After 50,000 generations, bacteria are still evolving greater fitness

Not quite this kind of fitness...

Flickr user: Dave_Murr

In 1988, Richard Lenski's lab at Michigan Sate University started an experiment—50,000 generations of bacteria later, the experiment is still going. Lenski has watched the bacteria evolve to compensate for the stresses of harsh culture conditions, and he's been able to track the exact changes that allow them to do so. In the process, Lenski's learned a few things about the nature of evolution itself.

In his latest progress report on the bacteria, the lab set up a competition, pitting bacteria that had been adapting for different periods of time against each other. He found that those at the 50,000 generation mark not only beat the ones at 10,000 generations, but these bacteria also come out ahead of the ones at 40,000. The continual improvements suggest that, when it comes to fitness, these bacteria are nowhere close to reaching a point where improvement levels off.

Lenski's basic approach to evolution involves being cruel to E. coli. The organism evolved to survive in the rich environment of our guts and, for many generations, it has all its nutritional needs seen to by the media scientists provide it. Lenski put them on a starvation diet, with only enough glucose to get them through a few cell divisions. After that, the cells had to either come up with a different energy source or sit around and wait until the food was changed the next day. Every 500 generations, a sample from each of the dozen cultures was frozen, preserving the bacteria like a time capsule.