13 science-backed signs you're smarter than average

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 13 surprising signs of braininess. 

Keep in mind, however, that "intelligence" is often measured through tests that have been widely criticized for putting certain social groups at a disadvantage and for minimizing 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.

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You took music lessons.

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

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

• A 2004 study led by Glenn Schellenberg found that 6-year-olds who took nine months of keyboard or voice lessons had an IQ boost compared with kids who took drama lessons or no classes at all.

Meanwhile, a 2013 study, also led by Schellenberg, suggested that high-achieving kids were the ones most likely to take music lessons. In other words, in the real world, musical training may only enhance cognitive differences that already exist.

You're the oldest.

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're thin.

For a 2006 study, scientists gave roughly 2,200 adults intelligence tests over a five-year period and results suggested that the bigger the waistline, the lower the cognitive ability.

Another study published that same year found that 11-year-olds who scored lower on verbal and nonverbal tests were more likely to be obese in their 40s. The study authors say that smarter kids might have pursued better educational opportunities, landed higher-status and higher-paying jobs, and therefore ended up in a better position to take care of their health than their less intelligent peers.

Meanwhile, a more recent study found that, among preschoolers, a lower IQ was linked to a higher BMI. Those researchers also say environmental factors are at play, since the relationship between BMI and smarts was mediated by socioeconomic status.