We've studied human intelligence for centuries and still have few answers to what makes us think how we think and know what we know. Are men smarter than women, or vice versa? Are IQ tests biased? Does a bigger brain correlate to higher intellect?
What we do know about human intelligence has mostly been gleaned through intelligence testing (with IQ tests) that tends to focus on human analytical abilities. What we don't know far outweighs what we do know, but we have theories. Many, many theories. Here, we'll dive into 10 theories of human intelligence that have been disproved (or if not disproved, they've been highly criticized). Remember, a theory is just a guess until it's proven. One of these disproved theories may one day be proved. But for now, let's begin with whether or not heredity plays a role in human intelligence.
Are we born smart, or does intelligence change with age and experience? Scientists can't seem to agree.
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10: Heredity
If you're born to smart parents, will you also be smart? Some studies say yes, some say no. What is true is that heredity influences our intellectual quotient (IQ), which is how our cognitive abilities measure up to our peers'. But don't forget environment and culture's role in forming our intellect: How much is genes versus jeans? No one knows for sure, and the emerging data from ongoing research into the heritability of IQ could be anywhere from 40 to 80 percent [source: Norrgard].
Nature versus nurture is a controversial field of study, and the research being conducted today will help us understand not only our intelligence, but also human traits and behaviors, and possibly even the basis of some mental illnesses. What's important about this theory is that it advances the idea that race doesn't determine human intelligence, and that no one single element, such as heredity, determines a person's intellectual capacity and potential for achievement.
Will your daughter inherit your intelligence? Scientists aren't sure whether intelligence is heritable or a product of environment.
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9: Craniometry
Nineteenth-century scientists considered the idea of measuring skull and facial structure to be a good way of measuring a person's intelligence. When this theory began, surgeon Paul Broca theorized that the smaller the length ratio of forearm to upper arm, the greater the intelligence. When he couldn't prove that whites were the most intelligent race based on arm length, he turned to measuring skulls and facial structure to determine if cranial capacity -- how much brain can fit inside a skull -- would be a more accurate way to determine intellect. Craniometry measures the bones of the skull, because the bigger the skull, the bigger the brain -- and big brains meant big intellect.
The practice of craniometry died out in the early 20th century, criticized for its racial bias and lack of factual basis, but the scientists pursuing the theory did help to discover the brain's speech center as well as the concept of an intellectual quotient, or what we know as IQ.
8: Primary Mental Abilities
In the early half of the 20th century, psychologist L.L. Thurstone gave us the idea of primary mental abilities, a set of seven components that he theorized made up human intelligence. This differed from popular theories, which were all based on the idea that human intelligence is based on a single factor -- this is an argument still unsolved today.
The components or abilities that Thurstone described as intelligence included associative memory, numerical ability, perceptual speed, reasoning ability, spacial visualization, verbal comprehension and word fluency. While his seven abilities theory didn't stand the test of time, his work ignited the field of psychometrics, the quantitative study of psychology.
7: Birth Order
Researchers have long been studying how birth order influences everything from what your personality might be like to how intelligent you are. But a recent study published by the American Psychological Association (APA) finds that there's no direct link between your level of intelligence and your birth order within your family.
Scientists previously theorized that firstborn children score higher on IQ tests because they have no competition for parental attentions and therefore have more one-on-one time to learn from parents. Children born in the middle, or those who are youngest, were thought to have less parental time and therefore lower IQ scores. In the recent APA study, researchers compared siblings rather than comparing firstborns from different families, middle kids, and so on. They found that with this method of study, there really is no significant link between who was born first or last and who is most intelligent.
6: Single Intelligence
Some people will argue that the idea of single intelligence, a concept many theories are built upon, including the popular general intelligence factor (g factor), should be on this list. Others will argue that we're crazy for including it. Here's why it's included: A recent study found that there likely is such a thing as general intelligence, but it's not based on how a person's performance on intelligence tests compares to the general population. Gaining knowledge about how human intelligence works (or doesn't work) has so far been done through this type of testing, called psychometrics. But now, a study published in "Proceedings of the National Academy of Sciences" suggests that specific regions and network paths in the brain are involved in intelligence -- a step toward proving a biological basis for intelligence.
5: Tabula Rasa
Tabula rasa is the theory that humans are born with a blank mind. Philosophers and psychologists have kicked around this theory, also called blank slate, for centuries. It speculates that when we're born, our minds are fresh and empty, full of potential and waiting to be shaped by our personal life experiences and emotions.
These days, it's still an arguable concept -- nature versus nurture. Are we solely creatures of nature? What role does our environment play? Studies in the last few decades have specifically looked at twins separated at birth for answers because they carry the same genetic makeup but have differing environmental influences. Scientists have found that human intelligence -- along with other individual traits such as gender identity -- is most likely derived from a combination of the genes we inherit (nature) mixed with our individual experiences and environment (nurture).
4: IQ Tests
IQ tests, or intelligence quotient tests, are commonly used to evaluate a person's cognitive abilities, measuring intellect and achievement. School districts, psychologists, the military and college preparatory courses offer different types of IQ tests to measure a person's knowledge potential. Standardized IQ tests, such as the Stanford-Binet (administered to exceptionally gifted children) or the SAT, measure an individual's cognitive abilities against a population.
While IQ testing may still be in popular use, it's important to recognize that IQ tests are widely criticized. Critics of IQ testing argue that these types of tests are biased by gender, race, socioeconomic status and cultural heritage. They say that the tests are often based on an outdated notion that our intelligence capacity is something set at birth and that intelligence doesn't change as we experience life.
IQ tests are still in use, but don't take the results too seriously. Many psychologists challenge that the tests are biased.
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3: Triarchic Theory
When Robert Sternberg developed the triarchic theory of human intelligence, he went against common theories that suggest humans have a general intelligence factor, g factor, or general mental ability. Sternberg didn't consider intelligence as academic in nature. Instead, he theorized that people have something called practical intelligence, which is different from but equal to academic intelligence.
The theory is made up of three sub-theories: contextual, componential and experiential. The contextual component is how your intelligence relates to your external world experiences. The componential component is how your intelligence relates to your internal world. And the experiential factor is how you adapt to situations and perform tasks. This experiential factor is broken into two categories: how you handle new experiences and tasks (novel) and how you handle well-known, repeated experiences and tasks (automation).
Critics of the triarchic theory argue that what Sternberg describes is more of a set of practical skills than an explanation of human intelligence. They also claim that Sternberg neglects to back up his theory with direct observation and experience.
2: Theory of Multiple Intelligences
While the tabula rasa theory suggests that humans are born with a single, blank cognitive state ready to be shaped, the theory of multiple intelligences explains that human intelligence is made up of several types of intelligence. The theory's creator, Howard Gardner, suggests human intelligence lies in our abilities to create or provide value, to solve problems and to expand our knowledge by solving problems. He proposes that these nine intelligences are inherent in all of us and combine to make up our unique personal intelligence:
Although this theory hasn't been disproved and isn't outdated -- the theory was developed in 1983 -- it has yet to be tested.
1: Gender and Intelligence
Men are from Mars, women are from Venus? While men and women may think differently, there's no evidence that either gender is innately more intelligent than the other.
What researchers have discovered is that when it comes to intelligence, people have two types of brains: One type has a significant amount of gray tissue (information processing centers), and a second type has a significant amount of white tissue (tissue that networks the information processing centers). The study found that female brains have about 10 times more white matter than male brains, and male brains have about 6.5 times more gray matter [source: ScienceDaily]. What does this mean? While men and women have different types of tissue in their brains, overall performance is equal -- we just excel at different types of tasks.
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