Science News has a report on a very cool experiment done by Dr. Richard Lenski at Michigan State (Lenski is also with the Digital Evolution Lab at MSU, along with Rob Pennock and Wes Elsberry, but this is an experiment with real bacteria, not artificial organisms). This is a really cleverly designed test of how a mutation that does not confer a survival advantage can later be coopted by a second mutation that can be selected for.
Lenski’s team watched 12 colonies of identical E. coli bacteria evolve under carefully controlled lab conditions for 20 years, which equates to more than 40,000 generations of bacteria. After every 500 generations, the researchers froze samples of bacteria. Those bacteria could later be thawed out to “replay” the evolutionary clock from that point in time.
After about 31,500 generations, one colony of bacteria evolved the novel ability to use a nutrient that E. coli normally can’t absorb from its environment. Thawed-out samples from after the 20,000-generation mark were much more likely to re-evolve this trait than earlier samples, which suggests that an unnoticed mutation that occurred around the 20,000th generation enabled the microbes to later evolve the nutrient-absorption ability through a second mutation, the researchers report in the Proceedings of the National Academy of Sciences.
Check out the links.