In the muddy sediments beneath the deep sea, scientists have found ancient communities of bacteria that have remained virtually unchanged for 2.3 billion years.
Researchers say these microscopic organisms are an example of "extreme evolutionary stasis" and represent the greatest lack of evolution ever seen.
They may also, paradoxically, prove that Darwin's theory of evolution is true.
"If evolution is a product of changes in the physical and biological environment, and there are no changes in the physical and biological environment, then there will be no evolution," said J. William Schopf, a paleobiologist at UCLA.
He calls it the null hypothesis required of Darwin's equation.
In a paper published this week, Schopf and his colleagues describe three distinct communities of the deep sea microbes separated from each other in time by hundreds of millions of years.