Watching evolution in action

Getting a ringside seat to watch changes in bacteria due to natural selection.

From time to time Dr. Lenski also froze some of the bacteria from each of the 12 lines. It became what he likes to call a “frozen fossil record.” By thawing them out later, Dr. Lenski could directly compare them with younger bacteria.

Within a few hundred generations, Dr. Lenski was seeing changes, and the bacteria have been changing ever since. The microbes have adapted to their environment, reproducing faster and faster over the years. One striking lesson of the experiment is that evolution often follows the same path. “We’ve found a lot of parallel changes,” Dr. Lenski said.

In all 12 lines the speed of adaptation was greatest in the first few months of the experiment and has since been tapering off. The bacteria have all become larger as well, although Dr. Lenski is not sure what kind of adaptation this represents. When other scientists saw these sorts of results begin to emerge, they set up their own experiments with microbes. Today they are observing bacteria, viruses and even yeast as they adapt to challenges as diverse as infections, antibiotics and cold and heat.

Albert F. Bennett, a physiologist at the University of California, Irvine, is an expert on temperature adaptation. He started out studying animals like reptiles and fish, but he seized on bacteria after hearing about Dr. Lenski’s experiments. “It was one of those ‘Star Trek’ moments,” he said. “I was looking out the window, and for about 10 minutes my mind was going into hyperdrive.”