If you’d been adopted at birth, reared by different parents, gone to different schools and had different friends, you’d still be much the same personality you are today, says controversial geneticist Robert Plomin.
Though these were extremely dismaying odds, they were no surprise to the self-described “portly” King’s College London psychologist and behavioural geneticist; he was excited. In keeping with his thesis that genes are exponentially more important than environmental factors in determining what we are like as individuals, he saw his fat-destiny diagnosis as a potentially powerful tool. If parents know early on that, for a particular child, keeping weight off or concentrating on tasks or battling serious anxiety are going to be lifelong challenges, they and the child will be better prepared to fend off those potential problems.
Plomin says it’s just as useful to be forewarned about any positive traits or distinctive tendencies our genes have dealt us, so we don’t waste time and effort working against them.
What did initially dismay him about his polygenic project was that it appeared to overturn a fundamental tenet of the behavioural psychology he had spent his career studying and teaching. His research had found that, although nurture can modify nature, the power balance is strongly tilted toward nature as the prime determinant of who we are.
Naturally, given that so much is invested in the power of nurture, not everyone is buying Plomin’s headline advice from his latest book Blueprint: How DNA makes us who we are – that parenting isn’t nearly as influential as we’d like to think, and that it can’t override genetics.
Research into twins supplies a persuasive thread of the findings Plomin draws on. Separated twins raised in different families will show the same basic traits in relation to body-mass index, irrespective of those of their adoptive families. In other words, their upbringing will not override their genetics, whatever their adoptive family has supplied them with in terms of food intake and activity levels.
Much the same applies to personality traits. “I’ve studied identical twins who have grown up apart, and I find it amazing how they are so similar in things like the way they laugh or talk.”
Though Plomin stresses his controversial thesis has important qualifications and provisos, he is now convinced that even random events, known in behavioural science as “non-shared environment”, are more influential than parents or wider family and friends on what sort of people we turn out to be. That’s why children from the same families are very different, however seemingly identical their shared childhood environment. Think Queen Elizabeth and Princess Margaret, former US president Bill Clinton and his booze- and drug-prone brother Roger, and how, despite there being 10 Peters siblings, there is, irrefutably, only one Winston Raymond Peters, veteran politician.
“Children are not clay to be moulded,” says Plomin. “Parents are much better to work with their children’s traits than trying to change them.”
Plomin’s findings are strongly contested by many others in the behavioural-sciences field, including Richie Poulton, who heads the world-leading University of Otago longitudinal study. Although it’s now widely accepted that physiological traits, such as build, eye colour and athletic ability, are genetically determined, it has been considered unsound to suggest that personality might be in the same category rather than more of a social construct – the product of upbringing and environment. The popular shorthand for the supposed nexus between nature and nurture is that genes load the gun, but the environment pulls the trigger.
Echoes of eugenics
Plomin’s work also, at first glance, seems to head too close for comfort towards behavioural science’s third rail, genetic determinism, made infamous by past eras’ eugenics movements and 1994 book The Bell Curve, which was accused of linking differences between black and white Americans’ IQs to genetics.
Plomin says he has always been braced for critics to join the dots that way – even delaying finalising his study until he worked up his nerve – but says those who see his treatise as a eugenics rehash are approaching it from the wrong direction.
He says patterns are slowly starting to emerge from huge new DNA datasets, showing the summative effects on mental health of thousands of gene variants associated with schizophrenia, autism, depression, anxiety, bipolar disorder and attention hyperactivity disorder. “It’s early days, but the conclusion already is that we are all ‘on the spectrum’, with varying quotients and infinitely different combinations of these genes. That the ‘abnormal is normal’ is one of the profound insights of genomics.
Everything is just a matter of degree.”
Blueprint contends that genes account for about half of the psychological differences between us, from personality to mental abilities. By extension, that leaves about 50% influence accounted for by our environment. But it presents research findings that most of the latter 50% is not attributable to deliberate or planned influences, such as parenting. Rather, it’s made up of unpredictable events that we experience as individuals rather than collectively, as in the context of a family or peer group. And, of the environmental influences we experience that can be moderated, much of the way we respond, he argues, is really an expression of genetics. One’s parents parent the way they do because of their genetic tendencies. Although it’s been a common assumption that high socio-economic-status parents beget high socio-economic-status children, Plomin turns the causals over, saying it’s more likely the parents were successful because of their genetic make-up, and that is what ensures the children succeed, rather than the circumstance of money and privilege.
