It's no secret that hundreds of millions of people around the world now routinely use the Internet to indulge their sexual curiosity. Today you can ogle more naked bodies in a single minute online than the most promiscuous Victorian could have seen in a lifetime. Because this online activity leaves behind a trail of digital crumbs, for the first time we can gather reliable data on the erotic interests of a broad swath of humanity.

My colleague Sai Gaddam and I have analyzed a billion of these web searches, using data sets that firms like AOL and Excite make publicly available, obtaining other data from adult web sites, and using web-analysis techniques to gather additional data.

One of our most interesting findings was that women are very different from men in how they use these online services. All across the planet, what most women seek out, in growing numbers, are not explicit scenes of sexual activity but character-driven stories of romantic relationships.

The female cortex contains a highly developed system for finding and scrutinizing a prospective partner—a system that might be dubbed the Miss Marple Detective Agency. Agatha Christie's fictional sleuth is often dismissed as scatterbrained, but she is actually a shrewd judge of character and harbors deep knowledge of the dark side of human nature. She uses her surprising analytical acumen to solve mysteries that have stumped the police.

Using similar investigative skills, the female brain evaluates all available evidence regarding a potential mate's social, emotional and physical qualities to make an all-important decision: Is he Mr. Right or Mr. Wrong? Only if Miss Marple gives her stamp of approval do physical arousal and psychological arousal harmoniously unite in the female brain.