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The g Factor: The Science of Mental Ability (Human Evolution, Behavior, and Intelligence)

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Jensen's definitions and descriptions of his science are fascinating. g stands for General Ability. It is neither IQ nor intelligence itself. Intelligence, per Jensen, is the capacity of all animals to perceive and act upon the natural world.

The Intelligence Quotient is a statistical artifice that maps individuals' problem solving abilities into a linear scale according to a Gaussian bell-curve distribution. By definition the average IQ is 100 and the standard deviation (SD) 15. By the properties of the bell curve approximately 2/3 of the population falls within one SD of the median, that is, between 85 and 115.

However, as Jensen points out repeatedly, general ability is not a linear function. The discriminators are whether or not an individual can solve specific problems. There is no way to define a lineal relationship between two individuals if once can figure out (for instance) the lowest primo number greater than 90 and another cannot, or one can figure that context requires the word above to be "prime" not "primo" and another cannot. There is no metric for "g" itself. Rather, all tests of mental ability have a degree of "g loading." Psychometrics is the science of assessing and manipulating information about a quality that cannot be measured directly.

Jensen devotes much energy to defending the validity of "g", this thing that defies direct measurement. It is real because:
a) It is statistically "there." It is highly correlated among myriad tests.
b) It works in the real world. There is no single discriminator that approaches the value of "g", usually proxied by an IQ test score, as a predictor of educational or job performance.
c) It has equal predictive power for both sexes, all ages and all populations of mankind. It is independent (as he takes endless pages to prove) of race, language and socio-economic status (SES).
d) Many seemingly unrelated kinds of tests all turn out to measure the same thing. Tests may be verbal or pictorial, or may simply measure the time it takes to react to and act upon a visual or auditory stimulus.
e) By adulthood it no longer has much to do with advantages such as hearing Mozart in the womb or a Montessori kindergarten, or disadvantages such as Jim Crow and slavery.

The other reviews of this book are quite good. Some of Jensen's many fascinating observations:
o Incest is a bad idea. The offspring have a significant intelligence deficit.
o Smart parents, alas, can't count on having equally smart kids. On average their intelligence regresses halfway back to the mean (100 for white Americans). On the bright side, the average people manage by dumb luck to produce enough smarties for each succeeding generation.
o Breast feeding makes a huge difference, about 7 IQ points. Blacks do not breast feed as often or as long as whites. Big, easy change to make in society.
o The factors generally agreed to comprise "g" differ among races and sexes. Blacks exceed whites in short term memory. Men exceed women in spatial intelligence. When the many individual factors are aggregated they reveal different means for different races, with whites in the middle with an average of 100.
o Individuals with IQs below 70 are generally considered to be retarded. White retarded kids frequently look and act somehow different, while retarded kids of other races are more normal in terms of socialization, motor skills and energy. This is related to the two types of retardation, familial and organic. In simple words, there is something "wrong with" an organically retarded child. A bad forceps delivery, spina difida or one of a number of identifiable anomalies. Familial retardation, on the other hand, simply represents a bad spin of the chromosomal wheel of fortune that is sexual reproduction. The odds are higher in populations whose median IQs are lower.
o Cause for concern: If Vanhansen and Lynn are right in "IQ and the Wealth of Nations" there are perhaps a dozen countries in which the average citizen would be considered retarded and hence marginally educable by U.S. standards.
o Illiteracy is not always a matter of reading. Below the threshold of retardation people often have the same inability to understand a sentence whether it is written or spoken. The issue is having enough "g" to make sense out of the words.
o People with lower IQs are markedly more fertile than those with higher IQs. This dysgenic (opposite of eugenic) trend stands to lower "g" within the U.S. population. Average intelligence will of course remain at 100 because by definition it is the population mean.

