Parenting does not have a large impact on how children turn out. An incendiary claim, to be sure, but if you can bear with me until the close of this article I think I might be able to persuade you — or at the very least chip away at your certainty about parental influence.

First, what if later today the phone were to ring and the voice at the other end informed you that you have an identical twin. You would have lived your entire life up to that point not realising that you had a clone. The bearer of this news says arrangements have been made to reunite you with your long-lost sibling. In something of a daze, you assent, realising as you hang up that you’ve just agreed to meet a perfect stranger.

There was a time when separating identical twins at birth, while infrequent, did happen thanks to the harsh nature of adoption systems. One of the people who helped reunite many of them was the great psychologist Thomas Bouchard. I first read about Professor Bouchard’s work, wonderfully described by the psychologist Nancy Segal, when I was a graduate student. I still think about it often. What would it be like to live a large chunk of my life not knowing that I had a twin, and then meet him as an adult? Would our conversations ever go beyond polite small talk about the weather, sport or current events?

I’m sure similar thoughts went through the minds of the people in Bouchard’s study, and yet person after person realised — happily, I suspect — that they had a lot in common with the image of themselves sitting across the table. Their characters were often remarkably in step, as were their intellects, their behaviours, even their hobbies and eccentricities. The similarities often ran deep, cutting to the bone of their beliefs and their morality.

Our intuition sometimes seems to testify against the work of Bouchard and his team. The emphasis on nurture dictates that identical twins, reared apart and reunited later in life, should not be all that similar. And yet they are. Contrastingly, adopted children who share no distinguishing DNA with one another but are raised together should be quite similar. Yet they are not, and this poses some problems for traditional ideas about how parents shape children.

It’s not just Bouchard’s work that suggests parents have less influence than we think. Decades of research into behavioural genetics — twin studies, family studies and the adoption and identical-twin stories I have already mentioned — all point in the same direction. The shared environment, the experiences that create similarities between siblings raised together — the part of the environment that most often captures parenting influences — are all secondary when it comes to personality, behaviour or intelligence. What’s more, my own work as a criminologist, and that of my colleagues, has revealed the same pattern of findings when applied to violence, antisocial behaviour and crime.

This apparent puzzle (which is something of a scientific heresy) becomes clearer if we accept that genetic factors play an important role in making us who we are. Yes, the environment matters, but not just the environment that the child experiences in the home. The environment in this sense is far more nebulous and hard to nail down — behavioural geneticists call it the ‘non-shared’ environment and it includes anything that causes two siblings to be different from each other. And I really mean anything. The psychologist Steven Pinker puts it this way: ‘A cosmic ray mutates a stretch of DNA, a neurotransmitter zigs instead of zags, the growth cone of an axon goes left instead of right, and one identical twin’s brain might gel into a slightly different configuration from the other’s.’ In other words, we should not presume that random chance plays a vanishingly small role in making us the people that we are today.

Beyond the randomness of life, we already have a window on to what parts of culture children are swayed by. Both Pinker and the psychologist Judith Rich Harris remind us that the children of immigrants adopt and speak with the accent and language of their peers. The movies people watch, the music we listen to, and much else that we’d put under the general heading of ‘culture’ are deeply affected by our peers. What else would you expect, really? Wanting and needing to fit in is not just a passing phase of childhood. To some extent, it’s essential for living.

So ‘the environment’ does play a role in shaping who we are, but it’s not ‘the environment’ in merely the conventional sense of how your folks parent you and your siblings.

All of this is indicative of something deeper — an aspect which is less arcane and more relevant to daily life. A great many pundits, advice givers, and professional psychologists have spent decades being wrong about why people turn out the way they do.

A child is not a blank canvas. How many books have been written about the way people should and should not parent their children? How many approaches have been suggested by experts who are not really in a position to know? Yes, they may hold advanced degrees, but the truth is that the advice they offer tends to ignore the genetic influences that we now know to be at work. The studies that identify those influences often find that parenting — unless it is actually malign — has very little impact on how children turn out. The huge ‘parenting advice’ industry is largely bunkum.

What does this mean for you if you’re a parent wanting to know how to raise a happy, well-adjusted child? I generally loathe parenting advice columns, so that is not what is on offer here. I can sympathise with the idea that having a child brings with it a host of responsibilities that are exciting but also terrifying.

At this point, I would turn again to the psychologist Judith Rich Harris, who authored the definitive book on this subject. Harris writes: ‘We may not hold their tomorrows in our hands but we surely hold their todays, and we have the power to make their todays very miserable.’

Pinker, meanwhile, makes the point that it should be enough for us to remember that our children are human beings, worthy of the same ethical treatment we give to our friends, other relatives, and even to strangers. So protect your children, provide for them, be good to them, and make memories with them. Apart from that, don’t expect to have very much say in how they turn out.