Why is it that one high school student aces her SAT verbal section while another barely finishes the exam, scoring near the bottom of the heap?
Some would say that the teenager with the high score probably benefited from an advantageous environment, parents who could afford books and who read to her as a young child, instilling a lifelong passion for all things literary. The low-scoring adolescent may not have enjoyed those same advantages and may have experienced stress due to poverty. Those who subscribe to this theory–many of whom lean left–might go so far as to say that gaps like this one are why we need more policies like universal preschool and a stronger safety net for children.
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Others, meanwhile, would say that regardless of those environmental differences, the test-score gap between the two students was probably already baked into their genes. The top scorer just had natural talents from birth, and while it may not be fair, there’s not much we can do about it.
For decades, scientists have argued over whether our genes (nature) or our environment (nurture) shapes who we are. It’s one of the longest-running debates in human sciences. Are we born with certain abilities, personalities, and destinies already programmed in? Or do our experiences—the schools we attend, the books we read, the people we meet—mold us into who we become? Which one matters more?
Psychologists have spent over 50 years studying this, tracking twins raised apart, adoptees, and half-siblings to estimate how much of various traits are genetic. The big takeaway? On average, human traits are about half genetic and half environmental. Height, for example, is about 80% genetic in developed countries. Personality traits are on the lower end: Around 20% heritable. Educational attainment? About 40% inherited. And when it comes to reading ability—i.e. verbal test scores—it turns out that by age 18, it’s over 80% heritable.
It would seem like the hereditarians won the debate with respect to the case of the verbal SAT section and that differences in the population are mostly due to genetics.
But that framing—the idea of nature versus nurture—is all wrong. Just because some trait—like reading—is highly heritable doesn’t mean the environment doesn’t matter, it just means the environment matters in a certain way.
That’s one of the insights of a new field called sociogenomics. Instead of nature competing with nurture, sociogenomics shows how genes and environment interact in ways we never fully appreciated before. Your DNA isn’t a rigid blueprint dictating your fate, and your environment isn’t just some separate force shaping you independently. Instead, genes work through the environment. Scientists have long known that nature and nurture mutually reinforce each other. But what’s new here—in the past decade, when the genomics revolution has brought oodles of data to human scientists—is that we can now study exactly how the genes for, say, reading ability, are distributed across society and how they work their magic by creating or evoking environmental conditions and responses.
It’s common sense that kids who get read to a lot tend to have better verbal skills. But why do some kids get more bedtime stories than others? Is it just luck—having parents who love books? Not quite. Kids with an innate genetic tendency toward high verbal ability naturally receive more words. They may beg for “one more story” before bed, show an early fascination with books, and develop a hunger for language. In turn, their parents—whether consciously or not—respond to this interest by reading to them more. Over time, this extra exposure leads to even better verbal skills. It’s a cycle: genes create tendencies, which shape experiences, which reinforce those same genetic tendencies.
This cycle starts very early. A study that Asta Breinholt and I conducted showed that parents unknowingly invest more time and resources in kids who show early academic promise. If two average parents (say, both at the 50th percentile for genetic educational potential) happen to have a child who scores in the 60th percentile for genetic educational potential, they notice. That child, compared to a sibling who might be in the 40th percentile, gets more attention, more books, more educational experiences—as early as 18 months of age, long before any report cards have come home informing mom and dad about their kid’s talents or deficits. And then what happens? The child who was already slightly above average genetically likely ends up doing even better in school (and on the SATs)—not because the genes alone dictated success, but because those genes nudged the environment in their favor.
This means that much of what we think of as environmental is partly genes in action. A child’s genetic potential influences how parents treat them before they can even speak. And the effects can snowball—small genetic advantages may turn into big differences over time, thanks to the way the environment reacts. But that also means that genes are not destiny: If the environment niches they carve out are an important step from DNA to SAT verbal scores, then we can act on those environments for those with advantageous or disadvantageous genes. We can, for example, make sure that a kid with a high genetic risk for addiction stays away from opioids for pain management. In short, if we gain an understanding of someone’s genetic propensities, we may be able to adjust the environment in the way that most benefits them.
Of course it’s not always so simple. Genes need certain environmental inputs that they seek out in order to have their effects. If that environmental feedback is blocked, due to poverty, racism, or other forces outside the control of, for instance, an individual parent, then genetic tendencies cannot be reinforced. So, even if a child has a high genetic propensity for reading ability, without the environmental element, that 80% heritability figure for verbal skills is moot.
One of the best ways to think about how all this works is to move beyond the outdated “blueprint” analogy for DNA, in which DNA is a rigid set of instructions dictating who we become. Instead imagine your brain as a machine-learning model. Your genes set the parameters—how quickly you learn, what interests you, what behaviors you’re inclined toward. But just like an algorithm, you need training data. Your experiences, social interactions, and education all feed into this system. The more exposure you have to different ideas, the more refined your “model” becomes. Someone who’s genetically inclined toward curiosity will seek out more information, explore new ideas, and continuously refine their worldview. Meanwhile, a genetically cautious person might be more selective about new experiences, filtering their environment differently.
Over time, these genetic tendencies get reinforced by the environments we shape for ourselves. The curious kid seeks out books and interesting conversations, further sharpening their mind. The risk-averse person builds a life with stability and routine. As Joyce Carol Oates once said: “I don’t change; I become more myself.”
We can see Oates’ insight in the data. When we measure something like intelligence, we find that the genetic component becomes more predictive as we age into adulthood. At age 5, the genetic component is 45%, but by age 35, it has ballooned to 80%. As for verbal ability, the heritability rises from 48% at age 5 to over 70% by the time a kid takes the SAT. We can see a similar pattern with political views. Indeed, many, but not all, social and behavioral traits work this way. It’s like a fuzzy picture coming into focus—but that’s only made possible by “training” with our environmental interlocutors. What’s amazing is that the more we are exposed to the environment by living longer, the less the random aspects of the environment matter–the noise, so to speak–and the more our genes matter, picking and choosing the specific environmental information they incorporate into our brains.
This perspective fundamentally changes how we think about human development. It’s no longer about whether nature or nurture “wins”—because they’re not actually in competition. Instead, genetics and environment work in a dynamic loop, each shaping the other in constant, invisible, and powerful ways that ripple across our lives.
Conley is the author of The Social Genome: The New Science of Nature and Nurture
