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Are our IQs set to increase forever, or are we on the cusp of decline? David Robson explores the past, present and future of intelligence.

You may not have noticed, but we are living in an intellectual golden age.

Since the intelligence test was invented more than 100 years ago, our IQ scores have been steadily increasing. Even the average person today would have been considered a genius compared to someone born in 1919 – a phenomenon known as the Flynn effect.

We may have to enjoy it while we can. The most recent evidence suggests that this trend may now be slowing. It may even be reversing, meaning that we have already passed the summit of human intellectual potential.

Can we have really reached peak intelligence? And if that is the case, what can the subsequent decline mean for the future of humanity?

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Let’s begin by exploring the ancient origins of human intelligence, from the moment our ancestors began to walk upright more than three million years ago. Scans of fossil skulls suggest that the brains of the first bipedal apes, Australopithecus, were about 400 cubic centimetres – just a third the size of modern humans’.

That comes at a serious cost. The brains of modern humans consume around 20% of the body’s energy, so our bigger brains must have offered some serious benefits to make up for those excess calories.

according to one leading theory, it was a response to the increasing cognitive demands of group living.

From Australopithecus onwards, human ancestors began to congregate in bigger and bigger groups – perhaps, initially, as a protection against predators, which would have been a serious risk once they began sleeping on the ground rather than the trees. It would also allow individuals to pool resources – helping to spread out some of the risks of living in a changeable environment – and provide shared childcare.

For humans today, a lack of social understanding causes embarrassment; for our ancestors, it was a matter of life or death

But as many of us know from our own social circles, living with other people can be hard work: you need to keep track of each person’s personalities, their likes and dislikes, and whether or not they can be trusted with gossip. And if you are working on a group activity, like hunting, you need to be able to follow what each member is doing as you coordinate your activities. For humans today, a lack of social understanding causes embarrassment; for our ancestors, it was a matter of life or death.

Besides presenting those immediate challenges, the larger social groups would have allowed members to share ideas and build on each other’s inventions, resulting in new technological and cultural innovations, such as tools that could improve the efficiency of hunting. And for that to work, you need to have the intelligence to observe and learn from others – providing another push for greater brainpower.

By around 400,000 years ago, the brain of Homo heidelbergensis had reached around 1,200 cubic centimetres – just a shade smaller than the brains of modern humans, which are around 1,300 cubic centimetres. When our ancestors left Africa around 70,000 years ago, they were smart enough to adapt to life in almost every corner of the planet. The astonishing cave art suggests they were fully capable of thinking about huge cosmological questions – including, perhaps, their own origins.

Few experts would argue that the more recent changes to IQ are the product of this kind of genetic evolution – the timescales are simply too short.

It was only 100 years ago, after all, that scientists first invented the “intelligence quotient” to measure someone’s intellectual potential. Their success relies on the fact that many cognitive abilities are correlated. So your ability to perform spatial reasoning or pattern recognition is linked to your maths ability and your verbal prowess, and so on. For this reason, IQ is thought to reflect a “general intelligence” – a kind of underlying brainpower.

IQ is thought to reflect a “general intelligence” – a kind of underlying brainpower

Although IQ tests are often criticised, a vast body of research shows that their scores can be useful indicators of your performance on many tasks. They are especially good at predicting academic success (which is not surprising, considering that they were initially designed to be used in schools) but also predict how quickly you pick up new skills in the workplace. They are not a perfect measure, by any means – and many other factors will also shape your success – but in general they do show a meaningful difference in people’s capacity to learn and process complex information.

The rise in IQs seems to have started in the early 20th Century, but it’s only relatively recently that psychologists have started taking much notice of the phenomenon. That’s because IQ scores are “standardised” – meaning that after people take the test, their raw scores are transformed to ensure that the median of the population always remains 100. This allows you to compare people who took different forms of the IQ test, but unless you look at sources of the data, it means you would not notice differences between generations.

When the researcher James Flynn looked at scores over the past century, he discovered a steady increase – the equivalent of around three points a decade. Today, that has amounted to 30 points in some countries.

Although the cause of the Flynn effect is still a matter of debate, it must be due to multiple environmental factors rather than a genetic shift.

