But which specific genes are responsible? The search did not go well at first. Plomin failed to discover any links when he looked at the genomes of 7,900 children in 2010. He later became involved in a misadventure involving a Chinese sequencing company, BGI, to which he supplied the DNA of more than a thousand American geniuses. The project got derailed after news reports accused the Chinese of hatching a plot to breed “genius babies.”

The gene hunt finally paid off in May 2017. A Dutch-led study of the genetic makeup of 78,308 people who’d taken tests (including 2,825 of Plomin’s twins) zeroed in on variations in 22 genes linked to IQ scores. By this March, the tally had rapidly risen to 199,000 people and 500 genes. Plomin says a forthcoming report will establish links to 1,000 genes.

Each genetic variable found so far has only a tiny effect, either weakly increasing IQ on average or weakly decreasing it. The trick to turning the discoveries into a personal DNA IQ test? Simply add up all the pluses and minuses you find in a specific person’s genome.

These types of assessments are called “polygenic scores.” And they’re quickly becoming a very big deal (see “10 breakthrough technologies 2018: Genetic fortune telling”). That’s because they work for any trait, including heart disease, diabetes, and schizophrenia—in all, more than 2,000 traits so far.

Psychologist Robert Plomin spits in a DNA collection tube. He’s learned his genetic risk for dozens of traits. Courtesy of Dr. Robert Plomin

Plomin was quick to sign up. Last year, he spit in a tube and had his DNA scores calculated by his research center. Now, during talks, he presents his genetic rankings. He’s on the high end of the risk for arthritis (he has some), lower than average for depression, and in the 94th percentile for being overweight.

To Plomin, whose weight sometimes nears 240 pounds, the genetic prediction explains his lifelong battle with starches and sweets. “People will say, ‘Oh, there’s nothing you can do—you’re a genetic fatty,’ but it helps me to know. It’s a constant battle of the bulge,” he says.

Of course, he knows his percentile rank for predicted academic achievement, too. “It’s 99-point-something—it’s embarrassing,” he says.

Are you Einstein or Bozo?

Several scientists told MIT Technology Review they don’t believe genetic IQ tests can tell individuals anything useful and aren’t sure why Plomin is saying they will.

“We will never be able to look into someone’s DNA and say your IQ will be 120,” says Danielle Posthuma, who led the big 2017 IQ study. “I don’t think it makes much sense to use it that way. I would just give people an IQ test.” Posthuma says her main interest is in discovering how the brain works at a basic level, where finding genes associated with intelligence can help.

Plomin, however, points out that IQ tests with colored blocks barely work for little kids, failing to accurately capture how they will do on tests later in life. Your DNA, on the other hand, is there from the day you are born and doesn’t change. Early in life, Plomin says, DNA may already provide a better intelligence prediction than any test does.

Still, the issue is accuracy—or lack of it. Right now, the polygenic scores capture only a fraction of the genetic determinants of intelligence and none of the environmental ones. That means the predictions remain fuzzy.

This is clear from Plomin’s own data. His center calculated polygenic scores for hundreds of the twins he’s followed since their birth and whose DNA it has on file. He then compared the gene scores with how well the twins (now in their 20s) had done on a UK-wide exam that everyone takes as a teenager.

Genetic studies of intelligence may shed light on school choices and social mobility. Here, boys from the elite British school Harrow have onlookers. Jimmy Sime/Central Press/Hulton Archive/Getty Images

Plotted one against the other, the result looks more like a slightly elongated cloud of dots than a straight line. That is, the DNA predictions and the test scores tended to line up, though not perfectly. Some with low DNA scores had gotten great test results as teens. Others had bombed despite the promise in their genes.

To Aaron Panofsky, a sociologist of science with the University of California, Los Angeles, that’s a huge problem. With this technology, you could end up branding an Einstein as a Bozo, and vice versa. “Is the claim that you are going to have kindergarteners spit in test tubes and get some traction on their achievement when they graduate high school? Well, in aggregate, it looks like it will be better than rolling dice,” says Panofsky. “But what if we want to determine if your kid should be in the gifted or remedial program?”

When it comes to using DNA tests in the real world, Panofsky says, “I don’t think they thought about it very hard.”

IQ scores for sale

MIT Technology Review found that genetic IQ assessments are already being offered by websites that provide information to people who’ve previously had their DNA measured by 23andMe or Ancestry.com.

Users of GenePlaza, for example, can upload their 23andMe data and pay $4 extra to access an “Intelligence App,” which rates their DNA using data from the big 2017 study on IQ genes.

It shows users where their genes place them on a bell curve from lower to higher IQ. A similar calculation is available from DNA Land.