Does Parental Separation Lower Genetic Influences on Children's School Performance?

Does Parental Separation Lower Genetic Influences on Children's School Performance? Tina Baier  Zachary Van Winkle. Journal of Marriage and Family, October 2 2020. https://doi.org/10.1111/jomf.12730

Rolf Degen's take: https://onlinelibrary.wiley.com/doi/full/10.1111/jomf.12730

Abstract

Objective: A behavioral genetics approach is used to test whether parental separation lowers the importance of genes for children's school performance.

Background: The Scarr–Rowe hypothesis, which states that the relative importance of genes on cognitive ability is higher for advantaged compared to disadvantaged children, has been expanded to educational outcomes. However, advantage/disadvantage is predominantly conceptualized as parental socioeconomic status and neglects other important factors. This study expands upon the literature to include family structure as an indicator for advantage/disadvantage.

Method: Data from TwinLife, a new population‐register‐based sample of twins and their families in Germany, and ACE variance decomposition models are used to estimate the heritability of cognitive ability (NPairs = 896), school grades (NPairs = 740), and academic self‐concept (NPairs = 949) separately for single‐parent and two‐parent households.

Results: Findings show that the relative importance of genes on children's cognitive ability and academic self‐concept is lower for children in single‐parent households compared to two‐parent households (32–47% and 23–50%, respectively), but differences are negligible for math grades (41–43%). ACE models adjusted for mothers' education and household income retrieve substantively similar results.

Conclusion: The quality of the family environment that is important for the realization of children's genetic potential is not just shaped by socioeconomic status, but also family structure.

Conclusion

In this study, we sought to ascertain (a) whether parental separation lowers children's chances to realize genetic dispositions relevant for school performance and (b) whether differences in heritability are driven by socioeconomic differences between two‐ and single‐parent households. We studied genetic influences on three different indicators of school performance – cognitive skills, math grades, and math academic self‐concept – that are important predictors for children's educational attainment. Drawing on previous findings that show that parental separation can have a negative impact on children's school performance and enhancement theories rooted in behavioral genetics, we expected genetic influence on school performance to be higher in two‐parent compared to single‐parent families (H1). Furthermore, if parental separation moderates the impact of genetic influences due mechanisms above and beyond socioeconomic differences between households, then genetic influences on school performance should be lower in one‐parent compared to two‐parent families even when adjusted for parental education and household income (H2).

Our results supported both hypotheses and provided a clear pattern for cognitive ability and math academic self‐concept. Genetic influences accounted for substantially more variance in children's school performance in two‐parent compared to one‐parent families. Furthermore, the higher genetic influence in two‐parent compared to one‐parent families is not attributable solely to educational or income differences between households, but likely driven by mechanisms related with family instability. Specifically, our findings support the notion that processes associated with parental separation, such as more distant parenting, reduced parental monitoring, and higher levels of stress among children, lower the quality of the family environment (e.g., Cooper et al., 2011; Hadfield et al., 2018; Lee & McLanahan, 2015). Compared to the tailored environments of two‐parent households, the environments of children in single‐parent households seem less able to enhance children's chances to realize their genetic potential. Our results for cognitive ability and math academic self‐concept therefore support the expectation that parental separation indeed represents a distinct set of environmental conditions that moderate the impact of genetic influences although further research is needed to adjudicate the mechanisms at work.

For math grades differences in the heritability between one‐ and two‐parent households were negligible. One possible explanation for our math grade findings could lie in the highly stratified and differentiated German school system, which makes it difficult to compare school grades across different school types. While we controlled for the school type, we are likely not able to completely capture differences with respect to grading. For example, it's more difficult to obtain the best grade in the most demanding school tracks (“Gymnasium”) compared to lower tracks (“Hauptschule” and “Realschule”). Future research on school grades should therefore choose a country with a comprehensive schooling system that facilitates comparability. In addition, grades are plagued by slightly higher missingness compared to our other indicators. Therefore, our findings on grades should also be replicated once larger data sets are available for Germany.

Our study highlights promising avenues to facilitate a better understanding of heritability differences in children's school performance by family structure. For example, further research is needed to examine whether the impact of parental separation differs by children's age, because children's vulnerability for negative life events may vary over their childhood. Children rely almost exclusively on familial resources during early childhood, whereas more proximal contexts, such as schools, teachers, or peers, become more influential as children grow older. In sum, to gain a better understanding on the link of parental separation and genetic influences, future research needs to study different outcomes, while accounting for the timing of parental separation as well as the duration of exposure to marital conflict.

