This is a heartfelt love story: During the spring of 2008, before they found evidence of humanity’s first recorded kiss, Troels Pank Arboll and Sophie Lund Rasmussen kissed for the first time in their first goodnight kiss. A week earlier, they met at a pub near the University of Copenhagen, where they were undergraduates. Dr. Rasmussen said she asked her cousin if he knew any single guys with long beards and long hair, and he said he would introduce her to one.

In turn, Dr. Arboll had been looking for a partner who shared his interest in Assyriology, the study of Mesopotamian languages and the sources written in them, adding that not many people know what an Assyriologist does. However, Dr. Rasmussen knew precisely what they did because she had taken some of the same classes. At that point, Dr. Arboll knew she was a keeper. Three years later, the couple wed and now, Dr. Rasmussen is an ecologist at the University of Oxford’s Wildlife Conservation Research Unit and Aalborg University in Denmark.

One night, while at dinner in 2022, as scientists do, the couple discussed a new genetic study that connected modern herpes variants to mouth-to-mouth kissing in the Bronze Age, roughly 3300 B.C. to 1200 B.C. In the paper’s additional materials, a brief history of kissing identified South Asia as the place of origin, tracing the first kiss to 1500 B.C., when Vedic Sanskrit manuscripts were being translated from oral history. The University of Cambridge researcher suggested that the custom, a lip-kissing precursor that involved pressing and rubbing noses together, evolved into hardcore smooching. She noted that by 300 B.C., kissing had spread to the Mediterranean with the return of Alexander the Great’s troops from northern India.

However, the couple thought that wasn’t its start. Dr. Arboll said he knew of earlier accounts written in Akkadian and Sumerian languages. So, after dinner, they double-checked. They consulted handwritten texts on clay tablets from Mesopotamia and Egypt for clear examples of intimate kissing. Their investigation resulted in a commentary recently published that pushed back the earliest documentation of kissing by 1,000 years and upended the hypothesis that people from a specific region were the first to kiss and tell.

The husband and wife team maintained that since at least the late third millennium B.C., kissing was a well-established and widespread part of romance in the Middle East. According to Dr. Arboll, kissing wasn’t a custom that abruptly emerged in a single point of origin. Instead, it was standard across a range of cultures.

Carved in clay.

Dr. Rasmussen and Dr. Arboll projected that the earliest account of kissing was etched into the Barton Cylinder, a tablet that dates to around 2400 B.C. The object was uncovered in the ancient Sumerian city of Nippur in 1899 and named after George Barton, the professor of Semitic languages at Bryn Mawr College, who translated it in 1918. It’s currently housed in the Museum of Archaeology and Anthropology at the University of Pennsylvania, where Dr. Barton taught Semitic languages and the history of religion from 1922 to 1931. The artifact’s story involves the Sumerian creation myth and issues with food supplies in Nippur, the original religious capital of Babylonia and the seat of worship for Enil, the ruler of the cosmos.

In the second column of text, a male divinity, maybe Enil, is intimate with the mother goddess Ninhursag, Enil’s sister, and then kisses her. Amid the frolicking, the male divinity plants the seed of seven twins of deities in her womb. Gonzalo Rubio, an Assyriologist at Penn State University, said the most fascinating part of the story is the sequence of events. He said in the portrayals of the act of kissing in Sumerian literature, the subjects have sexual intercourse, and only afterward do they kiss. It’s afterplay of some sort instead of foreplay. The existence of Mesopotamian kissing records may be earth-shattering to philematologists, but to the academics who study the science of the kiss, it’s old news to Mesopotamian scholars. According to Dr. Rasmussen, in the small field of Assyriology, there’s a tendency to focus inward, not outward. As much as Assyriologists like to argue with each other, they don’t talk to other people.

Dr. Rubio, who wasn’t involved in the project, praised Dr. Rasumssen and Dr. Arboll for effectively rewriting the history of kissing. They aimed to clear things up and came to fix a reductionist approach to human behavior. However, was a Sumerian kiss just a kiss? Dr. Arboll said that in the earliest passages, kissing was depicted in relation to erotic acts, with the lips as the locus. In Akkadian, a Semitic language correlated to Arabic and Hebrew of today, he and Dr. Rasmussen found that references to kissing fell into two categories: the romantic sexual and the friendly parental.

The former is a demonstration of familial affection, submission or respect, like when a royal subject kisses the feet of a ruler. According to Dr. Arboll, the sexual romantic kiss happens in relation to a sexual act or love, which isn’t culturally universal. He added that kissing on the lips has been observed in bonobos and chimpanzees, our closest living relatives. The platonic chimp kiss may determine compatibility, but bonobos canoodle for sexual pleasure. Their erotic contact ranges from oral sex to tongue twisting. Dr. Rasmussen says that the kissing practices of these primates hint at something fundamental that dates way back in human history.

Cue the chemistry.

Dr. Rasmussen said that in ancient Mesopotamia, kissing outside of marriage was discouraged. He found one text from 1800 B.C. that shared how a married woman was almost led astray by a soul kiss from a male lover. Necking with someone who wasn’t supposed to be sexually active was seen as a crime on par with adultery, and kissing a priestess was thought to deprive the kisser of the ability to talk. For Romans of the imperial era, kissing a lover publicly was also considered inappropriate and a health risk.

In The Science of Kissing: What Our Lips Are Telling Us,” Sheril Kisherbaum discusses the chemistry of attraction, how a kiss brings two people together in an exchange of tastes, colors, and textures. Dr. Rasmussen thinks that kissing changed as a way of sizing up potential partners through their scent.

He still remembers that first kiss with Dr. Arboll, which bore the scent of the hibiscus tea she had just fixed for him. What’s a kiss? In her memory, it echoed a line from the poet Robert Herrick: “The sure, sweet cement, glue and lime of love.”