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How do complex systems evolve?

There is a typical off-the-mark article on the evolution of nervous system in Science. See below. This article seems to err whenever wrong statements could be made. However, the article has a useful summary of facts, which seem to corroborate the scenario in this book.

Greg Miller

On the Origin of The Nervous System   

Science  325 24 (2009)

Its useful part, a summary of facts, is quoted:

* Amphimedon queenslandica reported in PLoS ONE in 2007 contain a set of proteins typically found on the receiving side of a synapse, although electron microscope studies have failed to find synapses in sponges. Although their genomes contain genes for some neurotransmitter receptors, sponges appear to lack the type of receptors used for most excitatory neural communication in other animals. Cells in the sponge's larvae express a handful of genes that spur neural precursor cells to develop into full-fledged neurons in more complex animals. Inserting the sponge version of one of these genes into frog embryos and fruit fly larvae led to the birth of extra neurons. These cells sit on the outer surface of the sponge larvae.

*Physiological experiments with sponges have also turned up signs of neural foreshadowing. Glass spongeRhabdocalyptus dawsonigenerate action potentials (Leys and Mackie N 1997)

*Sponges have many of the right components, but some assembly is still required.

*However, Ctenophores may be the lowest. If ctenophores came before sponges, the assorted nervous system components that have turned up in sponges may not be foreshadowing after all but rather the remnants of a nervous system that was lost after the sponge lineage split off from that of ctenophores.

*Some jellyfish, such as the bell-shapedAglantha digitale, are more organized, with clearly defined bundles of nerves running around the base of the bell. Cnidarian neurons generate action potentials and release neurotransmitters to communicate across synapses. Nv reveals a surprisingly large array of genes encoding enzymes that synthesize or break down neurotransmitters, as well as receptors for these signaling molecules (Science, 6 July 2007, p. 86).

Thus, as stated in the book, to complexify the required materials must exist beforehand, and if an organism goes into sessile life before ‘synthesis,’ they are lost irreparably and no further complexification stage is possible.

The quoted article illustrates the conventional wrong ideas well:

Many scientists think Porifera are the living creatures most similar to the common ancestor of all animals. This is totally wrong.

And to many researchers, sponges look like animals on the verge of a nervous breakthrough. 　 They show the degenerate results.

It is totally wrong to regard Choanoflagellata as illustrating the path to Metazoa; it is again a result of degeneration due to inactive life style. They are not primitive. The author of this article says about Hemichordata as follows:

If the ancestor had a centralized nervous system, several lineages, including that of Saccoglossus , must have later reverted to a diffuse nervous systems an apparent downgrade that is ``hard to explain.’’

It is only a typical example adapted to filter feeding life.