The G Factor: The Science of Mental Ability

By Arthur R. Jensen | Go to book overview

ferent heterotic effects on the various tests are specifically related to the tests' g loadings. The column vector of the heterosis index on each of the fifteen tests and the column vector of the tests' g loadings show a rank-order correlation (with tests' reliability coefficients partialed out) of +.52 (p < .05). This finding for heterosis, along with the findings for inbreeding depression, leaves little doubt that a significant part of the genetic basis of psychometric g is attributable to dominance of the alleles that to some degree enhance phenotypic mental abilities.

I have found that many people outside the field of differential psychology (including a majority of psychologists and other social scientists) are very little aware of the presently vast methodological and empirical research literature directly related to the genetics of human mental ability, not to mention many other behavioral traits. Since its inception in 1970, the Behavior Genetics Association has published it own research journal ( Behavior Genetics), but much of the research in this field also appears in many other psychology and genetics journals (mostly in Intelligence and in Personality and Individual Differences). It is an almost full-time job just to keep up with the research literature in one specialized area of the whole field of behavior genetics, such as the genetics of mental ability. For those who have not devoted their career to this field, there are fortunately many excellent summaries that describe the essential logic of quantitative genetics methodology and report the main empirical findings derived from these methods in the study of human mental abilities. Various summaries can be recommended according to the amount of specialized background the reader may bring to them.

My own ( Jensen, 1981 a, Chapter 3, pp. 74-127) attempt to explain the genetics of mental ability as clearly and simply as possible for readers with no technical background whatsoever in this field begins with the earliest study by Galton, introduces the basic concepts of Mendelian and quantitative genetics, and succinctly reviews the main findings regarding the various sources of genetic and environmental variance in IQ. For those who have no prior knowledge of how behavioral genetics "works," this chapter may serve as an essential prerequisite for any of the other items listed below. Another good introduction to behavior genetics methodology, briefer but slightly more technical than Jensen ( 1981 a), is by Eysenck ( 1984a). Plomin ( 1990) offers a more extended elementary treatment. The reading level in Plomin ( 1994) presents no real technical difficulty for the uninitiated, but its main theme is somewhat specialized and would probably be more appreciated by readers who have some familiarity with the standard material presented in the previously mentioned references. Plomin, DeFries, & McClearn ( 1990) provide one of the standard introductory textbooks of behavioral genetics. There are also several fairly comprehensive reviews of genetic research on human abilities that assume some knowledge of the terminology and methodology of quantitative genetics (but do not make them absolutely essential for understanding the main conclusions): Bouchard, 1993; Bouchard et al., 1996; Plomin, 1988; Scarr & Carter-Saltzman, 1982; and Vandenberg & Vogler, 1985. A book edited by Plomin & McClearn ( 1993) presents elementary accounts of specialized topics in human behavioral genetics, although the first two chapters introduce the most basic general principles of quantitative genetics. Accounts of the historical and controversial aspects of the so-called "nature-nurture" debate


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The G Factor: The Science of Mental Ability
Table of contents

Table of contents

  • Title Page iii
  • Contents vii
  • Preface ix
  • Acknowledgments xiii
  • Chapter 2 - The Discovery of G 18
  • Notes 39
  • Chapter 3 - The Trouble with "Intelligence" 45
  • Notes 68
  • Chapter 4 - Models and Characteristics of G 95
  • Chapter 5 - Challenges to G 105
  • Notes 133
  • Chapter 6 - Biological Correlates of G 137
  • Notes 165
  • Chapter 7 - The Heritability of G 169
  • Notes 197
  • Chapter 8 - Information Processing and G 203
  • Notes 261
  • Chapter 9 - The Practical Validity of G 270
  • Notes 301
  • Chapter 10 - Construct, Vehicles, and Measurements 306
  • Notes 344
  • Chapter 11 - Population Differences in G 350
  • Notes 402
  • Chapter 12 - Population Differences in G: Causal Hypotheses 418
  • Notes 516
  • Chapter 13 - Sex Differences in G 531
  • Notes 542
  • Chapter 14 - The G Nexus 544
  • Notes 579
  • Appendix A - Spearman's "Law of Diminishing Returns" 585
  • Appendix B - Method of Correlated Vectors 589
  • Appendix C - Multivariate Analyses of a Nexus 593
  • References 597
  • Name Index 635
  • Subject Index 643
  • About the Author 649


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