The gene evolved about 30,000 to 50,000 years ago when humans were moving out of Africa.
"Having some individuals who have wanderlust and want to see what's on the other side mountain. It's important for new places to live. But it's also risk-taking. Sometimes, going to the other side of the mountain means that something eats you. There is a cost and a benefit."
Some of the implications of this study might be "huge," and not just in the bedroom. "The big question is what happens in drug rehab if you have a long allele and others don't? They might have different treatments."
The study also strongly suggests that sex drive and thrill can function independently of love.
That might be the case with Emma, a 20-year-old student from University of Southern Florida, who just broken up with her boyfriend after a two-year monogamous relationship.
She wanted to try something different, so she slept with three men in one month. Two were encounters with guys she had been friends with and another was a fling that transformed into a longer relationship.
"I'd never done anything like that before," said Emma, who did not want to reveal her last name. "It was something so new to me."
She said it's not in her personality to take risks. Defying college stereotypes, Emma's never touched alcohol and has only smoked marijuana once.
And now that she is in a committed relationship, Emma is certain she won't be unfaithful.
"We are learning more and more about genes implicated in behaviors," she said. "Every time a genetic study comes out, responsible scientists also stress that we have choice -- nature and nurture," she said.
"Not everyone with the gene is promiscuous and not everyone who is promiscuous will have that gene."
And can't risk-taking be a good thing?
"Sometimes that overlaps with creativity, with entrepreneurship and wanting to push the boundaries," she said. "In relationships that can be exciting and fulfilling and help the whole couple move into new areas."
So should a woman have her boyfriend tested before accepting his marriage proposal?
"By the time she meets him, unless he is very young, his track record will prove whether he has acted on his infidelity gene or not," said Quilliam. "If he has been unfaithful in the past, he is likely to do it in the future."
Maureen Finn, a 19-year-old television, film and radio major at Syracuse University, agrees.
"I mean if you meet a guy at a party and he's making out with three other girls, that's a hint," she said. "If you're disrespecting me, something tells me you're not going to respect me enough to be faithful."
ABC's On Campus reporters Sierra Jiminez of Syracuse University and Meg Wagner of University of Florida contributed to this story.