EARTH, Laniakea Supercluster—Your last make-out session has 20 million years of evolution to thank.

New research suggests lip-to-lip contact predates humans entirely, dating back to the Miocene Epoch, when early ape ancestors were already engaging in mouth-to-mouth behaviors long before homosapians emerged.

A team led by Matilda Brindle of the University of Oxford analyzed mouth-to-mouth gestures in modern great apes (chimpanzees, bonobos, and orangutans) and mapped them onto the primate family tree. They concluded that the behavior likely evolved in the common ancestor of large apes between roughly 21.5 million and 16.9 million years ago.

“This is the first time anyone has taken a broad evolutionary lens to examine kissing,” Brindle said in the press release announcing the peer-reviewed publication. “Our findings add to a growing body of work highlighting the remarkable diversity of sexual behaviors exhibited by our primate cousins.”

The research, published in Evolution and Human Behavior, suggests that what humans often regard as romantic or culturally learned may in fact have deep biological roots. Brindle and her colleagues argue that kissing-like gestures could have emerged from primitive mouth-to-mouth food sharing, such as maternal feeding or grooming behaviors, and were later repurposed into social bonding or sexual signaling over evolutionary time.

Still, romantic kissing is far from universal even if the evolutionary capacity for it stretches back millions of years. Oxford study co-author Catherine Talbot referenced a 2015 cross-cultural analysis of 168 societies, noting that “while kissing may seem like an ordinary or universal behavior, it is only documented in 46 percent of human cultures.”

“The social norms and context vary widely across societies, raising the question of whether kissing is an evolved behavior or cultural invention. This is the first step in addressing that question.”

Historically, many groups didn’t kiss at all, including Indigenous Australian communities, Polynesian cultures like pre-contact Tahitians, certain South American groups such as the Sirionó and Trumai, and several sub-Saharan African societies including the Tiv and the !Kung San. In many of these cultures, saliva exchange was considered spiritually risky, unsanitary, or simply irrelevant to courtship, with intimacy instead expressed through nose-rubbing, forehead touching, shared meals, or ritualized forms of physical closeness.

So even if humans inherited the capacity for kissing from ancient apes, individual societies built their own rules about what intimacy should look like. But for some early primates under the pristine Miocene night sky, connection definitely involved lips.