Mouth to Mouth: Why We Kiss

I was running laps around a park in my neighborhood. It's about the size of two big city blocks, up on a slope. One thing I like about this park is that it's just so well used. There's an older man running reps on the stairs, a 30-something couple doing lunges between the picnic tables, two moms doing aerobics to a boombox while their kids play in the grass.

And on this night, there's also a middle-aged couple using a park bench. It sits up on the high edge of the park, facing the lawn. They're seated side by side, their bodies rotated towards each other, their arms around each other's backs. And as the sun is going down, this man and woman are kissing... so, so deeply.

My running loop takes me right in front of them. So, about every three minutes, I come up the hill and around the bend and there they are, still kissing. Again and again. And each time I'm staring. And feeling a bit like a creep. It's like kisses bring out this struggle in us between "don't look" and "can't look away." It's kind of like public nudity, this exposure of such shameless intimacy.

Which makes me wonder why we do this weird gesture—mashing our faces together to show love. I mean there are a bunch of theories for why we first started kissing. It could have evolved from the suckling motion we make as nursing babies. Or maybe how moms pass chewed food to their newborn mouth to mouth when baby food is not around.

Or kissing could have come from a smelling gesture—a close sniff to take in a person fully, and judge if they're baby-making material. A bunch of cultures do nose kissing, totally lips-free. The Inuit in Canada kiss by pressing their nostrils against another person's skin, sucking in like a suction cup.

I later brought up that couple's kiss with Sheril Kirshenbaum, author of the book The Science of Kissing. She says what we do know is that men and women's neural pathways for kissing were laid down when they were newborns, being kissed by their parents. She says there's no other activity where all our senses are so actively engaged as when we kiss—lips to lips.

Kissing another person's lips releases the same hormones a baby gets when they nurse from their mom. You are loved. You are cared for. Good kisses bring out a euphoric burst of the neurotransmitter dopamine. That couple on the park bench are evidence, as if you needed any, that kissing just feels good.

And why my urge to stare? There are these things called mirror neurons. They help us feel the feelings of another person. So watching other people kiss can be like vicariously experiencing a kiss ourselves. Some of the same cells end up firing in our brains.

There is something that makes me feel a little cynical about my initial reaction to that couple. At first, I was a bit nervous they weren't just kissing. I was afraid if I looked too close, I might see a little more than I bargained for on a summer evening jog.

But, no, all that passion they were showing, that high that made them oblivious to a peeping jogger...that was all from kissing.