Question of the Day: Why are some people "mate poachers"?

I think at some point we've all come across people in our lives who have a reputation for stealing other people's mates. It's common knowledge that most people find more value in something (or someone) when it's highly coveted; regardless of their interest in it. I just read a fascinating article on this topic that provided information supporting this theory. Apparently in a prominent and highly publicized study, researchers divided single women into two groups and showed them pictures of a hot guy. They told one group of women that he was single and the other he was in a relationship; then, they asked the women how likely they were to pursue him. Only when the woman believed he was committed to someone else did interest in the male subject skyrocket!

Interesting right? So what the heck gives? Is it that people in relationships have already proven their willingness to commit, which causes a major draw to single people? Perhaps its the possibility of landing him or her making them feel special and superior? Why do you think some people go after the taken ones?