Kissing may have evolved to help people pick a compatible mate -- and to keep the love going in long-term relationships. 
 
 You've got to kiss a lot of frogs to find your prince, as the saying goes. New research suggests the cliché is true on an evolutionary level. 
 
 Kissing might have evolved as a way to assess the quality of potential mates, according to two new studies. Women, who tend to be pickier about romantic entanglements than men, also care more about kissing in the first phases of a relationship, suggesting that make-outs may weed out duds. What's more, women are especially attuned to the importance of kissing during fertile phases of the menstrual cycle. 
 
 Kissing exists in virtually every culture on Earth, said study researcher Rafael Wlodarski, a doctoral candidate at the University of Oxford. Some of the oldest records left by humanity, including the Hindu Veda and ancient Egyptian wall murals, depict kissing. 
 
 "Because it's so common," Wlodarski told LiveScience, "it might serve a purpose." 
 
 The evolution of make-outs 
 
 Theories about why kissing matters fall into three categories. Some believe kissing evolved to help people assess potential mates, perhaps by transmitting pheromones, or chemical signals that could carry information about health or immune compatibility. [50 Sultry Facts About Sex] 
 
 "It's just an excuse to get two people who are interested in each other close enough to have a sniff," Wlodarski said. 
 
 No particular compound has been proven to be a human pheromone, but there is evidence that scent carries information. One study published in April 2013 found that women prefer the scent of men who have high levels of the masculine hormone testosterone. 
 
 Kissing also may have evolved to keep romantic pairs bonded, or to increase arousal prior to sex. To test these theories, Wlodarski and his colleagues recruited 902 American and British adults to answer questions about their attitudes toward kissing. 
 
 The participants rated how important they considered kissing at various stages in relationships. The approximately half of participants who were in relationships also reported how much they and their partners kissed, and how satisfied they were in the relationship. 
 
 The results gave little support to the notion that kissing evolved to ease the way to sex (even if it may often be used that way). People in short-term relationships saw kissing as most important right before sex, but there was no other indication that people use kissing primarily as a sexual warm-up act. In fact, people in relationships closely associated the amount and quality of their kisses with relationship satisfaction. The more kissing, the happier they were. The amount of sex, on the other hand, wasn't related to relationship satisfaction at all. 
 
 Pucker up 
 
 The latter finding suggests kissing serves a pair-bonding purpose, helping couples show affection and commitment. But kissing also seems to help people gauge relationship potential. 
 
 If kissing is a way to assess mates, the pickiest people should place the highest importance on kissing. This appears to be the case: Women, who take on the risk of gestating, birthing and caring for a child when they have sex, are generally more choosy about mates than men. They're also more likely than men to rate kissing as important, and more likely to say that an initial kiss had changed their attraction to another person, Wlodarski and his colleagues found. [Busted! 6 Gender Myths in the Bedroom & Beyond] 
 
 People who rated themselves as attractive — and thus who likely can afford to be picky — were also the most interested in kissing and the most likely to say that a kiss could sway their perceptions of attraction. Wdolarski and his colleagues report these findings in an upcoming issue of the journal Archives of Sexual Behavior. 
 
 A second study by the researchers, this one published in the September issue of the journal Human Nature, examined only female attitudes toward kissing. If kissing communicates some information about health, fertility or genetic compatibility, the thinking went, women who are at risk of conceiving are more likely to think kissing is important — after all, they might end up with a baby if the romance goes well. 
 
 The researchers surveyed 84 American and British women, asking them to report the dates of their menstrual cycle and to answer questions about how important kissing is in various stages of a relationship. Fifty of the women were in the luteal, or less-fertile, phase of their cycle, and 34 were in the late follicular phase, the point at which fertility peaks. 
 
 The most fertile women were more likely than the least fertile women to say that kissing in the early stages of the relationship is important, lending credence to the idea that they might be subconsciously sniffing out the best genes for their potential offspring. Both groups were equally likely to say kissing later in a relationship is important, potentially pointing to kissing's bond-cementing role. 
 
 "At different times in the relationship, [kissing] is used for different things," Wlodarski said. He next plans to move beyond kissing into even murkier depths. 
 
 "I'm interested in doing more research on what love is in humans," he said. "What is it that makes us so intimately attracted to one specific person?" 
 
 Follow Stephanie Pappas on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience. ||||| Getty Images/OJO Images RF / Getty Images/OJO Images RF 
 
 What is the point, really, of kissing? Humans make such a big deal of it, but almost no other animals smooch. 
 
