Intelligence

Introduction

    Intelligence is perhaps the most prized trait a human being can have. Society puts a lot of focus on being smart and those who show high intellect are often held in high esteem. [2] There is a reason, after all, that we spend over a quarter of our lives attending schools that try and make us as smart as we can be. This raises a question. Is intelligence something that someone can attain or something they are born with? How do we define intelligence? Is it simply getting good grades and doing well on standardized tests, or is it something more? Scientists have worked hard to try and define intelligence, and there is still no clear universal definition. We know that intelligence is a very general term that describes a wide variety of abilities. It encompasses the reasoning and understanding of one's immediate environment, facts, truths, and meanings. [1]

The Physical Brain

Size
    To understand intelligence, it might be best to start at the source-- the physical brain. The human brain weighs an average of 3 pounds. It has long been implied that bigger brains equal more intelligence. This, of course, is not the case. Humans are more intelligent than elephants despite the fact that elephants have brains which weigh around 12 pounds. [3] The important thing to realize here is that humans have the highest brain-to-body-mass ratio of almost all the animals; bigger than the elephants. So in relation to bodies, humans have rather big brains. The theory is that if a brain is larger than normal and the body is relatively small, then more resources will be able to go toward higher level thinking rather than the autonomic nervous system and other housekeeping. [4] The theory, however nice it may sound, is not supported by science. Very few studies have been done to try and figure out whether brain size correlates with intelligence, and any studies which have been done provide little or no evidence of relationship. It is also noteworthy to point out that there are animals with higher brain-to-body-mass ratios than humans, like the shrew which has a brain that is 10% of its entire body weight. [5] The human brain makes up about 2% of entire body weight. So with size out of the way we can investigate other physical possibilities.
Gray and White Matter
    Intelligence does have to do with the actual construction of the brain; especially the amount of gray and white matter. Gray matter consists of neuron cell bodies, dendrites, axon terminals, and glial cells. [6] Gray matter is the brain's processing center and is an important part of the central nervous system. The cortex covering the brain is mostly gray matter. White matter is tissue that contains many long axons, and therefore carries information throughout the brain and body. [8] It is white because of the myelin insulation surrounding the axons. The spinal cord is mostly white matter.
    Since gray matter is where most of our thinking takes place, then it would make sense the more gray matter someone has the smarter they are. A study done by the University of California, Irvine and the University of New Mexico used brain imaging techniques to look at the brains of 47 adults. The adults then took an IQ test. It turned out that the brains with more gray matter in the frontal, temporal, parietal, and occipital lobes were smarter than the brains with less gray matter in these areas. [7] This study showed that intelligence comes from many areas of the brain, and that certain skills may be dependent on the distribution of gray matter in these areas of the brain.

Intelligence Tests

    Professionals have devised different tests with the purpose of measuring intelligence. Some hone in on certain skills or intelligences while others will cover a broad scope of everything we believe makes a person bright.

Wechsler Adult Intelligence Scale Version III (WAIS-III)

    The Wechsler Adult Intelligence Scale Version III (WAIS-III) was created in 1955 by the Psychological Corporation of the United States and United Kingdom. It is one of the most rigorous intelligence tests of all time. The WAIS-III is designed for people 16 years and older and can be administered only by professionals on a one-on-one basis following strict guidelines. [9] Because the WAIS-III is a test performed under very strict conditions, it usually gives a very reliable reading of one's mental capabilities.
    The WAIS-III is comprised of the following categories and tests. [10]
Verbal Comprehension
    These focus on the verbal abilities, testing the understanding a person has of their primary language.

• Vocabulary - To see the knowledge a person has of specific words.
• Comprehension - These are questions that relate to everyday situations, problems, or proverbs. This might mean reading a literary passage and then answering questions about the characters, plot, or sentences. It might ask if a person understands what is meant by statements like 'Has the cat got your tongue?'.
• Similarities - This tests a person's ability to explain what words have in common with one another, like 'shoe' and 'shirt' or 'gun' and knife'.
  
• Information - This tests general knowledge like 'What year did the United States get its independence?' or 'Who made the famous Renaissance sculpture called David?'

Perceptual Organization
    These focus on spatial abilities or the ability to manipulate shapes.

• Picture Completion - After seeing a picture the person is asked to point out what was missing or how it was incomplete. For instance, a bicycle that is missing a seat.
• Picture Arrangement - When given a bunch of random pictures the person has to rearrange them to tell a story.
• Block Design - Given pictures with designs of red and white squares and triangles, the person must recreate the design using red and white blocks.
  
