According to new research, one big reason is that we need to size up our future mates. The research, conducted by scientists from Oxford University, also explores the link between kissing and relationship quality, and differences in the value of kissing between men and women. The findings are published in two studies in the journal Archives of Sexual Behavior and the journal Human Nature. “Mate choice and courtship in humans is complex,” study researcher Robin Dunbar, a professor at Oxford, said in a statement. “It involves a series of periods of assessments where people ask themselves, ‘Shall I carry on deeper into this relationship?’ Initial attraction may include facial, body and social cues. Then assessments become more and more intimate as we go deeper into the courtship stages, and this is where kissing comes in.” For the study, researchers asked 900 people (308 men and 594 women), about half of whom were in long-term relationships at the time of the survey, what they thought about kissing and its importance in relationships, both short- and long-term. They found that in general, women were more likely than men to think that kissing is important in a relationship. People who rated themselves as attractive and people who had more casual or short-term romantic encounters were also more likely to assign kissing a high importance to a relationship. Interestingly, the importance of kissing changed when looking at a short-term relationship versus a long-term relationship. Women were more likely than men to say kissing was more important in long-term relationships. And what about timing of kissing with regard to sex? Researchers found that kissing was generally most important before sex, but then its importance decreased thereafter (it was rated as less important during sex, even less important after sex, and the least important during non-sex times). However, when researchers asked about kissing in the context of a committed relationship, it was rated as equally important before sex and during non-sex times. Past studies have also affirmed the idea that smooching is a way to vet future mates. CNN Health reported on research showing that kissing provides sensory clues, including taste, sound and smell, that can help a person decide if he or she wants to kiss that person again.