While kissing with tongues is associated with sexual passion, the act is actually super gross. After all, you're literally swapping saliva with another person. Ick!
But despite its yuck factor, there's a perfectly logical explanation for why we love to do it, and it's all thanks to evolution.
According to Dr. Sarah Johns, an evolutionary psychology expert at the University of Kent, kissing with tongues is our attempt to "sniff out" a genetically compatible partner.
Kissing with tongues is our attempt to "sniff out" a genetically compatible partner.
"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," Dr. Johns explained to The Telegraph.
This is because having a different immune response than your partner means there's a higher chance you'll have a child with a strong immune system and thus, a better ability to fight off infectious diseases.
Past studies support this and have actually shown that we're attracted to people with strong immune systems and not just their physical appearance.
"Initial attraction may include facial, body and social cues. Then assessments become more and more intimate as we go deeper into the courtship stages, and this is where kissing comes in," explained behavioural scientist Rafael Wlodarski, who conducted an Oxford University study on kissing in 2013.
By assessing compatible immune responses through kissing, we can also "reduce the risk of miscarriages — ultimately supporting the survival of the species," Fulvio D'Acquisto, an immunology professor at Roehampton University, added in an interview with The Telegraph.
Looks like kissing with tongues is about more than just arousal. However, arousal does play critical role when it comes to assessing a potential partner.
"Research shows that sexual arousal lessens feelings of disgust," Dr. Johns noted, which is why we're able to look past the grossness when it comes to swapping saliva. Who knew?
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