Here is a short video on virus evolution from the Instituto de Biologia Molecular y Celular de Plantas and the Santa Fe Institute Professor Santiago Elena.
Viruses can evolve fast and sometimes adapt quickly to a new host species. For example, an influenza virus that normally infects birds can become adapted to humans. The tobacco etch virus normally infects tobacco plants. Professor Santiago Elena from Valencia wants to find out what it takes to make the tobacco virus capable of infecting another plant: Arabidopsis. The movie shows how Santiago Elena does the evolutionary experiment and we see that after 30 rounds of experimental evolution the virus is indeed adapted to the new host plant! After the experiment, Elena looks at the genetic code of the adapted virus and finds that there are just three differences between the genetic code of the normal (tobacco loving) virus and the virus that is now adapted to Arabidopsis.