The DNA revolution has recently given us the power to predict our psychological strengths and weaknesses from birth. This is a gamechanger that has far reaching implications for psychology, for society and for each and every one of us.
For most of the twentieth century environmental factors were called nurture because the family was thought to be crucial in determining who we become. Genetic research showed that this is absolutely not true. In fact, the environment makes siblings reared in the same family as different as siblings reared in separate families.
The genetic contribution to our individual psychological characteristics, nature rather than nurture, is not just statistically significant, it is massive. DNA differences inherited from our parents at the moment of conception are the consistent, lifelong source of psychological individuality. You are 50 per cent similar genetically to your parents and siblings, but this means that you are also 50 per cent different.
DNA isn’t all that matters but it matters more than everything else put together in terms of the stable psychological traits that make us who we are.
The genome genie is out of the bottle and cannot be stuffed back in again.
What would you think if you heard about a new fortune telling device that is touted to predict psychological traits like depression, schizophrenia and school achievement? What’s more, it can tell your fortune from the moment of your birth, it is completely reliable and unbiased and it costs only £100.
This might sound like yet another pop-psychology claim about gimmicks that will change your life, but this one is in fact based on the best science of our times. The fortune teller is DNA. The ability to use DNA to understand who we are, and predict who we will become, has emerged only in the last three years, thanks to the rise of personal genomics. We will see how the DNA revolution has made DNA personal by giving us the power to predict our psychological strengths and weaknesses from birth. This is a gamechanger that has far-reaching implications for psychology, for society and for each and every one of us.
This DNA fortune teller is the culmination of a century of genetic research investigating what makes us who we are. When psychology emerged as a science in the early twentieth century, it focused on the environmental causes of behaviour. Environmentalism, the view that we are what we learn, dominated psychology for decades. From Freud onwards, the family environment, or nurture, was assumed to be the key factor in determining who we are. In the 1960s geneticists began to challenge this view. Psychological traits from mental illness to mental abilities clearly run in families, but there was a gradual recognition that family resemblance could be due to nature, or genetics, rather than nurture alone, because children are 50 per cent similar genetically to their parents.
Since the 1960s scientists conducting long-term studies on special relatives like twins and adoptees have built a mountain of evidence showing that genetics contributes importantly to psychological differences between us. The genetic contribution is not just statistically significant, it is massive. Genetics is the most important factor shaping who we are. It explains more of the psychological differences between us than everything else put together. For example, the most important environmental factors, such as our families and schools, account for less than 5 per cent of the differences between us in our mental health or how well we did at school once we control for the impact of genetics. Genetics accounts for 50 per cent of psychological differences, not just for mental health and school achievement, but for all psychological traits, from personality to mental abilities. I am not aware of a single psychological trait that shows no genetic influence.
The word ‘genetic’ can mean several things, but in this book it refers to differences in DNA sequence, the 3 billion steps in the spiral staircase of DNA that we inherit from our parents at the moment of conception. It is mind-boggling to think about the long reach of these inherited differences that formed the single cell with which we began life. They affect our behaviour as adults, when that single cell with which our lives began has become trillions of cells. They survive the long and convoluted developmental pathways between genes and behaviour, pathways that meander through gene expression, proteins and the brain. The power of genetic research comes from its ability to detect the effect of these inherited DNA differences on psychological traits without knowing anything about the intervening processes.
Understanding the importance of genetic influence is just the beginning of the story of how DNA makes us who we are. By studying genetically informative cases like twins and adoptees, behavioural geneticists discovered some of the biggest findings in psychology because, for the first time, nature and nurture could be disentangled. The implications of these findings are transformative for psychology and society and for the way you think about what makes you who you are.
For example, one remarkable discovery is that even most measures of the environment that are used in psychology such as the quality of parenting, social support and life events show significant genetic impact. How is this possible when environments have no DNA themselves? As we shall see, genetic influence slips in because these are not pure measures of the environment ‘out there’ independent of us and our behaviour. We select, modify and even create our experiences in part on the basis of our genetic propensities. This means that correlations between such so-called ‘environmental’ measures and psychological traits cannot be assumed to be caused by the environment itself.