• Matrix Reasoning - The person is presented with a series of shapes or designs and is asked to determine what the next shape or design in the sequence should be. This means finding some kind of pattern in the sequence and figuring out how to keep that pattern going.

Working Memory
    These test a person's ability to memorize and manipulate memory.

• Arithmetic - Basic adding or subtracting using nothing but one's head.
• Digit Span - A series of numbers is told to someone who must then recite them back in the correct order. The series of numbers may increase or the person may be asked to recite the numbers in the opposite order they were given.
• Letter-number Sequencing - The person is told a series of numbers and letters, such as F-3-9-B-5-A. They must then take these and recite them back in numerical and alphabetical order, like 3-5-9-A-B-F.

Processing Speed
    These test the overall speed at which a person's brain operates.

• Symbol Search - The person is shown a pair of abstract symbols and must then find those same symbols from a collection. Two minutes is given to match as many symbols as possible.
• Digit-symbol Coding - The person is presented with a 'key' that explains what symbols correspond to what numbers. They are then given a list of numbers and must match the symbols to those numbers as quickly as possible.

IQ

    In 1905 the Binet-Simon Intelligence Test was created by psychologists Alfred Binet and Theodore de Simon. [16] The Binet-Simon Intelligence Test was made of 30 sub-tests that were designed to cover a broad range of mental capabilities. The test scored by way of 'mental-age'. If someone scored as well as an average 14 year old, then they would have a mental age of 14.
    Then Lewis Terman published a new version of the Bidet-Simon Intelligence Test that incorporated William Stern's method of calculating intelligence quotient, or IQ. [17] To get an IQ score, the mental age is divided by the person's actual age, and then that number is multiplied by 100. [18] For example, if a 14 year old had the mental age of 14, then their IQ would be 140. Lewis Terman called this new test the Binet-Simon Intelligence Scale. But there was a problem with this new method. Intelligence stops increasing around the ages of 16 to 18, meaning this test could only measure children.

    A method called deviation IQ was developed to allow intelligence measurement in adults. The idea of measuring mental age was ditched and a percentile rank was implemented. Percentile rank is based on the proportion of similarly aged people that someone's test score matched or exceeded. A person's score was now calculated by comparing scores of other similarly aged individuals. If someone scored equal or better than 80% of the people who had taken the test, then they would fall in the 80th percentile. This percentile rank is then converted into an IQ score. IQ scores are based on a 'normal distribution', which is a bell-curved graph that has an average score of 100, since most people have an IQ of 100. [19] The higher the score, the more intelligent a person is.
    IQ is not a tell-all predictor of whether or not someone will succeed academically. The correlation between IQ score and the grades a person gets in school is around .50 -- .60. [30] This is not a perfect correlation, and studies have found that children who score well on IQ tests can get bad grades in school, and that people who have good grades in school don't necessarily do well on IQ tests. This means that doing academically well depends on more factors than general intelligence, such as motivation, interest, and persistence. Having a higher IQ seems to raise a person's self-confidence and feelings of competence, since poor children of all ethnicities with a high IQ will be more likely to get good grades, graduate high school, and go to college than those with lower IQ's.
    Low IQ scores are an indicator of adolescent delinquency, adult illiteracy, and criminal behavior in adulthood. [33] While high IQ's can increase resilience, low IQ's can increase vulnerability.

Triarchic Theory of Intelligence

General Intelligence Factor

    The data gathered from years of WAIS-III testing has shed insight on what human intelligence is and how the brain works. We have found that people are not better at one thing or the other, but rather good at everything or nothing. For instance, a person might think that someone could score exceptionally well on the verbal sections but do horribly bad on the perceptual sections. This does not happen. Of all the tests that have been analyzed, it seems that people who do well on one section will do well on all of them, while those who do bad on one section will do lousy on all thirteen tests. [12]
    Indeed, scientists have believed for awhile now that there is an underlying factor determining intelligence. Charles Spearman called this the general intelligence factor, or "g" for short, and it has been adopted by the scientific community. While observing children's test scores Spearman noticed that when a child did well on one test they usually did well on all of them. He then created a theory stating that the human brain has two layers. One layer is devoted to the current task at hand (specific factor, or "s") while the g factor, a higher layer, affects how well we perform on those tasks. [11] In other words, "g" is overall mental power or energy whole "s" stands for the specific ways in which we can channel that energy.

