Kissing is one of the most intimate acts between humans, yet its origins remain surprisingly enigmatic. When we discuss kissing, we often refer to the romantic lip-to-lip contact that involves suction and pressure, but that description lacks the allure often associated with this act.

But what drives humans to kiss?

Throughout history, the significance of kissing has varied across cultures. The earliest documented kiss can be traced back to ancient Mesopotamian texts from 2500 BC.

In ancient Rome, three distinct types of kisses existed: the palate, a friendly kiss on the cheek; the Basium, a platonic kiss shared between family and close friends; and the Sabium, a passionate kiss exchanged by lovers.

Clearly, kissing transcends mere romantic expression.

Despite its prevalence, kissing is not a universal practice. A 2015 study of 168 cultures published in American Anthropologist revealed that only 46% of people engage in romantic lip kissing. Cultures that do not incorporate kissing have alternative ways of expressing intimacy.

On the Trobriand Islands near Papua New Guinea, a couple may nibble each other’s eyelashes. Interestingly, during his explorations, Charles Darwin noted a particular Malayan kiss in which individuals squat and smell each other, implying that scent plays an important role in human intimacy.

Can biology provide insights into the reason we kiss? Research suggests that kissing serves a biological bonding function and facilitates emotional release through the release of oxytocin, hormones linked to trust and attachment.

Oxytocin reduces stress, fosters intimacy, and strengthens the bond between romantic partners, suggesting that you kiss because it feels good.

According to evolutionary theory, the origins of lip-to-lip kissing may stem from early maternal behaviors such as breastfeeding and pre-chewing food to feed infants directly.

This behavior is still observable among primates like chimpanzees, potentially laying the foundation for lip contact as a signal of care and bonding.

Human infants are biologically inclined towards lip contact, associating it with comfort and safety. This may have evolved into broader social behaviors linked to caregiving and emotional bonds.

However, theories emphasizing maternal lip-to-lip behavior may fail to fully explain romantic kissing.

A provocative recent theory by evolutionary psychologist Dr. Adriano Lameira of the University of Warwick proposes that kissing evolved from grooming behaviors.

In primates, grooming often culminates in oral contact, such as removing fur from one another. Lameira’s hypothesis suggests that as humans lost body hair, grooming became less feasible, leading to shorter grooming sessions and the enduring practice of kissing as a form of affection.

Indeed, kissing is a complex behavior, potentially shaped by the actions of our ancient ancestors. Whether it be the passionate Sabium or the simple pleasure of closeness, kissing addresses a profound human need for connection.

This article answers the question, “Why do we kiss?” as posed by Dani Castillo through email.

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