Isn't it True That the Bacterial Flagellum Could Not Have Evolved?
This is a statement often asserted by proponents of Intelligent Design, but it is simply not true. The argument goes that since the flagellum (the tail-like structure many bacteria have which helps them "swim") is a very complex machine, it could not have evolved naturally. This is because if you remove any of the proteins that make up the flagellum's motor, it can no longer function.
However, as this video beautifully demonstrates, the flagellum does function with fewer proteins, just not as a flagellum. Every part of the flagellum is made of proteins already in the cell, performing other functions. This is one of the most interesting aspects of Evolution: that adaptations can change roles, or combine with other adaptations to perform new roles.