An unnamed researcher secretly filmed more than 100 young single women from behind using a camera in his buttonhole when he examined the alluring sway of women’s hips when they walk.

The covert footage was viewed by two other men – who were asked to judge each wiggle on an attractiveness scale of one to five.

Their research revealed that women at the peak of their fertility cycles walk more slowly and seductively than those who are not.

This subtle change in behaviour is subconscious but has clear evolutionary benefits – as it makes a woman appear more attractive just at the time when she is most likely to fall pregnant, the research showed.

The women were unaware of the nature of the study and were asked for a saliva sample to test for the presence of a hormone.

Levels of the hormone indicated whether they were approaching the most fertile time of the month.

The secret of the wiggle, well known for leaving men smitten when demonstrated by attractive women such as the singer Beyonce, was confirmed when the researcher compared the hormone test with the ratings from the judging panel.

Professor Nicolas Gueguen led the study at the behavioural sciences unit of the University of Bretagne-Sud in France.

And it is not the first time Prof. Nicolas Gueguen has studied the female form. His previous research has examined whether a woman’s bust size affects her ability to hitchhike and whether a woman’s hair colour affects her success as a charity worker.

The secret of the wiggle, well known for leaving men smitten when demonstrated by attractive women such as the singer Beyonce, was confirmed when the researcher compared the hormone test with the ratings from the judging panel

He is currently studying whether women wear shoes with higher heels when they are fertile.

For the “wiggle test”, Prof. Nicolas Gueguen recruited 103 young women who were undergraduate business and social science students at his university – telling them he was conducting an experiment to test their word choices.

All were single, heterosexual and aged between 18 and 22.

Prof. Nicolas Gueguen had already ruled out any who were using the contraceptive pill in case the hormones affected the experiment.

Each woman was individually asked to sit in a room and wait. After a short time, an attractive man entered and sat with them. The man was asked to smile at them and engage them in friendly conversation.

Unknown to the women, the man had been pre-selected for his attractiveness by a separate group of 31 women who had awarded him an average of 7.28 on a scale of 1 to 9.

The man then accompanied the women down a corridor to the laboratory, where they were told the study would take place. But without their knowledge, the man deliberately walked behind to film them. Once they reached the room, the women’s saliva was tested.

They were also then told the purpose of the experiment and asked for their permission to use the video footage. All gave their consent.

The results showed women at the peak of their fertility cycles were rated an average of 2.96 on the scale for sexiness, compared with 2.31 for those at the least fertile point.

The most fertile women also took about three seconds longer on average to complete the same short walk. Prof. Nicolas Gueguen and his researchers concluded: “We found that women near ovulation spent more time walking down a long hallway and their gaits were perceived to be sexier by males.

“Such results confirm that subtle behavioural cues are influenced by menstrual cycle.”

In his research Prof. Nicolas Gueguen is keen to point out other studies that have observed female behaviour, including one which involved watching women while they were seated in university cafeterias, bars or nightclubs.

“The women used subtle nonverbal behaviours such as nodding, leaning forward, self-touching, hair-flipping and hair-tossing in courtship and flirting relationships”, it says.

A study at speed-dating events found women who mimicked the behaviour of the men they were talking to were deemed more attractive than the other participants. And another found women with slightly enlarged pupils were considered more feminine.