Commentary on The g Factor: The Science of Mental Ability (1998) by Arthur Jensen

The Gauntlet is Down: Jensen Takes the IQ Debate to a New Level

ARTHUR R. JENSEN is Professor Emeritus of Educational Psychology, Graduate School of Education, University of California, Berkeley. During the 40 years of his tenure at Berkeley, he has been a prolific researcher in the psychology of human learning, individual differences in cognitive abilities, psychometrics, behavioral differences in cognitive abilities, behavioral genetics, and mental chronometry. His work, published in six earlier books and some 400 articles in scientific and professional journals, has placed him among the most frequently cited figures in contemporary psychology. In a brilliant 40-year career that has earned him a place among the most frequently cited figures in contemporary psychology, Arthur Jensen has systematically developed a seminal concept first discovered by Charles Spearman in the 1920s: individual and group differences in mental ability exist, and these differences can be measured by a single, general factor, g. On its surface, this concept seems innocuous.  However, Jensen does not draw back from its most controversial conclusions: that the average differences in IQ and other abilities found between sexes and racial groups have a substantial hereditary component, and that these differences have important societal cosequences.  The culmination of his career is the most comprehensive treatment of g ever written, The g Factor.  In it, Dr. Jensen not only clearly explains the psychometric, statistical, genetic, and physiological basis of g, in the process he also refutes all major challenges that have been brought against the concept of general mental ability.  It is a title destined to be a classic in psychology for years to come that boldly addresses some of the most important questions in an increasingly complex and technological world. [Publisher's Introduction]

Arthur Jensen's new book The g Factor: The Science of Mental Ability finally puts an end to The Bell Curve debate started in 1994 by Herrnstein and Murray.  That block buster stood the race debate on its head and brought out the forces to do battle over the causes of human nature, specifically the 100 years of testing that consistently showed that blacks scored poorly on IQ tests, on an average of 85 in the United States.  But Herrnstein and Murray's book was not subject to rigorous academic review and was criticized for putting forth public policy as well as analyzing the causes of black pathologies.  In order to set the world straight, and bring some order to the chaos, the American Psychological Association (APA) put together a team of experts in 1995 to again look at psychometrics and concluded in their report APA Task Force Examines the Knowns and Unknowns of Intelligence that there indeed was a huge gap between whites and blacks in measured IQ, that the tests were not in any way biased, but the cause was still unknown.  The subterfuge and deception continued, as this was just too political a subject to be absolutely honest and candid about.  But it was a good start.  Now only the cause was in dispute, not the actual disparity that has been so well documented. Now, the most renowned and most frequently cited expert in the field, Arthur R. Jensen, has taken another step in bringing order to a subject as divisive and vitriolic as evolution was over 100 years ago.  In fact, in Sulloway's new book, Born to Rebel, he shows how the forces of reactionaries and radicals, many from the same families, will battle these highly charged views that infringe on the political turf of religionists, politicians, and social do-gooders.  The principals of scientific debate take a back seat to agendas.  But having experienced this anathema to pure science for the last 40 years himself, Arthur Jensen has produced the most thorough compilation of the science of psychometrics and differential psychology yet published.  Finally, until an equally qualified academic can summon forth evidence to the contrary, the record will show that general intelligence as defined shows a wide disparity between individuals and different ethnic and racial population groups, and this disparity is primarily genetic. The g Factor is so complete in its coverage, so mathematically thorough in its treatment of establishing  general intelligence as the engine that all other brain modules use in  solving life's problems, that it is hard to sum up in a few pages what the message is.  It is really the culmination of over a hundred years of research into what it is we mean by intelligence.  Why is it so important?  Because it is the foundation which the socialist/communitarian/egalitarian left must destroy to be able to move forward in trying to remake humans in their own image.  To do this, the genetic genie must be stuffed back into its bottle at any cost.  If the subject was love, or morality, or fairness and these subjects were attacked with the same vigor that intelligence has undergone, the media, government, and public debate would come to a halt.  All we would have to say is, "but no one knows what morality is, everyone has a different definition of it, so it must not exist."  Likewise for love, beauty, athleticism, virtue, etc.  None of these can be clearly defined, but we can learn much about each by understanding our past, how we evolved, and how and what these terms mean in relation to reproduction, survival, and life's meaning as we pass through this world. (In fact, anyone would have an even harder time defining a mutually acceptable and scientifically sound meaning of life . Does that mean that life is perhaps meaningless?)

In Chapter 1: A Little History, Jensen traces the history of differential psychology and its clear purpose of determining human nature by looking for the differences between people and groups.  With Darwinism, natural selection's mechanism of evolution has been understood to operate under differences in those traits, behaviors, immune responses and physical features that would allow different people to survive under different environments.  If we were all alike, then we would all perish or survive in the same environment.  If we were all alike, we would not try to find our own niche in life but would all compete for the same job to perform.  There would be no differences.  And since we all carry in our genes a history of our ancestors surviving under different environments, differences seen between individuals can also be seen between population groups.

Human mental ability is one of those traits that is both important to our survival and well being, but is the very essence of what makes us different from our closest living  ancestors, the chimpanzees. Ergo, it is why we are so interested in what it is and how it impacts our lives.  Jensen summarizes how Galton saw intelligence over a hundred years ago, "Human mental ability has both general and specific components; the general component is the larger source of individual differences; it is predominantly a product of biological evolution, and is more strongly hereditary than are specific abilities, or special talents. Mental ability, which ranges widely in every large population, is normally distributed, and various human races differ, on average, in mental ability."

The message throughout this book is that from the reptilian brain to our own, different modules evolved to handle specific tasks like face recognition, language acquisition, etc. Jensen points out that as far as differences are concerned, all races and individuals have these modules firmly in place and functioning about equal.  That is, for such localized brain functions as facial recognition, there is less difference between individuals and racial groups.  But what we all recognize as general intelligence, the ability to learn, to generalize, to use abstract concepts to formulate new solutions are not encapsulated in a  localized brain module but is the metabolic and neurological engine that drives the varying components of the brain.  This is what he calls g, general intelligence.

