No Valentine´s Days (Valentine’s Day), traditionally celebrated on February 14, the kiss is usually celebrated as a gesture of affection and affection. Science, in turn, brings comparative evidence in primates that indicates that the act may have appeared at least 21.5 million years ago.
The discussion was presented in an episode of podcast Science Quickly, da Scientific Americanled by American journalist Kendra Pierre-Louis.
To debate the topic, evolutionary biologist Matilda Brindle, from the University of Oxford, was invited, who researches the origin and social functions of in primates, including kissing.
Evidence among primates
According to the expert, the kiss was documented in around 168 different cultures alone, and of these, only 46% had this type of romantic or sexual kiss. She says that, as a researcher, she already knew that, at times, primates also kissed.
For scientific purposes, kissing is defined as a , with mouth-to-mouth contact between the same species and without exchanging food. The precision of the definition is necessary to distinguish the gesture from practices such as pre-chewing, common in some species, in which adults transfer food to young and can sound like a kiss.
Upon further research, Brindle observed that all great apes — with the exception of one species of gorilla — exhibit some type of lip contact that fits this definition. There are also similar records of kisses in some monkeys and baboons.
According to the researcher, the common ancestor of these primates probably already exhibited the gesture, which makes it possible to believe that they simply reproduced the act, supporting the estimate of an origin that dates back tens of millions of years.
Hypotheses for the function of kissing
In the human case, science works with at least two main hypotheses for the romantic kiss or sexual.
The first is partner assessment: close contact would allow the perception of chemical and biological signals associated with compatibility, something relevant in species in which reproduction involves high costs, such as pregnancy and prolonged care of offspring.
The second hypothesis is pre-copulatory excitement (foreplay). The kiss would function as a means of physiological preparation for copulation, increasing the probability of reproductive success. In simplified terms, excitement alters bodily conditions that favor fertilization, which gives the gesture a functional role beyond cultural symbolism.
There are also non-romantic uses of kissing. In humans and other primateslip contact appears in contexts of affiliation, such as interactions between parents and children, and in reconciliation processes after conflicts, helping to reduce social tensions and reinforce bonds within the group.
As an example of this line of research, Brindle talks about chimpanzees, which are classified as more aggressive beings, but which kiss and make up after a conflict. For a primate, she states that relieving social tension and relationships is extremely important for the species.
See animals with unique characteristics in nature
Kisses have existed for 21.5 million years
Brindle says that through his research, he was able to identify that kisses have existed for at least 21.5 million years. The finding was possible through a historical reconstruction, which estimates that kissing already existed in the ancestors of great apes millions of years ago, and could be even older.
Another interesting discovery would be that, according to research, . Through the reconstruction of the ancestral stages of the kiss and the top of the family tree it was possible to discover this fact.
Additional studies on oral microorganisms shared between ancient human populations and extinct relatives suggest close and frequent contacts, compatible with saliva exchange practices, which may further support the kissing hypothesis.
In summary, although kissing is often associated with contemporary romanticism, evidence indicates that it is a behavior with deep roots in primate evolution.
*Under AR supervision.
