In the Aug 5th issue of nature discusses the recent publication of the A. queenslandica genome. Sponges are among the very simplest multicelluar animals so if we want to ever really understand cancer we need to understand how the first multicellular animals were able to overcome it.
The one thing that stuck out the most to me was that the genome is more complex than many suspected. The sponge has a repertoire of 18000 genes including some distant homologues to genes that code for muscle tissue and neurons in vertebrates. The article quotes Douglas Erwin who claims that this kind of complexity indicates that perhaps sponges descended from more complex animals. Another indication of this is the fact that sponge phylogeny is so poorly resolved and there is even speculation that they may be paraphyletic. Perhaps, they represent the degenerate tips of a tree that is long ago extinct. This is all possible but, I think that such conclusions may be very premature. I think that the kind of complexity we find in the sponge is exactly what we should expect. The genes for the complex neuromuscular system we find in bilaterans today certainly did not come from nowhere. Their predecessors must have evolved in simpler creatures that used them in completely different ways. If this was not the case, then such systems would simply not exist.
This is a common theme in evolution. For example, the genes that comprise the vertebrate eye lurked in our common ancestor with sea squirts filling other functions about the body. Natural selection is not an inventor and it doesn't synthesize new structures out of thin air, it can only tinker with parts that are already at hand. It will be exciting as over the next several years we are able to tease out just exactly what sponges and their relatives used these genes for!
