A new study on lap dancers has found evidence to support the theory that women send out signals during their most fertile periods.
In September this year, Randy Thornhill challenged the belief that women do not experience bouts of hormone-induced oestrus, or "heat" during their most fertile period.
Now, Thornhill's colleague has found more evidence to support the challenge.
For the study, Geoffrey Miller and his team at the University of New Mexico, Albuquerque, compared the earnings of lap dancers who were menstruating naturally with those of dancers on the hormonal contraceptive pill.
During the non-fertile periods of their menstrual cycle, both groups conjured similar tips. However, when naturally cycling lap dancers were at their fertile period they earned higher tips than their counterparts on the pill.
"Lap dancers menstruating naturally earned more in tips during their fertile period than co-workers on the pill" This is the first evidence that oestrus, and its influence on attractiveness, has a real effect on women's earnings," New Scientist quoted Miller, as saying.
The study also showed that the dancers publicized their fertility to men, who found more attractive during this fertile phase.
"We don't know the mechanism of attraction. Are the men detecting the scent of oestrus? Or does the women's behaviour change," said Thornhill.
"Previous research has shown that women's faces, scent and clothing become more attractive in oestrus," Miller notes.
"For example, earlier this year, Martie Haselton at the University of California, Los Angeles, found that women were judged to dress more attractively during their fertile periods, although the correlation was slight. Other studies show women become more confident during oestrus," Thornhill said.