What would you think if you heard about a new fortune telling device that could predict psychological traits like schizophrenia and school achievement? This might sound like yet another pop psychology gimmick that claims to change our lives, but in fact this one is based on the best science of our times.

Inherited DNA differences are the primary force in making us who we are; it’s the blueprint for our individuality. A blueprint is a plan, not the finished 3D structure – we don’t look like a double helix of DNA. The environment can alter this plan temporarily, but we tend to bounce back to our genetic trajectory. Understanding how DNA makes us who we are will teach us to be more tolerant of each other. Genetics, not free will, is the reason why some people are prone to problems like depression, learning disabilities and obesity.

On average, overall, 50% of the differences in any trait you want to mention are due to inherited DNA differences between us. I thought, for example, kindness would be more due to the way your parents teach you to care about people for example, so I did a study where I hoped I’d show that it wouldn’t be very heritable, but it turns out to be as heritable as anything else. There’s now a challenge to find any trait at all in psychology – that’s reliably measured – that doesn’t show significant genetic influence.

On average, overall, 50% of the differences in any trait you want to mention are due to inherited DNA differences.

Up until the last few years, we haven’t been able to study DNA directly. We’ve had to use indirect methods like twin studies, comparing identical and non-identical twins, and adoption studies. We’re now able to, with new technology, to measure these polygenic scores that involve thousands of these DNA differences, in order to predict psychological problems and promise from birth. The evidence for the importance of genetics itself calls for a radical rethink about parenting, and education, and society.

The implications for parenting for example – we use the slogan ‘parents matter, but they don’t make a difference’ – and what that means is that parents obviously matter tremendously in children’s lives: they provide the essential psychological and physical ingredients for children’s development, but most of the reason why children turn out differently is due to genetic differences. Genetic research shows, it might be hard to believe this, but if you were adopted at birth and reared in a different family, you’d still be essentially the same person that you are.

The main message I think, is that parents need to realise that children are not blobs of clay that you mould to be whatever you want it to be. I hope that Blueprint helps relieve some of the guilt and anxiety that’s piled on parents by parent-blaming theories of socialisation. We’re talking about genetic influence, probabilistic propensities, not predetermine genetic hard-wiring. So you can change, but genetic propensities are the blueprint. Genetics is responsible for most of the differences that we observe in the population.

Genetics tells us some interesting things about differences within families, like most people recognise that relatives are genetically related; children in a family will be different, as well as similar. I grew up in a family in inner city Chicago where my parents didn’t go to university, none of my cousins went to university, my sister didn’t go to university. My sister had trouble at school, she just didn’t like school and had trouble learning, whereas I was interested in reading from very early on. We had no books in our house, so I used to go to the public library and bring books home, and even before I went to school I was reading.

So I often wondered: why is that? My parents didn’t discourage me, they were pleased I did well at school, but I loved school, I found it easy to learn. But now with genetics we know that individual differences in school achievement account for more than half the differences between children. So I know my polygenic score for educational achievement, and it is very high. I don’t know my sister’s, but I’d be willing to predict that hers isn’t so high, and that means that you don’t assume that she did do poorly at school because she wasn’t trying hard enough. My parents interacted with us similarly – they thought school was a good thing, but they didn’t push us very hard, but I did very well at school and my sister didn’t. So I think genetics will allow us to consider differences within families, not just differences between families and maybe to respect these genetic differences to a greater extent.

Understanding how DNA makes us who we are will teach us to be more tolerant of each other.

I’m glad in a way that I didn’t write this book twenty years ago, we had no idea about the DNA revolution at that time. Now the DNA revolution is sweeping into psychology. The key has been to recognise that thousands of tiny DNA differences are responsible for the ubiquitous genetic influence on psychological traits. And we can now measure these DNA differences in what are called polygenic scores – that is, many, many genes that you put together to predict risk, not just one or ten or even one hundred, but thousands of these DNA differences. In just the last two years, these polygenic scores have become the best predictor we have of some psychological traits, most notably schizophrenia and school achievement. There are no other predictors that can predict from birth, and this will promote research that aims to intervene to prevent problems before they occur.

I think that the ability to read our DNA blueprint will transform psychology, society and how we understand ourselves. 

Blueprint by Robert Plomin is available now.