"Since Sir Francis Galton coined the phrase “nature versus nurture” 150 years ago, the debate about what makes us who we are has dominated the human sciences.
Do genes determine our destiny, as the hereditarians would say? Or do we enter the world as blank slates, formed only by what we encounter in our homes and beyond?
What started as an intellectual debate quickly expanded to whatever anyone wanted it to mean, invoked in arguments about everything from free will to race to inequality to whether public policy can, or should, level the playing field.
Today, however, a new realm of science is poised to upend the debate — not by declaring victory for one side or the other, nor even by calling a tie, but rather by revealing they were never in opposition in the first place.
Through this new vantage, nature and nurture are not even entirely distinguishable, because genes and environment don’t operate in isolation; they influence each other and to a very real degree even create each other.
The new field is called sociogenomics, a fusion of behavioral science and genetics that I have been closely involved with for over a decade. Though the field is still in its infancy, its philosophical implications are staggering. It has the potential to rewrite a great deal of what we think we know about who we are and how we got that way. For all the talk of someday engineering our chromosomes and the science-fiction fantasy of designer babies flooding our preschools, this is the real paradigm shift, and it’s already underway.
Genes, it turns out, don’t affect who we become just on their own, inside our bodies — they work, in part, by shaping the environments we seek out or engender.
Picture a kid who is born with two working copies of what’s known as the sprinter’s gene, ACTN3. By elementary school she might be winning every game of tag, every race, and be chosen first whenever sides are drawn up. You could see how parents and coaches might encourage a kid like that to join an organized sports team and how she would be likely to receive positive feedback for her performance on it, which in turn might motivate her to train harder. By high school she makes varsity track and soccer, and the more she excels, the more coaching and training is made available to her.
Of course, any number of factors might cause her to quit sports — an injury, say, or a toxic team environment. But if she keeps at it, her starting position on a big college team won’t be the result of just her genes or her hard work. It will also be the result of how her genes shaped her environment, influencing the people and opportunities she encountered, and how her environment shaped the way and the degree to which her genes expressed themselves.
It’s a continuous feedback loop, in which neither nature nor nurture is a fixed entity.
At other times, the nature-nurture feedback loop may be more pernicious. It’s no surprise that terrible setbacks — the loss of a job, the end of a marriage — can cause people to fall into depression. I was stunned to learn, however, that people with a high genetic propensity for depression are more likely to encounter these setbacks, which in turn contribute to their depression. That’s not to say that any of it is their fault, just that the way we’re wired and the world we navigate are closely linked.
The part of this research that really blows me away is the realization that our environment is, in part, made up of the genes of the people around us. Our friends’, our partners’, even our peers’ genes all influence us. Preliminary research that I was involved in suggests that your spouse’s genes influence your likelihood of depression almost a third as much as your own genes do. Meanwhile, research I helped conduct shows that the presence of a few genetically predisposed smokers in a high school appears to cause smoking rates to spike for an entire grade — even among those students who didn’t personally know those nicotine-prone classmates — spreading like a genetically sparked wildfire through the social network.
The social environment, then, is genetics one degree removed. And vice versa.
When scientists started decoding the human genome, many assumed the nature-nurture debate was over and the hereditarians had essentially won. Soon we’d know the genetic blueprints for everything: obesity, intelligence, susceptibility to chronic diseases, even individual personality traits. Pharmaceutical companies would develop drugs that could target the handful of genes responsible for, say, arthritis or heart disease or schizophrenia. The end of illness would soon be at hand.
It wasn’t that simple. These outcomes are controlled not by a few genes but by thousands of tiny variants across all your chromosomes, far too many to be just zapped away. Scientists did get something out of the inquiry, however.
Starting around 2009, they found a way to summarize all these small genetic influences into a single metric that they called the polygenic index (PGI).
Think of it as a FICO credit score for your biology. Or rather scores, plural, since there is a different one for each and every outcome we can measure.
