Scientists Explore Deep Evolutionary Roots of Oral Contact in Primates

A new wave of scientific inquiry is delving into the profound evolutionary origins of oral contact, a behavior observed across a broad spectrum of primates, including Homo sapiens. Researchers affiliated with Oxford University, collaborating with colleagues from the Florida Institute of Technology, recently conducted an assessment suggesting that this specific behavioral pattern may have first emerged in early primates between 21.5 and 16.9 million years ago. This groundbreaking investigation, which sheds light on the formation of complex social rituals, was published in the esteemed journal, *Evolution and Human Behavior*.

The act of mouth-to-mouth contact does not possess immediately apparent direct advantages for survival, prompting scientists to explore alternative evolutionary drivers. According to the analysis performed by the research team, this gesture likely developed to fulfill crucial social functions, such as evaluating a potential mate or reinforcing existing social connections within a group structure. One dominant hypothesis posits that kissing may have originated from the practice of mutual grooming, a common activity among great apes. For instance, chimpanzees and bonobos frequently engage in kissing and embracing as methods of reconciliation or general social interaction, demonstrating a clear link between physical contact and maintaining group harmony.

Among the various theories attempting to explain the genesis of the kiss, one prominent idea links it directly to premastication—the practice of mothers transferring pre-chewed food directly from their mouth to their infant’s mouth. This functional act of nourishment served as an early expression of care and deep attachment. Another compelling explanation centers on the exchange of information: when individuals kiss, they unconsciously detect chemical signals via scent and taste. This process acts as a biological test for assessing a partner's genetic compatibility, providing subtle yet vital data about potential mates.

Further expanding on the possible origins, researcher Adriano Lameira of Warwick University proposed a unique version of events. He suggested that kissing might have evolved from the habit of using extended lips to remove debris or parasites from the fur of conspecifics. Over time, this practical cleaning action transformed into a gesture signifying affection and bonding, moving from a purely utilitarian function to a social one.

While grooming serves both hygienic and social bonding purposes among apes, humans, having lost their dense body hair, retained the kiss as a powerful non-verbal signal of affection and affiliation. Cultural variations significantly shape the interpretation of this act; for example, historical records show that in Ancient Rome, distinct types of kisses existed, such as the *osculum* (friendly kiss) and the *savium* (erotic kiss), underscoring the multifaceted nature of this behavior even in antiquity. Scientists at Perm Polytechnic have further documented the physiological effects associated with kissing, including a surge in adrenaline, elevated levels of serotonin and dopamine, and a reduction in cortisol. These hormonal changes enhance stress resilience. These findings collectively demonstrate that while the fundamental roots of kissing are biological, its modern manifestation is deeply interwoven with cultural norms and psychological well-being.