What is the name of Richard Lenski's ongoing experiment that tracks evolution in E. coli?

Richard Lenski’s ongoing experiment tracking evolution in E. coli is the long-term evolution experiment. Often abbreviated LTEE, it began on February 24, 1988, with 12 initially identical E. coli populations grown under controlled laboratory conditions.

Each day, researchers transfer a small sample from every population into fresh nutrient medium. This creates roughly 6.6 bacterial generations daily, allowing scientists to observe evolutionary change across tens of thousands of generations. Frozen samples taken at regular intervals form a kind of “frozen fossil record,” letting researchers revive and compare ancestors with later descendants.

The experiment has documented repeated increases in fitness, faster growth, larger cell size, and mutations affecting DNA repair. Its most famous discovery occurred in the Ara-3 population, which evolved the ability to use citrate aerobically—an unusual trait for E. coli—around generation 31,500.

A common mix-up is confusing the LTEE with Griffith’s transformation experiment or the Miller–Urey experiment. Those famous studies addressed bacterial heredity or the chemistry of life, whereas Lenski’s experiment directly observes evolution through mutation, selection, and competition.