General · EdgepediaSeptember 17, 20269 min read

Kiss

A kiss is an act of touching or pressing the lips against another person, especially their lips or cheek, as a greeting or to express love, that carries social or emotional meaning²⁰^•²¹. In humans the word covers a family of practices, from lip-to-lip romantic kissing to cheek greetings, hand-kissing, ritual kisses of respect, and the religious kiss of peace. Research across anthropology, evolutionary biology, psychology, and law treats the kiss as a distinctive case in which a behavior looks culturally variable, and in some places is absent altogether, yet shows signatures of deep biological continuity with other primates.

Key fact	Detail
Prevalence	In a survey of 168 cultures, romantic-sexual kissing (lip-to-lip contact, prolonged or not) was present in 46% of cultures and absent in the rest, so it is not a human universal¹
Social complexity	The frequency of romantic-sexual kissing correlates strongly with a society's relative social complexity; more socially complex cultures kiss more often¹
Oldest documentation	Sumerian and Akkadian texts record kissing in Mesopotamia about 4,500 years ago, functioning both as part of sexual acts and as an expression of affection among family and friends²^•³
Deep-time origin	A Bayesian phylogenetic analysis places the origin of kissing in the ancestor of the great apes at roughly 21.5 to 16.9 million years ago, and infers that Neanderthals likely kissed⁴
Comparative definition	In evolutionary terms, kissing is defined as non-agonistic, directed, intraspecific oral-oral contact with some movement of the lips and no food transfer⁴
Proposed mechanism	The "groomer's final kiss" hypothesis holds that kissing is the conserved final mouth-contact stage of a primate grooming bout, in which the groomer sucks with protruded lips at the fur or skin⁵
Health dimension	HIV transmission through kissing alone is extremely rare; deep open-mouth kissing matters only when blood is present through sores or bleeding gums⁶

Cross-cultural record

Not a universal. The most cited cross-cultural study of romantic kissing, published in American Anthropologist in 2015 by William R. Jankowiak of the University of Nevada, Las Vegas, Shelly L. Volsche, and Justin R. Garcia of the Kinsey Institute at Indiana University, used the eHRAF World Cultures database, the Standard Cross-Cultural Sample, and a survey of ethnographers to code the presence or absence of the romantic-sexual kiss in 168 cultures. They defined it strictly as lip-to-lip contact that may or may not be prolonged, and found it in a minority of the sample, 46% of cultures, with no evidence for it in the other 54%¹. Communities coded as lacking the practice included societies where it was reported as uncomfortable or even repulsive, and present-day cultures that practice kiss feeding (premastication of food for infants) but not social kissing⁷.

The same study found a strong correlation between romantic kissing and social complexity: the more socially complex the culture, the higher the frequency of the practice¹. One reading is that romantic kissing is a recent cultural development tied to stratified societies; another, defended by evolutionary researchers, is that the trait has biological roots and its cultural expression expands with social hierarchy⁵.

Variation in what a kiss means. Across societies, a kiss can operate as a greeting, ritual, promise, provocation, or offense, with its meaning shifting by culture, setting, power, and consent⁸. Rome distinguishes several kinds in its vocabulary: the osculum on the cheek for social or familiar affection, the basium on the lips for close family or lovers without sexual meaning, and the savium on the lips expressing erotic desire⁵. Herodotus described Persians kissing equals on the mouth and inferiors on the cheek⁹, and in modern Latin Europe two cheek-to-cheek kisses serve as a greeting between women or across sexes, while men typically shake hands⁵.

Ancient history

The ancient history of kissing is usually told through Greek and Roman sources, but cuneiform evidence reaches further back and outside those traditions¹⁰. In 2023 the Assyriologist Troels Pank Arbøll, a cuneiform expert at the University of Copenhagen specializing in the history of medicine, co-authored a Science perspective arguing that romantic kissing was widespread in ancient Mesopotamia. Sumerian and Akkadian texts record the practice with a double function, as part of sexual acts and as an expression of affection among family and friends²^•³. One tablet from Sippar, dated 1900-1595 BCE, reads: "My upper lip becomes moist, while my lower lip trembles! I shall embrace him, I shall kiss him"².

Interpreting the sources carries methodological difficulty: texts from the bottom of Mesopotamian society are rare in the cuneiform record, so estimates of whether kissing was an elite practice or embedded in everyday life are potentially biased¹⁰. Even a number of Akkadian love texts from the late third and early second millennium BCE that do not mention kissing explicitly were recovered at Kish, the original seat of Akkadian culture¹⁰. Arbøll himself holds that the origin of sexual-romantic kissing must lie further back in prehistory than present methods can detect².

