Kiss is a form of communication. Depending on how you feel about him, a kiss can be either a very complicated act of communication or a very simple one. Of course, you can argue that in the present age of fiber optics, the Internet, and global telecommunications, the good old kiss will not help bring nations closer together.
On the other hand, if a female seal swims past a salmon, say, its seal will be completely different. Seal pheromones tell him something completely different. Instead: “Well, swim to me, baby, let's play in love!” - Mr. Salmon will hear: “Raw salmon is my favorite breakfast!” - and right there he pulls fishing tackles, goes into the depths. A man on his way to his current status as a higher intelligent being lost many instincts that protect wise and cautious salmon. The organs of smell have ceased to play a vital role in our lives. The most that we use them for now is to check if the chef has refilled the vinegar we ordered. In ancient times, people were better able to read the information supplied by the pheromones, so the kiss must have told them more about each other than we are now. Of course, the kiss brings communication to a new dimension. People are getting as close as ever. And for the first time, they smell their partner. Smells of perfume, body, cigarettes and anything else, can either attract or repel, depending on the preferences of those who feel them. Therefore - who knows? - maybe it is exactly this hypothesis.