Recently, Alicia Silverstone uploaded a clip of herself mouth feeding her child. It seemed strange to some people, but even though, yeah, it exchanges saliva, which, like any contact with an infant, can transfer pathogens, healthy mothers and healthy children can benefit from the fact that kiss feeding provides nutrients: Carbohydrates, proteins, iron, and zinc, which are not always available in breast milk. Plus, an adult saliva can help pre-digest the food, making vitamins like B-12 easier for the baby to absorb.
Mouth-to-mouth attachment has a history of intimacy, trust, and closeness. Your saliva also carries information about who you are, your level of health, and, mucus membranes in our mouth are permeable to hormones like testosterone, making a kiss a way to taste-test a potential mate. A good kiss can be a biological evidence that your kisser might be a good mate. So, as a strategy for mate selection, pre-historic people who enjoyed kissing, and did it more often, may have made better decisions, picked better mates, reproduced more successfully, and, eventually, become the norm giving us…us. People who love kissing. Any infant could have seen those benefits coming from a mile away, even though an infant’s vision isn’t that great. From birth to four months, babies can only focus on things about 8-10 inches away from their face which, not surprisingly, is about the distance to their mothers face while breast feeding. So, faces, especially those looking right at us, tend to be the very first things in our lives we can focus on and see clearly. This might explain why we are so good at detecting faces. Humans are off the charts when it comes to this, in fact, we tend to see faces even when there aren’t any.