The yeast we study have a mutation that makes them build up a red pigment. But let them grow a little extra and sometimes they’ll end up changing color in parts of the colony! Mutations can build up really quickly, particularly if they’re adaptive. Every time I see this happen on my Petri dishes, I’m amazed both at nature and at the people who still don’t believe in evolution. Certainly, this is the micro-est of microevolution, but it happens in just a few weeks, under tightly controlled lab conditions. Seeing it on the small scale helps me relate a bit better to large-scale evolution, which is hard to conceptualize.