Humans have evolved to use a number of signals - including taste, smell and possibly silent chemical messengers called pheromones - to help us figure out whether someone is a suitable partner and a good person to reproduce with. A kiss means getting close to someone - close enough to suss out important clues about chemistry and genetics. At this range, our noses can detect valuable information about another person's health and perhaps even his or her DNA. Biologist Claus Wedekind has found, for instance, that women are most attracted to the scents of men with a different set of genetic coding for immunity than their own. This is probably because when there is greater genetic diversity between parents in this area, their children will have more versatile immune systems.
Sheril Kirshenbaum, who wrote the book The Science of Kissing, tells us how great kisses kick start our chemicals and hormones, and how a kiss' effects on our brains and bodies promote relationships. Link -via The Intersection