The following is a short summary of what I've learned about intelligence over many years studying cognitive science and adult education. I often need to refer to the issue of intelligence in economic and social discussions so I decided to produce this paper to illustrate my understanding of the issue and why I take certain social economic and political positions.
Recent brain research has contributed greatly to the precision of the following conclusions which broaden my acceptance of people as they are. The slow are not "bad" they are just slow. The smart are not "good" they are just smart. And there is very little that can be done to change either.
The details below are just facts of life, but facts that help me understand practical human limits. They also underscore the difficulty (almost futility) of economic or social "retraining" or "motivating" of the masses to become something radically different, something they simply are not. Pretending that anyone, through self or external motivation, can be reshaped as necessary to fit any particular idealized intelligence niche is simply not supported by research or experience. What you will learn below is that some dog's can't hunt, and it's not their fault. They are born that way.
A realistic economic goal is to ensure a range of opportunity for people of different intelligence levels. The realistic individual goal is to strive to use your abilities but in the end, whatever your potential might be, the ultimate goal is to be missed when you are gone.
Below you will see how I reached the above conclusions, that they are not idealisms, they are based on what we know today about intelligence. Hopefully, this will help you understand human, cultural and economic potentials better too. But then, it depends on your intelligence...
The ability to adapt favorably to new situations and to learn from mistakes.
Correlations between IQ/g (defined below) and life outcomes are pervasive, but interestingly there is no correlation between IQ/g and happiness. IQ/g correlates highly with school performance, less so with occupational prestige, income correlates moderately, and law-abidingness only to a small degree. The correlation between job performance and IQ (on a scale of 0-1) depends on the complexity of the job, ranging from .2 for unskilled jobs to .8 for the most complex.
The reason intelligence is popularly associated with grades and income is because IQ/g is relatively easy to measure with standardized tests and so it was until 1971 when the practice of using IQ employment tests was banned by the U.S. Supreme Court as being discriminatory. Thus, the best chance for corporate "intelligence recruiting" came from colleges and universities where IQ was covertly certified by classroom performance. Simply put: Those with high IQ's were less likely to flunk out of college.
Academia became the corporate intelligence filter. Employers competed for the top performers with salary incentives (hence grade and income associations). But, not all intelligent people go to college nor are they required to stay in college if they do go. It is estimated that for every intelligent college graduate there is at least one intelligent non-college graduate (I'm sure you know of a few of these too). Without college, without testing, these equally intelligent, possibly unassuming people are harder to identify. They exist, and demonstrate their capabilities in their own, often unrecognized, not necessarily well paid ways, but are hidden from public view in education statistics as part of the "lower-educated" classes. Many important situations are solved in this world without consulting academicians. Many apply their intelligence in different ways than school-type work (see "Multiple Intelligences" below).
IQ: Intelligence Quotient (also "g" as "general intelligence"):
IQ tests have been adjusted over the years to be gender neutral, meaning that gender factors will not affect the IQ score since verbal/linguistic elements (female strength) and logical/mathematical elements (male strength) is weighted so that a strength in one is essentially neutralized by the presence of the other.
Therefore a 100 IQ male equals a 100 IQ female (they are both equally of average intelligence as measured by a modern qualified IQ test), but the performance of these two in a given situation will likely be different. A given problem will be solved by either, but probably in two average but different ways. The female will more likely use verbal/linguistic solutions, the male will more likely use logical/mathematical solutions. The average female is equal in intelligence to the average male, but both extreme brightness and extreme dullness tend to belong to males. Significant gender differences are verified by brain research. For an easy and excellent description of gender differences read Brain Sex.
In the past 20 years, "Multiple Intelligence Theory" the identification of at least 8 distinct forms of intelligence, has taken hold. These forms interact with each other to form our "intellect" and also illustrate how IQ testing tells only part of the story. For more information on multiple intelligences, read Multiple Intelligences: The Theory in Practice.
So, IQ scores aren't the whole intelligence story. There are many ways to be intelligent, not just school or employment. Those who are conventionally intelligent (high IQ) may be lacking in other forms. We need to be aware of these real intelligence differences and give people credit for what they have. These differences are often hard for us to recognize since we might not share that form. But when you see someone performing exceptionally in music, or sports, the gift of gab, knowledge of self, naturalist observations, mathematics or language, you can bet that they are intelligent. If those intelligences seems to come naturally to them, it does. It's probably genetic!
An intelligence has to meet very specific criteria both cross-cultural, psychological and biological. Most talents are simply combinations of the multiple intelligences.
They might be different than you, have a DIFFERENT combination of intelligences, solve problems differently than you would, but are still intelligent. It is impractical to concentrate all forms of intelligence in one individual because different physical and sensory traits are associated with different intelligence forms. You only have one body with certain attributes. It makes sense that different individuals in different environmental and cultural conditions excel with different intelligence combinations.
How Intelligence IQ is Distributed
But there are other interesting conclusions here:
Thomas J. Bouchard Jr.; David T. Lykken; Matthew McGue; Nancy L. Segal; Auke Tellegen
"In each of the three prior studies of MZA twins (monozygotic (identical) twins reared apart), two independent estimates of intelligence were obtained. The sample sizes and intraclass correlations for all four studies are compared in Table 2. The table illustrates the remarkable consistency of the MZA correlations on IQ across measurement instrument, country of origin, and time period. These correlations vary within a narrow range (0.64 to 0.74) and suggest, under the assumption of no environmental similarity, that genetic factors account for approximately 70% of the variance in IQ.
