The grumpy poet Philip Larkin famously wrote about families: ‘They f*** you up, your mum and dad / They may not mean to, but they do.’ That was in 1971.

Now, nearly half a century on, the very latest science is proving he was right — but not in the way he meant.

Larkin’s bitter-tinged, blame-laying verse was picking up on the popular notion, going back to Sigmund Freud, that it is the things that happen to us, such as our relationships with our parents as we grow up, that make us who we are.

DNA accounts for at least half the variance in people’s psychological traits, much more than any other single factor

Environment is everything; nurture (or lack of it) is the key. But not any more.

Now, one of the country’s top psychologists and behavioural geneticists, Professor Robert Plomin, of King’s College London, offers an emphatic conclusion.

It is drawn from 45 years of research and hundreds of studies. He says the single most important factor in each and every one of us — the very essence of our individuality — is our genetic make-up, our DNA.

The basic building blocks of life that we inherit from our parents are what determine who we are — not how much they loved us, read us books or which school they sent us to.

DNA accounts for at least half the variance in people’s psychological traits, much more than any other single factor. Put simply, ‘nature’ trumps ‘nurture’ every time, and not just marginally, but by a long, long chalk.

Our DNA, fixed and unchangeable, determines whether we have a predisposition not just to physical traits — from how tall we are to how much we weigh — but also to our intelligence and our psychology, from a tendency to depression to having resilience and grit.

Our DNA, fixed and unchangeable, determines whether we have a predisposition not just to physical traits but also to our psychology

Plomin’s revolutionary conclusion — outlined in a challenging and thought-provoking new book, Blueprint: How DNA Makes Us Who We Are — is a game-changer, he claims, with far-reaching implications for psychology and for society.

He turns much conventional thinking on its head, controversially calling into question many basic assumptions, such as the value of formal education to change people’s lives.

It also undermines the parenting advice industry, the basis of all those groaning shelves of manuals telling us the right way to bring up our children and the disasters that will ensue if we get it wrong.

These sell because every parent wants to think they can make a difference to their child, that they can help him or her with reading and arithmetic or teach them how to be kind or conscientious. But, says Plomin, there’s no hard evidence that this is true.

On the contrary, our ability to read, to learn, to empathise and so on are all ruled primarily by our genes.

Being a tiger mum (or dad) and laying down a strict regime of learning won’t be of the slightest use unless those tendencies already exist in the child’s DNA.

The raw material of our natural selves is what overwhelmingly determines what we can — and cannot — achieve, not how we are brought up. And all those parenting books that promise to deliver developmental outcomes for children are, he maintains, merely ‘peddling snake oil’.

If Plomin is right — and he offers an impressive array of research over many years — then dear old Philip Larkin was a grumpy old man not because of his upbringing, but because that tendency was in the genetic blueprint he was born with. The good news, of course, is that his huge talent came from the same source.

Chicago-born Plomin’s startling conclusions come from two of his long-term studies. Over the course of 40 years, he tracked 250 adopted children in Colorado along with the birth parents who gave them their genes, and the adoptive parents who raised them. After moving to London in 1994, he launched a 20-year study of more than 12,000 pairs of twins.

From these studies, it was possible to unravel the relative importance of genes as opposed to environment when it came to their development.

Being a tiger mum (or dad) and laying down a strict regime of learning won’t be of the slightest use unless those tendencies already exist in the child’s DNA

Millions of pieces of data were amassed from the parents, teachers and the children themselves, about psychological traits such as hyperactivity and inattention, talents such as school achievement and the ability to learn languages, and physical characteristics, such as the propensity to put on weight and become obese.

From all this, he found overwhelming evidence that adopted children are similar to their birth parents, not the parents who raised them. Identical twins (ie, from a single egg and therefore with the same DNA) develop much more similarly to each other as compared with non-identical twins (from separate eggs and with different DNA).

The conclusion was clear — DNA makes us who we are. In the long term, the environment you grow up in has little impact on the way you turn out.

Even stressful life events such as relationship break-ups, financial difficulties and illness don’t have the impact that people generally assume.

The conclusion was clear — DNA makes us who we are. In the long term, the environment you grow up in has little impact on the way you turn out

In fact, what really matters in such situations is our genes, because it is our genes that determine how well or badly an individual deals with such setbacks. And whether we’re resilient to life’s catastrophes or cave in is determined by our DNA, too.

Take divorce. Even though the children in a family are all affected, how each individual deals with it often differs. It is often harder on one sibling than the other(s) — and that difference is because of their different DNA.

