The Heritability of Intelligence

Matt McGue, Regents Professor, has conducted extensive research on the behavior genetics of intelligence. Upon the occasion of his retirement, Tobias Edwards, alum, Emily Willoughby, staff, and James Lee, faculty, revisited and expanded on his findings in a recent article, “Durable Lessons on Intelligence from Twin and Adoption Research.”

The researchers outlined that over his career, McGue’s research and scholarship has shown that the influence of genetics seems to increase from childhood to adulthood and remains in later life, even as shared environmental effects diminish. Also, some complex, socially contingent outcomes can be heritable to a certain extent, such as the risk of divorce. Finally, using twin and adoption methods, McGue found that social mobility and academic success are driven by a variety of factors, including cognitive ability, social-emotional skills, and family background.  One critique of McGue’s work, however, is that because adoption agencies screen prospective homes, the range of environmental factors affecting cognitive ability is somewhat restricted, perhaps limiting his findings. However, after statistically correcting for any limits in range, his initial findings were not meaningfully altered.

To expand on McGue’s work, the researchers reported new results from their analysis of selective placement based on parental phenotypes and the polygenic scores of their adopted children using data from the Sibling Interaction and Behavior Study (SIBS). Their findings showed that for adoptees of East Asian descent, there was no significant correlation between parental education and offspring polygenic scores, confirming quasi-random placement. For those of European ancestry, domestic placements highlighted a pattern where maternal education negatively predicted child polygenic scores while paternal education positively predicted them, though combined parent averages showed no net correlation. Therefore, while minor placement effects can occur in domestic sub-samples, the overall impact of selective placement is too small to invalidate adoption-based estimates of heritability or shared environmental influence, thus supporting McGue’s findings.