Browsing through a recent volume of Evolution and Quirky Behavior, I was startled by the title of an American study: "Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus?"
As you know, 'estrus' (or oestrus, as we say in the UK) is a phase of increased female sexual receptivity, selectivity and attractiveness.
Whilst many scientists carry out their research in laboratories, this team of libidinous psychobiologists (from the University of Night Life) collected their data from the real-world work setting of lap dancers (who typically perform in 'gentlemen's clubs' late at night).
After looking at their tits, the researchers measured the tips earned by professional lap dancers, and came up with the "first real-world economic evidence of male sensitivity to cyclic changes in female attractiveness".
These lap dancers apparently became more attractive to male club patrons at mid-cycle, just before ovulation. The evidence for this was that they were in higher demand and earned bigger tips for showing their tits during this phase.
The researchers (or economically-biased oglers) were clearly excited by their findings. "We suspect," they say, "that human estrous cues are likely to be very flexible and stealthy - subtle behavioural signals that fly below the radar of conscious intention or perception, adaptively hugging the cost-benefit contours of opportunistic infidelity."
So there you have it - you've been warned.