linda geddes, the truth about intelligence newscientist

Putting the political and historical baggage to one side, the latest science of intelligence is surprisingly enlightening, finds Linda Geddes
IS INTELLIGENCE something you are born with, or a skill that you can hone and develop throughout life? Is someone whose brain is packed with esoteric facts more intelligent than an artist who prompts people to see the world differently, or a mathematician who designs an algorithm that enables a computer to beat a human at chess? Is that computer more intelligent than the human?

Intelligence is a slippery concept. Even psychology textbooks on the subject are riddled with myths and errors. Yet recent research means that we are finally getting to grips with some of the key questions about intelligence. We all have skin in this game whether it be taking an IQ test for a job application, helping our children achieve their potential or simply doing the cryptic crossword. It is time to wise up.

What is intelligence?

When researchers talk about intelligence, they are referring to a specific set of skills that includes the abilities to reason, learn, plan and solve problems. The interesting thing is that people who are good at one of them tend to be good at all of them. These skills seem to reflect a broad mental capability, which has been dubbed general intelligence org.

That's not to say people don't specialise in different areas. Some will be particularly good at solving mathematical problems, others will have particularly strong verbal or spatial abilities, and so on. When it comes to intelligence tests, although these specific skills account for about half of the variation between people's performance, the other half is down to g. "If you took a sample of 1000 people and gave them all IQ tests, the people who do better on the vocabulary test will also do better, on average, on the reaction speed test, and so on," says Stuart Ritchie, an intelligence researcher at the University of Edinburgh, UK.

This seems to fly in the face of old ideas. In the early 1980s, Harvard psychologist Howard Gardner argued for the existence of multiple intelligences, including "bodily-kinaesthetic", "logical-mathematical" and "musical". However, most researchers now believe these categories reflect different blends of abilities, skills and personality traits, not all of which are related to cognitive ability. Likewise, recent research indicates that so-called emotional intelligence - the ability to regulate one's emotions and relate to other people - is simply a mixture of general intelligence and personality.

Even creativity is related to g. There is a linear correlation up to an IQ of about 120 - classified as above average intelligence - although the link breaks down after that. "The idea that you can be creative without being intelligent is a myth: it takes a certain level of intelligence to acquire raw data to be creative with," says neuropsychologist Rex Jung at the University of New Mexico.

So, what is the biological basis of g? One suggestion is that it reflects "mental energy": the brains of people with high IQs seem to use less energy when performing mental tasks, and their neurons conduct signals faster. Possibly then, clever brains are more efficient. Another idea is that smart people have greater working memories, so can hold onto and process more information at any given moment. For now, the g-factor has a lot in common with the X factor: we don't know precisely why it makes someone stand out, just that it does.

Can I become cleverer?

During the early 1990s, a paper was published in Nature revealing that students performed better on an intelligence test if they listened to Mozart while taking it. So was born the billion-dollar brain-training industry. Sadly, other researchers have been unable to replicate the "Mozart effect". Studies of computer games that claim to improve mental performance have produced mixed results too. "Brain training, Baby Einstein, and so on have been fairly disappointing in terms of being able to boost IQ" says Stuart Ritchie at the University of Edinburgh, UK.

However, one intervention has repeatedly been shown to work: education. True, intelligent children often remain in school for longer, but that can't be the whole story. During the 1960s, the Norwegian government added two extra years of compulsory education to its curriculum and rolled out the change gradually, allowing comparisons between different regions. When researchers investigated IQ scores from tests taken by all Norwegian men as part of their compulsory military service, they concluded that the additional schooling added 3.7 IQ points per year.

This pattern has been seen elsewhere. In a recent meta-analysis, Ritchie and a colleague concluded that each additional year of schooling boosted IQ by between 1 and 5 points. "That's not to say that if we left people in school forever they would all become super-geniuses; it must plateau out at some point," he says. "But given the variance in schooling we have now, education does provide some degree of boost." It might simply be that reading, studying arithmetic and accruing general knowledge are good training for the kind of abstract thinking you need to perform well in IQ tests. Schooling may also teach children to maintain their concentration. Or it could be doing something else.

Whether adult education has a similar effect is less clear. "It is plausible," says Ritchie, although it hasn't been tested directly. But not all learning is in the classroom. One study, which compared people's IQ scores at the ages of 11 and 70 found that being in a more complex job was related to being smarter in later life - even after controlling for how smart a person was to begin with. This group still had some age-related decline, but it was less pronounced than in other people. "That is evidence consistent with the 'use it or lose it' hypothesis," says Richie.

Can intelligence really be measured?

Russell Warne has spent many hours scrutinising undergraduate psychology textbooks. As a professor of psycho logy at Utah Valley University, he wasn't looking for insight, but for mistakes - and he found plenty. Some of the worst concerned IQ tests. "The most common inaccuracy I found, by far, was the claim that intelligence tests are biased against certain groups," he says. Yet intelligence researchers are at pains to ensure that IQ tests are fair and not culturally biased. "Another, very common one was the idea that intelligence is difficult to measure."

