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Probability and Controversy: Response to Carl Zimmer and Joseph Thornton

The science writer Carl Zimmer posted an invited reply on his blog from Joseph Thornton of the University of Oregon to my recent comments about Thornton's work. This is the last of four posts addressing it. References appear at the bottom of this post.

At the end of his post Thornton waxes wroth.


Behe's argument has no scientific merit. It is based on a misunderstanding of the fundamental processes of molecular evolution and a failure to appreciate the nature of probability itself. There is no scientific controversy about whether natural processes can drive the evolution of complex proteins. The work of my research group should not be misintepreted by those who would like to pretend that there is.

Well, now. I'll leave it to the reader of my previous replies to Thornton to decide whether she thinks they have scientific merit, and whether it is I or he who misunderstands the disputed facets of molecular evolution. As for "the nature of probability itself" and "no scientific controversy," I will briefly address those here.

To illustrate his own grasp of probability Professor Thornton talks baseball.


[Behe] supposes that if each of a set of specific evolutionary outcomes has a low probability, then none will evolve. This is like saying that, because the probability was vanishingly small that the 1996 Yankees would finish 92-70 with 871 runs scored and 787 allowed and then win the World Series in six games over Atlanta, the fact that all this occurred means it must have been willed by God.

Let me first say that, as a devout fan of the Philadelphia Phillies, I would never think that a Yankees title was intended by the deity. (Bought by George Steinbrenner, perhaps, but certainly not "willed by God.") That aside, I don't think Thornton's analogy captures the evolutionary problem. The example he chose posits a fully functioning team for a very specific game, baseball, performing within the parameters it was designed to -- hitting the ball, playing defense, winning and losing games. Even the 1962 Mets did all those things (in somewhat different proportions). Yet the problem for the steroid receptor proteins Thornton's lab designed was to work at all. To do so they needed to have the correct tools (the right amino acid residues) oriented in the right directions. So let's change his example a bit. Instead of asking if the Yankees would have won the title with a different number of runs, let's ask if they would have won if their batters lay down on the ground instead of standing when at bat. And let's ask if they would have won if they swung towels instead of wooden bats. And if their pitchers threw the ball in random directions. And if their fielders all huddled together in left field, or ran away from a hit ball instead of towards it. I'll bet even Professor Thornton would be surprised if they won under those circumstances.

Which of those strange behaviors would the imaginary Yankees have to change to win a Series title? -- All of them. And how long would it likely take if each season they randomly changed one behavior a bit (say, fielders ran in a direction 173 degrees from a hit ball instead of 180 degrees straight away from it)? -- Very, very long. The bottom line is this: it is Thornton who, frankly, doesn't understand probability applied to evolutionary possibilities. His set of conceivable examples is severely restricted to ones that simply have to work, or that lead inexorably in the direction he wants them to go, without comprehending that there is no evolutionary law that says anything has to work, or that the best current innovation has to lead along a path to something even better. The remarkable thing is that his own admirable laboratory research illustrates this, but he is too enthralled by Darwinian theory to see it.

As for "no scientific controversy," even a brief excursion into the history of science shows many uncontroversial, widely-accepted theories that were in fact wrong. There was no scientific controversy in the 19th century about the existence of the ether, or the adequacy of Newton's laws. And, if one relies on science journals for her entire perspective, there is no controversy today about whether undirected natural processes can account for the origin of life. Yet neither can any scientist today detail a plausible theory of the origin of life. So the bare question of whether some idea is or is not controversial within the scientific community is itself simply a sociological question, not a scientific one. And when the idea is defended so weakly by someone as intelligent as Professor Thornton, it would seem that sociology is pretty much all the idea has going for it.


References

1. Bridgham, J.T., Ortlund, E.A., and Thornton, J.W. 2009. An epistatic ratchet constrains the direction of glucocorticoid receptor evolution. Nature 461:515-519.

2. Bridgham, J.T., Carroll, S.M., and Thornton, J.W. 2006. Evolution of hormone-receptor complexity by molecular exploitation. Science 312:97-101.

3. Ohno, S. 1970. Evolution by gene duplication. Springer-Verlag, Berlin, Germany.

4. Behe, M.J. and Snoke, D.W. 2004. Simulating evolution by gene duplication of protein features that require multiple amino acid residues. Protein Sci. 13:2651-2664.