“Well sung of Yore, a Bard of Wit/That some Folks read, but all Folks shit/But now the Case is alter’d quite/Since all who come to Boghouse write.”

So was written on a boghouse sometime in the early 18th century—a boghouse being a public toilet. An Englishman going by the pseudonym “Hurlo Thrumbo” collected this and other such vintage graffiti in his book The Merry Thought: Or, The Glass Window and the Bog-House, published in 1731.

This is far from the first recorded instance of someone scrawling a bit of mid-poo poetry—for example, the Roman poet Martial, who lived in the first century AD, totally zinged a rival writer with the suggestion that if he wanted to get published, he should go find a bathroom wall.

“If you aim at getting your name into verse, seek, I advise you, some sot of a poet from some dark den, who writes, with coarse charcoal and crumbling chalk, verses which people read as they ease themselves.”

An oft-cited 1983 study defines three categories of graffiti: Tourist graffiti (“John wuz here”), inner-city graffiti (like tagging and street art), and toilet graffiti (or “latrinalia” as it’s sometimes called in academic literature).

What makes toilet graffiti special, and worthy of its own entire category, is the uniqueness of the space in which people are writing. Public bathrooms are weird places. There’s a tension to doing private activities in a public space, with only the flimsiest of boundaries hiding some of our culture’s biggest taboos—genitals and bodily functions. Hence all the scatological and sexual prose that latrinalia often consists of: People are just deriving inspiration from their surroundings.

Public bathrooms are also (usually) gender-segregated, creating institutionalized single-gender spaces that you almost never see anywhere else. Perhaps because of this, most research on toilet graffiti has studied the differences between what men and women write in their respective stalls. Alfred Kinsey (yes, that Alfred Kinsey) was the first to do this, in the 1950s. He and his team found that men wrote more, and dirtier, things than women, who were more likely to write about romantic love.

“Kinsey and his colleagues suggested that women’s lesser tendency to produce erotic graffiti was due to their greater regard for moral codes and social conventions,” writes Nick Haslam, a professor of psychology at Melbourne University, in his book Psychology in the Bathroom.

These fairly stereotypical analyses persist in toilet graffiti studies over the years. Though some studies say women write just as much as men, men’s is typically seen as being more aggressive and more sexual, while women’s is more conversational and more likely to be about love. Though most bathroom graffiti research was done in the 60s, 70s, and 80s, a couple studies done in the past few years have found similar things.

Nicholas Matthews, a PhD candidate at Indiana University, was the lead author on a 2012 study that analyzed toilet graffiti in nine bars in a Midwestern town. He and his fellow researchers found that the most common type of graffiti was “presence-identifying” (just scrawling your name, for example), but men were identifying their presence more than women. Women, on the other hand, wrote more insults. Matthews explains this using evolutionary psychology, saying that boosting oneself up is a typical male mating strategy, whereas putting other women down is a classic female gambit.

These are tidy explanations, but if I can stop you from furiously scribbling a book proposal titled Women Draw Hearts, Men Draw Penises for just a moment, the difference between men’s and women’s bathroom graffiti isn’t necessarily indicative of hard-wired differences between the genders. The mere fact of being in a public bathroom could be skewing how people choose to present themselves when they uncap that Sharpie.

When a woman goes into a women’s restroom and finds herself surrounded by only women (in a room full of mirrors, no less), she may very well become hyper-aware of the fact that she is a woman. People might be putting on makeup, performing their gender, and behind closed doors, they’re dropping their pants. Meanwhile, next door in the men’s room, dudes are standing next to each other at the urinal, aggressively not making eye contact, trying to ignore the miasma of testosterone that I assume hangs in the air like a fog.

So it’s very gendery in the bathroom, and at least one researcher has suggested that this could cause people to exaggerate their maleness or femaleness—he found that in the mixed-gender space of study booths, “language style… was broadly in between that of the male and female toilets.”

A copy of Hurlo Thrumbo's The Merry-Thought (Wikimedia

When you write on a bathroom wall, “you have a staggeringly diverse audience,” Matthews points out. “Many different races, classes, all walks of life, but it’s completely confined to a single gender. So it suddenly lets gender-specific issues emerge.”

Bathroom graffiti artists have a “captive audience,” Haslam notes, for whatever issues may be on their minds. “There’s a space, there’s some time on your hands, and people love to communicate. We’re social creatures. A tradition grew up of people doing this.”

In trying to explain the appeal of this tradition, some researchers have gotten… creative. Folklorist Alan Dundes, in a 1965 study, suggested that the desire to draw on a bathroom wall comes from “a primitive smearing impulse, the desire that infants allegedly have to manipulate their feces… People who carve or write their names are leaving a memento of themselves which may injure and spoil something beautiful.” If we cannot smear our poop itself, then let us smear our poopy words, I guess. Though I’m not sure who’d call a bathroom stall “beautiful” in the first place.

Dundes also suggested that men were more prominent potty poets because they are jealous of women’s childbearing abilities, and a bowel movement is basically just like having a baby. “When a man defecates, he is a creator, a prime mover,” Dundes writes. So male creativity is inextricably linked to shit. Hey, he said it, not me.

“[In] the heyday of latrinalia studies,” Haslam says, “psychoanalysis was something that was taken seriously, and there was the idea that there had to be an unconscious dimension to everything if you were going to be taken seriously.”

“For those who may be skeptical of the theory that the psychological motivation for writing latrinalia is related to an infantile desire to play with feces and to artistically smear it around, I would ask only that they offer an alternative theory,” Dundes challenges at the end of his article. “For those who doubt that the greater interest on the part of males in latrinalia is related to anal creativity stemming from pregnancy envy, I would ask the same.”

Very well.

While it would be impossible to come up with a comprehensive unified theory of why people write poop jokes and names with hearts around them while they’re on the pot (other than the perhaps scientifically unsatisfying “Because it’s fun”), there are several factors that seem to be at play. One is that bathroom graffiti is a forum for anonymous, often-inappropriate expression, not unlike an Internet comments section, except with the added bonus of creating something tangible that exists in the real world. Plus, as Matthews notes, “It’s still illegal. It’s deviant, but it’s a low-cost deviant thing to do.” There’s a low likelihood of getting caught, and it’s usually something that can be washed off, or painted over.

Toilet graffiti also offers an interesting contrast to the way people typically behave in the bathroom. The unspoken rules of keeping to oneself, not making eye contact, and avoiding talking to strangers, all contribute to a sometimes-tense environment with the goal of shifting focus away from what’s actually happening behind stall doors. But the graffiti on the stall doors does not ignore it one bit. It crudely acknowledges and pokes fun at what we all go to the bathroom to do, and flouts the politeness surrounding it as well. “Sorry,” you say when you reach for a paper towel at the same time as someone else. “Go fuck yourself,” says the bathroom graffiti.