The influence of genes on school achievement has now been well established by researchers using the “natural experiment” afforded by identical and non-identical twins. Between 50% and 75% of the differences among students in the same grade in literacy and numeracy is estimated to be attributed to genes; the rest to environmental factors.
The same researchers have also been interested in whether genetic influence remains constant across differing levels of some environmental factors, such as socio-economic status (SES). Are differences among students from poorer households as subject to the influence of genetics as those from richer households? Technically, this is referred to as the search for a gene-by-environment interaction.
The question matters, because if an interaction exists between genes and SES, for example, that would mean environmental influences affect children differently depending on a family’s economic position in society. This in turn could have important implications for social and educational policy.
Further reading: Genes can have up to 80% influence on students’ academic performance
In our research on Australia-wide tests of literacy and numeracy (the NAPLAN tests), we show that the profile of the relative influence of genetic and environmental factors for Australian students remains pretty constant across all SES levels, both family- and school-based.
That is, we have no evidence for a gene-by-SES interaction. This result becomes interesting in contrast to the situation in the United States, where studies havegenerally found a gene-by-SES interaction for academic and cognitive abilities such as literacy, numeracy and intelligence.
Lower socioeconomic status in the US is associated with lower genetic and higher environmental influence. This is particularly so for environmental factors that twins might share, such as family wealth, health access, nutrition and school.
Thus the higher environmental influence at lower SES levels in the US may result from the presence of adverse environments that occur when SES is low, and that are rare or at least less influential when SES is higher. In other words, poverty constrains genetic potential; children from poorer families are more subject to their (adverse) life circumstances than ones from better-off families.
Interestingly, our data, showing an absence of SES influence on heritability of school achievement, are in line with a major international review that has shown that the gene-by-SES interaction identified in US samples does not hold in western Europe and in an Australian study of IQ.
This is good news for Australia. It appears that whatever factors are constraining genetic potential among less well-off students in the US do not exert a similar influence in Australia. Here are some contrasts between the two countries that may be part of the explanation.
In the US, 8.2% of families report not accessing health services because they cannot afford them, with about one-in-five of the poorest people but only one-in-20 of the richest in that category.
A further sign is that, among 21 OECD countries, visits to GPs for equally serious illnesses are unaffected by wealth in Australia, but are affected by wealth in the US, which had the highest “pro-rich” index of all the countries in the survey.
Poorer health is known to be associated with poorer academic outcomes.
The proportion of families living below the poverty line (less than half the median family income) in the US is 25% – in Australia it is 28%. But after income redistribution through the taxation system and other support, the respective figures are 23 and 11.
In other words, the effective rate of poverty in Australia is about half that of the US.
It is also known that poverty can directly influence brain structure in children and adolescents, with smaller brain surface area among poorer individuals, particularly in those regions associated with language and some cognitive functions.
Australia has tended towards centralised school curricula, both at the state and federal levels. In the US, moves towards a “common core” are relatively recent and not fully implemented as yet. Higher levels of uniformity in the content and delivery of instruction mean less environmental variability among classrooms and schools.
These potential explanations are not exhaustive, nor are they mutually exclusive.
So when it comes to academic progress, genes are not destiny. Children struggling with the basics of literacy and numeracy can be taught to ensure they reach or more closely approach normal levels of achievement with well-designed and well-delivered programs.
The message here is that, by designing appropriate social services, a society can endeavour to avoid the situation where financial status undermines academic potential right from the start of a child’s life.
In Australia’s case that means at least preserving, if not improving, current arrangements for health access and income redistribution and its commitment to uniform educational standards.
Brian Byrne receives funding from the Australian Research Council and the National Health and Medical Research Council.
Richard Olson receives funding from the U.S. National Institutes of Health.
William Coventry receives funding from the Australian Research Council.
Katrina Grasby does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.