A leading genetic expert tackles the nature vs. nurture debate

Can you capture the essence of a human in a vial?
Can you capture the essence of a human in a vial?
Image: Reuters / Carlo Allegri
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Robert Plomin is no stranger to controversy. It comes with the territory, he tells me, for someone who has spent over four decades studying the role genetics play in making us who we are.

That question is at the heart of a field of science known as behavioral genetics, or the study of the interplay of genetic and environmental influences on human behaviors. The question of how much of a role genetics play in making us who we are is controversial, not just because no one seems to be able to agree on an answer, but also because figuring out how we become who we are is filled with social, historical, and political minefields.

In the past, the belief that genes exclusively determine who we are has led humanity down some dark paths, including social Darwinism, a belief that people were subject to survival-of-the-fittest laws of nature, which was used by some political theorists to justify laissez-faire capitalism and political conservatism. That, in turn, spawned eugenics, a pseudoscience used by various authoritarian regimes to rationalize inhumane policies like selective breeding, sterilization, and even genocide. It’s sensible, then, that social scientists are hesitant to embrace any line of thinking that, in their minds, might lead history to repeat itself.

Plomin, a psychologist and professor of behavioral genetics at King’s College in London, has little patience for this argument. His research tells him that genes account for about half of the differences between us, and that the rest is mostly attributable to random experiences, not systemic forces like the family you are born in. Accepting that, says Plomin, can free us of the anxieties that come from believing everything we do—as parents, as teachers, as friends and neighbors—can irreparably harm our fellow man. That’s why he wrote his book, Blueprint: How DNA Makes Us Who We Are.

Quartz spoke with Plomin about behavioral genetics, what it means to be “us,” and whether we can control our own destiny.

This interview has been lightly condensed and edited for clarity.

Quartz: Let’s start with the basics. Why did you write this book, and why now?

Plomin: I was asked to write this book 30 years ago. But I realized at the time that more research was needed. It was a dangerous time to put your head above the parapet and say “genetics is important.” I had just started graduate school, and psychology was dominated by environmentalism; that’s the view that you are what you learn. Genetics never got mentioned.

[But] in these 40 years I’ve been working in the field, the evidence has accumulated and accumulated, so that most scientists now accept that inherited DNA differences account for a lot of the differences between us. I would say, on average, it’s about half of the differences between us in personality, in psychopathology (mental health and illness), and also in mental abilities and disabilities. The other thing that no one anticipated, though, is the DNA revolution. It changes everything, because now we can use DNA itself to predict psychological propensities from birth.

What difference has that made in your field?

That really will change how we do psychology, how we do clinical psychology, and even parenting and education, and society as a whole. I think it will actually change our understanding of ourselves. Because it becomes very real now; we’re not saying “in the abstract, on average, genetics is important.” You could say “yeah, yeah.” But, when I say, “here is your DNA. Here is your sister’s DNA. You’re at risk for alcoholism; your sister isn’t,” it really is going to be a transformation. So, I’m very glad I waited, because now that the evidence is there, people are more accepting.

We need to have this discussion, and to get that conversation going, and that’s why I launched the book. Also, to give people the DNA literacy that they need to join the conversation, because I am amazed about how little people really know about genetics and DNA.

Let’s talk about that. For people who haven’t read your book, what are the basic concepts that anyone trying to understand your work needs to know?

The main message is that these are not mysterious; it’s just dumb chemicals. But they are the molecule of life. And that’s because [DNA] replicates itself very reliably. That’s why you start life as a single cell, a fertilized egg, and the DNA in that cell is the same DNA as the fifty trillion cells in your body now. And 99% of the steps in the spiral staircase of the DNA…are identical for all of us. The 1% that differs is what we’re talking about.

The biggest problem I have is to stop people from using the word “determine”; oh, genes determine who you become. But they don’t! They influence you. They’re like nudges, and other things being equal, they’ll push you in one direction or another. But that doesn’t mean you can’t change.

It’s hard to understand these concepts. But I find one thing that helps people get it is I say: “If you were adopted away at birth, raised in a different family, gone to a different school, had different friends, had a different occupation, I would say, you’d be essentially the same person.” [Editor’s note: This is the subject of a recent documentary film, Three Identical Strangers.]

Just so readers understand: You’re talking about variations across a group of individuals, not genetic variations in an individual person. Can you clarify that?

That is such a critical issue. The short hand is: Height is 90% heritable. What does that mean? It means, of the individual differences between people [when it comes to] height, 90% of the differences are due to inherited genetic differences, on average, in the populations we studied.

And it’s not to say, then, that for an individual, 90% of your height is due to genetics. That’s a completely different issue. And it could be that, although on average, 90% of the differences between people in height is due to inherited genetic differences, any one individual, their short height could be due to environment; they could’ve had a childhood illness.

So, I think most people can get behind the idea that genetics influence height, or weightbut not things like intelligence or kindness. You’ve worked a lot on proving the link between genetics and intelligence. Can you explain your findings?

I started out doing work 45 years ago in personality, and then I kind of moved into cognitive development, language development, and then as my kids grew up in my sample, I studied education attainment—how they do at school.

