Human intelligence is a wonderful thing. At both the individual and collective level it drives our complex communication, our fundamental discoveries and inventions, and impressive and accelerating progress. Intelligence allows us to innovate, to design, to build; and it underlies our superior capacity, over other animals, for empathy, altruism, art, and social and cultural evolution. Yet, despite our intellectual abilities and seemingly limitless potential, we humans still do lots of stupid things. Why is this?

From New Scientist:

“EARTH has its boundaries, but human stupidity is limitless,” wrote Gustave Flaubert. He was almost unhinged by the fact. Colourful fulminations about his fatuous peers filled his many letters to Louise Colet, the French poet who inspired his novel Madame Bovary. He saw stupidity everywhere, from the gossip of middle-class busybodies to the lectures of academics. Not even Voltaire escaped his critical eye. Consumed by this obsession, he devoted his final years to collecting thousands of examples for a kind of encyclopedia of stupidity. He died before his magnum opus was complete, and some attribute his sudden death, aged 58, to the frustration of researching the book.

Documenting the extent of human stupidity may itself seem a fool’s errand, which could explain why studies of human intellect have tended to focus on the high end of the intelligence spectrum. And yet, the sheer breadth of that spectrum raises many intriguing questions. If being smart is such an overwhelming advantage, for instance, why aren’t we all uniformly intelligent? Or are there drawbacks to being clever that sometimes give slower thinkers the upper hand? And why are even the smartest people prone to – well, stupidity?

It turns out that our usual measures of intelligence – particularly IQ – have very little to do with the kind of irrational, illogical behaviours that so enraged Flaubert. You really can be highly intelligent, and at the same time very stupid. Understanding the factors that lead clever people to make bad decisions is beginning to shed light on many of society’s biggest catastrophes, including the recent economic crisis. More intriguingly, the latest research may suggest ways to evade a condition that can plague us all.

The idea that intelligence and stupidity are simply opposing ends of a single spectrum is a surprisingly modern one. The Renaissance theologian Erasmus painted Folly – or Stultitia in Latin – as a distinct entity in her own right, descended from the god of wealth and the nymph of youth; others saw it as a combination of vanity, stubbornness and imitation. It was only in the middle of the 18th century that stupidity became conflated with mediocre intelligence, says Matthijs van Boxsel, a Dutch historian who has written many books about stupidity. “Around that time, the bourgeoisie rose to power, and reason became a new norm with the Enlightenment,” he says. “That put every man in charge of his own fate.”

Modern attempts to study variations in human ability tended to focus on IQ tests that put a single number on someone’s mental capacity. They are perhaps best recognised as a measure of abstract reasoning, says psychologist Richard Nisbett at the University of Michigan in Ann Arbor. “If you have an IQ of 120, calculus is easy. If it’s 100, you can learn it but you’ll have to be motivated to put in a lot of work. If your IQ is 70, you have no chance of grasping calculus.” The measure seems to predict academic and professional success.

Various factors will determine where you lie on the IQ scale. Possibly a third of the variation in our intelligence is down to the environment in which we grow up – nutrition and education, for example. Genes, meanwhile, contribute more than 40 per cent of the differences between two people.

These differences may manifest themselves in our brain’s wiring. Smarter brains seem to have more efficient networks of connections between neurons. That may determine how well someone is able to use their short-term “working” memory to link disparate ideas and quickly access problem-solving strategies, says Jennie Ferrell, a psychologist at the University of the West of England in Bristol. “Those neural connections are the biological basis for making efficient mental connections.”

This variation in intelligence has led some to wonder whether superior brain power comes at a cost – otherwise, why haven’t we all evolved to be geniuses? Unfortunately, evidence is in short supply. For instance, some proposed that depression may be more common among more intelligent people, leading to higher suicide rates, but no studies have managed to support the idea. One of the only studies to report a downside to intelligence found that soldiers with higher IQs were more likely to die during the second world war. The effect was slight, however, and other factors might have skewed the data.

Intellectual wasteland

Alternatively, the variation in our intelligence may have arisen from a process called “genetic drift”, after human civilisation eased the challenges driving the evolution of our brains. Gerald Crabtree at Stanford University in California is one of the leading proponents of this idea. He points out that our intelligence depends on around 2000 to 5000 constantly mutating genes. In the distant past, people whose mutations had slowed their intellect would not have survived to pass on their genes; but Crabtree suggests that as human societies became more collaborative, slower thinkers were able to piggyback on the success of those with higher intellect. In fact, he says, someone plucked from 1000 BC and placed in modern society, would be “among the brightest and most intellectually alive of our colleagues and companions” (Trends in Genetics, vol 29, p 1).

This theory is often called the “idiocracy” hypothesis, after the eponymous film, which imagines a future in which the social safety net has created an intellectual wasteland. Although it has some supporters, the evidence is shaky. We can’t easily estimate the intelligence of our distant ancestors, and the average IQ has in fact risen slightly in the immediate past. At the very least, “this disproves the fear that less intelligent people have more children and therefore the national intelligence will fall”, says psychologist Alan Baddeley at the University of York, UK.

In any case, such theories on the evolution of intelligence may need a radical rethink in the light of recent developments, which have led many to speculate that there are more dimensions to human thinking than IQ measures. Critics have long pointed out that IQ scores can easily be skewed by factors such as dyslexia, education and culture. “I would probably soundly fail an intelligence test devised by an 18th-century Sioux Indian,” says Nisbett. Additionally, people with scores as low as 80 can still speak multiple languages and even, in the case of one British man, engage in complex financial fraud. Conversely, high IQ is no guarantee that a person will act rationally – think of the brilliant physicists who insist that climate change is a hoax.

It was this inability to weigh up evidence and make sound decisions that so infuriated Flaubert. Unlike the French writer, however, many scientists avoid talking about stupidity per se – “the term is unscientific”, says Baddeley. However, Flaubert’s understanding that profound lapses in logic can plague the brightest minds is now getting attention. “There are intelligent people who are stupid,” says Dylan Evans, a psychologist and author who studies emotion and intelligence.

Read the entire article after the jump.