It’s fitting that the discovery of post-synaptic proteins in sponges was published the week after Behe‘s new book tries to flog the dead horse of “irreducible complexity“. Over a decade ago when Behe was writing Darwin’s Black Box his primary sin may have been “lack of imagination”…in essence, he had grounds to make an “argument from ignorance” based on the existence of real holes in what was then known about biochemical evolution. Even so, I think that it took a bit of wishful thinking to come to his conclusion. In the decade since then, things have changed. At the Kitzmiller trial, Behe chose to dismiss a large stack of subsequent publications as irrelevant.
I am willing to consider that Johnson, Behe and a lot of the others were acting in good faith when then first jumped onto the intelligent design bandwagon. Belief is a powerful thing, especially in a mind that needs literal absolutes. When Johnson wrote Darwin on Trial he probably was trying to defend something he needed to believe – Johnson’s writings seem to suggest that, in order to believe, he needs the Bible to be literally true (otherwise it would be “a lie”). Behe was inspired by Johnson’s book, and took it upon himself to find confirmation for his own ideas. That’s the difference between real science and a science-based polemic – having made up his mind, the author is unwilling to be swayed by any evidence to the contrary.*
In the critical synaptic scaffold gene, dlg, residues that make hydrogen bonds and van der Waals interactions with the PDZ ligand are 100% conserved between sponge and human, as is the motif organization of the scaffolds.
Again, as Ed has pointed out, this level of conservation cannot have occurred in the absence of selection – unless these genes are essential to the survival of both groups, there is almost no way that they would have remained unmodified by accumulated mutations. Sponges lack synapses, so these proteins must serve some other purpose in them.
Sponges are a basal group – they branched off before the evolution of true multicellular organisms (or we branched off from them, the sequence doesn’t matter). Thus, these proteins were present in organisms ancestral to the two groups. Since these organisms presumably did not have nerve synapses the elements used in nerve synapses were probably built out of existing “parts”. This is, of course, the most powerful argument against irreducible complexity – the “scaffolding” argument…just because you can find a system in which all the parts are needed for the system to function doesn’t mean that it didn’t evolve – it just suggests that it may not have evolved to do this task initially.
(Ed Brayton does a nice job of explaining why this is exaptation and not “front loading” – the idea that that the necessary components for future species were added into ancestral species by the “intelligent designer”.)
*This isn’t unique to pseudoscientific crankery, of course. Many actual scientists paint themselves into a corner while trying to preserve their own ideas. The truth is that, having seen something as “true”, it’s easy to see conflicting evidence as “equivocal”, while blaming the lack of supporting evidence on experimental error.