If the sound or sight of people swapping spit makes your stomach churn, don’t worry–it would seem that half the world’s cultures agree.
A study published in American Anthropologist shows that of the 168 cultures studied, only 46% partook in “lip-to-lip contact that may or may not be prolonged,” more commonly referred to as romantic kissing.
The researchers from the University of Nevada, Las Vegas and Indiana University looked through standard collections of data on world cultures for the examples of the words “kiss” and “kissing.” They then wrote to 88 individual ethnographers for cultures they hadn’t covered, asking, “Did you observe or hear of people kissing on the mouth in a sexual, intimate setting?” Their results broken out by region:
The researchers also mapped their findings according to the complexity of the society, defined by size and hierarchy of decision making, one of the authors, Shelly Volsche, tells Quartz. This showed a correlation between more stratified societies—which feature mass production and industrialization—and the presence of kissing. In other words: more government, more saliva.
The next step was to try to figure out why. “Our hypothesis moving forward is that perhaps there’s something going on with stratifying societies that provides the time and interest in erotic play, and therefore the romantic kiss,” Volsche says.
She also notes that spit-swapping is “not as common in societies that don’t have the ability to brush teeth.” (Though one interesting wrinkle to that hypothesis is that certain egalitarian groups, like the Chukchi of Siberia and the Bering Sea and the Iñupiat of Alaska, have a tradition of kissing that appears throughout their folktales.)
Although the study pulls from some ethnographic research dating back to the early 1900s, Volsche says this is to avoid the possibility of cultural transmission, such as between American settlers and the Cherokee, which was previously a non-kissing culture. “We were looking for specific ethnographies before Western or European influence on cultures,” she says.
The researchers hope to dispel the idea that romantic kissing is universal or evolutionarily beneficial. Volsche says, at times, kissing could be even be harmful: in some cultures, she says, it is “extremely dangerous–you could be passing on pathogens, sharing bacteria.”