February 23, 2006 | David F. Coppedge

It’s a Long (Roundabout) Way from Amphioxus

“Every solution breeds new problems” laments a Murphyism, and Henry Gee feels the pain.  In Nature this week,1 he delved into the growing quandary about where to put the common ancestor of starfish, sea squirts and chordates, including the vertebrates and us human beings.  His challenge is to prove the idiot’s sanity:

So, if lancelets really are close relatives of echinoderms, what are the implications for our picture of deuterostome evolution?  The short answer is that the textbook scheme is turned on its head.  Rather than the steady acquisition of progressively more chordate-like (and, by implication, human-like) features from an ancestor with nothing much to recommend it, the story becomes one of persistent loss.  The last common ancestor of extant deuterostomes would have been a free-living, bilaterally symmetrical creature with a distinct throat region perforated by gill slits, segmented body-wall musculature and possibly a reasonably sophisticated brain and central nervous system.  In a sentence, the ancestor would have looked like a cross between an amphioxus and a larger, brainier, tunicate tadpole larva.  Crazy? Possibly. But possibly not. (Emphasis added in all quotes.)

Reporting on phylogenetic study by Delsuc et al. from fossils and genetics in the same issue,2 the senior editor at Nature tried to be upbeat about the latest proposal, but called it another exercise in humility.  “Time and again,” he preached, “further work has exposed our prejudices for the parochial conceits that they are.” A quote from the paper by Delsuc et al. shares this view, and demonstrates the revolutionary nature of the proposed new phylogeny:

The monophyly of Olfactores invalidates the traditional textbook representation of chordate, and even deuterostome, evolution as a steady increase towards complexity culminating in the highly specialized brain of vertebrates.  This anthropocentric interpretation is perhaps best reflected by the terms ‘Euchordata’ (that is, ‘true chordates’) or ‘chordates with a brain’, which are used to designate the grouping of cephalochordates and vertebrates.  Tunicates should therefore no longer be considered as ‘primitive’ but rather as derived chordates with highly specialized lifestyles and developmental modes.

    Meanwhile, over in Science Now, Elizabeth Pennisi quoted some other evolutionists not quite ready to accept the new phylogenetic tree.  Calling the tunicate an “ugly sister,” Pennisi quoted experts saying the proposal will turn some heads, and the jury is still out.  She said they said, “Tunicates and larvaceans evolve rapidly and have gained and lost so many genes that it’s very hard to position them properly in an evolutionary tree.”

1Henry Gee, “Evolution: Careful with that amphioxus,” Nature 439, 923-924 (23 February 2006) | doi:10.1038/439923a.
2Delsuc et al., “Tunicates and not cephalochordates are the closest living relatives of vertebrates,” Nature 439, 965-968 (23 February 2006) | doi:10.1038/nature04336.

Evolutionists could use a lot more humility.  They should quit the parochial school of Pope Charlie that is producing a class of lemmings who cling to crazy ideas.  What Gee is saying contradicts evolution.  This new story line puts the advanced muscles, nervous system and mobility of Amphioxus before organisms that were assumed more primitive (in the old “progressive” evolution picture), and describes subsequent evolution as a story of persistent loss.
    Meanwhile, Eugenie Scott and Alan Gishlick sit on a Grand Canyon beach trying to whoop up enthusiasm for their evening song service: “It’s a long way from amphioxus / It’s a long way to us. / It’s a long way from amphioxus to the meanest human cuss. / Goodbye fins and gill slits / Hello lungs and hair! / It’s a long, long way from amphioxus, / But we come from there” (10/06/2005 commentary).  It’s even longer when you’re going backwards.  Gee’s story gives them more food for cuss.

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Categories: Fossils, Genetics

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