These Signs show 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.

Business Insider 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.

1. 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-oldsrose 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.

2. 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."

3. 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.

4. You have a cat

A 2014 study of 600 college students found that individuals who identified as "dog people" were more outgoing than those who identified as "cat people," according to a test that measures personality and intelligence. 

But guess what? Those same cat people scored higher on the part of the test that measures cognitive ability.

5. You were breastfed

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.)

6. 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 "a high childhood IQ may prompt the adoption of behaviors that are potentially harmful to health (i.e., excess alcohol consumption and drug use) in adulthood."

7. You're left-handed

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 associated 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.

Source: MSN