Genetic factors drive the link between cognitive ability and socioeconomic status

A new study published in Scientific Reports suggests that the connection between a young adult’s cognitive ability and their future socioeconomic status is largely driven by their genes. The findings provide evidence that genetic factors play a larger role in educational and occupational success than environmental conditions. This underlying biology may help explain why some social interventions aimed at reducing inequality tend to fall short over the long term.

Social scientists have spent decades trying to understand the psychological mechanisms that drive socioeconomic status. Getting an education and securing a job are the primary ways young adults begin earning a living and establishing their place in society. Past research reliably shows that general cognitive ability, often measured as an intelligence quotient, is the strongest predictor of a person’s future socioeconomic position.

However, it has remained unclear whether this relationship is primarily driven by a person’s unique genetics or by their personal life experiences. Such experiences might include the social networks a person builds in college or the specific opportunities they encounter in the job market. Petri J. Kajonius, an associate professor and personality researcher at the Department of Psychology at Lund University in Sweden and host of Personlighetspodden, conducted this study to answer that question.

“Most people, even psychology researchers, are not aware that most correlations in psychological science are mostly driven by genetics, and not the environment. This unawareness may be particularly true in Sweden — famous for its focus on societal equality through interventions — and not many studies in social sciences attempt to control for individual genetics. This is arguably one of the first genetically informed studies from Sweden testing the well-known and very strong IQ-socioeconomic status relationship.”

In particular, Kajonius wanted to quantify exactly how much of the link between a young adult’s cognitive ability and their later socioeconomic status can be attributed to genetic inheritance. To examine this, the researcher utilized data from the TwinLife project, a large and representative study of families in Germany. The sample included 440 twin pairs, consisting of 228 identical twin pairs and 212 fraternal same-sex twin pairs.

Analyzing twins allows scientists to estimate how much of a particular trait is due to genetics. Identical twins share all of their genes, while fraternal twins share about half of their genes on average. By comparing the similarities between these two types of twins, researchers can mathematically calculate how much of a trait is due to genetic inheritance versus environmental exposure.

The participants in this specific analysis were young adults transitioning into their careers. They had an average age of about 23 during the first wave of data collection and an average age of about 27 during the second wave four years later. During the first wave of the study, the participants completed a computer-based cognitive assessment.

This assessment measured a person’s ability to reason and solve problems using unfamiliar information, which is a core component of general intelligence. Four years later, the researchers measured the participants’ socioeconomic status using four distinct variables. Two of these variables focused on educational attainment, classifying the complexity and level of schooling each participant had completed on a scale from zero to ten.

The other two variables measured occupational status to capture a full picture of their career success. One ranked the social prestige of their current job. The other categorized their occupation based on the level of autonomy and status it held in the broader labor market. The researcher used statistical models to separate the influence of genetics from the influence of the environment.

The data revealed that cognitive ability is highly heritable in young adulthood. Specifically, about 75 percent of the differences in cognitive ability between individuals could be explained by their genetic makeup.

Socioeconomic outcomes at age 27 also showed significant genetic influence. Genetic factors explained between 49 and 66 percent of the differences in educational attainment among the participants. For occupational status, genetics accounted for between 32 and 71 percent of the individual differences.

When looking at the relationship between cognitive ability at age 23 and socioeconomic status at age 27, genetic factors played a dominant role. Shared genetic traits explained between 69 and 81 percent of the association between cognitive ability and educational outcomes. For the link between cognitive ability and occupational status, genetics explained up to 98 percent of the connection.

This means that the same genetic predispositions that contribute to higher cognitive ability also tend to promote socioeconomic success. The overlap in genetic factors was multiple times larger than any overlap in environmental factors. These environmental factors usually consist of shared family resources or random life events, like meeting the right person at the right time.

The shared genetic influence between cognitive ability and socioeconomic status could operate in a few different ways. The same genes might simultaneously affect brain development and behaviors that promote career success, creating a direct biological link. Alternatively, genes could enhance cognitive ability, which then makes it easier for a person to navigate higher education and secure a better-paying job.

“The take-home message for the average person is that psychology manifests in life mostly through genetic make-up, not so much through environmental conditions,” Kajonius told PsyPost. “The individual is arguably more important than given credit when it comes to life outcomes, such as education, occupation, and income. This may consequently also be one reason societal interventions aimed at equality often don’t work in the long-term.”

While these findings highlight the heavy influence of biology on life outcomes, it is important not to misinterpret heritability as absolute destiny. A high genetic explanation for a trait only indicates an increased probability, not a predetermined certainty.

“Heritability does not necessarily mean determinism, only increased probabilities,” Kajonius said. “Genes for bad eye-sight could easily be solved with glasses, as a mundane example.”

The study does have some limitations. The four-year gap between the first and second measurements is a relatively short time span. Tracking these young adults from age 23 to 27 might not provide enough time for cognitive ability to fully shape their long-term career trajectories.

Additionally, the statistical models used in the study simplified the analysis by dividing influences strictly into genes and the environment. This approach did not account for more complex interactions, such as how specific genes might react differently in entirely different environments. Future research should aim to explore these complicated interactions over longer periods of a person’s life.

Ultimately, Kajonius hopes this line of research will help both scientists and the public understand that psychological differences are heavily influenced by our biology. Recognizing that people have different genetic predispositions may help policymakers design more effective societal interventions. Treating the population as entirely uniform often leads to programs that do not yield the intended long-term results.

The study, “Longitudinal associations between cognitive ability and socioeconomic status are partially genetic in nature,” was authored by Petri J. Kajonius.