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  • Why do we kiss? Well, easy, because it feels good. But why?

  • [Music]

  • Kissing is weird. We love doing it, but let's face it, it's weird. You're rubbing your open

  • mouth on another human being's open mouth. So there must be a good reason that we do

  • it. According to scientists, there's actually many good reasons, and they start with the

  • eyes. And those eyes are looking at lips.

  • Human lips are unique in the animal world - they are "everted" or exposed outward. Today,

  • 8 out of 10 women paint their lips, often some shade of red. And men, well they say

  • they're more attracted to fuller, redder lips. Our primate relatives are attracted to rosy

  • colors too, just in a different place. As we evolved to walk upright, we began to advertise

  • our fertility face-to-face.

  • As you start to kiss, you engage 5 of your 12 cranial nerves, and more than a dozen facial

  • muscles. One of those, your orbicularis oris, allows you to make this puckering shape, the

  • same shape as a nursing baby. That's our first clue to kissing's origins. Breastfeeding is

  • an incredibly neurologically pleasurable experience, it releases waves of the hormone oxytocin,

  • which promotes bonding and comfort in mother an child. This bond is so strong that there's

  • a two-thirds chance that when you kiss, you tilt your head to the right. This might be

  • because 80% of mothers hold their babies to the left, so we're used to turning our heads

  • to the right for comfort, and puckering up.

  • As you get closer, it's time to engage your nose. Our oldest references to kissing come

  • from Vedic Sanskrit texts from 1500 BC, which refer to it as a "sniff" or a "smell". And

  • for many cultures, kissing is still a primarily nasal experience.

  • Breath can be an indicator of health in a potential mate, we might even be able to smell

  • a good genetic match. In one famous experiment, woman smelled t-shirts worn by different men,

  • and then rated their smell preferences. They overwhelmingly preferred the smell of men

  • with different immune system genes from their own. It's almost like we're testing compatibility

  • with a kiss.

  • Finally, contact. Our lips are some of the thinnest and most nerve-rich skin in our bodies,

  • and our brain's somatosensory cortex devotes more neural real estate to our lips than even

  • our genitals. The sensation of kissing sends signals directly to the brain's pleasure and

  • reward centers, and unleashes a spectrum of neurotransmitters and hormones.

  • While no one brain chemical can be responsible for something as complex as kissing, we can

  • feel a few of them at work. A first kiss brings on a rush of novelty, as a flood of dopamine

  • acts on the same brain reward centers triggered by drugs like cocaine. It can even bring on

  • feelings of withdrawal and addiction.

  • Thanks to epinephrine and norepinephrine, your heart beats faster, you get a wave of

  • oxygenated blood to your brain, and your pupils dilate, and maybe that's why we close our

  • eyes. The pituitary gland and hypothalamus can release waves of endorphins, bringing

  • on feelings of euphoria. Despite all that action on the microsecond scale, it can feel

  • like time is standing still. As the minutes of kissing turn to days and weeks, the body

  • produces less of the stress hormone cortisol. Seems like kissing can actually be good for

  • your long-term health.

  • In surveys women consistently rate kissing as more important in relationships than men

  • do. Maybe that's because they actually have to physically carry the children, and they're

  • a little more biologically invested in all those things that come after kissing.

  • As important as kissing is to sex, the two can be and often are completely separated.

  • Not only do people often view kissing as a more intimate act than sex itself, researchers

  • say that people can usually remember more about their first kiss than they can about

  • their first time going all the way.

  • Clearly, people take smooching very seriously. Romans would certify the sharing of property

  • in marriage based on whether the betrothed had shared a kiss, and in the Middle Ages,

  • men who couldn't read or write would seal a contract by kissing a written "x", a symbol

  • we still use today.

  • Even though kissing, in an evolutionary sense, isn't required to reproduce, more than 90%

  • of human cultures do it in some way. We call it locking lips, making out, playing tonsil

  • hockey, snogging, pecking, even osculation. Maybe we have so many words for kissing because

  • kissing can be so many things. Kissing has evolved from its biological origins into a

  • complex, diverse human behavior, that often doesn't mean the same thing to any two people,

  • even when those people are kissing each other.

  • While we understand bits and pieces of the science of kissing, it's dangerous to make

  • generalizations about something so diverse, or as diverse as the people who do it. Most

  • research on kissing has centered around heterosexual, cis-gendered couples, and usually college

  • students, but there's so many more different types of kissing out there. Like most science,

  • there's a lot left to learn about the science of kissing. Maybe that's why we keep doing

  • it. Stay curious.

  • If you want to know more about this amazing science of kissing, check out the book "The

  • Science of Kissing" by my friend Sheril Kirshenbaum, link down in

  • the description.

Why do we kiss? Well, easy, because it feels good. But why?

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B1 INT US kissing kiss brain smell science men

The Science of Kissing

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    Bruce Lan   posted on 2014/05/24
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