Robert Plomin. Blueprint. Allen Lane, London. 2018

Plomin has written the book that summarizes his career, the one that he previously avoided writing because of what he describes as his own cowardice. Harsh judgement, but investigators into the genetics of intelligence are given a rough ride in contemporary academia, where genetics generates a hostility not meted out to sociological explanations. Over his long and highly productive career Plomin thought it prudent to publish in scientific journals, rather than to go public with all his views, which would invite even more criticism than he was already getting from doing his scholarly work. So, this is his “coming out” book.

The analogy of a blueprint, of course, makes more sense to my generation than it probably does to more recent ones. No engineering analogy will fit the intricacies of biology, but the implication is clear: DNA is what makes stuff happen, given only some basic environmental circumstances habitually found on this planet. The genetic code is causal.

A blueprint is a plan. It is obviously not the same as the finished three-dimensional structure – we don’t look like a double helix. DNA isn’t all that matters but it matters more than anything else put together in terms of the stable psychological traits that make us who we are. (Prologue, ix)

I agree with the sentiment. I merely note that people now often say of organizations and products and cultural creations that “they have the DNA of their predecessors”. DNA is now a meme.

So, what does Plomin say, now that no reticence is required?

1 Plomin has written a clear and non-technical account which ought to be accessible to a wide audience. For example, pages 24 and 25 explain variance, covariance and correlation in simple terms, with two illustrative scatter plots, and subsequent pages show how correlations found in identical and fraternal twins are used to estimate heritability. Plain language is hard to write. This book reads well, and ought to reach a wider public. Even for those who have been reading his papers for the last decade, there are new things to learn from seeing the whole story in one place.

One natural casualty of writing for a general audience is that the text is reference-free. Some scholars may be hurt not to see their names in print, but it is the findings that matter. There is no author index, but a full 59 pages of supporting notes. These differ in their nature and intensity: some list relevant publications, others explain ideas and misconceptions in far more detail. Readers will differ in whether they read the notes, and if so, at what stage. I mostly left them to the end of each chapter, so as to let the narrative flow while scribbling in my own questions in the margins.

2 Plomin has given an enlightening account of his research career, culminating in the long-term Twins Early Development Study, which has become a front runner in the DNA revolution. Research is a life-consuming business. Some researchers give up their weekends, most don’t. TEDS has more than 12,000 twins, and has generated 55 million items of data, described in over 300 published papers and 30 PhDs. Respect.

3 Plomin shows that there is strong evidence that, as a rule of thumb, most human characteristics are 50% heritable. He concludes his second chapter saying: “Inherited DNA differences are by far the most important systematic force in making us who we are”.

4 Plomin makes big inroads into that great big squashy thing “the environment” by showing that important aspects of it are heritable. At first this sounds nonsensical, but I think Plomin wins through. For example, at first glance it would appear that because some mothers read to their children and others do not, the former habit is the key to children’s language development. Whole programs have been devoted to this supposition, including well meaning projects giving books to families, because it has been found that number of books in the house predicts children’s scholastic achievements. On the contrary, Plomin shows, “parents who like to read have children who like to read”.

Plomin first found this when studying stressful life events (relationship problems, financial status and illness) which seemed to be truly external to the individuals concerned. Identical twins were twice as similar as fraternal twins on these measures (correlations of .30 and .15 respectively). These apparently completely environmental events were almost a third due to genetics.

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Identical twins are more concordant for divorce (55%) than fraternal twins (16%). Divorce does not rain down unbidden from the sky: it happens more frequently to those who are joyful, engaged with life, emotional and impulsive. So there. In 20,000 adopted individuals the likelihood of divorce was higher if their real mother, who played no part in their upbringing, later got divorced, than if their adoptive mothers later got divorced. After controlling for genetics, Plomin says, no environmental causes of divorce have been identified.

Divorce doesn’t just happen by chance. We make or break our relationships. We are not just passive bystanders at the whim of events “out there”. Pg 39.

TV has been associated with many unfavourable outcomes, perhaps unfairly. Interestingly, parents and their children are more similar (.30) than adoptive parents and their adopted children (.15) in the time they devote to this freely chosen activity. In fact, heritable components are found in many traits which had been classified as “external” such as chaotic family environments, being bullied, neighbourhood safety, being exposed to drugs, and quality of marriage. Plomin calls this “the nature of nurture”. Smart, but confusing. I said in 2013 that they were “self-made environments” or “personally created niches”. Our genetics influences us in the way we build our nests.

