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Pucker up: Exploring ‘The Science of Kissing’

Is the impetus to kiss based simply on the primal premise that “red equals reward”? Sheril Kirshenbaum takes a brief, tantalizing glimpse into “The Science of Kissing” and the research behind it. Read an excerpt.
/ Source: TODAY books

Sheril Kirshenbaum delves into the origins of one of the most intimate forms of human expression. Here's an excerpt.

Chapter 1: The hunt for kissing's origins: First contact

When it comes to humanity’s first kiss, or its predecessor in another species, we have no way of knowing exactly how and why, once upon a time, it happened.

After all, there are kisses of joy, of passion and lust, of love and endearment, of commitment and comfort, of social grace and necessity, of sorrow and supplication. It would be silly to assume all these different types of kisses developed from a single behavior or cause; in all likelihood, we kiss as we do today for multiple reasons, not just one. In fact, scientists suspect that kissing arose and disappeared around the globe at different times and different places throughout history.

So while there are certainly some convincing theories out there about how kissing may have emerged, nobody claims that they represent absolute truth. At best, they possess a degree of plausibility that makes them persuasive. In this chapter, we’ll survey four such theories, each of which has a basis in the scientific literature.

Scientists have proposed two separate relationships between kissing and our feeding experiences in infancy and early childhood. They have also suggested that kissing may have emerged from the practice of smelling another individual of the species as a means of recognition. I will examine each of these theories, but will begin with perhaps the most intriguing one of all: the idea that the behavior arose due to a complex connection between color vision, sexual desire, and the evolution of human lips.

A woman’s lips make an indelible impression. They draw attention to her face, advertising her assets in deeply hued and rosy colors. The effect is further enhanced because human lips are “everted,” meaning that they purse outward.

This trait sets us apart from other members of the animal kingdom. Unlike other primates, the soft, fleshy surface of our lips remains exposed, making their shape and composition intensely alluring.

But what makes them so attractive that we want to kiss the lips of another person?

A popular theory takes us back millions of years, when our ancestors had to locate food among leaves and brush. Calories were hard to come by, and wandering far into the jungle could be dangerous. In this context, some of our ancestors evolved a superior ability to detect reddish colors, giving them the advantage of locating the ripest fruits, which in turn helped them survive long enough to pass on their color-detecting genes to their offspring. Over many generations, the signal “red equals reward” became hardwired into our ancestors’ brains. Indeed, the color continues to grab our attention today — something marketing professionals know and exploit regularly.

Contemporary psychologists report that looking at red quickens the heart rate and pulse, making us feel excited or even “out of breath.” In fact, red seems so important to humans that time and again, across early cultures, it is one of the first colors to be named. In their 1969 book "Basic Color Terms: Their Universality and Evolution," anthropologist Brent Berlin and linguist Paul Kay studied twenty languages and determined that after cultures develop words for black and white (probably because these help to determine day from night), red is frequently the third.

But how does this relate to kissing? Neuroscientist Vilayanur S. Ramachandran of the University of California, San Diego, suggests that once our ancestors were primed to seek red for a food reward, they were probably going to check out the source of this color wherever it occurred — including on parts of the female anatomy. Eventually, red likely served as a flashy signal to help facilitate another essential and enjoyable behavior besides eating: sex.

Comparative evolutionary research has demonstrated that in primates, skin and hair coloring evolved after color vision. In other words, once our ancestors developed the ability to detect this color, it became emphasized on their bodies and particularly in the labial region, serving to indicate a female’s peak period of fertility, called estrus. Those with the most conspicuous sexual swellings were probably also most successful at attracting males and passed their flamboyantly endowed posteriors on to their daughters. Today, there’s no mistaking the females of many species when they are ready to mate. As Duke University primate scientist Vanessa Woods puts it, “Female bonobos look like they are carrying their own bright red bean bag attached to their bottoms to sit down on when they get tired.”

But how did an attraction to the color red move from our nether regions to our facial lips? The most likely scenario is that when our ancestors stood upright, their bodies underwent many associated changes in response, including a shift in the location of prominent sexual signals.

Over time, the delectable rosy color, already so attractive to males, shifted from our bottoms to our faces through a process called evolutionary co-option. And the male gaze followed.

That’s why human females do not have to advertise our reproductive cycle on our rear ends. We exhibit what’s called “hidden estrus” instead. But following this theory, our lips are quite literally a “genital echo,” as the British zoologist Desmond Morris put it, resembling the female labia in their texture, thickness, and color. Indeed, when men and women become sexually excited, both our lips and our genitals swell and redden as they are engorged with blood, becoming increasingly sensitive to touch.

To test the “genital echo” hypothesis, Morris showed male volunteers photographs of women wearing various lipstick colors and asked them to rate the attractiveness of each. The men consistently chose those featuring the brightest (most aroused-looking) red lips as most appealing.

To quote Morris, “These lipstick manufacturers did not create an enhanced mouth; they created a pair of super labia.”

And if a plump, rosy smile gets noticed, it probably means men themselves are rewarded for paying attention — in an evolutionary sense. A woman’s naturally large, reddish lips may provide clues about her fertility. They swell when she reaches puberty, and thin with age. Multiple studies have linked full lips to higher levels of the hormone estrogen in adult women, meaning that they serve as a reliable indicator of her reproductive capacity.

No wonder that across cultures, men report that fuller lips on women are an asset, and in turn women have recognized for millennia that there’s power in highlighting them. The first record of lipstick dates back five thousand years to the Sumerian region, and ancient Egyptians, Greeks, and Romans used dyes and strong wines to tint their lips.

Today’s men continue to respond to the stimulus of a sexy mouth, and many women are eager — even desperate — to achieve Angelina Jolie–like proportions. Not only do 75 to 85 percent of American women wear lipstick, but we are taking the obsession to new extremes. We purchase plumpers to achieve the “beestung effect,” and purposely irritate our outer lip membranes with everything from cinnamon to alpha hydroxy acids and retinol. We coat our mouths with formulas from sheep glands and regularly inject fillers and fat. Some women even insert Gore-Tex strips through painful lip implant procedures, which are increasing in popularity (even though a partner can sometimes feel them during a kiss). In the end, women are paying billions of dollars for a result that may be driven by the same impulses that first attracted our primate ancestors to ripe fruit.

Granted, the science suggests that all those fancy creams and glosses actually work ... up to a point, anyway. According to psychologist Michael Cunningham of the University of Louisville, men really do prefer larger lips. However, they also report that fake-looking lips are a turnoff, suggesting that the size of a woman’s mouth in relation to her other facial features is most important. Therefore, when those natural proportions are upset through cosmetic surgery, the result may not be as attractive as the original package. So it’s true: Our lips probably did evolve to look the way they do because they elicit a magnetic sexual attraction.

But in the quest to understand the origins of kissing, there’s a lot more ground (and face) to cover.

From “The Science of Kissing: What Our Lips Are Telling Us” by Sheril Kirshenbaum. Copyright © 2011 Reprinted by permission of Grand Central Publishing.