Why Do We Kiss?

Hey, Vsauce, Michael here. Attachment of two people's lips kissing. The average person will spend about 20,160 minutes of his or her life kissing. And the world record for the longest, continuous kiss is 58 hours, 35 minutes, and 58 seconds. But why do we kiss? I mean, if you think about it, it seems kind of weird... right? I mean, sure, today kissing represents peace, respect, passion, love. But when the first two people in human history kissed, were they just kind of being gross?

Well, let's begin with what we do know: kissing feels good and it's good for you. A passionate kiss burns about 2-3 calories per minute and releases epinephryn and norepinephryn into the blood, making your heart pump faster. Kissing more often is correlated with a reduction of bad cholesterol and perceived stress. But these positive effects didn't become widespread by accident. Why did brains and bodies that love kissing become so common?

Well, a popular story holds it that Pacman's shape was inspired by the shape of a pizza with a slice missing. But Toru Iwatani, the creator of Pacman, admitted that this was only half-true. Pacman's shape was also inspired by rounding out the shape of the Japanese character for "mouth." And it's mouths and Pacman's favorite activity, eating, which together bring us closer to the heart of the kiss.

Evolutionary psychologists have argued that what we know today as "kissing" may have come from "kiss-feeding," the exchange of pre-chewed food from one mouth to another. Mother birds are famous for doing this, and many primates are frequently seen doing it as well. Not that long ago, it was common between human mothers and their children. In fact, before commercially produced or DIY baby-food instructions were readily available, it made a lot of sense. Recently, Alicia Silverstone uploaded a clip of herself mouth feeding her child. It seemed strange to some people, but even though, yeah, it exchanges saliva, which, like any contact with an infant, can transfer pathogens, healthy mothers and healthy children can benefit from the fact that kiss feeding provides nutrients.

Carbohydrates, proteins, iron, and zinc, which are not always available in breast milk. Plus, an adult's saliva can help pre-digest the food, making vitamins like B-12 easier for the baby to absorb. So, mouth-to-mouth attachment has a history of intimacy, trust, and closeness. Your saliva also carries information about who you are, your level of health, and mucus membranes in our mouths are permeable to hormones like testosterone, making a kiss a way to taste-test a potential mate. A good kiss can be biological evidence that your kisser might be a good mate.

So, as a strategy for mate selection, prehistoric people who enjoyed kissing and did it more often may have made better decisions, picked better mates, reproduced more successfully, and, eventually, become the norm. Giving us... us, people who love kissing. Any infant could have seen those benefits coming from a mile away, even though an infant's vision isn't that great. From birth to four months, babies can only focus on things about 8-10 inches away from their face, which, not surprisingly, is about the distance to their mother's face while breastfeeding.

So, faces, especially those looking right at us, tend to be the very first things in our lives we can focus on and see clearly. This might explain why we are so good at detecting faces. Humans are off the charts when it comes to this; in fact, we tend to see faces even when there aren't any. It's called "pareidolia." Because humans are so cooperative, it makes sense for us to be good at recognizing faces.

And, more importantly, detecting when someone is looking directly at us and clearly expressing when we are looking at someone else. A predator who lives by not being seen needs a gaze that's less obvious. In fact, research has shown that our surprisingly white scleras, the area that borders the iris, isn't just an accident, but is a vital piece of human eye morphology that makes it easier for us to ascertain the direction of someone else's gaze at a glance. We also have impressive gaze-direction networks inside our brains, containing individual neurons that fire when someone is staring directly at us, but that stop firing if the gaze shifts just a degree or two.

So, yeah, you can tell when you're being watched. We humans are quite sensitive to it, even those of us with "Scopophobia," the fear of being stared at. But to be sure, in order for this to work, the other person's gaze must be within your line of sight, your field of vision; that is, you can see them. Otherwise, if the stare is coming, say, from behind, there is no evidence that people can tell they are being watched. The "Psychic Staring Effect" falls within the realm of pseudo-science.

No widely-accepted studies have ever found evidence that it exists. Anecdotally, what's more likely is that the very act of rubber-necking to see who's watching causes people to look up and for your gazes to attach. But what about attachment when no one is watching? One explanation for an infant's love, attachment to their mother, doesn't involve vision or staring, but instead, food. The idea is that we love our mothers because as soon as we are born, they are a source of life-sustaining nourishment.

But what if that nourishment came not from a loving mother, but from a scary "Wire Mother"? In the 1950s, Harry Harlow conducted a series of famous, but controversial, experiments on monkeys at the University of Wisconsin, Madison. Harlow's findings had substantial implications on our understanding of attachment. But by today's standards, his work would largely be considered unethical.

In one of his most famous experiments, Harlow separated young monkeys from their mothers as soon as they were born and stuck them in cages with two fake mothers: a soft one wrapped in cloth that did nothing, and a cold, mechanical mother made of wire that, nonetheless, did provide food. But despite being a cupboard mother, the young baby monkeys didn't bond with her. When Harlow and his team scared the baby monkeys with a strange contraption, the monkeys ran and clinged not to their wire source of life-sustaining nourishment, but to the soft, cuddly, and otherwise useless cloth mother.

This suggested that warmth and comfort were more important than food when it came to nurturing attachment. Harlow also built a rejecting mother, which used a blast of pressurized air to push baby monkeys away. But instead of finding another source of comfort, these monkeys clung even tighter at all times than monkeys raised without rejecting mothers. And this is what blows my mind. The instinct for warmth and comfort in newborn creatures is so strong it not only resists attempts to frustrate it but is paradoxically strengthened by it.

Eckhard Hess tested this by using electric shocks to discourage ducklings from following the object they were imprinted on. But it only strengthened the behavior and made them follow more closely than ever before. The fact that a "wire mother," or a rejecting mother, or receiving electric shocks for attaching to your mother would cause more attachment, more love, and more dependence seems like a paradox.

But paradoxes can teach us. As Oscar Wilde put it, "a paradox is the truth standing on its head to attract attention." And what gets our attention here is the effect uncertainty can have. In 1955, A.E. Fisher conducted an experiment on puppies. His team separated puppies into three groups. Members of the first group were treated kindly every time they approached a researcher. Members of the second group were punished for approaching the researchers. And puppies in the third group were randomly treated kindly or punished.

They grew up never knowing what to expect. Their world was not a world of kindness or punishment but rather one of uncertainty. What's really chilling is that the study found that that group, the third group of puppies, wound up being the most attached to the researchers. The third group loved the researchers the strongest and was the most dependent upon them. Guy Murchie called this the "Polarity Principle": "stress, including the mental stress of uncertainty, is an ingredient in attachment or love and perhaps even manifestations of hatred (its polar opposite) somehow enhance love."

Uncertainty, psychologically, can lead to some of the greatest feelings of attachment and dependence. Good things, and bad things, in our lives often seem random and out of our control. So, it's no surprise that we often react with blind love and acceptance in the face of an unfair existence because, what else are we supposed to do? We are that third group of puppies. But investigating uncertainty, conquering it, so as to make the best decisions possible is advantageous.

So, over time, life has favored activities that turn uncertainty into knowledge. Not every person out there is the best mate for you, but if it didn't matter which one you picked, a kiss, a taste-test, wouldn't be necessary, and it wouldn't need to feel so good or bring us so much pleasure. So, go out there and kiss someone today. And as always, thanks for watching.

By the way, tomorrow I am headed to the European Space Agency's Space Port in South America with Euronews to watch a rocket launch in real life. Do you have any questions about space or space travel today? Let me know in the comments below, and I will ask the experts your questions.