His argument has been taken as an afront by many of those seeking to address inequality and underprivilege. “Plomin’s core thesis is that genes are by far the most important determinants of who we are and what we become,” says Poulton, an adviser to New Zealand state sector agencies on social policy. “In pushing this line, he appears indifferent to both conflicting scientific evidence and to potential harms that might flow from his interpretation.
“Both the population at large, including parents, and policymakers in particular, invest a lot of time and energy trying to create ‘good’ environments for their communities, in order to promote fulfilling and productive lives. According to Blueprint, however, these efforts are essentially futile because genes trump everything else.
“Today, most scientists agree that it is the interaction between the two – what you inherit from your parents and your life experiences – that determines why people differ and why life turns out well for some and not so well for others.
“Do genes matter? Of course they do. Are genes deterministic? Of course they’re not. Does the environment matter? Of course it does.”
Lightly on the reins
Plomin is the first to concede that his contention that people should relax more and go along with their children’s traits may be confronting, given the long-honed “should and shouldn’t” list experts have heaped on to parents for many decades. But he says it should be liberating. The “should” about reading to children, for instance, need no longer trouble a parent whose child wriggles and fidgets and would rather play with Lego than hear a story. Provided the child is developing oral-language skills, the reading will come.
“You can relax a bit more and let your child be your child.”
He says it doesn’t much matter what school you send your child to beyond a certain point of educational quality, because the level of academic achievement is not down to the school, it’s down to the child. Private schools? Save your money, he says, arguing private schools tend to preselect for children with a particular level of academic achievement, so their scholastic outcomes are largely predetermined. A child who is doing well before attending private school is apt to do just as well at any other school.
As he told the New Scientist and confirmed to the Listener: “If you want your kid to go to a private school because it’s just a nicer place and has lots of sports fields, fine. Some parents admit it’s also because they want them to meet the right sort of people. But I think it’s good to be clear about what it is you’re doing. Don’t do it because you think you’re going to make them achieve more, because they won’t.”
What Plomin is postulating is not a new golden rule, but a general principle. He says there will always be outliers – exceptions that don’t break the general rule. If children are neglected, malnourished, traumatised, abused or starved, their genes won’t get nearly as much of a chance to manifest themselves. Those outliers, he estimates, may comprise about 20% of the population, and no one would contend that these disadvantaged people don’t need compensatory nurture.
He’s certainly not trying to downplay the importance of state and welfare intervention, or the role of schools. He says the quality and safety of schools should be as high as we can possibly afford – for all schools, not just private ones. But we need not blame schools to the extent we often do for the disparities in children’s achievement.
“No specific policy implications necessarily follow from [our] finding that inherited DNA differences are by far the most important source of individual differences in school achievement and that schools make so little difference.
“Regardless of the predispositions of their students, schools should be supportive places for children to spend more than a decade of their lives, places where they can learn basic skills but also learn to enjoy learning.”
Means and variances
Anticipating a stampede of furious wokies, he urges people to remember that his findings are applicable to “averages in a population”. In order to understand the importance of genes, it’s vital to distinguish between means (as in averages or midpoints) and variances. He gives the example of the increase in the average height of northern European men, of more than 15cm, during the past 200 years. That’s clearly down to environment. But the variation in height among the men is down to genetics.
As he told the Guardian, “The causes of average differences aren’t necessarily related to causes of individual differences. So, that’s why you can say heritability can be very high for a trait, but the average differences between groups – ethnic groups, gender – could be entirely environmental; for example, as a result of discrimination. The confusion between means and variances is a fundamental misunderstanding.”
Heritability is frequently misunderstood, he says. “It is not a constant like the speed of light. It is a statistic that describes a particular population at a particular time with that population’s particular mix of genetic and environmental influences.”
