The newest, niftiest, most fascinating edition of the Tangled Bank is now available online at Salto Sobrius.
Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
The newest, niftiest, most fascinating edition of the Tangled Bank is now available online at Salto Sobrius.
That irreverent rapscallion Larry Moran suggested that I read this article by Natalie Angier. She begins by telling us that scientists are always asking her to help out in the fight against those loony creationists, but then she turns around and chews them out for their hypocrisy. I say, give ’em hell, Natalie.
A reader sent me copy of a letter that will be published in Science this week, criticizing the dishonest tactics of the anti-scientific adult stem cell “advocates” (in quotes because they aren’t really science advocates of any kind—they’re only using it as an issue to limit stem cell research.) Anyway, it raises the interesting question of who you’re going to believe: scientists with expertise in the issues under discussion, or a flunky for Sam Brownback and shill for the religious right?
Carl Zimmer wrote on evolution in jellyfish, with the fascinating conclusion that they bear greater molecular complexity than was previously thought. He cited a recent challenging review by Seipel and Schmid that discusses the evolution of triploblasty in the metazoa—it made me rethink some of my assumptions about germ layer phylogeny, anyway, so I thought I’d try to summarize it here. The story is clear, but I realized as I started to put it together that jeez, but we developmental biologists use a lot of jargon. If this is going to make any sense to anyone else, I’m going to have to step way back and explain a collection of concepts that we’ve been using since Lankester in the 19th century.
I’m taking it easy here in the fabulous Van Dusen mansion, a bed and breakfast where I’m staying tonight, and I thought I’d browse through the stem cell legislation that’s being considered in the senate right now. It’s strange: one substantive bill has come up from the House, and all of a sudden two more bills have been proposed on the floor of the Senate.
Do vertebrate embryos exhibit significant variation in their early development? Yes, they do—in particular, the earliest stages show distinct differences that mainly reflect differences in maternal investment and that cause significant distortions of early morphology during gastrulation. However, these earliest patterns represent workarounds, strategies to accommodate one variable (the amount of yolk in the egg), and the animals subsequently reorganize to put tissues into a canonical arrangement. Observations of gene expression during gastrulation are revealing deeper similarities that are common in all deuterostomes—not just vertebrates, but also the invertebrate chordates (tunicates and cephalochordates) and echinoderms.
What does all that mean? If you think of development as a formal dance, the earliest stages are like the prelude; everyone is getting out of their chairs around the ballroom, looking for partners and working their way towards the floor. The dispositions of the dancers are variable and somewhat chaotic, and vary from dance to dance. Once they get to their positions, however, we’re finding that not only is there a general similarity in their arrangements, but they’re all dancing to the very same tune. In this case, one of the repeated motifs in that tune is a gene, Nodal, which is active in gastrulation and shows a similar pattern in animal after animal.
Eugenie Scott is going to have to increase the length of her list of scientists out to “destroy religion.” Larry Moran (fans of Talk.Origins will recognize the name) has posted an article, Theistic Evolution: The Fallacy of the Middle Ground.
There is no continuum between science and non-science. You can’t practice methodological naturalism 99% of the time and still claim to be a scientist. It’s all or nothing. Either your explanations of the natural world are scientific or they are not.
It’s too bad his site isn’t set up like a blog—you can’t make comments there, so you’ll have to settle for making howls of outrage here, or tracking him down on usenet to complain there.
I also like this wonderful quote:
My practise as a scientist is atheistic. That is to say, when I set up an experiment I assume that no god, angel, or devil is going to interfere with its course; and this assumption has been justified by such success as I have achieved in my professional career. I should therefore be intellectually dishonest if I were not also atheistic in the affairs of the world. And I should be a coward if I did not state my theoretical views in public.
J.B.S. Haldane
Yesterday, I reposted an article on homology within the neck and shoulder, which describes an interesting technique of using patterns of gene expression to identify homologous cellular pools; the idea is that we can discern homology more clearly by looking more closely at the molecular mechanisms, rather than focusing on final morphology and tissue derivation. Trust me, if you don’t want to read it all—it’s cool stuff, and one of the interesting points they make is that they’ve traced the fate of a particular bone not found in us mammals, but common in our pre-synapsid ancestors, the cleithrum. They argue from a common cellular origin that this bone has been reshaped into a ridge on our shoulder blade, the scapular spine.
As many readers might know, though, the word “homology,” especially when coupled with a novel technique for its determination, is always good for an argument. This one is no exception.
A new report in this week’s Nature clears up a mystery about an enigmatic fossil from the Cambrian. This small creature has been pegged as everything from a chordate to a polychaete, but a detailed analysis has determined that it has a key feature, a radula, that places it firmly in the molluscan lineage. It was a kind of small Cambrian slug that crawled over matted sheets of algae and bacteria, scraping away a meal.
Neck anatomy has long terrified me. Way back when I was a grad student, my lab studied the organization and development of the hindbrain, which was relatively tidy and segmental; my research was studying the organization and development of the spinal cord, which was also tidy and segmental. The cervical region, though, was complicated territory. It’s a kind of transitional zone between two simple patterns, and all kinds of elaborate nuclei and new cell types and structural organizations flowered there. I drew a line at the fifth spinal segment and said I’m not even going to look further anteriorly…good thing, too, or I’d probably still be trying to finish my degree.
Fortunately, Matsuoka et al. were braver than I was and they have applied some new molecular techniques to sort out some of the details of how the neck and shoulder are assembled. This is a developmental study of how the muscles and bones of the shoulder girdle and neck are derived, and what they’ve identified is 1) a fairly simple rule for part of the organization, 2) an explanation for some human pathologies, and 3) some interesting observations about evolution. It is very cool to find a paper that ties together molecular genetics, development, paleontology, and medicine together so inseparably.
