Kissing is not universal among human beings, and, even today, there are some cultures that have no place for it. This suggests that it is not innate or intuitive, as it so often seems to us. Another possibility is that kissing is a learned behavior that evolved from "kiss feeding," the process by which mothers in some cultures feed their babies by passing masticated food from mouth-to-mouth. Yet, there are some modern indigenous cultures in which kiss feeding is practiced, but not social kissing. Kissing could also be a culturally determined form of grooming behavior, or, at least in the case of deep or erotic kissing, a representation, substitute for, and complement to, penetrative intercourse.
Whatever the case, kissing behavior is not unique to human beings. Primates such as Bonobo apes frequently kiss one another; dogs and cats lick and nuzzle one another, and members of other species; even snails and insects engage in antennal play. It could be that, rather than kissing, these animals are in fact grooming, smelling, or communicating with one another, but even so, their behavior implies and strengthens trust and bonding.
Vedic texts from ancient India seem to talk about kissing, and the Kama Sutra, which probably dates back to the 2nd century, devotes an entire chapter to modes of kissing. Some anthropologists have suggested that the Greeks learned about erotic kissing from the Indians when Alexander the Great invaded India in 326 BC. However, this need not mean that kissing originated in India, or indeed that it does not predate the oral roots of the Vedic texts. In Homer, which dates to the 9th century BC, King Priam memorably kisses Achilles’ hand to plead for the return of his son’s cadaver:
