Lenski's experiment: 25 years and 58,000 generations

25 years ago, according to a recent article in Science magazine, Richard Lenski put samples of E. coli bacteria into a dozen flasks filled with a solution of glucose and other nutrients, incubated them, stirred them, and every day removed 1 % and repeated the process, day after day, for 25 years (except for a brief interruption when he moved from one university to another). The author of the article, Elizabeth Pennisi, notes that Lenski’s bacteria

are proving as critical to understanding the workings of evolution as classic paleontology studies such as Stephen Jay Gould’s research on the pace of change in mollusks. Lenski’s humble E. coli have shown, among other things, how multiple small mutations can prepare the ground for a major change; how new species can arise and diverge; and that Gould was mistaken when he claimed that, given a second chance, evolution would likely take a completely different course. Most recently, the colonies have demonstrated that, contrary to what many biologists thought, evolution never comes to a stop, even in an unchanging environment.

You may read Pennisi’s article for yourself, but what I (a nonbiologist) found most interesting was that evolution keeps going, even in a stable environment; there are no fitness peaks (at least among E. coli in bottles). Equally, the fact that several different lines learned to metabolize citrate by means of different series of mutations suggests (as in the Pennisi quotation above) that the course of evolution might be more predictable than we had thought. Finally, the photograph of the graduate student sitting in front of a pyramid of Petri dishes convinces me that physics is better.