One reason bacteria are so useful for studying evolution is that their character and quantity make it possible to observe their mutations in real time. Recently, a team at Michigan State University observed the emergence of a complex new ability in E. Coli bacteria.
[S]ometime around the 31,500th generation, something dramatic happened in just one of the populations – the bacteria suddenly acquired the ability to metabolise citrate, a second nutrient in their culture medium that E. coli normally cannot use.
Indeed, the inability to use citrate is one of the traits by which bacteriologists distinguish E. coli from other species.
The bacteria came from one of twelve cultures that started growing twenty years ago. Since frozen samples have been taken at intervals of 500 generations, it should be possible to sequence the bacterial DNA and identify when and perhaps how the mutation took place. That could offer some interesting insight into how complex biochemical pathways emerge.