In Chapter 2: The Discovery of g, Jensen writes, "Spearman invented a method, factor analysis, that permitted a rigorous statistical test of Spencer's and Galton's hypothesis that a general mental ability enters into every kind of activity requiring mental effort. A well-established empirical finding--positive correlations among measures of various mental abilities--is putative evidence of a common factor in all of the measured abilities. The method of factor analysis makes it possible to determine the degree to which each of the variables is correlated (or loaded) with the factor that is common to all the variables in the analysis. Spearman gave the label g to this common factor, which is manifested in individual differences on all mental tests, however diverse."

I like to think of general intelligence as the hologram the unifies all of the components of the mind, something akin to the concept of metacognition.  It is the engine that allows you to concentrate to the point when someone comes up and asks you a simple question your brain needs time to refocus and generalize.  The hologram reconfigures to tie a different set of modules together for the task at hand.

This general intelligence, or g, is not a physical part of the brain, but a measurement of how efficiently the engine is operating or as Spearman called "mental energy," or in my vision, a hologram of energy that permeates the brain.  And factor analysis is the mathematical tool used to weight different tests that reveal this "mental energy" g. That is, g is just what it is, the results of a mathematical construct, and different tests reveal different amounts of general intelligence versus training or learning.

In Chapter 3: The Trouble with "Intelligence", Jensen writes, "The word intelligence as an intraspecies concept has proved to be either undefinable or arbitrarily defined without a scientifically acceptable degree of consensus. The suggested remedy for this unsatisfactory condition is to dispense with the term intelligence altogether when referring to intraspecies individual differences in the scientific context and focus on specific mental abilities, which can be objectively defined and measured. The number of mental abilities, so defined, is unlimited, but the major sources of variance (i.e., individual differences) among myriad abilities are relatively few, because abilities are not independent but have sources of variance in common. . . The term intelligence, then, would apply only to the whole class of processes or operating principles of the nervous system that make possible the behavioral functions that mediate an organism's adaptation to its environment, such as stimulus apprehension, perception, attention, discrimination, stimulus generalization, learning, learning-set acquisition, remembering, thinking (e.g., seeing relationships), and problem solving. These functions are subsumed in the term intelligence."

In Chapter 4: Models and Characteristics of g, Jensen writes: "The g factor is found to be remarkably invariant across all the various methods of factor analysis except those that mathematically preclude the appearance of a general factor.  The g factor is found to be relatively invariant across different batteries of diverse tests of mental ability. This fact justifies the postulation of a true g (analogous to true score in classical measurement theory), of which the g obtained in any empirical study is an estimate. The g factor is also found to be ubiquitous and relatively invariant across various racial and cultural groups.  The form of the population distribution of g is not known, because g cannot yet be measured on a ratio scale, but there are good theoretical reasons to assume that the distribution of g approximates the normal, or bell-shaped, curve. The g factor is ubiquitous in all mental ability tests, and tests' g loadings are a continuous variable, ranging from values that are slightly greater than zero on some tests to values that are near the reliability coefficient of some tests. Although certain types of tests consistently show higher g loadings than other tests, it is conceptually incorrect to regard characteristics (e.g., relation eduction and abstract reasoning) of such tests as the "essence" or "defining characteristic" of g.  These features of tests may indicate the site of g, but not its nature. Unlike the group factors, the g factor cannot be described in terms of the item characteristics and information content of tests. Nor is g a measure of test difficulty; a test's g loading and its difficulty are conceptually separate. It is wrong to regard g as a cognitive process, or as an operating principle of the mind, or as a design feature of the brain's neural circuitry. At the level of psychometrics, ideally, g may be thought of as a distillate of the common source of individual differences in all mental tests, completely stripped of their distinctive features of information content, skill, strategy, and the like. In this sense, g can be roughly likened to a computer's central processing unit. The knowledge and skills tapped by mental test performance merely provide a vehicle for the measurement of g. Therefore, we cannot begin to fathom the causal underpinning of g merely by examining the most highly g-loaded psychometric tests. At the level of causality, g is perhaps best regarded as a source of variance in performance associated with individual differences in the speed or efficiency of the neural processes that affect the kinds of behavior called mental abilities (as defined in Chapter 3)."

Chapters one through four lay the groundwork for the rest of the book where Jensen begins to challenge other explanations for intelligence, including those who would like to see it go away in a perfectly egalitarian world. In Chapter 5: Challenges to g, Jensen discusses the alternative viewpoints and theories: "Those following the academic journals are familiar with Cattell's theory of fluid intelligence (Gf) and crystallized intelligence (Gc).  Using statistical analysis this theory has been shown to be nothing more than fluid intelligence equating to g and crystal intelligence equating to what is learned by an individual.  In the hierarchical formation of intelligence, Cattel's theory puts g at the apex with Gc and Gf just below."

Of more interest to the lay public is Howard Gardner's popularized multiple intelligences.  The seven intelligences found by Gardner (and now I understand there is an 8th)  are really just four that are accepted within g, two (intrapersonal and interpersonal) which have no more credibility than anecdotal scientific underpinnings that may be better located as personality traits, and kinesthetics, which is really just athletic ability.  Gardner's theory makes for a lot of feel-good rationalizations for intelligence disparities, but lacks any scientific basis.

Another popular doctrine Jensen calls the specificity doctrine is described as ". . . the belief that 'intelligence' consists of nothing other than a learned repertoire of many bits of knowledge and skills, and that environments differ in the opportunity they afford each individual to acquire these various bits of knowledge and skills. Therefore, people's repertoires of knowledge and skills differ to varying degrees. IQ tests are designed to sample some very limited and selected portion of all these environmentally acquired bits of knowledge and skill, particularly those elements to which the socially dominant group attaches special value as requisites for gaining and maintaining their status."

