Given how it’s often discussed and described, particularly in the more brazen and annoying ads for puzzle-based app games, you’d be forgiven for assuming that intelligence is something well understood and easily measured, like your weight or height.
The truth is far more complicated, confusing, and even controversial. For one, while the dictionary definitions are fairly straightforward, describing intelligence as, for example, ‘the ability to acquire and apply knowledge and skills’, the scientific consensus on what intelligence actually is, regarding how it should be defined and assessed, is still disputed.
For a lot of recent scientific history, there was much debate as to how many intelligences the human brain possessed. As in, do we have one general intelligence that does everything, or several different types of intelligence that are used for more specific tasks? Like spatial intelligence, musical intelligence, linguistic intelligence, and so on.
Both models were the subject of much study. At present, evidence leans more in favour of us only having the one general intelligence, but as ever, the picture is more nuanced than that.
Distinctions can also be drawn between fluid and crystallised intelligence. The latter is the information you know and have access to, stored as memories in your brain. The former is your ability to use and apply information, whether derived from memory, or from what you’re perceiving in the moment.
A professional quizzer who wins contests thanks to their vast general knowledge is utilising impressive crystallised intelligence. Alternatively, Sherlock Holmes, who uses the information available from a crime scene, combines it with what he’s got in his head, and applies it to a situation to work out solutions and explanations, is relying more on fluid intelligence. In a sense, crystallised and fluid intelligence are like your computer’s hard drive and CPU, respectively.
Evidence suggests that crystallised intelligence keeps building up for as long as we’ve got a working brain, while fluid intelligence declines as we get older, as the complex but intricate parts of our brain that support it wear down over time.
Is intelligence genetic?
While there is still much debate over what intelligence actually means, few dispute that your genes play an important part. This isn’t to say that there is an established intelligence gene, which directly determines how smart you’ll end up being. Our environment, upbringing, education and experiences all shape our adult intellect.
But even so, our genes clearly play a role. Exactly what this role is remains to be pinned down, but it’s undeniable that intelligence has a hereditary component, meaning your eventual intelligence will skew towards that of your biological parents, even if you have a substantially different upbringing (by being adopted, for example). There’s also the surreal link between height and intelligence, meaning tall people tend to be more intelligent on average.
Of course, one of the reasons it’s hard to be specific or certain is because intelligence it so hard to pin down and measure. You might be surprised about this, because isn’t that what we have IQ tests for?
Technically yes, but the use and application of IQ tests has long been mired in controversy, given how no two scientists can seemingly 100 per cent agree on what intelligence actually is. And there have long been scandals and problems with IQ tests, largely because they’re created by scientists who are prey to their own biases and prejudices.
Nobody is arguing that intelligence isn’t a thing, it’s just that there’s a lot of debate around what sort of thing it is, how it works, how it’s influenced, and how it should be measured. About the only thing anyone can agree on is this; IQ and intelligence definitely can’t be determined by how well you do on a rudimentary puzzle game, no matter how many ads for apps insist otherwise.
- This article first appeared in issue 370 of BBC Science Focus Magazine – find out how to subscribe here
Read more about the brain:
- Brain food: The best foods to eat for better attention, memory and mental health
- Neuroscience says there’s no such thing as free will. A psychologist explains why that might not be true
- What is brain fog? A neuroscientist reveals what causes it and how to get rid of it
- A neuroscientist explains how your genes affect your mental health
Dean is a neuroscientist, author, blogger, occasional comedian and all-round ‘science guy’. He is the author of the the popular Guardian Science blog ‘Brain Flapping’ (now ‘Brain Yapping’ on the Cosmic Shambles Network with accompanying podcast), the bestselling books The Idiot Brain and The Happy Brain, and his first book aimed at teens, Why Your Parents Are Driving You Up the Wall and What To Do About It.