Searching all the porn on the Internet might not seem like the most scientifically productive activity, but computational neuroscientists Ogi Ogas and Sai Gaddam did it anyway.

For their new book, A Billion Wicked Thoughts: What the World’s Largest Experiment Reveals about Human Desire, Ogas and Gaddam analyzed the results of 400 million online searches for porn and uncovered some startling insights into what men and women may really want from each other — at least sexually. I spoke recently with Ogas.

Why did you decide to analyze online porn searches?

I’m a computational neuroscientist. I view the mind as software. Most computational neuroscientists study higher functions like memory, language and vision. We wanted to apply the same techniques to a lower part of the brain, the sexual part.

So is “Rule 34” true — that if you can imagine it, there’s porn of it?

When we first started, Rule 34 was almost a guiding idea. The Internet has every kind of imaginable porn; searches are going to reflect immense diversity. We quickly realized that [the data] didn’t really support that.

Even though you can find an instance of any kind of porn you can imagine, people search for and spend money and time on 20 sexual interests, which account for 80% of all porn. The top five are youth, gays, [sexy mothers], breasts and cheating wives.

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Why are cheating wives so popular? You’d expect that would not be something men would like to think about.

It’s one of the top interests all around the world. Men are wired to be sexually jealous. And, certainly, men can fly into murderous rages, but simultaneously they’re also sexually aroused.

This is an example of what biologists call a sperm competition cue. Across the animal kingdom, when males see other males mating, it tends to provoke arousal. If he is going to compete with the other male, he has to produce more sperm

Human men also respond like this, if a man sees a woman — including his partner — with another man, he becomes more aroused.

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There’s been a lot of concern that porn is getting more violent and more misogynistic and that the Internet is making it harder for women because porn makes men want more extreme sex. What does your research show?

It’s not at all more violent or misogynistic. We really looked at all porn searches. Truly violent pornography is extremely rare. It truly is rare and the kind of people who watch it are a clearly identifiable group.

So why do we keep hearing that it’s getting worse and worse?

I wouldn’t say there’s a trend. It’s been pretty consistent. There’s lots of male dominant porn. He blackmails the woman into having sex; the professor seduces a student, they’re having sex to get cash for schoolbooks. We think all of these are creative variations to trigger male-dominance cues [which are sexually arousing to men].

Why do the themes of dominance and submission keep recurring?

Women are often aroused by women being submissive. It’s more complicated for women because of the separation between physical and psychological arousal. Women have very mixed feelings when [it comes to sexual submission]. But rape fantasies are extremely prevalent.

Obviously, that doesn’t mean that women want to be raped, but doesn’t the prevalence of forced sex in porn make men think that they do?

It’s not teaching men to be misogynistic; it doesn’t spill over into social life. It’s really no different from looking at large breasts. But women react to these psychological elements and understandably and accurately see them as a kind of misogyny.

However, we’re talking sex and arousal, not social politics. A rape fantasy doesn’t mean a woman really wants to be raped — it’s just something that turns [her] on [in the bedroom].

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There are real concerns, though, that Internet porn will increase sex crimes because of the way it portrays things like that.

Anybody can do a simple thought experiment [to refute that]. In the late ’60s and early ’70s, feminists were saying that porn trained guys to be rapists. That was before home video, and there were probably only 100 different porn magazines in the country. You had to go to [sleazy places to watch porn]. Now there are a million websites where you can get it for free around the clock.

You would expect rape to skyrocket. There are more guys watching more porn more often. But, in fact, rape has gone down in America. Also, in Japan in the mid-’90s, they loosened their obscenity laws. Now rape is down there too. It certainly seems to be case that more access to porn is associated with less rape. Rather than making people want to go out and rape, it satisfies the urge.

What types of porn are most popular for men?

It’s youth by a wide margin, like cheerleaders. But we were surprised to find that even though men prefer youth mostly, there’s also a very significant interest in porn with women in their 40s, 50s and even 60s. That’s called granny porn.

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That’s fabulous for older women who seem to have been written off by evolutionary psychology. Seriously, though, the interest appears to be completely counter to evolutionary predictions that overt signs of fertility are crucial.

Yes, we found something that overturns narrow evolutionary psychology predictions. Some of our findings require other explanations than evolutionary ones.

What do women prefer?

Women prefer stories to visual porn by a long shot. The most popular erotica for women is the romance novel. That has more punch than any other kind of erotica. The second most popular would be fan fiction. This is something that has really exploded on the Internet. These are stories written by amateurs, mostly women, about characters from pop culture, movies, books, etc.

Is this the kind of thing in which Kirk and Spock from Star Trek would have an affair?

Yes, that’s called slash. Stories about two male characters are very popular. But the most popular fan fiction is about Harry Potter by a wide margin, followed by Twilight.

Why do women prefer stories and men prefer visuals?

There are two reasons. Both come down to fundamental differences between the male sexual brain and the female sexual brain. One of the most basic differences is that the male brain responds to any single sexual stimulus. A nice chest, two girls kissing, older women — if that’s what they’re attracted to. Any one thing will trigger arousal in a male.

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Female desire requires multiple stimuli simultaneously or in quick succession. It takes more stimuli and more variety of these stimuli to trigger genuine arousal.

For a guy, the most common form of [masturbation material] is a 60-second porn clip. For a woman, it can be a 250-page novel or a 2,000-word story. That’s the way to get multiple stimuli. Stories have greater flexibility to offer a greater variety of stimuli.

In male erotica, sex appears in the first one-quarter of the story [or film]. For women, it’s halfway in. There’s more time to develop the character before sex.

How else does male and female sexuality differ?

Another fundamental difference between men and women — perhaps the most important defining difference — is that in the male brain, physical and psychological arousal are united. If a man is physically turned on, he’s mentally turned on too.

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With women, physical arousal and mental arousal are separate. [Research finds that women get physically aroused sometimes even when they find the situation disgusting.] The female brain is designed to be cautious, most likely because historically the woman who slept with the first guy she met might have a harder time raising children; he might not stick around. Women are designed to be cautious and gather more information.

That’s why fan fiction is all about exploring the emotions and character of the hero. In romance novels, the heroine learns about the secret inner life of the hero. That’s especially true in slash: that’s doubling up. There are two men — two masculine, strong alpha males who reveal their tender side. The emotional process of revealing true character is what’s so appealing to women.

Why would straight men want to watch lesbians, and why would women write stories about gay men?

[Straight] guys are turn on by lesbians because it’s a doubling of visual cues. And one psychological cue for arousal in men is female sexual pleasure. Seeing lesbians kissing doubles that too.

For women in slash fiction, it’s the psychological cues of a man’s character, stature, passion and emotional communication — slash doubles those.

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What’s up with men’s interest in mothers?

It’s not so much that they’re moms, but that they’re older women. They are usually portrayed as aggressive and seductive. They are not timid. They’re quite confident and bold. Men who like that like the idea of an innocent younger man being seduced or taught by an older woman.

Did you find evidence that porn is addictive?

We looked at individual search histories for half a million people using an AOL data set [which does not identify the users]. It seems to be less than 2% of people, among the people who search for porn, who have a significantly elevated number of searches.

And there’s a [shared] characteristic among these searchers: they search for a really wide variety of porn, which is atypical. Usually, people search for the same things over and over. But these people who search for notably more porn tend to search for [many different things].

Two things tend to show up in these searches, oddly: bestiality and granny porn. There’s clearly something different about that group. Having said that, there isn’t overwhelming evidence that porn addiction exists. Probably the best way to define whether it’s a problem is if you want to stop and you can’t.