Which is more important, genes or environment? It’s an argument that goes back far before the concept of genes was developed. The advent of genomics has given us a new perspective on the role of genetic variants in many traits, but it hasn’t necessarily stopped the discussion. The reasons are nicely highlighted by a new paper describing a massive genetic screen for factors associated with educational success.
The study screened more than a million people for genetic variants related to time spent in school. And while the study revealed many genomic regions associated with schooling, the average difference made by each individual gene is just 1.7 weeks; together, the regions are only responsible for slightly more than 10 percent of the differences in study time. Critically, they may only be relevant to the European populations used to identify them.
Find the genes
Time spent in school is a rough measure of academic achievement. While there can be radical differences between two people who have completed college, there are likely to be consistent differences between people who have dropped out after high school and those who have completed graduate studies. And it appears to be a relevant metric because it correlates with the improved economic and health outcomes typically associated with successful careers. And it’s a less biased way to achieve educational achievement than things like standardized tests.
For all these reasons, there have been previous attempts to identify which parts of the genome are related to time spent in school. A study examined the DNA of more than a quarter of a million people to identify 74 different regions of the genome associated with education endurance. But the new work goes far beyond 1.1 million subjects.
The additional topics offer a very different perspective, identifying 1,271 locations in the genome that appear to be related to time spent in school. The researchers then looked at genes located near these locations and found that a large majority of them were active in the nervous system — during development, in adulthood, or both. The genes affected almost every aspect of nerve function, such as allowing ions to move through cell membranes, the metabolism of nerve cells, forming and maintaining connections between nerve cells, and more.
However, one category of genes was conspicuously absent: those expressed in glial cells, which support and maintain the nerve cells. Among other things, glial cells build sheaths of a fatty material called myelin, which acts as an insulator to isolate the electrical activity of nerve impulses. It had been suggested that some aspects of cognition depended on the speed and efficiency of nerve impulses, which in turn depend on this isolation. So the study raises questions about that idea.
Big and small
All this information suggests that the basic approach is on to something. But the “something” turns out to be dramatic or not that interesting, depending on how you look at it. With nearly 1,300 genes involved, the differences between people who fall into one of the extremes can be dramatic. Someone with many variants that predispose them to stay in school is much more likely to do so than someone with very few.
But many people don’t lie in one of these extremes. And when it comes to individual genomic sites, the effects are small; even the strongest only add an average of 2.6 weeks extra time in school (it’s 1.1 for many of the weaker). And the entire set of 1,271 sites can only explain about 12 percent of the total variation in education level, meaning nearly 90 percent of the variation is caused by something else. We know of some of those causes: These genes outnumber family income in terms of the strength of their impact, but find themselves behind having a parent with an extensive educational background.
In other words, if your mother has a PhD, it will probably have a stronger impact on your education path than your genes.
The authors themselves suggest that these genomic sites are not necessarily useful for studying education per se. Instead, they should be used as a control when studying the factors that influence the other 90 percent. If you can explain genetic influences, environmental factors would be more noticeable.
At least in some populations. While the study was done in the US, the researchers limited the experimental population to people of European descent because that would make it easier to secure a large number of participants. However, the researchers also looked at African Americans and testing the same markers on them showed that they were only a weak predictor of education level. There are many possible explanations for this, from African Americans having an equal but different set of factors to the fact that social factors have historically dominated their access to education. However, at the moment we just don’t know enough to say.
While we may learn more by examining other human populations, the pieces of genome identified here are likely pushing the limit of what we’re about to discover. If we push the number of people screened well above a million, we can probably only identify factors with even weaker effects, and the 1,271 sites we identified already account for nearly five percent of all human genes (assuming one gene per site). So any significant progress from now on will likely depend on trying to figure out how these genes might interact with environmental factors.
Natural Genetics2018. DOI: 10.1038/s41588-018-0147-3 (About DOIs).