Scientists don’t all agree about what to make of this new data or whether it can apply equally to all populations, but today roughly 6,000 studies have identified polygenic indexes, or PGIs, for more than 3,500 traits, from sleep habits to right- or left-handedness and extroversion. These indexes are not crystal balls, to say the least. They can’t tell you anything with certainty, and in some arenas they can’t really tell you anything at all, at least not yet. But they can offer some very tantalizing clues. Take the PGI for educational attainment — that is, how far we go in school. Research I participated in found that among adults whose scores were in the lowest tenth on that PGI, only 7 percent had finished college. Among those whose scores were in the top tenth, that number was 71 percent. That’s a significant gap.
At the same time, it’s far from destiny. Clearly, genes alone are not enough to explain the course of people’s lives, even if someday we get much better data than this nascent field can currently provide.
So what, then, should we do with those PGI scores, which — as the field of sociogenomics reveals — tell us so much and yet so little?
If doctors start using them to identify people at high risk for heart disease and get them started on preventive regimens long before they’re in danger, the benefit would be pretty uncontroversial. What if life insurance companies start adjusting premiums based on genetic risk for stroke? That’s more complicated.
From there things get pretty dizzying. Will sperm and egg donor banks optimize genetic profiles based on what a customer is willing to pay? Will elite schools, gravely misunderstanding what these scores mean, use PGIs to screen applicants? It’s not beyond imagining that dating apps might someday link profiles to genetic scores. And since wealthier families will have the first access to these tools, social inequality could literally get encoded in our DNA. Then these limited bits of data could indeed become predictive of life outcomes, but for the very worst reasons and with terrible consequences.
Which brings me to a fertility clinic visit nine years ago.
As a social scientist, I have spent a long time studying people’s environments. As a biologist, I’ve worked in the laboratory studying DNA. As a parent, I’ve brought it all home, test-driving research in real life. (My kids humor me, mostly.)
When my wife and I decided to embark on I.V.F., I had just become involved in the field of sociogenomics. I was fascinated by the new technology of polygenic indexes but not yet aware of how small a piece of the puzzle they represent. So I handed our doctor a journal article explaining how to calculate these scores and asked her to screen the embryos’ genetic predisposition for autism and schizophrenia.
My wife cringed. The doctor looked at me just the way you would imagine.
I wish I could say that I stopped there, that I didn’t go on to summarize the plot of the 1997 sci-fi movie “Gattaca” to explain what I intended — but alas, that was not the case. “This child is still you,” I said, earnestly quoting the words that a genetic counselor tells the parents of Ethan Hawke’s character. “Simply the best of you.”
Part of me was driven by pure scientific curiosity: What if we could conceive the world’s first PGI-optimized baby? But personal anxiety also played a role. I was an older father, and I worried about the known risks that my age posed for our child. I even pitched the doctor on writing up our case for a medical journal, which earned me another swift kick under the table from my wife.
At our next appointment, the doctor shut me down. The clinic didn’t have the capability to screen embryos in that way. Instead, it would put the embryos under a microscope and pick the one that looked the most symmetrical. It all seemed so unscientific.
I was fixating on DNA, but I didn’t yet understand the extent to which the genes our child would inherit and the environment in which the child would be raised were linked through a giant feedback loop, or the way that kids carve out their own environmental niches, even within their families.
Years after that visit to the I.V.F. clinic, I worked with the Danish social scientist Asta Breinholt to study how parents interacted with their children. We found that children who have genes that correlate to more success in school evoke more intellectual engagement from their parents than kids in the same family who don’t share these genes. This feedback loop starts as early as 18 months old, long before any formal assessment of academic ability. Babies with a PGI that is associated with greater educational attainment already receive more reading and playtime from parents than their siblings without that same genotype do. And that additional attention, in turn, helps those kids to realize the full potential of those genes, that is, to do well in school. In other words, parents don’t just parent their children — children parent their parents, subtly guided by their genes.
Even the historical era and social conditions into which a child is born — their environment writ large — can affect how their genes do or do not find expression.
Take the PGI associated with body mass. A hundred years ago, when calories were more scarce and physical labor was more common, genes didn’t play much of a role in predicting who would become thin or heavy. The overwhelming majority of people were thin, and that was that. Fast-forward to today when both kale salads and venti Frappuccinos are available in abundance, and suddenly we see much wider variation in body mass index — and research I led suggests that PGI plays a bigger role in determining B.M.I. than it had in the past.
