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If you care about these things, ...

Posted Sep 13 2008 4:14pm

If you care about these things, there is an exiting paper in yesterday's Science that flat out refutes Michael Behe's argument that certain "irreducible complex" biological organisms couldn't possibly have been formed by evolution. Here's the paper's abstract:

According to Darwinian theory, complexity evolves by a stepwise process of elaboration and optimization under natural selection. Biological systems composed of tightly integrated parts seem to challenge this view, because it is not obvious how any element's function can be selected for unless the partners with which it interacts are already present. Here we demonstrate how an integrated molecular system—the specific functional interaction between the steroid hormone aldosterone and its partner the mineralocorticoid receptor—evolved by a stepwise Darwinian process. Using ancestral gene resurrection, we show that, long before the hormone evolved, the receptor's affinity for aldosterone was present as a structural by-product of its partnership with chemically similar, more ancient ligands. Introducing two amino acid changes into the ancestral sequence recapitulates the evolution of present-day receptor specificity. Our results indicate that tight interactions can evolve by molecular exploitation—recruitment of an older molecule, previously constrained for a different role, into a new functional complex.

While the authors doesn't relate their findings to the ID issue, in an accompanying news perspective Cristoph Adami sets everybody straight:

Although these authors have not directly addressed this controversy in the discussion of their work–because the work itself is intrinsically interesting to biologists–such studies solidly refute all parts of the intelligent design argument. Those "alternate" ideas, unlike the hypotheses investigated in these papers, remain thoroughly untested. Consequently, whatever debate remains must be characterized as purely political.

Naturally, Behe has been quick to argue that the system Bridgham and colleagues discuss is not really "irreducible complex" in his sense. Is he right? Well, Carl Zimmer checked out what Behe earlier wrote in "Darwin's Black Box" and the definition of "irreducible complex" seems to change according to Behe's whim, so I'll let you all make up your own minds!

[Post scriptum. With the publication of the Tiktaalik roseae find in Thursday's Nature it has been a VERY good week for evolution. Why, it almost seems like God doesn't want people "of faith" to win!]

Bridgham, J. et al. (2006): Evolution of hormone-receptor complexity by molecular exploitation. Science 312: 97-101.

- Martin

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