How pleasant it is to live in the 21st century, enlightened, no longer scared of science. We can marvel at the diversity of life with David Attenborough; face the vastness of the cosmos with Brian Cox. These days we talk of colliders and particles as casually as we shop for milk. Science is our oyster.

Except of course when it comes to genetics. Just try starting an excited conversation about gene therapy, or about the young Chinese genius Zhao Bowen, who is, right now, hunting down the genes for intelligence. Faces will fall, there’ll be talk of eugenics, perhaps a sudden burst of inexplicable fury. This I know because I’ve felt it myself.

I felt it first with a friend who tried to tell me about the research being done by Professor Robert Plomin — who I’m now here waiting to meet. Professor Plomin is one of the world’s leading behavioural geneticists, which means he studies genes; not down a microscope, but by looking at the population and how we behave.

He’ll pick some interesting and measurable traits: weight, height, intelligence; and survey thousands of kids. Then take the spread of results — the variation — and figure out to what degree nature or nurture is responsible. He’s asking: why do we differ from each other?

Twins are obviously useful in studies like these — especially identical ones because they share 100 per cent of their DNA — and Professor Plomin runs the Twins Early Development Study (Teds) of all twins born in England and Wales from 1994 to 1996.

And what his research shows time and time again (said my friend) is that nature is often more important than we like to think, particularly in the contentious area of IQ. Yes, there’s a complicated interplay of genes and environment, but even so, it’s striking how heritable IQ is. Clever parents are more likely to have clever kids, and once it is born there’s little you can do to up a child’s long-term IQ.

Well, here’s when the fury rose up in me. An anger I at first took to be righteous rage in defence of the genetic underdog, but on retrospect I recognised as pique. Being told that IQ — or any other trait — is highly heritable makes me feel limited. I’m a child of the West: we can do or be whatever we want, thanks very much.

So Professor Robert Plomin gets a wary look from me as he lopes into the restaurant for lunch: 60-odd, tall in a way a Yank might call ‘rangy’. He has just come from the Department for Education, he says, which for a geneticist is a little like swimming with sharks, because if there’s a group of people who especially don’t want to hear that IQ is highly heritable, it’s teachers.

‘Education is the last — well, backwater,’ says Dr Robert with a grin. Then he tells a story about the dark old days of the 1970s when he was young and antagonism to genetics was the norm.

‘My very first conference was by this old guy Leon Kamin, the author of a book called The Science and Politics of IQ,’ says Plomin. ‘Kamin came back to academia just so as to stop this pernicious stuff about genetics entering psychology. There were 2,000, maybe 3,000 people. It was dark and he was bald with kinda craggy features. I mean he looked scary. Then he started saying: “We’ve got to stop this talk of genetics now!” And I realised it didn’t matter to Kamin what was true. He believed in what he called “science for the people”, which was what he thought it would be useful for the people to know. I mean, that killed me because it was Kamin and these elite Harvard professors deciding what’s for the people! The idea was that science should serve politics.

‘Well,’ Plomin spreads his hands wide, ‘that’s just anathema if you’re doing science — I mean that’s heresy!’ He looks at me, expectantly. There’s just a hint of Tom Jones about his blue eyes. Who wants to be a Kaminite? Not me. For the rest of our conversation, I try hard, and mostly remember that my own discomfort with a finding has no bearing on its truth.

So what does the science say? What’s the state of the new nature/nurture debate?

Just being in the same family doesn’t make siblings similar

‘OK, the reason we did genetic research,’ says Plomin, ‘was because we know traits run in families, right?’

You mean, families are more alike than strangers?

‘Exactly. So we look at both nature and -nurture to see why. At one time people thought family members were similar because of the environment, but it turns out that the answer — in psychopathology or personality, and in cognition post-adolescence — the answer is that it’s all genetic! What runs in families is genetic!’

So any way in which I’m like my parents or siblings is because of their genes, not because of how they brought me up? ‘Yes.’

I can feel the old anxiety open an eye. Surely families have some effect on how children turn out, what sort of adults they become?

Yes, Plomin explains, but it doesn’t make family members more similar — in the lingo, it’s not a ‘shared effect’. Imagine identical twins separated at birth. Bill and Rob. Bill and Rob are brought up by different adopted parents and never meet. But when Professor P knocks on the door and tests them both for various traits — IQ, let’s say — it turns out that they are just as similar to each other as other identical twins brought up in the same family. How weird is that?

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‘I did an adoption study on weight, IQ and cognitive abilities,’ says Plomin, ‘and parents who don’t see their children after the first few hours of life are just as similar in terms of both weight and IQ to them after adolescence as are parents who reared their own kids. And [killer blow] adopted parents are zero similar!’

It’s riveting, once you get your head around it. It puts paid to the parental delusion that the family is a great binding force, experienced by siblings in the same way. One of Professor P’s findings is, for instance, that the love parents think they distribute to their children so evenly turns out to be experienced very differently by each child.

