Edward Conard

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  • “…challenges misconceptions that distort our economic debates.” - Arthur Brooks, President of the American Enterprise Institute
  • “…a must-read for serious students of economic policy.” - Glenn Hubbard, Dean, Columbia Business School, and former Chairman of the Council of Economic Advisers
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AI Summary. The study estimates that a 1 standard deviation increase in the quality of the parental environment raises IQ by about 2.83 points, with the parental environment accounting for 4% of the variance in full-scale IQ at age 15. Genetic factors account for 42% of IQ variance in adulthood.

Emily Willoughby, Matt McGue, William Iacono and James Lee Intelligence
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A 1SD increase in parental environment quality boosts IQ by ~2.83 points, highlighting the economic benefits of investing in family environments. @MattMcGue

How much do parental environment and genes each shape adult IQ?

Core argument: A 1 SD increase in parental environment quality is associated with an IQ gain of about 2.83 points in the study of adoptive and biological families with 30-year-old offspring.

The study highlights that a 1 standard deviation (SD) increase in the quality of the parental environment can enhance IQ by approximately 2.83 points, emphasizing the economic implications of investing in family environments. The biometric decomposition of variance shows that the parental environment contributes 4% to the variance in full-scale IQs at age 15, with a standard deviation of 14.2 for adopted offspring. Despite the modest impact of the parental environment, genetic factors remain predominant, accounting for 42% of IQ variance in adulthood. These findings suggest that while genetic influences are significant, targeted improvements in parental environments could yield measurable benefits in cognitive outcomes, potentially influencing workforce productivity and economic growth.

Takeaways by Macro Roundup® AI

  1. A 1 SD increase in parental environment quality is associated with an IQ gain of about 2.83 points in the study of adoptive and biological families with 30-year-old offspring.
  2. Biometric decomposition attributes 4% of the variance in full-scale IQ at age 15 to the parental environment, with a standard deviation of 14.2 among adopted offspring.
  3. Genetic factors account for 42% of IQ variance in adulthood, exceeding the contribution of the parental environment.

Emily Willoughby, Matt McGue, William Iacono and James Lee, "Genetic and environmental contributions to IQ in adoptive and biological families with 30-year-old offspring," Intelligence, September/October 2021
https://www.gwern.net/docs/iq/2021-willoughby.pdf

Genetic and environmental contributions to IQ in adoptive and biological families with 30-year-old offspring: Extended Excerpt Image 1


The sample:"...The ethnic composition of offspring in this sample is additionally unique; while 95% of parents and biological offspring are of non- Hispanic white European ancestry, 21% of the adoptive offspring are white, 66% are Asian, and 13% are of other ethnicities (McGue et al., 2007; Miller et al., 2012). McGue et al. (2007) reported minimal ethnicity effects in the SIBS sample at intake, which we largely replicate in the current follow-up assessment. While rearing family socioeconomicstatus and polygenic scores were both moderately higher among Asian offspring (Cohen’s d = 0.36-0.46; p <.01), no measure of cognitive ability differed significantly between offspring of different ethnicities. See SI Table S6 for these and other comparisons, along with a discussion of their relevance...."

Genetic and environmental contributions to IQ in adoptive and biological families with 30-year-old offspring: Extended Excerpt Image 2


Results:"...Measures of full-scale IQ taken at follow-up 3 were moderatelycorrelated over time for both offspring and parents (all p <.001). For offspring, ICAR-16 scores (follow-up 3) correlated with intake Total IQ at r = 0.46; for parents, this correlation was also r = 0.46. The moderate size of these correlations partially reflects the approximately 17-year gap between testing sessions, especially for offspring who were of adolescent age at intake assessment (see, e.g., Hoekstra, Bartels, & Boomsma, 2007), but are nevertheless within the range reported by Condon and Revelle (2014) for the ICAR-16 and various measures of general ability. Offspring Vocabulary scores taken at intake correlated with their Vocabulary scores at follow-up 3 at r = 0.53. SI Tables S8—S10 show full correlation tables between these and other intake measures of IQ for each sub-sample of individuals. At intake, parent-offspring correlations were significant and moderately sized only in biological families, with two exceptions (Table 2). Picture Completion showed very low correlations between all relatives except father and biological child (r =.30). Vocabulary was an exception in that the correlations between adoptive relatives were also moderate in size. At follow-up 3, familial correlations for the ICAR-16 are largely consistent with the expected patterns of correlations between biological and adoptive relatives for a heritable trait little affected by shared environment (Table 2). The correlations between biological relatives are significant and moderate in size, whereas those between adoptive relatives are consistently smaller. Vocabulary, by contrast, shows surprisingly persistent correlations between both adoptive and biological relatives in adulthood. The correlations specifically between parent andoffspring are displayed in Fig. 2….”

Genetic and environmental contributions to IQ in adoptive and biological families with 30-year-old offspring: Extended Excerpt Image 3

Bottomline, “.. Our biometric decomposition of variance is consistent with this figure: the parental environment contributing 4% of the variance in full scale IQs at age ~15 (Table 3), with a standard deviation of 14.2 for fullscale IQ in adopted offspring, indicates that a 1-SD increase in the quality of the parental environment would increase IQ by approximately 2.83 points (i.e., 14.2.04 √; Burks, 1938)...."

Study published in Intelligence finds that adoptive parents had no impact on their (adopted) children's adult intelligence, "...While adoption studies have provided key insights into the influence of the familial environment on IQ scores of adolescents and children, few have followed adopted offspring long past the time spent living in the family home. To improve confidence about the extent to which shared environment exerts enduring effects on IQ, we estimated genetic and environmental effects on adulthood IQ in a unique sample of 486 biological and adoptive families. These families, tested previously on measures of IQ when offspring averaged age 15, were assessed a second time nearly two decades later (M offspring age = 32 years). We estimated the proportions of the variance in IQ attributable to environmentally mediated effects of parental IQs, sibling-specific shared environment, and gene-environment covariance to be 0.01, 0.04, and 0.03 respectively; these components jointly accounted for 8% of the IQ variance in adulthood. The heritability was estimated to be 0.42. Together, these findings provide further evidence for the predominance of genetic influences on adult intelligence over any other systematic source of variation...."

Ed Comment:Here’s the problem with this study: a shocking 66% of the children were Asian while 95% of the parents were white. Which white parents are eager to adopt Asian children? …the smart ones that really want smart children. so this study is likely to find more relation with parents IQ then actually exists but for selection bias.

Note their takeaway on twin studies, "...A long history of twin and family studies has found that between 50 and 80% of variance in IQ is associated with genetic factors in industrialized countries, with perhaps 50% attributable to additive genetic factors alone..."

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