Seven years ago, I took a bet from one of the most controversial figures in the scientific world. Charles Murray, the political scientist who—along with the late psychologist Richard Herrnstein—wrote The Bell Curve in 1994, wagered that one of his core ideas about genetics and intelligence would be proved true by 2025. He emailed me some time after I’d helped stoke an online furor about his insistent defense of The Bell Curve’s main points, which he’d recently reiterated on a popular podcast and which I, along with two other psychologists and intelligence researchers, had denounced in Vox. I took the bet because I was confident I would win.
In The Bell Curve, Murray and Herrnstein argue that intelligence, as measured by an IQ score, is a crucial determinant of success in modern society. They also argue that a person’s intelligence is substantially determined by genetics, leading to the establishment of “cognitive elites” as intelligent people select one another for reproduction. Most controversially, Herrnstein and Murray entertain the possibility that socioeconomic and educational differences among racial groups could be explained by differences in their IQ scores, and that these differences are at least partially attributable to genetic differences among the groups.
The bet’s premise was simple enough. Murray quoted himself on the podcast, arguing that “we will understand IQ genetically. I think most of the picture will have been filled in by 2025—there will still be blanks, but we’ll know basically what’s going on.” And he proposed that, in seven years, he’d sit through a lecture I gave on the topic: “Who Was More Right?”
It is now 2025, and I am here to declare that I was more right. (This article can sub in for the lecture Murray proposed.) We do not understand the genetic or brain mechanisms that cause some people to be more intelligent than others. The more we have learned about the specifics of DNA associated with intelligence, the further away that goal has receded. Even given a softer goal of predicting, rather than explaining, intelligence differences, we still can’t do it very well. If anything, we are further away now than in 2018 to knowing “basically what’s going on” with genetic influences on intelligence. (When I reached out to Murray for his view on this, he insisted that he is still right. “Of course I think I won the bet, and I will lay out my reasons for thinking that,” he wrote in an email. He told me he plans to do so in a few months, when he has more time.)
When The Bell Curve was released, scientists’ best understanding of how genetics influenced human behavior was based on differences and similarities among family members, especially twins. It had been established that identical twins are quite a bit more similar in their IQ than fraternal twins and that intelligence differences are heritable in a limited statistical sense. But heritable does not mean “inherited.” This statistical measure of heritability is notoriously difficult to interpret and limited in its import; twin studies, developed decades before the DNA molecule was discovered, also offered little insight into the biology of any particular trait. Herrnstein and Murray, however, took these findings as a strong indicator of genetic transmission of intelligence from parents to children.
A decade after The Bell Curve’s publication, the Human Genome Project made human DNA available to scientists on a large scale, and researchers anticipated that they would figure out what was going on with genes and human behavior. But all of the most direct methods of searching for IQ genes were unsuccessful. Reports of individual genes that were purported to cause IQ differences (or personality traits or mental illness) failed to replicate over and over again. Although we have known for a long time about genes that cause profound mental disabilities, such as Tay-Sachs disease and Huntington’s disease, no single gene is known to increase intelligence.
Scientists were still hopeful that, by looking at the smaller building blocks of individual genes, they might find a clear genetic map of human behaviors. Murray’s proposed bet came at just about the peak of intrigue around a technology called “genome-wide association studies,” which promised to offer those insights. The technology scans the entire genome for single nucleotide polymorphisms, or SNPs—the spots where one person’s genome might have a T, while another’s has a C—for associations with human behaviors. As the costs of these analyses went down and sample sizes went up, researchers identified many tiny but statistically significant associations between these small genetic variations and intelligence. The total effect of those associations was slowly inching upward, and many scientists hoped to soon be able to make meaningful predictions of IQ based on DNA.
But this line of research, too, has turned out to be far less revelatory than anticipated. The cumulative effect of the associations between SNPs and intelligence has leveled off, and correlations remain only that. The resulting estimates of heritability are only about a third of those based on twin studies. Even taken together, the associations don’t add up to anything resembling a neurogenetic explanation of IQ differences.
In fact, the more researchers have learned about associations between DNA and IQ, the more complex and less deterministic this relationship looks. Some associations between SNPs and intelligence are not the direct result of DNA. (For example, if rich people send their kids to fancy schools to increase their IQ and some SNPs are associated with being rich for whatever reason, those SNPs wind up being associated with IQ as well.) Studies that compare genetic variation between pairs of siblings have been able to better control for socioeconomic backgrounds, as well as parenting practices and ethnicities; in these studies, the direct effects of DNA on IQ look even smaller, still with no hint of a biological mechanism.
That is where things stand today. Scientists might disagree about what we are going to learn in the future and when we are going to learn it, but in 2025, we do not remotely understand what Murray hoped we would.
In our email exchange, Murray said that any argument I’d lay out here would be insufficient to make this case. “We’re not talking about something that lends itself to 1,500 words, or 3,000 for that matter, written for a lay audience, but a 20-page (at least) technical presentation,” he wrote. (He did not respond to an invitation to elaborate on this, or respond to the argument made in this piece.) Certainly, one could tease out in more detail the work that has been done to identify associations between SNPs and intelligence, the significance of those findings, and their limits. But to argue that any of this research adds up to a substantial account of intelligence misunderstands the nature of such human traits and what can be expected from scientific explanations of them.
Consider another human difference: financial solvency, which can be measured and quantified, just like IQ. It is heritable in twin studies and (less so) in SNPs. But would you bet that sooner or later we are going to know “what’s going on” with your bank account at the level of genes? I think most people would accept that financial well-being is modestly correlated with genetic differences but also both highly malleable and responsive to a person’s environment. So is IQ.
Murray wants more. He is forever repeating the prediction that we are on the threshold of a settled genetic explanation of intelligence differences because, without one, IQ cannot play the deterministic role The Bell Curve requires.
Can I prove that scientists will never discover the genetic recipe for intelligence? Of course not. That’s why the terms of the bet mattered: They took an unanswerable question about what might be discovered on some indefinite timescale and made it real. The world would be a different place if scientists understood intelligence at the genetic level. But right now, like wealth and health, IQ remains a node in the uncontrolled matrix of human development, causing some things and being caused by others, as genes and environment interact in the background.
