Nice case of evolution observed in the lab

Richard Lenski of Michigan State University used a single cell of E. coli to start 12 lab populations, which he observed for more than 44,000 generations. At the 31,500th generation, one of the populations suddenly developed the ability to metabolize citrate. He had saved frozen samples of each 500th population, and found that only that one of the twelve populations would re-evolve this ability, and then only when he started at the 20,000th generation or later, leading him to conclude that something had developed around the 20,000th generation of that population that provided the necessary foundation.

As New Scientist reports, "the experiment stands as proof that evolution does not always lead to the best possible outcome. Instead, a chance event can sometimes open evolutionary doors for one population that remain forever closed to other populations with different histories."

UPDATE (June 11, 2008): Michael Behe has written a commentary on this result, which Ed Brayton criticizes at Dispatches from the Culture Wars.

UPDATE (June 13, 2008): Science writer Carl Zimmer has written a nice summary of this research, and the primary author of the research shows up in the comments to answer questions at comment #80.

UPDATE (June 18, 2008): Lenski responds to a letter from Andy Schlafly of Conservapaedia.

UPDATE (June 24, 2008): In a further exchange with Schlafly, Lenski politely shows Schlafly to be an idiot and a jerk. (The link edited out by Conservapaedia is to RationalWiki's article on banning at Conservapaedia.)