How much are our lives really dictated by our DNA? Photo: Shutterstock

Does DNA really define destiny?

Robert Plomin's Blueprint argues—correctly—that genes have a profound effect on human traits from intelligence to mental health. But what happens in our lives matters, too
October 15, 2018

Godwin’s law dictates that all online arguments, if they run for long enough, will end up comparing someone to Hitler. But the Nazis are apt to turn up sooner rather than later in arguments about genetics and human behaviour. If the left too often flinches at what the science says, invoking the spectre of eugenics, the hard-right latches on eagerly hoping to confirm its prejudices about race and inequality. Robert Plomin transcends this divide.

While he insists that pretty much all of our behaviours are governed to some degree by genetics, his politics are on the liberal left. He wants research to inform progress towards a fairer society. Our prospects for health, wealth and happiness, he argues, are substantially influenced by the shake of the dice when sperm meets egg. But, he adds, “genetic wealth is its own reward.” We should, says Plomin, challenge a value system that confers extra rewards on those who got lucky in the genetic lottery.

What exactly do genes imply about our behaviour and abilities? Plomin shows persuasively that the genes we inherit affect, sometimes profoundly, our personality, temperament, physical and mental health and, thereby, our life outcomes. But the metaphor invoked in his title, while common enough, is deeply misleading. In an engineer’s blueprint, individual elements map directly, transparently and predictively on to real-world outcomes. But genes don’t do any such thing. And although Plomin tries to dispel accusations of biological determinism by repeating the slogan of today’s geneticists that “genes are not destiny,” I suspect many readers of Blueprint will be left wondering why not.

Plomin, an American psychologist now working at King’s College London, has long been at the forefront of efforts to understand our genes. He has seen his research denounced as irresponsible and even quasi-fascistic—not to mention scientifically mistaken. He has seen the field suffer from false claims and a lack of hard evidence; but he has also seen it transformed by the sudden availability of genomic data from large numbers of individuals. This data glut is due to the dramatic drop in the cost and timescale of decoding genomes in the wake of the Human Genome Project.

“I have been waiting 30 years to write Blueprint,” Plomin says. “My goal is to tell the truth as I see it, without pulling punches for the sake of perceived political correctness.” Plomin believes that naysayers should now accept that genes influence not only our health, height, appearance and hair colour but pretty much every behavioural trait we can measure.

While some of the statistical tools and their interpretation remain under discussion, he is broadly right to say that behavioural genetics has established that link. To deny these facts leaves the door open to abuse by those with dangerous political agendas, as well as to overlook a biomedical resource of immense potential for health, social policy and our understanding of human nature.

As far as political sensitivities go, modern behavioural genetics shows why “eugenic” solutions to intellectual disability or assertions of “innate” racial differences that justify hierarchies or stereotypes are flawed from a scientific point of view, as well as an ethical one. One of the key messages of Blueprint is that traits such as intelligence or mental health—vulnerability to schizophrenia or autism, say—are not determined by a few genes, but influenced by tens, hundreds or even thousands of them. In general, the relationships are neither linear nor confined to single traits; so neat divisions between populations seem implausible, and any simple winnowing of “bad” mutations impossible.

Thus the popular notion that there are “genes for” some complex trait such as height or sexual orientation is plain wrong. Some researchers are now even talking about “omnigenetic” traits (including height), affected by more or less the whole genome made up of some 23,000 genes. In one especially valuable discussion, Plomin shows that many common mental illnesses and disabilities are not all-or-nothing “defects” but extremes on a spectrum (hence the term) that includes us all.

Plomin says the discovery that most traits are “polygenic”—influenced by many genes that have individually near-negligible effects—was “shocking” to those in the field. This is an inadvertent admission that the “genes for” trope now so lamented by experts was created not by the media but by scientists who spun them this tale. Yet it was already evident by the 1990s that many genes, which operate at a very basic level in governing the biochemistry and growth of our cells and tissues, are multitaskers. The time it took for scientists to shift their views shows how even empirical disciplines can develop collective myopia.

Today’s evidence shows that almost any human propensity is influenced by (many) genes, although the process is more complicated than most media reports acknowledge. Plomin recounts his involvement in a study in the 1980s reporting significant correlations between how much children watched television and their genes (as assessed by adoptive and non-adoptive siblings). How could such a genetic trait have possibly emerged from natural selection over just the few generations with access to television?

Of course, it didn’t—and Plomin and his fellow researchers had never suggested that. Newspapers couldn’t resist headlines about a “television gene,” but the real point was that our inclination to watch television—as well as what we choose to watch—depends on many general aspects of behaviour: attention span, imaginativeness, visual perception and so on. These things have long been subject to selection.

Looked at this way, “it is difficult to point to any psychological experiences completely devoid of possible genetic influence,” Plomin says. To suppose that television-watching is a trait isolated from any other behavioural characteristic is foolish, and yet that is what many sceptics, some of them eminent scientists, implied when they ridiculed Plomin’s original claim. There will be genetic correlations with divorce, sexual orientation, criminality and so on: all are real, but also ripe for misunderstanding and silly reporting.

Plomin also explains that what we take to be environmental influences can also have a strong genetic component. A child’s reading ability will be influenced by cognitive factors under genetic control, but also by whether their parents read to them. Yet a parent’s readiness to read to a child will itself depend on genetic traits, which the child may inherit.

