Genetics, not shared environments, drives parent-child similarities in cognitive ability

How much of your cognitive ability is shaped by your genetic inheritance compared to the environment you grow up in? A new study published in Research in Social Stratification and Mobility suggests that the transmission of cognitive ability from parents to children is primarily driven by genetics, with little influence from shared environmental factors like family resources. The findings challenge traditional assumptions in social mobility research that often attribute these correlations primarily to socio-economic status.

The intergenerational transmission of cognitive abilities has long been a subject of interest because of its implications for social mobility and educational outcomes. Past research has shown that children often mirror their parents’ cognitive abilities, but it has been unclear whether this is due to shared genetics, shared environments, or a combination of both.

“We were interested in this topic because cognitive ability is a crucial factor in social mobility and life outcomes, yet its transmission between generations is rarely studied using comprehensive models that combine both twin and family data,” said study author Tobias Wolfram, a behavioral geneticist affiliated with Bielefeld University.

“The German TwinLife study provided an exciting opportunity to do this, particularly because it included different age cohorts ranging from early childhood to young adulthood. This allowed us to examine how the mechanisms of transmission might change over time, which is especially interesting given the well-known ‘Wilson effect’ – the observation that environmental influences on intelligence are stronger in childhood while genetic influences become more prominent with age.”

The German TwinLife survey is a large, longitudinal study designed to explore the interplay between genetic and environmental factors in shaping various life outcomes, including cognitive abilities, educational attainment, and social mobility. The survey focuses on same-sex twin pairs and their biological families, enabling researchers to separate the effects of genetic inheritance from those of shared family environments. For example, monozygotic twins, who share 100% of their genetic material, can be compared with dizygotic twins, who share about 50% of their genetic material, to estimate the relative contributions of genetic and environmental factors.

By incorporating multiple family members—including parents and siblings—across four birth cohorts, the survey spans an extensive developmental range, from early childhood (ages 5–6) to young adulthood (ages 21–25). This breadth allows researchers to examine how genetic and environmental influences evolve over the life course.

Cognitive abilities were measured using standardized tests tailored to different age groups. For children aged 9 and younger, the researchers used the Culture Fair Test 1-R, while the Culture Fair Test 20-R was applied to individuals aged 10 and older. These tests are widely used for assessing cognitive ability in a way that minimizes cultural and educational biases.

The data collection spanned multiple waves, capturing changes over time and enabling a dynamic analysis of developmental processes. Other data, such as demographic information, socioeconomic status, and family relationships, were also included, providing a rich context for interpreting the findings.

In their new study, Wolfram and his colleagues utilized a nuclear twin family design, an advanced statistical framework that incorporates data from twins, their parents, and sometimes siblings. This model goes beyond traditional twin study designs by explicitly including intergenerational data, enabling researchers to examine how traits are transmitted across generations. The nuclear twin family design also addressed potential confounding factors, such as assortative mating—a phenomenon where individuals with similar traits, such as intelligence, are more likely to pair and have children.

The results provided evidence that the intergenerational transmission of cognitive ability is driven primarily by genetic inheritance rather than shared environmental factors. Across all age groups examined, the researchers found minimal evidence that parental cognitive ability significantly influenced children’s cognitive development through environmental mechanisms. Instead, the observed similarities in cognitive abilities between parents and children were largely attributed to shared genetic factors.

The researchers also failed to find evidence for passive gene-environment correlations. These correlations occur when parents pass on genetic predispositions to their children while simultaneously creating environments that align with those predispositions—for instance, high-ability parents fostering intellectually enriching environments. Despite being theoretically expected, the study found no significant evidence for these correlations. This suggests that the family environment does not mediate the relationship between parental and offspring cognitive abilities.

Even in the youngest cohort, where environmental effects are typically most pronounced, the study found no significant evidence that parental cognitive ability shaped offspring abilities through these pathways.

“Perhaps the most surprising finding was how little impact parental cognitive ability had on children’s cognitive development through environmental pathways, even in young children aged 5-6,” Wolfram told PsyPost. “This was unexpected because we know that environmental factors in general have a stronger influence on cognitive ability in early childhood. While we found substantial environmental effects shared between siblings in young children, these effects weren’t related to parental cognitive ability. This raises interesting questions about what drives these early environmental effects.”

“The key takeaway is that the similarity in cognitive ability between parents and children appears to be driven primarily by shared genes rather than shared environment. While we often assume that parents influence their children’s cognitive development through factors like education style, resources, and parenting, our study finds little evidence for environmental transmission that occurs through parental cognitive ability specifically.”

However, the researchers emphasized that this does not imply that parents play no role in their children’s development. “This doesn’t mean parents don’t matter—our model can only detect environmental influences that are linked to parents’ cognitive ability and that affect all siblings similarly,” Wolfram explained. “There could be other important parental influences that operate through different pathways or affect children differently.”

For example, parents might influence their children’s development through unique, individualized interactions that are not captured by models focusing on shared family environments. A parent’s encouragement of a child’s specific interests or their response to a child’s emotional needs could shape the child’s learning and development in ways that differ between siblings.

Additionally, non-shared environmental factors, such as differences in peer groups, extracurricular activities, or even random life events, can play a significant role in cognitive development. These influences, while potentially shaped by parental decisions, would not necessarily correlate directly with parental cognitive ability and therefore fall outside the scope of this study’s analysis.

“While we can distinguish between genetic and environmental transmission at a broad level, we can’t identify specific genes or particular environmental factors that might be important,” Wolfram noted.

Another limitation relates to the assumptions their statistical model makes regarding assortative mating. “The model assumes that people directly choose partners based on their observed cognitive ability, but in reality, partner selection might happen indirectly through other related characteristics or through more complex patterns,” Wolfram explained. “This assumption about assortative mating could affect our estimates of how cognitive ability is transmitted across generations as a new preprint by Sunde et al. shows in the case of educational attainment.”

Despite these caveats, the study makes a significant contribution to social mobility research by emphasizing the dominant role of genetic pathways in the intergenerational transmission of cognitive ability. The findings indicate that the influence of the family environment in this transmission process is limited, highlighting the importance of accounting for genetic confounding when interpreting parent-offspring similarities in cognitive ability.

“Our long-term goal is to better understand the complex interplay between genetic and environmental factors in cognitive development,” Wolfram told PsyPost. “We hope to extend this research by incorporating more sophisticated models of assortative mating and by examining how specific measured environments might moderate genetic effects.”

“While our findings strongly support the importance of genetic factors in cognitive ability, it’s crucial to remember that genes are not destiny,” he added. “Environmental factors still play a role, and understanding their interaction with genetic predispositions remains an important area for future research.”

The study, “Disentangling genetic and social pathways of the intergenerational transmission of cognitive ability – A nuclear twin family study,” was authored by Tobias Wolfram, Mirko Ruks, and Frank M. Spinath.