It may sound strange, but researchers have found a possible connection between wide open pupils and something called fluid intelligence.

"Of course, dilated pupils occur when the eye needs to let in more light, such as when you need to adjust to the dimmer light of a dark room," Bryan Nelson noted on Mother Nature Network. But that's not the type of pupil dilation psychologist Jason S. Tsukahara observed in his study.

"It turns out, changes in pupil size happen in a number of circumstances that don't necessarily relate with changes in light levels," Nelson noted. "For instance, in a simple memory span task, pupil size precisely tracks changes in memory load, dilating with each new item held in memory and constricting as each item is subsequently recalled." While more research is needed to determine a true correlation, there's no denying it's an interesting connection.

Science has shown that left-handed folks may have an advantage, intelligence-wise, in one key area. According to an article on Business Insider, "there are certain cognitive domains where left-handed people do seem to excel. One such area is called 'divergent thinking,' or the ability to generate new ideas based on existing information." Which may explain why so many presidents have been left-handed.

While it doesn't mean they're smarter overall, they may have a few advantages that "influence not only their performance in psychological experiments, but also the professional paths they pursue and the areas they thrive in," Business Insider notes.

If someone often finds themselves burning the midnight oil, or doing their best work at 3 a.m., there's a good chance they're intelligent. "Being a night owl is a possible sign of intelligence as we were evolved to do most of our activities in the daytime, and then sleep at night," Dr. Neo says. "Anything that is evolutionarily novel, therefore, is expected to be adopted by more intelligent individuals, according to the Savanna-IQ Interaction Hypothesis."

Staying up late can also contribute to creativity, which can in turn expand someone's mind. "Night is when the world is quiet, and there is significantly less chatter," Dr. Neo says. "This creates conditions where people can be more reflective, which leads to more intelligent or wiser approaches and solutions. Otherwise, when tired, our brains are more fluid as the brakes on 'the right ways to think' are looser — this gives rise to higher levels of creativity, because we can combine two or more otherwise-disparate concepts and birth something new."

Studies have shown a link between frequents use of curse words and higher intelligence. According to an article by Dana Dovey on Medical Daily, "A 2016 study published in Language Sciences found that using swear words is positively associated with overall verbal fluency. This means that individuals who use more curse words may have a better vocabulary, a trait associated with intelligence."

As Dr. Neo says, "Openness in the form of non-conformism both fuels and is a product of creativity and innovation." Which may explain why open-mindedness and creativity are often associated with intelligence.

"We can march to our own drum beats, confident in our wisdom. Being open and creative means that we can easily piece together new insights that are qualitatively different from the sum of their parts," Dr. Neo says. "Take for instance, Steve Jobs drew from his love of calligraphy to create his Apple interface." And as we all know, Jobs was pretty darn smart.

If someone is a major risk taker, it may be a sign of their intelligence. This was shown in a 2015 Finnish study, which found that individuals who were less afraid to take risks tended to have higher intelligence. And when you think about the way quick-thinking is often associated with risky decisions, that connection makes sense.

In the study, volunteers were put through a driving simulation test where they had to either drive past yellow traffic lights, or wait for the lights to turn red. Researchers found that the participants who made the riskier decisions during the simulation had more white brain matter, which is an area of the brain associated with cognitive function.

Birth order may play a role in intelligence, since some studies have revealed that the way older children are parented may result in higher intelligence down the road. This may have something to do with parents being stricter with their first born children, and perhaps even being more encouraging when it comes to homework, etc.

According to Medical Daily, "parental subject belief" may also play a role. First children may receive more praise from their parents, which can serve as a sort of self-fulfilling prophecy; if they're encouraged to do well, they may be more likely to succeed.

Of course, none of these traits guarantee intelligence. And if someone doesn't have these traits, it doesn't mean they aren't as likely to be intelligent. But it is interesting to think about possible connections between evolution, biology, and even things like birth order, when it comes to determining intelligence.