People get jealous - it's human nature. A new study from Oakland University shows what that means when it comes to heterosexual relationships.

According to the study, heterosexual women, who are not single and hang around males frequently, whether it be platonic friends or simply co-workers, have more sex in their relationships than females in relationships that do not have as many guy friends. 

Researchers studied 393 men who were, at the time of the study, in relationships for an average length of 35.9 months.

The subjects then provided information, both objective and subjective, about their significant other - their partner's attractiveness, the amount of male friends and co-workers they think their female partner has, if they think the other men find their partner attractive and how many times in the past week they had sex with their partner.

Results show that the men who reported their girlfriends as having a lot of male attention, at work and in other social settings, and felt those other attention-givers are attracted to their female partners, have more sex with their girlfriends.

This is traced back to a biological reaction known as sperm competition, which basically means that if a man feels his sex life is being threatened by other male competition, subconsciously he will try harder to perform better in bed.

"This is human nature," Michael Pham, lead author on the study, told Fusion.net. "We need to be reminded that our partner is valuable to us and desirable to others. This makes us keep working at maintaining relationship satisfaction. Finding that right balance of inducing your partner's jealousy will optimize a couple's sex life." 

Todd K. Shackelford, professor and chair of psychology at Oakland University and a co-author of the study, explained to The Huffington Post that the subconscious desire goes beyond just sex.

"The example Shackelford gave had to do with the porn men could watch when they provide semen samples. If you ask one man to provide a masturbatory ejaculate while watching a scene of multiple men having sex with one woman, and ask another man to do it while watching a scene of one man having sex with multiple women, you'll find that the quality of the ejaculate is higher in man who observed the sperm competition environment, i.e. the former scenario," the site reported.