Perhaps the best comparison is our change in height: we are 11cm (around 5 inches) taller today than in the 19th Century, for instance – but that doesn’t mean our genes have changed; it just means our overall health has changed.

Indeed, some of the same factors may underlie both shifts. Improved medicine, reducing the prevalence of childhood infections, and more nutritious diets, should have helped our bodies to grow taller and our brains to grow smarter, for instance. Some have posited that the increase in IQ might also be due to a reduction of the lead in petrol, which may have stunted cognitive development in the past. The cleaner our fuels, the smarter we became.

Whatever the cause of the Flynn effect, we may have already reached the end of this era – with the rise in IQs stalling

This is unlikely to be the complete picture, however, since our societies have also seen enormous shifts in our intellectual environment, which may now train abstract thinking and reasoning from a young age. In education, for instance, most children are taught to think in terms of abstract categories (whether animals are mammals or reptiles, for instance). We also lean on increasingly abstract thinking to cope with modern technology. Just think about a computer and all the symbols you have to recognise and manipulate to do even the simplest task. Growing up immersed in this kind of thinking should allow everyone to cultivate the skills needed to perform well in an IQ test.

Whatever the cause of the Flynn effect, there is evidence that we may have already reached the end of this era – with the rise in IQs stalling and even reversing. If you look at Finland, Norway and Denmark, for instance, the turning point appears to have occurred in the mid-90s, after which average IQs dropped by around 0.2 points a year. That would amount to a seven-point difference between generations.

Partly because they have emerged so recently, these trends are even harder to explain than the original Flynn effect. One possibility is that education has become slightly less stimulating than it once was – or at least, has not targeted the same skills. Some of the IQ tests used have assessed people’s mental arithmetic, for instance – but as Ole Rogeberg at the University of Oslo points out to me, students are probably more used to using calculators.

For now, it seems clear that our culture can shape our minds in mysterious ways.


This article is part of a BBC Future series about the long view of humanity, which aims to stand back from the daily news cycle and widen the lens of our current place in time.

Modern society is suffering from “temporal exhaustion”, the sociologist Elise Boulding once said. “If one is mentally out of breath all the time from dealing with the present, there is no energy left for imagining the future,” she wrote.

That’s why the Deep Civilisation season is exploring what really matters in the broader arc of human history and what it means for us and our descendants.

While scientists continue to untangle the causes of those trends, it’s worth questioning what these changes in IQ actually mean for society at large. Has the IQ boost of the Flynn effect brought us the dividends we might have hoped? And if not, why not?

A special issue of the Journal of Intelligence recently raised that specific question, and in the accompanying editorial, Robert Sternberg, a psychologist at Cornell University, wrote:

People are probably better at figuring out complex cell phones and other technological innovations than they would have been at the turn of the 20th Century. But in terms of our behaviour as a society, are you impressed with what 30 points has brought us? The 2016 US presidential election was probably about as puerile as any in our history… Moreover, higher IQs have not brought with them solutions to any of the world’s or the country’s major problems – rising income disparities, widespread poverty, climate change, pollution, violence, deaths by opioid poisoning, among others.

Sternberg may be a little too pessimistic here. Medicine has made huge strides in reducing problems like infant mortality, for example, and while extreme poverty is by no means solved, it has declined globally. That’s not to mention the enormous benefits of scientific technological advances that have, of course, relied on an intelligent workforce.

He is not alone in questioning whether the Flynn effect really represented a profound improvement in our intellectual capacity, however. James Flynn himself has argued that it is probably confined to some specific reasoning skills. In the same way that different physical exercises may build different muscles – without increasing overall “fitness” – we have been exercising certain kinds of abstract thinking, but that hasn’t necessarily improved all cognitive skills equally. And some of those other, less well-cultivated, abilities could be essential for improving the world in the future.

Take creativity. When researchers such as Sternberg discuss creativity, they are not just talking about artistic expression, but more grounded skills. How easily can you generate novel solutions to a problem? And how good is your “counterfactual thinking” – the ability to consider hypothetical scenarios that haven’t yet come to pass.

Intelligence should certainly help us to be more creative, but we do not see a rise in some measures of individual creative thinking over time, as our IQs increased. Whatever caused the Flynn effect, it hasn’t also encouraged us each to think in new and original ways.

