We tend to assume that our intelligence is simply a matter of nature and nurture – but as the celebrated psychologist James Flynn explains to BBC Future, many other factors can stunt or boost your IQ, right down to the person you choose to marry.

James Flynn is worried about leaving the world to millennials. As a professor at the University of Otago in New Zealand, he regularly meets bright students with enormous potential, only to find that many of them aren’t engaging with the complex past of the world around them.

“They have all these modern skills and yet they come out of university no different than the medieval peasant who is anchored in his own little world,” he tells me mid-way through our conversation. “Well, actually they are anchored in a much bigger world – the world of the present – but with no historical dimension.” The result, he thinks, is that we have overly simplistic views of current issues, leaving us open to manipulation by politicians and the media.

We are talking in the living room of his son Victor, who is a mathematician at the University of Oxford, during a flying visit from his home in New Zealand. Open on the sofa is his latest reading, Alice Munro’s Runaway, the result of a recent foray into literary criticism – again, with the hope that he can encourage younger people to look beyond their smartphone screens. “I have a second book out this year that says to young people ‘for god’s sake, you are educated, why don’t you read!’” he tells me. When he was young, he says, “girls wouldn’t date you if you hadn’t read the recent novels”.

I am here to discuss his latest book, Does Your Family Make You Smarter? It is a wide ranging conversation on the ways that human thinking has changed over time, including a mysterious rise in IQ – the “Flynn Effect” for which he is now best known – and the various competing influences that shape our intellect over our lifetime.

At 82, Flynn is now a towering figure in intelligence research, but it was only meant to be a short distraction, he says. “I’m a moral philosopher who dabbles in psychology,” he says. “And by dabbling I mean it’s taken over half my time for the past 30 years.” As part of this philosophical research on the nature of objectivity, he came across dubious claims that certain races are intellectually inferior. Examining the evidence, he saw that the average scores for everyone – black and white alike – had been rising consistently by around three points a decade. Yet few people had noted on the fact.

Why aren’t psychologists dancing in the street over this? What the hell is going on? – James Flynn

“I thought, why aren’t psychologists dancing in the street over this? What the hell is going on?” These were no small, incremental, improvements – between 1934 and 1964, the Dutch had gained 20 points – yet it had been ignored by the very people administering the tests. “It was sitting there right in front of their noses and they didn’t see it.”

Psychologists had long known that our genes play a role in our intelligence, and that its influence only increases as we get older. At kindergarten, genetics matter relatively little: what’s more important is whether your parents talk to you, read to you and practise things like counting. Sure enough, twin studies suggest that your genes account for about 20% of the variation in IQ at this age.

As you grow up and begin to think for yourself, however, your parents’ influence wears off. You spend most of your time at school anyway, and if you have the potential, your brain will develop in line with the extra stimulation. Your genes may also push you to find new ways to stimulate your mind yourself – you might pursue more intellectually demanding pastimes, join a book club, or you might be selected for a harder maths class, which should in turn raise your score. So you begin to create your own niche that reflects your genetic potential. That’s not to say that your family background doesn’t count at all – it still matters if you attend a better school or if your parents buy you lots of books. And chance factors can add up; if you find yourself unemployed or beset by a personal tragedy, your IQ may take a blow. But overall, as an adult your genes can predict about 80% of the differences between you and the next person.

Yet the Flynn Effect was just too pronounced and too rapid to be explained by changing genes; natural selection happens slowly across thousands of years. So what could it be? Other psychologists were dumbfounded. “They were so wedded to the notion that intelligence only changed slowly that they couldn’t see what was in front of them.”

In fact, the answer is not so puzzling if you compare it to another trait that has slowly grown over the decades: body height. Within one generation you will find that tall parents have taller children, and short parents have shorter children, showing a large genetic component; but if you compare different generations, you will find we are all much taller than our grandparents – and that’s not because our genes have changed. It’s because modern life, with better medicine and diet, has allowed our bodies to grow.

Scientific spectacles

Flynn and his colleague William Dickens have hypothesised that exactly the same thing was happening to our minds thanks to shifts in the cognitive demands of our society. IQ measures a variety of qualities, such as vocabulary, spatial reasoning and the ability to think abstractly and recognise categories, which together are meant to reflect a “general intelligence”. And even though we are not schooled in all these skills explicitly, our education nevertheless exercises a more abstract way of seeing the world that could help us with that task.

Just think of the elementary school lessons that lead us to consider the different branches of the tree of life, the different elements and the forces of nature – we are slowly beginning to group things together into categories and classes and logical rules, which is central to many questions on the IQ test. The more children are asked to view the world through these “scientific spectacles”, the higher they will score, Flynn suggests. “Society makes highly different demands on us over time, and people have to respond.”

