LEWISTON – In a barren valley near the top of the world – right where they hoped to find it – biologist Neil Shubin and his colleagues found a missing piece of evolution’s puzzle.

It was a fish but not a fish, with both gills and lungs, a crocodile-like flat head and the skeletal hints of arms, fingers and toes.

To Shubin, the discovery gave evolution theorist Charles Darwin one more piece of credibility and a spiritual boost.

“We can trace the origins of our own humanity,” said Shubin, a University of Chicago scientist and professor who lectured Wednesday at the Lewiston Public Library. “It’s a story written in fossils, embryos and DNA.”

The similarities among all life on Earth was what first drew Shubin to search for a link in the 1980s.

If Darwin was correct in his theory that all life evolved from common ancestors, Shubin figured there must be some evidence of a creature that resembled a fish and walked on land. Based on the discoveries of previous fossils, he guessed that it would have lived sometime between 360 million and 380 million years ago.

He searched for the right place to dig. He wanted a marshy, delta area where amphibians might thrive. And he wanted surface rock that was just the right age and likely to contain fossils.

He spent years with colleagues searching the Catskills, one former marshland that filled the requirements. Then, in 1998, he glimpsed a map that showed a group of islands in northern Canada. A year later, he led the first of several expeditions into the region.

In 2006, beneath a carpet of fish bones, they found the first fish-not-fish, later named the tiktaalik.

A colleague had carefully scrapped away some of the stone from the fossilized bone.

“Here, I had a flat-headed fish looking out at me,” he said. “At that moment, I knew we’d found what we were looking for.”

The 2006 discovery made Shubin famous. He made the front page of the New York Times and was named ABC News’ “Person of the Week.” Shubin authored a book about his journey, titled, “Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body.”

The tiktaalik had a fish-like body but the beginnings of a neck and shoulders. Each fin had bones that resembled an arm and a wrist, with a humerus, ulna, radius and carpals, Shubin said.

He found great peace in the discovery, he said.

“You see the connections between yourself and all life,” he said.