That’s the central insight of sociogenomics: Genes alone aren’t enough to determine these outcomes and neither is environment, but it’s not just because nature and nurture both shape the individual. It’s because they both shape each other, with nature influencing the way we experience nurture and nurture influencing the way our nature expresses itself.
Smoking offers another example. In 1950, almost half of Americans smoked. It was such a common activity that genetic variation didn’t play much of a role in determining who did or didn’t take it up. That changed after the 1964 surgeon general’s report on the dangers of smoking (and subsequent interventions). Today just over a tenth of Americans smoke. Doing so reflects a much more particular act. In this environment, research I was involved with has shown, smokers have a much higher average PGI for smoking than the rest of the population does.
In both of these examples, the more opportunities and information the environment provides — the more varied environments become — the bigger the role that genetic variation plays in sorting us into different categories.
This sorting is happening spatially, too. Many different factors come to bear on people’s decisions to leave the places they live in search of opportunity. Education turns out to be one of them: Studies, including ones I’ve worked on, show that those who have more schooling are more likely to make that choice. Because we know that there’s a correlation, however loose, between education PGIs and how far people go in their schooling, migration of diplomas also, to some extent, means a migration of genes, as studies have shown. A result is that societies are becoming not just economically polarized; they may be becoming biologically polarized, too. If so, this will have serious implications for economic opportunity that public policy will have to reckon with.
Genetic sorting is happening even in our most intimate environments. Looking across the whole genome, people in the United States tend to marry people with similar genetic profiles.
Very similar: Spouses are on average the genetic equivalents of their first cousins once removed.
Another research project I was involved with showed that for the education PGI, spouses look more like first cousins.
For the height PGI, it’s more like half-siblings.
In the darkest view of this new technology, the science of PGIs locks us into a future with no regard for the environment in which those genes express themselves, for the individual human being who possesses them, for the choices we make and for the emotions we experience. It’s a dystopian future, like “Gattaca,” but without the cool, ultra-minimalist production design.
I see a brighter possibility. I believe that knowing how our environment shapes the expression of our DNA gives us the chance to change our genetic pathways.
If I screened my kid and learned he was off the charts for innate musical potential, I would start him on piano lessons from toddlerhood (and at least see if he took to them). If I found out he was at high risk for opioid addiction, I’d make sure, when he grew up, that he knew to avoid those medications for pain management. If a kindergarten could screen students for the dyslexia PGI, it could make special literacy support available to those at high risk — early, when it can be most effective, rather than after they’ve fallen behind and started to feel bad about themselves.
We certainly need strong policies to keep insurance companies, admissions committees and police departments from exploiting our PGIs, as some institutions are bound to try to do. But overall, I really do believe that knowledge — about our genetic predispositions and how our environments affect them — can be power.
In 2019, three years after that fertility clinic visit, our son was born. He was conceived the old-fashioned way. Well, not quite Chevy-back-seat old-fashioned, but without polygenic screening or selection.
The next year, the first PGI-optimized baby, Aurea, was born. Some I.V.F. clinics now offer the screening as part of a package. Aurea’s father told Wired that he considered screening embryos to be “really a no-brainer.”
Given what I have learned about the amazing possibilities of PGI technology — but also about its limitations, and its potential for abuse — I no longer think of it that way.
Every night, as my son snuggles up to me for a bedtime story, I’m grateful we let fate take its course in that petri dish. I wouldn’t trade any detail of who he has become for the chance to maximize some slight statistical probability. I once thought genes were simple blueprints, something we could tweak like an app setting. Now I know better. Nature and nurture aren’t separate forces — they’re a Möbius strip, endlessly looping back on each other.
And my son’s future? It won’t be fated by a biological FICO score, even if it will be subtly guided by his genes as they shape his environmental path through life. It’ll be an unpredictable, surprising choose your own adventure — just as it should be.
Dalton Conley, a sociology professor at Princeton and a faculty affiliate at the New York Genome Center, is the author of “The Social Genome: The New Science of Nature and Nurture.”" [1]
1. A New Scientific Field Is Recasting Who We Are and How We Got That Way: Guest Essay. Conley, Dalton. New York Times (Online) New York Times Company. Mar 13, 2025.
