Look at any list of the qualities that women look for in a potential romantic partner, and "sense of humor" lands somewhere at the top. A study conducted at Stanford University School of Medicine found that biology may be to blame for women finding funny men irresistible.

The study, which involved 22 children aged six to 13, sought to investigate the developmental origins of differences in the way males and females respond to different stimuli. The study participants were shown a series of clips, some funny and some not so funny. As they watched the clips, the children were hooked up to a functional magnetic resonance imaging machine (fMRI) to measure their brain's responses. After watching the clips, the children were given short questionnaires about the clips and asked to answer them on a number scale.

During the funny clips, girl's brains showed more heightened activity than boys. According to the researchers, this meant that the girls experienced more positive feelings in response to the funny clips than boys did. Girls felt more of a sense of reward in watching the funny clips than boys did.

"Our data for the first time disclose that sex differences in humor appreciation already exist in young children," they wrote.

Fast forward 20 years and you have the reason why attractive women sometimes go for not as physically attractive, yet funny, men. According to the researchers, a potential mate's humor is effective in captivating women because "the female brain, particularly the reward circuit, is biologically better prepared to respond accordingly."

Perhaps that's the reason why comedians with seemingly unattractive characteristics tend to land very attractive mates: Kevin Hart and girlfriend Emiko; Katy Perry and Russell Brand; Eddie Murphy and ex-wife Nicole Murphy; Jerry Seinfeld and wife Jessica... the list goes on and on.

But the researchers warn against jumping to any concrete conclusions too quickly. They note that the study is relatively small and a larger participant group would yield better results.

For now though, revel in the fact that we're one step closer to knowing why you just can't stop thinking about that guy who told those hilarious knock, knock jokes at happy hour.

Source: Vrticka P, Neely M, Shelly E. Sex differences during humor appreciation in child-sibling pairs. Social Neuroscience. 2013.