There’s a very interesting post on the Newsweek blog by science journalist Sharon Begley about the existence of genes for synapses in the sea sponge, which has no need for such structures. Begley is discussing an article in PLoS One that found that the same genes that code for synapses are present in sea sponges, one of the most primitive multicellular organisms on the planet, which have no nervous system and therefore no need for synapses. Begley writes:
Considered among the most primitive and ancient of all animals, sea sponges have no nervous system (or internal organs of any kind, for that matter), notes Todd Oakley, assistant professor in the Department of Ecology, Evolution and Marine Biology at the University of California, Santa Barbara. But, he adds, they “have most of the genetic components of synapses.”…
He, Oakley and the rest of the team listed all the genes known to be operative in synapses in the human nervous system. They then examined the sponge genome. “That was when the surprise hit,” said Kosik. “We found a lot of genes to make a nervous system present in the sponge.”
Not only do sea sponges have the genes to produce synapses, many of those genes are absolutely identical to the same gene in humans, yet we did not evolve until more than 600 million years later. From the PLoS paper:
We show that the genome of the demosponge Amphimedon queenslandica possesses a nearly complete set of post-synaptic protein homologs whose conserved interaction motifs suggest assembly into a complex structure. 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.
What does all this mean in terms of the dispute over evolution and intelligent design? Begley makes the (correct) argument that IDers ignore the ability of evolution to use already existing components with one function and adapt them for a new function, what Gould famously called exaptation:
What were genes for synapses doing in a sponge, which has no neurons and therefore no synapses? This is where the irreducible-complexity crowd makes a fatal error: they assume that whatever the function of a biological component (gene, protein, biochemical pathway . . . ) today must have been its function in the past. Maybe you noticed that my mouse trap example above wasn’t very persuasive; even without a base and a bar, a spring can be a useful little device. So it goes with biological systems. For instance, of the 42 proteins known to make up the bacterial flagellum, 40 have been found to serve as ion channels or something else in bacteria. It is therefore perfectly plausible that they really were hanging around–serving some function that would have allowed evolution and natural selection to keep them around generation after generation–until they all got together and formed a flagellum.
So it seems to be with the genes for synapses. The sea sponge did not use them for their current purpose, but that doesn’t mean the genes had no use. “We found this mysterious unknown structure in the sponge, and it is clear that evolution was able to take this entire structure and, with small modifications, direct its use toward a new function,” said Kosik. “Evolution can take these ‘off the shelf’ components and put them together in new and interesting ways.”
This is accurate as far as it goes, but there is much more to be said. What ID advocates would likely say in response to this finding is that it is an example of front loading rather than exaptation. Front loading is the idea that God (no, I’m not going to engage in the ridiculous fiction that the generic designer they posit is anything other than God) programmed in all of the genetic information necessary for later developments in to the first cell. Michael Behe famously proposed this in Darwin’s Black Box:
Suppose that nearly four billion years ago the designer made the first cell, already containing all of the irreducibly complex biochemical systems discussed here and many others. (One can postulate that the designs for systems that were to be used later, such as blood clotting, were present but not “turned on.” In present-day organisms plenty of genes are turned off for a while, sometimes for generations, to be turned on at a later time.)
So which is the best explanation for the existence of such genes in the sea sponge, exaptation or front loading? Le’ts look at what each explanation would predict. Back when Behe proposed this idea, Ken Miller pointed out the most obvious problem with it: runaway mutations. Natural selection can only work on genes that are expressed. If a gene is “turned off” then it is subject to runaway mutations that will render if useless in short order. Miller wrote:
This means that billions of years ago a humble prokaryote was packed with genes that would be turned off for hundreds of millions of years before they produced the eukaryotic cilium, and genes for blood clotting proteins that would pass more than a billion inactive years in genetic “cold storage.” And what happens during those billions of years? As any student of genetics will tell you, because those genes are not expressed, natural selection cannot weed out genetic mistakes. This means that mutations will accumulate in these genes at breathtaking rates, rendering then hopelessly changed and inoperative hundreds of millions of years before Behe says that they will be needed.
Quite right. But remember, some of those genes are highly conserved or 100% conserved – that is, identical or nearly identical – between sponges and humans. And while front loading means those genes had to be “turned off” for hundreds of millions of years, exaptation posits that those genes were turned on, expressed in the phenotype and serving different functions. Thus, exaptation is consistent with the preservation of those genes while front loading is not.
Equally as important, while front loading presumes that those genes serve no function before they are later expressed, exaptation predicts that they must have some function if they are highly preserved over a long period of time. They simply must be expressed in the phenotype for some function or they will mutate in to uselessness. And that is exactly the case here, as this study found that those genes, though virtually identical between sponges and humans, serve a different function in sponges than they do in humans (obviously so, since the sponges have no nervous system).
There are only two ways out of this for ID advocates: either they have to accept that those front-loaded genes had different functions in earlier species (which effectively makes front loading synonymous with exaptation, rendering the idea meaningless) or they have to posit that God not only loaded the genes for all those later developments in to earlier organisms that didn’t need them, but he also put some sort of mystical force field around them to prevent them from mutating over the last 4 billion years.
The other problem, of course, is that no one has ever found an organism that has all of the genes needed for later developments (feathers, wings, lungs, flagella, etc); that is, no organism actually has a fully complete genome front-loaded with all the goodies to be used later. If front loading was true, then the prokaryotes – the earliest existing life form on Earth – should have all of those genes. They don’t, of course. The bottom line is that the evolutionary hypothesis, exaptation, predicts the evidence perfectly; the ID hypothesis is flatly contradicted by it and can only try to explain it away or invent mystical and unknown processes to circumvent the evidence.