This estimate of the broad heritability of IQ is higher than the recent estimates (0.47 to 0.58) based on a review of the literature that includes all kinship pairings [9, 15]. Virtually the entire literature on IQ similarity in twins and siblings is limited, however, to studies of children and adolescents. It has been demonstrated  that heritability of cognitive ability increases with age. A heritability estimate of approximately 70% from these four studies of mainly middle-aged adults is not inconsistent with the previous literature. "
For more fascinating results and details from twins studies read:
The above suggests that at least 70% of your adult intelligence (your ability to adapt and to learn from mistakes) is basically as unchangeable as your eye color. Other recent studies have pushed that figure in adults to 80% genetic concluding that the remaining 20%-30% of IQ variability is environmental, a product of living and adapting to the conditions of your life. In the real world, where few get maximum enrichment opportunity, enrichment potential variation is minimal, 5%-10% of the environmental 20% - 25% (1-3 IQ points) compared to the genetic effect of 75% to 80%.
We inherit our genes from our grandparents through our parents. Just as each sibling in a given family is similar because they are essentially genetic combinations from a common grandparent gene pool each is also inherently different in many ways, each individual inherits a somewhat different IQ tool box.
So genetics, not environment or education, is still the primary factor driving people's intelligence. A genetically average adult with a normal 100 IQ (75% genetic) probably has a practical MAXIMUM of +/- a few percentage points due to enrichment factors that are extraordinary to the normal environmental factors of everyday life already experienced to reach 100. In other words, enriched environmental factors (nearly unlimited opportunity, college, enriched life experiences, etc.) may yield little more than a few more (1-3) modest points of IQ by providing a chance to practice using the tools in your IQ toolbox. Deprivation (lifelong denial of opportunity) can have a GREATER negative effect than the positive effects of enrichment. In other words, lifelong deprivation can hold back your otherwise normal IQ by 5-10 environmental IQ points by extraordinarily denying you a chance to practice using the tools in your IQ toolbox. Research confirms these conclusions.
Look for verifiable IQ change processes (claims like: "Because of process X, my IQ rose 17 points!"). You won't find them. Not even the best colleges will make that claim (they know better) otherwise IQ improvement would be an excellent criteria for judging any school's performance, wouldn't it? Measurable IQ improvement of each school in a table sorted best to worst! You won't find it. The focused college environment certainly SHOULD, more than anyone else, be able to claim that if it were true, but they don't, cause it isn't.
College can't change your normal IQ from low to high. That is a genetic impossibility. At BEST you get a couple points of IQ from college, but don't count on it. The value of college or other enrichment experiences is that they essentially FEED whatever IQ you have. It potentially gives your mostly genetic IQ something extra to work with. It allows your existing IQ to apply itself through expanding opportunities, to use new tools without changing its core tool box. College feeds your IQ, it doesn't significantly increase it. That is how non-college intelligent people, feeding their intelligence through self directed life experiences instead of academia, can be comparably intelligent AND "uneducated" (in the academic sense).
Genetic factors inherent in different racial and geographical populations produce genetic cultural IQ differences. These are documented in detail in the very controversial book titled The Bell Curve. The modern controversy surrounding intelligence and race focuses on the results of IQ studies conducted during the second half of the 20th century in the United States, Western Europe, and other industrialized nations.
In almost every testing situation where the tests were administered and evaluated correctly, a difference of approximately one standard deviation was observed between the mean IQ score of blacks and whites. That is, the mean IQ score among blacks is approximately 85 and the mean IQ score among whites is approximately 100. In the United States, the mean IQ score of Hispanics is usually reported to be intermediate to the mean black and white scores.
The mean score for people of East Asian and Jewish descent is usually higher than the mean score of whites, but the extent of that difference is not precisely known. However, several studies place the median IQ of Ashkenazi Jews (who make up the overwhelming majority of American Jews) at approximately one standard deviation above the mean for other whites. Yet, there are wide IQ variations within any race so that any one individual from a low mean race could easily have a higher score than someone from a high mean race.
In other words, you must treat individuals, regardless of race, as individuals. ANY ONE INDIVIDUAL could be sharper or duller than you, regardless of race.
The bottom line:
The unacceptable alternative is eugenics. American Eugenics came into vogue in the early 20th century With a name coined in 1883 by British anthropologist Francis Galton, who hoped to see arranged marriages improve mankind (read War Against the Weak: Eugenics and America's Campaign to Create a Master Race).. The movement eventually led to racist laws, such as ones prohibiting miscegenation, in many U.S. states, and the sterilization of more than 60,000 mental and moral "defectives." The Nazis took inspiration from the American eugenicists which culminated in the Nazi Holocaust.
We eventually learned that genetic purity is undesirable. "Hardy-Weinberg equilibrium" tells us is that populations are able to maintain a reservoir of variability so that if future conditions require it, the gene pool can change. Variability is a good thing. Inconsistency is an insurance policy!
Accepting people as they are, including their varied strengths and weaknesses, is an important and accurate practice. You have to realize we are not universal machines equipped with the latest IQ attachments, we are all different machines with differing capabilities and only certain attachments fit, most don't.
A realistic social, economic and political goal is to ensure a range of opportunity for people of different intelligence levels. A realistic individual goal is to strive to use your abilities but in the end, whatever your potential might be, the ultimate and achievable goal for all is to be missed when you are gone.