An unusual blinking fish is helping scientists understand how human ancestors adapted to life on land.

It is thought that life on Earth first began in the ocean around 3.5 million years ago.

Descendants began to live in shallower waters and eventually moved to land, developing limbs and lungs.

Researchers have discovered that mudskippers blink to clean and protect the eyes like humans and other animals do.

"We think [blinking] was likely part of the suite of traits that evolved when tetrapods were adapting to live on land," Thomas Stewart, assistant professor of biology at Penn State University, said.