Scientists who are starting to understand the biochemistry of kisses say that saliva increases sex drive.

Those in the kissing-science field of philematology are finding links between kissing and the hormones that affect coupling, researchers said at the annual meeting of the American Association for the Advancement of Science as quoted by media Monday.

And these hormones are one of the keys to our reproductive success, so there's a link to evolution and passing on our genes to the next generation.

"There is evidence that saliva has testosterone in it," said Rutgers University anthropologist Helen Fisher, and testosterone increases sex drive.

"And there is evidence that men like sloppier kisses with more open mouth. That suggests they are unconsciously trying to transfer testosterone to stimulate sex drive in women," Fisher said.

Men also could be using the saliva transfer to assess women's fertility and estrogen cycle, but they might want to be wary of turning women off with too much slobber, she added.

More than 90 percent of human societies exchange smooches, Fisher said. And the behavior is rampant among pygmy chimpanzees and bonobos, some of our fellow primates. Foxes lick each others' faces, birds tap their bills together, elephants put their trunks into one another's mouths. Charles Darwin himself thought that kissing was a natural instinct.

One study found that 66 percent of women and 59 percent of men say that the quality of the first kiss can kill a relationship, Fisher said.

Psychologist Wendy Hill at Lafayette College in Pennsylvania is hot on the trail of those chemical systems. In a 2007 study, Hill and her team found interesting differences between the hormone levels of college-aged male-female couples who had kissed and those who had just held hands and listened to music for 15 minutes in a room in a student health center.

Donald Lateiner, a history and classics professor at Ohio Wesleyan University who spoke to reporters at AAAS, has investigated who kissed whom and why and when in ancient Athens, Rome and nearby. In his work, he looked at depictions of romantic, familial and social kissing-up in poetry and prose, public and private art, including vase paintings, sculpture and mirror cases.

Kissing is relatively infrequently represented in the art of ancient Greece and Rome, Lateiner said. "That isn't to say there isn't a lot of sex, but there isn't a lot of kissing, which is somewhat different," he added.

Source: Xinhua/Agencies