Less than half of all societies kiss with their lips, according to a study of 168 cultures from around the world. William Jankowiak, a professor of anthropology at the University of Nevada Las Vegas, found that only 46% use lip-to-lip kissing in a romantic sense, excluding things like parent-child kissing or greetings.
Two theories for why humans have a need to kiss stem from the idea that as babies we have an innate liking for lip touching. In one case, it might be that we associate lip touching with breastfeeding, and that reflex is innate in everyone. There is also a suggestion that mothers and their children bond over lip-on-lip kissing because of something called “premastication food transfer“.
If kissing has an evolutionary purpose, why don’t we see more animals kissing?
Melissa Hogenboom answered that question for BBC Earth in 2015. One of the reasons we might have been compelled to get up close to the face of a partner is to give them a good sniff. Scent can reveal all sorts of useful information: diet, presence of disease, mood and relatedness, to name some. Many animals have far more sophisticated senses of smell than we do, so they don’t have to be nearly as close.