When I opened this book and read its sales pitch (I paraphrase: “What if I told you of a new fortune-telling device that can predict psychological traits – it’s called the DNA revolution!”) I raised my inquisitive but sceptical eyebrow somewhat. Did I just pick up another piece of pop-psychology pulp? Oh boy, was I wrong! Behavioural geneticist Robert Plomin has written an incredibly interesting book with Blueprint, explaining how rapid advances in DNA sequencing technology are opening vast new vistas on the genetics underlying psychology. And is it ever so different, and more complex, than what hyped-up newspaper headlines have tried to sell us so far.

No doubt you will have heard of the long-running nature vs. nurture debate: is your character and behaviour determined by your genes (nature), or by environmental factors such as your upbringing or education (nurture)? Psychology has traditionally favoured nurture, though some prominent scientists have spoken out against this over the years, notably Steven Pinker in The Blank Slate: The Modern Denial of Human Nature, but also Rutter in Genes and Behavior: Nature-Nurture Interplay Explained.

Plomin started several long-term longitudinal studies on adopted children in the mid-70s and twins in the mid-90s, revealing that genes are far more important in determining behaviour than they have been given credit for. Adopted children end up resembling their biological, rather than their foster parents. And identical twins (those that come from the same fertilised egg splitting in two after fertilisation) resemble each other far more than fraternal twins (those where two eggs are fertilised simultaneously).

But pointing to genetics has not been without problems, and the field of behavioural genetics has been mired in controversy. Especially where research on intelligence is concerned, it quickly gets mixed up in debates on racial differences with eugenic undertones. The 1994 book The Bell Curve: Reshaping of American Life by Differences in Intelligence was roundly criticised (see The Bell Curve Wars: Race, Intelligence, and the Future of America, Inequality by Design: Cracking The Bell Curve Myth, or Intelligence, Genes, & Success: Scientists Respond To The Bell Curve).

Twin studies, too, have been under fire (see for example The Trouble with Twin Studies: A Reassessment of Twin Research in the Social and Behavioral Sciences), partially for not being able to find genes for behavioural differences. That last has been a big problem as researchers were hoping to find single or a few genes of big effect on traits of interest such as intelligence. Hundreds of studies reported such findings, and media headlines were rife with claims of “gene for X found!”. This came crashing down with the publication of a 2005 article Why Most Published Research Findings are False, which set off the reproducibility crisis (see also my review of Stepping in the Same River Twice: Replication in Biological Research). It turned out that virtually none of these studies on candidate genes for big effects could be replicated.

“the field of behavioural genetics has been mired in controversy with research on intelligence getting mixed up in debates on racial differences with eugenic undertones.”

What I like about this book, and what increases Plomin’s credibility in my view, is that he acknowledges all of this troubled legacy. He admits that some of what he writes will be controversial to some, but he avoids hyping things. He openly confronts the reproducibility crisis and shows how, at least in the field of behavioural genetics, it came about and is now being resolved.

So, what are some of these potentially controversial claims then? I do not have space here go into these in-depth – and the book does a far better job of properly building cases for them, but to whet your appetite…

One, a lot of what we thought of as effects of nurture are actually underpinned by genetics. For example, stressful life events such as divorce or bereavement correlate with depression in adults, which was long been interpreted as the former causing the latter. Plomin turned the tables on this, saying “actually, your personality and the way you respond to these events has a large genetic component to it”.

Two, that reproducibility crisis? Well, genetics is complex and there are only very few psychological traits or disorders caused by a few genes of large effect (Plomin wryly remarks on page 116 that natural selection did not tinker with the genome to make things simple for scientists). It took the Human Genome Project to spur technological innovation to allow researchers to quickly and cheaply sequence not just bits of DNA but the whole of a person’s genetic makeup (their genome). And, lo and behold, it turns out that many traits are influenced by thousands of genes, each with a very small effect (in particular single nucleotide polymorphisms or SNPs, all explained in detail with great clarity in the book). Biologists call this polygenicity and it is very frustrating when you are trying to study the biochemical pathways that lead from gene to behaviour. The upside is that fears of modern gene-editing tools such as CRISPR (see A Crack in Creation: The New Power to Control Evolution and Modern Prometheus: Editing the Human Genome with CRISPR-Cas9) being used to create designer babies with certain character traits are unfounded. For now.

“psychiatry has been getting it all wrong with its dichotomous diagnostics of disorders […] We are all a bit schizo.”

Three, as a corollary of number two (and this idea blew my mind) – psychiatry has been getting it all wrong with its dichotomous diagnostics of disorders. Rather than qualitative differences (you are or aren’t, say, schizophrenic), people can all be classified on a quantitative scale, on a spectrum. We are all a bit schizo, but only people at the extreme end of the spectrum experience problems in their day-to-day life. Plomin raises the interesting question: what is at the opposite end of the spectrum? Normal behaviour or other unhealthy extremes?

Four, as a consequence of all of the above Plomin puts forth the controversial claim that parenting, education and life experiences matter, but ultimately do not make a difference. By which Plomin means to say that research shows that our genetic make-up has a far larger impact on who we are. He even takes this one step further by effectively saying “relax, just accept who you are rather than trying to go against your genetic grain”.

Throughout, Plomin is at pains to prevent misinterpretation of these findings (possibly best summarised by the title of Heine’s 2017 book DNA is Not Destiny: The Remarkable, Completely Misunderstood Relationship Between You and Your Genes). Does he get repetitive? I do not think so. Given the controversial nature of his findings compared to what most people still understand, pointing out the caveats bears repeating.

I am sure that some of Plomin’s peers will disagree with some of the ideas put forth here, and it will not be the last word on this topic. But in the end I found this to be a remarkable and thought-provoking book. Together with books such as She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity and The Genome Factor: What the Social Genomics Revolution Reveals about Ourselves, Our History, and the Future, Blueprint is painting a picture of genetics and heritability for the 21st century.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

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