If a picture is worth a 1,000 words, so may be a kiss - or certainly to a woman anyway, researchers say.
A State University of New York team quizzed over 1,000 students, finding women place a big emphasis on kissing.
They use kissing as a way of assessing the recipient as a potential partner, and later to maintain intimacy and to check the status of a relationship.
But men placed less importance on it, using it to increase the likelihood of sex, Evolutionary Psychology reported.
The questionnaires revealed men were less discriminating when it came to deciding who to kiss or who to have sex with.
"While both sexes participate in the adaptive benefits of kissing, we found sex differences when considering the pursuit of short-versus long-term mating strategies"
They were more willing to have sex with someone without kissing, to have sex with someone they are not attracted to and agree to have sex with someone they considered to be a bad kisser.
But kissing was more important as a bonding mechanism to women.
In long-term relationships females not only rate kissing as more important than men, but they indicated that kissing was important throughout a relationship.
Meanwhile, men placed less importance on kissing as the relationship progresses.
There was also a difference in the sort of kisses the two sexes preferred, with men liking wet, tongue kisses.
Lead researcher Dr Gordon Gallup said kissing had developed over time to become an essential part of the courtship process.
But he added: "While both sexes participate in the adaptive benefits of kissing, we found sex differences when considering the pursuit of short- versus long-term mating strategies."
Dr Glenn Wilson, an expert in relationships at London's Institute of Psychiatry, said: "Kissing is used by everyone as a bonding and testing mechanism.
"But the fact is women are more discriminatory than men. Men can just go out and spread their seed, but women have to take more responsibility because of the consequences and so they are likely to want to test more."
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