Co-option is the standard neo-Darwinian explanation for the evolution of the bacterial flagellum, but when you???re dealing with something that has 30 parts, and the nearest functional sub-unit is a piece that has 10 parts, then I???d say you still have a lot of explaining to do. (That???s why the TTSS story doesn???t impress me: it???s a very long way from 10 to 30.) You could suppose the existen