18 July 2007

Science of smooching

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The origins and role of the kiss in human relations remain a hotly controversial topic in science.
Science of smooching

PASH, PECK, SMACK, SMOOCH, SNOG. In its various forms the kiss has long been a source of inspiration to lovers, musicians and poets — less well-known is that scientists have also been getting some of the action. Philematology is the formal name for the study of smooching, an act known affectionately in the lab as ‘osculation’.

Renowned 19th century American physician and diehard romantic, Henry Gibbons, described the kiss as “the anatomical juxtaposition of two orbicularis oris muscles in a state of contraction”.

If that doesn’t leave you swooning, consider the work of bacteriologist Arthur Bryan at Baltimore City College, Maryland, in the 1950s. He reported that up to 250 colonies of bacteria can be transferred in a single passionate kiss. Which brings us to an important question. Why, exactly, do we kiss?

Lip-smacking mystery

Mystery still surrounds the motive for that very first kiss. As anthropologist Helen Fisher, of Rutgers University in New Jersey, notes, many species engage in behaviour that looks suspiciously similar. Snails use their antennae to caress, birds nibble beak-to-beak, and many mammals lick or gently gnaw each other. So maybe kissing is just an animal impulse?

“When you find something in 90 per cent of cultures around the world and you also find it in a great many mammalian species, that’s something innate,” says Fisher.

Chimpanzees and bonobos, our closest relatives, kiss in wildly different ways and contexts. According to Frans de Waal, a primatologist at Emory University in Atlanta, chimps specialise in a platonic kiss of reconciliation. “Within a minute of a fight having ended, the two former opponents may rush towards each other, kiss and embrace long and fervently, and then proceed to groom each other,” he writes in his book, Chimpanzee Politics.

Bonobo kisses, on the other hand, are usually given during play, and have sexual overtones: while chimp kisses don’t get more lascivious than a quick peck, bonobous revel in sloppy, tonguey tonsil-hockey.

Some trace the evolutionary origins of the kiss to mouth-to-mouth feeding of offspring, a behaviour observed in many species of birds and mammals. This could have led to kissing as a sign of affection between mother and child; a gesture that spread to other relationships. But some anthropologists point out that the people who still feed their young in this way — the Papuans of New Guinea and the San of southwest Africa — were strangers to kissing before Europeans arrived.

Little nibble

For Freud, kissing was a subconscious return to infancy and suckling at the mother’s breast, and many researchers since have noted the parallels. “When a baby is looking for a nipple it’s already making the movements and the facial expression and the pouted lips that we later apply in the kiss,” says Glenn Wilson of the Institute of Psychiatry in London, England.

De Waal thinks kissing evolved as a way of communicating good intentions. “Superficially, a kiss resembles a bite. So you’re showing that you could do something harmful, but you’re not — instead you’re making yourself vulnerable.”

Slightly less charming is de Waal’s comparison of kissing with another behaviour in monkeys and dogs: “They turn their behind and ‘present’ it to another individual, they take a vulnerable position so the other can inspect them or smell them or climb onto them. It is the same principle, I think, as the kiss.”

However, not everyone is convinced that kissing is a product of evolution. “Kissing is a behaviour that’s 100 per cent learned and it has absolutely nothing to do with genetics,” says Vaughn Bryant, professor of anthropology at Texas A&M University in College Station, USA. “If it were innate, everybody would be doing it — and they’re not.”

There is some evidence that some cultures never engaged in the practice. The indigenous inhabitants of the island of Mangaia in the South Pacific, for example, were enthusiastic lovers but knew nothing of kissing until the 1700s, when Europeans arrived.

The same was true of Australian aborigines and of tribes in sub-Saharan Africa. As recently as 1990, an editorial in the Beijing Workers’ Daily declared that kissing “is a vulgar practice which is all too suggestive of cannibalism”. Today in China, kissing is common, but not among older people.

So if kissing isn’t genetic, what possessed people to get so intimate with each other’s faces? “The smell”, says Bryant. He thinks kissing began as a way of screening potential partners by scent.

So the original kiss might have been something like the Polynesian or Eskimo kiss, in which lips are left out and noses are rubbed across the face. This provides kissers with the chance to inhale the odour emanating from scent glands on the cheeks.

“Through the roof with euphoria”

The idea makes sense because your smell can reveal a surprising amount about a potential partner (see Sexual Chemistry 101, Cosmos Online). But whether it’s entirely cultural or has an innate component, there’s a much simpler explanation for our love affair with the kiss.

“Apart from fingertips and genitals, the lips are as well supplied with nerve endings as any part of the body, so that makes them particularly sensitive,” says Glenn Wilson. And when you fall in love, the brain’s reward system is triggered, so if you lock lips “you go through the roof with euphoria,” adds Rutgers University’s Fisher.

Key to the reward system is the neurotransmitter dopamine. It’s responsible for those crazy feelings you experience when you’re swept off your feet: the elation, the craving and obsessive thoughts. As Fisher points out: “The part of your brain that becomes active when you look at a photograph of your sweetheart is exactly the same region that becomes active when you feel the rush of cocaine. So it’s no surprise a kiss can be such an overwhelming experience.”

So next time you’re leaning in for the pash, close your eyes and think of science. You might even be doing something that’s good for your health. “The brain likes stimulation,” says Fisher. “I think if you kiss the right person, it’s wonderful for you.”

Erica Harrison is a freelance science writer and photographer based in Sydney.
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