 A new study out of Oxford University suggests that kissing may actually have a purpose beyond the obvious — it’s a mating audition. Potential mates are doing a taste test. And that could explain why women and guys who think they’re good-looking enjoy it more than other people do. 
 
 Kissing, which is practiced in almost every human society in various forms, is something of a mystery to those who study mating behavior. Chimps and bonobos kiss, but not with the same intensity or high levels of mooniness before and after the act that Homo sapiens display. There are three working theories about why we, as opposed to other species, like to lock lips: kissing can arouse, it cements relationships together or it’s a trial run of a potential mate. 
 
 Two researchers from Oxford’s department of experimental psychology, Rafael Wlodarski and Robin Dunbar, provide evidence for the latter explanations in their latest investigation. They set up an online survey and asked about 900 adults (about two-thirds of whom were women) to answer questions about how important kissing was in both long and short relationships. Overall, women valued kissing more than men (no surprise), but guys who rated themselves as more attractive than others or who had lots of girlfriends also placed more emphasis on the smooch. 
 
 (MORE: How My Nut Allergy Made Me More Monogamous) 
 
 That makes sense, say the researchers, since both women and good-looking guys tend to be more picky about their mating partners. For women, bearing and raising children is a huge investment of their life and health, so they want to choose the right co-parent. As anthropologist Helen Fisher told U.S. News and World Report, “When you get a highly intelligent, pair-bonding species that requires years to raise a baby, you evolve more and more brain mechanisms to weed out the losers.” The hottie guys are picky because, well, they can be; they have a lot of choices, so they need a way to winnow them down. Kissing, says the Oxford team, may therefore be a way of trying on potential partners. 
 
 “Mate choice and courtship in humans is complex,” Dunbar said in a statement discussing the work. “It involves a series of periods of assessments where people ask themselves, ‘Shall I carry on deeper into this relationship?'” The early judgment calls are all based on facial, body and social cues. “Then assessments become more and more intimate as we go deeper into the courtship stages,” he said, “and this is where kissing comes in.” 
 
 How does a kiss determine mateworthiness? It’s not really clear, but some philematologists (those are the people who study kissing) believe that it has to do with smell. In her book The Science of Kissing, Sheril Kirshenbaum cites Claus Wedekind, who she says found that “women are most attracted to the scent of men who have a very different genetic code for their immune system in a region of DNA known as the major histocompatibility complex.” Having different DNA from the individual you are kissing heightens the chance of having healthy offspring should the kissing lead somewhere. And juxtaposing two orbicularis oris muscles in a state of contraction is usually more fun than having a genetic test. 
 
 Other scientists believe women send off a signal if they’re ovulating that can be subconsciously detected if a mate is close enough. As the authors of a study published in the Archives of Sexual Behavior put it, “It is unclear, for example, whether kissing aids in the process of mate assessment by facilitating the evaluation of pheromonal cues for overall health, genetic fitness, or menstrual-cycle phase and fertility, or alternatively by aiding gustatory assessment of skin oils and saliva compounds.” (Translation: it could be a subconscious thing, or it could be that mates are actually figuring out whether each other smells good.) 
 
 (MORE: The Truth About College Hookups) 
 
 Women in the study also ranked kissing as more important for longer relationships, suggesting it was a way of communicating and enhancing affection and attachment. In fact, more kissing was strongly correlated than more sex with a higher-quality relationship (although the people who had a lot of both had the highest relationship satisfaction). Moreover, the researchers suggest that although kissing does cause arousal, arousal doesn’t seem to be what is driving people to kiss. 
 
 Maybe the couples in this event could shed some light on the matter. ||||| What's in a kiss? A study by Oxford University researchers suggests kissing helps us size up potential partners and, once in a relationship, may be a way of getting a partner to stick around. 
 
 "Kissing in human sexual relationships is incredibly prevalent in various forms across just about every society and culture," says Rafael Wlodarski, the DPhil student who carried out the research in the Department of Experimental Psychology at Oxford University. "Kissing is seen in our closest primate relatives, chimps and bonobos, but it is much less intense and less commonly used. 
 
 "So here's a human courtship behavior which is incredibly widespread and common and, in extent, is quite unique. And we are still not exactly sure why it is so widespread or what purpose it serves." 
 
 To understand more, Rafael Wlodarski and Professor Robin Dunbar set up an online questionnaire in which over 900 adults answered questions about the importance of kissing in both short-term and long-term relationships. 
 
