Responding to Behe and “Irreducible Complexity”

April 1999
by Steven Novella, MD

I received the following question regarding Michael Behe book, Darwin’s Black Box:

I recently read a book called “Darwin’s Black Box” by Behe. It’s thesis is that there are systems called “irreducibly complex systems” which appear to have no evolutionary advantage until all of their parts are present, and so would not seem to be candidates for evolving via natural selection through small changes. His conclusion is that these systems are evidence for intelligent design. I’d like to see an analysis of his example systems by a skeptic or hear a proposal for how such systems might have evolved.

Behe’s conclusions in “Darwin’s Black Box” are really nothing new, and have been part of the standard creationist objections to evolution since the time of Darwin. Behe’s line of reasoning, however, suffers from several critical logical flaws.

The first is called the Argument from Personal Incredulity, which is basically the argument that because a person cannot conceive of or imagine a solution, no solution therefore exists. Nature, however, is not limited to the imagination of Behe, or even evolutionary biologists. There are many very complex biological systems in nature, and it is not always possible to think of a compelling evolutionary sequence to explain every step in the formation of such systems. This lack of an ability to weave a convincing evolutionary tale, however, does not rule out the possibility that the complex system in question did in fact evolve.

The second fatal flaw in Behe’s line of reasoning is that a complex structure must have evolved directly for its current utility. Since it could not function in its current utility if it were any simpler, he argues, then it could not have evolved. His unspoken major premise, however, is false. Darwin himself recognized that structures may have evolved from precursors that had completely different functions. A classic example is that of bird wings. Half a wing is certainly no good for flying, and many creationists have therefore argued that it could not have been selected for. There is now stunning fossil evidence of bird ancestors with half wings, and even before this discovery it was speculated that such creatures must have existed and perhaps used their protowings for stabilization during long jumps or gliding descents, thermoregulation, catching insects, or some other purpose. There is now good evidence that insect wing precursors were used for skimming along the surface of water, before they were ever usurped for flapping flight.

Behe uses, as one of his examples, the cilia of a cell. This is a fairly safe example for him to use, since such microscopic structures do not fossilize and we will likely never be able to document the evolution of cilia. Modern cilia are certainly complex, but their precursors did not have to be. Pre-cilia likely served a different function for the cell than do modern cilia. Behe is correct in stating that no one has proposed a completely fleshed out pathway for the evolution of cilia, but this is hardly surprising, nor is it a black mark against the feasibility of evolution.

Single cells evolved over three billion years. All multicellular life evolved over the next 600 million years. Three billions years is a tremendous amount of time, and allowed for the evolution of a great deal of complexity on the cellular level. The possible evolutionary pathways that cellular proteins and structures could have taken in this time is tremendous, and it is no wonder that reconstructing these pathways stretches the human imagination. It is not reasonable to demand that this should be an obvious or simple task, lest doubt be cast upon the fact of evolution.

Behe also makes other unspoken assumptions in his reasoning – namely that structures must work well or efficiently in order to be of value to the organism. This is not true, and nature is full of examples of clumsy and imperfect structures that merely get by. Also, he assumes that while a structure is evolving through necessarily useless stages, it would be a detriment to the organism since it would not serve any useful function. Behe, however, ignores the possibility of redundancy – an important concept in evolution. If a structure is redundant, then it is free to evolve in essentially random directions (so called, genetic drift), even ones that serve no immediate purpose, while its redundant structures perform the tasks for which it originally evolved. Every step in an evolutionary sequence does not have to serve some specific purpose, or offer a concrete benefit to the organism. In this way evolution may be chaotic and messy, and almost impossible to “reverse engineer.”

There is a clear genetic basis for such redundancy. Genes are often duplicated in an organism’s DNA, even many times. Gene multiplication may easily occur through errors in DNA copying during reproduction. Sometimes, entire chromosomes may be copied. This genetic material, although it may still produce useful proteins and structures, will be redundant, and therefore free to safely evolve in novel directions while copies of itself continue to perform its original essential function. Mutations in regulatory genes may result in the creation of redundant organs or tissues, which again would be free to take on novel functions.

In short, Behe’s arguments display a fair degree of ignorance for modern evolutionary theory and rest ultimately on faulty logic. Intelligent design is not a viable scientific hypothesis and is not being taken seriously by biologists or other scientists. It is, in fact, just warmed over creationism trying to find a new face so that it may masquerade as legitimate science.

Also, Behe’s approach to the whole question of evolution is flawed in that it is far too narrow in scope. He attempts to refute the fact of evolution through a single line of argument. Such attempts at dismissing an entire field of study through a single line of evidence have a history of failing miserably. Lord Kelvin, for example, attempted to refute all the various conclusions of modern geology (of his time) in a short paper which argued for a young Earth based upon the current temperature of the Earth and the theoretical rate of the Earth’s cooling. Kelvin, however, ignored all of the independent lines of evidence from geology that spoke of a much older Earth. Kelvin was not a geologist and was not intimately aware of this large body of evidence. It turns out that Kelvin was fatally wrong in his calculations because he did not take into account the warming effect of the radioactive decay of certain materials in the Earth’s crust. Kelvin could not have known about this factor, since radioactivity had not yet been discovered.

Behe, in the style of Kelvin, is attempting to dismiss all of the findings of evolutionary biology through a single line of argument, that of a biochemist who is not an evolutionary biologist. He does not address the multiple independent line of evidence that point to the fact that life on Earth evolved. This evidence includes a mountain of fossil evidence, including many transitionary forms, geological evidence of strata, genetic evidence showing evolutionary relationships between living species, embryological evidence, and evidence of an evolutionary past captured in some current structures of modern organisms.