On Monday in London’s Emmanuel Centre a debate took place that pitted two Quillette contributors—Robert Plomin and Stuart Ritchie—against two “experts” on child psychology—Susan Pawlby and Ann Pleshette Murphy. The motion was “Parenting doesn’t matter (or not as much as you think)” and we knew from the outset where people stood thanks to the format adopted by Intelligence Squared, the company that organized the debate. The ushers asked people to vote for or against the motion on their way in and then again at the end, the idea being that the “winners” would be the side that persuaded the most people to change their minds rather than the side that got the most votes. Which was just as well for Plomin and Ritchie since only 17 percent agreed with them at the beginning of the evening, with 66 percent against and 17 percent saying “Don’t Know.” Would they be able to level that up a bit over the course of the next 90 minutes?

Plomin, a professor of behavioral genetics at King’s College London, went first, summarizing the evidence from twin and adoption studies—his area of expertise, having designed and overseen many of those studies himself. Using slides, which is unusual in a public debate, he drew the audience’s attention to two key findings that have emerged from this research—that siblings raised together are as different from each other as siblings raised apart, and identical twins raised separately are as similar to each other as identical twins brought up in the same home. In short, genetic differences between people influence how different they are from one another, but parenting seems to have little effect.

Plomin made it clear he wasn’t claiming genetic differences accounted for all the differences in how children turn out. He estimated that genes explain about half the variance when it comes to the Big Five personality traits, with the environment accounting for the other half. However, that doesn’t mean nurture is as important as nature. The salient environmental inputs are not those things we normally think of as “nurture,” such as parents and schools. Rather, what matters, according to Plomin, are random, serendipitous events—what he refers to as the “non-shared” environment and which are, by definition, non-systematic.

Quoting from Blueprint: How DNA Makes Us Who We Are, his recently-published book, Plomin said: “Parenting matters, but it doesn’t make a difference.” He acknowledged that this left him feeling slightly ambivalent about the motion—”Parenting doesn’t matter”—and was at pains to make clear that he wasn’t providing deadbeat dads with a license to goof off. Parenting matters in the sense that how parents behave affects their children’s well-being in the moment, if not over the course of their lifetimes, and we have a duty to look after our children and make sure they’re happy, at least while they’re under our care. It also matters in the sense that it affects what will be among the most important relationships of our lives. Finally, he acknowledged that parents have an important role to play in helping children discover and cultivate those talents that they’ve been genetically endowed with.

But parenting doesn’t affect how children will turn out when it comes to key psychological traits like conscientiousness—the ones correlated with important life outcomes, such as educational attainment and socio-economic status. If we think helicopter parenting will boost our children’s IQ or increase their chances of getting into Harvard, we’re kidding ourselves. So parenting matters, but not in the way that overanxious, middle-class parents imagine, according to Plomin. However, he did add one important caveat: Terrible parents—those guilty of extreme neglect or abuse—can have a long term, negative impact on their children.

Next up was Susan Pawlby, a development psychologist with a background in research as well as clinical practice. She began by citing a number of studies showing that the experiences of pregnant women can have an effect on their children’s personalities. For instance, high levels of stress in expectant mothers is correlated with higher levels of cortisol in their blood, as well as their amniotic fluid. That, in turn, she said, can affect a prenatal baby’s brain and lead to problems later on, like developmental delay. Another example she gave was the Dutch famine of 1944–45, which had created a natural experiment, enabling researchers to measure the effects of maternal undernutrition on the life course of the offspring who’d experienced the famine in utero. The IQ of this cohort, many of whom are still alive, hasn’t been affected, but they are more prone to obesity, schizophrenia and anti-social behavior.

Pawlby also brought up epigenetics and claimed that some environmental inputs affect gene expression, such as breast feeding. She didn’t spell out how this undermined Plomin’s argument, exactly, but perhaps what she meant was that some of the findings from twin and adoption studies might be confounded by epigenetics. For instance, it could be that some of the genetic variance that Plomin and others have linked to phenotypic variance could have been influenced by environmental differences that triggered epigenetic effects.

Pawlby closed by entreating everyone in the audience to ask themselves one question: “Have your parents made a difference to who you are?” If the answer was “yes,” you had to vote against the motion.

The next speaker was Stuart Ritchie, a lecturer in the Social Genetic and Developmental Psychiatry Centre at King’s College London, and the author of Intelligence: All That Matters. He queried whether the research studies cited by Pawlby constituted evidence that parenting matters since they all concerned environmental effects on prenatal babies. Does the behavior of pregnant women come under the heading of “parenting”? It would be particularly odd to describe the undernutrition of expectant mothers during the Dutch famine as a form of parenting.

However, he allowed that there was plenty of research that appeared to show parenting did have an impact on important life outcomes and, as an example, cited a recent paper that had been covered in the Guardian under the following headline: “Growing up in a house full of books is major boost to literacy and numeracy, study finds.” Looking at a sample of more than 160,000 adults from 31 different countries, the authors of that study found that subjects who’d grown up in homes containing a large number of books performed better in literacy and numeracy tests than those brought up in homes with almost no books.

