Illusion of an Impossibility Proof

The serious way forward is to amend our ignorance, by sequencing the genomes of different bacteria, with and without flagella. Using our current knowledge of the genetic basis of the flagellum, researchers would be able to specify more clearly what the intermediate forms—those with some, but not all, of the crucial genes—might have been like, and what functions the rele- vant proteins might have served. Until we know these things, efforts to de- scribe intermediates will be so much whistling in the dark. Behe’s examples rely on guesses that simply anticipate what this hard work would reveal.

So we have the illusion of an impossibility proof. Allegedly there could be no sequence of intermediates concluding with the fortunate, flagellum-bearing bacterium, in which each member of the sequence enjoyed a selective advan- tage over its predecessor. Behe’s story (quite charmingly told in Darwin’s Black Box) offers his own preferred version of what the sequence would have to be like. Since Darwinians have no commitment to simpleminded stories of sequential addition of components, there is no reason to accept Behe’s descrip- tion. Because the same rhetorical strategy pervades his entire book, showing up in all the instances of the concrete case argument he provides, all the parade of examples really shows is that there are some interesting problems for molec- ularly minded evolutionists to work on, problems they might hope to solve in the light of increased understanding from comparative studies of the genetics and development of a wide variety of organisms.

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The computational argument occurs in a variety of forms in current in- telligent design literature, sometimes with relatively simple calculations of infinitesimal probabilities, on other occasions with much more technical specification of conditions under which we should make the “design infer- ence” and conclude that some aspect of life has been intelligently de- signed.* Whether or not intelligent designers attempt to be fully explicit about the requirements for invoking design, all their versions require the preliminary step of arguing that it is highly improbable that various as- pects of life on earth could have emerged through natural selection. To use an analogy much beloved by earlier creationists, Darwinian claims about selection and the organization of life are equivalent to the idea that a hur- ricane in a junkyard could assemble a functioning airplane.

Besides providing the concrete case argument, Behe offers several ver- sions of its computational cousin. Here’s his attack on a scenario for the evo- lution of a blood-clotting mechanism, tentatively proposed by the eminent biochemist Russell Doolittle:

Let’s do our own quick calculation. Consider that animals with blood-clotting cas- cades have roughly 10,000 genes, each of which is divided into an average of three pieces. This gives a total of about 30,000 gene pieces. TPA [tissue plasminogen activator] has four different types of domains. By “variously shuffling,” the odds of getting those four domains together is 30,000 to the fourth power [presumably Behe means that the chance is one-thirty-thousandth to the fourth power], which is approximately one-tenth to the eighteenth power. Now, if the Irish Sweepstakes had odds of winning of one-tenth to the eighteenth power, and if a million people played the lottery each year, it would take about a thousand billion years before anyone (not just a particular person) won the lottery. . . . Doolittle apparently needs to shuffle and deal himself a number of perfect bridge hands to win the game.*