In fact, genetics is responsible for half of these correlations. For example, what appears to be the environmental effect of parenting on children’s psychological development actually involves parents responding to their children’s genetic differences.
A second crucial discovery at the intersection of nature and nurture is the unexpected way in which the environment makes us who we are. Genetic research provides the best evidence we have for the importance of the environment because genetics accounts for only half of the psychological differences between us.
For most of the twentieth century environmental factors were called nurture because the family was thought to be crucial in determining who we become. Genetic research showed that this is absolutely not true. In fact, the environment makes siblings reared in the same family as different as siblings reared in separate families. Family resemblance is due to our DNA rather than to our shared experiences like TLC, supportive parenting or a broken home. What makes us different environmentally are random experiences, not systematic forces like families.
The implications of this finding are enormous. Such experiences affect us, but their effects do not last; after these environmental bumps we bounce back to our genetic trajectory. Moreover, what look like systematic long-lasting environmental effects are often reflections of genetic effects, caused by us creating experiences that match our genetic propensities.
As I will demonstrate in this book, the DNA differences inherited from our parents at the moment of conception are the consistent, lifelong source of psychological individuality, the blueprint that makes us who we are. 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 everything else put together in terms of the stable psychological traits that make us who we are.
These findings call for a radical rethink about parenting, education and the events that shape our lives. The first part of Blueprint concludes with a new view of what makes us who we are that has sweeping, and no doubt controversial, implications for all of us. It also provides a novel perspective on equal opportunity, social mobility and the structure of society.
These big findings were based on twin and adoption studies that indirectly assessed genetic impact. Twenty years ago the DNA revolution began with the sequencing of the human genome, which identified each of the 3 billion steps in the double helix of DNA. We are the same as every other human being for more than 99 per cent of these 3 billion DNA steps, which is the blueprint for human nature. The less than 1 per cent of these DNA steps that differ between us is what makes us who we are as individuals, our mental illnesses, our personalities and our mental abilities. These inherited DNA differences are the blueprint for our individuality, which is the focus of the second part of Blueprint.
Recently, it has become possible to directly assess each of the millions of inherited DNA differences between us and to find out which of these are responsible for the ubiquitous genetic influence on psychological traits. One of the extraordinary discoveries was that we are not just looking for a few DNA differences with big effects but rather thousands of small differences whose weak effects can be aggregated to create powerful predictors of psychological traits. The best predictors we have so far are for schizophrenia and school achievement, but other DNA predictors of psychological traits are being reported every month.
These are unique in psychology because they do not change during our lives. This means that they can foretell our futures from birth. For example, in the case of mental illness, we no longer need to wait until people show brain or behavioural signs of the illness and then rely on asking them about their symptoms. With DNA predictors we can predict mental illness from birth, long before any brain or behavioural markers can be detected. In this way, DNA predictors open the door to prediction and, eventually, prevention of these problems before they create collateral damage that is difficult to repair. These DNA predictors are also unique in genetics because for the first time we can go beyond predicting the average risk for different members of a family to predict risk separately for each member of the family. This is important because family members differ a lot genetically, you are 50 per cent similar genetically to your parents and siblings, but this means that you are also 50 per cent different.
These new DNA developments are described in the second part of Blueprint, which concludes by showing how this new era of DNA predictors will transform psychology and society and how we understand ourselves. The applications and implications of DNA predictors will be controversial. Although we will examine some of these concerns, I admit I am unabashedly a cheerleader for these changes. At any rate, the genome genie is out of the bottle and cannot be stuffed back in again.
Blueprint focuses on psychology for two reasons. First, psychology is the essence of who we are, our individuality. Most of the same conclusions apply to other sciences such as biology and medicine, but the implications of the DNA revolution are more personal for psychology.
