Things are heating up here at the AAAS meeting. For Valentine's Day, scientists explored the evolutionary importance of the kiss. Almost all cultures seek out its spine-tingling sensation, but exactly why we do is a matter of debate. In some preliminary work, researchers reported what could be a valuable insight for kissers around the world: Disney may be the anti-aphrodisiac.
Scientists still don't know why kissing might have evolved or whether its roots are primarily cultural or biological. There are analogous behaviors in the rest of the animal world: Foxes lick one another, for example, birds tap their beaks, and primates have been known to kiss. As for humans, some researchers think that kissing could harken back to nursing or premastication, when a mother chews food for her children and transfers it into their mouths. The oral and neural stimulation of kissing might reignite subconscious feelings of early attachment.
Another idea is that chemicals in saliva may help adults assess whether they have found a good mate. Studies show that men prefer sloppy, wide-mouthed kisses, and that could potentially allow them to subconsciously assess a woman's menstrual cycle and fertility through chemical cues in her saliva, said anthropologist Helen Fisher of Rutgers University in New Jersey at a news briefing yesterday.
A few years ago, neuroscientist Wendy Hill of Lafayette College in Easton, Pennsylvania, wondered whether kissing makes couples feel more attached, so she decided to look into kiss-induced hormonal changes. The experiment started with 15 heterosexual college couples showing up to a student health clinic, offering a blood sample, and drooling into a cup. Hill used this to measure their oxytocin levels, a hormone associated with social bonding, and cortisol levels, a stress hormone that tends to go down when oxytocin increases.
The couples were led to clinical rooms with flowers and Disney music playing in the background (this music had been used in other kissing studies from Japan). About half of the students were asked to hold hands and talk for 16 minutes while the others were asked to open-mouth kiss. Afterward, she ran the hormone tests again to see if anything had changed. As expected, levels of stress hormones dropped in all cases. And men who had been kissing experienced a significant increase in oxytocin, whereas levels increased only slightly in those who had just held hands.
But Hill and her team were baffled by what happened to the women. Oxytocin levels fell in both the kissing groups and the non-kissing groups, and the drop was much stronger in the kissers. "We are exploring the possibility that the setting was not very romantic," said Hill, who suspects that the sterile environment of a health clinic might have had a greater impact on woman than it did men. So Hill and her team ran experiment number two in a secluded room at the back of the academic building, fitted with a couch, electric candles, light jazz, and flowers to enhance the mood.