I love the Bonobos, those crazy little apes. You know what I like best about them? Just like us, those little guys like to have sex all the time. I am not kidding; living in the primal horde is like having been 20 years old in the 1970s. Unlike other ape species, female bonobos engage in sex even when they are not fertile. They do it just for fun. They even like girl-ape on girl-ape action from time to time.

Human females also have sex when they are not fertile and, in fact, most women cannot tell you when they are at peak fertility. The evolutionarily dominant strategy for human females appears to have been to conceal their fertile phase from their mates. You see how this could improve the fitness, which is dependent on the survivability of their children, of one of our ancient ancestors. If her mate knew she was fertile, then she would have a pretty hard time sneaking out to get herself inseminated by a superior male. Even if she did, her mate might be suspicious and refuse to provide for any offspring she then has. So she conceals her fertility from her mate to prevent mate-guarding and she does so well that eventually she conceals it from herself.

So it is accepted that humans have concealed fertility, but maybe we let up little clues from time to time and swing our hips a little more when we walk, dress a little more provocatively, smile a little more, and become a little chattier. These little hints of fertility are called "estrus cues" and their existence has been tested in a laboratory. It turns out that, maybe, we don’t conceal our fertility as well as we think. There is a way of determining this without experiments that uses the theory of revealed preference that I wrote about in my last post, Do Women Value Ethnicity Over Income in a Mate? If a man reveals that he prefers a woman who is at peak fertility to an identical woman who is not, then we would have proven that he has picked up on subtle clues that the woman is fertile. The best way to measure just how much he prefers her is by seeing how much money he is prepared to spend to be close to her. So, who pays to be close to a woman? Well, patrons in lap dancing clubs of course.