Self | Relationships

Why Do Humans Kiss? What Science and History Tells Us

The biological and cultural origin story of our chosen unit of affection.

Sean Kernan
5 min readSep 20


Unsplash Images via Jonathan Borba

Ryan’s mother walked to the front door and abruptly turned to his sister, Julie, “No boys, tonight. You got it?” She was our babysitter that night.

“Of course not!” Julie said with a wry smile. Her mother stared back, hard, to emphasize the point. Julie was 16 and quite beautiful, with big eyes and long curly brown hair. You had to get in line to have a crush on her.

Ryan’s parents left and just 15 minutes later, Julie’s boyfriend seemingly rappelled in from the ceiling. They were instantly making out in the pool. Ryan and I stared out the window in disgust at them. They were like two suckerfish attached at the face.

I vividly remember thinking, “Why do people kiss? It’s so weird.” My confused curiosity was at least partially driven by my lack of male hormones. But even today— it still feels like an unusual practice. What gives? Why do we like lip-on-lip contact so much? There are a few reasons.

The origin story

Evolutionary psychologists argue that what we know today as “kissing” may have come from “kiss-feeding” which was an exchange of pre-chewed food from mother to baby. It’s an ancient practice, often used during the weaning process. The mother helped the baby swallow and digest food through the use of saliva and chewing. The process also looks a heck of a lot like french kissing.

There are other factors at work too. A baby can only see 8–10 inches in front of its face. So from an early age, we are primed to recognize faces with spectacular accuracy relative to other animals.

The whites of our eyes are also evolved to help distinguish the direction of gaze from another person, so much so that special neurons fire when you recognize someone looking at you (they turn off when the person looks away). Faces are highly important to us and are a key component of social cohesion.

In addition, our wiring causes us to mimic behavior as a form of social bonding (such as someone kissing you back). When you combine this with our drive to seek out…



Sean Kernan

Always on the hunt for a good story. That guy from Quora. Writing out of Tampa, Florida.