“In other words, while many forces lead two people to connect romantically, the kiss, particularly the first kiss, can be a deal breaker,” lead researcher Prof Gordon G  Gallup of the University of Albany was quoted by the Science Daily as saying.

According to the study, sex differences also play a key role in the importance and the type of kissing.

While males tend to kiss as a means to an end — to gain sexual favours or to reconcile, females smooch just 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. The researchers came to the conclusion after analysing a sample of 1,041 college students. They found that only five had never experienced romantic kissing while more than 200 admitted to having kissed more than 20 partners.

According to the researchers, kissing between sexual or romantic partners occurs in more than 90 per cent of human cultures. Some non-human animals, such as chimpanzees and bonobos, appear to engage in kissing-like behaviours as well. “Kissing is part of an evolved courtship ritual. 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,” Prof Gallup said. They also found that not only do females place more emphasis on kissing, but most would never engage in sex without kissing. Females are more likely than males to insist on kissing before a sexual encounter, and are more likely to emphasise on 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, according to the researchers.

Males, however, were found to be 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.