the uni I work at have been involved in some really interesting research recently (nothing that I'm involved in unfortunately!) and they've been putting details of the research on their website. I thought I'd share a few. This bit of research is quite fascinating, scientists have estimated that it would take around 24 million generations for a mouse-sized mammal to evolve into something elephant sized! Apparantly dwarfism is easier, occurring at a rate ten times faster. Size change also occurs faster in aquatic mammals, presumably because the water supports a lot of their weight.
http://www.bris.ac.uk/news/2012/8208.html
and the original paper's here;
http://www.pnas.org/content/early/2012/01/26/1120774109.full.pdf+html
How interesting!