Science Friction_ Where the Known Meets the Unknown - Michael Shermer [108]
Figure 11.2. The poorly designed human eye. The anatomy of the human eye shows that it is anything but “intelligently designed.” It is built upside down and backward, with photons of light having to travel through the cornea, lens, aqueous fluid, blood vessels, ganglion cells, amacrine cells, horizontal cells, and bipolar cells, before reaching the light-sensitive rods and cones that will transduce the light signal into neural impulses, where they are then sent to the visual cortex at the back of the brain for processing into meaningful patterns.
Finally, the bacterial flagellum, although a remarkable structure (figure 11.3), comes in many varieties of complexity and functions. In fact, bacteria in general may be subdivided into eubacteria and archaebacteria; the former are more complex and have more complicated flagella, while the latter are simpler and have correspondingly simpler flagella. Eubacterial flagellum, consisting of a three-part motor, shaft, and propeller system, is actually a more complicated version of the archaebacterial flagellum, which has a motor and a combined shaft-propeller system. So, when IDers describe the three-part flagellum as being irreducibly complex, they are wrong. It can be reduced to two parts. Additionally, the eubacterial flagellum turns out to be one of a variety of ways that bacteria move about their environment. Finally, the flagellum has functions other than just for propulsion. For example, for many types of bacteria the primary function of the flagellum is secretion, not propulsion. For others, the flagellum is used for attaching to surfaces and other cells. As for the evolution of the flagellum, we know that between eighteen and twenty genes are involved in the development of the simpler two-part flagellum, twenty-seven genes make up the slightly more complex Campylobacter jejuni flagellum, and forty-four genes make up the still more complicated E-coli flagellum, a smooth genetic rise in complexity corresponding to the end product. And phylogenetic studies on flagella indicate that the more modern and complex systems share common ancestors with the simpler forms. So here an evolutionary scenario presents itself—archaebacteria flagella were primarily used for secretion, although some forms were co-opted for adhesion or propulsion. With the evolution of more complicated eubacteria, flagellum grew more complex, refining, for example, the two-part motor and shaft-propeller system into a three-part motor, shaft, and propeller system, which was then co-opted for more efficient propulsion.
Figure 11.3. The bacterial flagellum: evolution at work. Long a favorite among IDers as an example of irreducible complexity and intelligent design, it turns out that there are a number of different types of bacterial flagella, ranging in complexity as well as serving a number of different functions, not just propulsion. Evolution well explains how, for example, the flagellum may have originally evolved as a mechanism for secretion, then later co-opted for propulsion.
5. Inference to Design. In a special issue of the Christian magazine Touchstone, dedicated to Intelligent Design, Whitworth College philosopher Stephen Meyer argues that ID is not simply a “God of the gaps” argument to fill in where science has yet to give us a satisfactory answer—it is not just a matter of “we don’t understand this so God must have done it.” ID theorists like Meyer and Phillip Johnson, William Dembski, Michael Behe, and Paul Nelson (all leading IDers and contributors to this issue) say they believe in ID because the universe really does appear to be designed. “Design theorists infer a prior intelligent cause based upon present knowledge of cause-and-effect relationships,” Meyer writes. “Inferences to design