Open access article in last week’s PNAS: Stepwise formation of the bacterial flagellar system. Of course, the Intelligent Design crowd will continue saying the same things they’ve always said without blinking, but it’s always nice to have a citation ready at hand for refutation.

The authors look at the relationships of the genes involved in building a flagellum, and are able to deduce that they arose through duplication – mutation and natural selection copied pre-existing components and exapted them to put together more and more advanced structures. It’s possible that all the intricately interdependent components of the flagellum originated from one ancestral protein.