Researchers have debated for years whether men or women are likelier to engage in "mate poaching." Some surveys indicated that men had a stronger tendency to go after other people's partners, but was that just because men were more likely to admit engaging in this behavior? Now there's experimental evidence that single women are particularly drawn to other people's partners, according to a report in the Journal of Experimental Social Psychology by two social psychologists, Melissa Burkley and Jessica Parker of Oklahoma State University.
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To the men in the experiment, and to the women who were already in relationships, it didn't make a significant difference whether their match was single or attached. But single women showed a distinct preference for mate poaching. When the man was described as unattached, 59 percent of the single women were interested in pursuing him. When that same man was described as being in a committed relationship, 90 percent were interested. . . .
This may be because an attached man has demonstrated his ability to commit and in some ways his qualities have already been ‘‘pre-screened" by another woman.
http://tierneylab.blogs.nytimes.com/2009/08/13/do-single-women-seek-attached-men/
http://www.synergy-pr.com/files/JESP72009%281%29.pdf