Participants in the study revealed that their fantasies about someone other than their current partner was "65 to 80 percent higher during the high fertility phase," says Garver.
"That's an impressive statistic," she adds.
Mates Pay Attention
The women were also asked to fill out another questionnaire to see if they noted a change in the amount of attention they got from their main squeeze during the time when they were fertile. Was he vigilant (making that unexpected phone call)? Did he try to monopolize her time? Did he try to spoil her with flowers and a romantic dinner?
All of the above.
Or as Gangestad puts it: "It was clear from the results that the women's primary partners were more attentive and proprietary near ovulation."
So that brings us to this fundamental question: How do men know when their mate is fertile?
"We don't know the answer to that question," says Randy Thornhill, professor of biology at the university and the third author of the study. "But there's some suspect cues that men may use."
Clued In by Sight and Scent?
Thornhill and Gangestad have completed many studies in this general area over the years, and one study indicated that men like T-shirts worn by women who are "at high conception risk," or fertile.
"So there's a scent component, perhaps, that is influencing men's mate-guarding," Thornhill says.
Another clue, he adds, is the fact that women tend to act and dress differently when they are ovulating.
"Some studies indicate that women who are at high conception risk behave differently in terms of exposing more skin," he adds. One study used photos taken at a disco to detect differences in the exposure, so to speak, of ovulating women.
"The dressing difference would imply behavioral differences that potentially men pick up on," Thornhill says.
Hey, maybe we guys aren't quite as dense as we seem.
Still, it's not a bad idea to send those flowers.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.