He’s also, most emphatically, not saying parenting doesn’t matter or that we shouldn’t strive to improve people’s social outcomes. He says it remains vital that parents give a child a safe, secure, loving and stimulating environment and teach values such as consideration for others and the so-far-undisputed predictor of success in life, self-control. Parents absolutely do need to teach their children not to hit one another, how to be polite and generally coexist well in society, but that’s not the sort of teaching that will ever change their innate personalities.
Poulton says that Plomin’s thesis “immediately begs the question: why bother trying to do anything?
“Interestingly, Plomin himself acknowledges that high levels of disadvantage and adversity can drive susceptibility to environmental inputs, but only at the extremes; that is, outliers. It is indeed a happy coincidence, then, that it is exactly this group of people that governments are most interested in supporting via ‘environmental’ means.
“I would suggest this group comprises roughly 20% of the population who seem to struggle from conception onward. The exact proportion, however, is not nearly as important as the principle. Thus, it still seems that trying to create better environments, and a better world, for people remains a sensible activity.”
Weight and personality
Blueprint cites twin and adoption studies that show children adopted at birth are similar in weight to their birth mother and siblings from whom they have been separated. “There is no correlation between their weight and their adoptive families or siblings. Given that they are being offered the same diet, the same school lunches, the same pocket money, one can only assume that they are genetically driven to eat more or less of it, or to have more or less exercise. In many ways the obesity epidemic is a psychological problem.”
Plomin says the same is true of cognitive abilities, and, though there hasn’t been as much work done to study personality traits, it has generally been found that separated twins display each other’s mannerisms rather than their adoptive family’s. “We know that identical twins reared apart are as similar in personality as identical twins reared together.”
Again, Plomin says, we must allow for the proviso of key one-off events. A virus could rewire a person’s brain; an accident or emotional trauma can have a lasting effect. But for most of us, generally, it will be true that genetics have the most effect on what we’re like, along with our individual life experiences.
He says all this helps explain why children in the same families are so often wildly different, despite being 50% the same biologically. “It turns out that your shared environment has a negligible effect. Any resemblance between you and your siblings is down to your shared genes, and that’s where it ends.
Having spent decades studying biological and adopted siblings, he initially baulked at this finding, but he has come to terms with it by distinguishing between the effect of one’s individual experience and one’s shared experience.
“In fact, it is now understood that your upbringing isn’t really shared. Everyone experiences their parents, home and school, and the events that happen in families, through the coloured lens of their genes.”
An example might be the differing outcomes for Bill and Roger Clinton of having a brutal, alcoholic father. Clearly, each son “processed” that influence differently.
Parents do have favourites
“Also, parents do not actually treat all child-ren equally, no matter what they say. They respond differently to different personality types, which, again, is genetic influence calling the shots rather than nurture.
“A smiley, affectionate child invites smiley, affectionate responses. Parents can get into negative feedback spirals with more difficult children.
“And depending on personality, children perceive and react differently to events such as divorce or moving house.
“Just listen to siblings compare memories of their upbringing. It is almost as if they’ve been living in different families, especially when it comes to their perceptions of how they were treated by their parents.
“What this means is that if you had been adopted at birth, reared by different parents, gone to different schools and had different friends, you would be similar to who you are now in personality, mental health and illness, and cognitive abilities and disabilities. More specifically, you would be as similar to this version of yourself as identical twins are to one another … Parents cannot make kids kind, or determined, or neurotic, unless they give them the genes for those traits.”
He is quick to soften the blow for all those conscientious parents with shelves of child- development books.
“Parents matter, of course they do – they just don’t make a difference to your personality, your cognitive abilities and disabilities, your predisposition to become depressed or overweight.
“They can make all the difference to your quality of life by making you feel loved and secure, and caring for you well, creating the conditions for your good genes to shine.
“They can help children discover and develop their talents, and train them to develop self-control and manage behavioural problems.
“Self-control alone is a major factor in later life success.”
