A University of Oregon research team has found that evolution can never go backwards, because the paths to the genes once present in our ancestors are forever blocked. The findings — the result of the first rigorous study of reverse evolution at the molecular level — appear in the Sept. 24 issue of Nature.
The team used computational reconstruction of ancestral gene sequences, DNA synthesis, protein engineering and X-ray crystallography to resurrect and manipulate the gene for a key hormone receptor as it existed in our earliest vertebrate ancestors more than 400 million years ago. They found that over a rapid period of time, five random mutations made subtle modifications in the protein’s structure that were utterly incompatible with the receptor’s primordial form.
The discovery of evolutionary bridge burning implies that today’s versions of life on Earth may be neither ideal nor inevitable, said Joe Thornton, a professor in the UO’s Center for Ecology and Evolutionary Biology and the Howard Hughes Medical Institute.
“Evolutionary biologists have long been fascinated by whether evolution can go backwards,” Thornton said, “but the issue has remained unresolved because we seldom know exactly what features our ancestors had, or the mechanisms by which they evolved into their modern forms. We solved those problems by studying the problem at the molecular level, where we can resurrect ancestral proteins as they existed long ago and use molecular manipulations to dissect the evolutionary process in both forward and reverse directions.”
There is no such thing as “de-evolution” but traits that once existed to cope with a past environment can and will evolve again if the Earth’s environment changes back to what it once was (low oxygen, for example.)