But… hang on: weight? How can the family environment not have an effect on how much a child weighs? Surely that’s about how much you eat, right? And isn’t that about what a parent chooses to put on the table: a KFC family bucket of fried chicken, or salad? Genes are important, but doesn’t the family’s eating habits create shared tastes?

If you’re fatter than your friends, it’s probably genetic

‘Yes, weight is really interesting, isn’t it?’ Plomin says. ‘Because all the theories as to what causes obesity are about family. People keep going earlier and earlier into a child’s life to look for causes, but they need to keep going right back further, into their genes!’

Here’s where it’s important to remember that Plomin is not studying individuals, but variation in populations. You are of course free to starve your own individual fat kid. His genes can’t smuggle cakes into the cellar. But in the population as a whole, in the absence of a psychopathic parent or a famine, most of the reason why people come in different sizes is because of their different genes.

The most contentious trait of course isn’t weight but IQ. ‘Well,’ says Plomin, ‘familial resemblance for IQ is just due to genetics.’

So if you’re adopted, your IQ will stay resolutely correlated with your birth parents?

‘Yes. And the Texas adoption study is one of the best on this,’ says Plomin, ‘because it’s longitudinal — it tracks kids as they grow up. At one time everybody thought that adoptive parents correlated 0.2 to 0.3 with the IQ of their adopted children.’ (A correlation of 1 means that children are exactly like parents, and zero means they are no more alike than a random person.) ‘But nobody noticed that these were just young children!’ says Plomin. ‘The Texas longitudinal study found that by 18, the correlation was zero.’

‘Tiger – mothering’ won’t make much difference in the end

It’s another counterintuitive mind-melt. The environment, all that maths coaching and tiger-mothering, can maybe have an effect on a kid’s IQ when he’s young — bump him up a few notches. But as he gets older, his IQ will become ever more closely correlated with that of his blood relatives.

Genes really have more effect the older you get? Plomin’s face is lit up with interest. ‘It’s such an amazing story, isn’t it? That the heritability of IQ goes up lineally across the lifespan. From 30 per cent to 40, 50, 60 — some people even say it becomes 80 per cent heritable.’

(Now remember, the 80 per cent isn’t about any individual’s intelligence — the question Plomin is asking is: how much of the reason that we’re all different is genetic? That’s what 80 per cent is an answer to.)

‘Why does it go up? We don’t know, but it’s probable that little early genetic differences become bigger and bigger as you go through life creating environments correlated with your genotype.’ I must look baffled. ‘The simplest way of saying this is that bright kids read more, they hang out with kids who read more.’

Robert Plomin himself is a good example. The young Plomin grew up poor in inner-city Chigaco, to a family where no one went to university. ‘Because there were no books in our house, I used to go to the public library and get lots out,’ he says. See? His bright little genes seeking out an environment they liked. Then: ‘A real formative experience for me was a book on Darwin’s Beagle trip. I brought it to my Catholic school to show them, and I was kicked out!’ Plomin shakes his head. ‘I mean it was a mortal sin, go straight to Hell! But then I realised it was so obviously true and they were stonewalling, so it made me wonder what else they had wrong.’

It’s a great argument for public libraries — young Plomins need an environment in which to forage for facts. But the other lesson is just as important: Plomin’s classmates shared his environment, but not his questing genes; you can’t just put a kid with a low IQ in a library and expect him to become a genius.

‘There’s this slightly misleading fact,’ says Plomin, ‘that kids’ cognitive abilities is related to the number of books in the house. And it’s true that kids who grow up in houses with books are smarter. But that’s not why they’re smarter!

‘Sometimes, if you talk to teachers they behave as if it’s books themselves that cause the cognitive development of kids. They say: “See? Books don’t have DNA!” But they don’t consider that the fact that there are books in the house is because the parents are smart and like to read! Oh, it makes me feel as if I’m in Alice in Wonderland!’

But I can see the teachers’ point. Wouldn’t it just be too depressing for them to accept that there’s not much they can do to up a kid’s intelligence? ‘We’re talking about IQ, but remember it’s not just aptitude that’s important in a child,’ says Plomin. ‘It’s what I call appetite, just for the alliteration. I mean, conscientiousness, which means things like grit and sticking to it.’

But isn’t that genetic too?

‘So, there’s a genetic component to everything, but it’s a lot less than IQ.’

GCSE results are in the genes too!

Certainly Professor P’s enquiries into GSCEs should be of interest to everyone in this country, because he has no political axe to grind. He’s looked at the GCSE results of over 10,000 twins in the Ted study and will soon be publishing his data.

And there are several striking results. First, GSCE and IQ only correlate 0.5. Which means GCSEs aren’t a great measure of what we would normally call academic intelligence.