Jensen comes across through this book as first and foremost an inquisitive mind, a scientist. He often states with unashamed candor that he (nor anybody else) knows the answer to some knotty problems of psychometrics, like the Flynn effect that shows overall intelligence rising 3 points per generation. Contrast his thoroughness and openness with the tone of advocacy found in Stephen Jay Gould (Mismeasure of Man) and sites such as fairtest dot org. Steven Pinker describes in "The Blank Slate, the Modern Denial of Human Nature" the extreme and prolonged abuse Jensen has taken from the academic community. I'm happy to report he hasn't lost his sense of balance. Or sense of humor.

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 researched and extended Charles Spearman's (1927) seminal concept of g, the general factor of intelligence. The g Factor is an awesome and monumental exposition of the case for the reality of g. It does not draw back from its most controversial conclusions -- that the average differences in IQ found between Blacks and Whites has a substantial hereditary component, and that this difference has important societal consequences. However, The g Factor is not about race, as such. The first five chapters deal with the intellectual history of the discovery of g and various models of how to conceptualize intelligence. Other chapters deal with the biological correlates of g (excluding race), its heritability, and its practical predictive power. The fact that psychometric g has many physical correlates proves that it is not just a methodological artifact. Among biological variables, g loads on heritability coefficients determined from twin studies and inbreeding depression scores calculated in children born from cousin-marriages. g is also related to brain size measured by Magnetic Resonance Imaging (MRI), brain evoked potentials, and intracellular brain pH levels. It (g) is a product of human evolution and is also found in non-human animals. Despite these caveats, The Bell Curve affair allows one to safely predict that The g Factor's coverage of race will strike many as of central importance. All the issues Jensen raised in 1969 are still with us today. Indeed, much of the opposition to IQ testing and heritability would probably disappear if it were not for the stubborn and unwelcome fact that, despite extensive well funded programs of intervention, the Black-White difference refuses to go quietly into the night. Chapter 11 of The g Factor fully documents that, on average, the American Black population scores below the White population by about 1.2 standard deviations, equivalent to 18 IQ points. (This magnitude of difference gives a median overlap of less than 15 percent, meaning that less than 15 percent of the Black population exceeds the White average of 50 percent). The difference between Blacks and Whites in average IQ scores has scarcely changed over the past 80 years (despite some claims that the gap is narrowing) and can be observed as early as three years of age. Controlling for overall socioeconomic level only reduces the mean difference by 4 IQ points. Chapter 12 presents Jensen's technical arguments for why he believes that race differences are about 50 percent heritable. He emphasizes the fact that it is precisely those components of intelligence tests that are most heritable and that most relate to brain size which most profoundly differentiate Blacks from Whites.

First, I am not a professional psychologist nor do I plan to become one. My BS is in Psychology and I have done Cognitive and Neuroscience research. This is a demanding book if you are not versed the field of psychometrics. Jensen cannot avoid having to present some of this information in a technical manner. He does, however, present the technical details of the subject in the clearest possible way. In fact this book has done much to strengthen my intrest in statistics.

The g-factor would be great reading for someone who has read some of the more popular books about human intelligence(Bell Curve, Mismeasure of Man, etc..) and is looking for a broader perspective on these issues. The highly controvesial subjects (race, environment vs. heredity, education) only account for a few parts of the book. Many of the other subjects(like world IQ increases, biological correlates, the history of g, and the politicizing of IQ) are equally facinating. Perhaps the greatest aspect of the book is Jensen's perspective on this subject. Many of his views are as fresh and creative as they are comprehensive.

There has been a conspiracy, of sorts, by the popular press, the news media, and other entrenched powers that be, to hide what is really known about intelligence. This book is a complete survey of all the research known about intelligence. The simplest definition of intelligence is "the ability to reason and learn". The evidence is compelling that intelligence is a real trait, it's biologically based, strongly influenced by heredity, and different racial groups have different average levels of intelligence and a big part of that difference is genetic and not based on environment.

There is nothing really "new" in this book. But it compiles together in one book all the research about intelligence. There hasn't been a comprehensive survey of this sort written in decades.

