Sloppy male kissers may have a method behind their messiness.
Men in general seem to like wet kisses with more "tongue action," said anthropologist Helen Fisher of Rutgers University.
This could be because modern males are instinctually using kisses to pick up traces of estrogen in a woman's saliva and thus gauge her fertility.
Wet kisses could also be an unconscious attempt to transfer testosterone to the woman, which would stimulate her sexual interest, Fisher said Friday at a meeting of the American Association for the Advancement of Science in Chicago.
"Men see kissing early in a relationship directly as a step to copulation," she said.
Sloppy smooching could therefore be an "all-purpose mechanism" to get the reproductive juices flowing.
Kiss of Death
Kissing may also serve as a way to assess the quality of a mate, said Wendy Hill, a neuroscientist at Lafayette College in Easton, Pennsylvania.
Technique aside, the chemical cocktail of saliva may tell us if the person we're kissing is a genetically appropriate choice to mate with.
In fact, Rutgers' Fisher said, research has shown that the majority of men and women rate their first kiss as either "the kiss of death" or the blossoming of a new relationship.
The idea adds to mounting research that shows humans are naturally drawn to certain people based on biological cues that run deeper than looks.
Using statistics from 40,000 people on the Internet dating site Chemistry.com, Fisher recently developed a personality test that measures four universal temperaments.
Each temperament type was linked to activity levels of the brain chemicals dopamine/norepinephrine, serotonin, testosterone, and estrogen/oxytocin.
Fisher found that a person's temperament guides which type of mate they select—boosting her belief that love involves some very powerful brain chemistry.
"People sing for love; they dance for love; they write about love; live for, kill, and die for love," Fisher told National Geographic News.
"It's a wonderful addiction when [a relationship is] working well—but perfectly horrible when it's working poorly."