Secondly, GSCE results turn out to be strikingly heritable — 60 per cent, when at that age, 16, IQ is only 40 per cent heritable. So the reason why children’s GCSE results vary is more to do with their genes than their environment. Blimey. This is utterly at odds with the conventional wisdom. Most supporters of GSCEs imagine that an equal education (teaching the same curriculum to every child) will iron out inherited advantages; in fact, it only makes them more significant. (For those who care, the results for Michael Gove’s phonics tests are even starker: performance is about 70 per cent -heritable.)

Crucially, I suppose, what educationalists of a leftish bent must consider is this: if IQ is measurable (it is) and highly heritable (that, too), then the diversity we see now in exam results isn’t going to melt away. In fact, in the best school, with excellent teachers and rigorous exams, a normal, randomly selected bunch of kids will see a greater spread of results, reflecting their inherited abilities. The little Plomins, rich and poor, will pull away. The other kids’ results will get better too, but the gap will grow.

It’s no surprise really, to find out towards the end of our conversation that Plomin is not just at the cutting edge of behavioural genetics, but also at the heart of molecular genetics as well. Remember that Chinese programme I mentioned? It turns out that the young Zhao Bowen, in his quest to discover the genes for intelligence, is in fact using samples that Plomin collected — data from some of the brightest people in America. And though pinning down the actual genes for intelligence has proved tricky, Plomin (as ever) is optimistic: ‘I think it’s going to happen, I hope this is going to happen! I hope we do find the genes.’

No reason why not: DNA sequencing becomes cheaper all the time, meaning thousands of people can be sequenced, and the first results are coming in.

Babies may soon have their genes read

In fact, it will become so cheap that, as Plomin says, ‘Newborns may well have their DNA sequenced as a matter of course.’

I pale. The anxiety returns: but doesn’t that mean a segregated world, children with low IQs condemned from birth to clean the loos?

‘Oh, I go to an education meeting and this is all I get,’ Plomin says, showing the first sign of mild exasperation. ‘They think it’s just terrible because we’re going to start labelling kids from really young. But kids label each other already — they know who’s sporty, who’s bright. And if we can read a kid’s genome, we can predict and prevent disease. If we can read their DNA, we can tailor the teaching to help a kid with learning difficulties. Surely it’s worse,’ he says, ‘to just sit in a classroom and sink, unable to read because no one has identified that you might have trouble? At least consider that it’s not an open-and-shut case.’

I do, and it’s not, and what convinced me in the end was to think about the awful harm done in the past by not knowing that certain traits or diseases have a genetic cause. ‘There was a time,’ says Plomin, ‘when people thought bad parenting caused autism and schizophrenia. Those mums not only had to deal with the children but with the world thinking it was their fault.’

And consider ADD — attention deficit disorder — still routinely supposed to be a product of bad parenting or letting kids exist on fizzy pop. Not so, says Plomin: it’s highly heritable — and I feel a wash of shame for the way I’ve judged parents in the past.

Before we leave, Plomin admits it’s not just teachers who don’t like to think about how heritable IQ is. Many of his clever friends, ‘post-doc types’, left having kids too late and so adopted. ‘They’re in this field, in genetics — and will they take genetics into account? They won’t,’ says Plomin. ‘They know how heritable certain traits are, but for their own kid, they think: I can make him just like me! A little TLC can do anything!’

I think Professor Robert Plomin is trying to sympathise, to show he understands it’s not just dolts who find genetics hard to stomach. But it shows me something else as well: that the maternal will is indomitable. No one’s going to love a child, adopted or otherwise, less because its genome has been sequenced, read and found wanting; no one thinks IQ is a measure of worth. So perhaps there’s less to fear than we think.

GCSEs are more nature than nurture

An abstract of Plomin et al’s forthcoming paper

We have previously shown that individual differences in educational achievement are highly heritable in the early and middle school years in the UK. The objective of the present study was to investigate whether similarly high heritability is found at the end of compulsory education (age 16) for the UK-wide examination, called the General Certificate of Secondary Education(GCSE). In a representative twin sample of 11,117 16-year-olds, heritability was substantial for GCSE performance for compulsory core subjects (58%) as well as for each of them individually: English (52%), Mathematics (55%) and Science (58%). In contrast, the overall effects of shared environment, which includes all family and school influences shared by members of twin pairs growing up in the same family and attending the same school, accounts for about 36% of the variance of mean GCSE scores. The significance of these findings is that individual differences in educational achievement at the end of compulsory education are not primarily an index of the quality of teachers or schools: much more of the variance of GCSE scores can be attributed to genetics than to school or family environment. We suggest a model of education that recognises the important role of genetics. Rather than a passive model of schooling as instruction (instruere, ‘to build in’), we propose an active model of education (educare, ‘to bring out’) in which children create their own educational experiences in part on the basis of their genetic propensities, which supports the trend towards personalised learning.

Mary Wakefield is deputy editor of The Spectator.

Tags: Dna, genes, genetics, IQ, Nature, nurture, Professor Robert Plomin, Zhao Bowen