Your inherited genes control your IQ and may affect how well you do at exams

We know that genes play a role in how well children do in school, but there are gaps in our knowledge: is this the same for different topics in school? And can this be explained largely by intelligence, or do other genetic factors contribute?

A recent paper in Nature Scientific Reports conducted a large-scale study on twins and unrelated people, finding that genes contribute to success in the full range of subjects from maths to art—and that the genetic influence stuck around even after they factored out the effects of intelligence. Other genetic, inherited traits might include mental health, personality, or motivation.

Twin studies are used widely in behavioural genetics, because they remain one of the best methods we have to tease apart the effects of genes and environment. Both identical twins and non-identical twins share an environment, but identical twins have a more similar genome than their non-identical counterparts. If identical twins show greater similarity in some regard—like school results—than non-identical twins, we can infer that genes are responsible for some of the variation on that behaviour.

Twin studies are not without their critics. Most importantly, there’s the argument that identical twins are treated more similarly than non-identical twins, meaning that they share a more similar environment as well as a more similar genome.

Taking this criticism into account, the authors of the recent paper used the standard twin method but backed up their results by looking at DNA from unrelated individuals. They used 2,245 identical twin pairs, 4,071 non-identical pairs, and 7,432 unrelated people to explore the effect of genes and environment on General Certificate of Secondary Education (GCSE) results.

When they looked at the results from the twins, they found that genetic factors explained between 54 and 65 percent of the test achievements; shared environment (like home and school) accounted for a further 14 to 21 percent. Individual environmental factors—each person’s unique experiences—accounted for the final 14 to 32 percent.

The exact results differed depending on the type of subject, but every field showed a substantial genetic effect. Some (like mathematics) were higher than others (like art).

The exam results were also highly correlated with the students’ IQ scores, so the researchers wanted to see how much intelligence was affecting the results. After controlling for intelligence, they found very similar patterns: genes accounted for slightly less of the difference than before but still played a substantial role. Overall, inherited traits other than intelligence—possibly including mental health, personality, and motivation—seemed to explain between 45 and 58 percent of the difference. Shared environment made more of a difference for some subjects (like maths and English) than for others (like business studies).

The results from unrelated individuals were weaker and looked only at the core subjects of English, maths, and science, but the results pointed in the same direction: genetics seemed to influence achievement in these subjects even after factoring out intelligence.

Implied equality

High heritability in intelligence is a sensitive subject, because it can be seen to carry the implication that poor-performing schools or communities have bad results because of immutable characteristics in those populations—the implication that we should give up on the poor kids, because they’re just like that.

However, understanding what makes the school system easy for some people and difficult for others is vital to being able to figure out a system that can be tailored to individual strengths. High heritability also doesn’t mean total heritability: there’s still an important environmental role that needs to be considered, and that environmental role tells us how much we can improve results by changing the environment.

A population that shows high levels of heritability can be interpreted as a sign of equality—the environment can't be radically different, or it would be the dominant influence. Take height as an example: people become taller or shorter adults because of a combination of their genes and various environmental factors, like nutrition in early childhood.

In a country with high inequality, where some children receive adequate or excellent childhood nutrition and others starve, nutrition will play a very important role in how tall people are able to grow regardless of their genes—children with the genetic capacity to be very tall could be stunted by a poor environment. On the other hand, in a population where pretty much everyone is well-fed, the differences between people’s heights will be decided largely by genetics.

The same goes for education: when everyone is receiving pretty much the same standard of education and has an equally good home life, their inherited traits and tendencies will play a more important role in their eventual results. When some people receive excellent education and others receive a much lower standard, educational “nutrition” will play an important role in the academic heights people can reach.

This also means that an estimate of heritability in one population can’t really be extended to another. Because the population of the twin study is representative of the general UK population, it’s probably safe to draw conclusions about the UK as a whole. However, we can’t really conclude much about the exact levels of heritability in any other country, although we can expect that factors other than intelligence play a very important role in school results everywhere.

A false notion of fixed destiny

For the authors, the most important result here is that intelligence isn’t the only heritable trait affecting results: echoing decades-old popular sentiment, they point to other traits like personality and motivation as important factors. They note that genes aren’t just a passive inheritance: genetic tendencies are likely to affect the choices made by teenagers and children, both selecting and interpreting their experiences of the world.

They see the results as carrying important implications for policy, suggesting that these findings could be used to develop effective learning programs that help each child reach their maximum potential. Other researchers, however, are more reserved. “The results are interesting, but by no means definitive and it would be unwise to make educational decisions based on these data,” said John Hardy, Professor of Neuroscience at UCL, in a public statement.

As always, there's the risk that the results will be over-extrapolated and interpreted out of context. “Unfortunately [studies showing genetic influences] are usually over-interpreted as presenting falsely a notion of fixed destiny,” said Timothy Spector, Professor of Genetic Epidemiology at King’s College London.

There's still more work to be done before we overhaul our education system to introduce personalised curricula, and this result certainly shouldn't be taken to mean that there's no hope for low-achieving students. That said, it's an interesting confirmation of the folk-psychology insistence that traits other than intelligence are important too.

Nature Scientific Reports, 2015. DOI: 10.1038/srep11713  (About DOIs).