“William Paley, who argued that the natural world is full of designed complexity which must have a creator, would have considered the bacterial flagellum an excellent example. The flagellum, with its intricate arrangement of interconnecting parts, looks no less designed than a watch.
Modern biology, of course, has no need for omniscient designers. Evolution – Richard Dawkins’s blind watchmaker – is all that is needed to explain the origin of complexity in nature.
The bacterial flagellum has become a focal point in science’s ongoing struggle against unreason.
The study of complex molecular systems has been given added impetus by the ID movement. ID claims that such systems cannot be explained by the stepwise process of natural selection.
The bacterial flagellum is a prime example of a complex molecular system – an intricate nanomachine beyond the craft of any human engineer.
Until recently biologists all too often fell back on the assertion that “bacterial flagella evolved and that is that”.
In the 1990s, microbiologists discovered “type III secretion systems”. Variants of seven T3SS proteins are found in the flagellum, strong evidence that the two systems evolved from a common ancestor. “The most parsimonious explanation is that the T3SS arose later.”
Bacterial flagella are all built to roughly the same specifications, additional strong evidence that the flagellum evolved, as it is exactly what you would expect to see if today’s flagella had diversified from a common ancestor.
Why would an intelligent designer go to all the trouble of reinventing the flagellum over and over and reinventing the basic design twice more in the other two domains of life?
All bacterial flagella have much in common – exactly what you would expect if they shared a common ancestor. 23 of the proteins present in all, are required for a fully functional flagellum. Homology provides incontrovertible evidence that bacterial flagella are cobbled together from recycled components of other systems through gene duplication and diversification.
The scientific imperative is not to reconstruct the entire process but simply to prove that the evolution of the flagellum is plausible using well-established natural processes.”