When it comes to intelligence, do schools and parents make a difference?

Almost twenty years ago I interviewed the behavioural geneticist Robert Plomin for a left wing magazine. Plomin was then relocating from America to Britain to pursue his work aiming to identify the genes for intelligence. A campaign was launched to protest his work, and many of my friends and colleagues poured scorn on the idea that genes could be responsible for anything as complex, and socially constructed, as intelligence. I was less convinced. By the early 21st century there were many dozens of studies involving tens of thousands of twins that clearly demonstrated the possibility of genes influencing intelligence. The logic of those studies was simple and compelling. Identical (monozygotic or MZ) twins share all of their genes while fraternal (dizygotic or DZ) twins share half their genes. All things being equal, therefore, MZ twins should be more similar than DZ twins for any trait where genes cause variability, and that is exactly what the studies demonstrated for intelligence.

Wait what about my childhood?

Of course, most of us were raised in families alongside any twins or fraternal brothers and sisters. Under those circumstances there is also a shared environment as well as shared genes. Height, for example, is genetically controlled to an extent, but it is also controlled by what and how much we eat. Families who feed their children identically will make the variability in height due to consumption identical, leaving any observed variability in height as due to genetics only. In contrast, families who compensate for the slow growth of one child by feeding them more will introduce an environmental factor that will reduce variability in height. Similarly, families that send all their children to the same school and provide the same home tuition will tend to produce children that vary in intelligence only due to genetics. In contrast, families who compensate a less bright child with increased tuition will tend to produce children that will vary less in intelligence.

The environment that families provide is also dependent on historical, national and social conditions. The modern nation state typically mandates that children remain in full time education until they reach a certain age, usually 16 or 17. Consequently everyone will reach a general basic level of intelligence associated with literacy, numeracy and so forth. Almost all citizens will also receive a basic historical and cultural inheritance through their education system and shared national institutions. Better off families can also spend more time with their children and provide additional tuition in formal or informal ways. To the extent that these conditions are shared across nations or strata within nations, children will all reach a shared base level of intelligence, just like children who all receive a standard nutritional intake will all reach a minimum height. The variability on top of that minimum might then be due to genetic differences or to non-shared environmental differences.

But how do we know which one matters more?

In practice it can be very difficult to unravel the various influences on intelligence (or anything else) that come from genes and shared or non-shared environments. Studies of children adopted from birth, however, provided a neat way of separating the influence of genes and environment. Children who are adopted live with families that they are not related to, and sometimes MZ or DZ twins were separated at birth to live in different families. Under such circumstances, if variation in intelligence is driven by environments created by different families or different schools, then the intelligence of adopted children should gravitate towards that of their adopted family and separate peer groups. On the other hand, if variation in intelligence is driven by genes then the intelligence of adopted children should remain more similar to their biological parents and twins than to their adopted parents and peer groups.

Many dozens of adoption studies had been performed by the start of this century and they all pointed overwhelmingly towards genes having a significant impact on variation in intelligence. Taking all the studies together and shaking out all the different sources of variability, about 50% of the observed variability in intelligence was attributed to shared genes with the other 50% being due to environment. When Plomin moved to London in 2000 his stated aim was to find the genes responsible for that variability in intelligence; he set up his lab to sort through the strands of DNA and identify those making a substantial contribution to intelligence. But he failed. Over and over again, potential DNA candidates turned out to make no detectable contribution to the variability on intelligent tests, or to variability in school achievement, or to any other possible measure of intelligence.

So which are the intelligence genes that make or break us?

Plomin struggled because he assumed that variability in intelligence would be due to the presence or absence of a relatively small number of genes each accounting for a few percentage points of the overall genetic effect. That assumption was wrong. Newer technologies can scan the entire genome and associate all the genetic variability between people with variability in traits such as intelligence. The approach, known as genome wide association studies (GWAS), has demonstrated that intelligence is associated with many thousands of genes, each one contributing just a tiny fraction of the overall genetic effect. The combined effect is known as the polygenic score, and the score is achieved by associating a trait of interest, such as intelligence, with variability in the DNA of the sample. The DNA variability is the result of variations in single nucleotides occurring at specific positions in the genome, known as a single-nucleotide polymorphism, often abbreviated to SNP and pronounced “SNiP”. The more people that are sampled in a GWAS (at least thousands of people) then the greater the power to detect smaller and smaller SNP effects. The largest GWAS so far has looked at years of education and involved more than a million people. That huge sample size enabled the investigators to uncover more than a thousand significant SNP associations.

The growth of GWAS is allowing genetic researchers to make bold statements about the influence of genes on traits such as intelligence. After years of struggling with seemingly null effects, Plomin has come out with some of the boldest statements of all. He has recently documented his adoption studies and the impact of GWAS on the field in his book, Blueprint, and towards the end he concludes:

“…DNA is the most important factor in making us who we are. Inherited DNA differences are the essence of human individuality… Polygenic scores are already the best predictors we have for schizophrenia and school achievement… and their prediction is causal.”

Behavioural Geneticist Robert Plomin

But do genes impact our chances of success?

Elsewhere in the book Plomin explains that polygenic scores can lead to strong predictions about educational achievement. Students scoring in the 10th percentile for the educational attainment polygenic score are much less likely to go to university than those in the 90th percentile. Only 32% of students in the lowest decile go to university, whereas 70% in the highest decile go to university.

