And they say scientists are all nerds.
"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 taking the hormonal contraceptive pill. During the non-fertile periods of their menstrual cycle, both sets of dancers earned similar tips. But when naturally cycling lap dancers entered their fertile period they earned significantly more in tips than their co-workers on the pill."
The aptly named Randy Thornhill is an expert in women on heat.
The study does appear to show that the dancers somehow advertise their fertility to men, who then consider them more attractive during this fertile phase, as reflected in their tips. How they advertise, however, and whether they do it consciously, is unclear. "We don't know the mechanism of attraction," says Thornhill, who is also at the University of New Mexico but was not involved with the study. "Are the men detecting the scent of oestrus? Or does the women's behaviour change?" he asks.
"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, says Thornhill. In the context of lap dancing, that may subtly change their behaviour and make them more appealing to clients.
If the abstract is correct, the differences are large.
Normally cycling participants earned about US$335 per 5-h shift during estrus, US$260 per shift during the luteal phase, and US$185 per shift during menstruation. By contrast, participants using contraceptive pills showed no estrous earnings peak. These results constitute the first direct economic evidence for the existence and importance of estrus in contemporary human females, in a real-world work setting. These results have clear implications for human evolution, sexuality, and economics.
Certainly they do for the economics of lapdancing. The tips for a girl who's (biologically) ready to become pregnant are double than for a girl who's menstruating. How do the guys (subconsciously) know ?
If it's scent, there's a fortune to be made for the first cosmetics house to get it into a perfume and market it.
UPDATE - Susan says "I'm sure it's scent. Isn't there research where a load of girls watched a film, then a smaller number of men saw the next showing ? The men tended to choose the seats the fertile girls had been sitting in". Can't find the research on the web, though.