Book contents
- Frontmatter
- Contents
- List of contributors
- Preface
- Part I The nature–nurture question: New advances in behavior-genetic research on intelligence
- 1 Behavior-Genetic and Socialization theories of intelligence: Truce and reconciliation
- 2 The puzzle of nongenetic variance
- 3 Identifying genes for cognitive abilities and disabilities
- 4 Heredity, environment, and IQ in the Texas Adoption Project
- 5 IQ similarity in twins reared apart: Findings and responses to critics
- Part II Novel theoretical perspectives on the genes and culture controversy
- Part III Specific issues in the nature–nurture controversy
- Part IV Integration and conclusions
- Name index
- Subject index
3 - Identifying genes for cognitive abilities and disabilities
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- List of contributors
- Preface
- Part I The nature–nurture question: New advances in behavior-genetic research on intelligence
- 1 Behavior-Genetic and Socialization theories of intelligence: Truce and reconciliation
- 2 The puzzle of nongenetic variance
- 3 Identifying genes for cognitive abilities and disabilities
- 4 Heredity, environment, and IQ in the Texas Adoption Project
- 5 IQ similarity in twins reared apart: Findings and responses to critics
- Part II Novel theoretical perspectives on the genes and culture controversy
- Part III Specific issues in the nature–nurture controversy
- Part IV Integration and conclusions
- Name index
- Subject index
Summary
I predict that the next generation of psychologists will wonder what all the nature–nurture fuss was about. It will seem obvious that genetic differences as well as environmental differences contribute to individual differences in cognitive abilities and disabilities. This prediction relies on the hope that psychology will continue to be a science, because in science, data reign supreme, and the data are clear: Genetics is important. Converging evidence from family, twin, and adoption studies provides a better case for significant and substantial genetic contributions to cognitive abilities, especially general cognitive ability (intelligence), than for any other domain of behavior or medicine (Plomin, Owen, & McGuffin, 1994b). Few scientists seriously dispute any longer the conclusion that cognitive abilities show significant genetic influence. (See, chapters 4 and 5, this volume, for discussions of this issue.)
The magnitude of genetic influence is still not universally appreciated, however. For general cognitive ability, the world's literature suggests that about half of the total variance in IQ scores can be accounted for by genetic variance (Chipuer, Rovine, & Plomin, 1990; Loehlin, 1989). It should be noted that the total variance includes error variance. Correcting for unreliability of measurement, heritability would be higher. Also, the world's literature includes disproportionate numbers of young children. As discussed below, new evidence indicates that adults show greater heritability. Estimating the magnitude of the genetic effect is more difficult than determining its statistical significance, but regardless of the precise estimate of heritability (the genetic effect size), the point is that genetic influence on IQ test scores is not only significant; it is also very substantial.
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- Intelligence, Heredity and Environment , pp. 89 - 104Publisher: Cambridge University PressPrint publication year: 1996
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