http://www.usatoday.com/tech/science/discoveries/2006-01-03-infidelity-study_x.htm
Some men cheat on their partners. So do some women. Now researchers say it is more than a wandering eye that might cause a woman to stray.
This conclusion was based on two studies of college men and women using questionnaires where the test group was asked how they felt (how scientific) about other men/women outside of their steady relationships.
Studies from the University of California-Los Angeles and the University of New Mexico-Albuquerque suggest an evolutionary tendency toward infidelity during ovulation, which is the most fertile part of the menstrual cycle. The studies suggest the propensity is more likely if women don’t view their partners as sexy. [They needed a study for this???]
“Something biologically wakes up around high fertility and says, ‘Is your romantic partner the best sexual partner for you, given that you’re likely to conceive?’ ” says Martie Haselton, assistant professor of communication and psychology at UCLA’s Center for Behavior, Evolution, and Culture.
Along those evolutionary lines, men more than women desire a variety of sexual partners because genes carrying that trait were passed along in men, Haselton says.
The one thing the article didn’t make clear is whether they actually analyzed (selfish?) genes responsible–if only indirectly–for “men more than women desir[ing] a variety of sexual partners” or if they’re just extrapolating an evolutionary reason for human behavior.