A team of microbiologists at Michigan State University have just revealed the results of a 20 year experiment looking at the evolution of the bacterium E. coli over 44,000 generations. The report is too long to paste here so the link is below.
http://richarddawkins.net/articles/2669
Breifly, the team incubated the bacteria in bottles containing glucose (which E. coli can use as a food and carbon source) and continuously took samples, adding them to new bottles with a fresh supply of glucose (freezing samples periodically). After repeating this process for 20 years they got some very interesting results. The bacteria in the most recent bottles are able to grow ~75% faster than the original strains showing that they have adapted to feed of a pure glucose source (at the expense of other sugars that they could previously use).
Even more fascinating was the discovery that some cultures of the E. coli were now using citrate present in the media as their sole carbon source (something E. coli could not previously do). Somewhere along the line (~31,500 generations) a mutation occured allowing the E. coli to consume the citrate and these descendants then began to outcompete the non-citrate eaters.
I thought this was a really intersting study that shows evolution at work. If you read the full text in the link you'll see that they suggest small mutations through out the bacteriums history were key in allowing such a key step to evolve.
