Your typical adult from 1900 was pretty dumb, by today’s standards. Yank one off the street and run them through a modern standardised intelligence test like Raven’s Progressive Matrices or a Wechsler Intelligence Scale and they’d probably score an IQ of about 70. Given that the median score in these tests today is 100, and an IQ of 70 is often regarded as a sign of intellectual disability, that bodes ill for our recent ancestors.

It seems that we’re a lot smarter today than we were in 1900, and we’re getting smarter by the year. This phenomenon is known as the Flynn effect: every decade that passes sees the average IQ in developed countries rise by about three points.

However, the gains haven’t been across the board. Tests that focus on abstract reasoning, conceptual categorisation and dealing with hypothetical situations have all seen the greatest gains. Others focusing on arithmetic, vocabulary and general knowledge have remained fairly flat.

So are we really getting smarter? What could be behind the observed IQ inflation? And why are there gains in some areas but not in others?

In a way, intellectual progress is not surprising. If you had to summarise the history of our species in three words it would be: ‘explosive intellectual growth’. Consider that a few million years ago the last common ancestor of chimpanzees and humans looked a heck of a lot like chimps still do today. Chimps haven’t changed terribly much over a few million years, but we have changed a great deal. Our greatest transformation has not been standing upright or losing most of our hair, it has been in the blossoming of our minds.

However, this intellectual growth has not only been in terms of raw brainpower, but also in fundamentally changing the way we think compared to our primate brethren. Brains are expensive things to grow and maintain. At some point it simply wasn’t tenable to make them any larger. So we extended our minds in other ways.

Over hundreds of millennia we have become particularly adept at pushing much of our thinking outside of our skulls and offloading it onto the world around us. We have engineered rich informational environments that actually help us to think better. We have then built upon these environments to enable new tools that lift us to even greater intellectual heights.

You could call this process ‘intellectual scaffolding’. However, with each layer, the neural foundations have to adjust to accommodate the new modes of thought. This process might even explain why IQs are rising, and why they are rising the way they are.

Things started off with the brains of our distant primate ancestors, which were largely geared towards eking out an existence in a hostile world. They came to be adept at grappling with concrete tasks like manipulating objects, navigating across the landscape and solving problems in the tangible world. On the other hand, they weren’t terribly good at maths or abstraction.

Our forebears’ intellectual explosion was triggered when they became intensely social creatures. There are plenty of benefits to living social. That oft-lambasted motivational poster that says ‘T.E.A.M.: Together Everyone Achieves More’ - gag-worthy though it is – actually has a point. There are many things we can achieve through social and cooperative living that are simply impossible alone.

However, social life also brings its own problems, largely because every individual has their own interests, values and a tendency to think they know best. Cooperation is fragile, and it can easily crumble under the weight of self-interest and conflict. Our ancestors diverged from our primate cousins after they somehow managed to maintain cooperation for long enough that it started to radically change their brains, entrenching their social nature and enabling them to offload some of their thinking on to others. Why try to figure out a problem from scratch when someone with experience can show you how they solved it? Why try to remember all the best hunting spots when you can just ask an experienced hunter?

Why try to figure out the optimal route to the next watering hole when you can just learn a song line and sing your way there?

Yet social life also placed new cognitive demands on our ancestors. Managing relationships and anticipating how other people are going to behave is, as we all know, difficult. So their brains adapted by developing whole new systems dedicated to parsing social relations, tracking reputations, gauging honesty and managing relationships. Their brains became more capable – not necessarily at navigating from one waterhole to another, but rather at managing the relationships necessary to learn the song line that guided them across the landscape.

The next step came when early humans embraced technology, which pushed our minds even further beyond our skull. Writing enabled information to be stored in a durable state that could persist over generations. A pen and paper facilitated even more complex thought than introspection or dialogue alone. Today a computer can help us perform calculations that no single mind could hope to achieve. Technology also lubricates the spread of culture, enriching the informational environment even further.

Again, our brains adapted to this new environment. A child born in this decade will be raised in a very different environment to a child raised in 1900, or 100,000 BCE. Today information and tools abound. There is far less cause for a child today to ever need to navigate by their own ken or solve concrete engineering problems, except for their own amusement. Rather, they race to acquire language, to read the words others have left for them and to manipulate symbols on screens to acquire the information they seek.

Their brains have become more capable – not necessarily at performing the old concrete tasks, but rather at managing the new technological environment necessary to perform the tasks demanded of them today. They are better at tool use rather than better at the tasks they use the tools for. Their minds are more practiced in the abstract than the concrete. They readily employ hypothetical speculation and are encouraged to engage their imagination.

It comes as no surprise that it is in these tasks that people today outperform their elders. Nor is it surprising that tests like Raven’s Progressive Matrices or the Wechsler Intelligence Scale – which focus on abstraction, comprehension and hypothetical thinking – are where the greatest gains have been seen, while concrete thinking has plateaued.

But are we really smarter? Perhaps, but not necessarily in the way the Flynn effect suggests. We have become more adept at being social and technological creatures. We have pushed our minds beyond the bounds of our skull. We now use the world to do some of the thinking for us. However in the process, we have lost the skill of interacting with the natural world.

There is no doubt that we are now dependent on technology and would be lost without it; we are also dependent on social living. Sever our social bonds and we’d be even more helpless than without our technological crutches.

What of the risks of scaffolding our minds onto the world? One is that we offload too much thinking and forget to nurture what’s inside our skull. Another is that we have become dependant on technology and the system in which we live; we have lost our survival skills. We may have unprecedented access to other people or technology to help us think, but ceasing to think for ourselves isn’t exactly a sensible strategy.

Although test results may suggest otherwise, that typical Australian adult from 1900 wasn’t intellectually disabled. They simply had a different kind of intelligence, more grounded in the concrete and less in the abstract and the hypothetical.

In the past century our minds have changed, particularly in response to technology. We may appear to be smarter because of it, but we shouldn’t let that go to our heads.