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Rebuttal to Paul Gross’ Review of The Edge of Evolution – Error #3: Ignoring Behe’s Rebuttal of Exaptation Speculation

Casey Luskin

[This four part series responding to Paul Gross can be seen in: Part 1, Part 2, Part 3, Part 4.]

An urban legend has cropped up among Darwinists that Michael Behe ignores indirect routes of evolution, commonly called “exaptation,” when he argues for irreducible complexity. In his review of The Edge of Evolution in The New Criterion, anti-ID biologist Paul Gross wrongly accuses that “Behe had failed to understand ‘exaptation’ (the use of an available part in function ‘B’ despite its original function ‘A’).” But in Darwin’s Black Box, Behe clearly accounts for exaptation and explains why it does not refute irreducible complexity:

“Even if a system is irreducibly complex (and thus cannot have been produced directly), however, one can not definitively rule out the possibility of an indirect, circuitous route. As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously. And as the number of unexplained, irreducibly complex biological systems increases, our confidence that Darwin’s criterion of failure has been met skyrockets toward the maximum that science allows.” (Michael Behe, Darwin’s Black Box, pg. 40.)

“Because the cilium is irreducibly complex, no direct gradual route leads to its production. So an evolutionary story for the cilium must envision a circuitous route, perhaps adapting parts that were originally used for other purposes. … For example, suppose you wanted to make a mousetrap. In your garage you might have a piece of wood from an old Popsicle stick (for the platform), a spring from an old wind-up clock, a piece of metal (for the hammer) in the form of a crowbar, a darning needle for the holding bar, and a bottle cap that you fancy to use as a catch. But these pieces couldn’t form a functioning mousetrap without extensive modification, and while the modification was going on, they would be unable to work as a mousetrap. Their previous functions make them ill- suited for virtually any new role as part of a complex system. In the case of the cilium, there are analogous problems.” (Michael Behe, Darwin’s Black Box, pgs 65-67.)

Moreover, as I explain here, the typical discussions of exaptation do not meet the required standards of proof, for this requires that showing:

  • (1) The parts were available for co-option;
  • (2) The availability of the parts was synchronized in both time and space;
  • (3) The availability parts must be coordinated so that they assemble properly;
  • (4) The parts must have interface-compatibility so they can work together.

To my knowledge, no Darwinist has ever explained each of these for any complex biological system.

Gross claims that Behe has “redefin[ed]” irreducible complexity “in an effort to meet the flood of negation.” But what is this “flood of negation” or what is the “redefinition”? Gross doesn’t tell us about either. Yet in 2001, Biochemist Franklin Harold stated that “there are presently no detailed Darwinian accounts of the evolution of any biochemical or cellular system, only a variety of wishful speculations.” (Franklin M. Harold, The Way of the Cell: Molecules, Organisms and the Order of Life, pg. 205 (New York, Oxford University Press 2001).)

It seems that the reality is that Behe’s original argument is still quite potent.


Casey Luskin

Associate Director, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and B.S. and M.S. degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



Michael BehePaul GrossThe Edge of Evolution