Plomin also has bad news for parents and schools who might wish to push against this genetic destiny. Although it is true that 50% of the variability in intelligence is due to environment, those environmental influences are unsystematic, idiosyncratic and serendipitous — we don’t really know what environments matter, we don’t really know what the environment does, and so we cannot control environment to deliver beneficial effects. Such pessimism might strike many parents and school heads as bizarre given that both spend much of their time constructing positive environments to improve educational outcomes. Plomin rebuts the idea that schools and parents make a difference by explaining that parents don’t so much mould their children’s characters as give them their character genetically (“nice” parents have “nice” kids) and respond to their genetically driven character traits. A naturally literate child will enjoy being read to and so will encourage his or her parents to read to them, and then will themselves seek out literature to read for themselves. Plomin also explains that “good” schools are not good because of their inherent teaching practices but because of the children they select:

“When we control for the factors that are used to select students the average difference in GCSE scores is negligible and overall GCSE variance explained by school type shrinks to less than 1 per cent. In other words, selective schools do not improve students’ achievement once we take into account the fact that these schools preselect students with the best chance of success.”

Plomin summarises the non-impact of parents and schools with the following flourish:

“In summary, parents matter, schools matter and life experiences matter, but they don’t make a difference in shaping who we are. DNA is the only thing that makes a substantial systematic difference, accounting for 50 per cent of the variance in psychological traits. The rest comes down to chance environmental experiences that do not have long-term effects.”

At a recent conference I was able to ask Plomin what he meant when he says that parents and schools matter but they don’t make a difference. What he explained is that parents and schools matter because they provide the ground floor physiological requirements such as nutrition, shelter and love, and also the basic necessary scholastic skills such as literacy, numeracy and culture. Because all children, except the severely neglected, receive all that as a given, those things don’t make a difference, those things make children the same and not different. All children born in modern, industrialised, countries will have their physiological needs met and will be taught a language, given instruction in reading and the basic principles of mathematics, and be introduced to important cultural and historical events. And so they will all be able to speak, read, write, and perform simple calculations. It matters that those skills are imparted to children and so parents and schools matter, but all children learn those skills to a basic level and so parents and schools don’t make a difference.

Society Matters, Schools Matter, and Parents Matter

Ultimately I think Plomin’s message is a little sneaky. By focusing on variability in intelligence, which contains a genetic component, Plomin distances himself from the historical and social contributions to intelligence, which are vastly larger, more environmentally controllable, and of greater significance.

Plomin admits that social changes will impact intelligence in ways that genetic studies will not detect. Genetic studies won’t detect the impact of social change because social change lifts everybody upwards in similar ways, and genetic studies can only find effects relating to how people differ. Genetic studies cannot find effects relating to how people are the same. What genetic studies fail to detect, therefore, is the bulk of what makes us similar and similarly intelligent. Sharing a common national language, for example, means that people can more easily share in a common national story and share in the political, cultural, and scientific advances that will be part of that story. But sharing a common national language is relatively new in human history. At the time of the French Revolution, for example, only half the French population spoke French, and only 12–13 percent spoke it well. More recently, after Singapore became independent, Lee Kuan Yew constructed a language policy to unite Singaporeans. He used English as a tool of social cohesion to unite a country made up of Chinese, Malay and Indian peoples. English was the platform for common government, shared social interaction, and a common, equitable school education

The Singaporean school system was radically reformed after 1965 so that Singaporean children could catch up with levels of literacy and numeracy already achieved in other modern industrialised countries. In the early 1970s, less than half the pupils entering primary grade in Singapore went on to secondary grade. Today, approaching 90% of Singaporeans have a post-secondary education. Raffles Junior College in Singapore ranks number one for the highest number of offers to attend Cambridge and is consistently one of the top feeder colleges for attendance at Oxford, Cambridge and the US Ivy League.

Dramatic improvements in the living standards of Singaporeans has also freed parents to provide the kind of physically and mentally supportive home environment that can enable their children to benefit from education. All those social changes, school reforms, and parental inputs will benefit Singaporean children similarly and so will be missed by Plomin in his hunt for genetic influence on variation in intelligence. That’s why Plomin can say that schools and parents matter, but they don’t make difference.

That message is sneaky because when we read that genes are important for intelligence we tend not to separate the average level of intelligence from the variation in intelligence, and we tend to assume that genes are somehow dictating intelligence per se rather than just influencing the variation in intelligence. In the quote above, for example, Plomin states that “DNA is the most important factor in making us who we are” — who we are rather than variation in who we are. Plomin makes a mistake in eliding the person with the variation in personal characteristics. The mistake is a serious one. Who you are is massively dependent on when and where you were born, and much less dependent on your genes.

The message is also sneaky because although variation is important, missing the vast universal improvement in human intelligence thanks to the collective development of human society misses far too much. It seems to me that if we want to improve educational attainment, intellectual achievements, work performance, and so on, then it serves us well to focus on the social changes we can make to the benefit of everyone rather than to overly focus on the genetic variations that make each of us a little bit different. That said, Plomin argues that the variation around the average is what really matters in a meritocratic society. Elite institutions don’t care about the average, they just want those people who push that little bit above it. What do you think? Post your comments and questions below.

About the Author

Stuart is faculty in the psychology department at NUS and at the Clinical Imaging Research Centre (CIRC). His work involves theoretical and empirical research on the nature of pain. In particular, Stuart is examining the possible causes of a rising incidence of pain and somatic illness in the absence of identifiable pathology and in the context of improving health and longevity. Consequently, his research abuts psychology, cognitive science, and philosophical ethics. He writes regularly for the online magazine Spiked.