Mollusks’ Ever-“Evolving” Nervous Systems

Rearranged evolutionary tree puts the brains on the bottom.

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The Mollusca phylum has been giving evolutionists a headache for years because it contains such diverse members. “Evolutionary relationships among the eight major lineages of Mollusca have remained unresolved”1 despite traditional genetic sequencing and morphological comparisons. An analysis of genome sequences recently published in Nature suggests redrawing the evolutionary history of mollusks. To do so, however, requires the “fall back and punt” maneuver of appealing to parallel evolution to explain the brains.

“A primary goal of resolving molluscan phylogeny is to improve our understanding of their early evolutionary history,” write Kevin Kocot and colleagues. “Perhaps more than any other animal group, understanding of molluscan early evolution has been constrained by the notion of a generalized bauplan [body plan] or ‘archetype’ which is still propagated in some invertebrate zoology textbooks.”2 Because mollusks include creatures as variable as snails, squid, and clams, evolutionists have not been able to come up with an “ancestral state reconstruction” that could morph into such disparate forms.

Genetic analysis should have freed evolutionists from such reliance on things visible, but up to now it has not. By performing a more extensive genetic analysis of protein-coding genes and making the usual evolutionary assumption that more similarities imply closer evolutionary relationships, the researchers have proposed a new phylogenetic tree.

Traditionally, snails and slugs (gastropods)—because they have clusters of nerve cells which are fused in some species—are believed to be evolutionary ancestors of cephalopods. (Octopus, squid, and cuttlefish are cephalopods.) Cephalopods have highly developed central nervous systems and amaze us with their navigational abilities and adeptness at solving complex problems.

On Kocot’s new tree, “gastropods are sister to bivalves (not cephalopods).”3 Bivalves, such as clams and scallops, have extremely simple nervous systems lacking any rudiments which could be imagined to precede real brains. Furthermore, molecular clock-type calculations indicate cephalopods actually evolved before snails, slugs, or clams. Thus, the researchers suggest that the brainier members of the mollusk phylum evolved their complex brains independently at different times.

Traditionally, most neuroscientists and biologists think complex structures usually evolve only once.

“Traditionally, most neuroscientists and biologists think complex structures usually evolve only once,” says co-author Leonid Moroz. “We found that the evolution of the complex brain does not happen in a linear progression. Parallel evolution can achieve similar levels of complexity in different groups. I calculated it happened at least four times.” Moroz calculates that the octopus, a freshwater snail (Helisoma), and two kinds of sea slugs evolved complex central nervous systems without any ancestral help from each other.

Within the evolutionary worldview, there is a built-in safety valve for situations in which evolutionary ancestry becomes too implausible even for evolutionists. That fall-back position is parallel or convergent evolution—the notion that the same thing evolved multiple times in different lineages. Paul Katz, a neurobiologist, commenting on this research, said, “This is more evidence that you can get complexity emerging multiple times.”

Yet the relatedness of the organisms here is based on the number of proteins they share. As these researchers assert, “These [protein-coding] genes are usually informative for inferring higher-level phylogeny because of their conserved nature due to their functional importance.”4 Their assertion is based on an interpretation of the genetic “facts” in accordance with their faith that evolution must have happened. An alternate faith holds that a common Designer—the God of the Bible—created each kind of creature independently and naturally used some of those “functionally important” proteins in more than one place. Because of a faith-based commitment to their worldview, evolutionists are willing to accept the fantastic implausibility of “complexity emerging multiple times” than consider letting “a Divine Foot in the door.”5 We each choose our faith and interpret the facts accordingly. Similar genes do not prove ancestral evolutionary progression, but they are completely consistent with the work of our common Designer, Christ, by whom “all things were created” (Colossians 1:16).

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  1. Kevin M. Kocot et al., “Phylogenomics Reveals Deep Molluscan Relationships,” Nature 477 (September 22, 2011): 452–456, doi:10.1038/nature10382.
  2. Ibid.
  3. Ibid.
  4. Ibid.
  5. Richard C. Lewontin, “Billions and Billions of Demons” (review of The Demon-haunted World: Science as a Candle in the Dark by Carl Sagan, 1997), The New York Review, January 9, 1997,


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