In addition, future research should examine the diversity of single‐ and two‐parent households in greater detail. For example, we were not able to include step‐parent families in this study. However, research on family instability highlights that divorce is one of many transitions that may affect children negatively (Cavanagh & Fomby, 2019; Hadfield et al., 2018). Future research is needed, for example, to examine to what extent the presence of a step‐parent changes the quality of the family environment. An additional adult in the household may be able to help facilitate a rearing environment tailored to the needs of children and thereby help children express their genetic potential. In contrast, stress and conflict associated with remarriage and merging two households may further suppress the realization of children's innate abilities. More information on the socioeconomic well‐being of households than household income and mothers' education, such as occupation status, as well as indicators of family processes, such as custody arrangements and father involvement, are needed to capture all the latent constructs that should be considered.

In addition, our findings refer to Germany, often considered an ideal typical conservative welfare state that provides a relatively high level of social security. However, German labor market and family policy also actively incentivizes a male‐breadwinner female‐homemaker division of labor with low coverage of all‐day childcare and schooling. Differences in the realization of children's genetic potential by household composition may be larger in liberal societies, such as the United States, where women are at a considerably higher risk of poverty following divorce (Van Winkle & Struffolino, 2018). Compared to social democratic states where social systems secure divorced women's socioeconomic well‐being and facilitate labor market participation, such as Sweden, differences in the heritability may be lower. Future research should estimate the heritability of school‐related skills by household composition in other contexts to gain insight on the extent that institutional arrangements ameliorate or exacerbate the effects of parental separation.

One limitation of our study lies in the CTD and its inability to account for gene–environmental correlations. Previous research shows that parental divorce itself is heritable, with estimates ranging from 0.13 to 0.50 (McGue & Lykken, 1992; Salvatore et al., 2018). If genetic influences that affect parental separation also affect children's school performance, for example, via problem or nonconfirmatory behavior in school, then the link between parental separation and children's school performance would be genetically confounded (e.g., Jaffee & Price, 2007). To date, several studies have investigated to what extent gene–environment correlations drive the impact of separation or divorce (see for an overview Amato, 2010). These studies have used adoption‐ or children of twin (CoT) designs. Previous research shows that negative influences on abnormal behavior are driven by environmental exposure, while evidence is mixed for internalizing problems and educational outcomes (e.g., D'Onofrio et al., 2005, 2006, 2007). Although O'Connor et al. (2000) provided evidence for gene–environment correlations for reading competencies, parental reports on children's achievement, and children's self‐reported attitudes about educational achievement, D'Onofrio et al. (2006) provided conflicting evidence for grade repetition and years of education. In light of the weak support for gene–environmental correlations, the current literature indicates that gene–environmental correlations are likely not the main driver of the association between parental separation and children's outcomes.

Another promising route for future research is to examine whether the negative impact of parental separation is driven by genetic nurturing (e.g., Dalton & Fletcher, 2017; Kong et al., 2018; Liu, 2018). Genetic nurturing describes how genetic influences that are not passed down to children still affect their outcomes. For example, it could be that specific genes that are associated with parental separation are also associated with specific parenting behaviors. Even if these genes are not transmitted they could still affect children as they lead to specific parenting behavior. Such research questions, however, can only be addressed using methodological approaches developed in molecular genetics.

In conclusion, our study has for the first time shown that genetic influences on certain indicators of children's school performance differ considerably in single‐ and two‐parent families. In addition, our findings indicate that parental separation is associated with processes that affect the realization of children's genetic potential above and beyond socioeconomic differences. Our study highlights an important but until now mainly neglected factor in the intergenerational transmission of disadvantage among children who experienced a parental separation and live in single‐parent households (Mclanahan, 2004; McLanahan & Percheski, 2008; Raley & Sweeney, 2020). Our study has implications for policies targeted at improving the educational disadvantages of children living in single‐parent households. For example, tailored learning environments within and outside of schools targeted at children living in single‐parent households could complement income transfers to ensure children's chances for the realization of their genetic potential. A shift from traditional structural characteristics to family structure is needed to enhance our current understanding on the mechanisms behind the gene–environment interplay leading to the reproduction of inequalities across generations.