The “Vacanti Mouse.” The “earmouse.” That freaky thing you saw in a biology textbook or email chain. Whatever you call it, one thing’s for sure: the mouse with the ear on its back is an icon of science, and it has been for more than 20 years.

Maybe it even represents mad science. However, many misunderstand how and why the mouse was created in the first place.

Why Scientists Put an Ear on a Mouse

In the late ’90s, doctors Charles Vacanti, Joseph Vacanti, and Bob Langer wanted to create human body parts in a lab. They had experimented with creating “biodegradable scaffoldings,” or structures that would dissolve inside a body, in various shapes. One day, Joseph Vacanti heard his colleague complain that it was so hard to create new ears for patients who are missing them, as ears have such peculiar and complicated shapes. That’s when he decided to make a scaffolding in the shape of a human ear.

Shaping the Scaffolding

The researchers created an ear-shaped scaffolding and put cells of cartilage from a cow on it. Cartilage is a type of semi-rigid tissue found in your ears, nose, and chest.

Then, the scientists took a strain of mouse that was immunocompromised, meaning that it didn’t have an immune system that would attack the foreign cow cells. They put the mouse under anesthetic, made a surgical incision, and placed the ear shape under its skin.

As predicted, the mouse’s system fed the cow cartilage cells, and as the scaffolding dissolved, the mouse was left with an artificial shape of a human ear. Although, It was only the outside part of the ear with no eardrum, making the function of the ear completely obsolete.

Then, the researchers repeated the process again and again, as they often do with experiments. “There were lots and lots of animals, because it was science,” said Vacanti. That means that the iconic earmouse was just one of many earmice!

When the scientists had important results, they published a study in the journal Plastic and Reconstructive Surgery.

Rumors and Hoaxes

In 1998, the BBC aired a program with an earmouse in the trailer. And, to say the least, the world was stunned. Many were impressed by the feats of science, but some were concerned, leaving rumors and explanations to run amuck.

In 1999, a group took out a full-page ad in the New York Times with a picture of the mouse and the question: “Who Plays God in the 21st Century?” The ad suggested that the mouse was a product of genetic engineering, but that’s incorrect. The ad also says that Biotech companies are “blithely removing components of human beings, and other creatures, and treating us all like auto parts at a swap meet.”

However, the ears on the mice never came from, nor went to, any humans. Instead, the project on the mice was intended to be practice. If the doctors could perfect this technique in mice, and then in large animals, maybe one day they could help humans grow their own missing body parts.

Helping Humans Today

The Vacanti mouse was not simply an exercise in creating Kronenberg-style horrors. It was meant to help scientists understand how to grow body parts in humans, using their own skin and cartilage cells.

In January of 2018, doctors in China and Japan published a study showing that they had achieved just that. Two-and-a-half years prior, they had recruited children with one malformed ear each. The scientists scanned their normal ears, reversed the shape using a computer, and 3D-printed a new biodegradable scaffolding. They added cartilage cells from their patients and put the scaffoldings under the skin. As a result, the children now have two ears that are mostly normal.

Without the strange, pink mouse in the biology textbook, these types of medical advancements may have never happened.

By Kristin Hugo, contributor for Ripleys.com

Kristin Hugo is a science journalist with writing in National Geographic, Newsweek, and PBS Newshour. She’s especially experienced in covering animals, bones, and anything weird or gross. When not writing, Kristin is spray painting, and cleaning bones in her New York City yard. Find her on Twitter at @KristinHugo, Tumblr at @StrangeBiology, and Instagram at @thestrangebiology.