How kissing may have evolved in humans. Here’s evidence of great apes

A kiss may be on your list as one of the best things in life. But have you ever thought about how kissing evolved into such a meaningful activity for humans in the first place? After all, although kissing can give you all the feels and stimulate certain feel-good hormones, it is not clear what practical purpose kissing can serve. For example, kissing won’t help you eat, unless the other person happens to have a turkey sandwich in his or her mouth at that moment. Well, here’s some food for thought: a recent publication in the magazine Evolutionary anthropology offered a possible origin based on some scientific observations. And there are some really dirty things involved, but not in the way you might think.

Different types of kisses

Of course, not all kisses are the same. You probably wouldn’t give a mouth-to-mouth, tongue-involved kiss to someone you met for the first time at a professional meeting. Such a situation may instead call for one osculumwhat would be a polite kiss on the cheek without romantic overtones. And suppose you wanted to kiss someone to show closeness, with no intention of even just opening the gates of Mordor, so to speak. Then, one basium– a kiss on the lips without sexual meaning – may be appropriate. If you still want to move on to the horizontal tango, a savium– a kiss on the lips that is sexual in nature – could in turn be the right dance move. But all these kisses have one thing in common: they all involve puckering the lips and mouth-to-something contact.

Previous hypotheses

Therefore, if you want to figure out how kissing evolved, it would make sense to look at different ways that other animals use their mouths. In the publication, Adriano Lameira, PhD, associate professor of psychology at the University of Warwick, mentioned several previously advanced hypotheses behind the evolution of kissing and the evidence against them.

One of those hypotheses was that kissing began as a form of sniffing, kind of like what you might do when examining a piece of cheese. But as you may have learned the hard way, there’s a big difference between sniffing your partner and kissing him or her.

Another such hypothesis was that kissing resulted from breastfeeding and breast sucking. But that would mean going from a very obvious breast sucking motion to kissing, which would be quite a leap. Yes, even though “sucking face” is a slang term for kissing, using such a sucking motion while kissing may prompt the other person to tell you that you are bad at kissing.

A third such hypothesis was that kissing arose from premastication. That’s forchew, in which a parent or other caregiver first chews food in his or her mouth to break it down and then passes the food to a child through mouth-to-mouth contact. It’s something that some birds, some non-human primates and… Alicia Silverstone apparently yes. But going from “Let me dump pre-chewed food in your mouth” to kissing might have been quite a leap too.

What great apes do

Of all the other animals in existence, humans are perhaps most closely related to great apes. Therefore, the behavior of great apes could provide more insight into what humans do. Lameira too the lead researcher of Ape Tankwhich is not a monkey version of the TV show Shark tank but instead, there is a research group that studies great apes to better understand the origins of human behavior and mind, including communication, cognition and culture. So Lameira thought it would be useful to look at how different great apes connect and interact with each other, to see if there is anything that resembles kissing.

Now it may be that not all great ape behavior translates directly into what humans do. Capuchin monkeys, for example, bond with each other by sticking their fingers in each other’s eyes and nostrils. But such behavior won’t win brownie points with your human date or partner. While it may be reasonable to complement your love interests’ eyes and ask for their digits, it’s a different story to put your digit in their eyes. And who knows what will happen if you stick your finger up your partner’s nose.

The Nursing Hypothesis

However, there is something dirty – or at least dirty-related – that great apes do to connect and bond with each other that is more analogous to what humans do: grooming. This is when animals pick dirt, dead skin cells, parasites and other things from each other’s hair or fur. When you see other animals doing this, you will notice the care and affection they put into it.

Now, if you say something like, “I’m going to look through your hair for some parasites,” it could be a turn-off for your partner or date. Picking dirt and parasites off of each other has probably become less common for humans due to the evolutionary loss of fur, the advent of showers, improved hygiene, and the ability to swipe left on Tinder if someone appears to be covered in dirt and parasites.

Nevertheless, several aspects of grooming behavior appear to have persisted in humans. Couples can show that they care for each other by brushing each other’s hair, adjusting each other’s clothes, wiping each other’s faces, massaging each other’s bodies, and other similar activities. And Lameira believes that kissing may have evolved from the final stage of grooming that many great apes exhibit: “sticking their lips to the other’s skin.” As the publication describes, this consists of “the groomer touching the groomed with protruding lips and sucking to grab and remove a parasite or debris.”

This type of sucking motion does not suck as much as the motion used when sucking at the breast. Lameira wrote in the publication that this final step in grooming “parallels in form, context and function to human kissing to an extent that no other proposed behavior has yet done” and called it the “groomer’s final kiss hypothesis “.

Kissing feels good

Grooming may have prompted people to start kissing, but the good sensations generated by kissing are what keep people there. There are many very sensitive nerves running through your lips and mouth. That’s part of what makes mouth-to-mouth kissing so good, even more so than contact between less innervated areas, like bumping heads or slapping ankles. Kissing is also associated with broader feel-good changes, including the release of:

• Serotonin: a neurotransmitter that influences happiness and regulates sexual behavior,
• Dopamine: a neurotransmitter associated with pleasure and reward
• Oxytocin: the so-called ‘love hormone’ that improves bonding and attachment.

All this suggests that at least at some point there were evolutionary benefits to maintaining kissing behavior.

Of course, without a time machine in the form of a DeLorean or access to the Quantum Realm like the Avengers had, it’s difficult to say for sure when and how exactly people started kissing. So the groomer’s “last kiss hypothesis” isn’t necessarily the absolute definitive answer when it comes to the question, “How did kissing evolve in humans?” But it does make sense to continue observing great apes to get more evidence about how one of life’s great things came to be.