One of the benefits of genetic studies of behaviour is, paradoxically, that it might be possible to strip out such seemingly environmental influences with a “hidden” genetic component so as to isolate genuine environmental influences. Then perhaps we can start to work out how to change the environment for the unluckiest in society. That should make for more effective social policy.


"Genes will out"?


Plomin has tried hard to do justice to these subtle and sensitive issues, but unfortunately some of his lexical formulas undermine his efforts. Take the vexed issue of human intelligence. He warns us that using polygenic “scores”—aggregates of the effects of many genes—to make predictions means placing people in categories with broad, overlapping probability distributions.

You could have a high polygenic score for educational attainment and yet fall in the trailing edge of the high-score bell curve, putting your actual outcome below someone else at the top end of the bell curve that describes those with low polygenic scores. But this technical caveat is undermined by what Plomin eye-catchingly calls “predicting school achievement” from a child’s DNA. That phrase suggests you can foretell the exact educational outcome from birth, which is simply not so.

Besides the extent to which our genes are active and the results they produce will be modified by environmental factors like diet, as well as by the random contingencies of development before and after birth. Genes guide the way our brains wire themselves, but they cannot wholly determine it: the complexity of the process means that small random effects during development can have significant consequences. As a result, aspects of our personalities and traits can be innate (“hard-wired”) without being specified by (and thus predictable from) our genes. As neuroscientist Kevin Mitchell has pointed out, this means that “any given genotype encodes a range of potential outcomes but only one—a completely unique individual—will actually be realised.”

Most confusing of all is Plomin’s mantra that some environmental influence (parenting, say, or education or a specific life experience) “matters but it doesn’t make a difference.” How can these things matter if they don’t make a difference?

What Plomin means by “difference” is not what you might think: it’s the difference between individuals, not to individuals. If you place a range of people in a given situation—a particular family, school or diet—they will have different outcomes. Some will achieve better in exams, or gain more weight. Many of these differences—and the only part of them that we can systematically understand—are due to differences in the individuals’ genes.

This is certainly important. It shows, for example, that obesity has a strong genetic basis (metabolic or behavioural) and so we should resist the urge to blame people for being overweight. It shows that expensive schools don’t add much to a child’s innate potential to succeed or fail academically.

The problem is that we don’t all have a shared “given situation”—we each have a distinct life. And our different experiences can have a profound effect on how we inhabit and respond to the world. Plomin suggests that such environmental influences are short-lived—that in the end “genes will out.” But there is no serious doubt that, say, poverty, deprivation and abuse have lifelong effects. To say, as he does, that such cases are rare and extreme is, to put it politely, a parochial perspective, especially for a psychologist.

Even for your average western youngster, individual experience can make a huge difference. A kind deed, a sensitive teacher or, conversely, a nasty encounter or accident can be life-changing. Sure, these things won’t show up among population averages—but to say that they “don’t make a difference” is deeply unhelpful.

It also overlooks much of what actually matters in most people’s lives. Many of us will know people (or be people) who hold down good jobs and perform well academically while labouring daily under the burden of an abusive childhood, the death of a loved one, or other sources of pain and constraint that won’t show up in surveys. In the eyes of those looking at the genetics of traits, though, the notion of “what makes us who we are” is too often defined by what can be readily measured, quantified and placed on a distribution.

The root of the problem is that any attempt to tell us “who we are” based on our genetic profiles is always going to collide with our sense that who we are is defined by the life we have lived. Implicit in our genomes is how, in considerable but incomplete measure, we will respond to the unique set of contingencies that life presents. But scientists should stop insisting that those sequences of chemical code are somehow fundamentally “us.” They are parts of a larger puzzle.

There is a lot of choice here in where you put your emphasis. Because Plomin’s concern is with the inheritable features of behaviour, he naturally focuses on generalities and variability among populations, and not on the experiences of individuals. This lays bare the hazard of popular science written by specialists: what you gain in authority, you lose in the big picture. A book that alleges to tell us “what makes us us” with little reference to (among other things) neuroscience, developmental biology or culture is failing in a way that only years of academic specialisation can make possible.

Frankly I fear for this book. It has an important and valid message, but is sometimes written in a way that almost wilfully invites misunderstanding and reactive opposition. You cannot tell the reader that their genome is their “blueprint that makes us who we are,” which can be used to “tell our genetic fortunes,” while at the same time expecting them to figure out why “genes are not destiny.” You cannot tell them on page 82 that parents “don’t make a difference” and on page 154 that “parents can make a difference.”

This isn’t just sloppy writing and editing; it is irresponsible. For a more complete overview of the biology of human behaviour you’d do better to consult Robert Sapolsky’s encyclopedic Behave, while genes, heredity and behaviour are discussed in a more balanced way in Carl Zimmer’s She Has Her Mother’s Laugh and Kevin Mitchell’s Innate.

Even so Blueprint, to its credit, shows that the argument about whether our genes affect our behaviour is largely over, and makes a strong case for why we need an urgent and open discussion of what that means for society.

Blueprint: How DNA makes us who we are by Robert Plomin is published by Allen Lane, £20