Three Stratum Theory

    The three stratum model was proposed by John Carroll, a psychologist who believed that Spearman's theory of intelligence was not complete.  Using statistics, Carroll showed that another layer should be added to Spearman's theory. The three stratum model is composed of a three-level hierarchy of factors. [13] In stratum three, which is at the top of the hierarchy, there is "g". Carroll believed that "g" was definitely the most important factor when determining intelligence, but that "g" could be divided into many more sub-factors. In stratum two there are eight factors:

• Fluid Intelligence (g_f) - This is the innate ability we have to solve problems, understand information, think abstractly, and make sense of the world. In other words, this is biological intelligence that we are born with and naturally attain as we grow older. [14]
  
• Crystallized Intelligence (G_c) - Crystallized intelligence is made up of the facts and skills we learn. Each tidbit of information we learn is like a crystal, and we accumulate millions or billions of them throughout our lifetime. [15]
• General Memory and Knowledge
• Broad Visual Perception
• Broad Auditory Perception
• Broad Retrieval Ability
• Broad Cognitive Speediness
• Processing Speed

Stratum two breaks down into 69 specific tasks. These 69 tasks make up stratum one.

Multiple Intelligences

    Psychologist Howard Gardner is a critic of intelligence tests like the WAIS-III. He believes that the definition of intelligence currently accepted by the mainstream is too limited and leaves out abilities that aren't verbally or mathematically related. [20] Howard Gardner therefore proposes a theory of intelligence that has eight dimensions or types:

• Linguistic intelligence - These people are good with words and language.
  
• Logical-mathematical intelligence - These people are good at reasoning and manipulation of numbers.
• Spatial intelligence - These people are good at working with pictures, art, and three-dimensional objects.
• Bodily-Kinesthetic intelligence - These people are able to move and control their bodies with ease. They are athletic with good coordination skills.
• Musical intelligence - These people excel at understanding and making music.
• Interpersonal intelligence - These are people understand humans well. They are highly sociable and friendly.
• Intrapersonal intelligence - These people are smart about themselves. They are highly introspective and understand their own inner workings to a degree others do not.
• Naturalist intelligence - These people are smart about the natural world, including animals, plants, laws of physics, etc. 

    Gardner is mainly interested in changing the way teachers approach their students. He hopes that they will realize that kids have many different abilities, and that curriculum needs to be tailored to their specific intelligence. Though the theory of multiple intelligences has become very popular, it has also received a fair share of critcism. [21] People argue that Gardner's theory is based on his own intuition rather than empirical evidence. They also point out that the theory is extremely broad in its definition of intelligence by including basic abilities or talents.

Sex Differences

    There is little to no difference between the IQ of men and women. When we look into the different sections of the IQ test, however, we begin to see some differences. Females seem to score better on verbal, linquistic, and memory tests. They excel in literature, English composition, reading, and spelling. They also do better than boys on math tests during their first years of school. But when puberty strikes males will begin to perform better than females at mathematics, visual-spatial tasks, and spatio-temporal tasks. [22] Scientists are still working to understand what causes these differences.
    Males have brains an average 10% larger than females, but this should not matter when brain-to-body-mass is taken into consideration. [23] The answer must not be in the mass of the brain, but in the construction. Researchers studied the difference between gray and white matter in the brains of men and women. What they found was that men have six times as much gray matter as women in the areas of the cortex believed to be key to intellectual ability. [24] They also tend to perform tasks with the left hemisphere of the brain, which is responsible for logic and reason. Women have ten times as much white matter than men in areas responsible for intellectual ability, including a bigger corpus callosum (connects the two hemispheres of the brain). [25] Since gray matter is responsible for localized processing power, it might explain why males are able to excel at taxing tasks like mathematical reasoning. Since white matter is responsible for carrying signals throughout the brain, this might explain why women are better at connecting the many different pieces of information needed to form complex language.
    The functional and structural differences between men and women are due, at least in part, to a difference in hormones. For instance, studies have found that women who receive testosterone will begin to do better at spatial tasks. [26][27]

