New research suggests that the act of kissing may have originated more than 20 million years ago, long before the emergence of modern humans. A team of scientists from Oxford University conducted an extensive review of decades of studies on primates to uncover the evolutionary background of this behavior.
By analyzing the kissing habits of contemporary species such as chimpanzees, bonobos, and orangutans, researchers employed statistical modeling to estimate the timeline for when kissing first appeared. Their findings, published in the journal Evolution and Human Behavior, indicate that an ancient ancestor of today’s apes likely engaged in mouth-to-mouth interactions between 16.9 million and 21.5 million years ago.
Understanding the Evolutionary Significance of Kissing
The study raises intriguing questions about the evolution of kissing, which Matilda Brindle, the lead author and an evolutionary biologist at Oxford, describes as an “evolutionary conundrum.” Kissing involves certain risks, such as the potential spread of germs, and does not appear to provide direct survival benefits. Nevertheless, Brindle emphasizes that across various primate species, kissing and similar behaviors serve multiple functions.
“Because kissing is not a behavior that leaves behind fossils, we must turn to existing species to draw insights about the past,” Brindle noted. The earliest written records of human kissing date back approximately 4,500 years to ancient civilizations in Mesopotamia and Egypt. Interestingly, kissing is not universally practiced; a study from 2015 revealed that only 46% of humans engage in the act.
Brindle explained that while researchers found a strong evolutionary signal related to kissing, this does not guarantee its permanence in modern species. “Primates are extremely flexible and intelligent species, so while kissing might be advantageous in certain contexts, it may not be beneficial in others. If it lacks utility, the risks associated with disease transmission become more significant,” she said.
Future Research Directions and Implications
To support their conclusions, the research team conducted over 10 million simulations to assess the likelihood that early ape ancestors engaged in kissing. The results imply that extinct relatives, such as Neanderthals, who coexisted with early humans, likely participated in similar behaviors.
Despite these insights, Brindle acknowledges that the model does not clarify the original purpose of kissing or its evolution over time. Much of the behavioral data analyzed comes from primates in captivity, highlighting the need for additional research focusing on wild populations.
Experts recognize the significance of this study in advancing the field. “This is a wonderful example of the interplay between nature and nurture, especially regarding a behavior many of us humans consider to be deeply intimate,” stated Justin Garcia, an evolutionary biologist and director of The Kinsey Institute at Indiana University in Bloomington. He added that kissing is both a biological and cultural phenomenon that engages the senses and has evident evolutionary roots while varying across individuals and cultures.
The findings pave the way for further exploration into the complexities of human behavior and its historical context, offering new avenues for understanding the role of intimate interactions in both human and primate societies.