A second reason is that I am a psychologist who has for forty-five years been at the centre of genetic research on mental health and illness, personality and mental abilities and disabilities. One of the best things in life is to find something that you love to do, and I fell in love with genetics when I was a graduate student in psychology at the University of Texas at Austin in the early 1970s. It was thrilling to be part of the beginning of the modern era of genetic research in psychology. Everywhere we looked we found evidence for the importance of genetics, which was amazing, given that genetics had been ignored in psychology until then. I feel lucky to have been in the right place at the right time to help bring the insights of genetics to the study of psychology.
I have been waiting thirty years to write Blueprint. My excuse for not doing it sooner is that more research was needed to document the importance of genetics, and I was busy doing that research. However, in hindsight, I have to admit to another reason: cowardice. It might seem unbelievable today, but thirty years ago it was dangerous professionally to study the genetic origins of differences in people’s behaviour and to write about it in scientific journals. It could also be dangerous personally to stick your head up above the parapets of academia to talk about these issues in public. Now, the shift in the zeitgeist has made it much easier to write this book. A huge bonus for waiting is that the story is much more exciting and urgent now because the DNA revolution has advanced in ways no one anticipated thirty years ago. Now, for the first time, DNA by itself can be used to make powerful predictions of who we are and who we will become.
Blueprint interweaves my own story and my DNA in order to personalize the research and to share the experience of doing science. I hope to give you an insider’s view of the exciting synergies that came from combining genetics and psychology, culminating with the DNA revolution. Although this book expresses my subjective view of how DNA makes us who we are, I have tried my best to present the research honestly and without hype. However, as I move further from the data to explore the implications of these findings, some issues will be controversial. My goal is to tell the truth as I see it, without pulling punches for the sake of perceived political correctness.
My focus on the importance of inherited DNA differences is likely to attract criticism for resurrecting the nature versus nurture debate long after its widely reported demise. Throughout my career I have emphasized nature and nurture, not nature versus nurture, by which I mean that both genes and environment contribute to the psychological differences between people. Recognition that both genes and environment are important fosters research at the interplay between nature and nurture, a very productive area of study.
However, the problem with the mantra ‘nature and nurture’ is that it runs the risk of sliding back into the mistaken view that the effects of genes and environment cannot be disentangied. No one has trouble accepting that the environment we experience contributes to who we are, but few people realize how important DNA differences are. My reason for focusing on DNA as the blueprint for making us who we are is that we now know that DNA differences are the major systematic source of psychological differences between us. Environmental effects are important but what we have learned in recent years is that they are mostly random unsystematic and unstable which means that we cannot do much about them.
I hope Blueprint launches a conversation about these issues. A good conversation requires DNA literacy, which this book attempts to provide, especially in relation to complex psychological traits. This requires some knowledge about DNA, the statistics of individual differences, and the technological advances that have led to the DNA revolution. I have attempted to explain these complicated ideas as simply as possible. A ‘Notes’ section at the end of the book provides references and additional explanation for these and other topics. Because the issues tackled in Blueprint are more than complicated enough, I have resisted digressions into research on topics that, although fascinating, are not essential to understanding inherited DNA differences as they relate to psychological traits. Some of these tangential topics that I have reluctantly let go include evolution, epigenetics and gene editing.
I hope this book conveys the excitement I feel about this historic moment in psychology. The message from earlier research has begun to sink in, that DNA is the major systematic force, the blueprint, that makes us who we are. The implications for our lives for parenting, education and society are enormous. However, this only sets the stage for what will be the main event: the ability to predict our psychological problems and promise from DNA. This is the turning point when DNA changes psychology scientifically and clinically and the impact of psychology on our lives. Our future is DNA.
PART 1: Why DNA matters
Disentangling nature and nurture
We are all similar in many ways. With few exceptions, we stand on two feet, we have eyes in the front of our heads that allow us to see in three dimensions and, most amazingly, we learn to speak. But we are also obviously different physically, physiologically and psychologically. Blueprint is about what makes us different psychologically.
