And it gets weirder. The environment might also influence how heritable IQ is. When kids are well off, with their basic needs met and plenty of cognitive stimulation, genes often explain much of the variation between them. Against a backdrop of deprivation, however, genes sometimes recede into the background, at least according to some research. It’s not only that both nature and nurture matter, but that they influence each other in different ways in different people.

Let’s say it turns out that there’s a genetic variant that helps make a person extremely verbal. You inherit this variant, get a graduate degree in English and marry a fellow academic in your department. Your first child gets a nice set of verbal genes, but he also gets all the benefits of a couple of English professors at home. You and your spouse talk all the time, and not just about The Odyssey. When you drive in the car, you chatter to your child about whether you’re turning right or left, what the “W” or “E” on your rearview mirror compass means, about the distance to your destination, and about maps. Maybe those conversations spark his curiosity, so you’ll set him on your lap and tinker around on Google Earth together. Before long, your kid is getting pretty good at spatial reasoning.

Now multiply your imaginary map-loving kid times a few hundred thousand and imagine they all get their genomes sequenced. A geneticist trying to understand intelligence might see that people with those verbal-boosting genes seem to be very good at spatial reasoning. “Aha,” she’ll think, “these genes must be driving general intelligence, the ability to work through multiple types of cognitive tasks.” But she’ll be wrong.

In other words, sweeping genome-wide studies can turn up correlations between genetic variants and a complex trait, but they can’t fill in the blanks that explain why that correlation exists. “It’s very fascinating, but it’s also muddy as all get-out,” says Johnson.

It’s possible that intelligence simply isn’t something understandable on the level of genes. Philosopher Rom Harré has compared the idea of studying intelligence on a genetic basis with researching what a carpet is using only a mass spectrometer. Sure, you might learn a bit about polyester blends, but it’s not going to tell you much about how to pull a room together.

“If a geologist wanted to explain plate tectonics and the way the continents have moved over millions of years, they wouldn’t want to be doing chemical analyses of little rocks that they pick up in their backyard,” says Eric Turkheimer, a psychologist at the University of Virginia. “You have to think about scale when you’re studying things, and not all things that human beings do are very explicable on the scale of neurons and genes.”

This is a jarring opinion in a world where new technologies have allowed us to look at the brain in smaller and smaller chunks. But Turkheimer’s argument recently got a boost from a paper published in the journal Cell. In the article, Stanford University geneticist Jonathan Pritchard and his colleagues argue that complex traits aren’t polygenic, or influenced by multiple genes, as geneticists have long assumed. No, Pritchard argues: They’re omnigenic, or influenced by every gene.

In essence, the omnigenic hypothesis posits that the networks regulating genes are so interconnected that any gene expressed in a given tissue is going to have some impact, no matter how infinitesimal, on the function of that tissue. What’s more, the genes likely aren’t neatly arranged in discrete clusters, as behavioral geneticists have hoped.

Indeed, many of the genetic variants linked to intelligence that have discovered so far are involved in expansive tasks in the very structure of the brain. For example, Posthuma and her colleagues found associations between intelligence and genes involved in the formation of synapses, in the development of different types of neurons, and in guiding the growth of the axons that neurons use to transmit messages. Logically, those processes of brain development would have a relationship to intelligence, says Terrance Deacon, a biological anthropologist at the University of California, Berkeley. But it’s also not exactly groundbreaking to say that being smart has something to do with your brain having, at some point, developed.

Some other genes associated with intelligence appear to be busy all over the body. One discovered by Posthuma and her team had previously been linked to bone formation and hypertension. The SNPs of note that were found in people with ultra-high IQs were located in a gene called ADAM12, which encodes an enzyme that binds to a protein that binds to insulin-like growth factors. Suffice it to say, the protein and its enzyme are found in basically every tissue, doing lots of different stuff.

It gets even messier. Posthuma and her team also found that genetic variants associated with intelligence were also overrepresented in people who are tall, in people who have autism, and in people who had successfully kicked a cigarette habit. They were less frequently found in people with depression, schizophrenia, and Alzheimer’s. Whatever these genes are doing for intelligence, they’re mixed up in a lot of other stuff, too. Start to tinker with them, and who knows what strings you’ll unravel.

Sharpening our minds

And yet, even amid all the noise and confusion, genetics may yet tell us something about intelligence and give us tools to boost it that are a lot less ethically fraught than embryo selection or genome editing.

For many behavioral geneticists, the biggest promise of the latest research is that even if the number of genetic variants is too big to ever think of manipulating, those variants could help explain what intelligence actually is. If, for example, SNPs correlated with intelligence do turn out to cluster in and around genes and regions involved in synapse formation, perhaps we’ll find that the way synapses develop and are maintained explains why some brains are better at reasoning than others. Research hasn’t yet illuminated that black box. Studying the differences between people in synapse structure is extremely difficult because the infinitesimally small spaces between neurons don’t preserve well in dead brain tissue. A few studies on surgically removed brain tissue have found gender differences in synapse structure, but no one has done that kind of work with an eye on human intelligence.