It is interesting that the government, especially the courts, has led the fight against disparate outcomes by advocating that everyone is equal, while the army has moved in an entirely different direction in using g as a measure of how soldiers can learn and do their jobs.  The army has been held up as a model for the rest of society, while at the same time they use intelligence testing to allow only the qualified in the ranks.  This same testing or screening program would be illegal if it were used by a company.

In addition, the army assigns recruits to different vocations depending on the demands of the job, and the intelligence of the recruits, because the trainability of people for different jobs based on their IQ's (and not their knowledge) is well recognized. Jensen writes: "The meager success of skills training designed for persons scoring below average on typical g-loaded tests illustrates the limited gain in job competence that can be obtained when specific skills are trained up, leaving g unaffected. In the early 1980s, for example, the Army Basic Skills Education Program was spending some $40 million per year to train up basic skills for the 10 percent of enlisted men who scored below the ninth-grade level on tests of reading and math, with up to 240 hours of instruction lasting up to three months. The program was motivated by the finding that recruits who score well on tests of these skills learn and perform better than low scorers in many army jobs of a technical nature. An investigation of the program's outcomes by the U.S. General Accounting Office (GAO), however, discovered very low success rates. Only a small percentage of the training program's enrollees completed the program successfully, in terms of achieving the level of competence required for adequate performance of many jobs. But to remedy the problem, the GAO suggested more highly specific forms of skills training. It recommended that the Army carry out task analyses to determine the specific skills required for each particular military job and provide training for just those ski1ls. The outcome of this approach was not reported, but there is massive evidence that g is reflected even in individual differences in the outcome of training highly specific skills. In jobs where assurance of competence is absolutely critical, however, such as airline pilots and nuclear reactor operators, government agencies seem to have recognized that specific skills, no matter how well trained, though essential for job performance, are risky if they are not accompanied by a fairly high level of g. For example, the TVA, a leader in the selection and training of reactor operators, concluded that results of tests of mechanical aptitude and specific job knowledge were inadequate for predicting an operator's actual performance on the job. A TVA task force on the selection and training of reactor operators stated: 'intelligence will be stressed as one of the most important characteristics of superior reactor operators...intelligence distinguishes those who have merely memorized a series of discrete manual operations from those who can think through a problem and conceptualize solutions based on a fundamental understanding of possible contingencies.' This reminds one of Carl Bereiter's clever definition of 'intelligence' as 'what you use when you don't know what to do.'"

The army program of assigning people to different units, based on their intelligence, has an interesting corollary.  For example, if communications technicians have an average IQ of 110, and the average motor pool mechanic has an average IQ of 90, and each unit has similar opportunities for advancement, it means an almost ideal formula for egalitarianism has been inadvertently put in place.  Each unit will have equal percentages of staff sergeants for example.  No where else do I know of is such a system in place outside of the army.  And no wonder it is held out as a model program, it is idealistic and anti-meritocratic.

Jensen then writes, "Finally, to the extent that a theory of mental ability tries to explain individual differences solely as the result of learning, it is doomed to refutation by the evidence of behavioral genetics, which shows that a preponderant proportion of the variance of IQ (even more so of g) consists of genetic variance. An individual's genes are certainly not subject to learning or experience. But it is certainly a naive mistake to suppose that the high heritability of g implies that a great variety of learning experience is not a prerequisite for successful performance on the tests that measure g. What high heritability means is that individual differences in test scores are not mainly attributable to individual differences in opportunity for the prerequisite learning."

Jensen then tackles the latest fad, contextualism, where the argument is made that intelligence only measures what a culture wants it to. Actually, many authors, including Levin in Why Race Matters, have adequately rebutted this absurdity, but it is so popular that it keeps coming back in the folk lore of its advocates.  Jensen writes, "Contextualism is trivial from the standpoint of research on mental ability because it provides no answer for the wide range of individual differences that exists even when the total context of performance is held constant (as, for example, among full siblings reared together). The interpretations of 'intelligence' offered by cultural relativism and contextualism indeed strengthen my contention that attempts to define 'the essence' of 'intelligence' are scientifically unproductive."

In Chapter 6: Biological Correlations of g, Jensen writes: "The physical characteristics correlated with g that are empirically best established are stature, head size, brain size, frequency of alpha brain waves, latency and amplitude of evoked brain potentials, rate of brain glucose metabolism, and general health.  It would therefore be most surprising and remarkable if IQ tests were significantly correlated with physical variables. Yet they are. IQ--especially the g factor of IQ tests--is correlated with a variety of physical variables. What does this mean? For the time being, about all one can say with certainty is that whatever is measured by IQ tests--mostly g--is somehow enmeshed in a host of organismic variables and therefore involves something beyond the purely psychological or behavioral. It also proves that g is not just an artifact of the way psychometric tests are constructed, nor is g a mere figment of the arcane mathematical machinations of factor analysis. Obviously, a correlation between psychometric g and a physical variable means that g is somehow connected with underlying biological systems."

Gould et al. has taken issue with the most debated of physical characteristics associated with IQ, brain size.  He went to great lengths to criticize several methods used to measure brain size and IQ and took great pleasure in pointing out to his readers that the numbers must have been "cooked" to be so similar.  Now, a hundred years later, with magnetic resonance imaging (MRI) and PET, the relationship is real and without dispute.  Jensen reports a correlation of 0.4 between brain size and g, and it could be higher as other confounding factors are considered. But there is no doubt the relationship is real and significant.