No wonder IQ tests are often considered controversial and flaky. But that simply isn't the case. "Despite the critiques, the intelligence test is one of the most reliable and solid behavioural tests ever invented," says Rex Jung at the University of New Mexico.

That said, you shouldn't trust the kind of 10-minute test that might pop up in your Facebook feed. A comprehensive IQ test takes well over an hour and is ideally administered by a professional examiner. It is designed to assess precisely those cognitive skills that constitute intelligence, so consists of a series of subtests that cover reasoning, vocabulary, mental processing speed, spatial ability and more. Shorter IQ tests, assessing fewer of these skills, can still provide a general indication of someone's mental abilities, however, because the nature of intelligence means that someone who scores highly on one type of cognitive test will also do comparatively well on others.

However, an individual's performance on an IQ test can be influenced by external factors such as motivation. And you can "game" the test by practising sample questions beforehand - although the average gain from such tutoring is just four or five points.

Is IQ up to the job?

Aside from questions over how robust the tests are, particular applications of IQ tests have also faced scrutiny. A common criticism of using them to screen job applicants is that they only measure a subset of cognitive skills. They don't expressly measure creativity, for instance. Neither do they measure personality traits such as conscientiousness - which tends to make for reliable and hard-working employees - or ability to get on with other people. However, it is rare for recruiters to test IQ in isolation: candidates might be given a personality test too and a practical exercise to assess job-related skills. They usually also have to name several referees.

What makes one person smarter than another?

One reason people may find discussing intelligence uncomfortable is the belief that it is something you are born with and so you can do nothing to influence it. This undercuts social equality, and feeds into the link between intelligence testing and eugenics, which still looms large for many.

However, there is no escaping the fact that intelligence is inherited to some degree. Researchers found that the IQ of children adopted at birth bore little correlation with that of their adoptive parents, but strongly correlated with that of their biological parents. What's more, this association became stronger as the children grew older.

"That's counter-intuitive for most people," says Robert Plomin at King's College London, who led the study. "They think as you go through life, the slings and arrows of outrageous fortune build up and environmental differences become cumulatively more important, because they think that genes only influence what happens at the moment of conception." That's not true, of course.

In fact, hundreds of studies all point in the same direction. "About 50 per cent of the difference in intelligence between people is due to genetics," he says.

But genes are not destiny

For many years, the search for specific intelligence genes proved unfruitful. Recently, however, genetic studies have grown big and powerful enough to identify at least some of the genetic underpinnings of IQ. Although each gene associated with intelligence has only a minuscule effect in isolation, the combined effect of the 500-odd genes identified so far is quite substantial. "We are still a long way from accounting for all the heritability," says Plomin, "but just in the last year we have gone from being able to account for about 1 per cent of the variance to maybe 10 per cent."

So genes matter, but they are certainly not destiny. "Genetics gives us a blueprint - it sets the limits. But it is the environment that determines where within those limits a person develops," says psychologist Russell Warne at Utah Valley University.

Consider height, another highly heritable trait. Children will grow taller if they eat a nutritious diet than if they eat a less nutritious one, because a good diet helps them achieve their full genetic potential. Likewise with intelligence. Iodine deficiency during childhood is associated with lower IQ, and addressing this in developing countries has boosted cognitive skills. So too has treating parasitic worms and removing lead from petrol.

Other environmental influences on IQ are not as obvious. Cases of abuse and neglect aside, twin studies reveal that the shared family environment has only a very small effect on cognitive ability. Plomin therefore suspects that intelligence has less to do with parenting style than chance. "It's idiosyncratic factors that make a difference," he says, "like the kid becomes ill or something like that - but even then, children tend to bounce back to their genetic trajectory."

Isn't intelligence just good for exams?

Exams are not the only route to success, as billionaire businessmen Richard Branson and Alan Sugar-who left school aged 15 and 16 -will attest. Nevertheless, good grades can open doors, and intelligence certainly helps when it comes to educational attainment. IQ test performance accounts for roughly two-thirds of the variance in people's school exam scores - other factors including motivation and mental and physical health also influence how well children do.

But intelligence isn't just useful in school. IQ predicts how people will respond to workplace training and how well they will do their job, even in non-academic professions such as being a car mechanic or carpenter. It also predicts social mobility. This is, perhaps, because general intelligence reflects people's ability to handle complexity in everyday affairs, according to Stuart Richie at the University of Edinburgh, UK. Many tasks, from supermarket shopping to juggling our diaries, require us to deal with unexpected situations, to reason and make judgements and to identify and solve problems. This is true of our social interactions too.

People who score better in IQ tests are also healthier and live longer. One explanation could be that they are better educated, so more likely to be in professional jobs that command higher salaries, helping them afford things like gym memberships and healthier foods. Another is that learning, reasoning and problem-solving skills are useful in avoiding accidents, preventing chronic disease and sticking to complex treatment regimes if you do fall ill. In addition, a lower IQ might be caused by events during fetal development or childhood - such as a blow to the head that influence health and longevity.