Nature vs. Nurture

    Intelligence seems determined by a mix of genetic and environmental influences. It is extremely difficult to pinpoint the exact level which genes and environmental factors have on intelligence. Scientists have studied twins and adoptions to try and gain some insight on this topic. Identical twins are especially of interest because any intelligence difference between them means that their environment had an effect on intellectual development. Amazingly, identical twins raised in different families will have an average IQ difference of only 5 points. Two random people completely unrelated to one another will show an average IQ difference of 18 points. This means that intelligence is largely determined by genetics. [28]
    Adoption studies seem to agree with the findings of twin studies, since adopted children will have IQ's that are closer in score to their birth mother's than to their adopted mother's. Environment seems to have more of an effect on people when they are children, but once they are adult their genes will almost completely determine their intelligence. [4]
    This is not to say that there has not been evidence in support of nurture. In one study of 38 French children adopted in infancy, half were born from parents of high-class while the other half had been born from working-class or poverty-class parents. [34] Some of these children were then adopted by people coming from the higher class of society, while others were adopted by lower class families. Those brought up in the upper-class homes had IQ's 15 to 16 points higher than the children who had been brought up in lower class homes.
    Parents of children with higher IQ's will tend to provide the children with interesting and complex environments. They provide toys appropriate for the child's age and developmental level, and give the children plenty of stimulation. For instance, parents of higher IQ children will talk to them a lot, teaching children vocabulary and language as well as boosting overall intellectual capability. [35] Parents of children who do academically well will also tend to be less restrictive, punitive, and controlling. This allows the children to explore and learn from their own mistakes. They ask questions rather than give commands and place a lot of emphasis on achievement in school. [36] This is not proof, however, that environment has more affect on IQ than genes since all the children mentioned above were already of a high IQ passed on to them by their parents.
Racial Differences
    There are some consistent racial differences in performance on IQ tests and other intelligence measurements. Whites, Chinese, and Japanese do better on IQ tests as children than other races seem to. Chinese and Japanese children score the highest on math related testing. In America, black children score, on average, 10 to 12 points lower on IQ tests than white people. this difference is not found in infants, but rather in tests performed on children 2 years of age and onward. [30] This 10 to 12 point difference is within the reaction range of the IQ test, meaning the intellectual differences between white and black children might not be due to genetics but rather the conditions in which the groups are typically raised.

Age

   Intelligence steadily increases from the day we are born until we are in our early twenties, where it seems to level out. Do we keep this intelligence for the rest of our lives, or does it decrease as we age? A couple of studies help us answer that question. The first study took place over a span of 35 years, in which cross-sectional participants were 7 years apart from one another and in between the ages of 25 and 67. They all took an IQ test and many came back to take an IQ test every 7 years for all 35 years. More participants were added to the study in 1963, who were also tested every 7 years. Participants were continually added to the study in 1970, 1977, 1984, and 1991. This is called the Seattle Longitudinal Study. [29] By the time 35 years passed, researchers had amassed an unbelievable amount of detailed data that has given us an unmatched look at the relationship of intelligence and age.
    
    What they discovered from the longitudinal part of the study was that cognitive ability stayed high up until around age 60, when it would then start to decline. The cross-sectional aspect of the study, which just looks at people of different ages at one point in time, showed a less optimistic finding. According the the cross-sectional data, IQ mostly decreased from age 25 onward. The good news is that other studies have supported the findings of the longitudinal data, meaning we have good reason to believe that intelligence stays high through most all of adulthood. [30]
Crystallized and Fluid Intelligence
    By studying changes in crystallized and fluid intelligence we are given better understanding about the relationship age has with mental decline. Results indicate that crystallized intelligence stays high throughout early and middle adulthood, while fluid intelligence declines steadily over adulthood beginning around the age of 40. [31] Scientists have also found direct correlation between fluid intelligence decline and brain shrinkage in the elderly, helping to strengthen the other studies on the subject. [32]
Advice
    It seems that the more one uses their brain, the more likely they will keep their intellect high for longer in their life. One survey conducted on intelligence in people of all ethnicities, culture, and ages found the following advice for those who want to maintain mental sharpness.

• Find a smart spouse
• Remain content yet flexible during mid-life
• Stay healthy (eat well, exercise, and refrain from alcohol, cigarettes, and other drugs)
  
• Try to stay in intellectually stimulating environments

    To keep the brain busy, one can engage in puzzles like Sudoku and crosswords, volunteer, play games, go to social gatherings, enroll in classes, and more.

Diet and Exercise

    Studies show that supplementing diet with essential vitamins and minerals will raise intelligence test scores. [4] It is also important to keep the body at a healthy weight. Being overweight or underweight can make a person tired and sluggish, which results in dimmer wits. [38] Lack of calories, vitamins, and nutrients in children can be especially damaging to their intelligence later in life. [39]
    Exercise increases circulation, stimulates growth of neuronal axons, and releases neurotransmitters, all of which help us think clearer and improve intelligence. [40]

Conclusion

    Intelligence-- what it is and how we can measure it-- will likely remain a hotly debated topic forever. Nevertheless, the information we have about intelligence right now is very interesting and astronomically helpful for the world of academics. The more parents and teachers know about intelligence, the better we will be able to accommodate all the different kinds of people there are and make sure that everyone can succeed to their full potential. As society becomes more and more geared toward serving people of higher intellect, the topic of intelligence becomes all the more vital.