Abstract
Direct estimates of IQ heritability based on a single family relationship such as adopted-apart relatives are often 50% greater than indirect estimates that rely on differences in correlations such as the classical twin method or nonadoptive-adoptive comparisons. Factors such as nonadditive genetic variance, assortative mating, selective placement, measurement error, age differences, and genotype-environment correlation and interaction do not obviously explain the difference between direct and indirect IQ heritability estimates. Because direct estimates are derived from separated individuals and indirect estimates are derived from individuals reared together in families, some aspect of the within-family environment seems a likely candidate but its exact nature remains to be understood.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Bouchard, T. J., Jr. (1987). Environmental determinants of IQ similarity in identical twins reared apart. Paper presented at the Seventeenth Annual Meeting of the Behavior Genetics Association, Minneapolis, June 25.
Bouchard, T. J., Jr., and McGue, M. (1981). Familial studies of intelligence: A review.Science 212:1055–1059.
Davidon, W. C. (1975). Optimally conditioned optimization algorithms without line searches.Math. Program. 9:1–30.
DeFries, J. C., and Plomin, R. (1978). Behavioral genetics.Annu. Rev. Psychol. 29:473–515.
Eaves, L. J. (1978). Twins as a basis for the causal analysis of human personality. In Nance, W. E. (ed.),Twin Research, Part A: Psychology and Methodology, Alan R. Liss, New York, pp. 151–174.
Horn, J. M., Loehlin, J. C., and Willerman, L. (1979). Intellectual resemblace among adoptive and biological relatives: The Texas Adoption Project.Behav. Genet. 9:177–207.
Horn, J. M., Loehlin, J. C., and Willerman, L. (1986). The TAP ten years later. Symposium at the Sixteenth Annual Meeting of the Behavior Genetics Association, June 18, Honolulu, Hawaii.
Lathrope, G. M., Lalouel, J. M., and Jacquard, A. (1984). Path analysis of family resemblance and gene-environment interaction.Biometrics 40:611–625.
Loehlin, J. C. (1979). Combining data from different groups in human behavior genetics. In Royce, J. R., and Mos, L. P. (eds.),Theoretical Advances in Behavior Genetics, Sijthoff & Noordhoff, Alphen aan den Rijn, The Netherlands, pp. 303–334.
Loehlin, J. C., and DeFries, J. C. (1987). Genotype-environment correlation and IQ.Behav. Genet. 17:263–278.
Loehlin, J. C., and Nichols, R. C. (1976).Heredity, Environment, and Personality: A Study of 850 Sets of Twins, University of Texas Press, Austin.
McClearn, G. E., Pedersen, N. L., Plomin, R., Nesselroade, J. R., and Friberg, L. (1988). The Swedish Adoption/Twin Study on Aging. (submitted for publication).
Mittler, P. (1971).The Study of Twins, Penguin, Baltimore, Md.
Pedersen, N. L., McClearn, G. E., Plomin, R., and Friberg, L. (1985). Separated fraternal twins: Resemblance for cognitive abilities.Behav. Genet. 15:407–419.
Plomin, R. (1986).Development, Genetics, and Psychology, Lawrence Erlbaum Associates, Hillsdale, N.J.
Plomin, R. (1987). The nature and nurture of cognitive abilities. In Sternberg, R. (ed.),Advances in the Psychology of Human Intelligence, Lawrence Erlbaum Associates, Hillsdale, N.J., Vol. 4, pp. 1–33.
Plomin, R., and Daniels, D. (1987). Why are children in the same family so different from each other?Behav. Brain Sci. 10:1–16.
Plomin, R., and DeFries, J. C. (1980). Genetics and intelligence.Intelligence 4:15–24.
Plomin, R., DeFries, J. C., and Loehlin, J. C. (1977). Genotype-environment interaction and correlation in the analysis of human behavior.Psychol. Bull. 84:309–322.
Plomin, R., DeFries, J. C., and Fulker, D. W. (1988a).Nature and Nurture in Infancy and Early Childhood, Cambridge University Press, New York.
Plomin, R., Pedersen, N. L., McClearn, G. E., Nesselroade, J. R., and Bergeman, C. S. (1988b). EAS temperaments during the last half of the life span: Twins reared apart and twins reared together.Psychol. Aging 3:43–50.
Skodak, M., and Skeels, H. M. (1949). A final follow-up on one hundred adopted children.J. Genet. Psychol. 75:85–125.
Snyderman, M., and Rothman, S. (1987). Survey of expert opinion on intelligence and aptitude testing.Am. Psychol. 42:137–144.
Snygg, D. (1938). The relation between the intelligence of mothers and of their children living in foster homes.J. Genet. Psychol. 52:401–406.
Tellegen, A., Lykken, D. T., Bouchard, T. J., Wilcox, K., Segal, N., and Rich, S. (1988). Personality similarities in twins reared apart and together.J. Personal. Soc. Psychol. 54:1031–1039.
Vandenberg, S. G. (1976). Twin studies. In Kaplan, A. R. (ed.),Human Behavior Genetics, Charles C Thomas, Springfield, Ill.
Author information
Authors and Affiliations
Additional information
The Colorado Adoption Project is supported by grants from the National Science Foundation (BNS-86443938) and the National Institute of Child Health and Human Development (HD-10333 and HD-18426). The Texas Adoption Project has been supported by grants from the National Institute of Mental Health (MH-24280) and the National Science Foundation (BNS-8209882).
Rights and permissions
About this article
Cite this article
Plomin, R., Loehlin, J.C. Direct and indirect IQ heritability estimates: A puzzle. Behav Genet 19, 331–342 (1989). https://doi.org/10.1007/BF01066162
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01066162