Plomin explains:

Some children have more accidents than others: the number of children’s scrapes and bruises shows genetic influence. For adults, automobile accidents are not always accidental either, of course. Automobile crashes are often caused by reckless driving – driving too fast, taking chances or driving under the influence of alcohol and other drugs. Pg 48.

Years ago I had hoped that the Home Observation for Measurement of Environment would provide detailed indications of which aspects of the environment were worth manipulating so as to boost children’s intelligence. Families showed the expected .5 correlation with HOME, adopted children half that. All the good parenting is revealed to be half of it due to genetic causes. Brighter parents have brighter children. Although it looks as if encouragement is doing the trick, it is at most half of the cause of the children being bright. Plomin concludes:

Genetic differences in children’s aptitudes and appetites affect the extent to which they take advantage of educational opportunities. [] This is a general model for thinking about how we use the environment to get what our DNA blueprint whispers that it wants. Pg 51

5 Plomin reveals the counter-intuitive finding that DNA matters more as time goes by. Heritability estimates for intelligence rise as we age, possibly because the niches we create help boost our intellectual skills over our lifetimes. Eventually, we become more like our parents.

6 Abnormal behaviour is the far end of the normal spectrum, a finding which is closer to the psychologist’s dimensional model than the psychiatrist’s categorization model.

7 Genetic effects are general rather than specific. Importantly, parental psychopathology predicts that children of such parents are more likely to have psychological problems, but not the same diagnosis as the parent. There are strong genetic links between generalized anxiety disorder and major depressive disorder. Perhaps the different presentations are due to unspecified environmental factors. Many studies confirm three genetic clusters of psychiatric disorders:

A) internalizing disorders like anxiety and depression;

B) externalizing disorders like conduct disorders and aggressiveness in childhood, and antisocial behaviour, and alcohol and drug problems in adulthood;

C) Psychotic disorders such as schizophrenia, bipolar disorder and major depression.

Psychiatry is going to have to be re-written. Symptoms are not everything when treating disorders: the genetic underpinnings matter.

The other genetic finding relates to intelligence. Most genetic effects are general across cognitive abilities. Vocabulary, spatial ability and abstract reasoning yield genetic correlations greater than .5 and there is a greater than 50% chance that a DNA difference associated with one cognitive ability will also be associated with other cognitive abilities. Some genetic effects are specific to each cognitive ability, but most genetic effects are general to all cognitive abilities. “g” has a biological reality.

Interestingly, the genetic correlation between the capacity to read real word and non-words is .9 showing that these apparently different skills have the same biological substrate. In general, notions of cognitive modularity are not supported at all. In fact, since genetic influence is caused by many genes of small effect, and these effects affect many traits, it seems likely that generalist genes result in generalist brains. The multi-purpose brain has led to humans surviving ancient threats, and it was not tuned to the specific problems of written English, but can cope with these challenges by using tried and tested general problem-solving abilities.

8 Children in the same family are different because, for example, siblings correlate only .4 for intelligence, an average 13 IQ point of difference, compared to 17 IQ points for pairs chosen at random in the general population. What adoption shows is that environmental influences shared by family members do not make a difference. This is an astounding finding for any psychologist brought up in the standard model of seeing the family as the origin of individual and group differences. It leads to the petulant enquiry: Does that mean that everything I did as a parent was wasted? No. Parenting is important, but does not lead to permanent differences in children. They are already different, for genetic reasons. The lack of shared family effects even holds true of altruism, caring and kindness, the very things that parents might be able to inculcate in their children. Plomin summarises his futile search for non-shared environmental influences thus:

Non-shared environmental influences are unsystematic, idiosyncratic, serendipitous events without lasting effects. The systematic, stable and long-lasting source of who we are is DNA. Page 80.

9 Parents matter but they don’t make a difference. “Put crudely, nice parents have nice children because they are all nice genetically.” Parenting is often a response to children’s genetic propensities, not a cause of them. “The most important thing parents give their child is their genes.” Parents should help their children become what they are.

