9 science-backed signs you're smarter than average

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

How do you know if someone’s smart?

Without administering an impromptu IQ test, there are certain clues you can use to gauge a person’s relative intelligence.

We combed through decades of scientific research and highlighted 9 surprising signs of braininess.

Keep in mind, however, that “intelligence” is often measured through tests that have been widely criticised for putting certain social groups at a disadvantage and for minimising the importance of creativity. Psychologists are constantly finding newer, more effective ways to measure cognitive ability — meaning the signs are ever-evolving.

Additional reporting by Chelsea Harvey.

You're the oldest.

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

Norwegian epidemiologists used military records to examine the birth order, health status, and IQ scores of nearly 250,000 18- and 19-year-old men born between 1967 and 1976. Results showed that the average firstborn had an IQ of 103, compared to 100 for second children and 99 for third children.

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, firstborns tend to be more successful (but not that much more successful) than their siblings.

You were breastfed.

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2007 research suggests that babies who are breastfed might grow up to be smarter kids.

In two studies, the researchers looked at more than 3,000 children in Britain and New Zealand. Those children who had been breastfed scored nearly seven points higher on an IQ test -- but only if they had a particular version of the FADS2 gene. (That version of the gene was present in roughly equal numbers among kids who were and weren't breastfed.)

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

You're left-handed.

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Left-handedness used to be associated with criminality, and researchers are still unclear as to whether and why there are slightly more lefties among criminal populations.

More recent research associates left-handedness with 'divergent thinking,' a form of creativity that allows you to come up with novel ideas from a prompt -- at least among men.

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

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.

You're tall.

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A 2008 Princeton study of thousands of people found that taller individuals scored higher on IQ tests as kids and earned more money as adults.

The researchers write: '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.'

You're funny.

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In one study, 400 psychology students took intelligence tests that measured abstract reasoning abilities and verbal intelligence.

Then they were asked to come up with captions for several New Yorker cartoons, and those captions were reviewed by independent raters.

As predicted, smarter students were rated as funnier.

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