The science behind the smooch

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Be my biological Valentine: How microbes define physical attraction

Kissing can mean many things to many different people. It can be an expression of mutual affection, an act of reconciliation, a desperate attempt at midnight on New Years Eve, or even a tad of Valentines haste.

The notion of exchanging 80million bacteria with another person in one fell swoop may seem repulsive, but scientists in the Netherlands have reported this is exactly what happens during a ‘passionate ten-second kiss’.

Still repulsive? Take heed, we’re more likely to get sick from shaking hands throughout the day. Alongside all the germs, there are many benefits shared between partners as a result of smooching.

The positive sensations felt from kissing are engrained in us from an early age. In early life, the neural pathways in a baby’s brain begin to develop quickly.

Babies tend to get their first experiences of love and security through behaviours such as bottle feeding or nursing – both of which involve lip pressure and stimulation, and mimic kissing. Such early events that associate lip pressure with positive emotion lay down important neural pathways very early on in our lives, and these neural pathways continue to be well trodden in later life.

Ever noticed a pouting cat? Or noticed a severe lack of advertisement for canine lipstick? There is a reason for this; unlike other animals, human lips are uniquely everted, meaning they purse outwardly. The lips are the most exposed erogenous zone on our bodies. Even the slightest sensations are felt on the lips due to the high concentration of nerve endings found here, which can send torrents of ‘feel-good’ information to the brain during a passionate kiss.

The section of the brain activated by kissing is associated with sensory information, influencing our thoughts and feelings by setting off a whirlwind of hormones and neurotransmitters throughout the body.  These neural impulses bounce between the brain, lips, tongue, skin and facial features, producing chemical signals from nerve connections around the body.

Dopamine levels, a neurotransmitter linked to feelings of desire, are known to spike during a passionate kiss. A fluttering heartbeat and sweaty palms can be accredited to adrenaline boosts, while stress levels drop due to a dip in cortisol. The so called “love hormone” oxytocin can flood the brain, nurturing feelings of attachment and intimacy. Temperatures rise, breathing deepens and cheeks flush. Overall, kissing – the mere act of touching lips with another human – can foster the described sensations of falling in love.

Kissing isn’t all about romance and neural fireworks. Most people will have experienced what they would class as an ‘unpleasant’ kiss during their lifetime. A team of evolutionary psychologists at the State University of New York at Albany found that 59 percent of men and 66 percent of women within a sample group had discontinued a blossoming romance as a result of a bad kiss.

In fact, a kiss acts as the ‘make or break’ moment for the brain, urging us to be most attracted to those that we judge to be the best genetic partners. The close proximity of a passionate kiss can aid partners in learning about each other by highly engaging their senses of smell, taste and touch. As unaware as we may be about it, kissing can act as a form of ‘DNA proficiency test’.

A team of Swiss scientists led by Claus Wedekind found that prospective partners can read subconscious clues about a man’s DNA through his scent, to which they will be highly tuned during a passionate kiss. Wedekind reported that women are found “to be most attracted to the scents of men who carry a different genetic code for their immune system in a region of DNA known as the major histocompatibility complex or MHC.”

There is some logic to this: scientists are now considering that a couple who carry distinctly different genetics for combating disease and illness will produce children with stronger immune systems. (However, Wedekind also found that women who are taking a contraceptive pill show the opposite preferences, being attracted towards men with similar MHC genetics, suggesting the contraceptive pill may fool female bodies in more ways than currently thought).

Kisses can come in many varieties, and are inherently linked to the most significant and meaningful moments of our lives – they provide a means of communication beyond the power of words. Scientists have barely touched upon a real study of kissing, despite clear evolutionary significance, but what we currently know tells us that there is a whole lot more going on than meets the eyes, or lips.

Alice Hargreaves Jones

Feature Image: Khol363/deviantart 

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