Abstract
Studies of intelligence in children reveal significantly higher heritability among groups with high socioeconomic status (SES) than among groups with low SES. These interaction effects, however, have not been examined in adults, when between-families environmental effects are reduced. Using 1,702 adult twins (aged 24–84) for whom intelligence assessment data were available, we tested for interactions between childhood SES and genetic effects, between-families environmental effects, and unique environmental effects. Higher SES was associated with higher mean intelligence scores. Moreover, the magnitude of genetic influences on intelligence was proportional to SES. By contrast, environmental influences were constant. These results suggest that rather than setting lower and upper bounds on intelligence, genes multiply environmental inputs that support intellectual growth. This mechanism implies that increasing SES may raise average intelligence but also magnifies individual differences in intelligence.
References
Section:
| Akaike H. (1987). Factor analysis and AIC. Psychometrika, 52, 317–332. doi:10.1007/BF02294359 Google Scholar CrossRef | |
| Bates T. C., Lewis G. J. (2012). Towards a genetically informed approach in the social sciences: Strengths and an opportunity. Personality and Individual Differences, 53, 374–380. doi:10.1016/j.paid.2012.03.002 Google Scholar CrossRef | |
| Boker S., Neale M., Maes H., Wilde M., Spiegel M., Brick T., . . . Fox J. (2011). OpenMx: An open source extended structural equation modeling framework. Psychometrika, 76, 306–317. doi:10.1007/s11336-010-9200-6 Google Scholar CrossRef, Medline | |
| Brim O.G., Ryff C.D., Kessler R. C. (Eds.). (2004). How healthy are we? A national study of well-being at midlife. Chicago, IL: University of Chicago Press. Google Scholar | |
| Bronfenbrenner U., Ceci S. J. (1994). Nature-nurture reconceptualized in developmental perspective: A bioecological model. Psychological Review, 101, 568–586. doi:10.1037/0033-295X.101.4.568 Google Scholar CrossRef, Medline | |
| Deary I. J. (2012). Intelligence. Annual Review of Psychology, 63, 453–482. doi:10.1146/annurev-psych-120710-100353 Google Scholar CrossRef, Medline | |
| Deary I. J., Spinath F. M., Bates T. C. (2006). Genetics of intelligence. European Journal of Human Genetics, 14, 690–700. doi:10.1038/sj.ejhg.5201588 Google Scholar CrossRef, Medline | |
| Duncan O. D. (1961). A socioeconomic index for all occupations. In Reiss J. J. (Ed.), Occupations and social status (pp. 109–138). New York, NY: Free Press of Glencoe. Google Scholar | |
| Flynn J. R. (2009). What is intelligence? Beyond the Flynn effect. London, England: Cambridge University Press. Google Scholar | |
| Giedd J. N., Blumenthal J., Jeffries N. O., Castellanos F. X., Liu H., Zijdenbos A., . . . Rapoport J. L. (1999). Brain development during childhood and adolescence: A longitudinal MRI study. Nature Neuroscience, 2, 861–863. doi:10.1038/13158 Google Scholar CrossRef, Medline | |
| Gottesman I. I., Shields J. (1982). Schizophrenia: The epigenetic puzzle. Cambridge, England: Cambridge University Press. Google Scholar | |
| Grant M. D., Kremen W. S., Jacobson K. C., Franz C., Xian H., Eisen S. A., . . . Lyons M. J. (2010). Does parental education have a moderating effect on the genetic and environmental influences of general cognitive ability in early adulthood? Behavior Genetics, 40, 438–446. doi: 10.1007/s10519-010-9351-3 Google Scholar CrossRef, Medline | |
| Hanscombe K. B., Trzaskowski M., Haworth C. M., Davis O. S., Dale P. S., Plomin R. (2012). Socioeconomic status (SES) and children’s intelligence (IQ): In a UK-representative sample SES moderates the environmental, not genetic, effect on IQ. PLoS ONE, 7, e30320. Retrieved from http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030320 Google Scholar | |
| Harden K. P., Turkheimer E., Loehlin J. C. (2007). Genotype by environment interaction in adolescents’ cognitive aptitude. Behavior Genetics, 37, 273–283. doi:10.1007/S10519-006-91134 Google Scholar CrossRef, Medline | |
| Harris J. R. (1995). Where is the child’s environment? A group socialization theory of development. Psychological Review, 102, 458–489. doi:10.1037/0033-295x.102.3.458 Google Scholar CrossRef | |
| Haworth C. M., Wright M. J., Luciano M., Martin N. G., de Geus E. J., van Beijsterveldt C. E., . . . Plomin R. (2010). The heritability of general cognitive ability increases linearly from childhood to young adulthood. Molecular Psychiatry, 15, 1112–1120. doi:10.1038/mp.2009.55 Google Scholar CrossRef, Medline | |
