Stephanie von Hinke and Michelle Kilfoyle
17/12/2021
Nature vs. nurture is an age-old debate. Are we products of our genes or of how we were raised? It is now widely accepted that both genes and environment are inextricably linked and jointly mould our lives. A recent study of siblings and their educational achievements provides evidence to further bolster this joint gene-environment theory. It finds that eldest siblings, typically blessed with extra attention from their parents, do especially well in education when they also possess certain genetic traits.
Firstborn children have the luxury of their parents’ undivided attention until the arrival of their younger siblings. In fact, firstborns can expect to have, on average, 20-30 minutes more daily quality time with their parents than laterborns, as parents find their time increasingly stretched with each child.
This privilege goes a long way in explaining why eldest siblings tend to do better at school than their younger siblings and can be seen as a form of investment by parents in their child’s future. However, it is not always the full story, as the study co-authored by Stephanie von Hinke of the University of Bristol’s Centre for Evidence-based Public Services (CEPS) in the School of Economics shows.
In an innovative step for economics, von Hinke and collaborators from Erasmus University Rotterdam used genetic data to help understand why some people do better than others in education. They analysed DNA from UK Biobank, a national repository of biological samples and individual data, for a sample of 14,850 adult siblings (aged 40-69 at the time of study).
They measured each sibling’s ‘genetic endowment’ for educational attainment using ‘polygenic scores’. These scores are based on specific genetic variants that correlate with educational attainment.
By comparing siblings from the same family, the researchers were able to cancel out the effects of factors like parental income and social class on children’s educational attainment. (It would be much more difficult to disentangle these wealth and class-derived influences from other non-genetic factors when comparing children from different families.)
Each family was akin to a controlled experiment that allowed the researchers to explore the relative influence of each child’s genetic variation and their environment. In this study, being firstborn or laterborn was used as a measure of a child’s environment as it, at least partly, indicates whether parents invested more or less time in each child.
The results first confirmed that genetic variations are very good at predicting educational attainment. In general, the higher a person’s genetic endowment, the more years they had spent in education. Firstborns were no more or less likely to have a high endowment than laterborns.
Second, the results confirmed that firstborns do better at school. Firstborns with an average genetic endowment completed, on average, an extra 4.5 months of schooling than their laterborn siblings.
However, firstborns who have an above-average genetic endowment completed, on average, an additional two months of education (on top of the 4.5 months) than their laterborn siblings with the same genetic endowment.
This study shows that neither genetics nor environment are solely responsible for determining our education, and that both matter. Furthermore, as well as emphasising the importance of investing in skills early in life, the research supports the idea of ‘dynamic complementarity’ between nature and nurture in this setting, that is the idea that people with higher initial skills benefit more from subsequent investment.