The first formal response to Darwin Devolves was published yesterday by Science. The content of the piece was entirely predictable, and Mike Behe will soon respond in detail. However, I could not resist pointing out the extent to which the authors rely on circular reasoning. They write:

Missing from Behe’s discussion is any mention of exaptation, the process by which nature retools structures for new function and possibly the most common mechanism that leads to the false impression of irreducible complexity…The feathers of birds, gas bladders of fish, and ossicles of mammals have similar exaptive origins…The evolutionary ancestors of whales lost their ability to walk on land as their front limbs evolved into flippers, for example, but flippers proved advantageous in the long run…and developmental innovations in all metazoans through the diversification of HOX genes.

Unlimited Creative Power

The authors argue that many of the traits found in life give evidence that they are the product of evolutionary processes having dramatically altered ancestral precursors. How do the authors come to this conclusion? First, they assume that all biological features are the result of undirected processes transforming features in ancestral organisms. Second, they identify some remarkable trait in life, such as the auditory ossicles in mammals. Then, they explain its origin through evolution without providing any substantive details. Finally, they use the “fact” that evolution formed the new trait as evidence for its unlimited creative power. 

This line of argumentation only appears compelling to those who assume from that start that the core assumptions of the standard evolutionary model are true.

Specific, Coordinated Mutations

In addition, such claims contradict the clear implications of the most pertinent empirical data and mathematical analyses. For instance, the evolution of any of the complex adaptations in aquatic mammals would require numerous specific, coordinated mutations before a new trait would provide any selective advantage. The need for specificity in the genetic re-engineering is supported by the striking similarities between the genes involved in echolocation in dolphins and in bats. However, the very research the authors cite indicates that the time frame in which an aquatic mammal is believed to have evolved from a completely terrestrial one is long enough to allow for only two coordinated mutations, far fewer than would have been required.

Likewise, the claim that undirected mutations in Hox genes could contribute to major transformations is contradicted by the fact that all such mutations that alter an organism’s design architecture (body plan) are harmful. This point applies particularly to all developmental genes involved in regulatory networks (dGRNs). Eric Davidson, who was a leader in the field, commented:

There is always an observable consequence if a dGRN subcircuit is interrupted. Since these consequences are always catastrophically bad, flexibility is minimal, and since the subcircuits are all interconnected, the whole network partakes of the quality that there is only one way for things to work. And indeed the embryos of each species develop in only one way.

The fact that critics must rely to such a great extent on circular reasoning does not bode well for their hopes of overturning the core arguments in Darwin Devolves.

Photo credit: Joe Mabel from Seattle, US [CC BY-SA 2.0], via Wikimedia Commons.