Unfortunately, Ritchie explained, this research tells us very little about the underlying reason for this correlation because the authors hadn’t made any attempt to control for genetic similarities between the children in the study and their parents, which could be confounding the results. After all, it’s probable that parents who have a large number of books in their home have above average levels of literacy and numeracy themselves, so it’s not surprising if their children turn out to score well in literacy and numeracy tests too, given that those traits are at least 50 percent heritable. He had looked at the paper and typed in Ctrl + T “genetics” but there was no mention of the word. That is a flaw in nearly all the research purporting to show a link between various outcomes and a person’s childhood home environment, he said, and then rattled off a list of parenting fads that some of these studies have given rise to, from “Baby Mozart” to “orgasmic childbirth.” (I made the same point in the Spectator recently about a study claiming to show that helicopter parenting had a negative effect on children’s ability to self-regulate.)

Ritchie also gave short shrift to epigenetics. The research showing large epigenetic effects in humans, particularly that relating to transgenerational inheritance, is pretty sketchy and more work needs to be done before any conclusions can be drawn. (There’s a Twitter account called @EpigeneticsBs that monitors some of the more outlandish claims made on behalf of epigenetics.)

In general, he said, the behavioral genetics studies showing that parenting effects are small are based on large samples, have been replicated numerous times and are being corroborated by work being done in molecular genetics. The parenting studies in developmental psychology, by contrast, are, for the most part, based on small samples, confounded by genetics and have proved hard to replicate—although he did say there are some exceptions to this rule, and singled out this study showing that early interventions can have a positive effect on conduct disorder. I daresay Ritchie will expand on this survey of the literature in in his forthcoming book about the replication crisis in psychology.

It was left to Ann Pleshette Murphy, the former parenting correspondent of ‘Good Morning America,’ to fight back. She had prepared a case against what she called Plomin’s “genetic determinism,” so began by expressing her disappointment that he’d taken up a more moderate position on this occasion, allowing that environmental inputs could have some effect. The man before us tonight, she said, was “a wolf in sheep’s clothing.” She then delivered the speech she’d written in advance, focusing on Plomin’s use of the word “blueprint” in his book title. According to her, that implies our genes provide a rigid schematic that dictates how we turn out, when they’re only responsible for half the variance in individual differences. “DNA may provide a blueprint, but it’s love that builds the house,” she said.

Listening to Murphy, I didn’t think her criticism of Plomin was fair. While the title of his book is a bit misleading, he makes it clear throughout that he’s not a genetic determinist, a point I stressed in my last article for Quillette. He didn’t make any concessions to environmentalists in his speech that he hadn’t made in Blueprint. His hypothesis is not that we are entirely determined by our DNA, but that DNA is the most important systematic force on how we turn out because the salient environmental inputs are almost entirely non-systematic. Interestingly, this is a point of slight disagreement between Plomin and Ritchie. Ritchie recently published a paper with Elliot Tucker-Drob that analyzed 42 data sets involving over 600,000 participants and concluded that school attendance does boost IQ. According to them, each additional year a child spends in school raises their IQ by between one and five points. Plomin isn’t completely dogmatic about this—he says in Blueprint that the shared environment is responsible for a modest amount of the variance in key psychological traits—but Ritchie certainly seems a bit less hereditarian. Had I been arguing against the motion, I would have brought up Ritchie’s most recent paper and asked him whether the surprisingly large effect size he and Tucker-Drob had discovered for years of education had made him reconsider his dismissal of parenting effects.

One of the weaknesses of Pawlby and Murphy’s case is that they didn’t have a convincing story to tell about why parenting effects don’t show up in twin and adoption studies if, as they were claiming, parents play such a critical role in influencing how children turn out. Murphy actually said, “What we do as parents makes a huge difference,” which begs the question. In fairness, she did take a stab at explaining why siblings brought up together are as dissimilar as those raised separately, saying it was because parents treat each of their children differently. She pointed out that they tend to be much more anxious about their first born, fussing about their exposure to germs and so forth, than they are about their younger siblings.

But that wasn’t very convincing. There isn’t much evidence that birth order has an effect on extraversion, emotional stability, agreeableness, conscientiousness, or imagination (see here), and you’d expect the dissimilarities in how the same parents treat their different children to be smaller than the dissimilarities between the parenting styles of two completely different sets of parents—and if parenting “makes a huge difference” for that discrepancy to show up in adoption studies. But it doesn’t.

The debate was well-chaired by Xand van Tulleken, a doctor and broadcaster who has an identical twin brother named Chris, and, after he’d taken plenty of questions and done his best to sum up, the audience was asked to vote again. As expected, a majority still disagreed with the motion, but Plomin and Ritchie had succeeded in persuading some people to change their minds. The number against the motion declined from 66 percent to 51 percent, while those in favor increased from 17 percent to 29 percent, with 20 percent saying “Don’t Know.” That made Plomin and Ritchie the winners.

Photos courtesy of Tim Bowditch/Intelligence Squared.

Toby Young is an associate editor of Quillette.

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