This sort of physical response to varied sexual stimuli notwithstanding that the women's brains may not be along for the ride may have its origins in evolutionary theory.
The men, on average, responded genitally in what Chivers terms "category specific" ways. Males who identified themselves as straight ... were mostly unmoved when the screen displayed only men. Gay males were aroused in the opposite categorical pattern. ....And for the male participants, the subjective ratings on the keypad matched the readings of the plethysmograph [sensors measuring physical reactions, the objective measure in the test].
All was different with the women.... [W]ith the women, especially the straight women, mind and genitals seemed scarcely to belong to the same person. The readings from the plethysmograph [objective measure] and the keypad [subjective measure] weren't in much accord.
Ancestral women who did not show an automatic vaginal response to sexual cues may have been more likely to experience injuries during unwanted vaginal penetration that resulted in illness, infertility or even death, and thus would be less likely to have passed on this trait to their offspring."
Chivers has scrutinized, in a paper soon to be published in Archives of Sexual Behavior, the split between women's bodies and minds in 130 studies by other scientists demonstrating, in one way or another, the same enigmatic discord. One manifestation of this split has come in experimental attempts to use Viagra-like drugs to treat women who complain of deficient desire.
[...]Quite by accident, though, one pharmaceutical company seems to have stumbled on a possible remedy.
The pills...don't, for the most part, manufacture wanting. And for men, they don't need to. Desire, it seems, is usually in steady supply. In women, though, the main difficulty appears to be in the mind, not the body, so the physiological effects of the drugs have proved irrelevant. The pills can promote blood flow and lubrication, but this doesn't do much to create a conscious sense of desire.
The medication was originally meant to treat depression ... [y]et in early trials, while it showed little promise for relieving depression, it left female — but not male — subjects feeling increased lust....[T]he chemical ... may catalyze sources of desire in the female brain.
The reason I mention this drug trial is that it's just so fascinating how serendipitous drug discoveries are. The birth control pill had a similar story of birth (heh heh). The drug was initially fashioned as a pill to regulate menstrual cycles in women who complained of irregular periods. Researchers found later that the pill also served to suppress pregnancies. And so came into being the birth-control pill. (Amrita's post "Pill of Shame" and Ra's post "A Brief History of Pain" are good indications of how culture trumps medical necessity when it comes to women's bodies.)
The 10-page article goes on to discuss the role of intimacy and culture in female sexuality. If you are interested in that sort of thing, the article, written by Daniel Bergner whose book The Other Side of Desire: Four Journeys Into the Far Realms of Lust and Longing is set to be released this month, is definitely worth a read.
Updated to add a link to Ra's post.