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he largest study of its kind has found 74 genetic variants that influence how many years of school people finish, scientists reported on Wednesday, but their effect is relatively minor, underlining how a complex behavior like going to college is not written in our DNA.

Although such behavioral genetics studies might once have been trumpeted as “genes for going to college,” the international consortium of 253 researchers reached a more modest conclusion: Altogether, the 74 genes explain slightly less than one-half of 1 percent of the differences between people’s education levels.

Behavioral genetics has long been notorious for producing spurious findings. It has also been controversial, with critics calling it pointless (because environmental factors exert stronger effects on behavior) and even dangerous, misleading the public into thinking that complex behaviors such as getting divorced or committing crimes or being a political liberal are the inevitable product of inherited genes.

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Experts who have raised cautions about some behavioral genetics studies, however, praised this one.

“I think this is a great paper,” said molecular psychiatrist Dr. Jonathan Flint of the University of California, Los Angeles, who was not involved in the new study. “They have made an immense step forward” from previous research.

He and other scholars emphasized the study’s modest claims.

“The authors are pretty careful to explain that the effect size is small [and] that these are not ‘genes for educational attainment,’” said Nita Farahany of Duke University School of Law, an expert on the ethical, legal, and social implications of behavioral genetics and a member of President Obama’s bioethics commission.

“Whenever you study things close to IQ there is a real fear that people will see this as genetic determinism,” in which DNA is fate, Farahany said. In fact, so many environmental factors shape educational attainment that the 74 genetic variants “don’t explain individual differences.”

Nevertheless, Farahany said, the finding that many of the years-of-school genes act in the developing brain before birth made the study “significant.”

The new research, published in Nature, was an extension of a 2013 study by many of the same scientists, who belong to the Social Science Genetics Association Consortium. Formed in 2011 and funded in part by the National Institutes of Health, the group aims to find links between genes and outcomes that interest social scientists, such as personality, levels of happiness, and preferences.

The earlier study, of 126,559 people, identified three genes whose different forms were associated with more or fewer years of schooling. Each of the three explained about 0.02 percent of the differences in years of schooling among the individuals.

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For the new study, the scientists extended their search to 293,723 people of European ancestry from 15 countries, all at least 30 years old. For each person, they analyzed 9.3 million genetic variants called SNPs (pronounced snips).

A SNP is a version of a gene that differs from another by a single DNA “letter” — an A instead of a T, for instance. That difference can affect how well a gene performs its function.

The 74 variants “tend to be strongly active in the brain, especially prenatally, and are especially likely to be involved in neural development,” said Daniel Benjamin of the University of Southern California, senior author of the study.

Some of the variants affect the proliferation of cells that give birth to brain neurons, the migration of new neurons through the cortex, the sprouting of fibers called dendrites through which neurons communicate, and the ability of brain neurons to form connections throughout life.

Another variant increases brain volume — suggesting the “big head = big brain” idea has merit — while others are more surprising. “The one that caught my eye was that the genetic correlation between schizophrenia and education years is positive,” said UCLA’s Flint. “It’s not a big effect, but still, if true, it’s deeply intriguing.”

After the scientists identified the 74 variants associated with schooling in the nearly 300,000 people, they tested whether the 74 had the same effect in a separate group of 111,349 people in Britain. Seventy-two of the 74 SNPs associated with schooling in the first group were in the second, too, strong evidence that the finding is real.

Despite that success, Benjamin and his colleagues emphasized that social and environmental factors had a much stronger effect on educational attainment than the 0.43 percent accounted for by the 74 variants. The most influential variant explained 0.035 percent of the difference in people’s years of school. On average, people with two copies of this SNP (one from mom and one from dad) had nine more weeks of school than people with none. Less influential SNPs explained differences of 2.7 weeks of school.

The findings cannot, however, be used “to predict a particular person’s educational attainment,” Benjamin said. That’s partly because environmental factors can weaken the impact of genetic variants. If, for instance, genes affect short-term memory, and an education system emphasizes rote, someone with poor short-term memory might leave school sooner than if teachers emphasized, say, creativity or problem-solving.

In a real-world example, in the 1950s and 1960s, Sweden introduced educational reforms such as postponing tracking from age 10 to 16. The influence of years-of-school genes was halved among Swedes post-reform compared to pre-reform generations, the scientists found.

The weak effect of genes, and the power of environmental factors to trump them, raised the question of what purpose the research served. Asked what policy lesson they draw from the study, Benjamin and his colleagues said “none whatsoever.”

But the study might eventually help identify ways to increase education. Benjamin said that “the most important consequence of this kind of study” is that it will enable scientists to statistically “remove” genetics when they measure what factors — free preschool or parenting classes or after-school programs, say — increase education.

“Even though we are really only beginning to understand how any of these variants could contribute to cognitive ability or educational attainment, at least we are clearly at the beginning of something,” said Jonathan King of NIH’s National Institute on Aging, which funds the social science genetics group.

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