Akiss, it seems, is not just a kiss.
It's a behavior that ties us to our closest primate relatives and to our own infancies, a trigger for our hormones and neurotransmitters to do a mad dance, perhaps even a way for us to unconsciously judge a partner's commitment level and genetic suitability for reproduction. Even puckering up isn't as simple as you think:
"The orbicularis oris muscle runs around the outside of our mouths, making it relatively easy to change the shape of our lips. . . . Meanwhile, the zygomaticus major, zygomaticus minor, and levator labii superioris work together to pull up the corners of the mouth and the top lip; and the depressor anguli oris and the depressor labii inferioris pull down the corners of the mouth and lower lip. And that's just the beginning — an open mouth and tongue movement involve a far more complicated network of facial and postural muscles."
Bringing analysis to the magic of a smooch is the purpose of The Science of Kissing: What Our Lips Are Telling Us, by marine biologist, science journalist and musician Sheril Kirshenbaum. Like some memorable kisses, the book is short and sweet but teaches us something new.
Kirshenbaum focuses mainly on the romantic, passionate kiss, rather than the many other kinds of kisses that can express everything from baby love to betrayal.
The romantic kiss is a complex subject, especially when, as she does, one looks at its history, biology, sociology and more. Humans aren't the only kissers; kissing and kisslike behavior, such as licking and nibbling, are common to many mammals as a way of expressing affection and gleaning information about another critter. As Kirshenbaum writes, "If it's a noun, dogs will probably lick it."
Bonobos, our closest primate relatives (we share 98.7 percent of our DNA) are "avid open-mouthed kissers." She relates the story of one zookeeper who accepted a proffered kiss from a bonobo and was startled when it slipped him some tongue.
But human beings are uniquely designed for kissing, given our everted lips, with soft tissue on the outside and, often, a striking rosy hue. As humans began walking upright, Kirshenbaum explains, women's genitalia became less visible, but lips grew to mimic them in shape and color. (There's a reason men say the shade of lipstick they find most attractive is red.)
Kissing is also related, not just in the muscles involved but in the brain chemicals it triggers, to how infants feed. Whether we tilt our heads right or left when we kiss seems to be related not to handedness but to the position in which we were held to our mother's breast.
Not everyone kisses; from Polynesia to Africa to Finland, Kirshenbaum writes, many cultures have disdained it. (And she notes that, in many times and places, prostitutes have adamantly avoided kissing their customers.)
But kissing's recorded history goes as far back as the Hindu Vedas, in about 1,500 B.C. And more people kiss than used to, a trend attributable to the giant cinematic liplocks Hollywood has sent around the world. "Considering that we also introduced cigarettes and fast-food chains," she writes, "kissing is probably one of the healthiest customs we've exported. . . ."
Not that it's always healthy. In one chapter, "There Are Such Things as Cooties," Kirshenbaum reviews some of the bacteria and viruses that kissing can convey, which can cause, among other things, dental cavities, meningitis and herpes simplex 1, a.k.a. the cold sore virus, which infects about half of us by the time we're teens, 80 to 90 percent of us by the time we're 50.
That's not stopping us, though. Kissing is simply too important to us, for emotional, biological and other reasons. She details all the information our bodies gather through taste, smell and touch when we kiss — possibly even elements of our partner's genetic profile.
Our brains reinforce kissing with a bath of chemicals such as oxytocin, the "love hormone," and dopamine, a neaurotransmitter that creates a natural high and is tied to addictive behaviors. Those biological reinforcements may explain why subjects in one study told researchers they could remember more details about first kisses than first sexual experiences — and why another study found that 59 percent of men and 66 percent of women reported they had dumped a potential partner because the first kiss didn't ring their chimes.
Kirshenbaum persuades a research lab to work with her on an experiment that measures subjects' reactions to pictures of kissing couples by scanning their brains' magnetic fields — with some unexpected results.
She ends each chapter with a kissing anecdote, including the only funny story I've ever heard about Calvin Coolidge. There's also one about Koko, the famous language-enabled gorilla. Dr. Penny Patterson, Koko's teacher, was looking for a suitable mate for the well-educated ape and auditioned partners by showing Koko videos of male gorillas. She signaled her responses with a thumbs-up or -down, until a 400-pound male named Ndume caught her fancy. "Koko pressed her lips directly to his image onscreen — leaving scientists with no question as to whom she preferred."
Colette Bancroft can be reached at firstname.lastname@example.org or (727) 893-8435.