Study Dates Kissing Origins to Great Apes' Ancestor 17-22 Million Years Ago

A new study has traced the origins of kissing to the common ancestor of great apes, estimating that the behavior first emerged between 16.9 million and 21.5 million years ago, long before the appearance of modern humans.

Researchers from the University of Oxford and the Florida Institute of Technology analyzed observations of primate behavior and mapped them onto the evolutionary family tree of primates. By running millions of simulations using Bayesian modeling, the team determined that kissing likely arose after the lineage of great apes diverged from lesser apes, such as gibbons. The study, published in the journal Evolution and Human Behavior, defined kissing as nonaggressive mouth-to-mouth contact between members of the same species, involving some movement of the lips or mouthparts but excluding food transfer or antagonistic interactions.

The analysis revealed kissing in all great ape species except eastern gorillas, including humans, chimpanzees, bonobos, and orangutans. No such behavior was documented among gibbons or most monkeys. Among great apes, kissing serves multiple roles. In sexual contexts, it may help assess mate suitability or increase arousal to enhance...