Well I doubt there's any actual research on this, but I'd expect it has to do with a little bit of each of the following... -socialization, expectations, arousal, endorphins, stimulation of the nucleus accumbus (reward center of the brain) what it amounts to is that a person who hasn't kissed wants to kiss or is nervous about it (through socialization). This causes an increase in arousal, getting the blood and other endorphin pumping. If the kiss is thought to be a good thing (whoa I finally kissed someone), nucleus accumbus is stimulated, rewarding the person. If it isn't liked (get your hands off of me) nucleas accumbus isn't stimulated. Flight may ensue. That's what I see as the basics of it. I don't see how you could "scientifically" measure the situation as a whole though. Why does any of this matter?
Get a copy of this month's Discover Magazine- with the cover article on traveling to Mars. The last article is about the chemistry of Love. It's an interesting read.
