A kiss may be on your list as one of the best things in life. But have you ever thought about how kissing evolved in the first place into such a meaningful activity for humans? After all, even though kissing may give you all the feels and stimulate some feel good hormones, it’s not clear what practical purpose kissing may serve. For example, kissing doesn’t help you eat, unless the other person happens to have a turkey sandwich in his or her mouth at the time. Well, here’s some food for thought: a recent publication in the journal Evolutionary Anthropology offered a possible origin based on some scientific observations. And it involves some very dirty stuff—but not in the way you might think.
Different Types Of Kisses
Of course, not all kisses are the same. You probably wouldn’t deliver a mouth-to-mouth-with-tongue-involved kiss to someone you are meeting for the first time in a professional meeting. Such a situation may instead call for an osculum, which would be a polite kiss on the cheek that has no romantic undertones. And say you wanted to kiss someone to show closeness with no intention of opening the gates of Mordor, so to speak, just yet. Then, a basium—a kiss on the lips without sexual meaning—may be in order. If you did want to proceed to the horizontal tango, a savium—a kiss on the lips that’s sexual in nature—might in turn be the right dance move. But all of these kisses do have one thing in common: they all involve the puckering of lips and mouth-to-something contact.
Previous Hypotheses
Therefore, if you want to figure out how kissing may have evolved, it would make sense to look at different ways ways other animals use their mouths. In the publication, Adriano Lameira, PhD, an 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 such hypothesis was that kissing started a form of sniffing, sort of what you might do when examining a piece of cheese. But as you may have learned the hard way, there is a big difference between sniffing your partner versus kissing him or her.
Another such hypothesis was that kissing evolved from nursing and breast suckling. But that would mean going from a very distinct breast sucking motion to kissing, which would be quite a jump. Yeah, 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 suck at kissing.
A third such hypothesis was that kissing arose from premastication. That’s premastication, which consists of a parent or other caregiver chewing food in his or her mouth first to break it down and then passing the food to a child through mouth-to-mouth contact. It’s something that some birds, some non-human primates and Alicia Silverstone apparently do. But going from “Let me dump pre-chewed food into your mouth” to kissing may have been quite a jump as well.
What Great Apes Do
Of all the other animals out there, humans may be most closely related to great apes. Therefore, the behaviors of great apes could provide more insight into what humans do. Lameira is also the principal investigator of Ape Tank, which isn’t an ape version of the TV show Shark Tank but instead is a research group that studies great apes to better understand the the origins of human behavior and mind including communication, cognition and culture. So, Lameira thought that it would be helpful to review how different great apes bond and connect with each other to see if there’s anything that resembles kissing.
Now, not all great ape bonding behaviors may translate directly to what humans do. For example, capuchin monkeys bond with each other by sticking their fingers into each others’ eyes and nostrils. But, such behaviors are not going to earn brownie points with your human date or significant other. While complementing your love interests’ eyes and ask for their digits may be reasonable, putting your digit in their eyes is a different story. And who knows what will happen if your were to stick your finger up your significant other’s nose.
The Grooming Hypothesis
However, there is something dirty—or at least dirt-related—that great apes do to connect and bond with each other that’s more analogous to what humans do: grooming. This is when animals pick dirt, dead skin, parasites and other things out of the hair or fur of each other. If watch other animals do this, you’ll notice the care and affection that they put into it.
Now, saying something like “I am now going to search through your hair for some parasites” might be a turn-off to your significant other or date. Plucking dirt and parasites off of one another probably became less common for humans with the evolutionary loss of fur, the advent of showers, improved hygiene and the option to swipe left on Tinder when someone appears to be covered in dirt and parasites.
Nonetheless, various aspects of grooming behaviors seem to have persisted in humans. Couples can show that they care for one another by brushing each other’s hair, adjusting each other’s clothes, wiping each other’s faces, massaging each other’s bodies and other such activities. And Lameira believes that kissing may have evolved from the last stage of the grooming exhibited by many great apes: “latching on their lips to the other’s skin.” As the publication described, this consists of “the groomer touching the groomed with protruding lips and sucking action to latch on and remove a parasite or debris.”
This type of sucking action doesn’t suck quite as much as the motion used in breast suckling. Lameira wrote in the publication, that this final step in grooming “exhibits parallels in form, context, and function to human kissing to an extent that no other proposed behavior thus far has” and called it the “groomer’s final kiss hypothesis.”
Kissing Feels Good
Grooming may have gotten people to come to kissing but the good sensations generated by kissing is what keeps people staying there. Your lips and mouth have many very highly sensitive nerves running through them. That’s part of what makes mouth-to-mouth kissing feel so good, more so than contact between less innervated areas such butting heads or slapping ankles. Kissing is also associated with broader feel-good changes, including the release of:
- Serotonin: a neurotransmitter that affects happiness and regulates sexual behavior,
- Dopamine: a neurotransmitter associated with pleasure and reward
- Oxytocin: the so-called “love hormone” that enhances bonding and attachment.
All of that suggests that at least at some point there were evolutionary advantages to maintaining kissing behaviors.
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 tell for sure when and how exactly humans started kissing. So, the “groomer’s final kiss hypothesis” may not necessarily be the absolute final answer when it comes to the question, “How did kissing evolve in humans?” But does make sense to further observe great apes to get more evidence about how one of the great things in life arose.
