development
pharyngula | March 31, 2007I must disagree with Larry Moran, who accuses the field of evo-devo of animal chauvinism — not that it isn't more or less true that we do tend to focus on metazoans, but I disagree with an implication that this is a bad thing or that it is a barrier to respectability. Larry says we need to cover the other four kingdoms of life in greater breadth, which I agree is a fine idea. I would like to have a complete description of the genome of every species on earth, a thorough catalog of every epistatic interaction between those genes during development, a hundred labs working on each species, and a…
pharyngula | March 22, 2007When we had last seen our basic embryo, it had gone through gastrulation — a process in which cells of a two-layered sheet had moved inward, setting up the three germ layers (endoderm, mesoderm, and ectoderm) of the early embryo. In particular, cells at the organizer, a tissue that induces or organizes migrating cells, had rolled inwards to set up specific axial mesoderm structures: the prechordal plate, which will underlie cranial structures, and the notochord, which resides under the future hindbrain and spinal cord. At this point, the embryo has an outer layer of ectoderm, and lying under…
pharyngula | March 16, 2007My latest column for Seed, Variant Genes-in-Waiting, is now online. If you subscribed, you would have already read it earlier this week.
By the way, my mom subscribes, too, and she gives it a thumbs up. I'll have to find out what she thinks about my next column, which is all about beetle testes (and that's all you get to know about it—you'll just have to wait).
pharyngula | March 16, 2007
The latest Nature reveals a new primitive mammal fossil collected in the Mesozoic strata of the Yan mountains of China. It's small and unprepossessing, but it has at least two noteworthy novelties, and first among them is that it represents another step in the transition from the reptilian to the mammalian jaw and ear.
Here's the beautiful little beast; as you can see, it's very small, and we need to look very closely at some details of its morphology to see what's special about it.
(click for larger image)Main part of the holotype (Nanjing University-Paleontology NJU-P06001A). b, Skeletal…
pharyngula | March 15, 2007Sphyrocephala beccarii
Here is a spectacularly pretty and weird animal: stalk-eyed flies of the family Diopsidae. There are about 160 species in this group that exhibit this extreme morphology, with the eyes and the antennae displaced laterally on stalks. They often (but not always) are sexually dimorphic, with males having more exaggerated stalks—the longer stalks also make them clumsy in flight, so this is a pattern with considerable cost, and is thought to be the product of sexual selection. The Sphyrocephala to the right is not even an extreme example. Read on to see some genuinely…
pharyngula | March 13, 2007
Stevie C sent along this article on
An unusual presentation of supernumerary breast tissue (just what were you googling for, Stevie?), in which a woman reports an annoying growth on her foot, and when examined, is discovered to have a breast growing there, complete with nipple and fatty tissue (but in this case, no glandular tissue).
It's in the Dermatology Online Journal, not the Onion.
I hadn't heard of this before myself, but it's fascinating. These supernumerary breasts can pop up all over the place, including the face, back, and thigh (and foot, obviously). They can be functionally…
pharyngula | March 13, 2007
What do you know…just last week, I posted an article dismissing a creationist's misconceptions about pharyngeal organization and development, in which he asks about the evidence for similarities between agnathan and gnathostome jaws, and what comes along but a new paper on the molecular evidence for the origin of the jaw, which describes gene expression in the lamprey pharynx. How timely! And as a plus, it contains several very clear summary diagrams to show how all the bits and pieces and molecules relate to one another.
The short summary is that there is a suite of genes (the Hox and Dlx…
pharyngula | February 28, 2007Well, not really—but the UK government will tolerate and support research into human-animal hybrids. No one is interested in raising a half-pig/half-man creature to adulthood, but instead this work is all about understanding basic mechanisms of development and human disease.