Snake oil and tiger mums
Although developmental-help books for parents can have useful tips on dealing with fussy eaters and problem sleepers, they’re “peddling snake oil” in claiming to do much else. “Remember that exceptions don’t break rules. We are talking about population averages. At one tail end of the distribution curve are children who are horribly mistreated, and whose outcomes are drastically affected by their upbringing. Such abuse can activate genes that launch a trajectory to prison or a mental institution. However, it is often noted that their siblings, subject to the same deprivation, go on to live successful and happy lives and be good parents. This is because of their different psychological make-up (genetics) and experience of their childhood.
“And where is the evidence, beyond anecdotes, that children’s success depends on parents being strict and demanding ‘tigers’, or giving their children grit? There is no evidence that these parenting practices make a difference in children’s development after controlling for genetics.
“Some novel influence could have a bigger effect. That could be tiger mums who devote their lives to getting their kids to play the violin. But you can’t assume that tiger mums do make a difference, because the mums who are so concerned about achievement probably have kids who are genetically more likely to be achieving anyway.”
Children make their own environments, regardless of their parents, he says. That is, they select, modify and create environments to suit their genetic propensities. Children who want to do something, such as playing sports or a musical instrument, will badger their parents to make it happen.
“We all move in the direction of our natural interests and abilities, though parents often make the mistake of trying to deflect us.”
A new term has been coined, “the nature of nurture”, which recognises how much of nurture or environment is conditioned by an individual’s genetic drivers.
“Most of what happens to children involves random experiences over which parents have no control, and the effects of these experiences are not long-lasting. These may be chance meetings, a small success or a serious illness, a book or film that fires the imagination.”
But parents will ultimately gain control over their children in one sense, Plomin’s work suggests. Like it or not, you are becoming more like your parents. Heritability increases with age, particularly for intelligence. According to Blueprint, “Genetic influence on cognitive abilities peaks at 80% by age 65.”
You might not do what they say, but you may end up doing what they do, or at least understanding what they understand.
“People may turn probability into prophecy.”
But local scientists say it has its uses. Tony Merriman, a professor of biochemistry and genetics at the University of Otago, respects Plomin’s approach and points out that he is careful to talk about genes influencing, rather than determining traits.
Merriman says genetic comparisons of human populations are a “no-go area” when it comes to intelligence but “very useful for a researcher like me studying diseases such as diabetes, gout and malaria, which some populations are more vulnerable to.”
Hamish Spencer, a professor of zoology at Otago and a eugenics historian, says we mustn’t lose sight of the importance of environments to how people turn out.
“Knowing your genetic make-up can be useful to warn you about your susceptibilities to, for example, breast cancer, but it could just blight your life with worry about things that may never happen and that you can’t do anything about,” Spencer says. “People may turn probability into prophecy.
“We must concentrate on what we can do to create environments and lifestyles that enhance our genetic advantages and minimise any disadvantages.
“We’re not going to be able to edit out the hundreds, if not thousands, of genes that contribute to autism, for example, but we can prevent known triggers for depression or schizophrenia. For example, some people have a predisposition to develop schizophrenia if they smoke cannabis at a young age.
“And a mother-to-be’s poor nutrition can precondition a fetus to develop diabetes and cardiovascular diseases later in life by moderating the function of genes. The fetus is trying to anticipate its ex-utero environment by adapting its physiology and getting it wrong. It seems that even obese fathers can have an influence on their offspring.”
Just as European males have grown taller because of better nutrition and less harsh environmental conditions, environment will continue to share the headlines with genes in making us who we are.
US nutritionist Michael Greger has compiled the latest randomised, controlled trials informing us about nutrition and dieting in his new book How Not to Diet, and environmental factors frequently emerge. He cites a famous Arizona study that compared obesity and diabetes prevalence between two groups of Pima Indians – one in Arizona and the other in neighbouring Mexico. The Arizona Pimas developed some of the highest rates of obesity and diabetes in the world after their traditional plant-based diet and farming lifestyle changed to a high-fat diet and sedentary lifestyle, while those of their Mexican neighbours were unchanged. Comparative studies concluded that even in genetically prone populations, the development of diabetes and obesity was largely determined by environmental considerations.
This article was first published in the February 22, 2020 issue of the New Zealand Listener.