Basics: Gastrulation, invertebrate style

The article about gastrulation from the other day was dreadfully vertebrate-centric, so let me correct that with a little addendum that mentions a few invertebrate patterns of gastrulation—and you’ll see that the story hasn’t changed.

Remember, this is the definition of gastrulation that I explained with some vertebrate examples:

The process in animal embryos in which endoderm and mesoderm move from the outer surface of the embryo to the inside, where they give rise to internal organs.

I described frogs and birds and mammals the other day, so lets take a look at sea urchins and fruit flies.

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Basics: Gastrulation

That guy, John Wilkins, has been keeping a list of presentations of basic concepts in science, and he told me I’m supposed to do one on gastrulation. First I thought, no way—that’s way too hard, and I thought this was all supposed to be about basic stuff. But then I figured that it can’t be too hard, after all, all you readers went through it successfully, and you even managed to do it before you developed a brain. So, sure, let’s rattle this one off.

In the simplest terms, gastrulation is a stage in early development; in human beings it occurs between two and three weeks after fertilization. It is that stage when a two-layered cell mass undergoes a set of specific movements and interactions that establish the three germ layers of the embryo (endoderm, mesoderm, and ectoderm) and the beginnings of a three-dimensional structure. The end result doesn’t look like much of an animal, but it has set up pools of cells that will contribute to specific future cell types, and has laid down the rough outline of tissues along the body axis.

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What use is an appendix?

Here’s an excellent and useful summary of the appendix from a surgeon’s perspective. Creationists dislike the idea that we bear useless organs, remnants of past function that are non-functional or even hazardous to our health; they make up stories about the importance of these vestiges. Sid Schwab has cut out a lot of appendices, and backs up its non-utility with evidence.

The study I cited most often to my patients when asked about adverse consequences of appendectomy is one done by the Mayo Clinic: they studied records of thousands of patients who’d had appendectomy, and compared them with equal thousands who hadn’t. (Back in the day, it was very common during any abdominal operation to remove the appendix. Like flicking a bug off your shoulder. No extra charge: just did it to prevent further problems: took an extra couple of minutes, is all.) The groups were statistically similar in every way other than presence of the worm. There were no differences in incidence of any disease. It’s as convincing as it gets, given the impossibility of doing a prospective double-blind study.

I have a personal interest in this: I was nearly killed by my appendix at the age of 9, and had it removed. I haven’t missed it since.

The Haeckel-Wells Chronicles

Lately, the Discovery Institute has stuck its neck out in response to the popularity of showings of Randy Olson’s movie, Flock of Dodos, which I reviewed a while back. They slapped together some lame critiques packaged on the web as Hoax of Dodos (a clunker of a name; it’s especially ironic since the film tries to portray the Institute as good at PR), which mainly seem to be driven by the sloppy delusions of that poor excuse for a developmental biologist, Jonathan Wells. In the past week, I’ve also put up my responses to the Wells deceptions—as a developmental biologist myself, I get a little cranky when a creationist clown abuses my discipline.

In case you are completely baffled by this whole episode, here’s a shorter summary.

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Would Chuck Terhark like a job writing science abstracts?

One of the subjects I mentioned at the Thursday Flock of Dodos discussion was that an obstacle to getting the public excited about science is the state of science writing. It’s a very formal style in which the passive voice is encouraged, caution and tentative statements are demanded, adverbs are frowned upon and adjectives are treated with suspicion, and all the passion is wrung out in favor of dry recitations of data. Now that actually has a good purpose: it makes it easy to get to the meat of the article for people who are already familiar with the subject and may not need any pizazz to get excited about nematode cell lineages or connectivity diagrams of forebrain nuclei. It makes the work impenetrable to those not already inculcated with the arcana of the discipline, however.

The City Pages illustrates the difference. On Tuesday, the Café Scientifique is going to be given by Cynthia Norton of College of St. Catherine in St. Paul, on the subject of snails. Just for comparison, I’ve put an example of a scientific abstract and the publicity copy for the talk below the fold, and you’ll see what I mean.

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Wells and Haeckel’s Embryos

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(This is a rather long response to a chapter in Jonathan Wells’ dreadful and most unscholarly book, Icons of Evolution)

The story of Haeckel’s embryos is different in an important way from that of the other chapters in Jonathan Wells’ book. As the other authors show, Wells has distorted ideas that are fundamentally true in order to make his point: all his rhetoric to the contrary, Archaeopteryx is a transitional fossil, peppered moths and Darwin’s finches do tell us significant things about evolution, four-winged flies do tell us significant things about developmental pathways, and so forth. In those parts of the book, Wells has to try and cover up a truth by misconstruing and misrepresenting it.

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Sagan joins the fray

The NYT has a nice article on Carl Sagan’s new posthumous book—it was put together by his widow, Ann Druyan, and she makes a few good points:

In the wake of Sept. 11 and the attacks on the teaching of evolution in this country, she said, a tacit truce between science and religion that has existed since the time of Galileo started breaking down. “A lot of scientists were mad as hell, and they weren’t going to take it anymore,” Ms. Druyan said over lunch recently.

I’ll say. It was a stupid truce, anyway, entirely to the benefit of the old guardians of mythology.

Scientists contributing to the moral decline of the universe, again

Uh-oh. Those evil scientists are up to no good again, blindly making discoveries and creating inventions without any thought to the long-term consequences. Dynamite, nerve gas, the atom bomb, the hydrogen bomb…what’s next? What new horror will they unleash on humanity?

Scientists are close to coming up with a vaccine against Chlamydia. The bastards.

Notice the trend? Develop better hygiene to end childbed fever, anesthetics to dull the pain of childbirth, cures for venereal diseases, the recent vaccine against human papilloma virus, and now this. It’s like they don’t think women deserve to suffer. You know this will only lead to licentiousness, rampant freedom, and orgies. Come on, fellow scientists, think. Do you really believe this kind of behavior will make the world a better place?

Just you wait. Someone will try to stop them.