Richard Lenski of the University of Michigan in East Lansing began a decade-long experiment with Escherichia coli bacteria, allowing them to evolve under constant conditions. By 2010, he had produced more than 50,000 generations. This was the Long-Term Evolution Experiment, which began with 12 strains of Escherichia coli incubated at 37°C in 12 test tubes. Each morning, a small amount of glucose (25 mg/L) was added to each tube, which was consumed by the afternoon. The following day, the same amount of each strain was removed from each tube, returned to another tube with a small amount of glucose, and so on. Every 75 days, equivalent to 500 generations of asexual reproduction, a portion of each strain was frozen to create a fossil library of the entire experiment. By 2008, every possible individual mutation had already manifested itself multiple times in the 45,000 generations. Indeed, once, in the 33,127th generation, a mutation with a very low probability also occurs. The same thing happens every day in the world: by calculating the number of E. coli present in the world, we deduce that every possible mutation occurs every day.
