During the call (e.g. around 19:30), Curtis, the caller, points out how evolution has never been observed in a lab. Stefan rebuts that it's an unreasonable standard of proof because evolution would take too long to be observed in a lab.
But actually, evolution has been observed in a lab! Specifically, evolution of bacteria: http://rationalwiki.org/wiki/Lenski_affair .
This is perhaps a bit more interesting an adaptation than humans changing skin color or bird beaks changing shapes or sizes.