Punctuated Evolution Seen in 10,000 Generations of Bacteria
Scientists recently attempted to answer the question of whether evolution proceeds with gradual changes among organisms or with clear-cut dramatic changes interspersed by periods of no change among organisms. To do this, they grew bacteria in the lab for 10,000 generations, taking and preserving samples of individuals over the years. What they found was that the features of individual cells changed very distinctly and suddenly and then remained constant for many generations before changing again.

The researchers report that this evidence supports a mechanism of punctuated versus gradual evolution. However, other scientists caution against extrapolating the results of a population of asexually reproducing bacteria to populations that reproduce sexually and to entire species. Still others comment that if the researchers had spaced out their sampling even more, they might have seen a more gradual change in characteristics.

Source: "Microbes Hint at a Mechanism Behind Punctuated Evolution" by Christine Mlot, Science, June 21, 1996