Using cerebral glucose metabolism as another biological correlation, Jensen reports on studies that show that smart brains are efficient brains.  Using radioactive isotopes to monitor energy usage in the brain while the subject is taking a highly g loaded test, subjects who are more intelligent use less glucose.  One fascinating aspect of these results that Jensen doesn't mention, as far as I was able to tell, is that if doing well on an IQ test meant merely putting forth effort, a so-called white culture thing, then it would show up as more energy used, not less.  So clearly, brighter people are not trying harder (conscientiousness) but are in fact more mentally able to do the assigned tasks with less effort, ergo, they have more innate intelligence.

In Chapter 7: The Heritability of g, Jensen writes: "The broad heritability of IQ is about .4 to .5 when measured in children, about .6 to .7 in adolescents and young adults, and approaches .8 in later maturity. Environmental variance can be partitioned into  two sources: (1) environmental influences that are shared among children reared in the same family but that differ between families, and (2) nonshared environmental influences that are specific to each child in the same family and therefore differ within families. The shared environmental variance diminishes from about 35% of the total IQ variance in early childhood to near 0% in late adolescence. The nonshared environmental variance remains nearly constant at around 20 to 30% from childhood to maturity. That is, virtually all of the nongenetic variance in adult IQs is attributable to within-family causes, while virtually none is attributable to the kinds of environmental variables that differ between families. The specific sources of much of the within-family environmental variance are still not entirely identified, but a large part of the specific environmental variance appears to be due to the additive effects of a large number of more or less random and largely physical events: developmental "noise" within small, but variable positive and negative influences on the  neurophysiological substrate of mental growth."

More of the genetic variance in test scores is associated with g than with any other  common factor. Hence the relative g loadings of various tests predict their relative heritability coefficients (the proportion of genetic variance in the test scores).  Traits that show genetic dominance provide evidence that they have been subjected to natural selection as a Darwinian  fitness character over the course of evolution.

It is now commonly accepted that as one approaches adulthood, the heritability of g goes to about 0.8 (contrary to what you will generally read in the press), most of the variance occurs within families and is therefore independent of the families poverty or wealth, and these determinations have been made by numerous investigations studying among other things twins and siblings raised together and apart.  The data is so overwhelming that there should be little argument that raising the living conditions of the underclass will not impact the intelligence of children raised in those environments, and yet the standard social science model persists in promising an end to the racial disparity in general intelligence if only we could pump enough money into bringing their standard of living up to the middle class.

Jensen is presenting data that is a compilation of all the available research, not just his own.  These same results are reported in a special issue of Intelligence, Jan/Feb 1997, and also by the above APA report by a panel of experts.  (Again, as stated above, one of the best books on how this within family variance comes about is Born to Rebel.)  Jensen considers this within-family variance as noise from slight differences between siblings, where Sulloway's analysis is more active on the part of the siblings each trying to establish there own niche within the family to better themselves, an evolutionary strategy (contrary to Marxist class struggle theories). It seems that both developmental noise and sibling rivalry must contribute the high variance within families.  In either case, these factors fall mostly within the family unit, outside of government intervention or attempts at egalitarianism.

What The g Factor adds to the commonly accepted results of heritability is the findings  that general intelligence, or g, is the critical component of heritability.  Jensen has firmly established that g is what is responsible for academic achievement and for workplace performance.  Pumping money into education to somehow raise up the cognitive abilities of "slow" students to the detriment of the gifted is not economic, as the military has found out.  They no longer even try, but restrict enlistment to those who come equipped with the innate ability to learn in the first place.  This is in stark contrast to social policy promoted by educators that assumes all it takes to make everyone equal is enough training (that is money) thrown at the problem.  There is no evidence that this approach will ever work.

Lowentin et al. likes to make an analogy between human environments and plants growing in different soils to prove that the condition of the organism depends more on the environment than on genes.  It goes something like this, take two plants with identical genes and grow one in sand and the other in rich soil and one will flourish while the other will wither and die.  The problem of course is that the difference between plants and animals is that animals have mobility to move about within environments precisely because it provides selective advantages over being stationary.  Jensen notes that any child raised in a humane child-rearing environment, that is a child that has not been severely deprived (kept in a dog cage in the basement as just recently happened to one child by abusive parents), will develop normally and progress along their own learning trajectory based on their innate intelligence.  That is the beauty of not being a plant, animals can move about to maximize environmental conditions for growth.

In Chapter 9: The Practical Validity of g, Jensen discusses all of the ways in which intelligence impacts how people work, learn, play and prosper.  This was primarily the message in The Bell Curve and Jensen expands on that subject.  In essence, the reason the heritability of g is so important is because it predicts more than any other human behavioral trait how successful a person will be (as Kevin MacDonald has shown, the Jews eugenic practices have paid off in financial rewards due to their exceptionally high IQ).  Jensen writes: "The validity of g is most conspicuous in scholastic performance, not because g-loaded tests measure specifically what is taught in school, but because g is intrinsic to learning novel material, grasping concepts, distinctions, and meanings. The pupil's most crucial tool for scholastic learning beyond the primary grades--reading comprehension--is probably the most highly g-loaded attainment in the course of elementary education. In the world of work, g is the main cognitive correlate and best single predictor of success in job training and job performance. Its validity is not nullified or replaced by formal education (independent of g), nor is it decreased by increasing experience on the job. Although g has ubiquitous validity as a predictor of job performance, tests that tap other ability factors in addition to g may improve the predictive validity for certain types of jobs--tests of spatial ability for mechanical jobs and tests of speed and accuracy for clerical and secretarial jobs. Meta-analyses of hundreds of test validation studies have shown that the validity of a highly g-loaded test with demonstrated validity for a particular job in a particular organizational setting is generalizable to virtually all other jobs and settings, especially within broad job categories. The g factor is also reflected in many broad social outcomes. Many social behavior problems, including dropping out of school, chronic welfare status, illegitimacy, child neglect, poverty, accident proneness, delinquency, and crime, are negatively correlated with g or IQ independently of social class of origin. These social pathologies have an inverse monotonic relation to IQ level in the population, and show, on average, nearly five times the percentage of occurrence in the lowest quartile (IQ below 90) of the total distribution of IQ as in the highest quartile (IQ above 110)."

