From Time Magazine:
“Males tend to kiss as a means of gaining sexual favors, or as a means of affecting reconciliation,” says Gallup. “Females kiss more as a mate-assessment device.”
Indeed, in studies of smooching styles in men and women, Gallup found that men were more likely to initiate tongue contact, preferring French kissing to closed-mouth pecks. One theory behind that finding is that men have small amounts of testosterone in their saliva. “In saliva exchange — whether that’s over weeks or months or even years — trace amounts of testosterone in male saliva could raise testosterone levels in the female and therefore increase her receptivity and her libido,” Gallup says. “In long-term relationships, the frequency of kissing is a good barometer of the health and well-being of that particular bond.”
In longer, committed relationships, Gallup found, women also continued to use kissing — to evaluate the state of their partnership. They were also far more likely than men to insist on kissing before, during and after sex.
Fifty-nine percent of men and 66 percent of women say they have ended a budding relationship because of a bad kiss.
Most of the info in the piece is taken from The Science of Kissing: What Our Lips Are Telling Us.