Category: Neuroscience

People with a bigger brain score better on cognitive tests, but the association is extremely small.

A bigger brain is, on average, more intelligent, a study of over 13,600 people has found (Nave et al., 2018).

The brain scans revealed that people with larger brains do indeed score better on cognitive tests.

However, the association is only very small, explained Dr Gideon Nave, the study’s first author:

“On average, a person with a larger brain will tend to perform better on tests of cognition than one with a smaller brain.

But size is only a small part of the picture, explaining about 2 percent of the variability in test performance.

For educational attainment the effect was even smaller: an additional ‘cup’ (100 square centimeters) of brain would increase an average person’s years of schooling by less than five months.”

Men have bigger brains than women

Men’s brains are, on average, 7 percent bigger than women’s brains.

So, are we saying that men are, on average 7 percent more intelligent than women?

Certainly not!

Dr Nave explained:

“Just like with height, there is a pretty substantial difference between males and females in brain volume, but this doesn’t translate into a difference in cognitive performance.”

In fact, there is very little measurable difference between men and women in their IQ, despite men having larger brains.

The disparity may be explained by some studies that find that the cerebral cortex is thicker in women.

The cerebral cortex is the outermost layer of the brain, which does most of our high level thinking.

Dr Nave said:

“This might account for the fact that, despite having relatively smaller brains on average, there is no effective difference in cognitive performance between males and females.

And of course, many other things could be going on.”

Big brain vs small brain

Despite all this, the link between a bigger brain and intelligence is certainly attractive in the first instance.

For example, imagine you measure both the bodies and brains of all the primates on Earth bar humans: beasties like bonobos, chimps and gorillas.

Then, using this ratio and based on the average human’s size, you estimate how big a human brain should be.

To check your estimate you decide to open up your friend’s head to take a peek inside.

When you do, you’re mighty surprised to find a brain about three times larger than you were expecting.

“Aha,” you say, “This is where our amazing capacity for language, emotion, social organisation and creativity comes from.”

Naturally, then, it’s an attractive idea that the bigger the brain, the more able the animal.

This argument soon breaks down, though, when you try chatting to an elephant – an animal with a brain three times the size of ours.

Political problems

OK, you might say, it doesn’t work across species, but maybe it works within species.

Well, now trouble is not far away, and here’s two reasons why:

1. As noted above, men’s brains are generally bigger than women’s, on average by 100 grams (say about 7 percent bigger).
2. Different races have different head sizes with Asian children averaging the largest at birth followed by White children, leaving Black babies with the smallest heads.

So you see the kind of dangerous, shark-infested waters we’re now swimming in?

This is no longer just science, it’s political; with claims to the answer potentially being seen as both sexist and racist.

A bigger brain not significantly better

This is why I’m more than a little relieved to report the view of neuroscientist Dr David P. Carey who has reviewed the research in this area and finds little evidence for the claim that bigger brains mean greater abilities (Carey, 2007).

He argues that the evidence from neuroimaging, behavioural genetics and comparative cognition is largely unconvincing:

“I have little confidence that looking at a sophisticated twenty-first century brain scan (in any number of impossibly sophisticated ways) of a collaborator, competitor or any old conspecific [other human] is going to tell me anything meaningful at all about their capabilities to perform in any cognitive way, psychometric or not.”

Intelligence sceptics

A second layer of scepticism about the bigger brain/intelligence connection is captured by an old joke that goes like this:

Q: What is intelligence?
A: Whatever intelligence tests measure.

The joke expresses a scepticism many harbour towards measures of intelligence.

Does intelligence really tell us anything useful about a person, or does it just tell us how good they are at taking intelligence tests?

The jury is very much out on this point.

The originators and manufacturers of intelligence tests will tell you they are good predictors of people’s real-world performance, while many others are not so sure.

In fact, you’ll likely hear equally strong answers from equally well-qualified people that are completely contradictory.

It’s not how big it is…

The default position should be a high level of scepticism about any claims for a relationship between a bigger brain and ability.

This is because:

1. The connection between a bigger brain and intelligence is largely unproven, and;
2. The relationship between measures of intelligence and real-world functioning and behaviour is highly contentious.