10 Schools matter but they don’t make a difference. Well, about 2% of a difference. Scholastic performance at age 16 is largely predicted by school performance at age 11.

11 Life experiences matter but they don’t make a difference, particularly as we get older. Life experiences matter a lot to us, but don’t change us the way we imagine they do. We differ in our propensities to experience life events. We don’t all climb mountains and hang glide down again. The heritability of life events is about 25% which allows much in the way of environmental variation, though little of it will be systematic. Falsifying these claims is easy: just demonstrate that parenting, schooling and life experiences make a difference after controlling for genetic influence.

This reminds me of a question I put to Stephen Pinker after David Lubinski had interviewed him about his career at ISIR 2017: were his accounts of intellectual influences and turning points in his life consistent with what we knew about genetics? Pinker didn’t blink. He took one of his cherished memories aged 13 years, of him reading an article in the New York Times about Chomsky’s work on transformational grammar and thinking “that is what I will study” and said of it: “Yes, you are right. What may have been more important than reading that article was having parents who took out a subscription to the New York Times.”

Perhaps all our biographies will have to be rewritten. I find I am very reluctant to give up my treasured narrative of my life, ascribing as I do some important effects to both family and education that seem to make sense to me, though perhaps they only serve as alibis. Any immigrant has to wonder how life would have turned out if they had stayed at home. Does life really have turning points, or are they only unfoldings? Arthur Koestler said somewhere that to think of human beings as no more than flotsam battered by waves of historical inevitability was are demeaning as viewing them as constructions propped up by genes. In all these confections the essential features of being human seem lost, subsumed into vexatious particulars, and stripped of agency and dignity. We are torn between our predicaments and our proclivities.

12 Plomin then goes on to make some even bolder claims:

Rather than blaming other people and ourselves for being depressed, slow to learn or overweight, we should recognize and respect the huge impact of genetics on individual differences. Genetics, not lack of willpower, makes some people more prone to problems such as depression, learning disabilities and obesity. Genetics also make it harder for some people to mitigate their problems. Success and failure – and credit and blame – in overcoming problems should be calibrated relative to genetic strengths and weaknesses. Going even further out on a limb, I’d argue that understanding the importance of genetics and the random nature of environmental influences could lead to greater acceptance and even enjoyment of who we are genetically. Rather than striving for an ideal self that sits on an impossibly tall pedestal, it might be worth trying to look for your genetic self and to feel comfortable in your own skin.

Plomin immediately corrects himself

I do not mean to imply that people should not try to work on any of their shortcomings or not try to improve certain aspects of themselves.

Sorry mate, too late. I am getting comfortable with my DNA, and you can get your own breakfast. (Just wait till all Plomin’s remarks fall into the hands of US criminal lawyers).

As Jensen pointed out, the idea that once the genetic basis of behaviour is understood we will all accept this result in the same way is silly. If my prospects are poorer because of the genes I was given, why should I not be compensated for this unfairness? Plomin understand this dilemma, and at his point (page 92) the book goes on a little excursion about opportunity and meritocracy. I wouldn’t have done this (so many others will plunge into this deep pool of policy implications) but it is relevant from a public point of view, and has interesting twists to it.

13 Here is Plomin’s argument on equal opportunity and meritocracy. While equal opportunity means that people are treated similarly and given equal access to schooling, health and the law, meritocracy only comes in when selection takes place, say in employment. People being “equal” does not mean they are identical: the essence of democracy is that people are treated fairly despite their differences.

From a genetic point of view, equality of opportunity does not translate to equality of outcome. One of the most extraordinary implications of genetics is that heritability of outcomes is an index of equality of opportunity: if environments were all-powerful and varied unfairly that would wash out the heritability effect and set it to zero. The high heritability of school achievement of 60% in the UK suggests that the system is uniformly good, or at least uniformly OK. Half the remaining variance, 20%, might be due to individual school quality, but this seems to wash out by the time children go to university.

Also, as already discussed, many apparently systematic environmental effects reflect actual genetic differences.