Scientists want to create the hybrid embryos to study the subtle molecular glitches that give rise to intractable diseases such as Parkinson's, Alzheimer's and cystic fibrosis. The researchers would take a cell from a patient and insert it into a hollowed out animal egg to make an embryo, which would be 99.9% human and 0.…
pharyngula | February 21, 2007The 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…
pharyngula | February 19, 2007That 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…
pharyngula | February 19, 2007
Cool: here's a duck with four hindlimbs.
I have to gripe about the description, though:
A rare mutation has left eight-day-old Stumpy with two extra legs behind the two he moves around on. … The mutation is rare but cases have been recorded across the world.
No, no, no. This is almost certainly not the result of a mutation, and it's one of my pet peeves when the media makes this wrong assumption, that every change in a newborn is the product of a genetic change. This is the result of a developmental error, not a genetic one, most likely caused by a fusion of two embryos in a single egg.
(…
pharyngula | February 17, 2007Lately, 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…
pharyngula | February 15, 2007
(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…
pharyngula | January 31, 2007I was thinking of doing something with this paper, but dang it, Omics! Omics! beat me to it. Read it anyway…I suppose there might be some other science in the universe left for me.
pharyngula | January 25, 2007Yesterday, I pointed out that Jonathan Wells was grossly ignorant of basic ideas in evo-devo. This isn't too surprising; he's a creationist, he has an agenda to destroy evolutionary biology, and he's going to rail against evolution…same ol', same ol'. That's nothing, though. Wells and his fellows at the Discovery Institute have an even more radical goal of fighting natural, material explanations of many other phenomena, and his latest screed at the DI house organ is against natural explanations of development. Not evolution, not evo-devo, just plain basic developmental biology—apparently, he…
pharyngula | January 23, 2007When I was a wee young lad, I remember making crystal radios and small-scale explosives for fun. The new generation can do something even cooler now, though: how about isolating your very own stem cells, using relatively simple equipment. It's fun, easy, and educational!
Step 3, "get a placenta", does rather gloss over some of the practical difficulties, though, and does require planning about 9 months ahead.
pharyngula | January 18, 2007
The vulva is one of my favorite organs. Not only is it pretty and fun to manipulate, but how it responds tells us so much about its owner. And it is just amazing how much we're learning about it now.
Don't worry about clicking to read more…this article is full of pictures, but it is entirely work safe because it's all about science.
It also helps that all I'm going to talk about is worm vulvas. Anybody who has taken a developmental biology class in the last ten years knew exactly what to expect: when a developmental biologist starts getting all enthusiastic about vulvas, you know he's…
pharyngula | January 14, 2007
Q: What unique organ is found only in mammals, but not in fish, amphibians, reptiles, or birds?
The title and that little picture to the left ought to be hint enough, but if not, read on.
A: The vagina. Aren't we lucky?
There's an old joke going around about poor design: what kind of designer would route the sewer pipes right through the center of the entertainment center? It's a good point. It doesn't make sense from a design standpoint to have our reproductive and excretory systems so intimately intermingled, but it does make a heck of a lot of sense from a purely historical point of view…
pharyngula | January 10, 2007
There's an important phenomenon in development called neurulation. This is a process that starts with a flat sheet of ectodermal cells, folds them into a tube, and creates our dorsal nervous system. Here's a simple cross-section of the process in a salamander, but in general outline we humans do pretty much the same thing. Cells move up and inward, and then zipper together along the length of the animal to produce a closed tube.
It's a seemingly simple event with a great deal of underlying complexity. It requires coordinated changes in the shape of ectodermal cells to drive the changes in…
pharyngula | January 9, 2007
If you've seen BladeRunner, you know the short soliloquy at the end by one of the android replicants, Roy, as he's about to expire from a genetically programmed early death.
"I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams…glitter in the dark near Tanhauser Gate. All those…moments will be lost…in time, like tears…in rain. Time…to die."
There's an interesting idea here, that death can be an intrinsic property of our existence, a kind of internal mortality clock that is always ticking away, and eventually our time will run out…