A blog about human evolution, economics, and sexual physiology
Why do strippers make more money at different times of the month?Hayley Chilton
As many of you may have noticed, human females don’t broadcast their ovulation in the same way their female counterparts in the animal kingdom do. Contrasting to the enlarged red genitalia displayed by primates, or your pet dog that has a distinct discharge, human females have a more discrete way of displaying signs of estrous (the time of the month when ovulation occurs and women are in their sexual peak) that is sometimes only detectable on a subconscious level. So what accounts for these behavioral signals between men and women that let men know when women are most fertile? How do men's perception of the same woman differ and varying points throughout her cycle? Women don’t really go into “heat” they way animals do, rather hormones and other factors at the crux of fundamental biology, which have been found to play a key role in sexual desire distinguish this hidden fertility. Until more recently researchers thought that estrous had been lost through evolution. However, a study done by psychologist Geoffrey Miller and his colleagues at the University of Mexico advocates otherwise. Results from a two month study at a local gentlemen’s club indicates that women do in fact give off these subtle cues that men can pick up, suggesting a natural selection pressure toward men who are better able to distinguish when women are ovulating, and a natural selection pressure toward women who send these signals and attract the most desirable mates. The basic principle that men are seeking to pass on their genes makes them inherently attracted to women that are nearing peak fertility.
The name of the institute itself, strip club, can be taken literally in that women strip off their clothes and inevitably strip men of their money through the power of seduction and forced intimacy. Strip clubs have been strategically designed to contain a labyrinth of private rooms that frame several stages displaying hyper-sexualized women, seducing men with their scantily clad outfits and surface conversations. In all, the atmosphere it creates is an ideal environment for studying the spending behavior patterns of lustful men. While the seduction between the patron and the dancer may be artificial, the biologically based mechanisms of attraction and chemical signaling cascades the encounters elicit are real.
Feelings of motivation and emotion are driven by neurochemical responses received by the limbic system. This system is involved in responses to sensory information, including feelings of anger, sadness, happiness, satiety, desire, and sexual behavior. The limbic system is comprised of several regions of the brain including the frontal cortex, the hypothalamus, and the amygdala – all of which are intricately interconnected by bundles of nerves. These connections are important for regulating hormone release. Thus, sex hormones (like testosterone) play an important role in regulating the endocrine response in males when they are exposed to mating cues. In particular, it has been found that a male's testosterone levels are up regulated in the presence of an estrous female.
So what makes some dancers more successful than others? The study by Geoffrey Miller followed several dancers over a period of two months while recording their work shifts, income, and menstrual periods. The same individuals were observed over the course of the study. Results provided economic evidence insinuating the importance of ovulation for the tip earnings of these dancers, with dancers earning $335 per shift during estrus, $260 during anestrous shifts, and $185 per shift during menstruation. Furthermore, women taking birth control pills did not see a spike in earnings during their ovulatory period, indicating that the hormones regulated by contraceptive pills possibly mask the cues women subtly exude during certain times of the month.
|Figure 1. A comparison of average dollars earned per shift for normally cycling women compared to those using oral contraceptives. This shows women earned more dollars per shift during periods of ovulation.|
|Figure 2. A comparison of average dollars earned per shift for normally cycling women compared to those using oral contraceptives. This shows women earned more dollars per shift during period of ovulation.|
So now that it has been established that men prefer estrous dancers, how can they tell which ones are ovulating and which ones aren’t? It has been found that in general ovulating women tend to indirectly play up their best features, as the quality of their skin naturally improves along with their curves, the sound of their voice, and their overall appearance. This is true for any female on a monthly basis, as the body naturally makes slight adjustments to increase their appeal to the opposite sex during fertile periods. A study by Cora Bobst and Janek Lobmaier from the University of Bern demonstrates that men have a greater propensity to be attracted to the face shape of an estrous female than that of an anestrous female based on two images of a given woman at two different points in her cycle. Yet, these changes are so subtle that not even the estrous woman herself may even be aware of them.
|Figure 3. The woman in panel A is considered estrous, while the woman in panel B is considered anestrous. Subtle face shape differences have been attributed to men's preference for estrous women.|
Aside from these physical changes, it has also been found that females, as sign of fertility, are releasing olfactory signals that can be perceived by men. The close proximity required for small talk in the dark and loud strip clubs allows men to detect these released pheromones, thereby eliciting a response in their own male testosterone levels. Another study by Saul Miller and Jon Maner of Florida State University demonstrated that men exposed to the scent of an ovulating female did experience spikes in testosterone levels compared to exposure to the scent of anestrous females. In this study men were allowed to smell three types of shirts: those worn by females during ovulation, those worn by women that were not ovulating, and those not worn by anyone.
|Figure 4. This graph shows that the average testosterone levels in men increased the most after smelling shirts worn by women during ovulation. All women in this study had regular menstrual cycles and did not use oral contraceptives.|
Conclusions drawn from this study again suggest that olfactory ovulation signals not only play a role in mating behavior patterns observed in animals such as rodents or primates, but they also provoke the up regulation of specific hormones, in this case testosterone, in the human male sexual response. Men use this response as a measure of their own stimulation, which in turn explains why they might be willing to spend more to be with a more sexually arousing woman at a strip club. So, despite that these dancers were unaware of their enhanced provocative display during certain times of the month, it would be in their best interest to take advantage of this natural physiological response during periods of fertility and schedule their shifts accordingly to maximize their revenue!
Bancroft, J. 2005. The endocrinology of sexual arousal. Journal of Endrocrinology 186: 411-427.
Bobst, C. and J. S. Lobmaier. 2012. Men’s preference for the ovulating female is triggered by subtle face shape differences. Hormones and Behavior 62: 413-417.
Miller, G., J. M. Tybur, and B. D. Jordan. 2007. Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus. Evolution and Human Behavior 28: 375–381.
Miller, S. L. and J. K. Maner. 2010. Scent of a Woman: Men’s Testosterone Responses to Olfactory Ovulation Cues. Psychological Science 21(2) 276–283.
Swenson, R. S. 2006. Limbic System. Review of Clinical and Functional Neuroscience.