The socioeconomic status of parents is a measure of their educational and occupational outcomes, which are both substantially heritable. This means that the correlation between parents’ socioeconomic status and their children’s outcomes is actually about parent-offspring resemblance in education and occupation. Parent-offspring resemblance is an index of heritability, and heritability is an index of equal opportunity. So, parent-offspring resemblance for education and occupation indicates social mobility rather than social inertia. Genetic differences in children’s aptitudes and appetites affect the extent to which they take advantage of educational opportunities. This is why equal opportunities cannot be imposed on children to create equal outcomes. [] To a large extent, opportunities are taken, not given.

When Norway expanded its educational provisions after World War II the first twin study found that the heritability of educational attainment increased and the impact of shared environment decreased, and the same pattern was found subsequently in other countries that increased the equality of schooling. Recent evidence in the US suggests that heritability estimates are decreasing, possibly because of increased educational inequality.

In the UK, children at selective secondary schools do a whole grade better than unselective state schools in their exams at 16 years, something they assure fee-paying parents is due to the quality of their teaching. Perhaps so. When Plomin controlled for the factors used to select students the difference shrinks to 1%, consistent with selection being meritocratic. Equally, when you look at university acceptances, the advantage of selective schools disappears when you control for selection factors: students would have been just as likely to be accepted by the best universities if they had not gone to a selective school. Indeed, given that those schools are seen as conferring an unfair advantage, it would be craftier to apply from an unselective State school. In the UK, private education is not worth the money.

Even “progress” measures, designed to show how much value schools add, are not a pure measure of student progress, because correcting for school achievement at the age of eleven does not correct for other heritable contributions to performance on the GCSE test (taken at 16) such as intelligence, personality and mental health.

Plomin also argues that shared environmental influence on occupational status is negligible, so the systematic effects of on job status and income can be attributed to genetics. Job selection is noisy, but not an effect of systematic bias.

He feels the fear of genetic castes is mistaken, because heritability is 60% not 100% so there is regression to the mean, with a shuffling down and shuffling up of intellects, and the more numerous middle ground will be the main source of high ability students. Perhaps so, but groups who consistently select high ability husbands and wives will regress to that higher group mean, not the population mean. It is possible to create cognitive elites by following strict rules for at least 16 generations.

Plomin concludes Part 1 of the book on page 105 saying “no specific policies necessarily follow from genetic findings, because policies depend on values.”

14 The shorter second part explains the DNA revolution. As one might expect, it is a clear and expert account and worth printing on its own. The basics of DNA are explained in Chapter 10: “dumb molecules, which are the same in each of our trillions of cells, produce life in all its amazing complexity”. These molecules are in a rope ladder held together by 3 billion weak, easily broken rungs, twisted into a double helix so that it forms a spiral, consisting of a 4 letter alphabet which creates 64 DNA words. 99% of the 3 billion rungs are identical for all human beings but 30 million rungs differ. Each difference in rungs is a SNP (snip) and we each have 4 million personal snips. The UK population has about 10 million SNPs. Chapter 11 is about the development of genome-wide association studies. Chapter 12 is a very substantial one about genetic prediction. Chapter 12 is Plomin’s real coming out: he reveals his polygenic scores for all to see. Naturally, this is a teaching opportunity, explaining the insights and the limitations of such measures. Figs 6 and 7 are worth showing again and again, if only to explain polygenic scores and their overlaps, and the fact that they provide probabilistic estimates, not certainties.

This is an explosive book. It leaves the environmentalist position looking threadbare. Whilst the DNA story is advancing and capturing new ground in the form of self-created environmental niches, the other environmental component is in retreat, reduced to saying that really bad environments would change the picture. Indeed they would, but the global story is of an improving world, with higher standards of living, of increasing access to education and health, and of more prosperity. As good environments become widespread the variance accounted for by genetics will only increase.

What can environmentalists turn to? I think their best bet is to find some good and solid long-term effects of adoption, since adoption is the most intense environmentalist intervention. Absent that, they will be left with a scorched earth policy, destroying everything they can in the hope of halting the spread of new ideas. In fact, the ideas in question are pretty old, known to most farm workers and every race horse breeder.

Deliberately absent from the discussion is any mention of genetic group differences. Questioned in an interview about this omission Plomin said “That’s the third rail” and questioning moved to other matters. Wise.

This is also a sobering book. It changes our views of ourselves and, shorn of any reassuring nostrums, invites us to understand our limitations, and to work within them. Genetics deals us a hand to play, and we must play it as best we can.