E. Selous, Bird Watching, 1901, p. 191. This author adds: "It seems probable indeed that the conferring a practical benefit of the kind indicated may be the origin of the caress throughout nature."
Tylor terms the kiss "the salute by tasting," and d'Enjoy defines it as "a bite and a suction"; there seems, however, little evidence to show that the kiss contains any gustatory element in the strict sense.
Compayre, L'Evolution intellectuelle et morale de l'enfant, p. 9.