But it’s not just education; some researchers have argued that our whole world is now engineered to make us think in this way, thanks to an increasing reliance on technology. Where our great-grandparents may have grappled with typewriters, our parents struggled to program their video recorder, while children today learn to use a touchscreen from an early age. Even reading the schematic London Underground map may have been tough for someone in the 1900s who was used to seeing the world more literally, Flynn says. This progression has forced us to think in hierarchies and symbols, to learn how to follow rules and draw analogies – and it is now so widespread that we forget the cognitive leaps it requires.

We are fine-tuning the mental machinery rather than upgrading it

As a consequence, we all became a bit better at thinking abstractly, leading to an increase of at least 30 points over the last century. The rise in IQ may not mean we have ramped up our raw brainpower – we are fine-tuning our ancient mental machinery for the modern world, rather than upgrading it completely – but he argues that the improvements are “sociologically significant”, reflecting real changes in thinking. The Flynn Effect seems to predict a country’s rising economic performance, for instance. “If the gains were hollow, they couldn’t do that,” he says.

Flynn compares it to physical exercise – we are shaped by our chosen sport. “The brain is a muscle – and a change in mental exercise influences the brain just as much as if you gave up swimming for weightlifting.”

Crucially, IQ is malleable over a lifetime. This means that the elderly can still gain ground, thanks to better overall health (which is linked to intelligence) and longer-lasting, more intellectually demanding careers keeping their brains active for longer and forestalling decline. “There has been such an enormous improvement that today someone of 70 just kills a person [of the same age] 15 years ago,” he says. Overall, the rate is about 11 points a decade, he says. Flynn himself could be proof of this. “My father never ran a step after 12 and he retired at 70. I exercise more and I’ve never retired.” The result is a healthier brain and more active mind.

Flynn’s latest book is an attempt to fill in some of the gaps left in this picture, using an ingenious new analysis that allows him to break down the effects depending on the person at hand, and the particular skills it will effect. Consider the part of the IQ test that measures vocabulary. Having more educated parents, who talk with more varied and erudite language, will help give a boost even to people with little genetic potential; conversely, people with a genetic advantage may find themselves dragged down by those around them (just think of Lisa Simpson).

The differences are small enough that many would like to ignore them, but Flynn’s analysis shows that even a few IQ points can determine your path in life. For a fairly bright kid entering university in America, for instance, living in a slightly more academic home could push their score from 500 to 566 on the SAT exams, for instance – the difference between a place at a prestigious or more mediocre college. “Universities use the SAT as their measure of the viability of the student and if you are lousy on that you won’t go to UCLA, or if you do you will probably flunk out in the first year.”

Flynn is not a defeatist: no matter what our family background, we all have the power to take our intellectual development into our own hands. After all, the studies show that our circumstances today shape our current IQ more than our past history. This is apparent, he says, with his mature students. “Plenty of people come to us from environments that look as if they provide very little intellectual stimulation, and compared to our average students, they gain like crazy.”

The major intellectual thing that disturbs me is that young people like you are reading less history and less serious novels than you used to – James Flynn

I ask him how else I could hope to get a brain boost. “You can marry a partner, not because they look like a star, but because you found them intellectually challenging,” he advises me. “They would introduce you into a world of ideas and peers that would make your life far more interesting.”

Which brings us round to his concerns about millennials. Despite the gains in IQ, he worries that we aren’t engaging our minds effectively on the issues that matter. “I’m not being gloomy but actually the major intellectual thing that disturbs me is that young people like you are reading less history and less serious novels than you used to,” he says, arguing that we should have a background in the crises that have shaped world history before we form opinions on current politics. He chastises me for my lack of knowledge of Europe’s Thirty Years’ War, for instance, which he believes has many parallels with today’s conflicts in the Middle East. (His criticism is perfectly fair, and he is persuasive enough to convince me to fill the gaps in my knowledge.)

George Orwell, he says, painted a dystopia where the government rewrites history to control and manipulate the population. “But all you need are ‘ahistorical’ people who then live in the bubble of the present, and by fashioning that bubble the government and the media can do anything they want with them,” Flynn adds.

In other words, our IQs may have risen, but this hasn’t made us any wiser. “Reading literature and reading history is the only thing that’s going to capitalise on the IQ gains of the 20th Century and make them politically relevant.” You may or may not agree, but Flynn is not the only person with this concern: as William Poundstone shows in his latest book Head In The Clouds, everyday ignorance is influencing the way we make decisions in many areas of our lives.

Whether or not Flynn will persuade young people to pick up a book, there’s no doubting that he has forever changed our views of intelligence. “Today I think I’m leaving a field where you can write genuine cognitive history,” he says – meaning that we can finally track and explain the ways the mind has changed and responded to our environment over time.

At 82, however, he hopes that other scientists will continue this work, as he plans to spend the rest of his career writing about philosophy and politics. The question of IQ was, after all, only ever supposed to be a temporary distraction. “I got sucked into this area accidentally and now thank God I may get out of it again.”

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David Robson is BBC Future’s feature writer. He is @d_a_robson on Twitter. James Flynn’s latest book Does Your Family Make You Smarter? is out now from Cambridge University Press.

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