Research by the University at Albany shows that information conveyed by a kiss can have profound consequences for romantic relationships, and can even be a major factor in ending one.

In a recently published article, Susan M. Hughes, Marissa A. Harrison, and Gordon G. Gallup, Jr. reveal that many college students have found themselves attracted to someone, only to discover after they kissed them for the first time that they were no longer interested. "In other words," said Gallup, an evolutionary psychologist, "While many forces lead two people to connect romantically, the kiss, particularly the first kiss, can be a deal breaker."

The UAlbany study also found sex differences in the importance and type of kissing. Males tended to kiss as a means to an end -- to gain sexual favors or to reconcile. In contrast, females kiss to establish and monitor the status of their relationship, and to assess and periodically update the level of commitment on the part of a partner.

In a sample of 1,041 college students, researchers found only five who had never experienced romantic kissing and more than 200 who estimated having kissed more than 20 partners.

According to the study, kissing between sexual or romantic partners occurs in more than 90 percent of human cultures. Some non-human animals, such as common chimpanzees and bonobos, appear to engage in kissing-like behaviors as well. Although kissing is a widespread practice among humans, few scientists have attempted to assess the adaptive significance of kissing behavior.

"Kissing is part of an evolved courtship ritual," said Gallup. "When two people kiss there is a rich and complicated exchange of information involving chemical, tactile, and postural cues. This may activate evolved mechanisms that function to discourage reproduction among individuals who are genetically incompatible."

According to the researchers, not only do females place more emphasis on kissing, but most would never engage in sex without kissing. Females were more likely than males to insist on kissing before a sexual encounter, and more likely to emphasize the importance of kissing during and after sexual encounters as well. By comparison, males said they would be happy to have sex without kissing, and far more males than females expressed a willingness to have sex with someone who was not a "good" kisser.

Males, however, were more likely than females to initiate open mouth kissing and kissing with tongue contact. The researchers speculate that the exchange of saliva during kissing may have biological consequences in its own right. Male saliva contains measurable amounts of the sex hormone testosterone which can affect libido.

The authors conclude that the study provides evidence that romantic kissing evolved as an adaptive courtship strategy that functions as a mate-assessment technique, a means of initiating sexual arousal and receptivity, and a way of maintaining a bonded relationship.

Full results are published in the August 2007 issue of the online journal Evolutionary Psychology [Volume 5(3) 2007],