Now this is some pretty interesting research. Here's the punch-line: Lap dancers earn more when they are fertile.
Because ScienceBlogs readers may be unfamiliar with the gentlemen's club sub-culture, some background may be necessary to understand why this is an novel setting for understanding real-world attractiveness effects of human female estrus.
Given that estrus - the outward signs of female ovulation - is concealed in humans, it is commonly thought that men cannot detect when women are fertile. Think again.
This theory is based on the idea that in evolutionary terms it benefits women to disguise when they are fertile so that their men stick around all the time. Otherwise, a man might go hunting for alternative opportunities at moments when he knew that his partner was infertile and thus that her infidelity could not result in children.
The result? An evolutionary arms race between the sexes, as men should evolve ever-heightened sensitivity to signs of female fertility. University of New Mexico Professor Geoffrey Miller was keen to test the hypothesis. He thought lap-dancing clubs were the perfect place to study this arms race, because male detection of female fertility would likely translate into a sure signal: dollars earned. He recruited female dancers for a experiment to to compare the earnings of those on the Pill with those that were not on birth control.
The results were shocking, and support the idea that if evolution has favored concealed ovulation in women, it has also favored 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-the same amount that women on the Pill made throughout the month.
The message is clear. A woman is sexier when she is fertile. And if she wishes to earn a good living as a dancer, she should stay off the Pill.
Dr. Miller published his research in the journal Evolution and Human Behavior.
Brain & Behavior
Humanities & Social Science
Comments
Birth control pills have also been shown to alter the smell preferences of women.
Posted by: Milan | March 21, 2008 8:14 PM
Kate did a great summary of that article back when it first came out.
Posted by: Coturnix | March 21, 2008 9:04 PM
The other female guest blogger at Pure Pedantry, Kara Contreary, also had a nice discussion of the article when it first came out.
Posted by: The Neurocritic | March 21, 2008 9:16 PM
Concealed ovulation isn't unique to humans: Orangutans, marmosets, vervet monkeys and spider monkeys do not show visible signs of ovulation, although most primates do. (I don't know about olfactory or other signals.)
Hrdy proposed that, if a primate father is never truly certain that a child is his, concealed ovulation reduces the likelihood of infanticide by males--a male might be killing a competitor's child...or he may be killing his own. Obviously infanticide is an evolutionary problem for females, so this could be a very effective way of combating the difficulty. By the same token, it'd make evolutionary sense for males to develop ways of 'seeing through' this deception in what sounds like a co-evolutionary arms race.
Sillen-Tullberg & Moller looked at the phylogenetics of concealed versus advertised ovulation and mating systems (monogamous through promiscuous) in primates. Most primate groups that advertised ovulation and then evolved concealed ovulations were promiscuous, thus supporting Hrdy's hypothesis. However, monogamy never evolved in species that advertised estrous boldly. Alexander & Noonan hypothesized that, if a male has no clue when the female is in estrous, he should stick around, both to improve the chances of fertilizing her and to guard her from male competitors. This hypothesis, the antithesis of Hrdy's, is supported by the evolution of monogamy in primates (such as it exists!).
Diamond points out that concealed ovulation has had multiple functions at different times in primate evolution. When primates are promiscuous, concealed ovulation may arise to reduce infanticide. Once concealed ovulation is in place, it may serve as a means to encourage male (but not female!) fidelity.
It's all pretty interesting especially with Mr. Spitzer's infidelity in the recent news, but these concepts really only apply to human behavior outside of a close and largely committed relationship. I'm making the dangerous assumption that most males are reasonably aware of where their partners are in their ovulatory cycle, at least to some approximation. One weakness with the Miller study (which they point out) was the absence of a test to determine whether the patterns observed were evidence of males over-coming a form of deception or females signaling their receptivity (of a sort).
Perhaps the shifting baseline here is the level of concealment necessary to hide human estrous. Evolution happens!
Posted by: Peter Nelson | March 24, 2008 4:36 PM
Conspicuous by their absence are any comments containing the the following words: ten, foot, pole...D'oh!
Posted by: doug l | March 28, 2008 11:32 AM
In what alternate universe can human women hide their ovulation cycle? My boobs and rear end balloon when I ovulate, and I'm downright grumpy when I menstruate. Maybe only my husband knows me well enough to notice the (good and bad) effects of my cycle.
Posted by: Rebecca | April 8, 2008 9:01 AM