You're not easily distracted
Frank Zhu says "people who can focus for long stretches at a time and tune out distractions" are highly intelligent. As evidence, he points to a 2013 paper published in the journal Current Biology.
The paper describes two small studies that found people with higher scores on an IQ test were slower to recognize large background movements in an image. That's likely because they focus on the most important information and filter out the rest.
The smarter you are, the more you're inclined to stay up into the wee hours of the morning, according to research.
One study, published in 2009 in the journal Personality and Individual Differences, looked at the link between childhood IQ and sleep habits among thousands of young adults. Sure enough, smarter individuals said they stayed up later and woke up later on both weekdays and weekends.
You're highly adaptable
Several Quora users noted that intelligent people are flexible and able to thrive in different settings. As Donna F Hammett writes, intelligent people adapt by "showing what can be done regardless of the complications or restrictions placed upon them".
Recent psychological research supports this idea. Intelligence depends on being able to change your own behaviors in order to cope more effectively with your environment, or make changes to the environment you're in.
You understand how much you don't know
The smartest folks are able to admit when they aren't familiar with a particular concept. As Jim Winer writes, intelligent people "are not afraid to say: 'I don't know.' If they don't know it, they can learn it".
Winer's observation is backed up by a classic study by Justin Kruger and David Dunning, published in the Journal of Personality and Social Psychology, which found that the less intelligent you are, the more you overestimate your cognitive abilities.
In one experiment, for example, students who'd scored in the lowest quartile on a test adapted from the LSAT overestimated the number of questions they'd gotten right by nearly 50 percent. Meanwhile, those who'd scored in the top quartile slightly underestimated how many questions they'd gotten right.
You have insatiable curiosity
Albert Einstein reportedly said, "I have no special talents, I am only passionately curious."
Or, as Keyzurbur Alas puts it, "intelligent people let themselves become fascinated by things others take for granted."
A study published in 2016, in the Journal of Individual Differences, suggests that there's a link between childhood intelligence and openness to experience — which encompasses intellectual curiosity — in adulthood.
Scientists followed thousands of people born in the UK for 50 years and learned that 11-year-olds who'd scored higher on an IQ test turned out to be more open to experience at 50.
Smart people don't close themselves off to new ideas or opportunities.
Hammett writes that intelligent people are "willing to accept and consider other views with value and broad-mindedness," and that they are "open to alternative solutions".
Psychologists say that open-minded people — those who seek out alternate viewpoints and weigh the evidence fairly — tend to score higher on the SAT and on intelligence tests.
At the same time, smart people are careful about which ideas and perspectives they adopt.
"An intelligent mind has a strong aversion to accepting things on face value and therefore withholds belief until presented with ample evidence," says Alas.
You like your own company
Dipankar Trehan points out that highly intelligent people tend to be "very individualistic".
Interestingly, recent research from the British Journal of Psychology suggests that smarter people tend to derive less satisfaction than most people do from socialising with friends.
You have high self-control
Zoher Ali writes that smart people are able to overcome impulsiveness by "planning, clarifying goals, exploring alternative strategies and considering consequences before [they] begin."
Scientists have found a link between self-control and intelligence. In one 2009 study, published in the journal Psychological Science, participants had to choose between two financial rewards: a smaller payout immediately or a larger payout at a later date.
Results showed that participants who chose the larger payout at a later date — i.e., those who had more self-control — generally scored higher on intelligence tests.
The researchers behind that study say that one area of the brain — the anterior prefrontal cortex — might play a role in helping people solve tough problems and demonstrate self-control while working toward goals.
Advita Bihani points out that highly intelligent people tend to have a great sense of humor.
University of New Mexico scientists agree. One study they conducted found that people who wrote funnier cartoon captions scored higher on measures of verbal intelligence. Another study they ran found that professional comedians scored higher than average on measures of verbal intelligence.
You're sensitive to other people's experiences
Smart people can "almost feel what someone is thinking/feeling," says one Quora user.
Some psychologists argue that empathy, being attuned to the needs and feelings of others and acting in a way that is sensitive to those needs, is a core component of emotional intelligence.
Emotionally-intelligent individuals are typically very interested in talking to new people and learning more about them.
You can connect seemingly unrelated concepts
Several Quora users suggested that smart people are able to see patterns where others can't. That's because they can draw parallels between seemingly disparate ideas.
As April Astoria notes: "You think there's no relation between sashimi and watermelon? You'd be wrong. Both are typically eaten raw and cold."
Interestingly, journalist Charles Duhigg argues that making these kinds of connections is a hallmark of creativity (which can be closely linked to intelligence). Duhigg studied the process through which Disney developed their hit movie Frozen and concluded that the movie only seems clever and original because it "takes old ideas and pushes them together in new ways".
You procrastinate a lot
Mahesh Garkoti says smart people are likely to procrastinate on quotidian tasks, mainly because they're working on things that are more important.
That's an interesting proposition — but some scientists would say that smart people procrastinate even on work they find meaningful. Wharton psychologist Adam Grant suggests that procrastination is key to innovation, and that Steve Jobs used it strategically.
As Grant told Business Insider, "The time Steve Jobs was putting things off and noodling on possibilities was time well spent in letting more divergent ideas come to the table, as opposed to diving right in with the most conventional, the most obvious, the most familiar."
You contemplate the big questions
According to Ram Kumar, intelligent individuals "wonder a lot about [the] universe and meaning of life." What's more, Kumar writes, "they always [ask] what's the point of everything?"
That existential confusion may be one reason why smart people are more likely to be anxious. As David Wilson reported in Slate, intelligent people may be better equipped to consider situations from a range of angles, meaning they're always aware of the possibility that things will go awry.
Perhaps their anxiety also stems from the fact that they consider a given experience and wonder: Why bother going through it in the first place?