The downside of smarts

"Psychologists have known for a hundred years that the relationship between success economically or in school - is not perfectly correlated with IQ" says Russell Warne at Utah Valley University. "You need other skills, such as persistence. On the other hand, by most measures of economic success, being smarter is better than not being smarter."

That said, intelligence can have drawbacks. People with high IQs are more likely to be short-sighted and having an extremely high IQ has also been linked to bipolar disorder.

Are big heads smarter than pea brains?

Over human evolutionary history, our brain size has increased dramatically as our cognitive capabilities have grown. Even among modern humans, brain size accounts for around 10 per cent of the difference in intelligence scores between individuals. Big brains may simply have more neurons and so greater processing power, or the neurons may possess more bulky insulating white matter, allowing them to communicate faster.

Nevertheless, when it comes to brains, size isn't everything. "Neanderthals had bigger brains than we do, and they are extinct," says Rex Jung at the University of New Mexico. "Men also have bigger brains than women. Does that mean men are smarter than women? Certainly not."

In fact, brain structure is a more reliable marker of smarts than brain size. On average, women have thicker cortices - the wrinkly, outer layer of the brain, responsible for higher-level functions - and thicker cortices have been associated with higher IQ scores. "All the wrinkles and convolutions allow more of that computational capacity to fit in," says Jung. Men, meanwhile, tend to have bigger sub-cortical regions, including the hippocampus, which is involved in memory and spatial awareness, and the amygdala, which handles emotions and decision-making, although that doesn't necessarily correspond with greater skill in these areas. There is also more variability in these measurements between men than between women - interesting because, although there is no overall difference in intelligence between the sexes, men tend to be over-represented at both ends of the intelligence spectrum.

Then there's connectivity. According to perhaps the best-supported theoretical model of intelligence, our cognitive abilities are highly reliant on a brain network linking the frontal lobes - associated with planning, organising and reasoning with the parietal lobes, which collect and organise perceptual information. These areas are most active when people perform IQ tests - although, interestingly, less so in people with higher IQs, which could indicate that their brains are working more efficiently. Strong white matter connections between these two lobes also correlate with better performance - particularly in subtests requiring mental speed and reasoning.

Yet other studies have fingered the chemical composition of the brain. For instance, higher intelligence is linked with high levels of N-acetyl-as part a tea substance associated with neural health and metabolism in a brain area that coordinates sensory and visual information.

Is humanity becoming more stupid?

Taken as a whole, it looks like humans are getting cleverer- a phenomenon known as the Flynn effect. A 2015 study, which examined test results from 48 countries, found that IQ scores have increased by an average of 20 points since 1950. The biggest gains were in developing countries, including India and China. This suggests the Flynn effect is linked to improvements in social conditions including nutrition and education.

However, certain aspects of intelligence maybe declining. When the researchers looked more closely they discovered that while short-term memory scores have risen, working memory is going in the other direction. Working memory involves

manipulating information, and is among several cognitive abilities that decline as we age, possibly because we become less good at ignoring distractions. The researchers also noticed an increase in the proportion of people aged over 60 sitting intelligence tests.

This suggests that, as human populations age, our average IQ will decrease. Then again, the gap between IQ scores in developed and developing countries still stands at around three points, and is likely to close up as social conditions improve further. Is humanity becoming more stupid? Not yet-but it's probably only a matter of time.

THE TRUTH BEHIND THE STEREOTYPES
Evil genius

Psychopaths may think of themselves as intellectually superior but, in general, they have below average IQ scores and do poorly at school. Instead, they often charm, manipulate and deceive their way to the top.

Specky geek

Highly intelligent people are twice as likely to be short-sighted as people who have low IQ scores. In part, this may be because they tend to spend more of their childhood indoors studying-and regular exposure to bright daylight is necessary for healthy eye development. However, it is possible there are also genes that link eyesight and IQ.

Rational intellectual

When asked to analyse a controversial issue, intelligent people often come up with more arguments both to support and critique it compared with less cognitively gifted individuals. They are not unbiased, however most of their statements reflect their existing world view.

Absent-minded professor

Some people are great at recalling facts, but struggle to remember personal encounters and experiences. Others can dredge up details of distant conversations but perform dismally in pub quizzes. Both are normal. But the more intelligent you are, the better your memory is likely to be overall.

Beautiful airhead

As if fortune hadn't smiled on them enough, beautiful people may also be more intelligent. British boys judged more physically attractive by their teachers had a 13.6 point IQ lead, and girls a 11.4 point lead compared with their less attractive peers.

Mumnesiac

A woman's brain shrinks by up to 7 per cent during pregnancy and she may experience a short-term decline in her memory for words. But, within six months of giving birth, original brain volume is regained. Motherhood can even sharpen minds in the long run.

It may seem unfair, but people who do well in exams tend to do well in life

Having bigger brains doesn't make men smarter than women

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By Linda Geddes

Linda Geddes is a writer based in Bristol, UK