 Rafael Wlodarski explains: "There are three main theories about the role that kissing plays in sexual relationships: that it somehow helps assess the genetic quality of potential mates; that it is used to increase arousal (to initiate sex for example); and that it is useful in keeping relationships together. We wanted to see which of these theories held up under closer scrutiny." 
 
 The researchers report their findings in two papers, one in the journal Archives of Sexual Behavior and the second in the journal Human Nature, both published by Springer. They were funded by the European Research Council. 
 
 The survey responses showed that women rated kissing as generally more important in relationships than men. Furthermore, men and women who rated themselves as being attractive, or who tended to have more short-term relationships and casual encounters, also rated kissing as being more important. 
 
 In humans, as in all mammals, females must invest more time than men in having offspring -- pregnancy takes nine months and breast-feeding may take up to several years. Previous studies have shown women tend to be more selective when initially choosing a partner. Men and women who are more attractive, or have more casual sex partners, have also been found to be more selective in choosing potential mates. As it is these groups which tended to value kissing more in their survey responses, it suggests that kissing helps in assessing potential mates. 
 
 It has been suggested previously that kissing may allow people to subconsciously assess a potential partner through taste or smell, picking up on biological cues for compatibility, genetic fitness or general health. 
 
 "Mate choice and courtship in humans is complex," says Professor Robin Dunbar. "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." 
 
 He adds: "In choosing partners, we have to deal with the 'Jane Austen problem': How long do you wait for Mr Darcy to come along when you can't wait forever and there may be lots of women waiting just for him? At what point do you have to compromise for the curate? 
 
 "What Jane Austen realised is that people are extremely good at assessing where they are in the 'mating market' and pitch their demands accordingly. It depends what kind of poker hand you've been dealt. If you have a strong bidding hand, you can afford to be much more demanding and choosy when it comes to prospective mates. 
 
 "We see some of that coming out in the results of our survey, suggesting that kissing plays a role in assessing a potential partner," Professor Dunbar explains. 
 
 Past research has also found that women place greater value on activities that strengthen long-term relationships (since raising offspring is made easier with two parents present). In the current study, the team found that kissing's importance changed for people according to whether it was being done in long-term or short-term relationships. Particularly, it was rated by women as more important in long-term relationships, suggesting that kissing also plays an important role in mediating affection and attachment among established couples. 
 
 While high levels of arousal might be a consequence of kissing (particularly as a prelude to sex), the researchers say it does not appear to be a driving factor that explains why we kiss in romantic relationships. 
 
 Other findings included: 
 
 * In short relationships, survey participants said kissing was most important before sex, less so during sex, was less important again after sex and was least important at other times. In committed relationships, where forming and maintain a lasting bond is an important goal, kissing was equally important before sex and at times not-related to sex. 
 
 * More frequent kissing in a relationship was linked to the quality of a relationship, while this wasn't the case for having more sex. However, people's satisfaction with the amount of both kissing and sex did tally with the quality of that relationship. 
 
 * In a companion paper in the journal Human Nature, the researchers report that women's attitudes to romantic kissing also depend on where in their menstrual cycle and their relationship they are. Women valued kissing most at initial stages of a relationship when they were in the part of their cycle when they are most likely to conceive. Previous studies have shown that hormonal changes associated with the menstrual cycle can change a woman's preferences for a potential mate. When chances of conceiving are highest, women seem to prefer men who display supposed signals of underlying genetic fitness, such as masculinized faces, facial symmetry, social dominance, and genetic compatibility. It appears that kissing a romantic potential partner at this time helps women assess the genetic quality of a potential mate, the researchers say.
– A new scientific study delves into that most important of questions: Why do humans kiss? It's a practice carried out by almost no other animals, especially not with the same level of intensity, Time notes. But researchers found locking lips may actually serve an evolutionary purpose: It helps us assess potential mates and weed out the lesser options, LiveScience reports. That explains why women (who are pickier than men when it comes to mating) and people who rate themselves as attractive (who are also pickier) said they found kissing more enjoyable and important than their male and/or less attractive counterparts, Science Daily reports. It also explains why women find kissing especially important when they're at their most fertile. One theory: Kissing might transmit pheromones or chemical information—some of which can be transmitted through smell—about a partner's health, fertility, or genetic and immune compatibility. As one researcher says, "It's just an excuse to get two people who are interested in each other close enough to have a sniff." Says another, "Mate choice and courtship in humans ... involves a series of periods of assessments where people ask themselves, 'Shall I carry on deeper into this relationship?'" Kissing can help answer that question. (And once a partner is found, one writer suggests applying the principles of software code to the relationship.)