It doesn’t take the proverbial rocket scientist to reach the conclusion that men and women walk differently. The greater pelvic obliquity and less vertical center of mass displacement in women compared with men has long been mentioned as a reason why some men are so distinctly uncool, even rude, staring as they are wont to do when women walk by.

The apparent conclusion that an armchair evolutionary psychologist would make is that women walk with a sway to attract men. Not so, say researchers led by Meghan Provost from Queen’s University in Ontario, Canada. The sexy walk women use is in fact a clever ruse to keep men unaware of women’s real ovulatory status.

Dr. Provost reports that women actually have the sexiest walk during the time of the monthly cycle when they are least fertile. That is women walk with less hip movement and with their knees closer together when they were in the most fertile phase of their menstrual cycle.

The researchers reached this conclusion by filming female volunteers while they walked wearing suits with sensors placed on their joints and limbs. This film was later analyzed for specific physical movements. These women also provided saliva samples for hormonal analysis to precisely identify the time of their menstrual cycle.

Further, the researchers had men rate the sexiness of how the women walked. Consistently men rated women in the less fertile times of their menstrual cycle as having the sexiest walks.

Needless to say all of these findings run counter to prior research, and common sense, which argues that men are most responsive to women when they are closest to ovulation.

Dr. Provost argues there is in fact no inconsistency, rather men just respond to different signals in different ways. Previous research that finds men respond to fertile women have evaluated signals that can be detected only at close range, such as smells and facial expressions. The attractiveness of a woman’s walk can be detected at a distance, however. Thus walking in a less sexy manner allows women to hide their fertility from men whom they may judge to be undesirable at a closer level.

Dr. Povost was reported in New Scientist as saying that it makes sense for women to advertise their attractiveness on a broad scale when they are not fertile as a means of protecting themselves when they are at peak fertility. Fertility is thus displayed using more intimate signals so women can more selectively chose who is informed of their fertility.

More information to question just how effective catcalls and whistles are as a means of attracting women.