Everyone should read this book. The Bell Curve is also a book that everyone should read, but this book should be read first. The Bell Curve starts with the assumption that intelligence is genetically influenced, but most people, indoctrinated by the liberal media, don't believe that or understand it. The g Factor presents the overwhelming evidence that there is indeed a genetically influenced general factor of intelligence.

Professor Jensen's work on mental abilities, as summarized in this book, examines the different aspects of intelligence in a great deal of detail, including the history of the subject along with the work of early researchers, the different schools of thought, the biological correlates, heritability, environmental factors, the gender and race differences and plausible explanations, the role of intelligence in a person's development and the social implications.

The subject of human intelligence had been a controversial one since its conception. To claim that different people have different levels of intelligence runs counter to the cherished notion that all men are created equal. However, empirical evidence is overwhelming that every human being is not born with equal potential.

Some people do not like the findings of scientific studies because the findings undermine the premises of their belief, and they tend to attack and discredit the scientist and impugn his motive. Others may not like the findings but accept them if they are satisfied that the findings are the results of scientific methods. This book appeals to the latter group, as the professor was very meticulous in explaining the hypothesis, the experiment, the data, and the analysis. He was very candid about what he was sure and what he was not so sure and why.

I learned a lot about the subject of human intelligence from this book. More importantly, as I read this book, I could see that even as the professor pursues the subject with uncommon vigor, he is also a healthy all-around skeptic and would not rest until all arguments, including "rival" ideas, have been thought through. For this reason, I believe what I learned is the best knowledge to date of the subject.

If you are seriously interested in the subject of mental abilities, there is frankly no substitute to this book.

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?)

George Bernard Shaw said that reading Das Capital by Karl Marx, "would make a man out of you." Actually, Marx's pie-in-the-sky egalitarianism is more the stuff of teenagers than of men. Jensen's G Factor, on the other hand, is about as sophisticated as social science gets, and he pulls no punches. So be ready to venture out from PC's reassuring bosom into the cold world of reality...and bring your statistics textbook with you for help.

The Bell Curve was a book that was well written and researched. Much of the theory was based on the work of Arthur Jenson. Arthur Jenson has longed argued and backed up with research that IQ is something real that can be measured and is important to human success. It is also largely inherited. Most of our IQ is measured by the 'g' factor, which put (very) simply is a measure for intellectual horsepower.

Don't be mistaken, this book is not light reading. It is very long and demands a lot of attention from the reader. You might say that while this book is easily followed by an intelligent reader, it makes the Bell Curve look like a simple magazine article in comparison. Jenson backs up everything he says with statistics and facts. He is a genious.

Of course the book is very senitive on political terms and falls
far short of being politically correct. While Jenson does not go out of his way to offend or be insensitive he also does not avoid controversy. May biggest problem is the price of the book. I would like to see it available in a much cheaper paperback version....or maybe even an abridged version. But the book looks and reads like a masterpeice. Unless you are looking for left-wing fluff you won't be dissapointed.

This is a great book. I have a BS in Psychology, so I did have some background on the subject before I jumped in, but anyone that's curious about the subject of human intelligence will find much of interest here. The only part of the book that I didn't "get" was the statistics (having only taken a couple of very basic stats courses in college). Overall, highly recommended!

I found the "The G Factor:...' to be enlightening and thoroughly researched book on a fascinating topic. Although the basic premise, that intellignece matters and that it is primarily inherited was evident, the book was rarely boring. The basic premise regarding intelligence was broadened by Jensen to explain intellignece, G, in statistical and physical terms with forays into G's manifestations in life. The book will not appeal to people without a strong interest in statistics; it will not appeal to people who believe that the environment is the primary shaper of our personailties. I have two criticisms of the book. The book could have been omposed better; sentences were sometimes very long with excessive flourish. My second criticism concerns the authors purpose. Although I have no doubt as to the validity of the information presented, I would wonder about the emphasis of black and white racial differences... I would have liked to see more racial balance in the examination of racial differences. Overall, I found the book to be a fascinating and enlightening.