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Sean Carroll Fails to Scale The Edge of Evolution (Part I): How Carroll Misrepresents Michael Behe’s Arguments

Casey Luskin

[Editor’s Note: This is Part 1 of a 4-part response. The full response can be read here.]

edgeofev.jpgA few months ago we discussed my review of Sean B. Carroll’s book The Making of the Fittest, the book in which Carroll intimates that the salvation of our species hangs upon accepting Darwin. Carroll has now invoked his own religious metaphors in his review of Michael Behe’s book The Edge of Evolution: The Search for the Limits of Darwinism in Science. While Michael Behe himself responds to Carroll here, I have a few comments which follow.

Carroll postures himself as Thomas Henry Huxley debating Bishop Samuel Wilberforce in a famous 19th century debate over evolution. Carroll even opens the review by invoking Huxley, saying, “The Lord hath delivered him into mine hands.” In his eagerness to attack Behe with the approval of “[t]he Lord,” Carroll completely fails to engage Behe’s actual arguments. Specifically, Carroll ignores that Behe quite contently acknowledges that at times multiple amino acids can change in a protein when there is a selective advantage for each mutation.

Carroll’s mistake begins when he claims Behe says that “multiple-amino acid replacements therefore can’t happen”:

Behe states correctly that in most species two adaptive mutations occurring instantaneously at two specific sites in one gene are very unlikely and that functional changes in proteins often involve two or more sites. But it is a non sequitur to leap to the conclusion, as Behe does, that such multiple-amino acid replacements therefore can’t happen. Multiple replacements can accumulate when each single amino acid replacement affects performance, however slightly, because selection can act on each replacement individually and the changes can be made sequential.

(Sean B. Carroll, “God as Genetic Engineer,” Science, Vol. 316:1427 – 1428 (June 8, 2007).)

In Carroll’s eagerness to attack Behe, he somehow fails to acknowledge that Behe makes precisely the same point throughout The Edge of Evolution. Behe repeatedly explains that when there is an advantage along each small step, evolution takes place. Early in his book Behe explains that “variation, selection, and inheritance will only work if there is also a smooth evolutionary pathway leading from biological point A to biological point B.” (pg. 5) Behe later states:

The Darwinian magic works well only when intermediate steps are each better (“more fit”) than preceding steps, so that the mutant gene increases in number I the population as natural selection favors the offspring…Yet its usefulness quickly declines when intermediate steps are worse than earlier steps and is pretty much worthless if several required intervening steps aren’t improvements).

(Michael Behe, The Edge of Evolution: The Search for the Limits of Darwinism, pg. 112, (Free Press, 2007).)

Behe makes this point impossible for any serious reviewer to miss:

This point is crucial: If there is not a smooth, gradually rising, easily found evolutionary pathway leading to a biological system within a reasonable time, Darwinian processes won’t work.

(Behe, 2007, pg. 7.)

Behe again concedes that evolution can sometimes occur when there are stepwise advantages along each mutational step of evolution:

Although it hasn’t yet occurred in nature, we shouldn’t be at all surprised to see resistance of mosquitoes to the new insecticides arise and spread by Darwinian processes. The necessary preconditions are all there: tiny, incremental steps–amino acid by amino acid–leading from one biological level to another.

(Behe, 2007, pg. 76.)

In each of these quotes, Behe acknowledges that evolution can happen when there is an advantage along each small step of an evolutionary pathway. Carroll thus completely misrepresents Behe’s position to claim that Behe says that mutations “can’t happen,” even when “each single amino acid replacement affects performance.”

But what happens when there is not an advantage gained at each step? This will be discussed as I recount Carroll’s further mistakes in a subsequent post.


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 BS and MS 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 BeheSean B. CarrollThe Edge of Evolution