Evolution of Blood Clotting

In the case of the evolution of blood clotting, our ignorance is deeper. Not only do we not know what the initial molecular conditions—the prior state of the organisms in the population in which blood clotting emerged—were, we also don’t know whether that initial state favored certain sorts of molecular changes rather than others. We have reason to think that Behe’s assumption that there’s a precise chance of 1 in 30,000 that each gene piece will participate in the “shuffling” process is incorrect. For, given what we know about mecha- nisms within the genome, the idea of exactly equal chances is suspect. But we don’t know whether, given the initial molecular state, the chance of the cas- cade Doolittle hypothesizes remains infinitesimally small or whether it is actually one. Any estimate of the probability here is an irresponsible guess.

My imagined experiment with the deck of cards suggests a different way to think about the problem. Imagine that all the hands you were dealt were mundane—fairly evenly distributed among the four suits, with a scattering of high cards in each. If you calculated the probability of receiving ten mun- dane hands in succession, it would naturally be a lot higher than the chance of being dealt those very particular mundane hands, with the cards arriving in precisely that sequence (although it wouldn’t be as high as you might expect). Blood clotting might also work in the same way, depending on how many candidates there are among the 30,000 “gene pieces” to which Behe al- ludes, that would yield a protein product able to play the necessary role. Suppose that there are a thousand acceptable candidates for each of the four positions in the molecule we need (TPA). The chance of success on any par- ticular draw is now about 1 in 2.5 million. If there were 10,000 tries a year, it would take, on average, two or three centuries to find an appropriate com- bination, a flicker of an instant in evolutionary time.

My assumptions are no better—and no worse—than Behe’s, for neither of us knows how tolerant the blood-clotting system is of the molecular combi- nations that the animals in question (whatever they were) might have sup- plied. We simply don’t know what the right way to look at this problem is. But, given our ignorance, we shouldn’t make wild guesses and then declare that the probabilities are so low that evolution under natural selection is impossible. A better research strategy would be to try to assemble informa- tion that will replace the guesses with serious estimates.