In Darwin's Black Box (1996) Michael Behe challenged fellow scientists to explain irreducibly complex molecular machines, like the cilium and bacterial flagellum, in Darwinian terms. In The Edge of Evolution (2007) he renewed that challenged and noted the failure of Darwinists to make significant progress on this topic in over a decade. Now we have an update regarding one of the thousands of molecular machines in living cells: The cilium. A research group in the Netherlands claim to have met Behe's challenge (without naming him). More on that below. First, we will review of what it means for a cilium to be "irreducibly complex," and why that poses an evidential challenge to Darwinism.
Cilia (plural form of the word cilium) are hairlike structures in your lungs that that beat in synchrony to sweep mucus and debris towards the throat for elimination. Smoking destroys them or reduces their function, which poses a health risk (thus showing their importance to keeping you alive). These tiny ciliary machines exist in many other kinds of cells as well.
How do cilia bend back and forth? Here is a schematic drawing of part of a cilium (there is more to them than just this). The power stroke of the motor protein, dynein, attached to one microtubule, against subfiber B of a neighboring microtubule causes the fibers to slide past each other. The flexible linker protein, nexin, converts the sliding motion to a bending motion.
Some single cell organisms use cilia to move themselves through water. In multicellular organisms like humans, the beating cilia serve to move fluid and debris along the surface of the cells in our lungs. In his 2007 book Behe reported a newly discovered complex transport system (Intraflagellar Transport) that acts like a system of freight cars at a construction site, moving goods up and down the cilium with forward and reverse motors. The intraflagellar transport (IFT) complex is an important component of the cilium. Virtually all the protein parts of a cilium need to exist and be properly coordinated for their to be any useful transportation function at all.
This is not the sort of system that Darwinism has been able to explain because Darwinists imagines a blind sequential sequence of events that produced the individual protein parts and then (blindly?) assembled them into cilia. Darwinists face the same kind of problem with thousands of other irreducibly complex molecular machines that exist in living cells. Behe illustrates the problem of irreducible complexity with a mousetrap.
The mousetraps that my family uses in our home to deal with unwelcome rodents consist of a number of parts. There are: (1) a flat wooden platform to act as a base; (2) a metal hammer, which does the actual job of crushing the little mouse; (3) a wire spring with extended ends to press against the platform and the hammer when the trap is charged; (4) a sensitive catch which releases when slight pressure is applied; and (5) a metal bar which holds the hammer back when the trap is charged and connects to the catch. There are also assorted staples and screws to hold the system together. [See the illustration and caption].
Recently a team of scientists in the Netherlands attempted to Darwinize the cilium. Did they succeed in their PNAS article "Evolution of modular intraflagellar transport from a coatomer-like progenitor"? Remember that in 2007 Behe had described a recently discovered complex transport system (Intraflagellar Transport, or IFT) that acts like a system of freight cars at a construction site, moving goods up and down the cilium with forward and reverse motors? Here is what the PNAS article claims:
Here, we have reconstructed the evolution of the IFT complex in detail, and provide phylogenetic evidence that the IFT complex is indeed a sister structure to COPI [coat protein complex I]....Our phylogenetic reconstruction provides compelling evidence for functional as well as structural modularity within the IFT complex. Furthermore, the complex evolution of the IFT and its origin from a protocoatomer complex provides a keystone for understanding how the eukaryotic cell was able, by repurposing existing pathways and complexes, to evolve such a complex and highly organized organelle as the cilium.
The essay that quotes this passage of the new PNAS article comments as follows:
The contest is on! ... Will they indeed show how blind, undirected processes produced an irreducibly complex molecular machine? ... Several problems appear immediately in the passages cited above. First, they are only going to talk about a "phylogenetic reconstruction" [by means of a] comparison of gene sequences, to try to build an "evolutionary scenario," assuming common ancestry of the coating complex and IFT. They are not going to get into which mutations led to functional order. In fact, they just assume that the functional order somehow emerged.
A "phylogenetic reconstruction" is an attempt to draw the alleged branching tree of evolutionary change that indicates when certain branches diverged at specific times. These scientists attempted to draw this family tree by measuring the similarities in gene sequences that store the information to build the ciliary IFT and the coating complex. But note that this research already assumes that these two systems were inherited and diverged over time from a common ancestral system. The gene sequence measurements merely estimate when they diverged from each other if evolution of this sort happened at all. They never get around to truly meeting Behe's challenge and indicate which mutations produces a series of intermediate forms that were functional enough to be selected by natural selection.
The PNAS article continues:
With respect to origins and acquisition of the IFT system, our results suggest that the BBSome and IFT-A emerged from an IFT-B-like complex by intracomplex duplications. Whether the IFT-A or the BBSome was the ﬁrst additional subcomplex to emerge is unresolved at this time.
Note that the authors use question-begging expressions like "arose" and "the acquisition of." This is an instance of the logical fallacy of assuming the very thing you are trying to prove (circular reasoning). They hide behind this wall of throw-away words in order to avoid the glaring admission of not actually explaining the cilium's origin by mutation and natural selection.
Read a detailed critique of the PNAS attempt to Darwinize cilia here. In short, they fail.