Can Evolution Run in Reverse? A Study Says It’s a One-Way Street

Carl Zimmer in the NYT:

Evolutionary biologists have long wondered if history can run backward. Is it possible for the proteins in our bodies to return to the old shapes and jobs they had millions of years ago?

Examining the evolution of one protein, a team of scientists declares the answer is no, saying new mutations make it practically impossible for evolution to reverse direction. “They burn the bridge that evolution just crossed,” said Joseph W. Thornton, a biology professor at the University of Oregon and co-author of a paper on the team’s findings in the current issue of Nature.

The Belgian biologist Louis Dollo was the first scientist to ponder reverse evolution. “An organism never returns to its former state,” he declared in 1905, a statement later dubbed Dollo’s law.

To see if he was right, biologists have reconstructed evolutionary history. In 2003, for example, a team of scientists studied wings on stick insects. They found that the insects’ common ancestor had wings, but some of its descendants lost them. Later, some of those flightless insects evolved wings again.

Yet this study did not necessarily refute Dollo’s law. The stick insects may indeed have evolved a new set of wings, but it is not clear whether this change appeared as reverse evolution at the molecular level. Did the insects go back to the exact original biochemistry for building wings, or find a new route, essentially evolving new proteins?