternative theories, all of which suggest that intelligence is the result of a number of independent abilities that uniquely contribute to human performance.
Despite the variety of concepts of intelligence, the approach to understanding intelligence with the most supporters and published research over the longest period of time is based on psychometrics testing. Such intelligence quotient (IQ) tests include the Stanford-Binet, Raven's Progressive Matrices, the Wechsler Adult Intelligence Scale and the Kaufman Assessment Battery for Children.
All forms of IQ tests correlate highly with one another. The traditional view is that these tests measure g or "general intelligence factor". However, this is by no means universally accepted. Charles Spearman is credited with having developed the concept of g. g can be derived as the principal factor using the mathematical method of factor analysis. One common view is that these abilities are hierarchically arranged with g at the vertex (or top, overlaying all other cognitive abilities). G itself is sometimes considered to be a two part construct, gF and gC, which stand for fluid and crystallized intelligence.[11][12] Carroll expanded this hierarchy into a Three-Stratum theory, also known as the Cattell-Horn-Carroll theory of cognitive abilities (or simply CHC Theory).[13]
Intelligence, as measured by IQ and other aptitude tests, is widely used in educational, business, and military settings due to its efficacy in predicting behavior. G is highly 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.[14] Intelligence is significantly correlated with successful training and performance outcomes, and g is the single best predictor of successful job performance.[15]
IQ tests were originally devised specifically to predict educational achievement. The inventors of the IQ did not believe they were measuring fixed intelligence. Despite this, critics argue that intelligence tests have been used to support nativistic theories in which intelligence is viewed as a qualitatively unique faculty with a relatively fixed quantity.[16]
Critics of the psychometric approach point out that people in the general population have a somewhat different and broader conception of intelligence than what is measured in IQ tests. In turn, they argue that the psychometric approach measures only a part of what is commonly understood as intelligence. Furthermore, skeptics argue that even though tests of mental abilities are correlated, people still have unique strengths and weaknesses in specific areas. Consequently they argue that psychometric theorists over-emphasize g.
Researchers in the field of human intelligence have encountered a considerable amount of public concern and criticism-- much more than scientists in other areas normally receive. A number of critics have challenged the relevance of psychometric intelligence in the context of everyday life. There have also been controversies over genetic factors in intelligence, particularly questions regarding the relationship between race and intelligence and sex and intelligence. Another controversy in the field is how to interpret the increases in test scores that have occurred over time, the so-called Flynn effect.
Stephen Jay Gould was one of the most vocal critics of intelligence testing. In his book, The Mismeasure of Man, Gould argued that intelligence is not truly measurable, and also challenged the hereditarian viewpoint on intelligence. Many of Gould's criticisms were aimed at Arthur Jensen, who responded that his work had been misrepresented,[17] also stating that making conclusions about modern IQ tests by criticizing the flaws of early intelligence research is like condemning the auto industry by criticizing the performance of the Model T.
Howard Gardner's theory of multiple intelligences is based on studies not only on normal children and adults but also by studies of gifted individuals (including so-called "savants"), of persons who have suffered brain damage, of experts and virtuosos, and of individuals from diverse cultures. This led Gardner to break intelligence down into at least eight different components: logical, linguistic, spatial, musical, kinesthetic, naturalist, intrapersonal and interpersonal intelligences. He argues that psychometric tests address only linguistic and logical plus some aspects of spatial intelligence; other forms have been entirely ignored. Moreover, the paper and-pencil format of most tests rules out many kinds of intelligent performance that matter in everyday life, as social intelligence.[18]
Most of theories of multiple intelligences are relatively recent in origin, though Louis Thurstone proposed a theory of multiple "primary abilities" in the early 20th Century.
Robert Sternberg's triarchic theory of intelligence proposes three fundamental aspects of intelligence-analytic, creative, and practical--of which only the first is measured to any significant extent by mainstream tests. His investigations suggest the need for a balance between analytic intelligence, on the one hand, and creative and especially practical intelligence on the other.
Daniel Goleman and several other researchers have developed the concept of emotional intelligence and claim it is at least as "important" as more traditional sorts of intelligence. These theories grew from observations of human development and of brain injury victims who demonstrate an acute loss of a particular cognitive function -- e.g. the ability to think numerically, or the ability to understand written language -- without showing any loss in other cognitive areas.
