Chapter 6 — The Wave That Cannot Stop

Cilia are hairlike projections on cell surfaces throughout the body—moving mucus from the lungs, transducing sound in the inner ear, propelling eggs in the female reproductive tract. Each cilium beats at approximately 10–20 cycles per second in coordinated wave patterns. The internal structure, called the axoneme, is the product of approximately 200 proteins in precise coordination.

The characteristic 9+2 arrangement—nine pairs of microtubules around a central pair, connected by dynein motor proteins—must be fully assembled and correctly positioned for any wave motion to occur. Every component is structural and functional simultaneously. The dynein arms generate force between adjacent doublets to produce the bending motion. Remove any of the core components and the cilium does not wave slowly. It does not wave at all.

Primary ciliary dyskinesia, a genetic condition in which ciliary structure is disrupted, illustrates the consequences: chronic respiratory infections, infertility, and in many cases situs inversus (reversal of organ positions in the body), because cilia in early embryonic development determine left-right body asymmetry. The system must be complete from the beginning. It has no functional intermediate.

Behe, M.J. Darwin's Black Box. Free Press, 1996. Chapter 3. Satir, P. and Christensen, S.T. "Overview of structure and function of mammalian cilia." Annual Review of Physiology 69 (2007): 377–400.

Chapter 7 — Death and Resurrection in Six Weeks

Butterfly metamorphosis is not reorganization. Inside the chrysalis the caterpillar partially dissolves. Most tissues break down into undifferentiated biological fluid. From that fluid an entirely different organism assembles: different legs, different eyes, wings that did not previously exist, a different nervous system, a different body plan, a different mode of feeding.

The instructions for both organisms are encoded in the same DNA. The same genome that built the caterpillar builds the butterfly. The genome also encodes the transformation process itself—the dissolution sequence, the signals triggering it, the suppression of caterpillar structures, and the activation of imaginal discs that hold the adult blueprint. The information specifying both end-states and managing the transition between them is present and functional before either organism exists.

The evolutionary challenge is the intermediate state. The intermediate state is liquid. A liquid intermediate cannot survive predation. It cannot feed. There is no gradual improvement pathway through a process whose intermediate state is biologically inert. The entire genetic specification for both organisms and the transformation between them must be present and coordinated simultaneously.

Truman, J.W. and Riddiford, L.M. "The origins of insect metamorphosis." Nature 401 (1999): 447–452. Blackiston, D., Silva Casey, E., Weiss, M.R. "Retention of memory through metamorphosis." PLoS ONE 3, no. 3 (2008): e1736.