We have the brains of worms


Way back in the early 19th century, Geoffroy St. Hilaire argued for a radical idea, that vertebrates and most invertebrates were inverted copies of each other. Vertebrates have a dorsal nerve cord and ventral heart, while an insect has a ventral nerve cord and dorsal heart. Could it be that there was a common plan, and that one difference is simply that one is upside down relative to the other? It was an interesting idea, but it didn't hold up at the time; critics could just enumerate the multitude of differences observable between arthropods and vertebrates and drown out an apparent similarity in a flood of documented differences. Picking out a few superficial similarities and proposing that something just looks like it ought to be so is not a persuasive argument in science.

Something has changed in the almost 200 years since Geoffroy made his suggestion, though: there has been a new flood of molecular data that shows that Geoffroy was right. We're finding that all animals seem to use the same early molecular signals to define the orientation of the body axis, and that the dorsal-ventral axis is defined by a molecule in the Bmp (Bone Morphogenetic Protein) family. In vertebrates, Bmp is high in concentration along the ventral side of the embryo, opposite the developing nervous system. In arthropods, Bmp (the homolog in insects is called decapentaplegic, or dpp) is high on the dorsal side, which is still opposite the nervous system. At this point, the question of whether the dorsal-ventral axis of the vertebrate and invertebrate body plans have a common origin and whether one is inverted relative to the other has been settled, and the answer is yes.

That raises more questions, of course. One is where the nervous system fits into this scheme.

Continue reading "We have the brains of worms" (on Pharyngula)


hmm, that sure seems like spam to me.

Yes. Yes, it was.

more spam.

btw, you should delete my initial message, and this one, so idiots like the one who just posted above this won’t confuse the issue.

er, OTOH, why should anyone care if idiots confuse the issue?

I’m not even a developmental biologist, but it’s been very interesting to see this story unfold over the last couple of years.

I’m glad you posted a link to your previous article on the subject in this post, too.

ok, three successive spam posts by obviously the same user using different aliases violates at least 2 rules of this board.

please boot this idiot forthwith.

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This page contains a single entry by PZ Myers published on May 4, 2007 11:48 AM.

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