Why it’s time to call time on the ‘nature vs nurture’ debate

Humans

How much of our make-up is predetermined by our genes, and how much by our environment? The truth is that we're asking entirely the wrong question

By Tiffany O'Callaghan

11 December 2019

Twins

IT IS an age-old debate that crops up everywhere from discussions of gender identity to our propensity to conditions such as obesity. How much is hardwired inside, the inescapable product of our genes, and how much is down to external factors?

Trouble is, this nature vs nurture debate is fundamentally wrong-headed. Even before conception, our make-up is influenced by “epigenetic” factors: choices our parents make, chemicals they are exposed to, infections they get. These don’t alter our genetic code, but just how the instructions it contains are carried out – how it is expressed. Environmental factors continue to change how our genes make us tick throughout life.

For developmental psychologist at the University of California, Berkeley, this constant interplay makes even asking how much we are nature and how much nurture meaningless. “People often think about it as if there’s some kind of formula you could use,” she says. “That’s fundamentally misguided.”

In some cases, identical twins grow up to have dramatically different personalities, while in others identical siblings separated at birth turn out to have strikingly similar personalities, mannerisms and more. Even some genetic disorders can be thought of as environmental. Phenylketonuria, for example, inhibits a body’s ability to break down the amino acid phenylalanine, and can cause devastating brain damage. But if the disorder is identified at birth, children can go on to live happy, healthy lives, by taking supplements and adopting a low protein diet. “In one sense, this syndrome is 100 per cent nature, in another it’s 100 per cent nurture,” says Gopnik.

That isn’t to say genes mean nothing. With very large data sets, we do see trends between our DNA and particular characteristics and behaviours: certain genetic profiles give you a higher risk of being obese, for example, or affect your musical ability or even to realise your musical talent.

Behavioural geneticist Robert Plomin of King’s College London is a proponent of this “genome-wide polygenic sequencing” technique. His group’s research has suggested that more than 50 per cent of children’s performance at school is down to genetics, for instance. “Educational achievement is highly heritable,” he says.

Gopnik is more circumspect about such general conclusions. Genetic determinism has been used to justify campaigns of eugenics during some of the darkest chapters of history. That is why Plomin is also clear. “Heritability does not mean immutability, it does not mean innate, it does not mean determinism,” he says. “It’s probabilistic, it increases your risk for something.”

at the Karolinska Institute in Stockholm, Sweden, echoes the point. A particular gene profile represents at most a predisposition, she says. “It’s not a determinant, it’s not a pregnancy test – it would be like telling you that you’re 40 per cent likely to be pregnant.”

Having even bigger data sets will allow us to unpick these complex interplays with more certainty. . The UK government recently proposed plans to sequence every British child’s genome at birth, and .

That’s an ethical and privacy minefield, but with the insights gleaned, we might end up beating both nature and nurture to live healthier, longer lives.

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Topics: Behaviour / Genes

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