So, there you have, confirmation of the oldest defence in the book: it’s not how big it is, it’s what you do with it.

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How much of our brain do we use? Certainly way more than the 10 percentage points suggested by the myth and here’s why…

How much of our brain do we use?

Unfortunately, it is a pure myth that we only use 10 percent of our brain.

The idea that we only use 10 percent of our brain is probably such an enduring mind myth because it’s comforting to think we have spare capacity.

The ‘unused’ 90 percent of our brain could take up the slack after brain injury or offer the possibility for miraculous self-improvement.

This flexible factoid has been used not only to sell products to enhance our brain’s performance, but also by psychics like Yuri Geller to explain mystical cutlery bending powers.

How much of our brain do we use?

Unfortunately, the idea we only use 10 percent of our brain is almost certainly false.

Here are four good reasons (Beyerstein, 1999):

1. If we only use 10 percent of our brains then damage to some parts of our brains should have no effect on us. As any neurologist will tell you, this is patently not true.
2. From an evolutionary perspective it is highly unlikely we developed a resource-guzzling organ, of which we only use 10 percent.
3. Brain imaging such as CAT, PET and fMRI shows that even while asleep there aren’t any areas of our brain that completely ‘switch off’.
4. Parts of the body that aren’t used soon shrivel and die. Same goes for the brain. Any neurons we weren’t using would soon shrivel and die.

Therefore, we must use way more than 10 percent.

New Age optimism

Despite these facts, the myth is constantly fuelled by New Agers hoping to unlock the untapped, hidden forces that will unleash previously unimagined human potential.

Just when all the evidence has been marshalled against its original incarnation, showing that, yes, actually we do physically use all our brains, it turns out ‘human potential’ can’t be measured empirically.

Apparently the unused 90 percent is hidden below the surface, out of sight and almost out of mind.

Which is convenient.

Scientific scepticism

The structure of the brain and its metabolic processes have been carefully examined, along with the diseases that afflict it.

None of this work has suggested there is a hidden percentage of our brain that we’re not using.

Anyone who still maintains we only use 10 percent of our brains after this fusillade of fact has to come up with a counter-argument for each one of these.

Actually, you might argue that imaging technology is rubbish or the neurons are only working at 10 percent capacity, but refuting all these facts, taken together?

Now that’s tricky.

Roots of the 10 percent brain myth

The roots of this myth about how much of our brains we use are very difficult to discern, probably because there are so many different, diffuse stories about its origin.

One apocryphal story is that Einstein once explained his brilliance by saying he used more than 10 percent of his brain, compared to the rest of us mere mortals (Wanjek, 2003).

Despite probably being based on a misquote, the repeating of this story can’t have hurt the 10 percent brain myth’s power.

Perhaps some of the earliest roots of the idea that we only use 10 percent of our brain comes from work by physiologists in the 1870s.

They routinely applied electrical currents to the brain to see which muscles moved.

They found that large parts of the human brain could be zapped without any corresponding bodily twitching.

This led them to dub parts of the brain ‘silent’.

But they didn’t mean silent in the sense of inactive, just that it didn’t make any muscles move.

Of course this didn’t stop the phrase being misinterpreted.

The first sighting of the myth

The actual confirmed first written sighting of the myth about how much of our brain we us, though, is in a 1940s advert for the book Cold Comfort Farm by Stella Gibbons (Wanjek, 2003, p.21):

“What’s holding you back? Just one fact — one scientific fact.

That is all.

Because, as Science says, you are using only one-tenth of your real brain-power!”

Whatever its provenance, the myth about how much of our brain we use is certainly a slippery customer.

The reason is two-pronged: first, it’s impossible to prove something doesn’t exist and second, people like to believe it.

If I say I’ve seen a Pegasus, or visited Mars, or that all our brains have huge untapped potential, you can’t definitively prove me wrong.

That’s why, despite a few good solid blows to the head, this myth refuses to go down.

Perhaps putting it the other way around might deliver the knock-out blow.

Instead of talking about the 90 percent of untapped potential, just ask people why they only use 10 percent of their brains.

Would anyone seriously admit to that?

I, for one, am working at maximum capacity.

Well, most of the time anyway…

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