Psychologists study hundreds of traits, which is their collective label for differences between us that are consistent across time and across situations. These traits include dimensions of personality, such as emotionality and energy level, and traits that are traditionally assessed as either, or disorders, for instance depression and schizophrenia. They also include cognitive traits such as general learning ability, often called intelligence, and specific mental abilities such as vocabulary and memory, as well as disabilities in these traits.
For most of the twentieth century it was assumed that psychological traits were caused by environmental factors. These environmental factors were called nurture because, from Freud onwards, their origins were thought to lie in the family environment. Because these traits run in families, it was reasonable to assume that the family environment is responsible for these traits.
But genetics also runs in families. Fifty years before we knew about DNA we knew that first-degree relatives, parents and their children, brothers and sisters, are 50 per cent similar genetically. So the reason why psychological traits run in families could be nature (genetics) as well as nurture (environment). However, it is more difficult to credit nature because DNA is invisible and silent but you can see, hear and feel the nurture of family life, for good and for bad.
So, what is the relative importance of nature and nurture for psychological traits? First, take a minute to note your opinions about nature (genetics) and nurture (environment). By rating the following traits now, you can then compare your ratings to those of other people and to the results of genetic research. Although this book is about psychological traits, it is useful to begin by contrasting psychological traits with a few physical traits (eye colour, height) and medical traits (breast cancer, stomach ulcers).
For the following fourteen traits, rate how much you think genetic factors are important in making people different in other words, how heritable do you think they are? If you think that a trait shows no genetic influence, rate it as 0 per cent. If you think that a trait is entirely due to genetic influence, rate it as 100 per cent. For some of the traits, you might not have any idea about how much DNA matters, but make a guess.
Here you can compare your ratings to those from a 2017 survey of 5,000 young adults in the UK. The last column shows estimates based on decades of genetic research which indicate that inherited DNA differences account for about 50 per cent of our psychological differences. In other words, inherited DNA differences are the main reason why we are who we are. The next chapter explores how we know this to be true, and the rest of the first part of Blueprint investigates what it means for psychology and society.
These fourteen traits were not selected because they are especially heritable. Substantial genetic influence has been found not only for schizophrenia and autism but for all types of psychopathology, including mood disorders, anxiety disorders, attention-deficit disorders, obsessive-compulsive personality disorder, antisocial personality disorders and drug dependence. Substantial genetic influence is also found for all aspects of personality and mental abilities and disabilities.
In fact, it is no longer interesting to show that another psychological trait is heritable, because all psychological traits are heritable. A sign of how much the situation has changed from the last century’s environmentalism is that I do not know of a single psychological trait that does not show genetic influence.
Estimates of genetic influence are called heritability, which has a precise meaning in genetics. Heritability describes how much of the differences between individuals can be explained by their inherited DNA differences. The word ‘differences’ is key to its definition. Blueprint is about what makes us different psychologically.
There are many related words that create confusion around heritability. ‘Innate’ and ‘inborn’ refer to universal characteristics that are so important evolutionarily that they do not vary, at least given the range of environments in which we evolved. We all walk on two legs, we all have eyes in the front of our heads to perceive depth, and we all have basic reflexes like blinking our eyes in response to a puff of air. These characteristics are programmed by the 99 per cent of our DNA that does not differ between us. In contrast, heritability is about the 1 per cent of DNA that differs between us and contributes to our differences in behaviour. Even though innate characteristics are programmed by DNA, we can’t talk about their heritability because innate characteristics do not vary between us.
Words like ‘genetic’ and ‘inherited’ and colloquial phrases like ‘in my genes’ or ‘in your DNA’ cover anything to do with DNA. They include the universal 99 per cent of our DNA as well as the 1 per cent that makes us different. They also include DNA mutations that are not inherited or passed on to our offspring, such as the DNA mutations in skin cells that cause skin cancer.
Blueprint. How DNA makes us who we are.
by Robert Plomin
get it at Amazon.com