You might assume that the more intelligent you are, the more rational you are, but it’s not quite this simple

Then there’s the question of rationality – how well you can make optimal decisions, by weighing up evidence and discounting irrelevant information.

You might assume that the more intelligent you are, the more rational you are, but it’s not quite this simple. While a higher IQ correlates with skills such as numeracy, which is essential to understanding probabilities and weighing up risks, there are still many elements of rational decision making that cannot be accounted for by a lack of intelligence.

Consider the abundant literature on our cognitive biases. Something that is presented as “95% fat-free” sounds healthier than “5% fat”, for instance – a phenomenon known as the framing bias. It is now clear that a high IQ does little to help you avoid this kind of flaw, meaning that even the smartest people can be swayed by misleading messages.

People with high IQs are also just as susceptible to the confirmation bias – our tendency to only consider the information that supports our pre-existing opinions, while ignoring facts that might contradict our views. That’s a serious issue when we start talking about things like politics.

Nor can a high IQ protect you from the sunk cost bias – the tendency to throw more resources into a failing project, even if it would be better to cut your losses – a serious issue in any business. (This was, famously, the bias that led the British and French governments to continue funding Concorde planes, despite increasing evidence that it would be a commercial disaster.)

Highly intelligent people are also not much better at tests of “temporal discounting”, which require you to forgo short-term gains for greater long-term benefits. That’s essential, if you want to ensure your comfort for the future.

Besides a resistance to these kinds of biases, there are also more general critical thinking skills – such as the capacity to challenge your assumptions, identify missing information, and look for alternative explanations for events before drawing conclusions. These are crucial to good thinking, but they do not correlate very strongly with IQ, and do not necessarily come with higher education. One study in the USA found almost no improvement in critical thinking throughout many people’s degrees.

Given these looser correlations, it would make sense that the rise in IQs has not been accompanied by a similarly miraculous improvement in all kinds of decision making.

As I explain in my book on the subject, a lack of rationality and critical thinking can explain why financial fraud is still commonplace, and the reason that millions of people dish out money on quack medicines or take unnecessary health risks.

For our society, it can lead to medical errors and miscarriages of justice. It may have even contributed to disasters like the Deepwater Horizon oil spill and global financial crises. It is also contributing to the spread of fake news, and the huge political polarisation on issues like climate change – preventing us from finding an agreed solution before it is too late.

Considering the sweep of human history to date, then, we can see how our brains grew to live in increasingly complex societies. And modern life, while allowing us to think more abstractly, does not appear to have corrected our irrational tendencies. We have assumed that smart people naturally absorb good decision making as they go through life – but it is now clear that is not the case.

Looking to the future, the “reverse Flynn effect” and the potential drop in IQs should certainly cause us to take stock of the ways we are using our brains, and preventing any further decline should undoubtedly be a priority for the future. But we might also make a more concerted and deliberate effort to improve those other essential skills too that do not necessarily come with a higher IQ.

We now know that this kind of thinking can be taught – but it needs deliberate and careful instruction. Promising studies of doctors’ decision making, for instance, suggest that common cognitive errors can be avoided if they are taught to be more reflective about their thinking. That could save countless lives.

But why not teach these skills in early education? Wandi Bruine de Bruin, now based at Leeds University Business School, and colleagues have shown that discussions of decision making errors can be incorporated in the history curriculum of high school students, for instance. Not only did it improve their performance of a subsequent test of rationality; it also boosted their learning of the historical facts too.

Others have attempted to revitalise the teaching of critical thinking in schools and universities – for instance, a discussion of common conspiracy theories teaches students the principles of good reasoning, such as how to identify common logical fallacies and how to weigh up evidence. Having taken those lessons, the students appear to be more sceptical of misinformation in general – including fake news.

These successes are just a small indication of what can be done, if rationality and critical thinking are given the same kind of respect we have traditionally afforded our other cognitive abilities.

Ideally, we might then start to see a steep rise in rationality – and even wisdom – in tandem with the Flynn effect. If so, the temporary blip in our IQ scores need not represent the end of an intellectual golden age – but its beginning.


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