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.
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.
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.