“I also get that on the left side,” he said. “Everything is cool. Many smart people end up there.”

Erlich explained that he designed the program to make people cautious about the connection between genes and intelligence. All those disclaimers and notes that surrounded the bell curve were intended to show that these predictions are, in a sense, worse than just wrong. They’re practically meaningless.

The inspiration for the program was a 2017 study pinpointing certain genes with some sort of connection to intelligence. For decades, scientists knew that the genes we inherit play a role in the variation in scores on intelligence tests. Studies on twins and families show that people who share more genes in common tend to get closer scores. The 2017 study, carried out by a team of researchers based at Vrije University Amsterdam, was one of the first to find a statistically strong connection between that variation in scores and specific genes.

DNA is composed of four units, known as bases, that are a bit like the alphabetic letters that spell out a recipe. For the most part, the DNA of any two people is identical. But here and there, the letters differ. In a study of over 78,000 people, the Amsterdam team found variants in 52 genes that are unusually common in people who score higher (or lower) on intelligence tests.

This kind of study is very different from the genetic tests that doctors order for patients. If a woman has a family history of aggressive breast cancer, for example, a doctor may order a test for mutations on the BRCA1 gene. A single mutation there can raise the risk of breast cancer by 50 to 85 percent.

If you discovered that you had one of the variants identified by the Amsterdam team, that would not jack up your IQ by 50 points. Each one is only associated, on average, with a shift of a fraction of one point.

Erlich’s program checks those 52 genes in the DNA of his volunteers. It determines the effect that each variant has on each person, adding up all the slightly positive and negative effects to determine their total impact.

In most cases, they all pretty much cancel each other out. That’s why Erlich ended up with a bell curve, with its peak around a net effect of zero. In my case, the score-lowering variants slightly outweighed the score-raising ones, leaving me—like Erlich—on the left side of the curve. And I do mean slightly. Each of those ticks on the horizontal axis of the bell curve represents five IQ points. Erlich predicted that the effect of my 52 genes added up to less than a point.

But there’s an even deeper illusion to my bell curve: The seeming precision is almost certainly wrong.

When geneticists use the word prediction, they give it a different meaning than the rest of us do. We usually think of predictions as accurate forecasts for particular situations. At a carnival, you might encounter a man who promises to predict your weight simply by looking you over. If you weighed, say, 130 pounds, and he guessed 132, you might be impressed. If he guessed 232, you’d expect to walk away with a giant teddy bear.