9 science-backed signs you're smarter than average

Natalie portmanJason Merritt/GettyHarvard grad Natalie Portman speaks six languages.

What makes someone smart?

Scientists have been investigating that question for decades, and the research suggests that everything from your mother’s breast milk to the size of your waistline can influence your intelligence.

Additional reporting by Chelsea Harvey.

You don't smoke.

A 2010 Israeli study compared the IQ and smoking status of 20,000 young men.

As the Daily Mail reported, the results were stark:

• The average 18- to 21-year smoker had an IQ of 94, and the non-smoker had an IQ of 101.

• Those who smoked more than a pack a day had an average IQ of 90.

• In sibling sets, nonsmoking brothers were smarter than smokers.

You took music lessons.

Research suggests that music helps kids' minds develop in a few ways:

• A 2011 study found that the verbal intelligence of 4- to 6-year-olds rose after only a month of music lessons.

• A 2004 study found that 6-year-olds who took nine months of piano lessons had an IQ boost in comparison to kids who took drama lessons or no classes at all.

But the researchers may be getting it backwards: A 2013 study suggested that high-achieving kids are the most likely to take music lessons, rather than the music making them smarter.

You're the oldest child.

Oldest siblings are usually smarter, but it's not because of genetics.

The New York Times reports, 'The new findings, from a landmark study published (in June 2007), showed that eldest children had a slight but significant edge in IQ -- an average of three points over the closest sibling. And it found that the difference was not because of biological factors but the psychological interplay of parents and children.'

For this and other reasons, first-borns tend to be more successful than their siblings.

You're thin.

For a 2006 French study, scientists gave 2,200 adults intelligence tests over a five-year period.

It suggested that the bigger the waistline, the lower the cognitive ability.

The Telegraph reports:

The researchers found that people with a Body Mass Index -- a measure of body fat -- of 20 or less could recall 56% of words in a vocabulary test, while those who were obese, with a BMI of 30 or higher, could remember only 44%.

The fatter subjects also showed a higher rate of cognitive decline when they were retested five years later: their recall dropped to 37.5%, whereas those with a healthy weight retained their level of recall.

A healthy body is closely linked to a healthy mind.

You have a cat.

A 2014 study found that people who identify as a 'dog person' are more outgoing than those who identify as a 'cat person.'

But guess what: Cat people did better on intelligence tests.

'It makes sense that a dog person is going to be more lively, because they're going to want to be out there, outside, talking to people, bringing their dog,' said lead researcher Denise Guastello, guessing at what might be behind the differences. 'Whereas, if you're more introverted, and sensitive, maybe you're more at home reading a book, and your cat doesn't need to go outside for a walk.'

You were breast-fed.

'In two studies of breast-fed infants involving more than 3,000 children in Britain and New Zealand, breastfeeding was found to raise intelligence an average of nearly seven IQ points if the children had a particular version of a gene called FADS2,' Duke University reported in a press release.

That gene version is 'involved in the control of fatty acid pathways,' said researcher and University of Illinois-Chicago psychologist Julia Kim-Cohen, and it 'may help the children make better use of the breast milk and promote the brain development that is associated with a higher IQ score.'

Figuring out the exact mechanism of this relationship between FADS2, breastfeeding, and IQ will require further study, the scientists noted in their 2007 paper on the finding.

You've used recreational drugs.

A 2012 study of more than 6,000 Brits born in 1958 found a link between high IQ in childhood and the use of illegal drugs in adulthood.

'In our large population-based cohort study, IQ at 11 years was associated with a greater likelihood of using selected illegal drugs 31 years later,' wrote researchers
James W. White,
Catharine R. Gale, and David Batty.

They conclude that 'in contrast to most studies on the association between childhood IQ and later health,' their findings suggest that 'a high childhood IQ may prompt the adoption of behaviours that are potentially harmful to health (i.e., excess alcohol consumption and drug use) in adulthood.'

You're left-handed.

While left-handedness used to be associated with criminality, more recent research associates it with 'divergent thinking,' a form of creativity where you come up with novel ideas from a prompt.

In her review of a 1995 paper, New Yorker reporter Maria Konnikova writes that:

The more marked the left-handed preference in a group of males, the better they were at tests of divergent thought.

Left-handers were more adept, for instance, at combining two common objects in novel ways to form a third -- for example, using a pole and a tin can to make a birdhouse. They also excelled at grouping lists of words into as many alternate categories as possible.

Maybe that's why lefties are over-represented in architecture and music.

You're tall.

Like left-handedness, being tall has been a heavily debated trait of smarter individuals. There are studies that back up this speculation.

As a Princeton study noted: 'As early as age 3 -- before schooling has had a chance to play a role -- and throughout childhood, taller children perform significantly better on cognitive tests.'

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