Have humans passed peak brain power?

What is intelligence? This may sound like a straightforward question with a straightforward answer — the Oxford English Dictionary defines it as “a capacity to understand” — but that definition itself raises an increasingly relevant question in the modern world. What happens if the extent to which we can practically apply that capacity is diminishing? Evidence is mounting that something exactly like this has been happening to the human intellect over the past decade or so.

Nobody would argue that the fundamental biology of the human brain has changed in that far-too-short time span. However, across a range of tests, the average person’s ability to reason and solve novel problems appears to have peaked in the early 2010s and has been declining ever since.

When the latest round of analysis from PISA, the OECD’s international benchmarking test for performance by 15-year-olds in reading, mathematics and science tests, was released, the focus understandably fell on the role of the Covid pandemic in disrupting education. But this masked a longer-term and broader deterioration.

Longer-term in the sense that scores for all three subjects tended to peak around 2012. In many cases, they fell further between 2012 and 2018 than they did during the pandemic-affected years. And broader in that this decline in measures of reasoning and problem-solving is not confined to teenagers. Adults show a similar pattern, with declines visible across all age groups in last year’s update of the OECD’s flagship assessment of trends in adult skills.

Given its importance, there has been remarkably little consistent long-running research on human attention or mental capacity. But there is a rare exception: every year since the 1980s, the Monitoring the Future study has been asking 18-year-olds whether they have difficulty thinking, concentrating or learning new things. The share of final year high school students who report difficulties was stable throughout the 1990s and 2000s, but began a rapid upward climb in the mid-2010s.

This inflection point is noteworthy not only for being similar to performance on tests of intelligence and reasoning but because it coincides with another broader development: our changing relationship with information, available constantly online.

Part of what we’re looking at here is likely to be a result of the ongoing transition away from text and towards visual media — the shift towards a “post-literate” society spent obsessively on our screens.

The decline of reading is certainly real — in 2022 the share of Americans who reported reading a book in the past year fell below half.

Particularly striking however is that we see this alongside decreasing performance in the application of numeracy and other forms of problem-solving in most countries.

In one particularly eye-opening statistic, the share of adults who are unable to “use mathematical reasoning when reviewing and evaluating the validity of statements” has climbed to 25 per cent on average in high-income countries, and 35 per cent in the US.

So we appear to be looking less at the decline of reading per se, and more at a broader erosion in human capacity for mental focus and application.

Most discussion about the societal impacts of digital media focuses on the rise of smartphones and social media. But the change in human capacity for focused thought coincides with something more fundamental: a shift in our relationship with information.

We have moved from finite web pages to infinite, constantly refreshed feeds and a constant barrage of notifications. We no longer spend as much time actively browsing the web and interacting with people we know but instead are presented with a torrent of content. This represents a move from self-directed behaviour to passive consumption and constant context-switching.

Research finds that active, intentional use of digital technologies is often benign or even beneficial. Whereas the behaviours that have taken off in recent years have been shown to affect everything from our ability to process verbal information, to attention, working memory and self-regulation.

The good news is that underlying human intellectual capacity is surely undimmed. But outcomes are a function of both potential and execution. For too many of us the digital environment is hampering the latter.

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