“I’m totally amazed,” says Hans Larsson, the principle investigator for the study. “It’s exciting because it’s the first time this has ever been demonstrated in an experiment.”

His team separated a group of polypterus senegalus fish, raising half in the water and half on land. They found the terrestrial fish were not only more efficient walkers, but also their bones had grown larger.

The land fish remained in humid environments to keep their skin wet, but the fish were walking on surfaces like land and gravel using their front fins to drag their bodies.

While these fish are known to survive on land for brief periods of time in the wild, they’ve never been tested to live out their lives completely on land. Their adaptive ability shows their “plasticity,” which is the way different plants and animals respond to different environments.

This goes against evolution, which suggests random genetic mutations. “Rather than evolution starting with genetic change, it’s actually starting with plasticity,” Larsson says.

One of those plastic changes was that the pectoral girdle, which is usually part of a fish’s skull, became loosely attached, making it more mobile. This sort of “dislocated shoulder” was found in the tetrapod fish from 400 million years ago.

Gill chambers also became more absorbed into the body of the land fish.

The fossil records show that the fish seem to have developed bones in their fins that look like elbow or wrist joints, which suggests they’ve been lumbering on land.

“Canada by far has some of the best fossil records about the origins of tetrapod,” Larsson says.

While these fish are still adapting, Larsson says this study reveals that plasticity could help guide evolutionary directions and even speed up evolution.