IQ proponents have pointed out that IQ's predictive validity has been repeatedly demonstrated, for example in predicting important non-academic outcomes such as job performance (see IQ), whereas the various multiple intelligence theories have little or no such support. Meanwhile, the relevance and even the existence of multiple intelligences have not been borne out when actually tested. A set of ability tests that do not correlate together would support the claim that multiple intelligences are independent of each other. However, thus far no one has developed such a set of tests.
Our hominid and human ancestors evolved large and complex brains exhibiting an ever-increasing intelligence through a long and mostly unknown evolutionary process. This process was either driven by the direct adaptive benefits of intelligence[19], or − alternatively − driven by its indirect benefits within the context of sexual selection as a reliable signal of genetic resistance against pathogens.[20]
Intelligence is an ill-defined, difficult to quantify concept. Accordingly, the IQ tests used to measure intelligence provide only approximations of the posited 'real' intelligence. In addition, a number of theoretically unrelated properties are known to correlate with IQ such as race, gender and height but since correlation does not imply causation the true relationship between these factors is uncertain. Factors affecting IQ may be divided into biological and environmental.
Evidence suggests that genetic variation has a significant impact on IQ, accounting for three fourths in adults. Despite the high heritability of IQ, few genes have been found to have a substantial effect on IQ, suggesting that IQ is the product of interaction between multiple genes.
Other biological factors correlating with IQ include ratio of brain weight to body weight and the volume and location of gray matter tissue in the brain.
Because intelligence appears to be at least partly dependent on brain structure and the genes shaping brain development, it has been proposed that genetic engineering could be used to enhance the intelligence of animals, a process sometimes called biological uplift in science fiction. Experiments on mice have demonstrated superior ability in learning and memory in various behavioural tasks.[21]
Evidence suggests that family environmental factors may have an effect upon childhood IQ, accounting for up to a quarter of the variance. On the other hand, by late adolescence this correlation disappears, such that adoptive siblings are no more similar in IQ than strangers.[22] Moreover, adoption studies indicate that, by adulthood, adoptive siblings are no more similar in IQ than strangers, while twins and full siblings show an IQ correlation.
Consequently, in the context of the nature versus nurture debate, the "nature" component appears to be much more important than the "nurture" component in explaining IQ variance in the general population.
Cultural factors also play a role in intelligence. For example, on a sorting task to measure intelligence, Westerners tend to take a taxonomic approach while the Kpelle people take a more functional approach. For example, instead of grouping food and tools into separate categories, a Kpelle participant stated "the knife goes with the orange because it cuts it"[23]
Since intelligence is susceptible to modification through the manipulation of environment, the ability to influence intelligence raises ethical issues. Transhumanist theorists study the possibilities and consequences of developing and using techniques to enhance human abilities and aptitudes, and ameliorate what it regards as undesirable and unnecessary aspects of the human condition; eugenics is a social philosophy which advocates the improvement of human hereditary traits through various forms of intervention.[24] The perception of eugenics has varied throughout history, from a social responsibility required of society, to an immoral, racist stance.
Neuroethics considers the ethical, legal and social implications of neuroscience, and deals with issues such as difference between treating a human neurological disease and enhancing the human brain, and how wealth impacts access to neurotechnology. Neuroethical issues interact with the ethics of human genetic engineering.
Although humans have been the primary focus of intelligence researchers, scientists have also attempted to investigate animal intelligence, or more broadly, animal cognition. These researchers are interested in studying both mental ability in a particular species, and comparing abilities between species. They study various measures of problem solving, as well as mathematical and language abilities. Some challenges in this area are defining intelligence so that it means the same thing across species (eg. comparing intelligence between literate humans and illiterate animals), and then operationalizing a measure that accurately compares mental ability across different species and contexts.
Wolfgang Köhler's pioneering research on the intelligence of apes is a classic example of research in this area. Stanley Coren's book, The Intelligence of Dogs is a notable popular book on the topic.[25] Nonhuman animals particularly noted and studied for their intelligence include chimpanzees, bonobos (notably the language-using Kanzi) and other great apes, dolphins, elephants and to some extent parrots and ravens. Controversy exists over the extent to which these judgments of intelligence are accurate.
Artificial intelligence (or AI) is both the intelligence of machines and the branch of computer science which aims to create it, through "the study and design of intelligent agents"[26] or "rational agents", where an intelligent agent is a system that perceives its environment and takes actions which maximize its chances of success.[27] General intelligence or strong AI has not yet been achieved and is a long-term goal of AI research.
Among the traits that researchers hope machines will exhibit are reasoning, knowledge, planning, learning, communication, perception and the ability to move and manipulate objects.[27][26]
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