Why do we like to kiss with our tongue?

Have you ever been repulsed by the idea of ​​tongue kisses?

To better explain the intention of that question, we are going to propose an analogy: can you imagine approaching a stranger in the middle of a party and, after exchanging a couple of smiles and another couple of phrases, saying «Can you let me use your toothbrush, now? “

It would never occur to you to do such a thing, because you know it would sound awful. And because you know that using someone else’s toothbrush is objectively dirty, unhygienic, and potentially unhealthy. The idea of ​​putting something in the mouth that has been poking around in the depths of someone else’s mouth causes gestures of disgust for sure in 90% of the population. But isn’t a french kiss exactly that?

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Saliva, cavities, food scraps, bacteria, phlegm, wounds … If you think about it cold, putting your tongue in the other’s mouth is a disgusting practice. So, why do we do it?

Is it simply a learned social behavior?

Does the search for sensual pleasure only motivate us?

The answer to both questions is no.

There is another, deeper reason. A reason that we have engraved in our DNA. An evolutionary reason.

KISSES AS AN IMMUNE SMELL

«Kissing – like touching and smelling – is an emotion-driven act that allows us to identify the most compatible and ‘evolutionary advantageous’ partner,» adds Fulvio D’Acquisto, professor of immunology at Roehampton University.

When he talks about more compatible couples, D’Acquisto does not mean that they can agree with us in tastes, or in character, much less that they kiss in a way that we like. The doctor talks about biochemical processes and genetic compatibility.

Other animals turn to smell to get clues about that information. But humans are bad with their nose. Kissing, licking our lips, twisting our tongues in a shake of saliva, is, in a sense, a substitute for a stunted smell.

“Humans don’t have strong olfactory skills and kissing allows you to smell and taste a person and see if you have different immune responses as we tend to feel more attracted to someone with a different immune response,” explains Sarah Johns, an expert in evolutionary psychology at the University of Kent.

Johns talks about what in scientific terms is known as the major histocompatibility complex (MHC), a family of genes that participate in the activation of critical processes for the generation of the immune response. «MHC is detectable through body odor, so kissing and tasting someone gives us a certain opportunity to assess how similar or different we are from that person in biochemical terms.»

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In summary, from a dual evolutionary and immunological perspective, when kissing we would be looking for potential partners who can provide us with a set of genes that give rise to immune responses different from ours. And even if we do not think about it, we do it that way because that means that, when procreating, the resulting little person would have a more complete immune system.

Without actually thinking about babies, the kiss works in a similar way on an individual level. When we kiss, we are exchanging pathogens. «These microorganisms constitute our microbiota, our mix of ‘friendly bacteria’ that define us as unique individuals from an immunological point of view,» explains D’Aquisto. «Enriching our microbiota through kissing can serve to test the ability of our partner to face the threat of harmful pathogens and thus favor the spread of the species.»

So now you know. That evolutionary aspiration would be the one that prompts us to kiss with our tongue, despite how disgusting that may be on paper. And yes, the sexual temperature that accompanies a good kiss also plays a role here: there are studies that show that sexual arousal reduces feelings of disgust and revulsion.

The next time you want to kiss someone’s mouth, think about this.