2. Michael Behe and Irreducible Complexity
Black Box 1996

3. Flagella, “intelligent design” and irreducible complexity
The U.S. Supreme Court has prohibited the teaching of creationism in public schools as a violation of the “establishment of religion” clause of the constitution.
Latest attempt to insert creationism into schools is the idea of “Intelligent Design.”

4. Irreducible Complexity
The modern form of The Argument from Personal Incredulity:
Irreducible Complexity
"An irreducibly complex system cannot be produced directly by numerous, successive, slight modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional Since natural selection can only choose systems that are already working, then if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on."

5. Flagella, “intelligent design” and irreducible complexity
The concept of “intelligent design” is outlined most clearly in Michael Behe’s book “Darwin’s Black Box.”
The central idea in “intelligent design” is that some structures in the body are so complex that they could not possibly have evolved by a gradual process of natural selection. These structures are said to “irreducibly complex.”

6. How did such a beautiful structure of a flagellum evolve?
Filament
Hook
Basal
body
The base of the flagellum is a motor that rotates the filament.
M is the rotor and S is the stator
KEGG database:

7. Flagellum is the “poster-child” of the intelligent-design movement
Bacteria swim by rotating their flagellum

8. A Mouse trap is “Irreducibly Complexity”
This argument seems to rise above the "argument from personal incredulity." by asserting that it is a structure "in which the removal of an element would cause the whole system to cease functioning"

9. Flagella, “intelligent design” and irreducible complexity
By “irreducibly complex” Behe means that a complex structure cannot be broken down into components that are themselves functional and that the structure must have come into existence in its complete form.

10. Flagella, “intelligent design” and irreducible complexity
If structures are “irreducibly complex” Behe claims that they cannot have evolved.
Thus, their existence implies they must have been created by a designer (i.e. God, although the designer is not explicitly referred to as such).

11. Flagella, “intelligent design” and irreducible complexity
One of Behe’s main examples is flagella/cilia.
Behe claims that because cilia are composed of at least half a dozen proteins, which combine to perform one task, and that all of the proteins must be present for a cilium to work and that cilia could not have evolved in a step-by step process of gradual improvement.

12. Flagella, “intelligent design” and irreducible complexity
The flagellum is not, in fact, irreducibly complex.
For example, the flagellum in eel sperm lacks several of the components found in other flagella (including the central pair of microtubules, radial spokes, and outer row of dynein motors), yet the flagellum functions well.

13. Flagella, “intelligent design” and irreducible complexity
The whole “irreducible complexity” argument could in reality be recast as an argument of “personal incredulity.”
“I personally cannot imagine a sequence of steps by which this complex structure could have evolved. Therefore, it must have been created.”

14. Consequences for the “irreducible complexity” argument
The existence of the type III secretory system in a wide variety of bacteria demonstrates that a small portion of the “irreducibly complex” flagellum can indeed carry out an important biological function.
Since such a function is clearly favored by natural selection, the contention that the flagellum must be fully-assembled before any of its component parts can be useful is obviously incorrect.
What this means is that the argument for intelligent design of the flagellum has failed.
Miller K.R. "Debating Design: from Darwin to DNA," edited by Michael Ruse and William Dembski