The g Factor: The Science of Mental Ability (Human Evolution, Behavior, and Intelligence) 1St Edition Edition

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.