Where did the kiss come from? Research introduces “Groomer’s Last Kiss Hypothesis”

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Researchers from the University of Warwick suggest that kissing in humans may have evolved from grooming behavior observed in our great ape ancestors. In a study published in the journal Evolutionary Anthropology titled “The Evolutionary Origins of Human Kissing,” researchers introduce the “Groomer’s Last Kiss Hypothesis.”
A kiss is just a kiss, but depending on when and where the kiss takes place, it requires some understanding of cultural conventions and historical context. Society has long established rules about who can kiss, when, where, and how it should be done.
In ancient Rome, different types of kisses were given unique names with distinct meanings based on the relationship between the individuals. There was sabium for palate, cheek to cheek, basium, kissing on the lips without sexual intent, and sabium for erotic kissing.
Kissing rings, hands, and feet to show respect, as well as ceremonial and religious kisses, all have a long history. Traditional kisses include wedding kisses, birthday kisses, New Year’s kisses, kisses under the mistletoe, and blowing kisses for good luck.
Kissing customs vary greatly from culture to culture. In some parts of Europe, two cheek-to-cheek kisses are the standard greeting, while in others three kisses are expected. If you travel to Belgium, you only get one.
These kisses usually cross genders or between women, but European men may limit kissing with other men to close relatives. When traveling to Oman, gentlemen may shake hands and then give each other a quick kiss on the nose.
Kissing is a versatile way to show signs of affection, intimacy, or social bonding in a well-regulated manner, but debate continues as to how kissing originated. Some studies have suggested the origin of nursing behaviors in which caregivers provide infants with pre-chewed food in the absence of a food processor, such as during infant feeding and pre-chewing. Other hypotheses link kissing to compatibility tests, sampling the subtle smells and tastes of the microbiome to determine genetic health.
When looking for similarities in the non-human animal world, it is difficult to find behaviors that match the form and function of human kissing. Although many animals engage in some form of nuzzling, the only non-human animals known to kiss are chimpanzees and bonobos, our closest evolutionary relatives.
Adriano R. Lameira from the University of Warwick’s School of Psychology led a comprehensive review of existing hypotheses to explore the evolutionary roots of this intimate behavior, finding that grooming establishes social bonds in the social structure of great apes. It was noted that this is the main means to maintain the
Assuming that our ape ancestors groomed themselves this way, it would be a fundamental part of our early culture. As time passes and humans evolve to have less body hair, the need for extensive grooming decreases and grooming times become shorter and shorter. While the need to be plucked may be gone, the social bonding aspect is still important.
Research shows that great apes’ final act of grooming, which involves protruding their lips and applying slight suction to remove debris and parasites, continued even when hygiene declined. That’s what it means. Researchers have dubbed this vestigial act the “Groomer’s Last Kiss Hypothesis,” which reflects the form, context, and function of kissing in modern humans.
By comparing the grooming behaviors of primate species and human societies, this study supports the notion that kissing functions as a symbolic gesture that indicates and strengthens social and kinship bonds. Other non-ape primates engage in social bonding activities, but they are quite different. An example is given of a capuchin monkey who shows social bonding by sticking his fingers into the eyes and nostrils of his loved ones.
To test this hypothesis, the researchers recommend that future research should focus on a detailed explanation of great ape grooming behavior. By examining the grooming patterns of populations with different coat thicknesses, the groomer’s final kiss hypothesis could provide further insight into the evolutionary trajectory of kissing.
Sticking your fingers in your co-worker’s eyes or nostrils may seem out of place as a human greeting, even though it’s perfectly normal for capuchin monkeys. A 2015 study published in the journal American Anthropologist looked at 168 cultures and found that only 46% of them practiced romantic kissing. Most indigenous hunter-gatherer cultures do not practice kissing of any kind. Some people find this behavior disgusting. Western ethnocentrism may recognize kissing as a universal human behavior, but for most human cultures, kissing is as strange as sticking your finger up someone’s nose.
Further information: Adriano R. Lameira, The Evolutionary Origin of Human Kissing, Evolutionary Anthropology: Issues, News, Reviews (2024). DOI: 10.1002/evan.22050
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