Can Men Tell If Women Are Fertile?

Few men consciously know that women are fertile, and outward signs of fertility in women called "oestrus" are less obvious than in many mammals, but our unconscious minds appear to be more canny. The latest evidence? The earnings of lap dancers (may be subscription only):

The average earnings per shift of women who were ovulating was $335. During menstruation (when they were infertile) that dropped to $185—about what women on the Pill made throughout the month.

This isn't the only study looking at the subtle impacts of the menstrual cycle on women. Among the most interesting is one suggesting that long documented differences in spatial ability between men and women is a function of testosterone levels and varies during each month in women (also here and here; see, reaching the opposite conclusion, this study; see reaching mixed conclusions here; meta-analysis weakly supporting the concept here).