In fact, Plomin argues, there are genetic influences in virtually everything we do. Those differences determine how we perceive and interpret the world we grow up in, and how we modify our behaviour accordingly.

In school, genetic differences in children’s aptitudes and interests, inherited from their parents, affect the extent to which they take advantage of educational opportunities. Similarly, genetic differences in our vulnerability to depression affect the extent to which we interpret experiences we undergo positively or negatively.

In school, genetic differences in children’s aptitudes and interests, inherited from their parents, affect the extent to which they take advantage of educational opportunities

The blueprint of our DNA even affects seemingly unrelated events such as road accidents. Car crashes are often caused by reckless driving, driving too fast, taking chances, or driving under the influence of alcohol and other drugs. Genetic differences in personality can increase the likelihood of accidents happening.

As his research developed over the years, Plomin was taken by surprise by the all-pervasiveness of genetic influences he discovered in almost every aspect of human behaviour — even down to being a nice person or not.

Altruism, caring and kindness are components of what personality researchers call ‘agreeableness’, and for years it seemed logical to him that these traits had to be the result of the environment we live in and the influence of those around us.

But his research showed this was not the case. Being nice is also something in our DNA. The same goes for grit and determination. Nurture and example do not teach some children to be tougher than others, their genes do.

All this leads Plomin to a conclusion that is hard to take: the family, he tells us, far from being the monolithic determinant of who we are, the bedrock from which we learn and grow, actually makes little difference to our personalities and the way we turn out.

Why siblings don't inherit the same DNA Siblings, other than identical twins, are only 50 per cent similar genetically, which means that they are also 50 per cent different. The basic reason is that our DNA comes in pairs, called chromosomes. For each of the 23 pairs of chromosomes, we inherit one from our mother, the other from our father. So siblings have a 50-50 chance of inheriting the same chromosome from their mother or their father. However, the chances that siblings inherit exactly the same chromosomes from their mother and father for all 23 pairs is vanishingly small. Advertisement

There are exceptions.

Abuse, for example, can make huge differences to individuals, but because these instances are comparatively rare they do not alter the general finding that overall it is DNA that rules the roost.

This, too, explains why siblings are often so different in personality and temperament from each other even though they grow up side by side — something that often has parents shaking their heads in frustration. ‘Why can’t you be hard-working like your sister?!’

For example, Boris Johnson, is chaotic and boisterous, a flamboyant extrovert — the opposite of his rather more restrained and quiet little brother, government minister Jo Johnson, though they were brought up in the same household went to the same school and the same college at the same university. This indicates that nature, not nurture, makes the difference

So what, then, is the role of parents if they can’t make much of a difference in their children’s development beyond the genes they provide at conception?

This is, Plomin concedes, a ‘shocking and profound’ issue and many parents will see the suggestion that all their efforts are useless as untrue, insulting even.

After all, they devote their time and love to encouraging their children to learn, to play sport or a musical instrument, to manoeuvre their way through life. Surely that’s not wasted? The answer is that at one level it is, because children are not blobs of clay that can be moulded to their parents’ wishes.

All the parental input in the world can’t make a tone-deaf child musical. Similarly, children who are wired by their DNA to be sporty or artistic will badger their parents to let them pursue their interests.

Parents, he insists, need to realise ‘that they are not carpenters building a child from scratch. They are not even much of a gardener, if that means nurturing and pruning a plant to achieve a certain result.

Parents, Plomin insists, need to realise ‘that they are not carpenters building a child from scratch

‘We can try to force our dreams on them, that they become, for example, a world-class pianist or a star athlete. But we are unlikely to be successful unless we go with the genetic grain.’

That, though, still leaves an important role for parents — to find out what their children do well and provide the opportunities for them to do it. What we should not do is try to change them into something they are not.

‘Each child is their own person genetically. We need to recognise and respect their genetic differences. If we go against the grain, we run the risk of damaging our relationship with them.’

This has positives for parents, too, relieving them of the anxiety and guilt piled on them in how-to parenting manuals.

‘These can scare us into thinking that one wrong move can ruin a child for ever.’

Plomin hopes his findings will ‘free parents from the illusion that a child’s future success depends on how hard they push them’.

And the same, he insists, goes for schools — a theory that challenges the principles on which our education system is based.

Schools, he says, matter in that they teach basic skills such as literacy and numeracy. They also dispense fundamental information about history, science, maths and culture. But choice of school makes very little difference to a child’s achievement.

‘Genetics is by far the major source of individual differences in school achievement.’

