Imagine if we had to explain the concept of kissing to a group of aliens (assuming they were friendly and didn’t come to destroy us). It would be pretty confusing for them.

Imagine explaining it out loud: “Yes, we press our mouths together. Sometimes with our eyes closed. Sometimes for ten whole minutes. Occasionally in the rain. It means anything from “hello” to “I want to spend the rest of my life with you.”

It sounds... kind of ridiculous?

And yet, humans have been kissing for thousands of years. Songs are written about it. Wars have probably started because of it. Bollywood can build an entire love story around two people almost kissing while flowers collide on screen.

So naturally, scientists have asked the same question the rest of us have: why do we kiss in the first place? Unfortunately, we don’t know for sure. Unlike walking upright or using tools, kissing doesn't leave behind fossils. Lips don’t fossilise into little clues saying, “Two early humans made out here.”

Instead, researchers have pieced together several theories using anthropology, neuroscience, evolutionary biology, and a surprising amount of observation. None of them fully explain kissing on their own. Together, though, they paint a fascinating picture.

First Things First: Not Every Culture Kisses

For a long time, people assumed romantic kissing was universal. Turns out, it isn’t.

In 2015, anthropologist William R. Jankowiak and his colleagues examined 168 cultures and found that fewer than half practiced romantic or sexual kissing. Many societies simply didn’t view mouth-to-mouth kissing as part of courtship at all.

That means kissing isn't a biological reflex like laughing or crying. It’s a behaviour that seems to emerge more often in certain social and cultural environments than others.

Which raises an even bigger question: If humans don’t have to kiss...why do so many of us enjoy it so much?

Theory 1: Kissing Helps Us Choose Good Partners

One of the most influential researchers studying kissing is psychologist Dr. Gordon Gallup Jr. His idea is surprisingly practical.

According to Gallup, kissing may have evolved as a way of gathering information about a potential partner before investing further in the relationship.

Think about what happens when you kiss someone: You’re suddenly very close. You notice how they smell. How they taste. Whether your bodies naturally sync up. Whether the chemistry you’ve been imagining actually exists outside the DMs.

Your brain is collecting an astonishing amount of information without you consciously realising it. Ever heard someone say, “They were objectively attractive... but there just wasn’t any chemistry.”

Gallup would argue that chemistry isn’t entirely metaphorical. Your body may genuinely be making biological assessments. Which also explains why a bad first kiss can feel like someone abruptly cancelling the season finale.

Theory 2: Your Nose Is Doing Most of the Work

Humans like to think we’re very visual creatures. Evolution says, “...yes, but also smell.”

Biologists believe scent plays a much larger role in attraction than most of us realise. Every person carries subtle chemical signals linked to their immune system, particularly genes called the Major Histocompatibility Complex (MHC).

Research suggests people are often more attracted to partners whose MHC genes differ from their own. From an evolutionary perspective, that could produce offspring with stronger immune diversity.

Kissing brings your faces close enough for your brain to quietly sample those cues. You liking their smell is your nervous system going, “Interesting. Continue, please.”

Theory 3: Maybe It Started With Food

This theory sounds bizarre until you remember birds exist.

Anthropologists have suggested that kissing may have evolved from mouth-to-mouth feeding, where parents passed softened food directly to infants before chewing became possible.

Many bird species still do this today. Some primates have also been observed transferring food mouth-to-mouth. Over thousands of years, behaviours associated with feeding, comfort, and caregiving may have gradually taken on new social meanings between adults.

Is this definitely how kissing began? No.

Is evolution often weird enough that this remains a serious hypothesis? Absolutely.

Theory 4: Kissing Is Basically Social Glue

Robin Dunbar, an evolutionary psychologist famous for studying social bonding, argues that humans needed efficient ways to maintain close relationships as our social groups grew larger.

Among other primates, grooming serves this purpose. Monkeys spend hours picking through each other’s fur, strengthening alliances one tiny insect at a time.

Humans, thankfully, found alternatives: conversations, shared meals, hugging, holding hands, and yes… kissing. Physical affection releases oxytocin, often nicknamed the “bonding hormone,” while also activating dopamine pathways associated with reward and pleasure.

In other words, kissing literally gives your brain reasons to think, “I’d like to spend more time with this person.”

Theory 5: Maybe It’s Learned 

Not everyone agrees kissing is an evolutionary adaptation. Some anthropologists believe it’s primarily a cultural invention that happened to spread because humans found it pleasurable.

Think about handshakes. They’re not genetically programmed, they’re learned.

Kissing might work similarly in many societies. Once a culture adopts it as a symbol of romance, films, books, music, and social norms reinforce it until it begins to feel completely natural. Which might explain why Bollywood spent decades making flowers kiss instead of people. The audience already understood what the flowers meant.

So... Why Do Some People Hate Kissing?

Here’s another reminder that humans refuse to fit neatly into categories.

Some people absolutely love kissing. Others are not a fan, and would happily skip straight to cuddling, sex, or ordering dessert. And that’s perfectly normal.

Research led by psychologist Rafael Wlodarski suggests people don’t all value kissing for the same reasons. Some see it as a way to assess compatibility early in a relationship. Others use it to maintain emotional closeness over time. Some simply don’t enjoy it very much.

Your relationship with kissing is shaped by biology, culture, personal experience, sensory preferences, and sometimes just... whether the other person knows what they’re doing.

Final Thoughts

Science still can’t tell us exactly why humans kiss. Maybe it’s mate selection, maybe it’s scent, maybe it’s bonding, maybe it’s ancient parenting behaviour that became flirting. Or maybe, like so many human behaviours, it’s a little bit of everything.

What we do know is this: kissing has survived across centuries, continents, religions, dating apps, arranged marriages, terrible first dates, and every rom-com ever made. It has meant romance, comfort, celebration, reconciliation, and sometimes simply, “I’ve missed you.”

Not bad for something that's essentially two people putting their faces extremely close together and hoping for the best.

About the Author

Madhu (she/her) has been an avid reader of all things spicy since her childhood. She writes sassy blog posts and listicles now so that others may benefit from her wholly inappropriate, wholly informative tastes, too.