Kissing is common among most living great apes and likely was practiced by Neanderthals, having evolved in the ancestors of these groups between 21.5 million and 16.9 million years ago, according to a study led by researchers from Oxford University.
Kissing can be observed in various animal species, yet it poses an evolutionary enigma. While it carries significant risks, such as disease transmission, it lacks clear reproductive or survival advantages.
Until now, the evolutionary background of kissing has received limited attention, despite its cultural and emotional importance across numerous human societies.
In this recent study, Dr. Matilda Brindle and her team from the University of Oxford undertook the first investigation into the evolutionary history of kissing, utilizing a cross-species perspective based on primate family trees.
The findings indicated that kissing is an ancient characteristic of great apes, having developed in their ancestors between 21.5 and 16.9 million years ago.
This behavior has persisted through evolution and is still evident in most great apes.
The researchers also concluded that Neanderthals, distant relatives of modern humans, likely engaged in kissing as well.
This evidence, alongside earlier studies showing that humans and Neanderthals exchanged oral microbes (through saliva) and genetic material (via interbreeding), strongly implies that kissing occurred between the two species.
Dr. Brindle stated: “This marks the first exploration of kissing from an evolutionary standpoint.”
“Our results contribute to an expanding body of research that illuminates the incredible variety of sexual behaviors found among our primate relatives.”
To carry out the analysis, scientists needed to define what constitutes a kiss.
This task was challenging due to the numerous mouth-to-mouth interactions resembling kisses.
Given their investigation spanned a diversity of species, the definition had to be suitable for a wide range of animals.
Consequently, they defined kissing as non-aggressive mouth-to-mouth contact that does not involve food transfer.
After establishing this definition, the researchers concentrated on groups of monkeys and apes that evolved in Africa, Europe, and Asia, gathering data from the literature where kissing has been documented in modern primates.
Among these are chimpanzees, bonobos, and orangutans, all of which have displayed kissing behavior.
Following that, they conducted a phylogenetic analysis, treating kissing as a “trait” to map onto the primate family tree.
Using a statistical method known as Bayesian modeling, they simulated various evolutionary scenarios along the tree’s branches and calculated the chances that different ancestors also kissed.
The model ran 10 million simulations, producing robust statistical estimates.
Professor Stuart West from the University of Oxford noted: “Integrating evolutionary biology with behavioral data enables us to draw informed conclusions about non-fossilized traits like kissing.”
“This paves the way for studying the social behaviors of both extant and extinct species.”
While the researchers caution that current data is limited, particularly beyond great apes, this study sets a framework for future inquiries and offers primatologists a consistent method for documenting kissing behaviors in non-human animals.
“Though kissing may seem like a universal act, it’s only documented in 46% of human cultures,” remarked Dr. Katherine Talbot from the Florida Institute of Technology.
“Social customs and situations differ vastly among societies, prompting the question of whether kissing is an evolved behavior or a cultural construct.”
“This research represents a first step in addressing that question.”
This is part of a study published this week in the journal Evolution and Human Behavior.
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Matilda Brindle et al. 2025. A comparative approach to the evolution of kissing. Evolution and Human Behavior in press. doi: 10.1016/j.evolhumbehav.2025.106788
Source: www.sci.news
