The Tree of Kink: What science teaches us about fetish clusters
How deep is your kink?
Most people reading this article have had sex. Most don’t talk about it much. This isn’t to say Big Think’s audience is especially prudish, but it just reflects a very modern sensibility: Sex is a private thing to talk about in private.
In fact, even reading about it right now can be jarring for many people. There’s a kind of “context collapse” that happens when you come to a site like ours to read about astrophysics, neuroscience, and philosophy, only to find you’re reading about fisting, BDSM, and foot fetishes. Hide the phone, check your surroundings, and make sure no one can read over your shoulder.
These are all things I spoke to Aella about for this week’s Mini Philosophy interview. Aella is a sex worker and writer who has one of the most popular newsletters in the world and is famous not only for her candor but also her rationalistic, data-driven attitude to all things sex. And, as I suspected, our conversation was insightful, intelligent, and philosophical.
You can hear the full conversation in this week’s newsletter (and it’s very much NSFW), but one of the more curious things we spoke about was the “tree of fetishes” — the idea that people’s kinks and sexual preferences are not isolated but clustered.
The “Tree of Kink”
No sexual act is the same. Even for the same couple, a person’s mood and body will be different. The location and the time will change. To paraphrase Heraclitus, “You cannot have the same sex twice, because neither you nor your partner will be the same.”
One of the key elements of this has to do with sexual preferences. At its most basic level, this might be about the when and how of sex. But it’s also about fetishes. Fetishes are those predilections people have that go beyond what is considered heterodox, most common, or “vanilla.” A fetish might vary from wanting to keep the lights always on all the way to dressing up as Pokémon. It might be an in-the-heat-of-the-moment thing, or something that requires weeks of planning.
In our interview, Aella mentioned that fetishes can change over the course of a lifetime. They can come and go. They might morph, but only so far. Aella introduced me to a curious fact: Fetishes tend to cluster. If you tend toward one kind of kink, you are more likely to tend toward another.
“I have built a tree out of a bunch of data based on fetish clusters,” Aella told me. “It’s called a dendrogram. And you can sort it by closeness. Like one interesting thing, for example, is that foot fetish guys are much more likely to be into pee and also armpits and other parts of the body. And this is like a cluster. Is this pointing at, like, something that’s conditioned or something that’s underlying? I’m not sure.”
The five kink clusters
Aella is famous for collecting data about all sorts of sexual topics, but most relevant is how she surveyed thousands of people on how taboo various fetishes felt, which also revealed how common they were, leading to her theory of kink clusters. However, what she has learned on her own has also been corroborated in the peer-reviewed academic literature.
In 2021, a team from Maastricht University looked at the vast variance of fetishes and isolated five “factors” underlying most of them. What the researchers called factors, Aella calls clusters. Here they are in order of how common they are:
First, submission/masochism.
Second, dominance/sadism. These two, collectively known as BDSM (whipping, handcuffs, gags, etc.), are by far the most common fetishes across almost all demographics. As Aella put it, “If you imagine fetishes as a tree where the trunk is the base sexual thing, then it actually splits off at BDSM in the first split. You get the BDSM fetishes and you get the rest of the fetishes.”
Third, fetishism bundles together arousal to non‑personal objects or unusual body parts — “such as plush, feet, and dwarfism.”
Fourth, mysophilia is about traditionally unhygienic activities, like urination, defecation, or body odor.
Finally, “forbidden sexual activities” covers illegal or non‑consensual behaviors like sex with family members, corpses, or animals.
Factors three to five are all considerably less common than BDSM.
Deep kinks
Fetishes are such a large part of sex, yet researchers know relatively little about their neurobiological mechanisms and psychological origins. Why do people have certain fetishes, and why do some seem to cluster together? Could it be that someone who’s into urine is also more likely to be into, say, armpits because both are considered unhygienic? Maybe. Then again, maybe not.
“It really depends on the person and the fetish and the gender,” Aella said. “And like, none of this has any rhyme or reason at all.”
There are similar uncertainties about when fetishes emerge. Aella told me that many of her clients will tell her of a single and transformational moment when “they just knew” they had a fetish, but she isn’t sure how accurate these may be. It’s very easy to retroactively isolate an incident. After all, almost everyone reading this has been exposed to naked feet, urine, and stuffed toys, but hasn’t felt a subsequent kink emerge.
Aella has a theory. She thinks that some kinks might be more or less “strong” and so may come and go more often than others. For example, if you like feet in your 20s, you might not by the time you retire. As she put it, “My theory is that different fetishes occur probably in different places of the brain and that some are more malleable than others. For example, BDSM, I think, is an extremely deep fetish, and either you’re into that or you’re not for your whole life. Whereas, like, others might not be. But, who knows?”
Jonny is the creator of the Mini Philosophy social network. He’s an internationally bestselling author of three books and the resident philosopher at Big Think. He's known all over the world for making philosophy accessible, relatable, and fun.
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