This suggests we should ignore all those league tables of exam results and Ofsted ratings. Plomin argues that differences in schools have very little effect on outcome.

This conclusion will inevitably trigger a great debate about the comparative merits of selective grammar schools and non-selective comprehensives.

On average, GCSE scores for children in selective schools are a grade higher than in non-selective schools, and this difference is usually assumed to be because selective schools provide better schooling. Genetic research, however, shows that if the best pupils are selected according to the abilities they showed at primary school, they’ll inevitably get better GCSE results.

This is because of who they are, not what they’ve learned in the classroom or the way they’ve been taught.

Those higher grades are simply a self-fulfilling prophecy.

Once you discount genetic factors, generally speaking there is little difference between school achievement at age 11 and GCSE results at 16.

The ‘value added’ — a measure used by many top schools — turns out to be very small.

The influence of our DNA is not completely confined to our early years when we’re growing up

The same principle applies in the debate about private and state schools. If, as Plomin claims, schools have little effect on individual differences in achievement, then those 7 per cent of parents who pay huge sums to send their children to private schools in the belief that it will give them an advantage may well be wasting their cash.

Plomin writes: ‘Expensive schooling cannot survive a cost–benefit analysis on the basis of school achievement itself.’

If your genes fit, you’ll do well; and, if they don’t, no amount of cash can change the abilities you’re born with.

What all schools should aspire to, he maintains, is to be places where children can learn to enjoy learning for its own sake, rather than frenetically teaching pupils to pass the exams that will improve the school’s standing in league tables.

Not that the influence of our DNA is confined to our early years when we’re growing up.

Indeed, Plomin shows that it gets stronger as we get older. More and more, we revert to type. Yes, other factors impact on us, such as our relationships with partners, children and friends, our jobs and interests. All contribute to give life meaning.

But they don’t fundamentally change who we are psychologically — our personality, our mental health and our cognitive abilities. Good and bad things happen to us, but eventually we rebound to our genetic trajectory. Many people, Plomin acknowledges, will be aghast at his ‘bold conclusion’.

It seems to make us automatons, devoid of free will, victims of our DNA. And, indeed, this level of determinism could be an excuse for apathy, a refusal to take responsibility for oneself: ‘Not my fault, guv, it’s my genes!’

However, he categorically rejects this notion.

Just because you have a genetic propensity to put on weight, for example, doesn’t mean that you shouldn’t try to lose some pounds.

You may have the devil inside you, but you can keep it at bay.

Plomin found that his own genetic mapping threw up a surprise.

‘I am genetically predisposed to put on the pounds and find it hard to lose them.

‘It means I can’t let my guard down and, in those weak moments, give in to those siren snacks in the cupboard whispering to me.’

Once you discount genetic factors, generally speaking Plomin said there is little difference between school achievement at age 11 and GCSE results at 16

The same applies to anyone with a genetic propensity to depression, learning disabilities or alcohol abuse.

‘Genes are not destiny,’ says Plomin. You don’t have to succumb.

Controversially, he can see a time soon when DNA information will routinely be on people’s medical records, though he acknowledges that this poses serious dilemmas.

Do you want to know if your child has a high genetic risk for schizophrenia when there’s nothing you can do to stop it? On the other hand, he says, many psychological disorders, such as alcohol dependence and anorexia, are difficult to cure.

Early warning is good, and preventing problems before they occur is much more cost effective, economically as well as psychologically.

It’s also good, he argues, that we can know our limits — those things that our DNA just won’t let happen, however hard we try.

Plomin quotes with approval the observation of American comedian W.C. Fields: ‘If at first you don’t succeed, try, try again. Then quit. There’s no use being a damn fool about it.’

Because, ultimately, it’s more sensible to go with the genetic flow rather than trying to swim upstream.

Equally, our DNA can tell us where our inborn talents lie, so that we do not waste them.

There was a telling example this week when former England captain Alastair Cook retired from Test cricket. In tribute, commentator Mike Atherton declared: ‘He made himself the best player he could be; he extracted every last ounce of his talent.’

Plomin’s radical new world may force us to bow to our genetic limits but, on the plus side, it will encourage us, like Alastair Cook, to do the best we can with the talents we’ve been given.

Blueprint: How DNA Makes Us Who We Are by Robert Plomin will be published by Allen Lane on October 4 at £20. © Robert Plomin 2018. To order a copy for £17 (15 per cent discount), visit www.mailshop.co.uk/books or call 0844 571 0640, p&p is free on orders over £15. Offer valid until September 22, 2018.