Jensen clearly shows that g is the most important trait that an individual would want to have in order be do well at work, at school and in life.  Of  course, the second most important trait that is part of the constellation of personality types is  conscientiousness.  That is the desire to achieve.  No matter how intelligent a person is, if they are lazy and have a disinterested or contented attitude towards work or academics, they will not have the drive to learn or to engage subjects with the intensity that makes some people stand out.  But without intelligence, no amount of training or drive will suffice to overcome this limitation.  Throwing money at a population of people that do not have the capabilities to acquire the technical skills needed in a modern work force will only waste valuable resources.  It is better to use technology to dumb down what is required than to teach those people to perform tasks they will never master (like grocery store check-out scanners).

On the down side, low IQ is also the major contributing factor for the underclass's condition. He writes: "The well-established correlation of IQ and similar cognitive measures with a number of social variables, such as poverty, crime, illegitimacy, and chronic welfare status, makes it almost a certainty that g itself is the major cognitive component in the relationship. However, I have not found a study that directly addresses the extent to which just g itself, rather than IQ or other highly g loaded measures, is related to social variables. The repeated finding that verbal test scores are somewhat more highly correlated with delinquent and criminal behavior than are nonverbal performance tests (generally loaded on the spatial factor) suggests that other cognitive factors in addition to g are probably responsible for the correlation of IQ with these most common forms of antisocial behavior."

Jensen points out that sibling studies show that the sibling with the low IQ turns to crime, while the others in the same family do not.  So a low IQ is responsible for the high level of crime, especially violent crime resulting from impulsiveness where the consequences are not well understood.  And again, if it was the socioeconomic status of the family that determined criminal behavior, then siblings from some families would be involved in crime regardless of intelligence.  Again, low crime rates follow population groups that are better endowed with g (See Rushton's international studies of population differences with regards to crime and numerous other behavioral traits).

In Chapter 10: Construct, Vehicles, and Measurement, Jensen covers many of the aspects of testing and what it means.  I will discuss just a couple of the more interesting and controversial items.  Anyone familiar with the Flynn effect, or apparent rising IQ scores, knows how contradictory the evidence is.  Jensen covers the Flynn affect in detail but here I will quote his rebuttal to those who use the Flynn effect as a means to dismiss the genetic importance of g: "What appears counterproductive to me, however, is the extent to which Flynn's argument is used to sidestep the real-world implications of race differences in IQ, particularly the black-white difference. This is even more so for less fair and technically unsophisticated commentators who invoke the Flynn Effect like a mantra in dismissing IQ.  Flynn's research on IQ gains, for example, is the centerpiece of his critique entitled Race and IQ: Jensen's Case Refuted and the same argument is reiterated in most of his publications on secular gains. Flynn hypothesizes that whatever unknown factors are responsible for the intergenerational gain in IQ scores (and are not reflected in 'real world problem-solving ability') also operate within generations, causing IQ differences between certain contemporary subgroups in the population, in particular the average one standard deviation IQ difference between blacks and whites in the United States. Therefore, Flynn argues, the black-white IQ difference doesn't represent a real functional difference in ability, that is, a difference in g, any more than does the IQ raw-score difference observed between successive generations of whites. Psychologist Robert C. Nichols characterized Flynn's argument as a faulty syllogism:
 1.  We do not know what causes the test score changes over time.
 2.  We do not know what causes racial differences in intelligence.
 3.  Since both causes are unknown, they must, therefore, be the same.
 4.  Since the unknown cause of changes over time cannot be shown to be genetic, it must be environmental.
 5.  Therefore. racial differences in intelligence are environmental in origin.
 If the Flynn effect is caused by environmental factors, it is most remarkable that a steady rise in the population's average test scores over a period of fifty or sixty years has had no effect on the mean IQ difference between blacks and whites, which has remained at about 1SD since World War I. This era has been one of steadily diminishing disparities between blacks and whites in educational, social, and economic opportunities. Yet the general upward secular trend in the overall population level of mental test scores has not changed the standardized difference between the mean test scores of blacks and whites."

This period has also seen the average stature of all populations rise, but no one expects people to grow for ever, or that we were all midgets not long ago. Likewise for intelligence, the increases cannot be sustained and seem only  to effect the lower half of the IQ bell curve, or bringing up the bottom. He later writes, "The nonexistence of predictive bias for the same test scores obtained by blacks or whites is a strong refutation of Flynn's supposition that the secular trend in test scores explains away the observed average racial differences in IQ (i.e., that there is no real difference in the level of functional ability between races.) As shown by the evidence reviewed in Chapter 9, g is the main functional ingredient of tests' practical predictive validity."  What he is describing is simply that when individuals are tested, and those tests are used to predict success in school or work performance, that blacks and whites do not differ.  That is, blacks with low scores do not perform any better in school than whites with the same scores.  And likewise on the job, and especially in the military where tests and work performance data has been rigorously collected and analyzed for many years.  Test scores do in fact predict how people will perform, regardless of race.

Finally, Jensen discusses the three most studied programs that have attempted to raise the IQ's of children at risk: Head Start, the Abecedarian Project, and the Milwaukee Project.  To date, all they seem to accomplish with regards to intelligence is that the children's IQ scores rise to the degree that they are being coached to do well on tests, or teaching to the test.  What The g Factor explains better than any other book I have read on the subject is that g is not the same as memorization, which seems to be fairly universal and not related to g.  What this means is that low intelligent children can be taught to memorize concentrated subject matter that shows up on tests, regurgitate the correct answers, but years later will not have broken out of their inability to generalize knowledge in a way that g predicts.  And this is precisely what schools are attempting to do today, teach the rudimentary basics in hopes that it will carry over into the job market.  But the evidence is not encouraging.  We have seen too many brilliant scholars (Noam Chomsky, Einstein, etc.) who have rejected formal education only to excel later, on their own, by their very innate intelligence and drive.