Evolutionary origin

Deep-time dating. In 2025 a team led by Matilda Brindle, an evolutionary biologist in the Department of Biology at the University of Oxford, treated kissing as a biological trait and applied Bayesian phylogenetic modeling to observational data across the Afro-Eurasian primates, running the model 10 million times to test how likely it was that different ancestors also kissed⁴^•¹¹. On the definition of kissing as non-agonistic oral-oral contact without food transfer, bonobos, gorillas, chimpanzees, orangutans, macaques, and baboons have all been observed kissing. The model concluded that kissing evolved once in the common ancestor of the great apes (Hominidae) sometime between about 21.5 and 16.9 million years ago, and probably occurred in Neanderthals⁴^•¹¹. Kissing was absent in the ancestors of the macaque and baboon lineages, implying that it evolved separately in those modern groups¹¹. The authors flag a major caveat about the quantity of available data, and note life-history variables that correlate reasonably but not perfectly with kissing across apes: multi-male mating systems, non-folivorous diets, and premastication⁴.

From grooming to kissing. A 2024 review by Adriano Lameira, Associate Professor at the Department of Psychology, University of Warwick, proposes the "groomer's final kiss" hypothesis. Great apes end grooming bouts by sucking with protruded lips at the fur or skin of the groomed individual to latch on debris or parasites. As fur loss reduced the hygienic value of grooming over human evolution, shorter sessions would predictably have retained a final "kissing" stage, leaving a vestige of a once routine behavior for signaling and strengthening social and kinship ties in an ancestral ape⁵. A related line suggests the practice may derive from pre-chewing food and transferring it mouth to mouth from mother to infant, a behavior repurposed into kissing¹¹. Earlier popular claims that great apes "kiss" in sexual contexts rest on similes and romanticized descriptions rather than scientific studies⁵. That all kissing etiquettes, whatever their local content, prescribe the gesture to specific relationships and contexts has been read as implying an underlying biological meaning older than the conventions themselves⁵.

Functions and variation in romantic kissing

Research on romantic kissing has organized explanations into three evidence streams: cultural history, comparative primate behavior, and functional hypotheses about bonding, assessment, or hygiene¹².

Pair bonding. A cross-national study of 3,109 participants from 13 countries on six continents tested whether kissing serves mate assessment or the maintenance of committed relationships. Kissing was valued more in established relationships than during courtship, and consistent with the pair bonding hypothesis, relative poverty as measured by income inequality predicted the frequency of kissing across romantic relationships; the aggregated correlation between income inequality and kissing frequency was r = 0.67 (95% CI 0.32 to 0.89), more than five times the size of the corresponding correlations for hugging, cuddling, or sex¹³.

Disease threat. Because mouth-to-mouth contact involves pathogen exposure, researchers have tested whether infectious-disease prevalence predicts cultural variation in close contact, comparing greetings, romantic kissing, and mortuary rituals in traditional cultures against epidemiological estimates of pathogen prevalence¹⁴. A separate line of work finds that health factors may not be a powerful motivator of cultural variation in kissing attitudes and behaviors¹³.

Cognitive attractors. A 2026 account in Evolution and Human Behavior proposes that infant cognition contributes to the pattern: even infants interpret physical closeness and saliva sharing as signals of intimate social relationships, and this early-emerging knowledge shapes "basins of attraction" for cultural practices, explaining both cross-cultural diversity and the recurrent independent invention of romantic kissing¹⁵.

Kissing, law, and disease

Because a kiss can be greeting or offense depending on context, legal systems regulate it along axes of consent, bodily autonomy, and public decency, with doctrine that treats meaning as dependent on culture, setting, power, and consent⁸. On the health side, kissing appears in transmission research beyond HIV. Evidence suggests gonorrhea transmission via kissing is possible, though whether it is rare or a main driver of transmission remains unresolved¹⁶, and the role of saliva exchange, rather than more direct mucosal contact, in gonococcal transmission is described as far from proven and an important topic for further research¹⁷. For HIV, exposure to saliva uncontaminated with blood is considered a rare mode of transmission⁶.

Kissing in culture

Kisses have carried symbolic weight across history, expressing affection, rank, faith, betrayal, and desire⁷. Auguste Rodin's sculpture The Kiss, first displayed in 1887, startled audiences with its nude figures; at the 1893 Chicago World's Fair it was kept in a private room¹⁸. Thomas Edison's 1896 film The Kiss, showing May Irwin and John Rice, is considered the first movie kiss, and many theaters refused to show it¹⁸. Alfred Eisenstaedt's 1945 "V-J Day in Times Square" photograph became one of the most reproduced images of the 20th century¹⁸. The mistletoe kissing custom is first documented in a 1784 English poem; by the 1820s, Washington Irving recorded that each berry on a sprig represented a kiss a man could bestow on a woman standing beneath it¹⁹.

References

Topic: Encyclopedia › Society and history › Social life and human behavior

Initially written Sep 17, 2026 · Reviewed: Sep 17, 2026; Sep 30, 2026; Oct 25, 2026 · Edited: Sep 30, 2026; Oct 25, 2026 · Last review: Oct 25, 2026

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