Oregon Public Broadcasting

Biologists have long wondered why some animals didn’t reacquire traits that could help them survive.

In the latest issue of the journal Nature, a University of Oregon researcher says he may have an explanation.

Ethan Lindsey reports.

Why didn’t birds regrow teeth?

Oregon associate professor Joe Thornton says it’s because evolution, at least on a molecular level, is irreversible.

Joe Thornton: “If we could rewind the history of life and let it run again, it is quite likely that we would end up with a very different outcome.”

Thornton, and his colleagues, looked at one protein that helps humans respond to stress.

They found that during one key evolutionary moment, seven mutations altered the protein. Thornton then reverse engineered those mutations, and found the protein to be functionally dead.

He says along with the key changes came other mutations that kept evolution moving forward only.

Some researchers say this might not hold true in a larger population, where “backward” paths would remain.

Thornton says besides the philosophical importance of his work – it will also help in drug development.