Education seems to be universally overrated as a means to learning skills that can be put to use later in life. Jensen writes: "The final summary chapter of a book in which 23 psychologists and educators addressed the issue of how intelligence might be increased by psychological methods concluded: 'We now return to the contrast made in the title between training cognitive skills and raising intelligence. We would argue that although the participants may eventually be quite successful at raising cognitive skills, their present papers are silent on the issue of intelligence and its modifiability. The training of specific skills (referred to under question number 3, above) has generally proven successful, when the degree of complexity of the particular skill and the method of instruction are properly geared to the learner's level of g. Skill training, though essential and valuable in its own right, demonstrates most clearly that g per se is not a skill, nor any combination of skills, nor can it be characterized in the psychological terms used to describe the nature of skill. Learned skills are, of course, every bit as important as g for getting along in life, but they are not a substitute for g (any more than g is a substitute for skills). The operative difference is that skills can be inculcated, within limits, by psychological means, while the level of g, as such, cannot be permanently raised by training, as far as we know."

Jensen notes that poor children gained less from intervention that did more affluent children.  This also seems to contradict the assertion that the Flynn effect, while it seems to increase those in the lower ranges of intelligence, is in any way amenable to intervention targeted at the disadvantaged.  Whatever the Flynn effect means, it is not good news for egalitarians who hope that eventually the disparities between people in genetic intelligence will go away anytime soon.

In Chapter 11: Population Differences in g, Jensen writes: "The approximately normal distribution of IQ, as measured by nationally standardized tests, shows that, on average, the American black population scores below the white population by about 1.2 standard deviations, equivalent to eighteen IQ points. (Blacks in sub-Saharan Africa score about two standard deviations [approximately thirty IQ points] below the mean of whites on nonverbal tests.)  This statistical mean difference between the American black and white populations has scarcely changed over the past eighty years for which IQ data have been available. However, it varies across different regions of the country, being largest in the Southeast and decreasing in magnitude on a gradient running north and west. The mean difference, which is in evidence by about three years of age, increases slightly from early childhood to maturity. These are simply the phenotypic, psychometric, and statistical facts. The average difference, of course, is relatively small compared to the range of variation within either population and, in fact, is not much greater than the average difference between full siblings reared together in the same family."

This is nothing new, and in fact it agrees with the APA report.  What Jensen does bring to the discussion is how important this disparity is.  In the media, the wide disparity within population groups is always used to dismiss the importance of the mean differences between groups (and also the standard deviation differences between groups).  When the number of people from each identifiable group is added up by IQ groups or occupational categories however, it is easy to see why some groups do better than others.  With a mean IQ of 85, there are very few blacks available with the intelligence to obtain a doctorate degree, while Jews with an average IQ of 117, dominate academics, medicine, etc. based on their small numbers.

Another important phenomena revealed by separating g from other faculties is the fact that on average, blacks exceed whites on short-term memory while whites exceed blacks on spatial visualization.  These areas of differentiation can be found between almost any group, including differences between men and women while they are not equivalent to there being differences in g. (Michael Levin in Why Race Matters notes that both Asians and Jews excel at mathematics, but in ways that use different faculties.)

Jensen also notes that the white-black difference in IQ is even larger when the black population does not have any white ancestry.  In sub-Saharan Africa the average black IQ is from 1.75 to 2 standard deviations below whites, or an IQ of 70, being on average in the retarded group.  Is it no wonder that no sub-Saharan Africans ever developed a written language or developed an advanced culture without outside influence (primarily Arabic before Western domination)?

Jensen also notes, and if my reading is correct this is the only part of the book where he relies on subjective observation rather than statistical data, that: "Their observations were indeed accurate, as I later confirmed by my own observation and testing of pupils in special classes in social and outdoor play activities, however, black children with IQ below seventy seldom appeared as other than quite normal youngsters--energetic sociable, active, motorically well coordinated, and generally indistinguishable from their age-mates in regular classes. But this was not so for as many of the white children with IQ below seventy. More of them were somehow different from their white age-mates in the regular classes. They appeared less competent in social interactions with their classmates and were motorically clumsy or awkward, or walked with a flatfooted gait. The retarded white children more often looked and acted generally retarded in their development than the black children of comparable IQ. From such observations, one gets the impression that the IQ tests are somehow biased against the black pupils and underestimate their true ability.  In most of the cognitive tasks of the classroom that call for conceptual learning and problem solving, however, black and white retarded children of the same IQ do not differ measurably either in classroom performance or on objective achievement tests. Trying out a variety of tests in these classes, I found one exception-tasks that depend only on rote learning and memorization through repetition. On these tasks, retarded black pupils, on average, performed significantly better than white pupils of the same IQ.  The explanation for these differences cannot be that the IQ test is biased in its predictive validity for the children's general scholastic learning, because predictive validity scarcely differs between black and white groups. Nor is the test biased according to any of the other standard criteria of bias (reviewed above). Rather, the explanation lies in the fact that IQ per se does not identify the cause of the child's retardation (nor is it intended to do so). There are two distinguishable types of mental retardation, usually referred to as endogenous and exogenous or, more commonly, as familial and organic. The lower tail (IQ < 70) of the normal distribution of IQ in the population comprises both of these types of retardation."

This quote can be read that black children with an IQ of 70 are more normal, whereas white children are not.  It would be interesting to duplicate these observations by comparing Jewish kids and white kids with say an IQ of 85.  Would the non-Jewish white children seem more normal than the Jewish kids?  What this is showing is that each group has their own genetic mean or average IQ that also impacts regression to the mean.

