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Some of the most popular porn in the United States reflects sex that has little to do with viewers’ actual sex lives. According to statistics released by Pornhub, the largest pornography website, hentai was the second-most-searched term on the platform in 2017, gaining traction in the U.S., in particular. This type of porn, inspired by classic anime, typically features animated figures with fantastic or cartoonishly exaggerated physical features: huge, bulging eyes or breasts larger than their waist. Sometimes they’ll have horns or tails or cat ears—or multiple sets of genitalia. “It’s like most foods we consume these days: built for maximum craveability,” said the sex therapist Stephen Snyder. “Like a Cronut, or cream-cheese sushi. They cook this stuff up. None of it is natural.”

While there’s very little data on the types of porn that were popular before Pornhub started keeping track a few years ago, “niche” and “novel” categories that allow viewers to escape to a fictional reality have certainly been gaining steam, said the social psychologist Justin Lehmiller, the author of Tell Me What You Want: The Science of Sexual Desire and How It Can Help You Improve Your Sex Life. As Kate Julian reported in her recent Atlantic cover story, for many of the Millennials she interviewed, porn viewing and real-life sex “existed on separate planes.” “My porn taste and partner taste are quite different,” one man in his early 30s told Kate.

Porn wasn’t always customized for viewers with niche interests. From the late 1960s through the mid-1980s, porn in the United States was primarily available in the about 1,000 select theaters across the country that specialized in “adult entertainment,” said Peter Alilunas, a porn historian at the University of Oregon. At first, these theaters screened what today is known as soft-core pornography, such as a series of 10-minute films of people taking off their clothes. Over time, these films become more naturalistic, and grew to develop narrative, plot-driven elements, including depictions of two people having sex that were more realistic than what is popular today.

What Alilunas calls the “theatrical era” gave way to the home-video era of the late ’80s and early ’90s. Porn consumers had more choice—movie stores sold and rented a variety of pornographic videos on VHS—but they were somewhat hamstrung by what they were willing to purchase in public.

The internet has introduced a “stunningly massive algorithmic system,” Alilunas told me, allowing consumers to choose from thousands of tailored categories and subcategories catering to a wide variety of fantasies. Since the early 2000s, one company, MindGeek, has taken a dominant position in the industry. It manages the vast majority of the biggest porn websites, and it's been using its reach in the marketplace to compile and categorize a massive database of porn videos. As a result, viewers can find exactly what they're looking for—whatever that is. “They’re doing the same thing that Netflix and Hulu are doing,” Alilunas said. “They’re just doing it for porn.” The result, Lehmiller told me, is “a catalog of endless diversity.” Almost anything can be found with a few keywords and the click of a button.

Because companies such as MindGeek “push what people pay for,” said Jennifer Johnson, a sociology professor at Virginia Commonwealth University who specializes in pornography, they might drive viewers toward more niche material. Most people don’t pay for porn—their viewing is underwritten by advertising. But porn websites, Johnson told me, cater most to their paying customers, giving prime placement to their tastes. “The porn that is most easily accessible is that which is most stimulating and interesting to the most active users,” Johnson said.

Humans, Lehmiller told me, also have an intrinsic desire for “newness” and “novelty.” Viewers of pornography tend to go through cycles of different pornographic interests, Alilunas said, watching a lot of one type of porn for a while before moving on to something else, and then sometimes circling back around. Lately, Lehmiller said, there’s been a steady stream of porn that incorporates elements of fantasy and science fiction, a trend likely spurred by evolving animation and CGI techniques. (Vampires and robots, he told me, have been especially popular.)

Humans may also want to watch sex they’d never have in real life precisely because they know they’d never have it in real life, suggests the psychologist David Ley, who specializes in treating issues of sexuality. “Why do you think people watch superhero movies?” he asked me in an interview. “We know we can’t fly, but we want to watch it anyway. It’s the same thing with porn.” The fantastical elements of porn can be particularly meaningful for people who have experienced some kind of sexual trauma. Hentai, Ley told me, is “distinct enough from regular sex that it allows [victims of sexual assault] to be erotic without being a trigger.”

It’s not clear how all this fantasy porn is affecting the sex lives of the people who watch it. In his research, Lehmiller has found a weak correlation between people who have more sci-fi–type fantasies and those who report lower sexual satisfaction. It’s hard to draw any significant conclusions from the studies that track how porn (of any genre) affects individuals over time, Ley wrote in an email, because results are “primarily driven by individual characteristics.” For example, Ley said, if a person is very religious, or has a partner who is, and reports viewing porn, she may be more likely to also report feeling unsatisfied with her sex life. The same could be true  if one partner watches far more porn than the other.

While hentai and vampires are the porn fads of the moment, Lehmiller told me, they probably won’t last long. He also said it’s impossible to determine what the next fad will be. Sometimes popular fantasies are inspired by cultural touchstones—movies, memes, or TV—but many just materialize, fully formed, in the human imagination. “You don’t necessarily need to have an external stimulus that prompts a sexual fantasy,” Lehmiller says. “Sometimes it just comes from within.”

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