Why do we want to bite cute things?

We all know cute things when we see them — but why don't we react to grownups the way we react to babies? Or flowers, instead of kittens?

The answer can be found in evolutionary biology, says Dr. Sandra Pimentel, a psychologist at the Montefiore Medical Center in New York. "If we think about evolution, our goal as a species is to survive and pass on our genes."

The way we pass on our genes is by having babies, but babies need us to take care of them and keep them alive.

"By finding things cute we're more likely to want to take care of them and protect them," Pimentel said. "They're more likely to get the attention of the adults around them, remind them, 'Hey, take care of me. We're helpless here.'"

Our brains make us enjoy looking at cute things by rewarding us with dopamine, a chemical that makes us feel intensely happy.

The physical traits of babies are also features that we find cute when they show up on other things: baby animals, cartoon characters, even cars.

These features were called kindchenschema by ethologist Konrad Lorenz in 1949. What do we find cute?

• Big head relative to body size
• Larger forehead
• Large eyes
• Round cheeks
• Small chin
• Small nose

Other studies have shown that our brains want to give cute things extra attention over non-cute things. So it makes sense that these characteristically cute features show up in marketing a lot, too.

"There's a ton of psychology in marketing so that's usually not by accident," Pimentel said. "What's going to make things more likely for people to buy them with money or their time."

If we like cute things so much, why do we want to bite them?

Our brains love looking at cute things, but why do we react them the way that we do?

Cuteness often elicits a reaction that appears aggressive on its surface. It is expressed as clenched fists, bared teeth and the utterance of something like, "You're so cute I could eat you up!"

Dr. Oriana Aragon, a psychologist at Clemson University, has studied this cute aggression: the desire to bite, squeeze, or eat something because it's so cute.

It's common — in fact, there are phrases to describe this feeling in many different languages. One is the Tagalog word gigil,which means the gritting of teeth and the urge to pinch or squeeze something that is unbearably cute. It's one of those excellent words that says in one what takes many to say in English.

So even though you might say you might want to eat something cute, you're not actually feeling aggression — you're just expressing it.

This is called dimorphous expression — when you express something different than what you're feeling. The same thing happens when you cry when you're happy or laugh when you're nervous.

Dimorphous expression is also behind another common reaction to cuteness. This one expresses as sadness: It involves the sound "awww" and an exaggerated frown.

So when you see something cute, you're filled with positive feelings, but they can come out looking like aggression or sadness.

Why can't we just smile and look happy when we're happy?

Why does this dimorphous expression happen?

"There are some indications that when people express this way they come down from this strong emotion a little better," Aragon said. "It seems it might help to regulate emotion."

Aragon is continuing to study these reactions. She wants to find out if these dimorphous expressions are the cause of the quick recovery, or if people who do that just happen to recover faster anyway.

She's also curious to know what babies think of these reactions to their cuteness.

"I wonder, as a psychologist, I wonder: What is that baby thinking?" Aragon said. "They encounter these little snarling faces of people looking at them who think they're adorable, and babies are soaking up information. I wonder if it gives baby an idea that faces can come about in a playful way or if it educates baby about emotion expression. These are things that still have to be tested."

So next time you want to nibble on a baby's cheeks, or cry at a wedding, or laugh when you're nervous, know that it's normal — and maybe even helpful — to deal with strong emotions in this way.

Brains On! is a science podcast for kids and curious adults produced by MPR News and Southern California Public Radio.