And I’m keen to keep my hand in until I make a difference in education. Because education is the last bastion of anti-genetic thinking—it’s not even just ignoring genetics, I mean they’re really quite hostile. And I think it’s a bit like clinical psychology 30 years ago, where they thought…it’ll put them out of business if things are genetic. But no one thinks that way anymore. They realized it’s a good thing for clinical psychologists to know “this is particularly heritable,” and the main point is that causes and cures aren’t necessarily related. So you could have a disorder that’s entirely genetic, but it doesn’t mean that you have to fix it genetically.

Education hasn’t gotten that message yet, so they’re still quite hostile, which is surprising, because the problems teachers are worried about are among the most heritable ones around.

How could information about a student’s genetic background help teachers?

Teachers recognize that students differ in how well they learn… and, when pushed, they’ll probably say they think it’s genetic, to some extent. It doesn’t mean you don’t teach kids, it just means some kids are going to have a hard time learning.

If there are teachers or parents who don’t recognize genetics, then it’s important they read this book, because it does have an effect. In the past, if kids didn’t do well in school, the first thing the governments would do is blame the schools, blame the teachers. But that doesn’t pan out very well empirically. So then, what do you do? You blame the parents, and then if you fail there, you blame the kids. But I think it’s very important to recognize that kids differ a lot genetically, even in terms of learning ability. And then to respect those differences to a greater extent.

Concretely, what does this mean for teachers?

The big example is personalized learning, which I get a lot of pushback on, but I just don’t get it. It’s the idea that it shouldn’t be a one-size-fits-all education system. It should be personalized. We recognize that kids are different and we try to give them the best boost we can to try to maximize their strengths and minimize their weaknesses. And genetics is part of that.

I think maths is the best example, because they have these wonderful computer programs that do what’s called “adaptive learning.” [Editor’s note: Adaptive learning is a personalized online course, tailored to a student’s strengths, weaknesses, goals, and engagement patterns, and that adapts in real-time to the student’s activity, performance, and interest level.] Computers are perfectly set up for personalized learning.

Aren’t you worried that will lead to lower expectations for kids who have genetic indicators that they are, say, likelier to be bad at math, and that in turn will lead them to underperform? Won’t that be a self-fulfilling prophecy?

It’s not as simple as that, really. You can make a difference, but kids aren’t stupid. You can push and get kids to do this stuff, but at what cost? It’s more appetites than aptitudes. We think of genetics as being hardwired; I think it’s a matter of finding what you like to do, and then you do it a lot, and you do it better, because it’s self-rewarding, as opposed to the old model of education, or tiger moms, where you pre-ordain what your kids are going to do. It just can’t be the right way to go. It doesn’t mean you can’t do it; you can make a kid who has very little mathematical skills get pretty good at math. But it’s going to be such an uphill battle; why not find something that the kid likes to do, and is better at?

The positive spin is “yeah, anyone can be president, and we can all do anything we want to do, all you need is a growth mindset, or 10,000 hours of practice [Editor’s note: Plomin is referring to a rule based on research by psychologist Anders Ericsson but made popular by the writer Malcolm Gladwell in his book Outliers, that 10,000 hours of dedicated practice can make anyone gifted in a particular field], or grit.” But I just don’t believe those things. You can make a difference, but why not go with the flow rather than swimming upstream?

That’s why you say that both teachers and parents matter but….

…but they don’t make a difference. And I know that’s a really hard one for people to accept.

I understand why! It seems fatalistic, and goes against a huge body of research, for example in early childhood development, that targeted interventions can reverse the course of someone’s life. You’re saying that’s not true.

I don’t think it is, no. There [are] several problems. One is effect size; people talk about these new interventions that really make a difference, [but] you have to ask, how much of an effect does it really have? Does it have a long-term effect?

People are looking for either quick fixes or magic-bullet interventions that will make a difference. I’m very skeptical, because the history of these [experiments] is that these things don’t replicate and they don’t make a difference in the long run.

It’s important to realize that a lot of what we think is environmental, isn’t. It’s disguised genetic. Not to say that the environment isn’t important, because it is. It accounts for about half of the differences that we see. But it’s not the environment of nurture that we always thought was so important. An intervention could make a big difference, but that’s could make a difference. Experiments are about what could be; that doesn’t mean it makes a difference in the real world.

All of your theories are pretty radical. What are the policy implications, for parents, teachers, and schools?

There’s no necessary policy implication. So, you could have the right-wing view [of education], which might be something stupid like “educate the best, forget the rest.” Or you could have a left-wing point of view, which would be to identify the kids who are going to have trouble, and realize we need to put as much resources as we need to get them up to some minimal level. That is being done—it’s called the Finnish model. And that works pretty well.

Another thing where people get confused is that this doesn’t mean parents can’t do anything. Parents can control the behavior of their children. If you have an aggressive child who is hitting another child over the head, you can say “that is not acceptable.” You’re not changing the aggressiveness, but you can control the behavior. And where we see that really works is zero-tolerance bullying policies in schools; they really work. You knock out the bullying behaviors, but it doesn’t mean you change the bullies.

Parents can have an effect, but what I’d like to argue for is that…it’s good for parents to relax. You can’t make much of a difference in the long run anyways.

Are you saying parents should just stop trying?

That is a possible problem, but I don’t think it works that way. You can work with the behavior. And if you love somebody, you don’t love them to change them. And I think it should be that way between parents and children to a larger extent. We should watch [our children] become who they are; we shouldn’t pre-ordain who they become.