"At the moment of the kiss, there's a very complicated exchange of information ... that may tap into underlying evolved mechanisms" cluing us in on whether we're genetically compatible, explains Gordon Gallup, co-author of the study and professor of psychology at the State University of New York at Albany. "A kiss can be a deal-breaker in terms of whether a relationship will flower or flounder, so to speak."

It's ashame people don't also have genitals in their mouths. It would make things interesting.