Recent studies maintain that the first known record of human romantic-sexual kissing originates in a Bronze Age manuscript deriving from South Asia (India), tentatively dated to 1500 BCE (1). Yet, a substantial corpus of overlooked evidence challenges this premise because lip kissing was documented in ancient Mesopotamia and Egypt from at least 2500 BCE onward.
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Because this behavior did not emerge abruptly or in a specific society but appears to have been practiced in multiple ancient cultures over several millennia, the kiss cannot be regarded as a sudden biological trigger causing a spread of specific pathogens, as recently proposed (2). Further understanding of the history of kissing in human societies—and its secondary effect on disease transmission—can be gained from a case study of sources from ancient Mesopotamia (modern-day Iraq and Syria).
In research, two types of kissing are generally differentiated, namely the friendly-parental kiss and the romantic-sexual kiss. Whereas friendly-parental kissing appears to be ubiquitous among humans across time and geography, romantic-sexual kissing is not culturally universal, and it is dominant in stratified societies (3). Research has suggested that romantic-sexual kissing evolved for the purposes of evaluating aspects of a potential mate’s suitability through chemical cues communicated in the saliva or breath, mediating feelings of attachment between pairbonded individuals, and facilitating sexual arousal and thereby sexual relations (3). Kissing is also attested in other animal species, such as mouth-to-mouth kissing with a romantic-sexual purpose in bonobos (Pan paniscus) and platonic kissing to manage social relationships in chimpanzees (Pan troglodytes) (1). These two species constitute the closest living relatives to humans, and their practices of kissing may hint at the presence and evolution of this behavior in human ancestors (4).
In a study investigating the transfer of the oral microbe Methanobrevibacter oralis, it has been hypothesized that Neanderthals could have engaged in lip kissing with modern humans more than 100,000 years ago (5, 6). Still, the advent of romantic-sexual kissing remains uncertain, although two prehistoric sculptures from Ain Sakhri (BM 1958,1007.1) and Malta (T/p1014) might imply its existence before the invention of writing.
Humanity’s earliest recorded kiss occurs in sources from the ancient Middle East. Kissing is attested in ancient Mesopotamian texts from 2500 BCE onward. Ancient Mesopotamia constituted the areas along the Euphrates and Tigris rivers, which today roughly cover Iraq and Syria. Writing was first invented simultaneously in southern Iraq and in Egypt around 3200 BCE. In Mesopotamia people wrote in cuneiform script on clay tablets, which primarily recorded the Sumerian and Akkadian languages from ∼3200 BCE to 75 CE. In the earliest texts in the Sumerian language, kissing was described in relation to erotic acts, possibly as a postcoital activity, and the locus was the lips (7). In the Akkadian language, references to kissing can be subdivided into two distinct groups, the first designating friendly and familial affection, describing a display of submission or respect through the act of kissing the feet or the ground, and the second being an erotic action with the lips as the primary locus (7).
Considering the thousands of cuneiform texts that are available, there are relatively few instances where romantic-sexual kissing is described. Regardless, there are clear examples illustrating that kissing was considered an ordinary part of romantic intimacy in ancient times. The texts imply that kissing was something that married couples did (8), though the kiss was regarded as part of an unmarried person’s sexual desire when in love (8). Two texts from ∼1800 BCE are especially revealing. One describes how a married woman was almost led astray by a kiss from another man, and the other describes an unmarried woman swearing to avoid kissing and having sexual relations with a specific man (9). Apparently, society tried to regulate such activities between unwed people or adulterers. Furthermore, the sexual aspect of kissing was frowned upon in public, and kissing a person who was not meant to be sexually active, such as a priestess, was believed to deprive the kisser of the ability to speak (9). Still, it seems that tokens of friendship and familial affection, such as that between mother and child, included kissing (7). Kissing was also used in ritual contexts, where a person in need of divine restoration could kiss a person in a state of trance, an old woman, or a slave girl.
Reaching beyond its importance for social and sexual behavior, the act of kissing may have played a secondary and unintentional role throughout history in facilitating the transfer of orally transmitted microorganisms, potentially causing disease. Infectious diseases have been around since the dawn of history, with a constant evolutionary arms