An age-old question, puzzling everyone from watchers of HBO's much-discussed comedy, Girls, to generations of frustrated moms and dads. One answer, suggests a series of psychology experiments, is that she isn't seeing that bad boy straight, and biology at least part of the time may be supplying the rose-colored glasses that makes a "sexy cad" look like a "good dad." "Why do women delude themselves about men who are terrible 'boyfriend' material," asks marketing professor Kristina Durante of the University of Texas at San Antonio, lead author of the forthcoming experiment report in the Journal of Personality and Social Psychology. "It's not just that they are attracted to them, but they actually see them as different people." Why does she say that? In the study, Durante and her University of Minnesota and Singapore Management University colleagues sought to explore psychological observations that women were more attracted to stereotypical masculine faces— symmetrical with strong jaws and sharp cheekbones ("I say Ryan Gosling to students now, because George Clooney is too old for them ," Durante says) — when they were at the most fertile part of the menstrual cycle. Some researchers have suggested hormones such as estrogen peak just then, firing their desire to run off with a good-looking cad. On a deeper level, some evolutionary psychologists have suggested that the high testorerone levels of swoon-worthy men, responsible for those chiseled good looks and come-hither self-confidence, served as a signal of evolutionary fitness and explained the attraction. But at the same time, Durante says, that high testosterone and enticing faces made these cads less-than-reliable mate material, there to help support the survival of offspring, which is the whole point of evolution. As the study says, "it is unclear why ovulating women would think it wise to pursue relationships with men who might be unfaithful and desert them." Instead, women should chase after dull dudes who seem likely to do the dishes and change the diapers, Durante says. But you don't have to watch Divorce Court every afternoon to know that doesn't always happen. How come? In a simple experiment the team first asked 33 college-age women to take part in a study assessing how health affected their taste in men. That was just the cover story for them to take over-the-counter fertility tests revealing where they were on their monthly cycle. At both the high fertility and low fertility points of their cycle, the women were randomly shown a biography and photo of a "sexy man," an award-winning skier and handsome adventurer, or the same for "reliable man," a hard-working average-looking accountant. Then they asked the women how the men would split the work of parenting, (giving baths, cooking, washing bottles etc.) if they had a baby with him. Good, old Mr. Reliable. The women estimated he would do around 40% of the household work no matter when they were asked. And the ski champ looked similarly helpful to the women when they were asked at low fertility moments. But the women actually estimated Prince Charming would do as much as 53% of the chores when they were ovulating, a statistically significant difference, "and a surprising one," Durante says. The "sexy cad" will be a "good dad" transformed into a caring father through the miracle of ovulation. Interesting, but the men did look different after all. So the researchers hired "twins." Well actually they hired two male actors to play twins, one a "sexy cad" and the other a "good dad."