For decades, many evolutionary biologists have viewed much of molecular evolution as surprisingly quiet. The idea was that many of the genetic changes that spread through populations are neither helpful nor harmful. They simply drift through nature without attracting much attention from natural selection.

A University of Michigan study challenges that picture. Led by evolutionary biologist Jianzhi Zhang, the research suggests that helpful mutations may be far more common than long standing theory predicts. But there is a catch. Many of those useful mutations may not last long enough to become permanent.

A Major Evolutionary Theory Faces a New Test

During evolution, mutations arise by chance. Some disappear. Others spread until every member of a population carries them, a process known as fixation.

For more than half a century, one of the most influential ideas in molecular evolution has been the Neutral Theory of Molecular Evolution.…