Do you have a tendency to crack a smile or burst into laughter a lot? Well, you may have what’s been come to be known as ‘the giggle gene’ – specifically a shortened version of the gene, or a short allele. Psychologist Robert Levenson of the University of California, Berkeley says this gene variant is involved in the regulation of serotonin and has been previously associated with depression or marital bliss – a subject he’s been studying for over two decades.

"We did a series of studies before we did this marriage study, where we just asked a simple question, and that is, "If you have the short allele, and we do something that's emotionally positive, will you have bigger positive emotions, too?" And it turned out that you do."

They found this out by videotaping study participants while watching funny movies or looking at humorous cartoons. But Levenson says that those with the short allele were more susceptible to emotions in general – positive or negative.

"So it didn't seem that the short allele produced a particular kind of emotional response, it just produced a bigger emotional response across the board."