Think about the people you like most in the world. Are they downers who are crabby and pessimistic? Probably not. In fact, they likely tend to do one simple thing more, compared with the people you'd rather not be around: Smile.

It's backed up by science. Check out what these recent studies have to say on the matter.

Not smiling can get you kicked out of a group.

Researchers at the University of Basel in Switzerland recently published findings from a series of studies in which 480 people were shown portraits of faces manipulated to appear warm or cold and competent or incompetent. After two seconds of looking at each image the participants had to decide whether it was acceptable to exclude the person in the photo from a group.

Once the numbers were tallied, it turns out the participants believed it was perfectly acceptable to ostracize people who looked cold and incompetent. It wasn't OK to oust the people whose faces were warm and incompetent, however. Only the folks wearing smiles should be protected from exclusion, the participants perceived.

Not smiling makes you appear older and more overweight.

It's not fair, but people who smile are perceived as younger and thinner. In one study conducted at the University of Missouri Kansas City, researchers asked college-aged participants to sort the emotional expressions of computer-generated images of male faces. They found that younger faces were more likely to be categorized as old when they displayed a sad facial expression compared to neutral expressions. Similarly, older-looking but happy faces were more often perceived to be young.

In another, the researchers asked study participants to quickly assess how much a person weighed by looking at faces on a computer screen. Sad faces were perceived to be more overweight than neutral ones.

Seeing you smile makes other people feel good.

And people are drawn to those who make them feel good.

Psychologists at the University of Wisconsin published a paper earlier this year which explained how people simulate the facial expressions of the people around them to create emotional responses in themselves. By "trying on" another person's expression someone subconsciously associates with the emotions he or she felt when making that expression in the past. And, this process takes place in only a few hundred milliseconds.

"You reflect on your emotional feelings and then you generate some sort of recognition judgment," researcher Paula Niedenthal says, "and the most important thing that results is that you take the appropriate action--you approach the person or you avoid the person."