why do people like to kiss? Do other animals kiss?

Why do people like to kiss? Do other animals kiss? Why are kisses so gross? — Gracie, age 5.

Gracie, you ask a question that puzzled me too when I was about your age. Why would two people want to smoosh their mouths together?

And I don’t just mean: “why does Aunty insist on kissing me to say hello when we visit for Easter lunch?”

I mean teenagers and adult couples — in real life and on TV — all of whom seemed to love long, sloppy kisses. That must be especially confusing for you now, after everything we’ve been told about social distancing because of the coronavirus.

For people who enjoy kissing, however, the answer is simple: “it feels good”. And they’re not lying, it often does. But that’s not a very good answer to your question.

If you have a younger sister or brother, you will know what’s coming next: “but why does kissing feel good?”

Well, that’s a question even scientists have found tricky to answer. And I’m not sure the answers so far are very satisfying. But let’s see what you think.

Kissing brings people together

Kissing seems to be important when people are first attracted to one another, like when they’ve got a crush on each other. To get close enough to kiss someone, you have to trust that person a lot and let them into your personal space.

If you don’t like somebody enough to kiss them, that’s a sign to them that they should look somewhere else for a girlfriend or boyfriend.

And, kissing aside, sometimes it might feel wrong just to touch another person’s skin. Or you may not like how they smell.

These are examples of our bodies telling us what we can’t put into words. In this case, they’re telling us we aren’t a good match with that person.

As adults, kissing can help us decide if another person is the right person to start a family with (if this is something both people want). Chances are if two people don’t enjoy kissing, they aren’t attracted enough to stay together long enough to raise a child.

Read more: Curious Kids: how did the first person evolve?

If both people do like and trust each other enough to kiss, they’ll probably kiss quite often. The good shared feelings they get from this makes them like and trust each other even more, and eventually that might lead to starting a family.

Some research has shown that couples benefit from kissing even after they’ve been together for many years. In one study, couples who agreed to kiss each other more often were happier with each another and with their lives than couples who carried on as normal.

Back to those germs

When I was in primary school, my friends referred to kissing as “swapping germs”. It’s true that kissing a person exposes you to their germs. But that might actually help explain why we do it.

If you’re going to spend time in a relationship, you’re going to be exposed to another person’s germs. So if we aren’t prepared to kiss somebody because they might make us sick, we surely won’t want to live with them.

And if we do decide to kiss someone we like, the nice feelings we get help us worry less about catching their germs.

Not everybody kisses

Other animals in nature appear to kiss sometimes. Common and bonobo chimpanzees give each other big wet kisses quite often, which look like human romantic kissing.

But, surprisingly, kissing isn’t something all humans do. Nearly everywhere in the world, there is some kind of loving kiss between parents and children. This is not “romantic”. And not all people kiss romantically.

One big scientific study looked at 168 different groups of people, from small communities that gather and hunt their own food, to bigger and busier cities. These experts found romantic kissing was common in less than half (46%) of the groups.

People from non-kissing cultures who live in sub-Saharan Africa, New Guinea, or the Amazon rainforest find it either funny or disgusting when shown photos of kissing. Then again, they have other ways of touching one another that probably help them build trust and keeps them feeling close.

Romantic kissing is more common in big, complex places where there are many different people living many different lives.

Being able to find and keep a partner is less simple in these settings, which may be why kissing becomes an important part of trying to find a romantic partner.

There are plenty of mysteries wrapped up in a romantic kiss, both for scientists to unravel and for the people doing the kissing to find out. So, if it sounds like I don’t know the exact answer — that’s why.