This theory is based on the idea that in evolutionary terms it benefits women to disguise when they are fertile so that their menfolk will stick around all the time. Otherwise, the theory goes, a man might go hunting for alternative mating opportunities at moments when he knew that his partner was infertile and thus that her infidelity could not result in children.
Well, it turns out that men are, not consciously, quite apt at this as the results showed a $150 dollar difference in earning potential while fertile.
The results support the idea that if evolution has favoured concealed ovulation in women, it has also favoured ovulation-detection in men. 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.
Usually my point would be look at this neat evolutionary thing, or that it's odd that the Christian worldview is wrong once again as women and men wouldn't need estrus or any of this detection ability to sleep around if they are just to be married and have children as God intended (this was Austin Cline's point). Nope, I think it is rather interesting that strippers could net $150 more on average (during estrus) if they didn't use hormonal birth control.