| Kennedy W. A., Vanderiet V., White J. C. (1963). A normative sample of intelligence and achievement of Negro elementary school children in the Southeastern United-States. Monographs of the Society for Research in Child Development, 28(6). Google Scholar CrossRef, Medline | |
| Lezak M. D. (1995). Neuropsychological assessment (3rd ed.). New York, NY: Oxford University Press. Google Scholar | |
| Loehlin J. C., Harden K. P., Turkheimer E. (2009). The effect of assumptions about parental assortative mating and genotype-income correlation on estimates of genotype–environment interaction in the National Merit Twin Study. Behavior Genetics, 39, 165–169. doi:10.1007/s10519-008-9253-9 Google Scholar CrossRef, Medline | |
| McGue M., Bouchard T. J.Jr. (1984). Adjustment of twin data for the effects of age and sex. Behavior Genetics, 14, 325–343. doi:10.1007/BF01080045 Google Scholar CrossRef, Medline | |
| Purcell S. (2002). Variance components models for gene-environment interaction in twin analysis. Twin Research, 5, 554–571. Google Scholar CrossRef, Medline | |
| R Development Core Team. (2013). R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing. Available from http://www.R-project.org Google Scholar | |
| Rhemtulla M., Tucker-Drob E. M. (2012). Gene-by-socioeconomic status interaction on school readiness. Behavior Genetics, 42, 549–558. doi:10.1007/s10519-012-9527-0 Google Scholar CrossRef, Medline | |
| Rowe D. C., Jacobson K. C., Van den Oord E. J. (1999). Genetic and environmental influences on vocabulary IQ: Parental education level as moderator. Child Development, 70, 1151–1162. doi:10.1111/1467-8624.00084 Google Scholar CrossRef, Medline | |
| Sackett P. R., Kuncel N. R., Beatty A. S., Rigdon J. L., Shen W., Kiger T. B. (2012). The role of socioeconomic status in SAT-grade relationships and in college admissions decisions. Psychological Science, 23, 1000–1007. doi:10.1177/0956797612438732 Google Scholar Link | |
| Salthouse T. A. (1996). The processing-speed theory of adult age differences in cognition. Psychological Review, 103, 403–428. doi:10.1037/0033-295X.103.3.403 Google Scholar CrossRef, Medline | |
| Salthouse T. A., Prill K. A. (1987). Inferences about age impairments in inferential reasoning. Psychology and Aging, 2, 43–51. doi:10.1037/0882-7974.2.1.43 Google Scholar CrossRef, Medline | |
| Shaw P., Greenstein D., Lerch J., Clasen L., Lenroot R., Gogtay N., . . . Giedd J. (2006). Intellectual ability and cortical development in children and adolescents. Nature, 440, 676–679. doi:10.1038/nature04513 Google Scholar CrossRef, Medline | |
| Taylor J., Roehrig A. D., Soden Hensler B., Connor C. M., Schatschneider C. (2010). Teacher quality moderates the genetic effects on early reading. Science, 328, 512–514. doi:10.1126/science.1186149 Google Scholar CrossRef, Medline | |
| Tucker-Drob E. M., Rhemtulla M., Harden K. P., Turkheimer E., Fask D. (2011). Emergence of a Gene × Socioeconomic Status interaction on infant mental ability between 10 months and 2 years. Psychological Science, 22, 125–133. doi:10.1177/0956797610392926 Google Scholar Link | |
| Tun P. A., Lachman M. E. (2005). Brief test of adult cognition by telephone (BTACT) (Technical Report). Retrieved from http://midus.wisc.edu/midus2/project3/TechReport_BTACT.pdf Google Scholar | |
| Turkheimer E., Gottesman I. I. (1991). Individual differences and the canalization of human behavior. Developmental Psychology, 27, 18–22. doi:10.1037/0012-1649.27.1.18 Google Scholar CrossRef | |
| Turkheimer E., Haley A., Waldron M., D’Onofrio B., Gottesman I. I. (2003). Socioeconomic status modifies heritability of IQ in young children. Psychological Science, 14, 623–628. doi:10.1046/j.0956-7976.2003.psci_1475.x Google Scholar Link | |
| van der Sluis S., Posthuma D., Dolan C. V. (2012). A note on false positives and power in G × E modelling of twin data. Behavior Genetics, 42, 170–186. doi:10.1007/s10519-011-9480-3 Google Scholar CrossRef, Medline | |
| van der Sluis S., Willemsen G., de Geus E. J., Boomsma D. I., Posthuma D. (2008). Gene–environment interaction in adults’ IQ scores: Measures of past and present environment. Behavior Genetics, 38, 348–360. doi:10.1007/s10519-008-9212-5 Google Scholar CrossRef, Medline | |
| Wechsler D. (1997). Wechsler Adult Intelligence Scale III. San Antonio, TX: Psychological Corp. Google Scholar |
