Gene mutations that are beneficial on their own combine to slow down progress
Evolution may be an exercise in diminishing returns, two new studies of bacteria suggest. When beneficial mutations team up in an organism, they tend to hold one another back.
The results, reported in the June 3 Science, could mean that the more evolutionarily fit an organism gets — reproducing more — the harder it becomes to improve on that success.
Experiments in which bacteria evolve in laboratories commonly show that the microbes initially increase in fitness rapidly, but then slow down over time. Scientists didn’t know whether that was because really good mutations that produce big fitness gains happen early on (and later beneficial changes tend to have smaller effects), or whether mutations interfere with one another.
To find out, an international team of researchers examined five mutations that appeared in a strain of E. coli that had been growing in the lab for thousands of generations (S