The Bacterial Flagellum
Way back in 1996 Behe published a book, Darwin's Black Box , claiming that so-called "Irreducibly Complex" (IC) systems disprove evolution. An IC system can be defined as one in which removing a part stops it working altogether. This supposedly means it cannot have evolved. The argument has been soundly trashed , including in a court of law, but IDists still use it because... well what else do they have? The modern argument involves two different definitions of IC, changing between them as convenient. Definition 1: A system is IC if it fails if a component is removed. Definition 2: A system is IC if there is no evolutionary route, direct or not, to it. We see systems that fail if a component is removed, and they are IC, by definition 1. Then we quietly swap to definition 2. If the system is IC then it cannot have evolved. The Bacterial Flagellum One such system is the bacterial flagellum. This is a tail-like structure in some bacteria that spins to provide forward motion.