Lastly, Jensen points out that recent Chinese-American immigrants who came from considerably lower SES than white children also scored 5 IQ points higher.  Over and over again, what we see is that IQ follows the expected mean of the population group being considered.  That g is highly heritable and that it is found variable within families and between groups is no longer disputable.

In Chapter 12: Population Differences in g: Causal Hypotheses, Jensen writes: "The relationship of the g factor to a number of biological variables and its relationship to the size of the white-black differences on various cognitive tests (i.e., Spearman's hypothesis) suggests that the average white-black difference in g has a biological component. Human races are viewed not as discrete, or Platonic, categories, but rather as breeding populations that, as a result of natural selection, have come to differ statistically in the relative frequencies of many polymorphic genes. The genetic distances between various populations form a continuous variable that can be measured in terms of differences in gene frequencies. Racial populations differ in many genetic characteristics, some of which, such as brain size, have behavioral and psychometric correlates, particularly g. What I term the default hypothesis states that the causes of the phenotypic differences between contemporary populations of recent African and European descent arise from the same genetic and environmental factors, and in approximately the same magnitudes, that account for individual differences within each population. Thus genetic and environmental variances between groups and within groups are viewed as essentially the same for both populations. The default hypothesis is able to account for the present evidence on the mean white-black difference in g. There is no need to invoke any ad hoc hypothesis, or a Factor X, that is unique to either the black or the white population. The environmental component of the average g difference between groups is primarily attributable to a host of microenvironmental factors that have biological effects. They result from nongenetic variation in prenatal, perinatal, and neonatal conditions and specific nutritional factors.  The many studies of Spearman's hypothesis using the method of correlated vectors show a strong relationship between the g loadings of a great variety of cognitive tests and the mean black-white differences on those tests. The fact that the same g vectors that are correlated with W-B (white-black) differences are also correlated (and to about the same degree) with vectors composed of various cognitive tests' correlations with a number of genetic, anatomical, and physiological variables suggests that certain biological factors may be related to the average black-white population difference in the level of g.
 The degree to which each of many different psychometric tests is correlated with all of the other tests is directly related to the magnitude of the test's g loading. What may seem surprising, however, is the fact that the degree to which a given test is correlated with any one of the following variables is a positive function of that test's g loading:
*Heritability of test scores.
*Amount of inbreeding depression of test scores.
*Heterosis (hybrid vigor, that is, raised test scores, due to outbreeding).
*Head size (also, by inference, brain size).
*Average evoked potential (AEP) habituation and complexity.
*Glucose metabolic rate as measured by PET scan.
*Average reaction time to elementary cognitive tasks.
*Size of the mean W-B difference on various cognitive tests.
 The one (and probably the only) common factor that links all of these non-psychometric variables to psychometric test scores and also links psychometric test scores to the magnitude of the mean W-B difference is the g factor. The critical role of g in these relationships is shown by the fact that the magnitude of a given test's correlation with any one of the above-listed variables is correlated with the magnitude of the W-B difference on that test. For example, Rushton reported a correlation (r=+.48) between the magnitudes of the mean W-B differences (in the American standardization sample) on eleven sub-tests of the WISC-R and the effect of inbreeding depression on the eleven subtest scores of the Japanese version of the WISC. Further, the subtests' g loadings in the Japanese data predicted the American W-B differences on the WISC-R sub-tests with r=.69-striking evidence of the g factor's robustness across different cultures. Similarly, the magnitude of the mean W-B difference on each of seventeen diverse psychometric tests was predicted (with r=.71, p<.01) by the tests' correlations with head size (a composite measure of length, width, and circumference).
 This association of psychometric tests' g loadings, the tests' correlations with genetic and other biological variables, and the mean W-B differences in test scores cannot be dismissed as happenstance. The failure of theories of group differences in IQ that are based exclusively on attitudinal, cultural, and experiential factors to predict or explain such findings argues strongly that biological factors, whether genetic or environmental in origin, must be investigated. Before examining possible biological factors in racial differences in mental abilities, however, we should be conceptually clear about the biological meaning of the term race."

The above introduction to Chapter 12, which will in my opinion be the most controversial, is where Jensen takes issue with the APA report's conclusion that not enough is known yet to ascribe environment or genetic differences to the W-B difference.  He clearly shows that unless the apologists can provide some evidence for an environmental explanation, then the genetic one must stand as the easiest and most coherent explanation in keeping with evolutionary principles of population differences.

Jensen builds his case starting with basic Darwinism.  From a selection of about 100,000 genes that contribute to genetic variation, most of these genes in the human genome have gone to fixity due to the fundamentals they perform in our species.  That is, for most of the genes that are responsible for how the kidneys work, the circulatory system, and a host of other primitive organs that function quite well without variation as they are, the genes between people are exactly the same.  These genes are too basic and yet fundamental to living to allow for variation.  As is often repeated, we share about 97% of our genes with chimpanzees for this very reason.  In addition, there is as much genetic variation between chimpanzees as there is between chimpanzees and gorillas.  Would any human who observes gorillas and chimpanzees suspect that they very as much as we do to chimpanzees?  This is fundamental to understanding population variation. There is no magic way of determining how much variation in genes is necessary to express behavioral or cognitive differences in people as part of nature's way of building in enough variation to improve survival of different phenotypes under a variety of environments.

