Ancient, unchanged microbes may prove Charles Darwin's theory
In the muddy sediments beneath the deep sea, scientists have found ancient communities of microbes that 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 the University of California, Los Angeles, in the US.
He calls it the null hypothesis required of Darwin's equation.
In a paper published this week in the journal PNAS, Schopf and his colleagues described three distinct communities of deep-sea microbes separated from each other in time by hundreds of millions of years.
The first is a fossilised community found in 2.3-billion-year-old rock in Western Australia. The second fossilised community was discovered in 1.8-billion-year-old rock, also from Western Australia. The third is a living community discovered in the last decade in sediments off the west coast of South America.
The researchers say that despite their vast age differences, the three communities look exactly the same, each exhibiting a telltale irregular weblike fabric, and a two-tier structure. "In form, function and metabolism, they are identical," Schopf said.
It may seem unlikely that any organism can remain the same for 2.3 billion years, but Schopf said that for these deep-sea microbes, the lack of evolution made sense.
"Surface environments change all the time and when they change, the biology changes," he said. "But the muds underneath the ocean don't receive any signals from the above environment."
The microbes described in the study live 10cm to 30cm in the sediment, in one of earth's most stable environments.
Their world is cold and dark - an endless night that feels none of the effects of either ice ages or warming spells.
"There is no turning of sediments, things don't get stirred up, there is no oxygen at all - they get no time signal, there is no change," Schopf said.
The microbes reproduce asexually, which keeps genetic changes to a minimum, and their simple ecosystem requires only nitrate and sulphur for energy.
"They are well-adapted for their environment, and there isn't any competition," Schopf said.
So with no pressure to change, Schopf proposes, these organisms did not.
"The rule of life is don't fix it if it isn't broken," he said.