I’ve always had unwritten rules about who you should and shouldn’t date. Friends’ exes are out, for example. So is asking someone out when you know a girlfriend is already interested in him.

Hitting on a girlfriend’s guy when they are already dating is definitely out.

In fact, in my books, hitting on any guy who’s already attached or married even if you’re not friends with his partner is a no-no. It’s just bad karma.

But it seems karma is no match for biology. Ninety per cent of the single women in an Oklahoma State University study on “mate poaching” were more interested in dating a man who was already in a relationship than a single man.

Past psychological studies have shown that some women may try to lure a man away from his current partner, a phenomenon known as “mate poaching.” One 2004 study published in the Journal of Personality and Social Psychology suggested that as many as one in five long-term relationships began when one or both partners was already in a relationship with someone else.

But this new study, published in the current issue of the Journal of Experimental Social Psychology, shows that most single women actually prefer men who are already in a committed relationship.

Men and women were matched with students based on a description of their ideal romantic partner. When researchers described the women’s match as single, 59 per cent of the single women in the study were interested in pursuing him. However, when they described the exact same man as being in a committed relationship, 90 per cent of the women were interested. Neither the men nor the already attached women who participated showed this preference.

Dr. Melissa Burkley, an assistant professor of social psychology at Oklahoma State University and one of the researchers behind the study, suggests that the reason behind this is that single women are more interested in pursuing unavailable men possibly because they are more interested in a guy who’s already shown he can commit by being in another relationship, indicating he’d be a reliable mating partner.

Of course, the study doesn’t show that, if you pursue the committed man and he goes for it, he’s also clearly capable of breaking that commitment and cheating.

• Would you pursue someone you knew was already attached? Post your answers in the comments section of The J Spot column online at metronews.ca.