Of the genes that do very between breeding population groups, Cavalli-Sforza et al. has been studying 42 races around the world who represent the genes present in those groups at about 1500 A.D. Jensen writes of these studies: "In fact, a PC analysis shows that most of the forty-two populations fall very distinctly into the quadrants formed by using the first and second principal components as axes (see Figure 12.3). They form quite widely separated clusters of the various populations that resemble the "classic" major racial groups--Caucasians in the upper right, Negroids in the lower right, Northeast Asians in the upper left, and Southeast Asians (including South Chinese) and Pacific Islanders in the lower left. The first component (which accounts for 27 percent of the total genetic variation) corresponds roughly to the geographic migration distances (or therefore time since divergence) from sub-Saharan Africa, reflecting to some extent the differences in allele frequencies that are due to genetic drift. The second component (which accounts for 16 percent of the variation) appears to separate the groups climatically, as the groups' positions on PC2 are quite highly correlated with the degrees latitude of their geographic locations. This suggests that not all of the genes used to determine genetic distances are entirely neutral, but at least some of them differ in allele frequencies to some extent because of natural selection for different climatic conditions. I have tried other objective methods of clustering on the same data (varimax rotation of the principal components, common factor analysis, and hierarchical cluster analysis). All of these types of analysis yield essentially the same picture and identify the same major racial groupings. "

It is clear that there are in fact differences between breeding population groups--contrary to what Gould et al. have been claiming, that Homo sapiens have not been around long enough for the mutations to emerge to have occurred that would produce such a large difference in intelligence between one group and another.  But the fact is, mutations are not required, just the distribution of different genes already present to be disproportionately distributed between individuals, races, ethnic groups and even left-handed versus right-handed groups of people.  Any definable group can show significant differences in genes.

 These same studies also have shown that the average IQ of blacks increases from a low in the Southeast to higher means in the rest of the country.  This same gradation in IQ can be seen in the amount of  Caucasoid blood in the black population with a low of 4% to 10% in the Southeast to a high of 40% in the Northeast and Northwest, just as would be expected if the average IQ of blacks without any Caucasoid admixture is an average of about 70.

Another rebuttal to Gould et al. is the impact the polymorphic genes have on the human brain.  Jensen points out that of the 100,000 genes that do vary between individuals (have not gone to fixation) about 50,000 of these are functional in the brain.  What this means is that of all the genes that express differences in people, half of those genes are responsible for differences in how the brain works.  It is clear that with regards to intelligence, differences between races clearly have a tremendous variety of different gene polymorphisms to account for the large differences in intelligence.

So now we are  down to the two alternative hypotheses for the W-B differences in intelligence. Jensen writes: "The psychological, educational, and social factors that differ between families within racial groups have been found to have little, if any, effect on individual differences in the level of g after childhood. This class of variables, largely associated with socioeconomic differences between families, has similarly little effect on the differing average levels of g between native-born, English-speaking whites and blacks. By late adolescence, the IQs of black and white infants adopted by middle or upper-middle SES white parents are, on average, closer to the mean IQ of their respective populations than to that of either their adoptive parents or their adoptive parents' biological children. Preschool programs such as Head Start and the much more intensive and long-term educational interventions (e.g., the Milwaukee Project and the Abecedarian Project) have been shown to have little effect on g."

He goes on to show how all of the small environmental effects that do alter g, taken together or impact a single individual, still would not add up to enough difference to account for the variance between groups.  That is, we know the environmental impacts as well as we know genetic effects, and they don't add up to a hill of beans.  The environmentalists spend more time criticizing the most solid hypothesis while providing no proof for an alternative one.

Finally, Jensen writes: "In contrast to these various ad hoc hypotheses intended to explain the average W-B population difference in cognitive ability, particularly g, the default hypothesis has the attributes of simplicity, internal coherence, and parsimony of explanation. Further, it does not violate Occam's razor by treating one particular racial population as a special case that is culturally far more different from any other populations. The size of the cultural difference that needs to be hypothesized by a purely environmental theory of the W-B difference is far greater than the relatively small genetic difference implied by our evolution from common human ancestors. The default hypothesis explains differences in g between populations in terms of quantitative variation in the very same genetic and environmental factors that influence the neural substrate of g and cause individual variation within all human populations. This hypothesis is consistent with a preponderance of psychometric, behavior-genetic, and evolutionary lines of evidence. And like true scientific hypotheses generally, it continually invites empirical refutation. It should ultimately be judged on the same basis, so aptly described by the anthropologist Owen Lovejoy, for judging the Darwinian theory of human evolution: 'Evolutionary scenarios must be evaluated much in the same way that jury members must judge a prosecutor's narrative. Ultimately they must make their judgment not on the basis of any single fact or observation, but on the totality of the available evidence. Rarely will any single item of evidence prove pivotal in determining whether a prosecutor's scenario or the defense's alternative is most likely to be correct. Many single details may actually fail to favor one scenario over another. The most probable account, instead, is the one which is the most internally consistent--the one in which all the facts mesh together most neatly with one another and with the motives in the case. Of paramount importance is the economy of explanation. There are always alternative explanations of any single isolated fact. The greater the number of special explanations required in a narrative, however, the less probable its accuracy. An effective scenario almost always has a compelling facility to explain a chain of facts with a minimum of such special explanations. Instead the pieces of the puzzle should fall into place.'"

I have tried to present some of the more interesting (to me at least) contents of The g Factor to try and show the breadth of the subject matter that Jensen covers.  The book is 672 pages of tightly packed, scientific analysis, and philosophical qualifications with regards to the issue of intelligence and its genetic basis.  Jensen does not address any policy issues, or make any recommendations about what should be done with this information.  But the book should be on every educator's bookshelf if they truly want to understand how to approach improving the quality of the workforce in the next millennium.

Christopher Brand's forthcoming book The g Factor (a few copies were published in 1997 but the publisher dropped the book under pressure) deal with this same subject with additional policy recommendations that should keep this debate going.  What will be more interesting than anything else however will be to see how Jensen's masterpiece is suppressed over the coming months.  It would be a tragedy, but the boycott seems to be working so far.  Very little about the book has been seen in the media.


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