The E. coli long-term evolution experiment (LTEE''') is an ongoing study in experimental evolution led by Richard Lenski at Michigan State University, and currently overseen by Jeffrey E. Barrick at The University of Texas at Austin. It has been tracking genetic changes in 12 initially identical populations of asexual Escherichia coli bacteria since 24 February 1988. Lenski performed the 10,000th transfer of the experiment on March 13, 2017. The populations reached over 73,000 generations in early 2020, shortly before being frozen because of the COVID-19 pandemic. In September 2020, the LTEE experiment was resumed using the frozen stocks. Over the course of the experiment, Lenski and his colleagues have reported a wide array of phenotypic and genotypic changes in the evolving populations. These have included changes that have occurred in all 12 populations and others that have only appeared in one or a few populations. For example, all 12 populations showed a similar pattern of rapid improvement in fitness that decelerated over time, faster growth rates, and increased cell size. Half of the populations have evolved defects in DNA repair that have caused mutator phenotypes marked by elevated mutation rates. The most striking adaptation reported so far is the evolution of aerobic growth on citrate, which is unusual in E. coli, in one population at some point between generations 31,000 and 31,500. On May 4, 2020, Lenski announced a 5-year renewal of the grant through the National Science Foundation's Long-Term Research in Environmental Biology (LTREB) Program that supports the LTEE. He also announced that Dr. Jeffrey E. Barrick, an associate professor of Molecular Biosciences at The University of Texas at Austin, would take over supervision of the experiment within the 5-year funding period. The experiment's time at Michigan State University ended in May 2022, when the populations reached 75,000 generations, and the experiment was transferred to Barrick's lab. The experiment was revived and restarted in Barrick's lab on June 21, 2022. Experimental approach The long-term evolution experiment was designed as an open-ended means of empirical examination of central features of evolution. The experiment was begun with three principal goals: To examine the dynamics of evolution, including the rate of evolutionary change. To examine the repeatability of evolution. To better understand the relationship between change on the phenotypic and genotypic levels. As the experiment has continued, its scope has grown as new questions in evolutionary biology have arisen that it can